| /* |
| * 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.lang.invoke.MethodHandles; |
| import java.lang.invoke.VarHandle; |
| import java.security.AccessController; |
| import java.security.AccessControlContext; |
| import java.security.Permission; |
| import java.security.Permissions; |
| import java.security.PrivilegedAction; |
| import java.security.ProtectionDomain; |
| import java.util.ArrayList; |
| import java.util.Collection; |
| import java.util.Collections; |
| import java.util.List; |
| import java.util.function.Predicate; |
| import java.util.concurrent.locks.LockSupport; |
| |
| /** |
| * 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. All worker threads are initialized |
| * with {@link Thread#isDaemon} set {@code true}. |
| * |
| * <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. The default policies may be |
| * overridden using a constructor with parameters corresponding to |
| * those documented in class {@link ThreadPoolExecutor}. |
| * |
| * <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 class="plain"> |
| * <caption>Summary of task execution methods</caption> |
| * <tr> |
| * <td></td> |
| * <td style="text-align:center"> <b>Call from non-fork/join clients</b></td> |
| * <td style="text-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 parameters used to construct the common pool may be controlled by |
| * setting the following {@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}. |
| * The {@linkplain ClassLoader#getSystemClassLoader() system class loader} |
| * is used to load this class. |
| * <li>{@code java.util.concurrent.ForkJoinPool.common.exceptionHandler} |
| * - the class name of a {@link UncaughtExceptionHandler}. |
| * The {@linkplain ClassLoader#getSystemClassLoader() system class loader} |
| * is used to load this class. |
| * <li>{@code java.util.concurrent.ForkJoinPool.common.maximumSpares} |
| * - the maximum number of allowed extra threads to maintain target |
| * parallelism (default 256). |
| * </ul> |
| * If no thread factory is supplied via a system property, then the |
| * common pool uses a factory that uses the system class loader as the |
| * {@linkplain Thread#getContextClassLoader() thread context class loader}. |
| * In addition, if a {@link SecurityManager} is present, then |
| * the common pool uses a factory supplying threads that have no |
| * {@link Permissions} enabled. |
| * |
| * 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 |
| */ |
| 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) |
| * in a circular buffer: |
| * q.array[q.top++ % length] = task; |
| * |
| * (The actual code needs to null-check and size-check the array, |
| * uses masking, not mod, for indexing a power-of-two-sized array, |
| * properly fences accesses, and possibly signals 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 ((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 ((the task at base slot is not null) and |
| * (CAS slot to null)) |
| * increment base and return task; |
| * |
| * There are several variants of each of these. In particular, |
| * almost all uses of poll occur within scan operations that also |
| * interleave contention tracking (with associated code sprawl.) |
| * |
| * 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 (but different than) the one used here. |
| * Extracting tasks in array slots via (fully fenced) CAS provides |
| * primary synchronization. The base and top indices imprecisely |
| * guide where to extract from. We do not always require strict |
| * orderings of array and index updates, so sometimes let them be |
| * subject to compiler and processor reorderings. However, the |
| * volatile "base" index also serves as a basis for memory |
| * ordering: Slot accesses are preceded by a read of base, |
| * ensuring happens-before ordering with respect to stealers (so |
| * the slots themselves can be read via plain array reads.) The |
| * only other memory orderings relied on are maintained in the |
| * course of signalling and activation (see below). A check that |
| * base == top indicates (momentary) emptiness, but otherwise may |
| * err on the side of possibly making the queue appear nonempty |
| * when a push, pop, or poll have not fully committed, or making |
| * it appear empty when an update of top has not yet been visibly |
| * written. (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) visibly completes. |
| * However, in the aggregate, we ensure at least probabilistic |
| * non-blockingness. If an attempted steal fails, a scanning |
| * thief 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 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. |
| * |
| * 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. Insertion of tasks in shared mode |
| * requires a lock but we use only a simple spinlock (using field |
| * phase), because submitters encountering a busy queue move to a |
| * different position to use or create other queues -- they block |
| * only when creating and registering new queues. Because it is |
| * used only as a spinlock, unlocking requires only a "releasing" |
| * store (using setRelease). |
| * |
| * 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 a few |
| * volatile variables that are by far most often read (not |
| * written) as status and consistency checks. We pack as much |
| * information into them as we can. |
| * |
| * Field "ctl" contains 64 bits holding information needed to |
| * atomically decide to add, enqueue (on an event queue), and |
| * dequeue (and release)-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 "mode" holds configuration parameters as well as lifetime |
| * status, atomically and monotonically setting SHUTDOWN, STOP, |
| * and finally TERMINATED bits. |
| * |
| * Field "workQueues" holds references to WorkQueues. It is |
| * updated (only during worker creation and termination) under |
| * lock (using field workerNamePrefix as lock), but is otherwise |
| * concurrently readable, and accessed directly. We also ensure |
| * that uses of the array reference itself never become too stale |
| * in case of resizing. 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 |
| * 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 total worker and |
| * "released" worker counts, plus the head of the available worker |
| * queue (actually stack, represented by the lower 32bit subfield |
| * of ctl). Released workers are those known to be scanning for |
| * and/or running tasks. Unreleased ("available") workers are |
| * recorded in the ctl stack. These workers are made available for |
| * signalling by enqueuing in ctl (see method runWorker). The |
| * "queue" is a form of Treiber stack. This is ideal for |
| * activating threads in most-recently used order, and improves |
| * performance and locality, outweighing the disadvantages of |
| * being prone to contention and inability to release a worker |
| * unless it is topmost on stack. To avoid missed signal problems |
| * inherent in any wait/signal design, available workers rescan |
| * for (and if found run) tasks after enqueuing. Normally their |
| * release status will be updated while doing so, but the released |
| * worker ctl count may underestimate the number of active |
| * threads. (However, it is still possible to determine quiescence |
| * via a validation traversal -- see isQuiescent). After an |
| * unsuccessful rescan, available workers are blocked until |
| * signalled (see signalWork). The top stack state holds the |
| * value of the "phase" 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. |
| * |
| * Creating workers. To create a worker, we pre-increment counts |
| * (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 (see |
| * externalPush). |
| * |
| * WorkQueue field "phase" is used by both workers and the pool to |
| * manage and track whether a worker is UNSIGNALLED (possibly |
| * blocked waiting for a signal). When a worker is enqueued its |
| * phase field is set. Note that phase field updates lag queue CAS |
| * releases so usage requires care -- seeing a negative phase does |
| * not guarantee that the worker is available. 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. |
| * |
| * The ctl field also serves as the basis for memory |
| * synchronization surrounding activation. This uses a more |
| * efficient version of a Dekker-like rule that task producers and |
| * consumers sync with each other by both writing/CASing ctl (even |
| * if to its current value). This would be extremely costly. So |
| * we relax it in several ways: (1) Producers only signal when |
| * their queue is empty. Other workers propagate this signal (in |
| * method scan) when they find tasks; to further reduce flailing, |
| * each worker signals only one other per activation. (2) Workers |
| * only enqueue after scanning (see below) and not finding any |
| * tasks. (3) Rather than CASing ctl to its current value in the |
| * common case where no action is required, we reduce write |
| * contention by equivalently prefacing signalWork when called by |
| * an external task producer using a memory access with |
| * full-volatile semantics or a "fullFence". |
| * |
| * Almost always, too many signals are issued. A task producer |
| * cannot in general tell if some existing worker is in the midst |
| * of finishing one task (or already scanning) and ready to take |
| * another without being signalled. So the producer might instead |
| * activate a different worker that does not find any work, and |
| * then inactivates. This scarcely matters in steady-state |
| * computations involving all workers, but can create contention |
| * and bookkeeping bottlenecks during ramp-up, ramp-down, and small |
| * computations involving only a few workers. |
| * |
| * Scanning. Method runWorker performs top-level scanning for |
| * tasks. Each scan traverses and tries to poll from each queue |
| * starting at a random index and circularly stepping. Scans are |
| * not performed in ideal random permutation order, to reduce |
| * cacheline contention. The pseudorandom generator need not have |
| * high-quality statistical properties in the long term, but just |
| * within computations; We use Marsaglia XorShifts (often via |
| * ThreadLocalRandom.nextSecondarySeed), which are cheap and |
| * suffice. Scanning also employs contention reduction: When |
| * scanning workers fail to extract an apparently existing task, |
| * they soon restart at a different pseudorandom index. This |
| * improves throughput when many threads are trying to take tasks |
| * from few queues, which can be common in some usages. Scans do |
| * not otherwise explicitly take into account core affinities, |
| * loads, cache localities, etc, However, they do exploit temporal |
| * locality (which usually approximates these) by preferring to |
| * re-poll (at most #workers times) from the same queue after a |
| * successful poll before trying others. |
| * |
| * 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 method scan) if the pool has |
| * remained quiescent for period given by field keepAlive. |
| * |
| * 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 cancelling their unprocessed tasks, |
| * and waking them up, doing so repeatedly until stable. Calls to |
| * non-abrupt shutdown() preface this by checking whether |
| * termination should commence by sweeping through queues (until |
| * stable) to ensure lack of in-flight submissions and workers |
| * about to process them before triggering the "STOP" phase of |
| * termination. |
| * |
| * 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 |
| * always 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. |
| * |
| * The ManagedBlocker extension API can't use helping so relies |
| * only on compensation in method awaitBlocker. |
| * |
| * The algorithm in awaitJoin entails a form of "linear helping". |
| * Each worker records (in field source) the id of the queue from |
| * which it last stole a task. The scan in method awaitJoin 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 if the to-be-joined task had |
| * 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 |
| * mainly in that we only record queue ids, not full dependency |
| * links. This requires a linear scan of the workQueues array to |
| * locate stealers, but isolates cost to when it is needed, rather |
| * than adding to per-task overhead. Searches can fail to locate |
| * stealers GC stalls and the like delay recording sources. |
| * Further, even when accurately identified, stealers might not |
| * ever produce a task that the joiner can in turn help with. So, |
| * compensation is tried upon failure to find tasks to run. |
| * |
| * Compensation does not by default 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. |
| * Rather than impose arbitrary policies, we allow users to |
| * override the default of only adding threads upon apparent |
| * starvation. The compensation mechanism may also be bounded. |
| * Bounds for the commonPool (see COMMON_MAX_SPARES) better enable |
| * JVMs to cope with programming errors and abuse before running |
| * out of resources to do so. |
| * |
| * 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. |
| * |
| * 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.afterTopLevelExec). 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 VarHandles. 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. 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. 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. |
| * Returning null or throwing an exception may result in tasks |
| * never being executed. If this method throws an exception, |
| * it is relayed to the caller of the method (for example |
| * {@code execute}) causing attempted thread creation. If this |
| * method returns null or throws an exception, it is not |
| * retried until the next attempted creation (for example |
| * another call to {@code execute}). |
| * |
| * @param pool the pool this thread works in |
| * @return the new worker thread, or {@code null} if the request |
| * to create a thread is rejected |
| * @throws NullPointerException if the pool is null |
| */ |
| public ForkJoinWorkerThread newThread(ForkJoinPool pool); |
| } |
| |
| static AccessControlContext contextWithPermissions(Permission ... perms) { |
| Permissions permissions = new Permissions(); |
| for (Permission perm : perms) |
| permissions.add(perm); |
| return new AccessControlContext( |
| new ProtectionDomain[] { new ProtectionDomain(null, permissions) }); |
| } |
| |
| /** |
| * Default ForkJoinWorkerThreadFactory implementation; creates a |
| * new ForkJoinWorkerThread using the system class loader as the |
| * thread context class loader. |
| */ |
| private static final class DefaultForkJoinWorkerThreadFactory |
| implements ForkJoinWorkerThreadFactory { |
| private static final AccessControlContext ACC = contextWithPermissions( |
| new RuntimePermission("getClassLoader"), |
| new RuntimePermission("setContextClassLoader")); |
| |
| public final ForkJoinWorkerThread newThread(ForkJoinPool pool) { |
| return AccessController.doPrivileged( |
| new PrivilegedAction<>() { |
| public ForkJoinWorkerThread run() { |
| return new ForkJoinWorkerThread( |
| pool, ClassLoader.getSystemClassLoader()); }}, |
| ACC); |
| } |
| } |
| |
| // Constants shared across ForkJoinPool and WorkQueue |
| |
| // Bounds |
| static final int SWIDTH = 16; // width of short |
| static final int SMASK = 0xffff; // short bits == max index |
| static final int MAX_CAP = 0x7fff; // max #workers - 1 |
| static final int SQMASK = 0x007e; // max 64 (even) slots |
| |
| // Masks and units for WorkQueue.phase and ctl sp subfield |
| static final int UNSIGNALLED = 1 << 31; // must be negative |
| static final int SS_SEQ = 1 << 16; // version count |
| static final int QLOCK = 1; // must be 1 |
| |
| // Mode bits and sentinels, some also used in WorkQueue id and.source fields |
| static final int OWNED = 1; // queue has owner thread |
| static final int FIFO = 1 << 16; // fifo queue or access mode |
| static final int SHUTDOWN = 1 << 18; |
| static final int TERMINATED = 1 << 19; |
| static final int STOP = 1 << 31; // must be negative |
| static final int QUIET = 1 << 30; // not scanning or working |
| static final int DORMANT = QUIET | UNSIGNALLED; |
| |
| /** |
| * The maximum number of local polls from the same queue before |
| * checking others. This is a safeguard against infinitely unfair |
| * looping under unbounded user task recursion, and must be larger |
| * than plausible cases of intentional bounded task recursion. |
| */ |
| static final int POLL_LIMIT = 1 << 10; |
| |
| /** |
| * 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. |
| */ |
| @jdk.internal.vm.annotation.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 phase; // versioned, negative: queued, 1: locked |
| int stackPred; // pool stack (ctl) predecessor link |
| int nsteals; // number of steals |
| int id; // index, mode, tag |
| volatile int source; // source queue id, or sentinel |
| 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 |
| |
| 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 (id & 0xffff) >>> 1; // ignore odd/even tag bit |
| } |
| |
| /** |
| * Returns the approximate number of tasks in the queue. |
| */ |
| final int queueSize() { |
| int n = base - top; // 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, al, b; |
| return ((n = (b = base) - top) >= 0 || // possibly one task |
| (n == -1 && ((a = array) == null || |
| (al = a.length) == 0 || |
| a[(al - 1) & b] == null))); |
| } |
| |
| |
| /** |
| * Pushes a task. Call only by owner in unshared queues. |
| * |
| * @param task the task. Caller must ensure non-null. |
| * @throws RejectedExecutionException if array cannot be resized |
| */ |
| final void push(ForkJoinTask<?> task) { |
| int s = top; ForkJoinTask<?>[] a; int al, d; |
| if ((a = array) != null && (al = a.length) > 0) { |
| int index = (al - 1) & s; |
| ForkJoinPool p = pool; |
| top = s + 1; |
| QA.setRelease(a, index, task); |
| if ((d = base - s) == 0 && p != null) { |
| VarHandle.fullFence(); |
| p.signalWork(); |
| } |
| else if (d + al == 1) |
| 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 oldSize = oldA != null ? oldA.length : 0; |
| int size = oldSize > 0 ? oldSize << 1 : INITIAL_QUEUE_CAPACITY; |
| if (size < INITIAL_QUEUE_CAPACITY || size > MAXIMUM_QUEUE_CAPACITY) |
| throw new RejectedExecutionException("Queue capacity exceeded"); |
| int oldMask, t, b; |
| ForkJoinTask<?>[] a = array = new ForkJoinTask<?>[size]; |
| if (oldA != null && (oldMask = oldSize - 1) > 0 && |
| (t = top) - (b = base) > 0) { |
| int mask = size - 1; |
| do { // emulate poll from old array, push to new array |
| int index = b & oldMask; |
| ForkJoinTask<?> x = (ForkJoinTask<?>) |
| QA.getAcquire(oldA, index); |
| if (x != null && |
| QA.compareAndSet(oldA, index, x, null)) |
| a[b & mask] = x; |
| } while (++b != t); |
| VarHandle.releaseFence(); |
| } |
| return a; |
| } |
| |
| /** |
| * Takes next task, if one exists, in LIFO order. Call only |
| * by owner in unshared queues. |
| */ |
| final ForkJoinTask<?> pop() { |
| int b = base, s = top, al, i; ForkJoinTask<?>[] a; |
| if ((a = array) != null && b != s && (al = a.length) > 0) { |
| int index = (al - 1) & --s; |
| ForkJoinTask<?> t = (ForkJoinTask<?>) |
| QA.get(a, index); |
| if (t != null && |
| QA.compareAndSet(a, index, t, null)) { |
| top = s; |
| VarHandle.releaseFence(); |
| return t; |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Takes next task, if one exists, in FIFO order. |
| */ |
| final ForkJoinTask<?> poll() { |
| for (;;) { |
| int b = base, s = top, d, al; ForkJoinTask<?>[] a; |
| if ((a = array) != null && (d = b - s) < 0 && |
| (al = a.length) > 0) { |
| int index = (al - 1) & b; |
| ForkJoinTask<?> t = (ForkJoinTask<?>) |
| QA.getAcquire(a, index); |
| if (b++ == base) { |
| if (t != null) { |
| if (QA.compareAndSet(a, index, t, null)) { |
| base = b; |
| return t; |
| } |
| } |
| else if (d == -1) |
| break; // now empty |
| } |
| } |
| else |
| break; |
| } |
| return null; |
| } |
| |
| /** |
| * Takes next task, if one exists, in order specified by mode. |
| */ |
| final ForkJoinTask<?> nextLocalTask() { |
| return ((id & FIFO) != 0) ? poll() : pop(); |
| } |
| |
| /** |
| * Returns next task, if one exists, in order specified by mode. |
| */ |
| final ForkJoinTask<?> peek() { |
| int al; ForkJoinTask<?>[] a; |
| return ((a = array) != null && (al = a.length) > 0) ? |
| a[(al - 1) & |
| ((id & FIFO) != 0 ? base : top - 1)] : null; |
| } |
| |
| /** |
| * Pops the given task only if it is at the current top. |
| */ |
| final boolean tryUnpush(ForkJoinTask<?> task) { |
| int b = base, s = top, al; ForkJoinTask<?>[] a; |
| if ((a = array) != null && b != s && (al = a.length) > 0) { |
| int index = (al - 1) & --s; |
| if (QA.compareAndSet(a, index, task, null)) { |
| top = s; |
| VarHandle.releaseFence(); |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| /** |
| * Removes and cancels all known tasks, ignoring any exceptions. |
| */ |
| final void cancelAll() { |
| for (ForkJoinTask<?> t; (t = poll()) != null; ) |
| ForkJoinTask.cancelIgnoringExceptions(t); |
| } |
| |
| // Specialized execution methods |
| |
| /** |
| * Pops and executes up to limit consecutive tasks or until empty. |
| * |
| * @param limit max runs, or zero for no limit |
| */ |
| final void localPopAndExec(int limit) { |
| for (;;) { |
| int b = base, s = top, al; ForkJoinTask<?>[] a; |
| if ((a = array) != null && b != s && (al = a.length) > 0) { |
| int index = (al - 1) & --s; |
| ForkJoinTask<?> t = (ForkJoinTask<?>) |
| QA.getAndSet(a, index, null); |
| if (t != null) { |
| top = s; |
| VarHandle.releaseFence(); |
| t.doExec(); |
| if (limit != 0 && --limit == 0) |
| break; |
| } |
| else |
| break; |
| } |
| else |
| break; |
| } |
| } |
| |
| /** |
| * Polls and executes up to limit consecutive tasks or until empty. |
| * |
| * @param limit, or zero for no limit |
| */ |
| final void localPollAndExec(int limit) { |
| for (int polls = 0;;) { |
| int b = base, s = top, d, al; ForkJoinTask<?>[] a; |
| if ((a = array) != null && (d = b - s) < 0 && |
| (al = a.length) > 0) { |
| int index = (al - 1) & b++; |
| ForkJoinTask<?> t = (ForkJoinTask<?>) |
| QA.getAndSet(a, index, null); |
| if (t != null) { |
| base = b; |
| t.doExec(); |
| if (limit != 0 && ++polls == limit) |
| break; |
| } |
| else if (d == -1) |
| break; // now empty |
| else |
| polls = 0; // stolen; reset |
| } |
| else |
| break; |
| } |
| } |
| |
| /** |
| * If present, removes task from queue and executes it. |
| */ |
| final void tryRemoveAndExec(ForkJoinTask<?> task) { |
| ForkJoinTask<?>[] wa; int s, wal; |
| if (base - (s = top) < 0 && // traverse from top |
| (wa = array) != null && (wal = wa.length) > 0) { |
| for (int m = wal - 1, ns = s - 1, i = ns; ; --i) { |
| int index = i & m; |
| ForkJoinTask<?> t = (ForkJoinTask<?>) |
| QA.get(wa, index); |
| if (t == null) |
| break; |
| else if (t == task) { |
| if (QA.compareAndSet(wa, index, t, null)) { |
| top = ns; // safely shift down |
| for (int j = i; j != ns; ++j) { |
| ForkJoinTask<?> f; |
| int pindex = (j + 1) & m; |
| f = (ForkJoinTask<?>)QA.get(wa, pindex); |
| QA.setVolatile(wa, pindex, null); |
| int jindex = j & m; |
| QA.setRelease(wa, jindex, f); |
| } |
| VarHandle.releaseFence(); |
| t.doExec(); |
| } |
| break; |
| } |
| } |
| } |
| } |
| |
| /** |
| * Tries to steal and run tasks within the target's |
| * computation until done, not found, or limit exceeded. |
| * |
| * @param task root of CountedCompleter computation |
| * @param limit max runs, or zero for no limit |
| * @return task status on exit |
| */ |
| final int localHelpCC(CountedCompleter<?> task, int limit) { |
| int status = 0; |
| if (task != null && (status = task.status) >= 0) { |
| for (;;) { |
| boolean help = false; |
| int b = base, s = top, al; ForkJoinTask<?>[] a; |
| if ((a = array) != null && b != s && (al = a.length) > 0) { |
| int index = (al - 1) & (s - 1); |
| ForkJoinTask<?> o = (ForkJoinTask<?>) |
| QA.get(a, index); |
| if (o instanceof CountedCompleter) { |
| CountedCompleter<?> t = (CountedCompleter<?>)o; |
| for (CountedCompleter<?> f = t;;) { |
| if (f != task) { |
| if ((f = f.completer) == null) // try parent |
| break; |
| } |
| else { |
| if (QA.compareAndSet(a, index, t, null)) { |
| top = s - 1; |
| VarHandle.releaseFence(); |
| t.doExec(); |
| help = true; |
| } |
| break; |
| } |
| } |
| } |
| } |
| if ((status = task.status) < 0 || !help || |
| (limit != 0 && --limit == 0)) |
| break; |
| } |
| } |
| return status; |
| } |
| |
| // Operations on shared queues |
| |
| /** |
| * Tries to lock shared queue by CASing phase field. |
| */ |
| final boolean tryLockSharedQueue() { |
| return PHASE.compareAndSet(this, 0, QLOCK); |
| } |
| |
| /** |
| * Shared version of tryUnpush. |
| */ |
| final boolean trySharedUnpush(ForkJoinTask<?> task) { |
| boolean popped = false; |
| int s = top - 1, al; ForkJoinTask<?>[] a; |
| if ((a = array) != null && (al = a.length) > 0) { |
| int index = (al - 1) & s; |
| ForkJoinTask<?> t = (ForkJoinTask<?>) QA.get(a, index); |
| if (t == task && |
| PHASE.compareAndSet(this, 0, QLOCK)) { |
| if (top == s + 1 && array == a && |
| QA.compareAndSet(a, index, task, null)) { |
| popped = true; |
| top = s; |
| } |
| PHASE.setRelease(this, 0); |
| } |
| } |
| return popped; |
| } |
| |
| /** |
| * Shared version of localHelpCC. |
| */ |
| final int sharedHelpCC(CountedCompleter<?> task, int limit) { |
| int status = 0; |
| if (task != null && (status = task.status) >= 0) { |
| for (;;) { |
| boolean help = false; |
| int b = base, s = top, al; ForkJoinTask<?>[] a; |
| if ((a = array) != null && b != s && (al = a.length) > 0) { |
| int index = (al - 1) & (s - 1); |
| ForkJoinTask<?> o = (ForkJoinTask<?>) |
| QA.get(a, index); |
| if (o instanceof CountedCompleter) { |
| CountedCompleter<?> t = (CountedCompleter<?>)o; |
| for (CountedCompleter<?> f = t;;) { |
| if (f != task) { |
| if ((f = f.completer) == null) |
| break; |
| } |
| else { |
| if (PHASE.compareAndSet(this, 0, QLOCK)) { |
| if (top == s && array == a && |
| QA.compareAndSet(a, index, t, null)) { |
| help = true; |
| top = s - 1; |
| } |
| PHASE.setRelease(this, 0); |
| if (help) |
| t.doExec(); |
| } |
| break; |
| } |
| } |
| } |
| } |
| if ((status = task.status) < 0 || !help || |
| (limit != 0 && --limit == 0)) |
| break; |
| } |
| } |
| return status; |
| } |
| |
| /** |
| * Returns true if owned and not known to be blocked. |
| */ |
| final boolean isApparentlyUnblocked() { |
| Thread wt; Thread.State s; |
| return ((wt = owner) != null && |
| (s = wt.getState()) != Thread.State.BLOCKED && |
| s != Thread.State.WAITING && |
| s != Thread.State.TIMED_WAITING); |
| } |
| |
| // VarHandle mechanics. |
| private static final VarHandle PHASE; |
| static { |
| try { |
| MethodHandles.Lookup l = MethodHandles.lookup(); |
| PHASE = l.findVarHandle(WorkQueue.class, "phase", int.class); |
| } catch (ReflectiveOperationException 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. |
| */ |
| 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 COMMON_PARALLELISM; |
| |
| /** |
| * Limit on spare thread construction in tryCompensate. |
| */ |
| private static final int COMMON_MAX_SPARES; |
| |
| /** |
| * 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 |
| |
| /** |
| * Default idle timeout value (in milliseconds) for the thread |
| * triggering quiescence to park waiting for new work |
| */ |
| private static final long DEFAULT_KEEPALIVE = 60_000L; |
| |
| /** |
| * Undershoot tolerance for idle timeouts |
| */ |
| private static final long TIMEOUT_SLOP = 20L; |
| |
| /** |
| * The default value for COMMON_MAX_SPARES. Overridable using the |
| * "java.util.concurrent.ForkJoinPool.common.maximumSpares" system |
| * property. 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; |
| |
| /** |
| * 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: |
| * RC: Number of released (unqueued) 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 unqueued |
| * 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 release count |
| * using getAndAddLong of RC_UNIT, rather than CAS, when returning |
| * from a blocked join. Other updates entail multiple subfields |
| * and masking, requiring CAS. |
| * |
| * The limits packed in field "bounds" are also offset by the |
| * parallelism level to make them comparable to the ctl rc and tc |
| * fields. |
| */ |
| |
| // Lower and upper word masks |
| private static final long SP_MASK = 0xffffffffL; |
| private static final long UC_MASK = ~SP_MASK; |
| |
| // Release counts |
| private static final int RC_SHIFT = 48; |
| private static final long RC_UNIT = 0x0001L << RC_SHIFT; |
| private static final long RC_MASK = 0xffffL << RC_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 |
| |
| // Instance fields |
| |
| volatile long stealCount; // collects worker nsteals |
| final long keepAlive; // milliseconds before dropping if idle |
| int indexSeed; // next worker index |
| final int bounds; // min, max threads packed as shorts |
| volatile int mode; // parallelism, runstate, queue mode |
| WorkQueue[] workQueues; // main registry |
| final String workerNamePrefix; // for worker thread string; sync lock |
| final ForkJoinWorkerThreadFactory factory; |
| final UncaughtExceptionHandler ueh; // per-worker UEH |
| final Predicate<? super ForkJoinPool> saturate; |
| |
| @jdk.internal.vm.annotation.Contended("fjpctl") // segregate |
| volatile long ctl; // main pool control |
| |
| // 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) { |
| do { |
| long nc = ((RC_MASK & (c + RC_UNIT)) | |
| (TC_MASK & (c + TC_UNIT))); |
| if (ctl == c && CTL.compareAndSet(this, c, nc)) { |
| 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 tid = 0; // for thread name |
| int fifo = mode & FIFO; |
| String prefix = workerNamePrefix; |
| if (prefix != null) { |
| synchronized (prefix) { |
| WorkQueue[] ws = workQueues; int n; |
| int s = indexSeed += SEED_INCREMENT; |
| if (ws != null && (n = ws.length) > 1) { |
| int m = n - 1; |
| tid = s & m; |
| int i = m & ((s << 1) | 1); // odd-numbered indices |
| for (int probes = n >>> 1;;) { // find empty slot |
| WorkQueue q; |
| if ((q = ws[i]) == null || q.phase == QUIET) |
| break; |
| else if (--probes == 0) { |
| i = n | 1; // resize below |
| break; |
| } |
| else |
| i = (i + 2) & m; |
| } |
| |
| int id = i | fifo | (s & ~(SMASK | FIFO | DORMANT)); |
| w.phase = w.id = id; // now publishable |
| |
| if (i < n) |
| ws[i] = w; |
| else { // expand array |
| int an = n << 1; |
| WorkQueue[] as = new WorkQueue[an]; |
| as[i] = w; |
| int am = an - 1; |
| for (int j = 0; j < n; ++j) { |
| WorkQueue v; // copy external queue |
| if ((v = ws[j]) != null) // position may change |
| as[v.id & am & SQMASK] = v; |
| if (++j >= n) |
| break; |
| as[j] = ws[j]; // copy worker |
| } |
| workQueues = as; |
| } |
| } |
| } |
| wt.setName(prefix.concat(Integer.toString(tid))); |
| } |
| 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; |
| int phase = 0; |
| if (wt != null && (w = wt.workQueue) != null) { |
| Object lock = workerNamePrefix; |
| long ns = (long)w.nsteals & 0xffffffffL; |
| int idx = w.id & SMASK; |
| if (lock != null) { |
| WorkQueue[] ws; // remove index from array |
| synchronized (lock) { |
| if ((ws = workQueues) != null && ws.length > idx && |
| ws[idx] == w) |
| ws[idx] = null; |
| stealCount += ns; |
| } |
| } |
| phase = w.phase; |
| } |
| if (phase != QUIET) { // else pre-adjusted |
| long c; // decrement counts |
| do {} while (!CTL.weakCompareAndSet |
| (this, c = ctl, ((RC_MASK & (c - RC_UNIT)) | |
| (TC_MASK & (c - TC_UNIT)) | |
| (SP_MASK & c)))); |
| } |
| if (w != null) |
| w.cancelAll(); // cancel remaining tasks |
| |
| if (!tryTerminate(false, false) && // possibly replace worker |
| w != null && w.array != null) // avoid repeated failures |
| signalWork(); |
| |
| if (ex == null) // help clean on way out |
| ForkJoinTask.helpExpungeStaleExceptions(); |
| else // rethrow |
| ForkJoinTask.rethrow(ex); |
| } |
| |
| /** |
| * Tries to create or release a worker if too few are running. |
| */ |
| final void signalWork() { |
| for (;;) { |
| long c; int sp; WorkQueue[] ws; int i; WorkQueue v; |
| if ((c = ctl) >= 0L) // enough workers |
| break; |
| else if ((sp = (int)c) == 0) { // no idle workers |
| if ((c & ADD_WORKER) != 0L) // too few workers |
| tryAddWorker(c); |
| break; |
| } |
| else if ((ws = workQueues) == null) |
| break; // unstarted/terminated |
| else if (ws.length <= (i = sp & SMASK)) |
| break; // terminated |
| else if ((v = ws[i]) == null) |
| break; // terminating |
| else { |
| int np = sp & ~UNSIGNALLED; |
| int vp = v.phase; |
| long nc = (v.stackPred & SP_MASK) | (UC_MASK & (c + RC_UNIT)); |
| Thread vt = v.owner; |
| if (sp == vp && CTL.compareAndSet(this, c, nc)) { |
| v.phase = np; |
| if (v.source < 0) |
| LockSupport.unpark(vt); |
| break; |
| } |
| } |
| } |
| } |
| |
| /** |
| * Tries to decrement counts (sometimes implicitly) and possibly |
| * arrange for a compensating worker in preparation for blocking: |
| * If not all core workers yet exist, creates one, else if any are |
| * unreleased (possibly including caller) releases one, else if |
| * fewer than the minimum allowed number of workers running, |
| * checks to see that they are all active, and if so creates an |
| * extra worker unless over maximum limit and policy is to |
| * saturate. Most of these steps can fail due to interference, in |
| * which case 0 is returned so caller will retry. A negative |
| * return value indicates that the caller doesn't need to |
| * re-adjust counts when later unblocked. |
| * |
| * @return 1: block then adjust, -1: block without adjust, 0 : retry |
| */ |
| private int tryCompensate(WorkQueue w) { |
| int t, n, sp; |
| long c = ctl; |
| WorkQueue[] ws = workQueues; |
| if ((t = (short)(c >>> TC_SHIFT)) >= 0) { |
| if (ws == null || (n = ws.length) <= 0 || w == null) |
| return 0; // disabled |
| else if ((sp = (int)c) != 0) { // replace or release |
| WorkQueue v = ws[sp & (n - 1)]; |
| int wp = w.phase; |
| long uc = UC_MASK & ((wp < 0) ? c + RC_UNIT : c); |
| int np = sp & ~UNSIGNALLED; |
| if (v != null) { |
| int vp = v.phase; |
| Thread vt = v.owner; |
| long nc = ((long)v.stackPred & SP_MASK) | uc; |
| if (vp == sp && CTL.compareAndSet(this, c, nc)) { |
| v.phase = np; |
| if (v.source < 0) |
| LockSupport.unpark(vt); |
| return (wp < 0) ? -1 : 1; |
| } |
| } |
| return 0; |
| } |
| else if ((int)(c >> RC_SHIFT) - // reduce parallelism |
| (short)(bounds & SMASK) > 0) { |
| long nc = ((RC_MASK & (c - RC_UNIT)) | (~RC_MASK & c)); |
| return CTL.compareAndSet(this, c, nc) ? 1 : 0; |
| } |
| else { // validate |
| int md = mode, pc = md & SMASK, tc = pc + t, bc = 0; |
| boolean unstable = false; |
| for (int i = 1; i < n; i += 2) { |
| WorkQueue q; Thread wt; Thread.State ts; |
| if ((q = ws[i]) != null) { |
| if (q.source == 0) { |
| unstable = true; |
| break; |
| } |
| else { |
| --tc; |
| if ((wt = q.owner) != null && |
| ((ts = wt.getState()) == Thread.State.BLOCKED || |
| ts == Thread.State.WAITING)) |
| ++bc; // worker is blocking |
| } |
| } |
| } |
| if (unstable || tc != 0 || ctl != c) |
| return 0; // inconsistent |
| else if (t + pc >= MAX_CAP || t >= (bounds >>> SWIDTH)) { |
| Predicate<? super ForkJoinPool> sat; |
| if ((sat = saturate) != null && sat.test(this)) |
| return -1; |
| else if (bc < pc) { // lagging |
| Thread.yield(); // for retry spins |
| return 0; |
| } |
| else |
| throw new RejectedExecutionException( |
| "Thread limit exceeded replacing blocked worker"); |
| } |
| } |
| } |
| |
| long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK); // expand pool |
| return CTL.compareAndSet(this, c, nc) && createWorker() ? 1 : 0; |
| } |
| |
| /** |
| * Top-level runloop for workers, called by ForkJoinWorkerThread.run. |
| * See above for explanation. |
| */ |
| final void runWorker(WorkQueue w) { |
| WorkQueue[] ws; |
| w.growArray(); // allocate queue |
| int r = w.id ^ ThreadLocalRandom.nextSecondarySeed(); |
| if (r == 0) // initial nonzero seed |
| r = 1; |
| int lastSignalId = 0; // avoid unneeded signals |
| while ((ws = workQueues) != null) { |
| boolean nonempty = false; // scan |
| for (int n = ws.length, j = n, m = n - 1; j > 0; --j) { |
| WorkQueue q; int i, b, al; ForkJoinTask<?>[] a; |
| if ((i = r & m) >= 0 && i < n && // always true |
| (q = ws[i]) != null && (b = q.base) - q.top < 0 && |
| (a = q.array) != null && (al = a.length) > 0) { |
| int qid = q.id; // (never zero) |
| int index = (al - 1) & b; |
| ForkJoinTask<?> t = (ForkJoinTask<?>) |
| QA.getAcquire(a, index); |
| if (t != null && b++ == q.base && |
| QA.compareAndSet(a, index, t, null)) { |
| if ((q.base = b) - q.top < 0 && qid != lastSignalId) |
| signalWork(); // propagate signal |
| w.source = lastSignalId = qid; |
| t.doExec(); |
| if ((w.id & FIFO) != 0) // run remaining locals |
| w.localPollAndExec(POLL_LIMIT); |
| else |
| w.localPopAndExec(POLL_LIMIT); |
| ForkJoinWorkerThread thread = w.owner; |
| ++w.nsteals; |
| w.source = 0; // now idle |
| if (thread != null) |
| thread.afterTopLevelExec(); |
| } |
| nonempty = true; |
| } |
| else if (nonempty) |
| break; |
| else |
| ++r; |
| } |
| |
| if (nonempty) { // move (xorshift) |
| r ^= r << 13; r ^= r >>> 17; r ^= r << 5; |
| } |
| else { |
| int phase; |
| lastSignalId = 0; // clear for next scan |
| if ((phase = w.phase) >= 0) { // enqueue |
| int np = w.phase = (phase + SS_SEQ) | UNSIGNALLED; |
| long c, nc; |
| do { |
| w.stackPred = (int)(c = ctl); |
| nc = ((c - RC_UNIT) & UC_MASK) | (SP_MASK & np); |
| } while (!CTL.weakCompareAndSet(this, c, nc)); |
| } |
| else { // already queued |
| int pred = w.stackPred; |
| w.source = DORMANT; // enable signal |
| for (int steps = 0;;) { |
| int md, rc; long c; |
| if (w.phase >= 0) { |
| w.source = 0; |
| break; |
| } |
| else if ((md = mode) < 0) // shutting down |
| return; |
| else if ((rc = ((md & SMASK) + // possibly quiescent |
| (int)((c = ctl) >> RC_SHIFT))) <= 0 && |
| (md & SHUTDOWN) != 0 && |
| tryTerminate(false, false)) |
| return; // help terminate |
| else if ((++steps & 1) == 0) |
| Thread.interrupted(); // clear between parks |
| else if (rc <= 0 && pred != 0 && phase == (int)c) { |
| long d = keepAlive + System.currentTimeMillis(); |
| LockSupport.parkUntil(this, d); |
| if (ctl == c && |
| d - System.currentTimeMillis() <= TIMEOUT_SLOP) { |
| long nc = ((UC_MASK & (c - TC_UNIT)) | |
| (SP_MASK & pred)); |
| if (CTL.compareAndSet(this, c, nc)) { |
| w.phase = QUIET; |
| return; // drop on timeout |
| } |
| } |
| } |
| else |
| LockSupport.park(this); |
| } |
| } |
| } |
| } |
| } |
| |
| /** |
| * Helps and/or blocks until the given task is done or timeout. |
| * First tries locally helping, then scans other queues for a task |
| * produced by one of w's stealers; compensating and blocking if |
| * none are found (rescanning if tryCompensate fails). |
| * |
| * @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 (w != null && task != null && |
| (!(task instanceof CountedCompleter) || |
| (s = w.localHelpCC((CountedCompleter<?>)task, 0)) >= 0)) { |
| w.tryRemoveAndExec(task); |
| int src = w.source, id = w.id; |
| s = task.status; |
| while (s >= 0) { |
| WorkQueue[] ws; |
| boolean nonempty = false; |
| int r = ThreadLocalRandom.nextSecondarySeed() | 1; // odd indices |
| if ((ws = workQueues) != null) { // scan for matching id |
| for (int n = ws.length, m = n - 1, j = -n; j < n; j += 2) { |
| WorkQueue q; int i, b, al; ForkJoinTask<?>[] a; |
| if ((i = (r + j) & m) >= 0 && i < n && |
| (q = ws[i]) != null && q.source == id && |
| (b = q.base) - q.top < 0 && |
| (a = q.array) != null && (al = a.length) > 0) { |
| int qid = q.id; |
| int index = (al - 1) & b; |
| ForkJoinTask<?> t = (ForkJoinTask<?>) |
| QA.getAcquire(a, index); |
| if (t != null && b++ == q.base && id == q.source && |
| QA.compareAndSet(a, index, t, null)) { |
| q.base = b; |
| w.source = qid; |
| t.doExec(); |
| w.source = src; |
| } |
| nonempty = true; |
| break; |
| } |
| } |
| } |
| if ((s = task.status) < 0) |
| break; |
| else if (!nonempty) { |
| long ms, ns; int block; |
| if (deadline == 0L) |
| ms = 0L; // untimed |
| else if ((ns = deadline - System.nanoTime()) <= 0L) |
| break; // timeout |
| else if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) <= 0L) |
| ms = 1L; // avoid 0 for timed wait |
| if ((block = tryCompensate(w)) != 0) { |
| task.internalWait(ms); |
| CTL.getAndAdd(this, (block > 0) ? RC_UNIT : 0L); |
| } |
| s = task.status; |
| } |
| } |
| } |
| return s; |
| } |
| |
| /** |
| * Runs tasks until {@code isQuiescent()}. Rather than blocking |
| * when tasks cannot be found, rescans until all others cannot |
| * find tasks either. |
| */ |
| final void helpQuiescePool(WorkQueue w) { |
| int prevSrc = w.source, fifo = w.id & FIFO; |
| for (int source = prevSrc, released = -1;;) { // -1 until known |
| WorkQueue[] ws; |
| if (fifo != 0) |
| w.localPollAndExec(0); |
| else |
| w.localPopAndExec(0); |
| if (released == -1 && w.phase >= 0) |
| released = 1; |
| boolean quiet = true, empty = true; |
| int r = ThreadLocalRandom.nextSecondarySeed(); |
| if ((ws = workQueues) != null) { |
| for (int n = ws.length, j = n, m = n - 1; j > 0; --j) { |
| WorkQueue q; int i, b, al; ForkJoinTask<?>[] a; |
| if ((i = (r - j) & m) >= 0 && i < n && (q = ws[i]) != null) { |
| if ((b = q.base) - q.top < 0 && |
| (a = q.array) != null && (al = a.length) > 0) { |
| int qid = q.id; |
| if (released == 0) { // increment |
| released = 1; |
| CTL.getAndAdd(this, RC_UNIT); |
| } |
| int index = (al - 1) & b; |
| ForkJoinTask<?> t = (ForkJoinTask<?>) |
| QA.getAcquire(a, index); |
| if (t != null && b++ == q.base && |
| QA.compareAndSet(a, index, t, null)) { |
| q.base = b; |
| w.source = source = q.id; |
| t.doExec(); |
| w.source = source = prevSrc; |
| } |
| quiet = empty = false; |
| break; |
| } |
| else if ((q.source & QUIET) == 0) |
| quiet = false; |
| } |
| } |
| } |
| if (quiet) { |
| if (released == 0) |
| CTL.getAndAdd(this, RC_UNIT); |
| w.source = prevSrc; |
| break; |
| } |
| else if (empty) { |
| if (source != QUIET) |
| w.source = source = QUIET; |
| if (released == 1) { // decrement |
| released = 0; |
| CTL.getAndAdd(this, RC_MASK & -RC_UNIT); |
| } |
| } |
| } |
| } |
| |
| /** |
| * Scans for and returns a polled task, if available. |
| * Used only for untracked polls. |
| * |
| * @param submissionsOnly if true, only scan submission queues |
| */ |
| private ForkJoinTask<?> pollScan(boolean submissionsOnly) { |
| WorkQueue[] ws; int n; |
| rescan: while ((mode & STOP) == 0 && (ws = workQueues) != null && |
| (n = ws.length) > 0) { |
| int m = n - 1; |
| int r = ThreadLocalRandom.nextSecondarySeed(); |
| int h = r >>> 16; |
| int origin, step; |
| if (submissionsOnly) { |
| origin = (r & ~1) & m; // even indices and steps |
| step = (h & ~1) | 2; |
| } |
| else { |
| origin = r & m; |
| step = h | 1; |
| } |
| for (int k = origin, oldSum = 0, checkSum = 0;;) { |
| WorkQueue q; int b, al; ForkJoinTask<?>[] a; |
| if ((q = ws[k]) != null) { |
| checkSum += b = q.base; |
| if (b - q.top < 0 && |
| (a = q.array) != null && (al = a.length) > 0) { |
| int index = (al - 1) & b; |
| ForkJoinTask<?> t = (ForkJoinTask<?>) |
| QA.getAcquire(a, index); |
| if (t != null && b++ == q.base && |
| QA.compareAndSet(a, index, t, null)) { |
| q.base = b; |
| return t; |
| } |
| else |
| break; // restart |
| } |
| } |
| if ((k = (k + step) & m) == origin) { |
| if (oldSum == (oldSum = checkSum)) |
| break rescan; |
| checkSum = 0; |
| } |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Gets and removes a local or stolen task for the given worker. |
| * |
| * @return a task, if available |
| */ |
| final ForkJoinTask<?> nextTaskFor(WorkQueue w) { |
| ForkJoinTask<?> t; |
| if (w != null && |
| (t = (w.id & FIFO) != 0 ? w.poll() : w.pop()) != null) |
| return t; |
| else |
| return pollScan(false); |
| } |
| |
| // External operations |
| |
| /** |
| * Adds the given task to a submission queue at submitter's |
| * current queue, creating one if null or contended. |
| * |
| * @param task the task. Caller must ensure non-null. |
| */ |
| final void externalPush(ForkJoinTask<?> task) { |
| int r; // initialize caller's probe |
| if ((r = ThreadLocalRandom.getProbe()) == 0) { |
| ThreadLocalRandom.localInit(); |
| r = ThreadLocalRandom.getProbe(); |
| } |
| for (;;) { |
| int md = mode, n; |
| WorkQueue[] ws = workQueues; |
| if ((md & SHUTDOWN) != 0 || ws == null || (n = ws.length) <= 0) |
| throw new RejectedExecutionException(); |
| else { |
| WorkQueue q; |
| boolean push = false, grow = false; |
| if ((q = ws[(n - 1) & r & SQMASK]) == null) { |
| Object lock = workerNamePrefix; |
| int qid = (r | QUIET) & ~(FIFO | OWNED); |
| q = new WorkQueue(this, null); |
| q.id = qid; |
| q.source = QUIET; |
| q.phase = QLOCK; // lock queue |
| if (lock != null) { |
| synchronized (lock) { // lock pool to install |
| int i; |
| if ((ws = workQueues) != null && |
| (n = ws.length) > 0 && |
| ws[i = qid & (n - 1) & SQMASK] == null) { |
| ws[i] = q; |
| push = grow = true; |
| } |
| } |
| } |
| } |
| else if (q.tryLockSharedQueue()) { |
| int b = q.base, s = q.top, al, d; ForkJoinTask<?>[] a; |
| if ((a = q.array) != null && (al = a.length) > 0 && |
| al - 1 + (d = b - s) > 0) { |
| a[(al - 1) & s] = task; |
| q.top = s + 1; // relaxed writes OK here |
| q.phase = 0; |
| if (d < 0 && q.base - s < -1) |
| break; // no signal needed |
| } |
| else |
| grow = true; |
| push = true; |
| } |
| if (push) { |
| if (grow) { |
| try { |
| q.growArray(); |
| int s = q.top, al; ForkJoinTask<?>[] a; |
| if ((a = q.array) != null && (al = a.length) > 0) { |
| a[(al - 1) & s] = task; |
| q.top = s + 1; |
| } |
| } finally { |
| q.phase = 0; |
| } |
| } |
| signalWork(); |
| break; |
| } |
| else // move if busy |
| r = ThreadLocalRandom.advanceProbe(r); |
| } |
| } |
| } |
| |
| /** |
| * Pushes a possibly-external submission. |
| */ |
| private <T> ForkJoinTask<T> externalSubmit(ForkJoinTask<T> task) { |
| Thread t; ForkJoinWorkerThread w; WorkQueue q; |
| if (task == null) |
| throw new NullPointerException(); |
| if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) && |
| (w = (ForkJoinWorkerThread)t).pool == this && |
| (q = w.workQueue) != null) |
| q.push(task); |
| else |
| externalPush(task); |
| return task; |
| } |
| |
| /** |
| * Returns common pool queue for an external thread. |
| */ |
| static WorkQueue commonSubmitterQueue() { |
| ForkJoinPool p = common; |
| int r = ThreadLocalRandom.getProbe(); |
| WorkQueue[] ws; int n; |
| return (p != null && (ws = p.workQueues) != null && |
| (n = ws.length) > 0) ? |
| ws[(n - 1) & r & SQMASK] : null; |
| } |
| |
| /** |
| * Performs tryUnpush for an external submitter. |
| */ |
| final boolean tryExternalUnpush(ForkJoinTask<?> task) { |
| int r = ThreadLocalRandom.getProbe(); |
| WorkQueue[] ws; WorkQueue w; int n; |
| return ((ws = workQueues) != null && |
| (n = ws.length) > 0 && |
| (w = ws[(n - 1) & r & SQMASK]) != null && |
| w.trySharedUnpush(task)); |
| } |
| |
| /** |
| * Performs helpComplete for an external submitter. |
| */ |
| final int externalHelpComplete(CountedCompleter<?> task, int maxTasks) { |
| int r = ThreadLocalRandom.getProbe(); |
| WorkQueue[] ws; WorkQueue w; int n; |
| return ((ws = workQueues) != null && (n = ws.length) > 0 && |
| (w = ws[(n - 1) & r & SQMASK]) != null) ? |
| w.sharedHelpCC(task, maxTasks) : 0; |
| } |
| |
| /** |
| * Tries to steal and run tasks within the target's computation. |
| * 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) { |
| return (w == null) ? 0 : w.localHelpCC(task, maxTasks); |
| } |
| |
| /** |
| * 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) && |
| (pool = (wt = (ForkJoinWorkerThread)t).pool) != null && |
| (q = wt.workQueue) != null) { |
| int p = pool.mode & SMASK; |
| int a = p + (int)(pool.ctl >> RC_SHIFT); |
| int n = q.top - q.base; |
| 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, terminate when next possible |
| * @return true if terminating or terminated |
| */ |
| private boolean tryTerminate(boolean now, boolean enable) { |
| int md; // 3 phases: try to set SHUTDOWN, then STOP, then TERMINATED |
| |
| while (((md = mode) & SHUTDOWN) == 0) { |
| if (!enable || this == common) // cannot shutdown |
| return false; |
| else |
| MODE.compareAndSet(this, md, md | SHUTDOWN); |
| } |
| |
| while (((md = mode) & STOP) == 0) { // try to initiate termination |
| if (!now) { // check if quiescent & empty |
| for (long oldSum = 0L;;) { // repeat until stable |
| boolean running = false; |
| long checkSum = ctl; |
| WorkQueue[] ws = workQueues; |
| if ((md & SMASK) + (int)(checkSum >> RC_SHIFT) > 0) |
| running = true; |
| else if (ws != null) { |
| WorkQueue w; int b; |
| for (int i = 0; i < ws.length; ++i) { |
| if ((w = ws[i]) != null) { |
| checkSum += (b = w.base) + w.id; |
| if (b != w.top || |
| ((i & 1) == 1 && w.source >= 0)) { |
| running = true; |
| break; |
| } |
| } |
| } |
| } |
| if (((md = mode) & STOP) != 0) |
| break; // already triggered |
| else if (running) |
| return false; |
| else if (workQueues == ws && oldSum == (oldSum = checkSum)) |
| break; |
| } |
| } |
| if ((md & STOP) == 0) |
| MODE.compareAndSet(this, md, md | STOP); |
| } |
| |
| while (((md = mode) & TERMINATED) == 0) { // help terminate others |
| for (long oldSum = 0L;;) { // repeat until stable |
| WorkQueue[] ws; WorkQueue w; |
| long checkSum = ctl; |
| if ((ws = workQueues) != null) { |
| for (int i = 0; i < ws.length; ++i) { |
| if ((w = ws[i]) != null) { |
| ForkJoinWorkerThread wt = w.owner; |
| w.cancelAll(); // clear queues |
| if (wt != null) { |
| try { // unblock join or park |
| wt.interrupt(); |
| } catch (Throwable ignore) { |
| } |
| } |
| checkSum += w.base + w.id; |
| } |
| } |
| } |
| if (((md = mode) & TERMINATED) != 0 || |
| (workQueues == ws && oldSum == (oldSum = checkSum))) |
| break; |
| } |
| if ((md & TERMINATED) != 0) |
| break; |
| else if ((md & SMASK) + (short)(ctl >>> TC_SHIFT) > 0) |
| break; |
| else if (MODE.compareAndSet(this, md, md | TERMINATED)) { |
| synchronized (this) { |
| notifyAll(); // for awaitTermination |
| } |
| break; |
| } |
| } |
| return true; |
| } |
| |
| // Exported methods |
| |
| // Constructors |
| |
| /** |
| * Creates a {@code ForkJoinPool} with parallelism equal to {@link |
| * java.lang.Runtime#availableProcessors}, using defaults for all |
| * other parameters (see {@link #ForkJoinPool(int, |
| * ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, |
| * int, int, int, Predicate, long, TimeUnit)}). |
| * |
| * @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, |
| 0, MAX_CAP, 1, null, DEFAULT_KEEPALIVE, TimeUnit.MILLISECONDS); |
| } |
| |
| /** |
| * Creates a {@code ForkJoinPool} with the indicated parallelism |
| * level, using defaults for all other parameters (see {@link |
| * #ForkJoinPool(int, ForkJoinWorkerThreadFactory, |
| * UncaughtExceptionHandler, boolean, int, int, int, Predicate, |
| * long, TimeUnit)}). |
| * |
| * @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, |
| 0, MAX_CAP, 1, null, DEFAULT_KEEPALIVE, TimeUnit.MILLISECONDS); |
| } |
| |
| /** |
| * Creates a {@code ForkJoinPool} with the given parameters (using |
| * defaults for others -- see {@link #ForkJoinPool(int, |
| * ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, |
| * int, int, int, Predicate, long, TimeUnit)}). |
| * |
| * @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(parallelism, factory, handler, asyncMode, |
| 0, MAX_CAP, 1, null, DEFAULT_KEEPALIVE, TimeUnit.MILLISECONDS); |
| } |
| |
| /** |
| * 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}. |
| * |
| * @param corePoolSize the number of threads to keep in the pool |
| * (unless timed out after an elapsed keep-alive). Normally (and |
| * by default) this is the same value as the parallelism level, |
| * but may be set to a larger value to reduce dynamic overhead if |
| * tasks regularly block. Using a smaller value (for example |
| * {@code 0}) has the same effect as the default. |
| * |
| * @param maximumPoolSize the maximum number of threads allowed. |
| * When the maximum is reached, attempts to replace blocked |
| * threads fail. (However, because creation and termination of |
| * different threads may overlap, and may be managed by the given |
| * thread factory, this value may be transiently exceeded.) To |
| * arrange the same value as is used by default for the common |
| * pool, use {@code 256} plus the {@code parallelism} level. (By |
| * default, the common pool allows a maximum of 256 spare |
| * threads.) Using a value (for example {@code |
| * Integer.MAX_VALUE}) larger than the implementation's total |
| * thread limit has the same effect as using this limit (which is |
| * the default). |
| * |
| * @param minimumRunnable the minimum allowed number of core |
| * threads not blocked by a join or {@link ManagedBlocker}. To |
| * ensure progress, when too few unblocked threads exist and |
| * unexecuted tasks may exist, new threads are constructed, up to |
| * the given maximumPoolSize. For the default value, use {@code |
| * 1}, that ensures liveness. A larger value might improve |
| * throughput in the presence of blocked activities, but might |
| * not, due to increased overhead. A value of zero may be |
| * acceptable when submitted tasks cannot have dependencies |
| * requiring additional threads. |
| * |
| * @param saturate if non-null, a predicate invoked upon attempts |
| * to create more than the maximum total allowed threads. By |
| * default, when a thread is about to block on a join or {@link |
| * ManagedBlocker}, but cannot be replaced because the |
| * maximumPoolSize would be exceeded, a {@link |
| * RejectedExecutionException} is thrown. But if this predicate |
| * returns {@code true}, then no exception is thrown, so the pool |
| * continues to operate with fewer than the target number of |
| * runnable threads, which might not ensure progress. |
| * |
| * @param keepAliveTime the elapsed time since last use before |
| * a thread is terminated (and then later replaced if needed). |
| * For the default value, use {@code 60, TimeUnit.SECONDS}. |
| * |
| * @param unit the time unit for the {@code keepAliveTime} argument |
| * |
| * @throws IllegalArgumentException if parallelism is less than or |
| * equal to zero, or is greater than implementation limit, |
| * or if maximumPoolSize is less than parallelism, |
| * of if the keepAliveTime is less than or equal to zero. |
| * @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")} |
| * @since 9 |
| */ |
| public ForkJoinPool(int parallelism, |
| ForkJoinWorkerThreadFactory factory, |
| UncaughtExceptionHandler handler, |
| boolean asyncMode, |
| int corePoolSize, |
| int maximumPoolSize, |
| int minimumRunnable, |
| Predicate<? super ForkJoinPool> saturate, |
| long keepAliveTime, |
| TimeUnit unit) { |
| // check, encode, pack parameters |
| if (parallelism <= 0 || parallelism > MAX_CAP || |
| maximumPoolSize < parallelism || keepAliveTime <= 0L) |
| throw new IllegalArgumentException(); |
| if (factory == null) |
| throw new NullPointerException(); |
| long ms = Math.max(unit.toMillis(keepAliveTime), TIMEOUT_SLOP); |
| |
| int corep = Math.min(Math.max(corePoolSize, parallelism), MAX_CAP); |
| long c = ((((long)(-corep) << TC_SHIFT) & TC_MASK) | |
| (((long)(-parallelism) << RC_SHIFT) & RC_MASK)); |
| int m = parallelism | (asyncMode ? FIFO : 0); |
| int maxSpares = Math.min(maximumPoolSize, MAX_CAP) - parallelism; |
| int minAvail = Math.min(Math.max(minimumRunnable, 0), MAX_CAP); |
| int b = ((minAvail - parallelism) & SMASK) | (maxSpares << SWIDTH); |
| int n = (parallelism > 1) ? parallelism - 1 : 1; // at least 2 slots |
| n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16; |
| n = (n + 1) << 1; // power of two, including space for submission queues |
| |
| this.workerNamePrefix = "ForkJoinPool-" + nextPoolId() + "-worker-"; |
| this.workQueues = new WorkQueue[n]; |
| this.factory = factory; |
| this.ueh = handler; |
| this.saturate = saturate; |
| this.keepAlive = ms; |
| this.bounds = b; |
| this.mode = m; |
| this.ctl = c; |
| checkPermission(); |
| } |
| |
| private Object newInstanceFromSystemProperty(String property) |
| throws ReflectiveOperationException { |
| String className = System.getProperty(property); |
| return (className == null) |
| ? null |
| : ClassLoader.getSystemClassLoader().loadClass(className) |
| .getConstructor().newInstance(); |
| } |
| |
| /** |
| * Constructor for common pool using parameters possibly |
| * overridden by system properties |
| */ |
| private ForkJoinPool(byte forCommonPoolOnly) { |
| int parallelism = -1; |
| ForkJoinWorkerThreadFactory fac = null; |
| UncaughtExceptionHandler handler = null; |
| try { // ignore exceptions in accessing/parsing properties |
| String pp = System.getProperty |
| ("java.util.concurrent.ForkJoinPool.common.parallelism"); |
| if (pp != null) |
| parallelism = Integer.parseInt(pp); |
| fac = (ForkJoinWorkerThreadFactory) newInstanceFromSystemProperty( |
| "java.util.concurrent.ForkJoinPool.common.threadFactory"); |
| handler = (UncaughtExceptionHandler) newInstanceFromSystemProperty( |
| "java.util.concurrent.ForkJoinPool.common.exceptionHandler"); |
| } catch (Exception ignore) { |
| } |
| |
| if (fac == null) { |
| if (System.getSecurityManager() == null) |
| fac = defaultForkJoinWorkerThreadFactory; |
| else // use security-managed default |
| fac = 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; |
| |
| long c = ((((long)(-parallelism) << TC_SHIFT) & TC_MASK) | |
| (((long)(-parallelism) << RC_SHIFT) & RC_MASK)); |
| int b = ((1 - parallelism) & SMASK) | (COMMON_MAX_SPARES << SWIDTH); |
| int n = (parallelism > 1) ? parallelism - 1 : 1; |
| n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16; |
| n = (n + 1) << 1; |
| |
| this.workerNamePrefix = "ForkJoinPool.commonPool-worker-"; |
| this.workQueues = new WorkQueue[n]; |
| this.factory = fac; |
| this.ueh = handler; |
| this.saturate = null; |
| this.keepAlive = DEFAULT_KEEPALIVE; |
| this.bounds = b; |
| this.mode = parallelism; |
| this.ctl = c; |
| } |
| |
| /** |
| * 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(); |
| externalSubmit(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) { |
| externalSubmit(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); |
| externalSubmit(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) { |
| return externalSubmit(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) { |
| return externalSubmit(new ForkJoinTask.AdaptedCallable<T>(task)); |
| } |
| |
| /** |
| * @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) { |
| return externalSubmit(new ForkJoinTask.AdaptedRunnable<T>(task, result)); |
| } |
| |
| /** |
| * @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); |
| return externalSubmit(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()); |
| |
| try { |
| for (Callable<T> t : tasks) { |
| ForkJoinTask<T> f = new ForkJoinTask.AdaptedCallable<T>(t); |
| futures.add(f); |
| externalSubmit(f); |
| } |
| for (int i = 0, size = futures.size(); i < size; i++) |
| ((ForkJoinTask<?>)futures.get(i)).quietlyJoin(); |
| return futures; |
| } catch (Throwable t) { |
| for (int i = 0, size = futures.size(); i < size; i++) |
| futures.get(i).cancel(false); |
| throw t; |
| } |
| } |
| |
| /** |
| * 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 = mode & SMASK; |
| return (par > 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 COMMON_PARALLELISM; |
| } |
| |
| /** |
| * 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 ((mode & 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 (mode & FIFO) != 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 = (mode & SMASK) + (int)(ctl >> RC_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() { |
| for (;;) { |
| long c = ctl; |
| int md = mode, pc = md & SMASK; |
| int tc = pc + (short)(c >>> TC_SHIFT); |
| int rc = pc + (int)(c >> RC_SHIFT); |
| if ((md & (STOP | TERMINATED)) != 0) |
| return true; |
| else if (rc > 0) |
| return false; |
| else { |
| WorkQueue[] ws; WorkQueue v; |
| if ((ws = workQueues) != null) { |
| for (int i = 1; i < ws.length; i += 2) { |
| if ((v = ws[i]) != null) { |
| if ((v.source & QUIET) == 0) |
| return false; |
| --tc; |
| } |
| } |
| } |
| if (tc == 0 && ctl == c) |
| return true; |
| } |
| } |
| } |
| |
| /** |
| * 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() { |
| long count = stealCount; |
| WorkQueue[] ws; WorkQueue w; |
| if ((ws = workQueues) != null) { |
| for (int i = 1; i < ws.length; i += 2) { |
| if ((w = ws[i]) != null) |
| count += (long)w.nsteals & 0xffffffffL; |
| } |
| } |
| 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() { |
| return pollScan(true); |
| } |
| |
| /** |
| * 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; |
| long st = stealCount; |
| 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 += (long)w.nsteals & 0xffffffffL; |
| if (w.isApparentlyUnblocked()) |
| ++rc; |
| } |
| } |
| } |
| } |
| |
| int md = mode; |
| int pc = (md & SMASK); |
| long c = ctl; |
| int tc = pc + (short)(c >>> TC_SHIFT); |
| int ac = pc + (int)(c >> RC_SHIFT); |
| if (ac < 0) // ignore transient negative |
| ac = 0; |
| String level = ((md & TERMINATED) != 0 ? "Terminated" : |
| (md & STOP) != 0 ? "Terminating" : |
| (md & 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 (mode & 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 md = mode; |
| return (md & STOP) != 0 && (md & 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 (mode & 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; |
| } |
| else { |
| for (long startTime = System.nanoTime();;) { |
| ForkJoinTask<?> t; |
| if ((t = pollScan(false)) != null) |
| t.doExec(); |
| else if (isQuiescent()) |
| return true; |
| else if ((System.nanoTime() - startTime) > nanos) |
| return false; |
| else |
| Thread.yield(); // cannot block |
| } |
| } |
| } |
| |
| /** |
| * 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; |
| WorkQueue w; |
| Thread t = Thread.currentThread(); |
| if ((t instanceof ForkJoinWorkerThread) && |
| (p = (wt = (ForkJoinWorkerThread)t).pool) != null && |
| (w = wt.workQueue) != null) { |
| int block; |
| while (!blocker.isReleasable()) { |
| if ((block = p.tryCompensate(w)) != 0) { |
| try { |
| do {} while (!blocker.isReleasable() && |
| !blocker.block()); |
| } finally { |
| CTL.getAndAdd(p, (block > 0) ? RC_UNIT : 0L); |
| } |
| break; |
| } |
| } |
| } |
| else { |
| do {} while (!blocker.isReleasable() && |
| !blocker.block()); |
| } |
| } |
| |
| /** |
| * If the given executor is a ForkJoinPool, poll and execute |
| * AsynchronousCompletionTasks from worker's queue until none are |
| * available or blocker is released. |
| */ |
| static void helpAsyncBlocker(Executor e, ManagedBlocker blocker) { |
| if (blocker != null && (e instanceof ForkJoinPool)) { |
| WorkQueue w; ForkJoinWorkerThread wt; WorkQueue[] ws; int r, n; |
| ForkJoinPool p = (ForkJoinPool)e; |
| Thread thread = Thread.currentThread(); |
| if (thread instanceof ForkJoinWorkerThread && |
| (wt = (ForkJoinWorkerThread)thread).pool == p) |
| w = wt.workQueue; |
| else if ((r = ThreadLocalRandom.getProbe()) != 0 && |
| (ws = p.workQueues) != null && (n = ws.length) > 0) |
| w = ws[(n - 1) & r & SQMASK]; |
| else |
| w = null; |
| if (w != null) { |
| for (;;) { |
| int b = w.base, s = w.top, d, al; ForkJoinTask<?>[] a; |
| if ((a = w.array) != null && (d = b - s) < 0 && |
| (al = a.length) > 0) { |
| int index = (al - 1) & b; |
| ForkJoinTask<?> t = (ForkJoinTask<?>) |
| QA.getAcquire(a, index); |
| if (blocker.isReleasable()) |
| break; |
| else if (b++ == w.base) { |
| if (t == null) { |
| if (d == -1) |
| break; |
| } |
| else if (!(t instanceof CompletableFuture. |
| AsynchronousCompletionTask)) |
| break; |
| else if (QA.compareAndSet(a, index, t, null)) { |
| w.base = b; |
| t.doExec(); |
| } |
| } |
| } |
| else |
| break; |
| } |
| } |
| } |
| } |
| |
| // 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); |
| } |
| |
| // VarHandle mechanics |
| private static final VarHandle CTL; |
| private static final VarHandle MODE; |
| private static final VarHandle QA; |
| |
| static { |
| try { |
| MethodHandles.Lookup l = MethodHandles.lookup(); |
| CTL = l.findVarHandle(ForkJoinPool.class, "ctl", long.class); |
| MODE = l.findVarHandle(ForkJoinPool.class, "mode", int.class); |
| QA = MethodHandles.arrayElementVarHandle(ForkJoinTask[].class); |
| } catch (ReflectiveOperationException e) { |
| throw new Error(e); |
| } |
| |
| // Reduce the risk of rare disastrous classloading in first call to |
| // LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773 |
| Class<?> ensureLoaded = LockSupport.class; |
| |
| int commonMaxSpares = DEFAULT_COMMON_MAX_SPARES; |
| try { |
| String p = System.getProperty |
| ("java.util.concurrent.ForkJoinPool.common.maximumSpares"); |
| if (p != null) |
| commonMaxSpares = Integer.parseInt(p); |
| } catch (Exception ignore) {} |
| COMMON_MAX_SPARES = commonMaxSpares; |
| |
| defaultForkJoinWorkerThreadFactory = |
| new DefaultForkJoinWorkerThreadFactory(); |
| modifyThreadPermission = new RuntimePermission("modifyThread"); |
| |
| common = AccessController.doPrivileged(new PrivilegedAction<>() { |
| public ForkJoinPool run() { |
| return new ForkJoinPool((byte)0); }}); |
| |
| COMMON_PARALLELISM = Math.max(common.mode & SMASK, 1); |
| } |
| |
| /** |
| * Factory for innocuous worker threads. |
| */ |
| private 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 ACC = contextWithPermissions( |
| modifyThreadPermission, |
| new RuntimePermission("enableContextClassLoaderOverride"), |
| new RuntimePermission("modifyThreadGroup"), |
| new RuntimePermission("getClassLoader"), |
| new RuntimePermission("setContextClassLoader")); |
| |
| public final ForkJoinWorkerThread newThread(ForkJoinPool pool) { |
| return AccessController.doPrivileged( |
| new PrivilegedAction<>() { |
| public ForkJoinWorkerThread run() { |
| return new ForkJoinWorkerThread. |
| InnocuousForkJoinWorkerThread(pool); }}, |
| ACC); |
| } |
| } |
| } |