| /* |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| /* |
| * This file is available under and governed by the GNU General Public |
| * License version 2 only, as published by the Free Software Foundation. |
| * However, the following notice accompanied the original version of this |
| * file: |
| * |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent; |
| |
| import java.lang.Thread.UncaughtExceptionHandler; |
| import java.util.ArrayList; |
| import java.util.Arrays; |
| import java.util.Collection; |
| import java.util.Collections; |
| import java.util.List; |
| import java.util.concurrent.AbstractExecutorService; |
| import java.util.concurrent.Callable; |
| import java.util.concurrent.ExecutorService; |
| import java.util.concurrent.Future; |
| import java.util.concurrent.RejectedExecutionException; |
| import java.util.concurrent.RunnableFuture; |
| import java.util.concurrent.ThreadLocalRandom; |
| import java.util.concurrent.TimeUnit; |
| import java.util.concurrent.atomic.AtomicLong; |
| import java.security.AccessControlContext; |
| import java.security.ProtectionDomain; |
| import java.security.Permissions; |
| |
| /** |
| * An {@link ExecutorService} for running {@link ForkJoinTask}s. |
| * A {@code ForkJoinPool} provides the entry point for submissions |
| * from non-{@code ForkJoinTask} clients, as well as management and |
| * monitoring operations. |
| * |
| * <p>A {@code ForkJoinPool} differs from other kinds of {@link |
| * ExecutorService} mainly by virtue of employing |
| * <em>work-stealing</em>: all threads in the pool attempt to find and |
| * execute tasks submitted to the pool and/or created by other active |
| * tasks (eventually blocking waiting for work if none exist). This |
| * enables efficient processing when most tasks spawn other subtasks |
| * (as do most {@code ForkJoinTask}s), as well as when many small |
| * tasks are submitted to the pool from external clients. Especially |
| * when setting <em>asyncMode</em> to true in constructors, {@code |
| * ForkJoinPool}s may also be appropriate for use with event-style |
| * tasks that are never joined. |
| * |
| * <p>A static {@link #commonPool()} is available and appropriate for |
| * most applications. The common pool is used by any ForkJoinTask that |
| * is not explicitly submitted to a specified pool. Using the common |
| * pool normally reduces resource usage (its threads are slowly |
| * reclaimed during periods of non-use, and reinstated upon subsequent |
| * use). |
| * |
| * <p>For applications that require separate or custom pools, a {@code |
| * ForkJoinPool} may be constructed with a given target parallelism |
| * level; by default, equal to the number of available processors. |
| * The pool attempts to maintain enough active (or available) threads |
| * by dynamically adding, suspending, or resuming internal worker |
| * threads, even if some tasks are stalled waiting to join others. |
| * However, no such adjustments are guaranteed in the face of blocked |
| * I/O or other unmanaged synchronization. The nested {@link |
| * ManagedBlocker} interface enables extension of the kinds of |
| * synchronization accommodated. |
| * |
| * <p>In addition to execution and lifecycle control methods, this |
| * class provides status check methods (for example |
| * {@link #getStealCount}) that are intended to aid in developing, |
| * tuning, and monitoring fork/join applications. Also, method |
| * {@link #toString} returns indications of pool state in a |
| * convenient form for informal monitoring. |
| * |
| * <p>As is the case with other ExecutorServices, there are three |
| * main task execution methods summarized in the following table. |
| * These are designed to be used primarily by clients not already |
| * engaged in fork/join computations in the current pool. The main |
| * forms of these methods accept instances of {@code ForkJoinTask}, |
| * but overloaded forms also allow mixed execution of plain {@code |
| * Runnable}- or {@code Callable}- based activities as well. However, |
| * tasks that are already executing in a pool should normally instead |
| * use the within-computation forms listed in the table unless using |
| * async event-style tasks that are not usually joined, in which case |
| * there is little difference among choice of methods. |
| * |
| * <table BORDER CELLPADDING=3 CELLSPACING=1> |
| * <caption>Summary of task execution methods</caption> |
| * <tr> |
| * <td></td> |
| * <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td> |
| * <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td> |
| * </tr> |
| * <tr> |
| * <td> <b>Arrange async execution</b></td> |
| * <td> {@link #execute(ForkJoinTask)}</td> |
| * <td> {@link ForkJoinTask#fork}</td> |
| * </tr> |
| * <tr> |
| * <td> <b>Await and obtain result</b></td> |
| * <td> {@link #invoke(ForkJoinTask)}</td> |
| * <td> {@link ForkJoinTask#invoke}</td> |
| * </tr> |
| * <tr> |
| * <td> <b>Arrange exec and obtain Future</b></td> |
| * <td> {@link #submit(ForkJoinTask)}</td> |
| * <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td> |
| * </tr> |
| * </table> |
| * |
| * <p>The common pool is by default constructed with default |
| * parameters, but these may be controlled by setting three |
| * {@linkplain System#getProperty system properties}: |
| * <ul> |
| * <li>{@code java.util.concurrent.ForkJoinPool.common.parallelism} |
| * - the parallelism level, a non-negative integer |
| * <li>{@code java.util.concurrent.ForkJoinPool.common.threadFactory} |
| * - the class name of a {@link ForkJoinWorkerThreadFactory} |
| * <li>{@code java.util.concurrent.ForkJoinPool.common.exceptionHandler} |
| * - the class name of a {@link UncaughtExceptionHandler} |
| * <li>{@code java.util.concurrent.ForkJoinPool.common.maximumSpares} |
| * - the maximum number of allowed extra threads to maintain target |
| * parallelism (default 256). |
| * </ul> |
| * If a {@link SecurityManager} is present and no factory is |
| * specified, then the default pool uses a factory supplying |
| * threads that have no {@link Permissions} enabled. |
| * The system class loader is used to load these classes. |
| * Upon any error in establishing these settings, default parameters |
| * are used. It is possible to disable or limit the use of threads in |
| * the common pool by setting the parallelism property to zero, and/or |
| * using a factory that may return {@code null}. However doing so may |
| * cause unjoined tasks to never be executed. |
| * |
| * <p><b>Implementation notes</b>: This implementation restricts the |
| * maximum number of running threads to 32767. Attempts to create |
| * pools with greater than the maximum number result in |
| * {@code IllegalArgumentException}. |
| * |
| * <p>This implementation rejects submitted tasks (that is, by throwing |
| * {@link RejectedExecutionException}) only when the pool is shut down |
| * or internal resources have been exhausted. |
| * |
| * @since 1.7 |
| * @author Doug Lea |
| */ |
| @sun.misc.Contended |
| public class ForkJoinPool extends AbstractExecutorService { |
| |
| /* |
| * Implementation Overview |
| * |
| * This class and its nested classes provide the main |
| * functionality and control for a set of worker threads: |
| * Submissions from non-FJ threads enter into submission queues. |
| * Workers take these tasks and typically split them into subtasks |
| * that may be stolen by other workers. Preference rules give |
| * first priority to processing tasks from their own queues (LIFO |
| * or FIFO, depending on mode), then to randomized FIFO steals of |
| * tasks in other queues. This framework began as vehicle for |
| * supporting tree-structured parallelism using work-stealing. |
| * Over time, its scalability advantages led to extensions and |
| * changes to better support more diverse usage contexts. Because |
| * most internal methods and nested classes are interrelated, |
| * their main rationale and descriptions are presented here; |
| * individual methods and nested classes contain only brief |
| * comments about details. |
| * |
| * WorkQueues |
| * ========== |
| * |
| * Most operations occur within work-stealing queues (in nested |
| * class WorkQueue). These are special forms of Deques that |
| * support only three of the four possible end-operations -- push, |
| * pop, and poll (aka steal), under the further constraints that |
| * push and pop are called only from the owning thread (or, as |
| * extended here, under a lock), while poll may be called from |
| * other threads. (If you are unfamiliar with them, you probably |
| * want to read Herlihy and Shavit's book "The Art of |
| * Multiprocessor programming", chapter 16 describing these in |
| * more detail before proceeding.) The main work-stealing queue |
| * design is roughly similar to those in the papers "Dynamic |
| * Circular Work-Stealing Deque" by Chase and Lev, SPAA 2005 |
| * (http://research.sun.com/scalable/pubs/index.html) and |
| * "Idempotent work stealing" by Michael, Saraswat, and Vechev, |
| * PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186). |
| * The main differences ultimately stem from GC requirements that |
| * we null out taken slots as soon as we can, to maintain as small |
| * a footprint as possible even in programs generating huge |
| * numbers of tasks. To accomplish this, we shift the CAS |
| * arbitrating pop vs poll (steal) from being on the indices |
| * ("base" and "top") to the slots themselves. |
| * |
| * Adding tasks then takes the form of a classic array push(task): |
| * q.array[q.top] = task; ++q.top; |
| * |
| * (The actual code needs to null-check and size-check the array, |
| * properly fence the accesses, and possibly signal waiting |
| * workers to start scanning -- see below.) Both a successful pop |
| * and poll mainly entail a CAS of a slot from non-null to null. |
| * |
| * The pop operation (always performed by owner) is: |
| * if ((base != top) and |
| * (the task at top slot is not null) and |
| * (CAS slot to null)) |
| * decrement top and return task; |
| * |
| * And the poll operation (usually by a stealer) is |
| * if ((base != top) and |
| * (the task at base slot is not null) and |
| * (base has not changed) and |
| * (CAS slot to null)) |
| * increment base and return task; |
| * |
| * Because we rely on CASes of references, we do not need tag bits |
| * on base or top. They are simple ints as used in any circular |
| * array-based queue (see for example ArrayDeque). Updates to the |
| * indices guarantee that top == base means the queue is empty, |
| * but otherwise may err on the side of possibly making the queue |
| * appear nonempty when a push, pop, or poll have not fully |
| * committed. (Method isEmpty() checks the case of a partially |
| * completed removal of the last element.) Because of this, the |
| * poll operation, considered individually, is not wait-free. One |
| * thief cannot successfully continue until another in-progress |
| * one (or, if previously empty, a push) completes. However, in |
| * the aggregate, we ensure at least probabilistic |
| * non-blockingness. If an attempted steal fails, a thief always |
| * chooses a different random victim target to try next. So, in |
| * order for one thief to progress, it suffices for any |
| * in-progress poll or new push on any empty queue to |
| * complete. (This is why we normally use method pollAt and its |
| * variants that try once at the apparent base index, else |
| * consider alternative actions, rather than method poll, which |
| * retries.) |
| * |
| * This approach also enables support of a user mode in which |
| * local task processing is in FIFO, not LIFO order, simply by |
| * using poll rather than pop. This can be useful in |
| * message-passing frameworks in which tasks are never joined. |
| * However neither mode considers affinities, loads, cache |
| * localities, etc, so rarely provide the best possible |
| * performance on a given machine, but portably provide good |
| * throughput by averaging over these factors. Further, even if |
| * we did try to use such information, we do not usually have a |
| * basis for exploiting it. For example, some sets of tasks |
| * profit from cache affinities, but others are harmed by cache |
| * pollution effects. Additionally, even though it requires |
| * scanning, long-term throughput is often best using random |
| * selection rather than directed selection policies, so cheap |
| * randomization of sufficient quality is used whenever |
| * applicable. Various Marsaglia XorShifts (some with different |
| * shift constants) are inlined at use points. |
| * |
| * WorkQueues are also used in a similar way for tasks submitted |
| * to the pool. We cannot mix these tasks in the same queues used |
| * by workers. Instead, we randomly associate submission queues |
| * with submitting threads, using a form of hashing. The |
| * ThreadLocalRandom probe value serves as a hash code for |
| * choosing existing queues, and may be randomly repositioned upon |
| * contention with other submitters. In essence, submitters act |
| * like workers except that they are restricted to executing local |
| * tasks that they submitted (or in the case of CountedCompleters, |
| * others with the same root task). Insertion of tasks in shared |
| * mode requires a lock (mainly to protect in the case of |
| * resizing) but we use only a simple spinlock (using field |
| * qlock), because submitters encountering a busy queue move on to |
| * try or create other queues -- they block only when creating and |
| * registering new queues. Additionally, "qlock" saturates to an |
| * unlockable value (-1) at shutdown. Unlocking still can be and |
| * is performed by cheaper ordered writes of "qlock" in successful |
| * cases, but uses CAS in unsuccessful cases. |
| * |
| * Management |
| * ========== |
| * |
| * The main throughput advantages of work-stealing stem from |
| * decentralized control -- workers mostly take tasks from |
| * themselves or each other, at rates that can exceed a billion |
| * per second. The pool itself creates, activates (enables |
| * scanning for and running tasks), deactivates, blocks, and |
| * terminates threads, all with minimal central information. |
| * There are only a few properties that we can globally track or |
| * maintain, so we pack them into a small number of variables, |
| * often maintaining atomicity without blocking or locking. |
| * Nearly all essentially atomic control state is held in two |
| * volatile variables that are by far most often read (not |
| * written) as status and consistency checks. (Also, field |
| * "config" holds unchanging configuration state.) |
| * |
| * Field "ctl" contains 64 bits holding information needed to |
| * atomically decide to add, inactivate, enqueue (on an event |
| * queue), dequeue, and/or re-activate workers. To enable this |
| * packing, we restrict maximum parallelism to (1<<15)-1 (which is |
| * far in excess of normal operating range) to allow ids, counts, |
| * and their negations (used for thresholding) to fit into 16bit |
| * subfields. |
| * |
| * Field "runState" holds lockable state bits (STARTED, STOP, etc) |
| * also protecting updates to the workQueues array. When used as |
| * a lock, it is normally held only for a few instructions (the |
| * only exceptions are one-time array initialization and uncommon |
| * resizing), so is nearly always available after at most a brief |
| * spin. But to be extra-cautious, after spinning, method |
| * awaitRunStateLock (called only if an initial CAS fails), uses a |
| * wait/notify mechanics on a builtin monitor to block when |
| * (rarely) needed. This would be a terrible idea for a highly |
| * contended lock, but most pools run without the lock ever |
| * contending after the spin limit, so this works fine as a more |
| * conservative alternative. Because we don't otherwise have an |
| * internal Object to use as a monitor, the "stealCounter" (an |
| * AtomicLong) is used when available (it too must be lazily |
| * initialized; see externalSubmit). |
| * |
| * Usages of "runState" vs "ctl" interact in only one case: |
| * deciding to add a worker thread (see tryAddWorker), in which |
| * case the ctl CAS is performed while the lock is held. |
| * |
| * Recording WorkQueues. WorkQueues are recorded in the |
| * "workQueues" array. The array is created upon first use (see |
| * externalSubmit) and expanded if necessary. Updates to the |
| * array while recording new workers and unrecording terminated |
| * ones are protected from each other by the runState lock, but |
| * the array is otherwise concurrently readable, and accessed |
| * directly. We also ensure that reads of the array reference |
| * itself never become too stale. To simplify index-based |
| * operations, the array size is always a power of two, and all |
| * readers must tolerate null slots. Worker queues are at odd |
| * indices. Shared (submission) queues are at even indices, up to |
| * a maximum of 64 slots, to limit growth even if array needs to |
| * expand to add more workers. Grouping them together in this way |
| * simplifies and speeds up task scanning. |
| * |
| * All worker thread creation is on-demand, triggered by task |
| * submissions, replacement of terminated workers, and/or |
| * compensation for blocked workers. However, all other support |
| * code is set up to work with other policies. To ensure that we |
| * do not hold on to worker references that would prevent GC, All |
| * accesses to workQueues are via indices into the workQueues |
| * array (which is one source of some of the messy code |
| * constructions here). In essence, the workQueues array serves as |
| * a weak reference mechanism. Thus for example the stack top |
| * subfield of ctl stores indices, not references. |
| * |
| * Queuing Idle Workers. Unlike HPC work-stealing frameworks, we |
| * cannot let workers spin indefinitely scanning for tasks when |
| * none can be found immediately, and we cannot start/resume |
| * workers unless there appear to be tasks available. On the |
| * other hand, we must quickly prod them into action when new |
| * tasks are submitted or generated. In many usages, ramp-up time |
| * to activate workers is the main limiting factor in overall |
| * performance, which is compounded at program start-up by JIT |
| * compilation and allocation. So we streamline this as much as |
| * possible. |
| * |
| * The "ctl" field atomically maintains active and total worker |
| * counts as well as a queue to place waiting threads so they can |
| * be located for signalling. Active counts also play the role of |
| * quiescence indicators, so are decremented when workers believe |
| * that there are no more tasks to execute. The "queue" is |
| * actually a form of Treiber stack. A stack is ideal for |
| * activating threads in most-recently used order. This improves |
| * performance and locality, outweighing the disadvantages of |
| * being prone to contention and inability to release a worker |
| * unless it is topmost on stack. We park/unpark workers after |
| * pushing on the idle worker stack (represented by the lower |
| * 32bit subfield of ctl) when they cannot find work. The top |
| * stack state holds the value of the "scanState" field of the |
| * worker: its index and status, plus a version counter that, in |
| * addition to the count subfields (also serving as version |
| * stamps) provide protection against Treiber stack ABA effects. |
| * |
| * Field scanState is used by both workers and the pool to manage |
| * and track whether a worker is INACTIVE (possibly blocked |
| * waiting for a signal), or SCANNING for tasks (when neither hold |
| * it is busy running tasks). When a worker is inactivated, its |
| * scanState field is set, and is prevented from executing tasks, |
| * even though it must scan once for them to avoid queuing |
| * races. Note that scanState updates lag queue CAS releases so |
| * usage requires care. When queued, the lower 16 bits of |
| * scanState must hold its pool index. So we place the index there |
| * upon initialization (see registerWorker) and otherwise keep it |
| * there or restore it when necessary. |
| * |
| * Memory ordering. See "Correct and Efficient Work-Stealing for |
| * Weak Memory Models" by Le, Pop, Cohen, and Nardelli, PPoPP 2013 |
| * (http://www.di.ens.fr/~zappa/readings/ppopp13.pdf) for an |
| * analysis of memory ordering requirements in work-stealing |
| * algorithms similar to the one used here. We usually need |
| * stronger than minimal ordering because we must sometimes signal |
| * workers, requiring Dekker-like full-fences to avoid lost |
| * signals. Arranging for enough ordering without expensive |
| * over-fencing requires tradeoffs among the supported means of |
| * expressing access constraints. The most central operations, |
| * taking from queues and updating ctl state, require full-fence |
| * CAS. Array slots are read using the emulation of volatiles |
| * provided by Unsafe. Access from other threads to WorkQueue |
| * base, top, and array requires a volatile load of the first of |
| * any of these read. We use the convention of declaring the |
| * "base" index volatile, and always read it before other fields. |
| * The owner thread must ensure ordered updates, so writes use |
| * ordered intrinsics unless they can piggyback on those for other |
| * writes. Similar conventions and rationales hold for other |
| * WorkQueue fields (such as "currentSteal") that are only written |
| * by owners but observed by others. |
| * |
| * Creating workers. To create a worker, we pre-increment total |
| * count (serving as a reservation), and attempt to construct a |
| * ForkJoinWorkerThread via its factory. Upon construction, the |
| * new thread invokes registerWorker, where it constructs a |
| * WorkQueue and is assigned an index in the workQueues array |
| * (expanding the array if necessary). The thread is then |
| * started. Upon any exception across these steps, or null return |
| * from factory, deregisterWorker adjusts counts and records |
| * accordingly. If a null return, the pool continues running with |
| * fewer than the target number workers. If exceptional, the |
| * exception is propagated, generally to some external caller. |
| * Worker index assignment avoids the bias in scanning that would |
| * occur if entries were sequentially packed starting at the front |
| * of the workQueues array. We treat the array as a simple |
| * power-of-two hash table, expanding as needed. The seedIndex |
| * increment ensures no collisions until a resize is needed or a |
| * worker is deregistered and replaced, and thereafter keeps |
| * probability of collision low. We cannot use |
| * ThreadLocalRandom.getProbe() for similar purposes here because |
| * the thread has not started yet, but do so for creating |
| * submission queues for existing external threads. |
| * |
| * Deactivation and waiting. Queuing encounters several intrinsic |
| * races; most notably that a task-producing thread can miss |
| * seeing (and signalling) another thread that gave up looking for |
| * work but has not yet entered the wait queue. When a worker |
| * cannot find a task to steal, it deactivates and enqueues. Very |
| * often, the lack of tasks is transient due to GC or OS |
| * scheduling. To reduce false-alarm deactivation, scanners |
| * compute checksums of queue states during sweeps. (The |
| * stability checks used here and elsewhere are probabilistic |
| * variants of snapshot techniques -- see Herlihy & Shavit.) |
| * Workers give up and try to deactivate only after the sum is |
| * stable across scans. Further, to avoid missed signals, they |
| * repeat this scanning process after successful enqueuing until |
| * again stable. In this state, the worker cannot take/run a task |
| * it sees until it is released from the queue, so the worker |
| * itself eventually tries to release itself or any successor (see |
| * tryRelease). Otherwise, upon an empty scan, a deactivated |
| * worker uses an adaptive local spin construction (see awaitWork) |
| * before blocking (via park). Note the unusual conventions about |
| * Thread.interrupts surrounding parking and other blocking: |
| * Because interrupts are used solely to alert threads to check |
| * termination, which is checked anyway upon blocking, we clear |
| * status (using Thread.interrupted) before any call to park, so |
| * that park does not immediately return due to status being set |
| * via some other unrelated call to interrupt in user code. |
| * |
| * Signalling and activation. Workers are created or activated |
| * only when there appears to be at least one task they might be |
| * able to find and execute. Upon push (either by a worker or an |
| * external submission) to a previously (possibly) empty queue, |
| * workers are signalled if idle, or created if fewer exist than |
| * the given parallelism level. These primary signals are |
| * buttressed by others whenever other threads remove a task from |
| * a queue and notice that there are other tasks there as well. |
| * On most platforms, signalling (unpark) overhead time is |
| * noticeably long, and the time between signalling a thread and |
| * it actually making progress can be very noticeably long, so it |
| * is worth offloading these delays from critical paths as much as |
| * possible. Also, because inactive workers are often rescanning |
| * or spinning rather than blocking, we set and clear the "parker" |
| * field of WorkQueues to reduce unnecessary calls to unpark. |
| * (This requires a secondary recheck to avoid missed signals.) |
| * |
| * Trimming workers. To release resources after periods of lack of |
| * use, a worker starting to wait when the pool is quiescent will |
| * time out and terminate (see awaitWork) if the pool has remained |
| * quiescent for period IDLE_TIMEOUT, increasing the period as the |
| * number of threads decreases, eventually removing all workers. |
| * Also, when more than two spare threads exist, excess threads |
| * are immediately terminated at the next quiescent point. |
| * (Padding by two avoids hysteresis.) |
| * |
| * Shutdown and Termination. A call to shutdownNow invokes |
| * tryTerminate to atomically set a runState bit. The calling |
| * thread, as well as every other worker thereafter terminating, |
| * helps terminate others by setting their (qlock) status, |
| * cancelling their unprocessed tasks, and waking them up, doing |
| * so repeatedly until stable (but with a loop bounded by the |
| * number of workers). Calls to non-abrupt shutdown() preface |
| * this by checking whether termination should commence. This |
| * relies primarily on the active count bits of "ctl" maintaining |
| * consensus -- tryTerminate is called from awaitWork whenever |
| * quiescent. However, external submitters do not take part in |
| * this consensus. So, tryTerminate sweeps through queues (until |
| * stable) to ensure lack of in-flight submissions and workers |
| * about to process them before triggering the "STOP" phase of |
| * termination. (Note: there is an intrinsic conflict if |
| * helpQuiescePool is called when shutdown is enabled. Both wait |
| * for quiescence, but tryTerminate is biased to not trigger until |
| * helpQuiescePool completes.) |
| * |
| * |
| * Joining Tasks |
| * ============= |
| * |
| * Any of several actions may be taken when one worker is waiting |
| * to join a task stolen (or always held) by another. Because we |
| * are multiplexing many tasks on to a pool of workers, we can't |
| * just let them block (as in Thread.join). We also cannot just |
| * reassign the joiner's run-time stack with another and replace |
| * it later, which would be a form of "continuation", that even if |
| * possible is not necessarily a good idea since we may need both |
| * an unblocked task and its continuation to progress. Instead we |
| * combine two tactics: |
| * |
| * Helping: Arranging for the joiner to execute some task that it |
| * would be running if the steal had not occurred. |
| * |
| * Compensating: Unless there are already enough live threads, |
| * method tryCompensate() may create or re-activate a spare |
| * thread to compensate for blocked joiners until they unblock. |
| * |
| * A third form (implemented in tryRemoveAndExec) amounts to |
| * helping a hypothetical compensator: If we can readily tell that |
| * a possible action of a compensator is to steal and execute the |
| * task being joined, the joining thread can do so directly, |
| * without the need for a compensation thread (although at the |
| * expense of larger run-time stacks, but the tradeoff is |
| * typically worthwhile). |
| * |
| * The ManagedBlocker extension API can't use helping so relies |
| * only on compensation in method awaitBlocker. |
| * |
| * The algorithm in helpStealer entails a form of "linear |
| * helping". Each worker records (in field currentSteal) the most |
| * recent task it stole from some other worker (or a submission). |
| * It also records (in field currentJoin) the task it is currently |
| * actively joining. Method helpStealer uses these markers to try |
| * to find a worker to help (i.e., steal back a task from and |
| * execute it) that could hasten completion of the actively joined |
| * task. Thus, the joiner executes a task that would be on its |
| * own local deque had the to-be-joined task not been stolen. This |
| * is a conservative variant of the approach described in Wagner & |
| * Calder "Leapfrogging: a portable technique for implementing |
| * efficient futures" SIGPLAN Notices, 1993 |
| * (http://portal.acm.org/citation.cfm?id=155354). It differs in |
| * that: (1) We only maintain dependency links across workers upon |
| * steals, rather than use per-task bookkeeping. This sometimes |
| * requires a linear scan of workQueues array to locate stealers, |
| * but often doesn't because stealers leave hints (that may become |
| * stale/wrong) of where to locate them. It is only a hint |
| * because a worker might have had multiple steals and the hint |
| * records only one of them (usually the most current). Hinting |
| * isolates cost to when it is needed, rather than adding to |
| * per-task overhead. (2) It is "shallow", ignoring nesting and |
| * potentially cyclic mutual steals. (3) It is intentionally |
| * racy: field currentJoin is updated only while actively joining, |
| * which means that we miss links in the chain during long-lived |
| * tasks, GC stalls etc (which is OK since blocking in such cases |
| * is usually a good idea). (4) We bound the number of attempts |
| * to find work using checksums and fall back to suspending the |
| * worker and if necessary replacing it with another. |
| * |
| * Helping actions for CountedCompleters do not require tracking |
| * currentJoins: Method helpComplete takes and executes any task |
| * with the same root as the task being waited on (preferring |
| * local pops to non-local polls). However, this still entails |
| * some traversal of completer chains, so is less efficient than |
| * using CountedCompleters without explicit joins. |
| * |
| * Compensation does not aim to keep exactly the target |
| * parallelism number of unblocked threads running at any given |
| * time. Some previous versions of this class employed immediate |
| * compensations for any blocked join. However, in practice, the |
| * vast majority of blockages are transient byproducts of GC and |
| * other JVM or OS activities that are made worse by replacement. |
| * Currently, compensation is attempted only after validating that |
| * all purportedly active threads are processing tasks by checking |
| * field WorkQueue.scanState, which eliminates most false |
| * positives. Also, compensation is bypassed (tolerating fewer |
| * threads) in the most common case in which it is rarely |
| * beneficial: when a worker with an empty queue (thus no |
| * continuation tasks) blocks on a join and there still remain |
| * enough threads to ensure liveness. |
| * |
| * The compensation mechanism may be bounded. Bounds for the |
| * commonPool (see commonMaxSpares) better enable JVMs to cope |
| * with programming errors and abuse before running out of |
| * resources to do so. In other cases, users may supply factories |
| * that limit thread construction. The effects of bounding in this |
| * pool (like all others) is imprecise. Total worker counts are |
| * decremented when threads deregister, not when they exit and |
| * resources are reclaimed by the JVM and OS. So the number of |
| * simultaneously live threads may transiently exceed bounds. |
| * |
| * Common Pool |
| * =========== |
| * |
| * The static common pool always exists after static |
| * initialization. Since it (or any other created pool) need |
| * never be used, we minimize initial construction overhead and |
| * footprint to the setup of about a dozen fields, with no nested |
| * allocation. Most bootstrapping occurs within method |
| * externalSubmit during the first submission to the pool. |
| * |
| * When external threads submit to the common pool, they can |
| * perform subtask processing (see externalHelpComplete and |
| * related methods) upon joins. This caller-helps policy makes it |
| * sensible to set common pool parallelism level to one (or more) |
| * less than the total number of available cores, or even zero for |
| * pure caller-runs. We do not need to record whether external |
| * submissions are to the common pool -- if not, external help |
| * methods return quickly. These submitters would otherwise be |
| * blocked waiting for completion, so the extra effort (with |
| * liberally sprinkled task status checks) in inapplicable cases |
| * amounts to an odd form of limited spin-wait before blocking in |
| * ForkJoinTask.join. |
| * |
| * As a more appropriate default in managed environments, unless |
| * overridden by system properties, we use workers of subclass |
| * InnocuousForkJoinWorkerThread when there is a SecurityManager |
| * present. These workers have no permissions set, do not belong |
| * to any user-defined ThreadGroup, and erase all ThreadLocals |
| * after executing any top-level task (see WorkQueue.runTask). |
| * The associated mechanics (mainly in ForkJoinWorkerThread) may |
| * be JVM-dependent and must access particular Thread class fields |
| * to achieve this effect. |
| * |
| * Style notes |
| * =========== |
| * |
| * Memory ordering relies mainly on Unsafe intrinsics that carry |
| * the further responsibility of explicitly performing null- and |
| * bounds- checks otherwise carried out implicitly by JVMs. This |
| * can be awkward and ugly, but also reflects the need to control |
| * outcomes across the unusual cases that arise in very racy code |
| * with very few invariants. So these explicit checks would exist |
| * in some form anyway. All fields are read into locals before |
| * use, and null-checked if they are references. This is usually |
| * done in a "C"-like style of listing declarations at the heads |
| * of methods or blocks, and using inline assignments on first |
| * encounter. Array bounds-checks are usually performed by |
| * masking with array.length-1, which relies on the invariant that |
| * these arrays are created with positive lengths, which is itself |
| * paranoically checked. Nearly all explicit checks lead to |
| * bypass/return, not exception throws, because they may |
| * legitimately arise due to cancellation/revocation during |
| * shutdown. |
| * |
| * There is a lot of representation-level coupling among classes |
| * ForkJoinPool, ForkJoinWorkerThread, and ForkJoinTask. The |
| * fields of WorkQueue maintain data structures managed by |
| * ForkJoinPool, so are directly accessed. There is little point |
| * trying to reduce this, since any associated future changes in |
| * representations will need to be accompanied by algorithmic |
| * changes anyway. Several methods intrinsically sprawl because |
| * they must accumulate sets of consistent reads of fields held in |
| * local variables. There are also other coding oddities |
| * (including several unnecessary-looking hoisted null checks) |
| * that help some methods perform reasonably even when interpreted |
| * (not compiled). |
| * |
| * The order of declarations in this file is (with a few exceptions): |
| * (1) Static utility functions |
| * (2) Nested (static) classes |
| * (3) Static fields |
| * (4) Fields, along with constants used when unpacking some of them |
| * (5) Internal control methods |
| * (6) Callbacks and other support for ForkJoinTask methods |
| * (7) Exported methods |
| * (8) Static block initializing statics in minimally dependent order |
| */ |
| |
| // Static utilities |
| |
| /** |
| * If there is a security manager, makes sure caller has |
| * permission to modify threads. |
| */ |
| private static void checkPermission() { |
| SecurityManager security = System.getSecurityManager(); |
| if (security != null) |
| security.checkPermission(modifyThreadPermission); |
| } |
| |
| // Nested classes |
| |
| /** |
| * Factory for creating new {@link ForkJoinWorkerThread}s. |
| * A {@code ForkJoinWorkerThreadFactory} must be defined and used |
| * for {@code ForkJoinWorkerThread} subclasses that extend base |
| * functionality or initialize threads with different contexts. |
| */ |
| public static interface ForkJoinWorkerThreadFactory { |
| /** |
| * Returns a new worker thread operating in the given pool. |
| * |
| * @param pool the pool this thread works in |
| * @return the new worker thread |
| * @throws NullPointerException if the pool is null |
| */ |
| public ForkJoinWorkerThread newThread(ForkJoinPool pool); |
| } |
| |
| /** |
| * Default ForkJoinWorkerThreadFactory implementation; creates a |
| * new ForkJoinWorkerThread. |
| */ |
| static final class DefaultForkJoinWorkerThreadFactory |
| implements ForkJoinWorkerThreadFactory { |
| public final ForkJoinWorkerThread newThread(ForkJoinPool pool) { |
| return new ForkJoinWorkerThread(pool); |
| } |
| } |
| |
| /** |
| * Class for artificial tasks that are used to replace the target |
| * of local joins if they are removed from an interior queue slot |
| * in WorkQueue.tryRemoveAndExec. We don't need the proxy to |
| * actually do anything beyond having a unique identity. |
| */ |
| static final class EmptyTask extends ForkJoinTask<Void> { |
| private static final long serialVersionUID = -7721805057305804111L; |
| EmptyTask() { status = ForkJoinTask.NORMAL; } // force done |
| public final Void getRawResult() { return null; } |
| public final void setRawResult(Void x) {} |
| public final boolean exec() { return true; } |
| } |
| |
| // Constants shared across ForkJoinPool and WorkQueue |
| |
| // Bounds |
| static final int SMASK = 0xffff; // short bits == max index |
| static final int MAX_CAP = 0x7fff; // max #workers - 1 |
| static final int EVENMASK = 0xfffe; // even short bits |
| static final int SQMASK = 0x007e; // max 64 (even) slots |
| |
| // Masks and units for WorkQueue.scanState and ctl sp subfield |
| static final int SCANNING = 1; // false when running tasks |
| static final int INACTIVE = 1 << 31; // must be negative |
| static final int SS_SEQ = 1 << 16; // version count |
| |
| // Mode bits for ForkJoinPool.config and WorkQueue.config |
| static final int MODE_MASK = 0xffff << 16; // top half of int |
| static final int LIFO_QUEUE = 0; |
| static final int FIFO_QUEUE = 1 << 16; |
| static final int SHARED_QUEUE = 1 << 31; // must be negative |
| |
| /** |
| * Queues supporting work-stealing as well as external task |
| * submission. See above for descriptions and algorithms. |
| * Performance on most platforms is very sensitive to placement of |
| * instances of both WorkQueues and their arrays -- we absolutely |
| * do not want multiple WorkQueue instances or multiple queue |
| * arrays sharing cache lines. The @Contended annotation alerts |
| * JVMs to try to keep instances apart. |
| */ |
| @sun.misc.Contended |
| static final class WorkQueue { |
| |
| /** |
| * Capacity of work-stealing queue array upon initialization. |
| * Must be a power of two; at least 4, but should be larger to |
| * reduce or eliminate cacheline sharing among queues. |
| * Currently, it is much larger, as a partial workaround for |
| * the fact that JVMs often place arrays in locations that |
| * share GC bookkeeping (especially cardmarks) such that |
| * per-write accesses encounter serious memory contention. |
| */ |
| static final int INITIAL_QUEUE_CAPACITY = 1 << 13; |
| |
| /** |
| * Maximum size for queue arrays. Must be a power of two less |
| * than or equal to 1 << (31 - width of array entry) to ensure |
| * lack of wraparound of index calculations, but defined to a |
| * value a bit less than this to help users trap runaway |
| * programs before saturating systems. |
| */ |
| static final int MAXIMUM_QUEUE_CAPACITY = 1 << 26; // 64M |
| |
| // Instance fields |
| volatile int scanState; // versioned, <0: inactive; odd:scanning |
| int stackPred; // pool stack (ctl) predecessor |
| int nsteals; // number of steals |
| int hint; // randomization and stealer index hint |
| int config; // pool index and mode |
| volatile int qlock; // 1: locked, < 0: terminate; else 0 |
| volatile int base; // index of next slot for poll |
| int top; // index of next slot for push |
| ForkJoinTask<?>[] array; // the elements (initially unallocated) |
| final ForkJoinPool pool; // the containing pool (may be null) |
| final ForkJoinWorkerThread owner; // owning thread or null if shared |
| volatile Thread parker; // == owner during call to park; else null |
| volatile ForkJoinTask<?> currentJoin; // task being joined in awaitJoin |
| volatile ForkJoinTask<?> currentSteal; // mainly used by helpStealer |
| |
| WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner) { |
| this.pool = pool; |
| this.owner = owner; |
| // Place indices in the center of array (that is not yet allocated) |
| base = top = INITIAL_QUEUE_CAPACITY >>> 1; |
| } |
| |
| /** |
| * Returns an exportable index (used by ForkJoinWorkerThread). |
| */ |
| final int getPoolIndex() { |
| return (config & 0xffff) >>> 1; // ignore odd/even tag bit |
| } |
| |
| /** |
| * Returns the approximate number of tasks in the queue. |
| */ |
| final int queueSize() { |
| int n = base - top; // non-owner callers must read base first |
| return (n >= 0) ? 0 : -n; // ignore transient negative |
| } |
| |
| /** |
| * Provides a more accurate estimate of whether this queue has |
| * any tasks than does queueSize, by checking whether a |
| * near-empty queue has at least one unclaimed task. |
| */ |
| final boolean isEmpty() { |
| ForkJoinTask<?>[] a; int n, m, s; |
| return ((n = base - (s = top)) >= 0 || |
| (n == -1 && // possibly one task |
| ((a = array) == null || (m = a.length - 1) < 0 || |
| U.getObject |
| (a, (long)((m & (s - 1)) << ASHIFT) + ABASE) == null))); |
| } |
| |
| /** |
| * Pushes a task. Call only by owner in unshared queues. (The |
| * shared-queue version is embedded in method externalPush.) |
| * |
| * @param task the task. Caller must ensure non-null. |
| * @throws RejectedExecutionException if array cannot be resized |
| */ |
| final void push(ForkJoinTask<?> task) { |
| ForkJoinTask<?>[] a; ForkJoinPool p; |
| int b = base, s = top, n; |
| if ((a = array) != null) { // ignore if queue removed |
| int m = a.length - 1; // fenced write for task visibility |
| U.putOrderedObject(a, ((m & s) << ASHIFT) + ABASE, task); |
| U.putOrderedInt(this, QTOP, s + 1); |
| if ((n = s - b) <= 1) { |
| if ((p = pool) != null) |
| p.signalWork(p.workQueues, this); |
| } |
| else if (n >= m) |
| growArray(); |
| } |
| } |
| |
| /** |
| * Initializes or doubles the capacity of array. Call either |
| * by owner or with lock held -- it is OK for base, but not |
| * top, to move while resizings are in progress. |
| */ |
| final ForkJoinTask<?>[] growArray() { |
| ForkJoinTask<?>[] oldA = array; |
| int size = oldA != null ? oldA.length << 1 : INITIAL_QUEUE_CAPACITY; |
| if (size > MAXIMUM_QUEUE_CAPACITY) |
| throw new RejectedExecutionException("Queue capacity exceeded"); |
| int oldMask, t, b; |
| ForkJoinTask<?>[] a = array = new ForkJoinTask<?>[size]; |
| if (oldA != null && (oldMask = oldA.length - 1) >= 0 && |
| (t = top) - (b = base) > 0) { |
| int mask = size - 1; |
| do { // emulate poll from old array, push to new array |
| ForkJoinTask<?> x; |
| int oldj = ((b & oldMask) << ASHIFT) + ABASE; |
| int j = ((b & mask) << ASHIFT) + ABASE; |
| x = (ForkJoinTask<?>)U.getObjectVolatile(oldA, oldj); |
| if (x != null && |
| U.compareAndSwapObject(oldA, oldj, x, null)) |
| U.putObjectVolatile(a, j, x); |
| } while (++b != t); |
| } |
| return a; |
| } |
| |
| /** |
| * Takes next task, if one exists, in LIFO order. Call only |
| * by owner in unshared queues. |
| */ |
| final ForkJoinTask<?> pop() { |
| ForkJoinTask<?>[] a; ForkJoinTask<?> t; int m; |
| if ((a = array) != null && (m = a.length - 1) >= 0) { |
| for (int s; (s = top - 1) - base >= 0;) { |
| long j = ((m & s) << ASHIFT) + ABASE; |
| if ((t = (ForkJoinTask<?>)U.getObject(a, j)) == null) |
| break; |
| if (U.compareAndSwapObject(a, j, t, null)) { |
| U.putOrderedInt(this, QTOP, s); |
| return t; |
| } |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Takes a task in FIFO order if b is base of queue and a task |
| * can be claimed without contention. Specialized versions |
| * appear in ForkJoinPool methods scan and helpStealer. |
| */ |
| final ForkJoinTask<?> pollAt(int b) { |
| ForkJoinTask<?> t; ForkJoinTask<?>[] a; |
| if ((a = array) != null) { |
| int j = (((a.length - 1) & b) << ASHIFT) + ABASE; |
| if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null && |
| base == b && U.compareAndSwapObject(a, j, t, null)) { |
| base = b + 1; |
| return t; |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Takes next task, if one exists, in FIFO order. |
| */ |
| final ForkJoinTask<?> poll() { |
| ForkJoinTask<?>[] a; int b; ForkJoinTask<?> t; |
| while ((b = base) - top < 0 && (a = array) != null) { |
| int j = (((a.length - 1) & b) << ASHIFT) + ABASE; |
| t = (ForkJoinTask<?>)U.getObjectVolatile(a, j); |
| if (base == b) { |
| if (t != null) { |
| if (U.compareAndSwapObject(a, j, t, null)) { |
| base = b + 1; |
| return t; |
| } |
| } |
| else if (b + 1 == top) // now empty |
| break; |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Takes next task, if one exists, in order specified by mode. |
| */ |
| final ForkJoinTask<?> nextLocalTask() { |
| return (config & FIFO_QUEUE) == 0 ? pop() : poll(); |
| } |
| |
| /** |
| * Returns next task, if one exists, in order specified by mode. |
| */ |
| final ForkJoinTask<?> peek() { |
| ForkJoinTask<?>[] a = array; int m; |
| if (a == null || (m = a.length - 1) < 0) |
| return null; |
| int i = (config & FIFO_QUEUE) == 0 ? top - 1 : base; |
| int j = ((i & m) << ASHIFT) + ABASE; |
| return (ForkJoinTask<?>)U.getObjectVolatile(a, j); |
| } |
| |
| /** |
| * Pops the given task only if it is at the current top. |
| * (A shared version is available only via FJP.tryExternalUnpush) |
| */ |
| final boolean tryUnpush(ForkJoinTask<?> t) { |
| ForkJoinTask<?>[] a; int s; |
| if ((a = array) != null && (s = top) != base && |
| U.compareAndSwapObject |
| (a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) { |
| U.putOrderedInt(this, QTOP, s); |
| return true; |
| } |
| return false; |
| } |
| |
| /** |
| * Removes and cancels all known tasks, ignoring any exceptions. |
| */ |
| final void cancelAll() { |
| ForkJoinTask<?> t; |
| if ((t = currentJoin) != null) { |
| currentJoin = null; |
| ForkJoinTask.cancelIgnoringExceptions(t); |
| } |
| if ((t = currentSteal) != null) { |
| currentSteal = null; |
| ForkJoinTask.cancelIgnoringExceptions(t); |
| } |
| while ((t = poll()) != null) |
| ForkJoinTask.cancelIgnoringExceptions(t); |
| } |
| |
| // Specialized execution methods |
| |
| /** |
| * Polls and runs tasks until empty. |
| */ |
| final void pollAndExecAll() { |
| for (ForkJoinTask<?> t; (t = poll()) != null;) |
| t.doExec(); |
| } |
| |
| /** |
| * Removes and executes all local tasks. If LIFO, invokes |
| * pollAndExecAll. Otherwise implements a specialized pop loop |
| * to exec until empty. |
| */ |
| final void execLocalTasks() { |
| int b = base, m, s; |
| ForkJoinTask<?>[] a = array; |
| if (b - (s = top - 1) <= 0 && a != null && |
| (m = a.length - 1) >= 0) { |
| if ((config & FIFO_QUEUE) == 0) { |
| for (ForkJoinTask<?> t;;) { |
| if ((t = (ForkJoinTask<?>)U.getAndSetObject |
| (a, ((m & s) << ASHIFT) + ABASE, null)) == null) |
| break; |
| U.putOrderedInt(this, QTOP, s); |
| t.doExec(); |
| if (base - (s = top - 1) > 0) |
| break; |
| } |
| } |
| else |
| pollAndExecAll(); |
| } |
| } |
| |
| /** |
| * Executes the given task and any remaining local tasks. |
| */ |
| final void runTask(ForkJoinTask<?> task) { |
| if (task != null) { |
| scanState &= ~SCANNING; // mark as busy |
| (currentSteal = task).doExec(); |
| U.putOrderedObject(this, QCURRENTSTEAL, null); // release for GC |
| execLocalTasks(); |
| ForkJoinWorkerThread thread = owner; |
| if (++nsteals < 0) // collect on overflow |
| transferStealCount(pool); |
| scanState |= SCANNING; |
| if (thread != null) |
| thread.afterTopLevelExec(); |
| } |
| } |
| |
| /** |
| * Adds steal count to pool stealCounter if it exists, and resets. |
| */ |
| final void transferStealCount(ForkJoinPool p) { |
| AtomicLong sc; |
| if (p != null && (sc = p.stealCounter) != null) { |
| int s = nsteals; |
| nsteals = 0; // if negative, correct for overflow |
| sc.getAndAdd((long)(s < 0 ? Integer.MAX_VALUE : s)); |
| } |
| } |
| |
| /** |
| * If present, removes from queue and executes the given task, |
| * or any other cancelled task. Used only by awaitJoin. |
| * |
| * @return true if queue empty and task not known to be done |
| */ |
| final boolean tryRemoveAndExec(ForkJoinTask<?> task) { |
| ForkJoinTask<?>[] a; int m, s, b, n; |
| if ((a = array) != null && (m = a.length - 1) >= 0 && |
| task != null) { |
| while ((n = (s = top) - (b = base)) > 0) { |
| for (ForkJoinTask<?> t;;) { // traverse from s to b |
| long j = ((--s & m) << ASHIFT) + ABASE; |
| if ((t = (ForkJoinTask<?>)U.getObject(a, j)) == null) |
| return s + 1 == top; // shorter than expected |
| else if (t == task) { |
| boolean removed = false; |
| if (s + 1 == top) { // pop |
| if (U.compareAndSwapObject(a, j, task, null)) { |
| U.putOrderedInt(this, QTOP, s); |
| removed = true; |
| } |
| } |
| else if (base == b) // replace with proxy |
| removed = U.compareAndSwapObject( |
| a, j, task, new EmptyTask()); |
| if (removed) |
| task.doExec(); |
| break; |
| } |
| else if (t.status < 0 && s + 1 == top) { |
| if (U.compareAndSwapObject(a, j, t, null)) |
| U.putOrderedInt(this, QTOP, s); |
| break; // was cancelled |
| } |
| if (--n == 0) |
| return false; |
| } |
| if (task.status < 0) |
| return false; |
| } |
| } |
| return true; |
| } |
| |
| /** |
| * Pops task if in the same CC computation as the given task, |
| * in either shared or owned mode. Used only by helpComplete. |
| */ |
| final CountedCompleter<?> popCC(CountedCompleter<?> task, int mode) { |
| int s; ForkJoinTask<?>[] a; Object o; |
| if (base - (s = top) < 0 && (a = array) != null) { |
| long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE; |
| if ((o = U.getObjectVolatile(a, j)) != null && |
| (o instanceof CountedCompleter)) { |
| CountedCompleter<?> t = (CountedCompleter<?>)o; |
| for (CountedCompleter<?> r = t;;) { |
| if (r == task) { |
| if (mode < 0) { // must lock |
| if (U.compareAndSwapInt(this, QLOCK, 0, 1)) { |
| if (top == s && array == a && |
| U.compareAndSwapObject(a, j, t, null)) { |
| U.putOrderedInt(this, QTOP, s - 1); |
| U.putOrderedInt(this, QLOCK, 0); |
| return t; |
| } |
| U.compareAndSwapInt(this, QLOCK, 1, 0); |
| } |
| } |
| else if (U.compareAndSwapObject(a, j, t, null)) { |
| U.putOrderedInt(this, QTOP, s - 1); |
| return t; |
| } |
| break; |
| } |
| else if ((r = r.completer) == null) // try parent |
| break; |
| } |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Steals and runs a task in the same CC computation as the |
| * given task if one exists and can be taken without |
| * contention. Otherwise returns a checksum/control value for |
| * use by method helpComplete. |
| * |
| * @return 1 if successful, 2 if retryable (lost to another |
| * stealer), -1 if non-empty but no matching task found, else |
| * the base index, forced negative. |
| */ |
| final int pollAndExecCC(CountedCompleter<?> task) { |
| int b, h; ForkJoinTask<?>[] a; Object o; |
| if ((b = base) - top >= 0 || (a = array) == null) |
| h = b | Integer.MIN_VALUE; // to sense movement on re-poll |
| else { |
| long j = (((a.length - 1) & b) << ASHIFT) + ABASE; |
| if ((o = U.getObjectVolatile(a, j)) == null) |
| h = 2; // retryable |
| else if (!(o instanceof CountedCompleter)) |
| h = -1; // unmatchable |
| else { |
| CountedCompleter<?> t = (CountedCompleter<?>)o; |
| for (CountedCompleter<?> r = t;;) { |
| if (r == task) { |
| if (base == b && |
| U.compareAndSwapObject(a, j, t, null)) { |
| base = b + 1; |
| t.doExec(); |
| h = 1; // success |
| } |
| else |
| h = 2; // lost CAS |
| break; |
| } |
| else if ((r = r.completer) == null) { |
| h = -1; // unmatched |
| break; |
| } |
| } |
| } |
| } |
| return h; |
| } |
| |
| /** |
| * Returns true if owned and not known to be blocked. |
| */ |
| final boolean isApparentlyUnblocked() { |
| Thread wt; Thread.State s; |
| return (scanState >= 0 && |
| (wt = owner) != null && |
| (s = wt.getState()) != Thread.State.BLOCKED && |
| s != Thread.State.WAITING && |
| s != Thread.State.TIMED_WAITING); |
| } |
| |
| // Unsafe mechanics. Note that some are (and must be) the same as in FJP |
| private static final sun.misc.Unsafe U; |
| private static final int ABASE; |
| private static final int ASHIFT; |
| private static final long QTOP; |
| private static final long QLOCK; |
| private static final long QCURRENTSTEAL; |
| static { |
| try { |
| U = sun.misc.Unsafe.getUnsafe(); |
| Class<?> wk = WorkQueue.class; |
| Class<?> ak = ForkJoinTask[].class; |
| QTOP = U.objectFieldOffset |
| (wk.getDeclaredField("top")); |
| QLOCK = U.objectFieldOffset |
| (wk.getDeclaredField("qlock")); |
| QCURRENTSTEAL = U.objectFieldOffset |
| (wk.getDeclaredField("currentSteal")); |
| ABASE = U.arrayBaseOffset(ak); |
| int scale = U.arrayIndexScale(ak); |
| if ((scale & (scale - 1)) != 0) |
| throw new Error("data type scale not a power of two"); |
| ASHIFT = 31 - Integer.numberOfLeadingZeros(scale); |
| } catch (Exception e) { |
| throw new Error(e); |
| } |
| } |
| } |
| |
| // static fields (initialized in static initializer below) |
| |
| /** |
| * Creates a new ForkJoinWorkerThread. This factory is used unless |
| * overridden in ForkJoinPool constructors. |
| */ |
| public static final ForkJoinWorkerThreadFactory |
| defaultForkJoinWorkerThreadFactory; |
| |
| /** |
| * Permission required for callers of methods that may start or |
| * kill threads. |
| */ |
| private static final RuntimePermission modifyThreadPermission; |
| |
| /** |
| * Common (static) pool. Non-null for public use unless a static |
| * construction exception, but internal usages null-check on use |
| * to paranoically avoid potential initialization circularities |
| * as well as to simplify generated code. |
| */ |
| static final ForkJoinPool common; |
| |
| /** |
| * Common pool parallelism. To allow simpler use and management |
| * when common pool threads are disabled, we allow the underlying |
| * common.parallelism field to be zero, but in that case still report |
| * parallelism as 1 to reflect resulting caller-runs mechanics. |
| */ |
| static final int commonParallelism; |
| |
| /** |
| * Limit on spare thread construction in tryCompensate. |
| */ |
| private static int commonMaxSpares; |
| |
| /** |
| * Sequence number for creating workerNamePrefix. |
| */ |
| private static int poolNumberSequence; |
| |
| /** |
| * Returns the next sequence number. We don't expect this to |
| * ever contend, so use simple builtin sync. |
| */ |
| private static final synchronized int nextPoolId() { |
| return ++poolNumberSequence; |
| } |
| |
| // static configuration constants |
| |
| /** |
| * Initial timeout value (in nanoseconds) for the thread |
| * triggering quiescence to park waiting for new work. On timeout, |
| * the thread will instead try to shrink the number of |
| * workers. The value should be large enough to avoid overly |
| * aggressive shrinkage during most transient stalls (long GCs |
| * etc). |
| */ |
| private static final long IDLE_TIMEOUT = 2000L * 1000L * 1000L; // 2sec |
| |
| /** |
| * Tolerance for idle timeouts, to cope with timer undershoots |
| */ |
| private static final long TIMEOUT_SLOP = 20L * 1000L * 1000L; // 20ms |
| |
| /** |
| * The initial value for commonMaxSpares during static |
| * initialization unless overridden using System property |
| * "java.util.concurrent.ForkJoinPool.common.maximumSpares". The |
| * default value is far in excess of normal requirements, but also |
| * far short of MAX_CAP and typical OS thread limits, so allows |
| * JVMs to catch misuse/abuse before running out of resources |
| * needed to do so. |
| */ |
| private static final int DEFAULT_COMMON_MAX_SPARES = 256; |
| |
| /** |
| * Number of times to spin-wait before blocking. The spins (in |
| * awaitRunStateLock and awaitWork) currently use randomized |
| * spins. If/when MWAIT-like intrinsics becomes available, they |
| * may allow quieter spinning. The value of SPINS must be a power |
| * of two, at least 4. The current value causes spinning for a |
| * small fraction of typical context-switch times, well worthwhile |
| * given the typical likelihoods that blocking is not necessary. |
| */ |
| private static final int SPINS = 1 << 11; |
| |
| /** |
| * Increment for seed generators. See class ThreadLocal for |
| * explanation. |
| */ |
| private static final int SEED_INCREMENT = 0x9e3779b9; |
| |
| /* |
| * Bits and masks for field ctl, packed with 4 16 bit subfields: |
| * AC: Number of active running workers minus target parallelism |
| * TC: Number of total workers minus target parallelism |
| * SS: version count and status of top waiting thread |
| * ID: poolIndex of top of Treiber stack of waiters |
| * |
| * When convenient, we can extract the lower 32 stack top bits |
| * (including version bits) as sp=(int)ctl. The offsets of counts |
| * by the target parallelism and the positionings of fields makes |
| * it possible to perform the most common checks via sign tests of |
| * fields: When ac is negative, there are not enough active |
| * workers, when tc is negative, there are not enough total |
| * workers. When sp is non-zero, there are waiting workers. To |
| * deal with possibly negative fields, we use casts in and out of |
| * "short" and/or signed shifts to maintain signedness. |
| * |
| * Because it occupies uppermost bits, we can add one active count |
| * using getAndAddLong of AC_UNIT, rather than CAS, when returning |
| * from a blocked join. Other updates entail multiple subfields |
| * and masking, requiring CAS. |
| */ |
| |
| // Lower and upper word masks |
| private static final long SP_MASK = 0xffffffffL; |
| private static final long UC_MASK = ~SP_MASK; |
| |
| // Active counts |
| private static final int AC_SHIFT = 48; |
| private static final long AC_UNIT = 0x0001L << AC_SHIFT; |
| private static final long AC_MASK = 0xffffL << AC_SHIFT; |
| |
| // Total counts |
| private static final int TC_SHIFT = 32; |
| private static final long TC_UNIT = 0x0001L << TC_SHIFT; |
| private static final long TC_MASK = 0xffffL << TC_SHIFT; |
| private static final long ADD_WORKER = 0x0001L << (TC_SHIFT + 15); // sign |
| |
| // runState bits: SHUTDOWN must be negative, others arbitrary powers of two |
| private static final int RSLOCK = 1; |
| private static final int RSIGNAL = 1 << 1; |
| private static final int STARTED = 1 << 2; |
| private static final int STOP = 1 << 29; |
| private static final int TERMINATED = 1 << 30; |
| private static final int SHUTDOWN = 1 << 31; |
| |
| // Instance fields |
| volatile long ctl; // main pool control |
| volatile int runState; // lockable status |
| final int config; // parallelism, mode |
| int indexSeed; // to generate worker index |
| volatile WorkQueue[] workQueues; // main registry |
| final ForkJoinWorkerThreadFactory factory; |
| final UncaughtExceptionHandler ueh; // per-worker UEH |
| final String workerNamePrefix; // to create worker name string |
| volatile AtomicLong stealCounter; // also used as sync monitor |
| |
| /** |
| * Acquires the runState lock; returns current (locked) runState. |
| */ |
| private int lockRunState() { |
| int rs; |
| return ((((rs = runState) & RSLOCK) != 0 || |
| !U.compareAndSwapInt(this, RUNSTATE, rs, rs |= RSLOCK)) ? |
| awaitRunStateLock() : rs); |
| } |
| |
| /** |
| * Spins and/or blocks until runstate lock is available. See |
| * above for explanation. |
| */ |
| private int awaitRunStateLock() { |
| Object lock; |
| boolean wasInterrupted = false; |
| for (int spins = SPINS, r = 0, rs, ns;;) { |
| if (((rs = runState) & RSLOCK) == 0) { |
| if (U.compareAndSwapInt(this, RUNSTATE, rs, ns = rs | RSLOCK)) { |
| if (wasInterrupted) { |
| try { |
| Thread.currentThread().interrupt(); |
| } catch (SecurityException ignore) { |
| } |
| } |
| return ns; |
| } |
| } |
| else if (r == 0) |
| r = ThreadLocalRandom.nextSecondarySeed(); |
| else if (spins > 0) { |
| r ^= r << 6; r ^= r >>> 21; r ^= r << 7; // xorshift |
| if (r >= 0) |
| --spins; |
| } |
| else if ((rs & STARTED) == 0 || (lock = stealCounter) == null) |
| Thread.yield(); // initialization race |
| else if (U.compareAndSwapInt(this, RUNSTATE, rs, rs | RSIGNAL)) { |
| synchronized (lock) { |
| if ((runState & RSIGNAL) != 0) { |
| try { |
| lock.wait(); |
| } catch (InterruptedException ie) { |
| if (!(Thread.currentThread() instanceof |
| ForkJoinWorkerThread)) |
| wasInterrupted = true; |
| } |
| } |
| else |
| lock.notifyAll(); |
| } |
| } |
| } |
| } |
| |
| /** |
| * Unlocks and sets runState to newRunState. |
| * |
| * @param oldRunState a value returned from lockRunState |
| * @param newRunState the next value (must have lock bit clear). |
| */ |
| private void unlockRunState(int oldRunState, int newRunState) { |
| if (!U.compareAndSwapInt(this, RUNSTATE, oldRunState, newRunState)) { |
| Object lock = stealCounter; |
| runState = newRunState; // clears RSIGNAL bit |
| if (lock != null) |
| synchronized (lock) { lock.notifyAll(); } |
| } |
| } |
| |
| // Creating, registering and deregistering workers |
| |
| /** |
| * Tries to construct and start one worker. Assumes that total |
| * count has already been incremented as a reservation. Invokes |
| * deregisterWorker on any failure. |
| * |
| * @return true if successful |
| */ |
| private boolean createWorker() { |
| ForkJoinWorkerThreadFactory fac = factory; |
| Throwable ex = null; |
| ForkJoinWorkerThread wt = null; |
| try { |
| if (fac != null && (wt = fac.newThread(this)) != null) { |
| wt.start(); |
| return true; |
| } |
| } catch (Throwable rex) { |
| ex = rex; |
| } |
| deregisterWorker(wt, ex); |
| return false; |
| } |
| |
| /** |
| * Tries to add one worker, incrementing ctl counts before doing |
| * so, relying on createWorker to back out on failure. |
| * |
| * @param c incoming ctl value, with total count negative and no |
| * idle workers. On CAS failure, c is refreshed and retried if |
| * this holds (otherwise, a new worker is not needed). |
| */ |
| private void tryAddWorker(long c) { |
| boolean add = false; |
| do { |
| long nc = ((AC_MASK & (c + AC_UNIT)) | |
| (TC_MASK & (c + TC_UNIT))); |
| if (ctl == c) { |
| int rs, stop; // check if terminating |
| if ((stop = (rs = lockRunState()) & STOP) == 0) |
| add = U.compareAndSwapLong(this, CTL, c, nc); |
| unlockRunState(rs, rs & ~RSLOCK); |
| if (stop != 0) |
| break; |
| if (add) { |
| createWorker(); |
| break; |
| } |
| } |
| } while (((c = ctl) & ADD_WORKER) != 0L && (int)c == 0); |
| } |
| |
| /** |
| * Callback from ForkJoinWorkerThread constructor to establish and |
| * record its WorkQueue. |
| * |
| * @param wt the worker thread |
| * @return the worker's queue |
| */ |
| final WorkQueue registerWorker(ForkJoinWorkerThread wt) { |
| UncaughtExceptionHandler handler; |
| wt.setDaemon(true); // configure thread |
| if ((handler = ueh) != null) |
| wt.setUncaughtExceptionHandler(handler); |
| WorkQueue w = new WorkQueue(this, wt); |
| int i = 0; // assign a pool index |
| int mode = config & MODE_MASK; |
| int rs = lockRunState(); |
| try { |
| WorkQueue[] ws; int n; // skip if no array |
| if ((ws = workQueues) != null && (n = ws.length) > 0) { |
| int s = indexSeed += SEED_INCREMENT; // unlikely to collide |
| int m = n - 1; |
| i = ((s << 1) | 1) & m; // odd-numbered indices |
| if (ws[i] != null) { // collision |
| int probes = 0; // step by approx half n |
| int step = (n <= 4) ? 2 : ((n >>> 1) & EVENMASK) + 2; |
| while (ws[i = (i + step) & m] != null) { |
| if (++probes >= n) { |
| workQueues = ws = Arrays.copyOf(ws, n <<= 1); |
| m = n - 1; |
| probes = 0; |
| } |
| } |
| } |
| w.hint = s; // use as random seed |
| w.config = i | mode; |
| w.scanState = i; // publication fence |
| ws[i] = w; |
| } |
| } finally { |
| unlockRunState(rs, rs & ~RSLOCK); |
| } |
| wt.setName(workerNamePrefix.concat(Integer.toString(i >>> 1))); |
| return w; |
| } |
| |
| /** |
| * Final callback from terminating worker, as well as upon failure |
| * to construct or start a worker. Removes record of worker from |
| * array, and adjusts counts. If pool is shutting down, tries to |
| * complete termination. |
| * |
| * @param wt the worker thread, or null if construction failed |
| * @param ex the exception causing failure, or null if none |
| */ |
| final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) { |
| WorkQueue w = null; |
| if (wt != null && (w = wt.workQueue) != null) { |
| WorkQueue[] ws; // remove index from array |
| int idx = w.config & SMASK; |
| int rs = lockRunState(); |
| if ((ws = workQueues) != null && ws.length > idx && ws[idx] == w) |
| ws[idx] = null; |
| unlockRunState(rs, rs & ~RSLOCK); |
| } |
| long c; // decrement counts |
| do {} while (!U.compareAndSwapLong |
| (this, CTL, c = ctl, ((AC_MASK & (c - AC_UNIT)) | |
| (TC_MASK & (c - TC_UNIT)) | |
| (SP_MASK & c)))); |
| if (w != null) { |
| w.qlock = -1; // ensure set |
| w.transferStealCount(this); |
| w.cancelAll(); // cancel remaining tasks |
| } |
| for (;;) { // possibly replace |
| WorkQueue[] ws; int m, sp; |
| if (tryTerminate(false, false) || w == null || w.array == null || |
| (runState & STOP) != 0 || (ws = workQueues) == null || |
| (m = ws.length - 1) < 0) // already terminating |
| break; |
| if ((sp = (int)(c = ctl)) != 0) { // wake up replacement |
| if (tryRelease(c, ws[sp & m], AC_UNIT)) |
| break; |
| } |
| else if (ex != null && (c & ADD_WORKER) != 0L) { |
| tryAddWorker(c); // create replacement |
| break; |
| } |
| else // don't need replacement |
| break; |
| } |
| if (ex == null) // help clean on way out |
| ForkJoinTask.helpExpungeStaleExceptions(); |
| else // rethrow |
| ForkJoinTask.rethrow(ex); |
| } |
| |
| // Signalling |
| |
| /** |
| * Tries to create or activate a worker if too few are active. |
| * |
| * @param ws the worker array to use to find signallees |
| * @param q a WorkQueue --if non-null, don't retry if now empty |
| */ |
| final void signalWork(WorkQueue[] ws, WorkQueue q) { |
| long c; int sp, i; WorkQueue v; Thread p; |
| while ((c = ctl) < 0L) { // too few active |
| if ((sp = (int)c) == 0) { // no idle workers |
| if ((c & ADD_WORKER) != 0L) // too few workers |
| tryAddWorker(c); |
| break; |
| } |
| if (ws == null) // unstarted/terminated |
| break; |
| if (ws.length <= (i = sp & SMASK)) // terminated |
| break; |
| if ((v = ws[i]) == null) // terminating |
| break; |
| int vs = (sp + SS_SEQ) & ~INACTIVE; // next scanState |
| int d = sp - v.scanState; // screen CAS |
| long nc = (UC_MASK & (c + AC_UNIT)) | (SP_MASK & v.stackPred); |
| if (d == 0 && U.compareAndSwapLong(this, CTL, c, nc)) { |
| v.scanState = vs; // activate v |
| if ((p = v.parker) != null) |
| U.unpark(p); |
| break; |
| } |
| if (q != null && q.base == q.top) // no more work |
| break; |
| } |
| } |
| |
| /** |
| * Signals and releases worker v if it is top of idle worker |
| * stack. This performs a one-shot version of signalWork only if |
| * there is (apparently) at least one idle worker. |
| * |
| * @param c incoming ctl value |
| * @param v if non-null, a worker |
| * @param inc the increment to active count (zero when compensating) |
| * @return true if successful |
| */ |
| private boolean tryRelease(long c, WorkQueue v, long inc) { |
| int sp = (int)c, vs = (sp + SS_SEQ) & ~INACTIVE; Thread p; |
| if (v != null && v.scanState == sp) { // v is at top of stack |
| long nc = (UC_MASK & (c + inc)) | (SP_MASK & v.stackPred); |
| if (U.compareAndSwapLong(this, CTL, c, nc)) { |
| v.scanState = vs; |
| if ((p = v.parker) != null) |
| U.unpark(p); |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| // Scanning for tasks |
| |
| /** |
| * Top-level runloop for workers, called by ForkJoinWorkerThread.run. |
| */ |
| final void runWorker(WorkQueue w) { |
| w.growArray(); // allocate queue |
| int seed = w.hint; // initially holds randomization hint |
| int r = (seed == 0) ? 1 : seed; // avoid 0 for xorShift |
| for (ForkJoinTask<?> t;;) { |
| if ((t = scan(w, r)) != null) |
| w.runTask(t); |
| else if (!awaitWork(w, r)) |
| break; |
| r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // xorshift |
| } |
| } |
| |
| /** |
| * Scans for and tries to steal a top-level task. Scans start at a |
| * random location, randomly moving on apparent contention, |
| * otherwise continuing linearly until reaching two consecutive |
| * empty passes over all queues with the same checksum (summing |
| * each base index of each queue, that moves on each steal), at |
| * which point the worker tries to inactivate and then re-scans, |
| * attempting to re-activate (itself or some other worker) if |
| * finding a task; otherwise returning null to await work. Scans |
| * otherwise touch as little memory as possible, to reduce |
| * disruption on other scanning threads. |
| * |
| * @param w the worker (via its WorkQueue) |
| * @param r a random seed |
| * @return a task, or null if none found |
| */ |
| private ForkJoinTask<?> scan(WorkQueue w, int r) { |
| WorkQueue[] ws; int m; |
| if ((ws = workQueues) != null && (m = ws.length - 1) > 0 && w != null) { |
| int ss = w.scanState; // initially non-negative |
| for (int origin = r & m, k = origin, oldSum = 0, checkSum = 0;;) { |
| WorkQueue q; ForkJoinTask<?>[] a; ForkJoinTask<?> t; |
| int b, n; long c; |
| if ((q = ws[k]) != null) { |
| if ((n = (b = q.base) - q.top) < 0 && |
| (a = q.array) != null) { // non-empty |
| long i = (((a.length - 1) & b) << ASHIFT) + ABASE; |
| if ((t = ((ForkJoinTask<?>) |
| U.getObjectVolatile(a, i))) != null && |
| q.base == b) { |
| if (ss >= 0) { |
| if (U.compareAndSwapObject(a, i, t, null)) { |
| q.base = b + 1; |
| if (n < -1) // signal others |
| signalWork(ws, q); |
| return t; |
| } |
| } |
| else if (oldSum == 0 && // try to activate |
| w.scanState < 0) |
| tryRelease(c = ctl, ws[m & (int)c], AC_UNIT); |
| } |
| if (ss < 0) // refresh |
| ss = w.scanState; |
| r ^= r << 1; r ^= r >>> 3; r ^= r << 10; |
| origin = k = r & m; // move and rescan |
| oldSum = checkSum = 0; |
| continue; |
| } |
| checkSum += b; |
| } |
| if ((k = (k + 1) & m) == origin) { // continue until stable |
| if ((ss >= 0 || (ss == (ss = w.scanState))) && |
| oldSum == (oldSum = checkSum)) { |
| if (ss < 0 || w.qlock < 0) // already inactive |
| break; |
| int ns = ss | INACTIVE; // try to inactivate |
| long nc = ((SP_MASK & ns) | |
| (UC_MASK & ((c = ctl) - AC_UNIT))); |
| w.stackPred = (int)c; // hold prev stack top |
| U.putInt(w, QSCANSTATE, ns); |
| if (U.compareAndSwapLong(this, CTL, c, nc)) |
| ss = ns; |
| else |
| w.scanState = ss; // back out |
| } |
| checkSum = 0; |
| } |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Possibly blocks worker w waiting for a task to steal, or |
| * returns false if the worker should terminate. If inactivating |
| * w has caused the pool to become quiescent, checks for pool |
| * termination, and, so long as this is not the only worker, waits |
| * for up to a given duration. On timeout, if ctl has not |
| * changed, terminates the worker, which will in turn wake up |
| * another worker to possibly repeat this process. |
| * |
| * @param w the calling worker |
| * @param r a random seed (for spins) |
| * @return false if the worker should terminate |
| */ |
| private boolean awaitWork(WorkQueue w, int r) { |
| if (w == null || w.qlock < 0) // w is terminating |
| return false; |
| for (int pred = w.stackPred, spins = SPINS, ss;;) { |
| if ((ss = w.scanState) >= 0) |
| break; |
| else if (spins > 0) { |
| r ^= r << 6; r ^= r >>> 21; r ^= r << 7; |
| if (r >= 0 && --spins == 0) { // randomize spins |
| WorkQueue v; WorkQueue[] ws; int s, j; AtomicLong sc; |
| if (pred != 0 && (ws = workQueues) != null && |
| (j = pred & SMASK) < ws.length && |
| (v = ws[j]) != null && // see if pred parking |
| (v.parker == null || v.scanState >= 0)) |
| spins = SPINS; // continue spinning |
| } |
| } |
| else if (w.qlock < 0) // recheck after spins |
| return false; |
| else if (!Thread.interrupted()) { |
| long c, prevctl, parkTime, deadline; |
| int ac = (int)((c = ctl) >> AC_SHIFT) + (config & SMASK); |
| if ((ac <= 0 && tryTerminate(false, false)) || |
| (runState & STOP) != 0) // pool terminating |
| return false; |
| if (ac <= 0 && ss == (int)c) { // is last waiter |
| prevctl = (UC_MASK & (c + AC_UNIT)) | (SP_MASK & pred); |
| int t = (short)(c >>> TC_SHIFT); // shrink excess spares |
| if (t > 2 && U.compareAndSwapLong(this, CTL, c, prevctl)) |
| return false; // else use timed wait |
| parkTime = IDLE_TIMEOUT * ((t >= 0) ? 1 : 1 - t); |
| deadline = System.nanoTime() + parkTime - TIMEOUT_SLOP; |
| } |
| else |
| prevctl = parkTime = deadline = 0L; |
| Thread wt = Thread.currentThread(); |
| U.putObject(wt, PARKBLOCKER, this); // emulate LockSupport |
| w.parker = wt; |
| if (w.scanState < 0 && ctl == c) // recheck before park |
| U.park(false, parkTime); |
| U.putOrderedObject(w, QPARKER, null); |
| U.putObject(wt, PARKBLOCKER, null); |
| if (w.scanState >= 0) |
| break; |
| if (parkTime != 0L && ctl == c && |
| deadline - System.nanoTime() <= 0L && |
| U.compareAndSwapLong(this, CTL, c, prevctl)) |
| return false; // shrink pool |
| } |
| } |
| return true; |
| } |
| |
| // Joining tasks |
| |
| /** |
| * Tries to steal and run tasks within the target's computation. |
| * Uses a variant of the top-level algorithm, restricted to tasks |
| * with the given task as ancestor: It prefers taking and running |
| * eligible tasks popped from the worker's own queue (via |
| * popCC). Otherwise it scans others, randomly moving on |
| * contention or execution, deciding to give up based on a |
| * checksum (via return codes frob pollAndExecCC). The maxTasks |
| * argument supports external usages; internal calls use zero, |
| * allowing unbounded steps (external calls trap non-positive |
| * values). |
| * |
| * @param w caller |
| * @param maxTasks if non-zero, the maximum number of other tasks to run |
| * @return task status on exit |
| */ |
| final int helpComplete(WorkQueue w, CountedCompleter<?> task, |
| int maxTasks) { |
| WorkQueue[] ws; int s = 0, m; |
| if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 && |
| task != null && w != null) { |
| int mode = w.config; // for popCC |
| int r = w.hint ^ w.top; // arbitrary seed for origin |
| int origin = r & m; // first queue to scan |
| int h = 1; // 1:ran, >1:contended, <0:hash |
| for (int k = origin, oldSum = 0, checkSum = 0;;) { |
| CountedCompleter<?> p; WorkQueue q; |
| if ((s = task.status) < 0) |
| break; |
| if (h == 1 && (p = w.popCC(task, mode)) != null) { |
| p.doExec(); // run local task |
| if (maxTasks != 0 && --maxTasks == 0) |
| break; |
| origin = k; // reset |
| oldSum = checkSum = 0; |
| } |
| else { // poll other queues |
| if ((q = ws[k]) == null) |
| h = 0; |
| else if ((h = q.pollAndExecCC(task)) < 0) |
| checkSum += h; |
| if (h > 0) { |
| if (h == 1 && maxTasks != 0 && --maxTasks == 0) |
| break; |
| r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // xorshift |
| origin = k = r & m; // move and restart |
| oldSum = checkSum = 0; |
| } |
| else if ((k = (k + 1) & m) == origin) { |
| if (oldSum == (oldSum = checkSum)) |
| break; |
| checkSum = 0; |
| } |
| } |
| } |
| } |
| return s; |
| } |
| |
| /** |
| * Tries to locate and execute tasks for a stealer of the given |
| * task, or in turn one of its stealers, Traces currentSteal -> |
| * currentJoin links looking for a thread working on a descendant |
| * of the given task and with a non-empty queue to steal back and |
| * execute tasks from. The first call to this method upon a |
| * waiting join will often entail scanning/search, (which is OK |
| * because the joiner has nothing better to do), but this method |
| * leaves hints in workers to speed up subsequent calls. |
| * |
| * @param w caller |
| * @param task the task to join |
| */ |
| private void helpStealer(WorkQueue w, ForkJoinTask<?> task) { |
| WorkQueue[] ws = workQueues; |
| int oldSum = 0, checkSum, m; |
| if (ws != null && (m = ws.length - 1) >= 0 && w != null && |
| task != null) { |
| do { // restart point |
| checkSum = 0; // for stability check |
| ForkJoinTask<?> subtask; |
| WorkQueue j = w, v; // v is subtask stealer |
| descent: for (subtask = task; subtask.status >= 0; ) { |
| for (int h = j.hint | 1, k = 0, i; ; k += 2) { |
| if (k > m) // can't find stealer |
| break descent; |
| if ((v = ws[i = (h + k) & m]) != null) { |
| if (v.currentSteal == subtask) { |
| j.hint = i; |
| break; |
| } |
| checkSum += v.base; |
| } |
| } |
| for (;;) { // help v or descend |
| ForkJoinTask<?>[] a; int b; |
| checkSum += (b = v.base); |
| ForkJoinTask<?> next = v.currentJoin; |
| if (subtask.status < 0 || j.currentJoin != subtask || |
| v.currentSteal != subtask) // stale |
| break descent; |
| if (b - v.top >= 0 || (a = v.array) == null) { |
| if ((subtask = next) == null) |
| break descent; |
| j = v; |
| break; |
| } |
| int i = (((a.length - 1) & b) << ASHIFT) + ABASE; |
| ForkJoinTask<?> t = ((ForkJoinTask<?>) |
| U.getObjectVolatile(a, i)); |
| if (v.base == b) { |
| if (t == null) // stale |
| break descent; |
| if (U.compareAndSwapObject(a, i, t, null)) { |
| v.base = b + 1; |
| ForkJoinTask<?> ps = w.currentSteal; |
| int top = w.top; |
| do { |
| U.putOrderedObject(w, QCURRENTSTEAL, t); |
| t.doExec(); // clear local tasks too |
| } while (task.status >= 0 && |
| w.top != top && |
| (t = w.pop()) != null); |
| U.putOrderedObject(w, QCURRENTSTEAL, ps); |
| if (w.base != w.top) |
| return; // can't further help |
| } |
| } |
| } |
| } |
| } while (task.status >= 0 && oldSum != (oldSum = checkSum)); |
| } |
| } |
| |
| /** |
| * Tries to decrement active count (sometimes implicitly) and |
| * possibly release or create a compensating worker in preparation |
| * for blocking. Returns false (retryable by caller), on |
| * contention, detected staleness, instability, or termination. |
| * |
| * @param w caller |
| */ |
| private boolean tryCompensate(WorkQueue w) { |
| boolean canBlock; |
| WorkQueue[] ws; long c; int m, pc, sp; |
| if (w == null || w.qlock < 0 || // caller terminating |
| (ws = workQueues) == null || (m = ws.length - 1) <= 0 || |
| (pc = config & SMASK) == 0) // parallelism disabled |
| canBlock = false; |
| else if ((sp = (int)(c = ctl)) != 0) // release idle worker |
| canBlock = tryRelease(c, ws[sp & m], 0L); |
| else { |
| int ac = (int)(c >> AC_SHIFT) + pc; |
| int tc = (short)(c >> TC_SHIFT) + pc; |
| int nbusy = 0; // validate saturation |
| for (int i = 0; i <= m; ++i) { // two passes of odd indices |
| WorkQueue v; |
| if ((v = ws[((i << 1) | 1) & m]) != null) { |
| if ((v.scanState & SCANNING) != 0) |
| break; |
| ++nbusy; |
| } |
| } |
| if (nbusy != (tc << 1) || ctl != c) |
| canBlock = false; // unstable or stale |
| else if (tc >= pc && ac > 1 && w.isEmpty()) { |
| long nc = ((AC_MASK & (c - AC_UNIT)) | |
| (~AC_MASK & c)); // uncompensated |
| canBlock = U.compareAndSwapLong(this, CTL, c, nc); |
| } |
| else if (tc >= MAX_CAP || |
| (this == common && tc >= pc + commonMaxSpares)) |
| throw new RejectedExecutionException( |
| "Thread limit exceeded replacing blocked worker"); |
| else { // similar to tryAddWorker |
| boolean add = false; int rs; // CAS within lock |
| long nc = ((AC_MASK & c) | |
| (TC_MASK & (c + TC_UNIT))); |
| if (((rs = lockRunState()) & STOP) == 0) |
| add = U.compareAndSwapLong(this, CTL, c, nc); |
| unlockRunState(rs, rs & ~RSLOCK); |
| canBlock = add && createWorker(); // throws on exception |
| } |
| } |
| return canBlock; |
| } |
| |
| /** |
| * Helps and/or blocks until the given task is done or timeout. |
| * |
| * @param w caller |
| * @param task the task |
| * @param deadline for timed waits, if nonzero |
| * @return task status on exit |
| */ |
| final int awaitJoin(WorkQueue w, ForkJoinTask<?> task, long deadline) { |
| int s = 0; |
| if (task != null && w != null) { |
| ForkJoinTask<?> prevJoin = w.currentJoin; |
| U.putOrderedObject(w, QCURRENTJOIN, task); |
| CountedCompleter<?> cc = (task instanceof CountedCompleter) ? |
| (CountedCompleter<?>)task : null; |
| for (;;) { |
| if ((s = task.status) < 0) |
| break; |
| if (cc != null) |
| helpComplete(w, cc, 0); |
| else if (w.base == w.top || w.tryRemoveAndExec(task)) |
| helpStealer(w, task); |
| if ((s = task.status) < 0) |
| break; |
| long ms, ns; |
| if (deadline == 0L) |
| ms = 0L; |
| else if ((ns = deadline - System.nanoTime()) <= 0L) |
| break; |
| else if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) <= 0L) |
| ms = 1L; |
| if (tryCompensate(w)) { |
| task.internalWait(ms); |
| U.getAndAddLong(this, CTL, AC_UNIT); |
| } |
| } |
| U.putOrderedObject(w, QCURRENTJOIN, prevJoin); |
| } |
| return s; |
| } |
| |
| // Specialized scanning |
| |
| /** |
| * Returns a (probably) non-empty steal queue, if one is found |
| * during a scan, else null. This method must be retried by |
| * caller if, by the time it tries to use the queue, it is empty. |
| */ |
| private WorkQueue findNonEmptyStealQueue() { |
| WorkQueue[] ws; int m; // one-shot version of scan loop |
| int r = ThreadLocalRandom.nextSecondarySeed(); |
| if ((ws = workQueues) != null && (m = ws.length - 1) >= 0) { |
| for (int origin = r & m, k = origin, oldSum = 0, checkSum = 0;;) { |
| WorkQueue q; int b; |
| if ((q = ws[k]) != null) { |
| if ((b = q.base) - q.top < 0) |
| return q; |
| checkSum += b; |
| } |
| if ((k = (k + 1) & m) == origin) { |
| if (oldSum == (oldSum = checkSum)) |
| break; |
| checkSum = 0; |
| } |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Runs tasks until {@code isQuiescent()}. We piggyback on |
| * active count ctl maintenance, but rather than blocking |
| * when tasks cannot be found, we rescan until all others cannot |
| * find tasks either. |
| */ |
| final void helpQuiescePool(WorkQueue w) { |
| ForkJoinTask<?> ps = w.currentSteal; // save context |
| for (boolean active = true;;) { |
| long c; WorkQueue q; ForkJoinTask<?> t; int b; |
| w.execLocalTasks(); // run locals before each scan |
| if ((q = findNonEmptyStealQueue()) != null) { |
| if (!active) { // re-establish active count |
| active = true; |
| U.getAndAddLong(this, CTL, AC_UNIT); |
| } |
| if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null) { |
| U.putOrderedObject(w, QCURRENTSTEAL, t); |
| t.doExec(); |
| if (++w.nsteals < 0) |
| w.transferStealCount(this); |
| } |
| } |
| else if (active) { // decrement active count without queuing |
| long nc = (AC_MASK & ((c = ctl) - AC_UNIT)) | (~AC_MASK & c); |
| if ((int)(nc >> AC_SHIFT) + (config & SMASK) <= 0) |
| break; // bypass decrement-then-increment |
| if (U.compareAndSwapLong(this, CTL, c, nc)) |
| active = false; |
| } |
| else if ((int)((c = ctl) >> AC_SHIFT) + (config & SMASK) <= 0 && |
| U.compareAndSwapLong(this, CTL, c, c + AC_UNIT)) |
| break; |
| } |
| U.putOrderedObject(w, QCURRENTSTEAL, ps); |
| } |
| |
| /** |
| * Gets and removes a local or stolen task for the given worker. |
| * |
| * @return a task, if available |
| */ |
| final ForkJoinTask<?> nextTaskFor(WorkQueue w) { |
| for (ForkJoinTask<?> t;;) { |
| WorkQueue q; int b; |
| if ((t = w.nextLocalTask()) != null) |
| return t; |
| if ((q = findNonEmptyStealQueue()) == null) |
| return null; |
| if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null) |
| return t; |
| } |
| } |
| |
| /** |
| * Returns a cheap heuristic guide for task partitioning when |
| * programmers, frameworks, tools, or languages have little or no |
| * idea about task granularity. In essence, by offering this |
| * method, we ask users only about tradeoffs in overhead vs |
| * expected throughput and its variance, rather than how finely to |
| * partition tasks. |
| * |
| * In a steady state strict (tree-structured) computation, each |
| * thread makes available for stealing enough tasks for other |
| * threads to remain active. Inductively, if all threads play by |
| * the same rules, each thread should make available only a |
| * constant number of tasks. |
| * |
| * The minimum useful constant is just 1. But using a value of 1 |
| * would require immediate replenishment upon each steal to |
| * maintain enough tasks, which is infeasible. Further, |
| * partitionings/granularities of offered tasks should minimize |
| * steal rates, which in general means that threads nearer the top |
| * of computation tree should generate more than those nearer the |
| * bottom. In perfect steady state, each thread is at |
| * approximately the same level of computation tree. However, |
| * producing extra tasks amortizes the uncertainty of progress and |
| * diffusion assumptions. |
| * |
| * So, users will want to use values larger (but not much larger) |
| * than 1 to both smooth over transient shortages and hedge |
| * against uneven progress; as traded off against the cost of |
| * extra task overhead. We leave the user to pick a threshold |
| * value to compare with the results of this call to guide |
| * decisions, but recommend values such as 3. |
| * |
| * When all threads are active, it is on average OK to estimate |
| * surplus strictly locally. In steady-state, if one thread is |
| * maintaining say 2 surplus tasks, then so are others. So we can |
| * just use estimated queue length. However, this strategy alone |
| * leads to serious mis-estimates in some non-steady-state |
| * conditions (ramp-up, ramp-down, other stalls). We can detect |
| * many of these by further considering the number of "idle" |
| * threads, that are known to have zero queued tasks, so |
| * compensate by a factor of (#idle/#active) threads. |
| */ |
| static int getSurplusQueuedTaskCount() { |
| Thread t; ForkJoinWorkerThread wt; ForkJoinPool pool; WorkQueue q; |
| if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) { |
| int p = (pool = (wt = (ForkJoinWorkerThread)t).pool). |
| config & SMASK; |
| int n = (q = wt.workQueue).top - q.base; |
| int a = (int)(pool.ctl >> AC_SHIFT) + p; |
| return n - (a > (p >>>= 1) ? 0 : |
| a > (p >>>= 1) ? 1 : |
| a > (p >>>= 1) ? 2 : |
| a > (p >>>= 1) ? 4 : |
| 8); |
| } |
| return 0; |
| } |
| |
| // Termination |
| |
| /** |
| * Possibly initiates and/or completes termination. |
| * |
| * @param now if true, unconditionally terminate, else only |
| * if no work and no active workers |
| * @param enable if true, enable shutdown when next possible |
| * @return true if now terminating or terminated |
| */ |
| private boolean tryTerminate(boolean now, boolean enable) { |
| int rs; |
| if (this == common) // cannot shut down |
| return false; |
| if ((rs = runState) >= 0) { |
| if (!enable) |
| return false; |
| rs = lockRunState(); // enter SHUTDOWN phase |
| unlockRunState(rs, (rs & ~RSLOCK) | SHUTDOWN); |
| } |
| |
| if ((rs & STOP) == 0) { |
| if (!now) { // check quiescence |
| for (long oldSum = 0L;;) { // repeat until stable |
| WorkQueue[] ws; WorkQueue w; int m, b; long c; |
| long checkSum = ctl; |
| if ((int)(checkSum >> AC_SHIFT) + (config & SMASK) > 0) |
| return false; // still active workers |
| if ((ws = workQueues) == null || (m = ws.length - 1) <= 0) |
| break; // check queues |
| for (int i = 0; i <= m; ++i) { |
| if ((w = ws[i]) != null) { |
| if ((b = w.base) != w.top || w.scanState >= 0 || |
| w.currentSteal != null) { |
| tryRelease(c = ctl, ws[m & (int)c], AC_UNIT); |
| return false; // arrange for recheck |
| } |
| checkSum += b; |
| if ((i & 1) == 0) |
| w.qlock = -1; // try to disable external |
| } |
| } |
| if (oldSum == (oldSum = checkSum)) |
| break; |
| } |
| } |
| if ((runState & STOP) == 0) { |
| rs = lockRunState(); // enter STOP phase |
| unlockRunState(rs, (rs & ~RSLOCK) | STOP); |
| } |
| } |
| |
| int pass = 0; // 3 passes to help terminate |
| for (long oldSum = 0L;;) { // or until done or stable |
| WorkQueue[] ws; WorkQueue w; ForkJoinWorkerThread wt; int m; |
| long checkSum = ctl; |
| if ((short)(checkSum >>> TC_SHIFT) + (config & SMASK) <= 0 || |
| (ws = workQueues) == null || (m = ws.length - 1) <= 0) { |
| if ((runState & TERMINATED) == 0) { |
| rs = lockRunState(); // done |
| unlockRunState(rs, (rs & ~RSLOCK) | TERMINATED); |
| synchronized (this) { notifyAll(); } // for awaitTermination |
| } |
| break; |
| } |
| for (int i = 0; i <= m; ++i) { |
| if ((w = ws[i]) != null) { |
| checkSum += w.base; |
| w.qlock = -1; // try to disable |
| if (pass > 0) { |
| w.cancelAll(); // clear queue |
| if (pass > 1 && (wt = w.owner) != null) { |
| if (!wt.isInterrupted()) { |
| try { // unblock join |
| wt.interrupt(); |
| } catch (Throwable ignore) { |
| } |
| } |
| if (w.scanState < 0) |
| U.unpark(wt); // wake up |
| } |
| } |
| } |
| } |
| if (checkSum != oldSum) { // unstable |
| oldSum = checkSum; |
| pass = 0; |
| } |
| else if (pass > 3 && pass > m) // can't further help |
| break; |
| else if (++pass > 1) { // try to dequeue |
| long c; int j = 0, sp; // bound attempts |
| while (j++ <= m && (sp = (int)(c = ctl)) != 0) |
| tryRelease(c, ws[sp & m], AC_UNIT); |
| } |
| } |
| return true; |
| } |
| |
| // External operations |
| |
| /** |
| * Full version of externalPush, handling uncommon cases, as well |
| * as performing secondary initialization upon the first |
| * submission of the first task to the pool. It also detects |
| * first submission by an external thread and creates a new shared |
| * queue if the one at index if empty or contended. |
| * |
| * @param task the task. Caller must ensure non-null. |
| */ |
| private void externalSubmit(ForkJoinTask<?> task) { |
| int r; // initialize caller's probe |
| if ((r = ThreadLocalRandom.getProbe()) == 0) { |
| ThreadLocalRandom.localInit(); |
| r = ThreadLocalRandom.getProbe(); |
| } |
| for (;;) { |
| WorkQueue[] ws; WorkQueue q; int rs, m, k; |
| boolean move = false; |
| if ((rs = runState) < 0) { |
| tryTerminate(false, false); // help terminate |
| throw new RejectedExecutionException(); |
| } |
| else if ((rs & STARTED) == 0 || // initialize |
| ((ws = workQueues) == null || (m = ws.length - 1) < 0)) { |
| int ns = 0; |
| rs = lockRunState(); |
| try { |
| if ((rs & STARTED) == 0) { |
| U.compareAndSwapObject(this, STEALCOUNTER, null, |
| new AtomicLong()); |
| // create workQueues array with size a power of two |
| int p = config & SMASK; // ensure at least 2 slots |
| int n = (p > 1) ? p - 1 : 1; |
| n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; |
| n |= n >>> 8; n |= n >>> 16; n = (n + 1) << 1; |
| workQueues = new WorkQueue[n]; |
| ns = STARTED; |
| } |
| } finally { |
| unlockRunState(rs, (rs & ~RSLOCK) | ns); |
| } |
| } |
| else if ((q = ws[k = r & m & SQMASK]) != null) { |
| if (q.qlock == 0 && U.compareAndSwapInt(q, QLOCK, 0, 1)) { |
| ForkJoinTask<?>[] a = q.array; |
| int s = q.top; |
| boolean submitted = false; // initial submission or resizing |
| try { // locked version of push |
| if ((a != null && a.length > s + 1 - q.base) || |
| (a = q.growArray()) != null) { |
| int j = (((a.length - 1) & s) << ASHIFT) + ABASE; |
| U.putOrderedObject(a, j, task); |
| U.putOrderedInt(q, QTOP, s + 1); |
| submitted = true; |
| } |
| } finally { |
| U.compareAndSwapInt(q, QLOCK, 1, 0); |
| } |
| if (submitted) { |
| signalWork(ws, q); |
| return; |
| } |
| } |
| move = true; // move on failure |
| } |
| else if (((rs = runState) & RSLOCK) == 0) { // create new queue |
| q = new WorkQueue(this, null); |
| q.hint = r; |
| q.config = k | SHARED_QUEUE; |
| q.scanState = INACTIVE; |
| rs = lockRunState(); // publish index |
| if (rs > 0 && (ws = workQueues) != null && |
| k < ws.length && ws[k] == null) |
| ws[k] = q; // else terminated |
| unlockRunState(rs, rs & ~RSLOCK); |
| } |
| else |
| move = true; // move if busy |
| if (move) |
| r = ThreadLocalRandom.advanceProbe(r); |
| } |
| } |
| |
| /** |
| * Tries to add the given task to a submission queue at |
| * submitter's current queue. Only the (vastly) most common path |
| * is directly handled in this method, while screening for need |
| * for externalSubmit. |
| * |
| * @param task the task. Caller must ensure non-null. |
| */ |
| final void externalPush(ForkJoinTask<?> task) { |
| WorkQueue[] ws; WorkQueue q; int m; |
| int r = ThreadLocalRandom.getProbe(); |
| int rs = runState; |
| if ((ws = workQueues) != null && (m = (ws.length - 1)) >= 0 && |
| (q = ws[m & r & SQMASK]) != null && r != 0 && rs > 0 && |
| U.compareAndSwapInt(q, QLOCK, 0, 1)) { |
| ForkJoinTask<?>[] a; int am, n, s; |
| if ((a = q.array) != null && |
| (am = a.length - 1) > (n = (s = q.top) - q.base)) { |
| int j = ((am & s) << ASHIFT) + ABASE; |
| U.putOrderedObject(a, j, task); |
| U.putOrderedInt(q, QTOP, s + 1); |
| U.putOrderedInt(q, QLOCK, 0); |
| if (n <= 1) |
| signalWork(ws, q); |
| return; |
| } |
| U.compareAndSwapInt(q, QLOCK, 1, 0); |
| } |
| externalSubmit(task); |
| } |
| |
| /** |
| * Returns common pool queue for an external thread. |
| */ |
| static WorkQueue commonSubmitterQueue() { |
| ForkJoinPool p = common; |
| int r = ThreadLocalRandom.getProbe(); |
| WorkQueue[] ws; int m; |
| return (p != null && (ws = p.workQueues) != null && |
| (m = ws.length - 1) >= 0) ? |
| ws[m & r & SQMASK] : null; |
| } |
| |
| /** |
| * Performs tryUnpush for an external submitter: Finds queue, |
| * locks if apparently non-empty, validates upon locking, and |
| * adjusts top. Each check can fail but rarely does. |
| */ |
| final boolean tryExternalUnpush(ForkJoinTask<?> task) { |
| WorkQueue[] ws; WorkQueue w; ForkJoinTask<?>[] a; int m, s; |
| int r = ThreadLocalRandom.getProbe(); |
| if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 && |
| (w = ws[m & r & SQMASK]) != null && |
| (a = w.array) != null && (s = w.top) != w.base) { |
| long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE; |
| if (U.compareAndSwapInt(w, QLOCK, 0, 1)) { |
| if (w.top == s && w.array == a && |
| U.getObject(a, j) == task && |
| U.compareAndSwapObject(a, j, task, null)) { |
| U.putOrderedInt(w, QTOP, s - 1); |
| U.putOrderedInt(w, QLOCK, 0); |
| return true; |
| } |
| U.compareAndSwapInt(w, QLOCK, 1, 0); |
| } |
| } |
| return false; |
| } |
| |
| /** |
| * Performs helpComplete for an external submitter. |
| */ |
| final int externalHelpComplete(CountedCompleter<?> task, int maxTasks) { |
| WorkQueue[] ws; int n; |
| int r = ThreadLocalRandom.getProbe(); |
| return ((ws = workQueues) == null || (n = ws.length) == 0) ? 0 : |
| helpComplete(ws[(n - 1) & r & SQMASK], task, maxTasks); |
| } |
| |
| // Exported methods |
| |
| // Constructors |
| |
| /** |
| * Creates a {@code ForkJoinPool} with parallelism equal to {@link |
| * java.lang.Runtime#availableProcessors}, using the {@linkplain |
| * #defaultForkJoinWorkerThreadFactory default thread factory}, |
| * no UncaughtExceptionHandler, and non-async LIFO processing mode. |
| * |
| * @throws SecurityException if a security manager exists and |
| * the caller is not permitted to modify threads |
| * because it does not hold {@link |
| * java.lang.RuntimePermission}{@code ("modifyThread")} |
| */ |
| public ForkJoinPool() { |
| this(Math.min(MAX_CAP, Runtime.getRuntime().availableProcessors()), |
| defaultForkJoinWorkerThreadFactory, null, false); |
| } |
| |
| /** |
| * Creates a {@code ForkJoinPool} with the indicated parallelism |
| * level, the {@linkplain |
| * #defaultForkJoinWorkerThreadFactory default thread factory}, |
| * no UncaughtExceptionHandler, and non-async LIFO processing mode. |
| * |
| * @param parallelism the parallelism level |
| * @throws IllegalArgumentException if parallelism less than or |
| * equal to zero, or greater than implementation limit |
| * @throws SecurityException if a security manager exists and |
| * the caller is not permitted to modify threads |
| * because it does not hold {@link |
| * java.lang.RuntimePermission}{@code ("modifyThread")} |
| */ |
| public ForkJoinPool(int parallelism) { |
| this(parallelism, defaultForkJoinWorkerThreadFactory, null, false); |
| } |
| |
| /** |
| * Creates a {@code ForkJoinPool} with the given parameters. |
| * |
| * @param parallelism the parallelism level. For default value, |
| * use {@link java.lang.Runtime#availableProcessors}. |
| * @param factory the factory for creating new threads. For default value, |
| * use {@link #defaultForkJoinWorkerThreadFactory}. |
| * @param handler the handler for internal worker threads that |
| * terminate due to unrecoverable errors encountered while executing |
| * tasks. For default value, use {@code null}. |
| * @param asyncMode if true, |
| * establishes local first-in-first-out scheduling mode for forked |
| * tasks that are never joined. This mode may be more appropriate |
| * than default locally stack-based mode in applications in which |
| * worker threads only process event-style asynchronous tasks. |
| * For default value, use {@code false}. |
| * @throws IllegalArgumentException if parallelism less than or |
| * equal to zero, or greater than implementation limit |
| * @throws NullPointerException if the factory is null |
| * @throws SecurityException if a security manager exists and |
| * the caller is not permitted to modify threads |
| * because it does not hold {@link |
| * java.lang.RuntimePermission}{@code ("modifyThread")} |
| */ |
| public ForkJoinPool(int parallelism, |
| ForkJoinWorkerThreadFactory factory, |
| UncaughtExceptionHandler handler, |
| boolean asyncMode) { |
| this(checkParallelism(parallelism), |
| checkFactory(factory), |
| handler, |
| asyncMode ? FIFO_QUEUE : LIFO_QUEUE, |
| "ForkJoinPool-" + nextPoolId() + "-worker-"); |
| checkPermission(); |
| } |
| |
| private static int checkParallelism(int parallelism) { |
| if (parallelism <= 0 || parallelism > MAX_CAP) |
| throw new IllegalArgumentException(); |
| return parallelism; |
| } |
| |
| private static ForkJoinWorkerThreadFactory checkFactory |
| (ForkJoinWorkerThreadFactory factory) { |
| if (factory == null) |
| throw new NullPointerException(); |
| return factory; |
| } |
| |
| /** |
| * Creates a {@code ForkJoinPool} with the given parameters, without |
| * any security checks or parameter validation. Invoked directly by |
| * makeCommonPool. |
| */ |
| private ForkJoinPool(int parallelism, |
| ForkJoinWorkerThreadFactory factory, |
| UncaughtExceptionHandler handler, |
| int mode, |
| String workerNamePrefix) { |
| this.workerNamePrefix = workerNamePrefix; |
| this.factory = factory; |
| this.ueh = handler; |
| this.config = (parallelism & SMASK) | mode; |
| long np = (long)(-parallelism); // offset ctl counts |
| this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK); |
| } |
| |
| /** |
| * Returns the common pool instance. This pool is statically |
| * constructed; its run state is unaffected by attempts to {@link |
| * #shutdown} or {@link #shutdownNow}. However this pool and any |
| * ongoing processing are automatically terminated upon program |
| * {@link System#exit}. Any program that relies on asynchronous |
| * task processing to complete before program termination should |
| * invoke {@code commonPool().}{@link #awaitQuiescence awaitQuiescence}, |
| * before exit. |
| * |
| * @return the common pool instance |
| * @since 1.8 |
| */ |
| public static ForkJoinPool commonPool() { |
| // assert common != null : "static init error"; |
| return common; |
| } |
| |
| // Execution methods |
| |
| /** |
| * Performs the given task, returning its result upon completion. |
| * If the computation encounters an unchecked Exception or Error, |
| * it is rethrown as the outcome of this invocation. Rethrown |
| * exceptions behave in the same way as regular exceptions, but, |
| * when possible, contain stack traces (as displayed for example |
| * using {@code ex.printStackTrace()}) of both the current thread |
| * as well as the thread actually encountering the exception; |
| * minimally only the latter. |
| * |
| * @param task the task |
| * @param <T> the type of the task's result |
| * @return the task's result |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public <T> T invoke(ForkJoinTask<T> task) { |
| if (task == null) |
| throw new NullPointerException(); |
| externalPush(task); |
| return task.join(); |
| } |
| |
| /** |
| * Arranges for (asynchronous) execution of the given task. |
| * |
| * @param task the task |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public void execute(ForkJoinTask<?> task) { |
| if (task == null) |
| throw new NullPointerException(); |
| externalPush(task); |
| } |
| |
| // AbstractExecutorService methods |
| |
| /** |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public void execute(Runnable task) { |
| if (task == null) |
| throw new NullPointerException(); |
| ForkJoinTask<?> job; |
| if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
| job = (ForkJoinTask<?>) task; |
| else |
| job = new ForkJoinTask.RunnableExecuteAction(task); |
| externalPush(job); |
| } |
| |
| /** |
| * Submits a ForkJoinTask for execution. |
| * |
| * @param task the task to submit |
| * @param <T> the type of the task's result |
| * @return the task |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) { |
| if (task == null) |
| throw new NullPointerException(); |
| externalPush(task); |
| return task; |
| } |
| |
| /** |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public <T> ForkJoinTask<T> submit(Callable<T> task) { |
| ForkJoinTask<T> job = new ForkJoinTask.AdaptedCallable<T>(task); |
| externalPush(job); |
| return job; |
| } |
| |
| /** |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public <T> ForkJoinTask<T> submit(Runnable task, T result) { |
| ForkJoinTask<T> job = new ForkJoinTask.AdaptedRunnable<T>(task, result); |
| externalPush(job); |
| return job; |
| } |
| |
| /** |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public ForkJoinTask<?> submit(Runnable task) { |
| if (task == null) |
| throw new NullPointerException(); |
| ForkJoinTask<?> job; |
| if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
| job = (ForkJoinTask<?>) task; |
| else |
| job = new ForkJoinTask.AdaptedRunnableAction(task); |
| externalPush(job); |
| return job; |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| * @throws RejectedExecutionException {@inheritDoc} |
| */ |
| public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) { |
| // In previous versions of this class, this method constructed |
| // a task to run ForkJoinTask.invokeAll, but now external |
| // invocation of multiple tasks is at least as efficient. |
| ArrayList<Future<T>> futures = new ArrayList<>(tasks.size()); |
| |
| boolean done = false; |
| try { |
| for (Callable<T> t : tasks) { |
| ForkJoinTask<T> f = new ForkJoinTask.AdaptedCallable<T>(t); |
| futures.add(f); |
| externalPush(f); |
| } |
| for (int i = 0, size = futures.size(); i < size; i++) |
| ((ForkJoinTask<?>)futures.get(i)).quietlyJoin(); |
| done = true; |
| return futures; |
| } finally { |
| if (!done) |
| for (int i = 0, size = futures.size(); i < size; i++) |
| futures.get(i).cancel(false); |
| } |
| } |
| |
| /** |
| * Returns the factory used for constructing new workers. |
| * |
| * @return the factory used for constructing new workers |
| */ |
| public ForkJoinWorkerThreadFactory getFactory() { |
| return factory; |
| } |
| |
| /** |
| * Returns the handler for internal worker threads that terminate |
| * due to unrecoverable errors encountered while executing tasks. |
| * |
| * @return the handler, or {@code null} if none |
| */ |
| public UncaughtExceptionHandler getUncaughtExceptionHandler() { |
| return ueh; |
| } |
| |
| /** |
| * Returns the targeted parallelism level of this pool. |
| * |
| * @return the targeted parallelism level of this pool |
| */ |
| public int getParallelism() { |
| int par; |
| return ((par = config & SMASK) > 0) ? par : 1; |
| } |
| |
| /** |
| * Returns the targeted parallelism level of the common pool. |
| * |
| * @return the targeted parallelism level of the common pool |
| * @since 1.8 |
| */ |
| public static int getCommonPoolParallelism() { |
| return commonParallelism; |
| } |
| |
| /** |
| * Returns the number of worker threads that have started but not |
| * yet terminated. The result returned by this method may differ |
| * from {@link #getParallelism} when threads are created to |
| * maintain parallelism when others are cooperatively blocked. |
| * |
| * @return the number of worker threads |
| */ |
| public int getPoolSize() { |
| return (config & SMASK) + (short)(ctl >>> TC_SHIFT); |
| } |
| |
| /** |
| * Returns {@code true} if this pool uses local first-in-first-out |
| * scheduling mode for forked tasks that are never joined. |
| * |
| * @return {@code true} if this pool uses async mode |
| */ |
| public boolean getAsyncMode() { |
| return (config & FIFO_QUEUE) != 0; |
| } |
| |
| /** |
| * Returns an estimate of the number of worker threads that are |
| * not blocked waiting to join tasks or for other managed |
| * synchronization. This method may overestimate the |
| * number of running threads. |
| * |
| * @return the number of worker threads |
| */ |
| public int getRunningThreadCount() { |
| int rc = 0; |
| WorkQueue[] ws; WorkQueue w; |
| if ((ws = workQueues) != null) { |
| for (int i = 1; i < ws.length; i += 2) { |
| if ((w = ws[i]) != null && w.isApparentlyUnblocked()) |
| ++rc; |
| } |
| } |
| return rc; |
| } |
| |
| /** |
| * Returns an estimate of the number of threads that are currently |
| * stealing or executing tasks. This method may overestimate the |
| * number of active threads. |
| * |
| * @return the number of active threads |
| */ |
| public int getActiveThreadCount() { |
| int r = (config & SMASK) + (int)(ctl >> AC_SHIFT); |
| return (r <= 0) ? 0 : r; // suppress momentarily negative values |
| } |
| |
| /** |
| * Returns {@code true} if all worker threads are currently idle. |
| * An idle worker is one that cannot obtain a task to execute |
| * because none are available to steal from other threads, and |
| * there are no pending submissions to the pool. This method is |
| * conservative; it might not return {@code true} immediately upon |
| * idleness of all threads, but will eventually become true if |
| * threads remain inactive. |
| * |
| * @return {@code true} if all threads are currently idle |
| */ |
| public boolean isQuiescent() { |
| return (config & SMASK) + (int)(ctl >> AC_SHIFT) <= 0; |
| } |
| |
| /** |
| * Returns an estimate of the total number of tasks stolen from |
| * one thread's work queue by another. The reported value |
| * underestimates the actual total number of steals when the pool |
| * is not quiescent. This value may be useful for monitoring and |
| * tuning fork/join programs: in general, steal counts should be |
| * high enough to keep threads busy, but low enough to avoid |
| * overhead and contention across threads. |
| * |
| * @return the number of steals |
| */ |
| public long getStealCount() { |
| AtomicLong sc = stealCounter; |
| long count = (sc == null) ? 0L : sc.get(); |
| WorkQueue[] ws; WorkQueue w; |
| if ((ws = workQueues) != null) { |
| for (int i = 1; i < ws.length; i += 2) { |
| if ((w = ws[i]) != null) |
| count += w.nsteals; |
| } |
| } |
| return count; |
| } |
| |
| /** |
| * Returns an estimate of the total number of tasks currently held |
| * in queues by worker threads (but not including tasks submitted |
| * to the pool that have not begun executing). This value is only |
| * an approximation, obtained by iterating across all threads in |
| * the pool. This method may be useful for tuning task |
| * granularities. |
| * |
| * @return the number of queued tasks |
| */ |
| public long getQueuedTaskCount() { |
| long count = 0; |
| WorkQueue[] ws; WorkQueue w; |
| if ((ws = workQueues) != null) { |
| for (int i = 1; i < ws.length; i += 2) { |
| if ((w = ws[i]) != null) |
| count += w.queueSize(); |
| } |
| } |
| return count; |
| } |
| |
| /** |
| * Returns an estimate of the number of tasks submitted to this |
| * pool that have not yet begun executing. This method may take |
| * time proportional to the number of submissions. |
| * |
| * @return the number of queued submissions |
| */ |
| public int getQueuedSubmissionCount() { |
| int count = 0; |
| WorkQueue[] ws; WorkQueue w; |
| if ((ws = workQueues) != null) { |
| for (int i = 0; i < ws.length; i += 2) { |
| if ((w = ws[i]) != null) |
| count += w.queueSize(); |
| } |
| } |
| return count; |
| } |
| |
| /** |
| * Returns {@code true} if there are any tasks submitted to this |
| * pool that have not yet begun executing. |
| * |
| * @return {@code true} if there are any queued submissions |
| */ |
| public boolean hasQueuedSubmissions() { |
| WorkQueue[] ws; WorkQueue w; |
| if ((ws = workQueues) != null) { |
| for (int i = 0; i < ws.length; i += 2) { |
| if ((w = ws[i]) != null && !w.isEmpty()) |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| /** |
| * Removes and returns the next unexecuted submission if one is |
| * available. This method may be useful in extensions to this |
| * class that re-assign work in systems with multiple pools. |
| * |
| * @return the next submission, or {@code null} if none |
| */ |
| protected ForkJoinTask<?> pollSubmission() { |
| WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t; |
| if ((ws = workQueues) != null) { |
| for (int i = 0; i < ws.length; i += 2) { |
| if ((w = ws[i]) != null && (t = w.poll()) != null) |
| return t; |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Removes all available unexecuted submitted and forked tasks |
| * from scheduling queues and adds them to the given collection, |
| * without altering their execution status. These may include |
| * artificially generated or wrapped tasks. This method is |
| * designed to be invoked only when the pool is known to be |
| * quiescent. Invocations at other times may not remove all |
| * tasks. A failure encountered while attempting to add elements |
| * to collection {@code c} may result in elements being in |
| * neither, either or both collections when the associated |
| * exception is thrown. The behavior of this operation is |
| * undefined if the specified collection is modified while the |
| * operation is in progress. |
| * |
| * @param c the collection to transfer elements into |
| * @return the number of elements transferred |
| */ |
| protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { |
| int count = 0; |
| WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t; |
| if ((ws = workQueues) != null) { |
| for (int i = 0; i < ws.length; ++i) { |
| if ((w = ws[i]) != null) { |
| while ((t = w.poll()) != null) { |
| c.add(t); |
| ++count; |
| } |
| } |
| } |
| } |
| return count; |
| } |
| |
| /** |
| * Returns a string identifying this pool, as well as its state, |
| * including indications of run state, parallelism level, and |
| * worker and task counts. |
| * |
| * @return a string identifying this pool, as well as its state |
| */ |
| public String toString() { |
| // Use a single pass through workQueues to collect counts |
| long qt = 0L, qs = 0L; int rc = 0; |
| AtomicLong sc = stealCounter; |
| long st = (sc == null) ? 0L : sc.get(); |
| long c = ctl; |
| WorkQueue[] ws; WorkQueue w; |
| if ((ws = workQueues) != null) { |
| for (int i = 0; i < ws.length; ++i) { |
| if ((w = ws[i]) != null) { |
| int size = w.queueSize(); |
| if ((i & 1) == 0) |
| qs += size; |
| else { |
| qt += size; |
| st += w.nsteals; |
| if (w.isApparentlyUnblocked()) |
| ++rc; |
| } |
| } |
| } |
| } |
| int pc = (config & SMASK); |
| int tc = pc + (short)(c >>> TC_SHIFT); |
| int ac = pc + (int)(c >> AC_SHIFT); |
| if (ac < 0) // ignore transient negative |
| ac = 0; |
| int rs = runState; |
| String level = ((rs & TERMINATED) != 0 ? "Terminated" : |
| (rs & STOP) != 0 ? "Terminating" : |
| (rs & SHUTDOWN) != 0 ? "Shutting down" : |
| "Running"); |
| return super.toString() + |
| "[" + level + |
| ", parallelism = " + pc + |
| ", size = " + tc + |
| ", active = " + ac + |
| ", running = " + rc + |
| ", steals = " + st + |
| ", tasks = " + qt + |
| ", submissions = " + qs + |
| "]"; |
| } |
| |
| /** |
| * Possibly initiates an orderly shutdown in which previously |
| * submitted tasks are executed, but no new tasks will be |
| * accepted. Invocation has no effect on execution state if this |
| * is the {@link #commonPool()}, and no additional effect if |
| * already shut down. Tasks that are in the process of being |
| * submitted concurrently during the course of this method may or |
| * may not be rejected. |
| * |
| * @throws SecurityException if a security manager exists and |
| * the caller is not permitted to modify threads |
| * because it does not hold {@link |
| * java.lang.RuntimePermission}{@code ("modifyThread")} |
| */ |
| public void shutdown() { |
| checkPermission(); |
| tryTerminate(false, true); |
| } |
| |
| /** |
| * Possibly attempts to cancel and/or stop all tasks, and reject |
| * all subsequently submitted tasks. Invocation has no effect on |
| * execution state if this is the {@link #commonPool()}, and no |
| * additional effect if already shut down. Otherwise, tasks that |
| * are in the process of being submitted or executed concurrently |
| * during the course of this method may or may not be |
| * rejected. This method cancels both existing and unexecuted |
| * tasks, in order to permit termination in the presence of task |
| * dependencies. So the method always returns an empty list |
| * (unlike the case for some other Executors). |
| * |
| * @return an empty list |
| * @throws SecurityException if a security manager exists and |
| * the caller is not permitted to modify threads |
| * because it does not hold {@link |
| * java.lang.RuntimePermission}{@code ("modifyThread")} |
| */ |
| public List<Runnable> shutdownNow() { |
| checkPermission(); |
| tryTerminate(true, true); |
| return Collections.emptyList(); |
| } |
| |
| /** |
| * Returns {@code true} if all tasks have completed following shut down. |
| * |
| * @return {@code true} if all tasks have completed following shut down |
| */ |
| public boolean isTerminated() { |
| return (runState & TERMINATED) != 0; |
| } |
| |
| /** |
| * Returns {@code true} if the process of termination has |
| * commenced but not yet completed. This method may be useful for |
| * debugging. A return of {@code true} reported a sufficient |
| * period after shutdown may indicate that submitted tasks have |
| * ignored or suppressed interruption, or are waiting for I/O, |
| * causing this executor not to properly terminate. (See the |
| * advisory notes for class {@link ForkJoinTask} stating that |
| * tasks should not normally entail blocking operations. But if |
| * they do, they must abort them on interrupt.) |
| * |
| * @return {@code true} if terminating but not yet terminated |
| */ |
| public boolean isTerminating() { |
| int rs = runState; |
| return (rs & STOP) != 0 && (rs & TERMINATED) == 0; |
| } |
| |
| /** |
| * Returns {@code true} if this pool has been shut down. |
| * |
| * @return {@code true} if this pool has been shut down |
| */ |
| public boolean isShutdown() { |
| return (runState & SHUTDOWN) != 0; |
| } |
| |
| /** |
| * Blocks until all tasks have completed execution after a |
| * shutdown request, or the timeout occurs, or the current thread |
| * is interrupted, whichever happens first. Because the {@link |
| * #commonPool()} never terminates until program shutdown, when |
| * applied to the common pool, this method is equivalent to {@link |
| * #awaitQuiescence(long, TimeUnit)} but always returns {@code false}. |
| * |
| * @param timeout the maximum time to wait |
| * @param unit the time unit of the timeout argument |
| * @return {@code true} if this executor terminated and |
| * {@code false} if the timeout elapsed before termination |
| * @throws InterruptedException if interrupted while waiting |
| */ |
| public boolean awaitTermination(long timeout, TimeUnit unit) |
| throws InterruptedException { |
| if (Thread.interrupted()) |
| throw new InterruptedException(); |
| if (this == common) { |
| awaitQuiescence(timeout, unit); |
| return false; |
| } |
| long nanos = unit.toNanos(timeout); |
| if (isTerminated()) |
| return true; |
| if (nanos <= 0L) |
| return false; |
| long deadline = System.nanoTime() + nanos; |
| synchronized (this) { |
| for (;;) { |
| if (isTerminated()) |
| return true; |
| if (nanos <= 0L) |
| return false; |
| long millis = TimeUnit.NANOSECONDS.toMillis(nanos); |
| wait(millis > 0L ? millis : 1L); |
| nanos = deadline - System.nanoTime(); |
| } |
| } |
| } |
| |
| /** |
| * If called by a ForkJoinTask operating in this pool, equivalent |
| * in effect to {@link ForkJoinTask#helpQuiesce}. Otherwise, |
| * waits and/or attempts to assist performing tasks until this |
| * pool {@link #isQuiescent} or the indicated timeout elapses. |
| * |
| * @param timeout the maximum time to wait |
| * @param unit the time unit of the timeout argument |
| * @return {@code true} if quiescent; {@code false} if the |
| * timeout elapsed. |
| */ |
| public boolean awaitQuiescence(long timeout, TimeUnit unit) { |
| long nanos = unit.toNanos(timeout); |
| ForkJoinWorkerThread wt; |
| Thread thread = Thread.currentThread(); |
| if ((thread instanceof ForkJoinWorkerThread) && |
| (wt = (ForkJoinWorkerThread)thread).pool == this) { |
| helpQuiescePool(wt.workQueue); |
| return true; |
| } |
| long startTime = System.nanoTime(); |
| WorkQueue[] ws; |
| int r = 0, m; |
| boolean found = true; |
| while (!isQuiescent() && (ws = workQueues) != null && |
| (m = ws.length - 1) >= 0) { |
| if (!found) { |
| if ((System.nanoTime() - startTime) > nanos) |
| return false; |
| Thread.yield(); // cannot block |
| } |
| found = false; |
| for (int j = (m + 1) << 2; j >= 0; --j) { |
| ForkJoinTask<?> t; WorkQueue q; int b, k; |
| if ((k = r++ & m) <= m && k >= 0 && (q = ws[k]) != null && |
| (b = q.base) - q.top < 0) { |
| found = true; |
| if ((t = q.pollAt(b)) != null) |
| t.doExec(); |
| break; |
| } |
| } |
| } |
| return true; |
| } |
| |
| /** |
| * Waits and/or attempts to assist performing tasks indefinitely |
| * until the {@link #commonPool()} {@link #isQuiescent}. |
| */ |
| static void quiesceCommonPool() { |
| common.awaitQuiescence(Long.MAX_VALUE, TimeUnit.NANOSECONDS); |
| } |
| |
| /** |
| * Interface for extending managed parallelism for tasks running |
| * in {@link ForkJoinPool}s. |
| * |
| * <p>A {@code ManagedBlocker} provides two methods. Method |
| * {@link #isReleasable} must return {@code true} if blocking is |
| * not necessary. Method {@link #block} blocks the current thread |
| * if necessary (perhaps internally invoking {@code isReleasable} |
| * before actually blocking). These actions are performed by any |
| * thread invoking {@link ForkJoinPool#managedBlock(ManagedBlocker)}. |
| * The unusual methods in this API accommodate synchronizers that |
| * may, but don't usually, block for long periods. Similarly, they |
| * allow more efficient internal handling of cases in which |
| * additional workers may be, but usually are not, needed to |
| * ensure sufficient parallelism. Toward this end, |
| * implementations of method {@code isReleasable} must be amenable |
| * to repeated invocation. |
| * |
| * <p>For example, here is a ManagedBlocker based on a |
| * ReentrantLock: |
| * <pre> {@code |
| * class ManagedLocker implements ManagedBlocker { |
| * final ReentrantLock lock; |
| * boolean hasLock = false; |
| * ManagedLocker(ReentrantLock lock) { this.lock = lock; } |
| * public boolean block() { |
| * if (!hasLock) |
| * lock.lock(); |
| * return true; |
| * } |
| * public boolean isReleasable() { |
| * return hasLock || (hasLock = lock.tryLock()); |
| * } |
| * }}</pre> |
| * |
| * <p>Here is a class that possibly blocks waiting for an |
| * item on a given queue: |
| * <pre> {@code |
| * class QueueTaker<E> implements ManagedBlocker { |
| * final BlockingQueue<E> queue; |
| * volatile E item = null; |
| * QueueTaker(BlockingQueue<E> q) { this.queue = q; } |
| * public boolean block() throws InterruptedException { |
| * if (item == null) |
| * item = queue.take(); |
| * return true; |
| * } |
| * public boolean isReleasable() { |
| * return item != null || (item = queue.poll()) != null; |
| * } |
| * public E getItem() { // call after pool.managedBlock completes |
| * return item; |
| * } |
| * }}</pre> |
| */ |
| public static interface ManagedBlocker { |
| /** |
| * Possibly blocks the current thread, for example waiting for |
| * a lock or condition. |
| * |
| * @return {@code true} if no additional blocking is necessary |
| * (i.e., if isReleasable would return true) |
| * @throws InterruptedException if interrupted while waiting |
| * (the method is not required to do so, but is allowed to) |
| */ |
| boolean block() throws InterruptedException; |
| |
| /** |
| * Returns {@code true} if blocking is unnecessary. |
| * @return {@code true} if blocking is unnecessary |
| */ |
| boolean isReleasable(); |
| } |
| |
| /** |
| * Runs the given possibly blocking task. When {@linkplain |
| * ForkJoinTask#inForkJoinPool() running in a ForkJoinPool}, this |
| * method possibly arranges for a spare thread to be activated if |
| * necessary to ensure sufficient parallelism while the current |
| * thread is blocked in {@link ManagedBlocker#block blocker.block()}. |
| * |
| * <p>This method repeatedly calls {@code blocker.isReleasable()} and |
| * {@code blocker.block()} until either method returns {@code true}. |
| * Every call to {@code blocker.block()} is preceded by a call to |
| * {@code blocker.isReleasable()} that returned {@code false}. |
| * |
| * <p>If not running in a ForkJoinPool, this method is |
| * behaviorally equivalent to |
| * <pre> {@code |
| * while (!blocker.isReleasable()) |
| * if (blocker.block()) |
| * break;}</pre> |
| * |
| * If running in a ForkJoinPool, the pool may first be expanded to |
| * ensure sufficient parallelism available during the call to |
| * {@code blocker.block()}. |
| * |
| * @param blocker the blocker task |
| * @throws InterruptedException if {@code blocker.block()} did so |
| */ |
| public static void managedBlock(ManagedBlocker blocker) |
| throws InterruptedException { |
| ForkJoinPool p; |
| ForkJoinWorkerThread wt; |
| Thread t = Thread.currentThread(); |
| if ((t instanceof ForkJoinWorkerThread) && |
| (p = (wt = (ForkJoinWorkerThread)t).pool) != null) { |
| WorkQueue w = wt.workQueue; |
| while (!blocker.isReleasable()) { |
| if (p.tryCompensate(w)) { |
| try { |
| do {} while (!blocker.isReleasable() && |
| !blocker.block()); |
| } finally { |
| U.getAndAddLong(p, CTL, AC_UNIT); |
| } |
| break; |
| } |
| } |
| } |
| else { |
| do {} while (!blocker.isReleasable() && |
| !blocker.block()); |
| } |
| } |
| |
| // AbstractExecutorService overrides. These rely on undocumented |
| // fact that ForkJoinTask.adapt returns ForkJoinTasks that also |
| // implement RunnableFuture. |
| |
| protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) { |
| return new ForkJoinTask.AdaptedRunnable<T>(runnable, value); |
| } |
| |
| protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) { |
| return new ForkJoinTask.AdaptedCallable<T>(callable); |
| } |
| |
| // Unsafe mechanics |
| private static final sun.misc.Unsafe U; |
| private static final int ABASE; |
| private static final int ASHIFT; |
| private static final long CTL; |
| private static final long RUNSTATE; |
| private static final long STEALCOUNTER; |
| private static final long PARKBLOCKER; |
| private static final long QTOP; |
| private static final long QLOCK; |
| private static final long QSCANSTATE; |
| private static final long QPARKER; |
| private static final long QCURRENTSTEAL; |
| private static final long QCURRENTJOIN; |
| |
| static { |
| // initialize field offsets for CAS etc |
| try { |
| U = sun.misc.Unsafe.getUnsafe(); |
| Class<?> k = ForkJoinPool.class; |
| CTL = U.objectFieldOffset |
| (k.getDeclaredField("ctl")); |
| RUNSTATE = U.objectFieldOffset |
| (k.getDeclaredField("runState")); |
| STEALCOUNTER = U.objectFieldOffset |
| (k.getDeclaredField("stealCounter")); |
| Class<?> tk = Thread.class; |
| PARKBLOCKER = U.objectFieldOffset |
| (tk.getDeclaredField("parkBlocker")); |
| Class<?> wk = WorkQueue.class; |
| QTOP = U.objectFieldOffset |
| (wk.getDeclaredField("top")); |
| QLOCK = U.objectFieldOffset |
| (wk.getDeclaredField("qlock")); |
| QSCANSTATE = U.objectFieldOffset |
| (wk.getDeclaredField("scanState")); |
| QPARKER = U.objectFieldOffset |
| (wk.getDeclaredField("parker")); |
| QCURRENTSTEAL = U.objectFieldOffset |
| (wk.getDeclaredField("currentSteal")); |
| QCURRENTJOIN = U.objectFieldOffset |
| (wk.getDeclaredField("currentJoin")); |
| Class<?> ak = ForkJoinTask[].class; |
| ABASE = U.arrayBaseOffset(ak); |
| int scale = U.arrayIndexScale(ak); |
| if ((scale & (scale - 1)) != 0) |
| throw new Error("data type scale not a power of two"); |
| ASHIFT = 31 - Integer.numberOfLeadingZeros(scale); |
| } catch (Exception e) { |
| throw new Error(e); |
| } |
| |
| commonMaxSpares = DEFAULT_COMMON_MAX_SPARES; |
| defaultForkJoinWorkerThreadFactory = |
| new DefaultForkJoinWorkerThreadFactory(); |
| modifyThreadPermission = new RuntimePermission("modifyThread"); |
| |
| common = java.security.AccessController.doPrivileged |
| (new java.security.PrivilegedAction<ForkJoinPool>() { |
| public ForkJoinPool run() { return makeCommonPool(); }}); |
| int par = common.config & SMASK; // report 1 even if threads disabled |
| commonParallelism = par > 0 ? par : 1; |
| } |
| |
| /** |
| * Creates and returns the common pool, respecting user settings |
| * specified via system properties. |
| */ |
| private static ForkJoinPool makeCommonPool() { |
| int parallelism = -1; |
| ForkJoinWorkerThreadFactory factory = null; |
| UncaughtExceptionHandler handler = null; |
| try { // ignore exceptions in accessing/parsing properties |
| String pp = System.getProperty |
| ("java.util.concurrent.ForkJoinPool.common.parallelism"); |
| String fp = System.getProperty |
| ("java.util.concurrent.ForkJoinPool.common.threadFactory"); |
| String hp = System.getProperty |
| ("java.util.concurrent.ForkJoinPool.common.exceptionHandler"); |
| String mp = System.getProperty |
| ("java.util.concurrent.ForkJoinPool.common.maximumSpares"); |
| if (pp != null) |
| parallelism = Integer.parseInt(pp); |
| if (fp != null) |
| factory = ((ForkJoinWorkerThreadFactory)ClassLoader. |
| getSystemClassLoader().loadClass(fp).newInstance()); |
| if (hp != null) |
| handler = ((UncaughtExceptionHandler)ClassLoader. |
| getSystemClassLoader().loadClass(hp).newInstance()); |
| if (mp != null) |
| commonMaxSpares = Integer.parseInt(mp); |
| } catch (Exception ignore) { |
| } |
| if (factory == null) { |
| if (System.getSecurityManager() == null) |
| factory = defaultForkJoinWorkerThreadFactory; |
| else // use security-managed default |
| factory = new InnocuousForkJoinWorkerThreadFactory(); |
| } |
| if (parallelism < 0 && // default 1 less than #cores |
| (parallelism = Runtime.getRuntime().availableProcessors() - 1) <= 0) |
| parallelism = 1; |
| if (parallelism > MAX_CAP) |
| parallelism = MAX_CAP; |
| return new ForkJoinPool(parallelism, factory, handler, LIFO_QUEUE, |
| "ForkJoinPool.commonPool-worker-"); |
| } |
| |
| /** |
| * Factory for innocuous worker threads |
| */ |
| static final class InnocuousForkJoinWorkerThreadFactory |
| implements ForkJoinWorkerThreadFactory { |
| |
| /** |
| * An ACC to restrict permissions for the factory itself. |
| * The constructed workers have no permissions set. |
| */ |
| private static final AccessControlContext innocuousAcc; |
| static { |
| Permissions innocuousPerms = new Permissions(); |
| innocuousPerms.add(modifyThreadPermission); |
| innocuousPerms.add(new RuntimePermission( |
| "enableContextClassLoaderOverride")); |
| innocuousPerms.add(new RuntimePermission( |
| "modifyThreadGroup")); |
| innocuousAcc = new AccessControlContext(new ProtectionDomain[] { |
| new ProtectionDomain(null, innocuousPerms) |
| }); |
| } |
| |
| public final ForkJoinWorkerThread newThread(ForkJoinPool pool) { |
| return (ForkJoinWorkerThread.InnocuousForkJoinWorkerThread) |
| java.security.AccessController.doPrivileged( |
| new java.security.PrivilegedAction<ForkJoinWorkerThread>() { |
| public ForkJoinWorkerThread run() { |
| return new ForkJoinWorkerThread. |
| InnocuousForkJoinWorkerThread(pool); |
| }}, innocuousAcc); |
| } |
| } |
| |
| } |