| /* |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent; |
| |
| import java.lang.Thread.UncaughtExceptionHandler; |
| import java.util.ArrayList; |
| import java.util.Arrays; |
| import java.util.Collection; |
| import java.util.Collections; |
| import java.util.List; |
| |
| /** |
| * An {@link ExecutorService} for running {@link ForkJoinTask}s. |
| * A {@code ForkJoinPool} provides the entry point for submissions |
| * from non-{@code ForkJoinTask} clients, as well as management and |
| * monitoring operations. |
| * |
| * <p>A {@code ForkJoinPool} differs from other kinds of {@link |
| * ExecutorService} mainly by virtue of employing |
| * <em>work-stealing</em>: all threads in the pool attempt to find and |
| * execute tasks submitted to the pool and/or created by other active |
| * tasks (eventually blocking waiting for work if none exist). This |
| * enables efficient processing when most tasks spawn other subtasks |
| * (as do most {@code ForkJoinTask}s), as well as when many small |
| * tasks are submitted to the pool from external clients. Especially |
| * when setting <em>asyncMode</em> to true in constructors, {@code |
| * ForkJoinPool}s may also be appropriate for use with event-style |
| * tasks that are never joined. |
| * |
| * <p>A static {@code commonPool()} is available and appropriate for |
| * most applications. The common pool is used by any ForkJoinTask that |
| * is not explicitly submitted to a specified pool. Using the common |
| * pool normally reduces resource usage (its threads are slowly |
| * reclaimed during periods of non-use, and reinstated upon subsequent |
| * use). |
| * |
| * <p>For applications that require separate or custom pools, a {@code |
| * ForkJoinPool} may be constructed with a given target parallelism |
| * level; by default, equal to the number of available processors. The |
| * pool attempts to maintain enough active (or available) threads by |
| * dynamically adding, suspending, or resuming internal worker |
| * threads, even if some tasks are stalled waiting to join others. |
| * However, no such adjustments are guaranteed in the face of blocked |
| * I/O or other unmanaged synchronization. The nested {@link |
| * ManagedBlocker} interface enables extension of the kinds of |
| * synchronization accommodated. |
| * |
| * <p>In addition to execution and lifecycle control methods, this |
| * class provides status check methods (for example |
| * {@link #getStealCount}) that are intended to aid in developing, |
| * tuning, and monitoring fork/join applications. Also, method |
| * {@link #toString} returns indications of pool state in a |
| * convenient form for informal monitoring. |
| * |
| * <p>As is the case with other ExecutorServices, there are three |
| * main task execution methods summarized in the following table. |
| * These are designed to be used primarily by clients not already |
| * engaged in fork/join computations in the current pool. The main |
| * forms of these methods accept instances of {@code ForkJoinTask}, |
| * but overloaded forms also allow mixed execution of plain {@code |
| * Runnable}- or {@code Callable}- based activities as well. However, |
| * tasks that are already executing in a pool should normally instead |
| * use the within-computation forms listed in the table unless using |
| * async event-style tasks that are not usually joined, in which case |
| * there is little difference among choice of methods. |
| * |
| * <table BORDER CELLPADDING=3 CELLSPACING=1> |
| * <caption>Summary of task execution methods</caption> |
| * <tr> |
| * <td></td> |
| * <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td> |
| * <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td> |
| * </tr> |
| * <tr> |
| * <td> <b>Arrange async execution</b></td> |
| * <td> {@link #execute(ForkJoinTask)}</td> |
| * <td> {@link ForkJoinTask#fork}</td> |
| * </tr> |
| * <tr> |
| * <td> <b>Await and obtain result</b></td> |
| * <td> {@link #invoke(ForkJoinTask)}</td> |
| * <td> {@link ForkJoinTask#invoke}</td> |
| * </tr> |
| * <tr> |
| * <td> <b>Arrange exec and obtain Future</b></td> |
| * <td> {@link #submit(ForkJoinTask)}</td> |
| * <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td> |
| * </tr> |
| * </table> |
| * |
| * <p>The common pool is by default constructed with default |
| * parameters, but these may be controlled by setting three |
| * {@linkplain System#getProperty system properties}: |
| * <ul> |
| * <li>{@code java.util.concurrent.ForkJoinPool.common.parallelism} |
| * - the parallelism level, a non-negative integer |
| * <li>{@code java.util.concurrent.ForkJoinPool.common.threadFactory} |
| * - the class name of a {@link ForkJoinWorkerThreadFactory} |
| * <li>{@code java.util.concurrent.ForkJoinPool.common.exceptionHandler} |
| * - the class name of a {@link UncaughtExceptionHandler} |
| * </ul> |
| * The system class loader is used to load these classes. |
| * Upon any error in establishing these settings, default parameters |
| * are used. It is possible to disable or limit the use of threads in |
| * the common pool by setting the parallelism property to zero, and/or |
| * using a factory that may return {@code null}. |
| * |
| * <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. |
| * |
| * 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). |
| * See also "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 (atomic, volatile etc) issues. 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. So, both a successful pop and poll |
| * mainly entail a CAS of a slot from non-null to null. Because |
| * we rely on CASes of references, we do not need tag bits on base |
| * or top. They are simple ints as used in any circular |
| * array-based queue (see for example ArrayDeque). Updates to the |
| * indices must still be ordered in a way that guarantees that top |
| * == base means the queue is empty, but otherwise may err on the |
| * side of possibly making the queue appear nonempty when a push, |
| * pop, or poll have not fully committed. Note that this means |
| * that the poll operation, considered individually, is not |
| * wait-free. One thief cannot successfully continue until another |
| * in-progress one (or, if previously empty, a push) completes. |
| * However, in the aggregate, we ensure at least probabilistic |
| * non-blockingness. If an attempted steal fails, a thief always |
| * chooses a different random victim target to try next. So, in |
| * order for one thief to progress, it suffices for any |
| * in-progress poll or new push on any empty queue to |
| * complete. (This is why we normally use method pollAt and its |
| * variants that try once at the apparent base index, else |
| * consider alternative actions, rather than method poll.) |
| * |
| * This approach also enables support of a user mode in which local |
| * task processing is in FIFO, not LIFO order, simply by using |
| * poll rather than pop. This can be useful in message-passing |
| * frameworks in which tasks are never joined. However neither |
| * mode considers affinities, loads, cache localities, etc, so |
| * rarely provide the best possible performance on a given |
| * machine, but portably provide good throughput by averaging over |
| * these factors. (Further, even if we did try to use such |
| * information, we do not usually have a basis for exploiting it. |
| * For example, some sets of tasks profit from cache affinities, |
| * but others are harmed by cache pollution effects.) |
| * |
| * WorkQueues are also used in a similar way for tasks submitted |
| * to the pool. We cannot mix these tasks in the same queues used |
| * for work-stealing (this would contaminate lifo/fifo |
| * processing). Instead, we randomly associate submission queues |
| * with submitting threads, using a form of hashing. The |
| * Submitter 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. However, because most |
| * shared/external queue operations are more expensive than |
| * internal, and because, at steady state, external submitters |
| * will compete for CPU with workers, ForkJoinTask.join and |
| * related methods disable them from repeatedly helping to process |
| * tasks if all workers are active. Insertion of tasks in shared |
| * mode requires a lock (mainly to protect in the case of |
| * resizing) but we use only a simple spinlock (using bits in |
| * field qlock), because submitters encountering a busy queue move |
| * on to try or create other queues -- they block only when |
| * creating and registering new queues. |
| * |
| * Management |
| * ========== |
| * |
| * The main throughput advantages of work-stealing stem from |
| * decentralized control -- workers mostly take tasks from |
| * themselves or each other. We cannot negate this in the |
| * implementation of other management responsibilities. The main |
| * tactic for avoiding bottlenecks is packing nearly all |
| * essentially atomic control state into two volatile variables |
| * that are by far most often read (not written) as status and |
| * consistency checks. |
| * |
| * Field "ctl" contains 64 bits holding all the information needed |
| * to atomically decide to add, inactivate, enqueue (on an event |
| * queue), dequeue, and/or re-activate workers. To enable this |
| * packing, we restrict maximum parallelism to (1<<15)-1 (which is |
| * far in excess of normal operating range) to allow ids, counts, |
| * and their negations (used for thresholding) to fit into 16bit |
| * fields. |
| * |
| * Field "plock" is a form of sequence lock with a saturating |
| * shutdown bit (similarly for per-queue "qlocks"), mainly |
| * protecting updates to the workQueues array, as well as to |
| * enable shutdown. When used as a lock, it is normally only very |
| * briefly held, so is nearly always available after at most a |
| * brief spin, but we use a monitor-based backup strategy to |
| * block when needed. |
| * |
| * Recording WorkQueues. WorkQueues are recorded in the |
| * "workQueues" array that is created upon first use and expanded |
| * if necessary. Updates to the array while recording new workers |
| * and unrecording terminated ones are protected from each other |
| * by a lock but the array is otherwise concurrently readable, and |
| * accessed directly. 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 wait queue |
| * field of ctl stores indices, not references. Access to the |
| * workQueues in associated methods (for example signalWork) must |
| * both index-check and null-check the IDs. All such accesses |
| * ignore bad IDs by returning out early from what they are doing, |
| * since this can only be associated with termination, in which |
| * case it is OK to give up. All uses of the workQueues array |
| * also check that it is non-null (even if previously |
| * non-null). This allows nulling during termination, which is |
| * currently not necessary, but remains an option for |
| * resource-revocation-based shutdown schemes. It also helps |
| * reduce JIT issuance of uncommon-trap code, which tends to |
| * unnecessarily complicate control flow in some methods. |
| * |
| * Event Queuing. Unlike HPC work-stealing frameworks, we cannot |
| * let workers spin indefinitely scanning for tasks when none can |
| * be found immediately, and we cannot start/resume workers unless |
| * there appear to be tasks available. On the other hand, we must |
| * quickly prod them into action when new tasks are submitted or |
| * generated. In many usages, ramp-up time to activate workers is |
| * the main limiting factor in overall performance (this is |
| * compounded at program start-up by JIT compilation and |
| * allocation). So we try to streamline this as much as possible. |
| * We park/unpark workers after placing in an event wait queue |
| * when they cannot find work. This "queue" is actually a simple |
| * Treiber stack, headed by the "id" field of ctl, plus a 15bit |
| * counter value (that reflects the number of times a worker has |
| * been inactivated) to avoid ABA effects (we need only as many |
| * version numbers as worker threads). Successors are held in |
| * field WorkQueue.nextWait. Queuing deals with several intrinsic |
| * races, mainly that a task-producing thread can miss seeing (and |
| * signalling) another thread that gave up looking for work but |
| * has not yet entered the wait queue. We solve this by requiring |
| * a full sweep of all workers (via repeated calls to method |
| * scan()) both before and after a newly waiting worker is added |
| * to the wait queue. Because enqueued workers may actually be |
| * rescanning rather than waiting, we set and clear the "parker" |
| * field of WorkQueues to reduce unnecessary calls to unpark. |
| * (This requires a secondary recheck to avoid missed signals.) |
| * Note the unusual conventions about Thread.interrupts |
| * surrounding parking and other blocking: Because interrupts are |
| * used solely to alert threads to check termination, which is |
| * checked anyway upon blocking, we clear status (using |
| * Thread.interrupted) before any call to park, so that park does |
| * not immediately return due to status being set via some other |
| * unrelated call to interrupt in user code. |
| * |
| * Signalling. We create or wake up workers only when there |
| * appears to be at least one task they might be able to find and |
| * execute. When a submission is added or another worker adds a |
| * task to a queue that has fewer than two tasks, they signal |
| * waiting workers (or trigger creation of new ones if fewer than |
| * the given parallelism level -- signalWork). These primary |
| * signals are buttressed by others whenever other threads remove |
| * a task from a queue and notice that there are other tasks there |
| * as well. So in general, pools will be over-signalled. On most |
| * platforms, signalling (unpark) overhead time is noticeably |
| * long, and the time between signalling a thread and it actually |
| * making progress can be very noticeably long, so it is worth |
| * offloading these delays from critical paths as much as |
| * possible. Additionally, workers spin-down gradually, by staying |
| * alive so long as they see the ctl state changing. Similar |
| * stability-sensing techniques are also used before blocking in |
| * awaitJoin and helpComplete. |
| * |
| * 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 if the pool has remained quiescent for a |
| * given period -- a short period if there are more threads than |
| * parallelism, longer as the number of threads decreases. This |
| * will slowly propagate, eventually terminating all workers after |
| * periods of non-use. |
| * |
| * Shutdown and Termination. A call to shutdownNow atomically sets |
| * a plock bit and then (non-atomically) sets each worker's |
| * qlock status, cancels all unprocessed tasks, and wakes up |
| * all waiting workers. Detecting whether termination should |
| * commence after a non-abrupt shutdown() call requires more work |
| * and bookkeeping. We need consensus about quiescence (i.e., that |
| * there is no more work). The active count provides a primary |
| * indication but non-abrupt shutdown still requires a rechecking |
| * scan for any workers that are inactive but not queued. |
| * |
| * Joining Tasks |
| * ============= |
| * |
| * Any of several actions may be taken when one worker is waiting |
| * to join a task stolen (or always held) by another. Because we |
| * are multiplexing many tasks on to a pool of workers, we can't |
| * just let them block (as in Thread.join). We also cannot just |
| * reassign the joiner's run-time stack with another and replace |
| * it later, which would be a form of "continuation", that even if |
| * possible is not necessarily a good idea since we sometimes need |
| * both an unblocked task and its continuation to progress. |
| * Instead we combine two tactics: |
| * |
| * Helping: Arranging for the joiner to execute some task that it |
| * would be running if the steal had not occurred. |
| * |
| * Compensating: Unless there are already enough live threads, |
| * method tryCompensate() may create or re-activate a spare |
| * thread to compensate for blocked joiners until they unblock. |
| * |
| * A third form (implemented in tryRemoveAndExec) amounts to |
| * helping a hypothetical compensator: If we can readily tell that |
| * a possible action of a compensator is to steal and execute the |
| * task being joined, the joining thread can do so directly, |
| * without the need for a compensation thread (although at the |
| * expense of larger run-time stacks, but the tradeoff is |
| * typically worthwhile). |
| * |
| * The ManagedBlocker extension API can't use helping so relies |
| * only on compensation in method awaitBlocker. |
| * |
| * The algorithm in tryHelpStealer entails a form of "linear" |
| * helping: Each worker records (in field currentSteal) the most |
| * recent task it stole from some other worker. Plus, it records |
| * (in field currentJoin) the task it is currently actively |
| * joining. Method tryHelpStealer 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. |
| * In essence, the joiner executes a task that would be on its own |
| * local deque had the to-be-joined task not been stolen. This may |
| * be seen as a conservative variant of the approach in Wagner & |
| * Calder "Leapfrogging: a portable technique for implementing |
| * efficient futures" SIGPLAN Notices, 1993 |
| * (http://portal.acm.org/citation.cfm?id=155354). It differs in |
| * that: (1) We only maintain dependency links across workers upon |
| * steals, rather than use per-task bookkeeping. This sometimes |
| * requires a linear scan of workQueues array to locate stealers, |
| * but often doesn't because stealers leave hints (that may become |
| * stale/wrong) of where to locate them. It is only a hint |
| * because a worker might have had multiple steals and the hint |
| * records only one of them (usually the most current). Hinting |
| * isolates cost to when it is needed, rather than adding to |
| * per-task overhead. (2) It is "shallow", ignoring nesting and |
| * potentially cyclic mutual steals. (3) It is intentionally |
| * racy: field currentJoin is updated only while actively joining, |
| * which means that we miss links in the chain during long-lived |
| * tasks, GC stalls etc (which is OK since blocking in such cases |
| * is usually a good idea). (4) We bound the number of attempts |
| * to find work (see MAX_HELP) and fall back to suspending the |
| * worker and if necessary replacing it with another. |
| * |
| * It is impossible to keep exactly the target parallelism number |
| * of threads running at any given time. Determining the |
| * existence of conservatively safe helping targets, the |
| * availability of already-created spares, and the apparent need |
| * to create new spares are all racy, so we rely on multiple |
| * retries of each. Compensation in the apparent absence of |
| * helping opportunities is challenging to control on JVMs, where |
| * GC and other activities can stall progress of tasks that in |
| * turn stall out many other dependent tasks, without us being |
| * able to determine whether they will ever require compensation. |
| * Even though work-stealing otherwise encounters little |
| * degradation in the presence of more threads than cores, |
| * aggressively adding new threads in such cases entails risk of |
| * unwanted positive feedback control loops in which more threads |
| * cause more dependent stalls (as well as delayed progress of |
| * unblocked threads to the point that we know they are available) |
| * leading to more situations requiring more threads, and so |
| * on. This aspect of control can be seen as an (analytically |
| * intractable) game with an opponent that may choose the worst |
| * (for us) active thread to stall at any time. We take several |
| * precautions to bound losses (and thus bound gains), mainly in |
| * methods tryCompensate and awaitJoin. |
| * |
| * Common Pool |
| * =========== |
| * |
| * The static common pool always exists after static |
| * initialization. Since it (or any other created pool) need |
| * never be used, we minimize initial construction overhead and |
| * footprint to the setup of about a dozen fields, with no nested |
| * allocation. Most bootstrapping occurs within method |
| * fullExternalPush during the first submission to the pool. |
| * |
| * When external threads submit to the common pool, they can |
| * perform subtask processing (see externalHelpJoin and related |
| * methods). 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, externalHelpJoin |
| * returns quickly (at the most helping to signal some common pool |
| * workers). 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. |
| * |
| * Style notes |
| * =========== |
| * |
| * 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 volatiles held |
| * in local variables. Methods signalWork() and scan() are the |
| * main bottlenecks, so are especially heavily |
| * micro-optimized/mangled. There are lots of inline assignments |
| * (of form "while ((local = field) != 0)") which are usually the |
| * simplest way to ensure the required read orderings (which are |
| * sometimes critical). This leads to a "C"-like style of listing |
| * declarations of these locals at the heads of methods or blocks. |
| * There are several occurrences of the unusual "do {} while |
| * (!cas...)" which is the simplest way to force an update of a |
| * CAS'ed variable. 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: |
| * (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 |
| */ |
| // android-note: Removed references to CountedCompleters. |
| |
| // Static utilities |
| |
| /** |
| * If there is a security manager, makes sure caller has |
| * permission to modify threads. |
| */ |
| private static void checkPermission() { |
| SecurityManager security = System.getSecurityManager(); |
| if (security != null) |
| security.checkPermission(modifyThreadPermission); |
| } |
| |
| // Nested classes |
| |
| /** |
| * Factory for creating new {@link ForkJoinWorkerThread}s. |
| * A {@code ForkJoinWorkerThreadFactory} must be defined and used |
| * for {@code ForkJoinWorkerThread} subclasses that extend base |
| * functionality or initialize threads with different contexts. |
| */ |
| public static interface ForkJoinWorkerThreadFactory { |
| /** |
| * Returns a new worker thread operating in the given pool. |
| * |
| * @param pool the pool this thread works in |
| * @return the new worker thread |
| * @throws NullPointerException if the pool is null |
| */ |
| public ForkJoinWorkerThread newThread(ForkJoinPool pool); |
| } |
| |
| /** |
| * Default ForkJoinWorkerThreadFactory implementation; creates a |
| * new ForkJoinWorkerThread. |
| */ |
| static final class DefaultForkJoinWorkerThreadFactory |
| implements ForkJoinWorkerThreadFactory { |
| public final ForkJoinWorkerThread newThread(ForkJoinPool pool) { |
| return new ForkJoinWorkerThread(pool); |
| } |
| } |
| |
| /** |
| * Class for artificial tasks that are used to replace the target |
| * of local joins if they are removed from an interior queue slot |
| * in WorkQueue.tryRemoveAndExec. We don't need the proxy to |
| * actually do anything beyond having a unique identity. |
| */ |
| static final class EmptyTask extends ForkJoinTask<Void> { |
| private static final long serialVersionUID = -7721805057305804111L; |
| EmptyTask() { status = ForkJoinTask.NORMAL; } // force done |
| public final Void getRawResult() { return null; } |
| public final void setRawResult(Void x) {} |
| public final boolean exec() { return true; } |
| } |
| |
| /** |
| * Queues supporting work-stealing as well as external task |
| * submission. See above for main rationale and algorithms. |
| * Implementation relies heavily on "Unsafe" intrinsics |
| * and selective use of "volatile": |
| * |
| * Field "base" is the index (mod array.length) of the least valid |
| * queue slot, which is always the next position to steal (poll) |
| * from if nonempty. Reads and writes require volatile orderings |
| * but not CAS, because updates are only performed after slot |
| * CASes. |
| * |
| * Field "top" is the index (mod array.length) of the next queue |
| * slot to push to or pop from. It is written only by owner thread |
| * for push, or under lock for external/shared push, and accessed |
| * by other threads only after reading (volatile) base. Both top |
| * and base are allowed to wrap around on overflow, but (top - |
| * base) (or more commonly -(base - top) to force volatile read of |
| * base before top) still estimates size. The lock ("qlock") is |
| * forced to -1 on termination, causing all further lock attempts |
| * to fail. (Note: we don't need CAS for termination state because |
| * upon pool shutdown, all shared-queues will stop being used |
| * anyway.) Nearly all lock bodies are set up so that exceptions |
| * within lock bodies are "impossible" (modulo JVM errors that |
| * would cause failure anyway.) |
| * |
| * The array slots are read and written using the emulation of |
| * volatiles/atomics provided by Unsafe. Insertions must in |
| * general use putOrderedObject as a form of releasing store to |
| * ensure that all writes to the task object are ordered before |
| * its publication in the queue. All removals entail a CAS to |
| * null. The array is always a power of two. To ensure safety of |
| * Unsafe array operations, all accesses perform explicit null |
| * checks and implicit bounds checks via power-of-two masking. |
| * |
| * In addition to basic queuing support, this class contains |
| * fields described elsewhere to control execution. It turns out |
| * to work better memory-layout-wise to include them in this class |
| * rather than a separate class. |
| * |
| * 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. (It would be best for queue objects |
| * and their arrays to share, but there is nothing available to |
| * help arrange that). The @Contended annotation alerts JVMs to |
| * try to keep instances apart. |
| */ |
| 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 |
| |
| // Heuristic padding to ameliorate unfortunate memory placements |
| volatile long pad00, pad01, pad02, pad03, pad04, pad05, pad06; |
| |
| volatile int eventCount; // encoded inactivation count; < 0 if inactive |
| int nextWait; // encoded record of next event waiter |
| int nsteals; // number of steals |
| int hint; // steal index hint |
| short poolIndex; // index of this queue in pool |
| final short mode; // 0: lifo, > 0: fifo, < 0: shared |
| volatile int qlock; // 1: locked, -1: terminate; else 0 |
| volatile int base; // index of next slot for poll |
| int top; // index of next slot for push |
| ForkJoinTask<?>[] array; // the elements (initially unallocated) |
| final ForkJoinPool pool; // the containing pool (may be null) |
| final ForkJoinWorkerThread owner; // owning thread or null if shared |
| volatile Thread parker; // == owner during call to park; else null |
| volatile ForkJoinTask<?> currentJoin; // task being joined in awaitJoin |
| ForkJoinTask<?> currentSteal; // current non-local task being executed |
| |
| volatile Object pad10, pad11, pad12, pad13, pad14, pad15, pad16, pad17; |
| volatile Object pad18, pad19, pad1a, pad1b, pad1c, pad1d; |
| |
| WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner, int mode, |
| int seed) { |
| this.pool = pool; |
| this.owner = owner; |
| this.mode = (short)mode; |
| this.hint = seed; // store initial seed for runWorker |
| // Place indices in the center of array (that is not yet allocated) |
| base = top = INITIAL_QUEUE_CAPACITY >>> 1; |
| } |
| |
| /** |
| * Returns the approximate number of tasks in the queue. |
| */ |
| final int queueSize() { |
| int n = base - top; // non-owner callers must read base first |
| return (n >= 0) ? 0 : -n; // ignore transient negative |
| } |
| |
| /** |
| * Provides a more accurate estimate of whether this queue has |
| * any tasks than does queueSize, by checking whether a |
| * near-empty queue has at least one unclaimed task. |
| */ |
| final boolean isEmpty() { |
| ForkJoinTask<?>[] a; int m, s; |
| int n = base - (s = top); |
| return (n >= 0 || |
| (n == -1 && |
| ((a = array) == null || |
| (m = a.length - 1) < 0 || |
| U.getObject |
| (a, (long)((m & (s - 1)) << ASHIFT) + ABASE) == null))); |
| } |
| |
| /** |
| * Pushes a task. Call only by owner in unshared queues. (The |
| * shared-queue version is embedded in method externalPush.) |
| * |
| * @param task the task. Caller must ensure non-null. |
| * @throws RejectedExecutionException if array cannot be resized |
| */ |
| final void push(ForkJoinTask<?> task) { |
| ForkJoinTask<?>[] a; ForkJoinPool p; |
| int s = top, n; |
| if ((a = array) != null) { // ignore if queue removed |
| int m = a.length - 1; |
| U.putOrderedObject(a, ((m & s) << ASHIFT) + ABASE, task); |
| if ((n = (top = s + 1) - base) <= 2) |
| (p = pool).signalWork(p.workQueues, this); |
| else if (n >= m) |
| growArray(); |
| } |
| } |
| |
| /** |
| * Initializes or doubles the capacity of array. Call either |
| * by owner or with lock held -- it is OK for base, but not |
| * top, to move while resizings are in progress. |
| */ |
| final ForkJoinTask<?>[] growArray() { |
| ForkJoinTask<?>[] oldA = array; |
| int size = oldA != null ? oldA.length << 1 : INITIAL_QUEUE_CAPACITY; |
| if (size > MAXIMUM_QUEUE_CAPACITY) |
| throw new RejectedExecutionException("Queue capacity exceeded"); |
| int oldMask, t, b; |
| ForkJoinTask<?>[] a = array = new ForkJoinTask<?>[size]; |
| if (oldA != null && (oldMask = oldA.length - 1) >= 0 && |
| (t = top) - (b = base) > 0) { |
| int mask = size - 1; |
| do { |
| ForkJoinTask<?> x; |
| int oldj = ((b & oldMask) << ASHIFT) + ABASE; |
| int j = ((b & mask) << ASHIFT) + ABASE; |
| x = (ForkJoinTask<?>)U.getObjectVolatile(oldA, oldj); |
| if (x != null && |
| U.compareAndSwapObject(oldA, oldj, x, null)) |
| U.putObjectVolatile(a, j, x); |
| } while (++b != t); |
| } |
| return a; |
| } |
| |
| /** |
| * Takes next task, if one exists, in LIFO order. Call only |
| * by owner in unshared queues. |
| */ |
| final ForkJoinTask<?> pop() { |
| ForkJoinTask<?>[] a; ForkJoinTask<?> t; int m; |
| if ((a = array) != null && (m = a.length - 1) >= 0) { |
| for (int s; (s = top - 1) - base >= 0;) { |
| long j = ((m & s) << ASHIFT) + ABASE; |
| if ((t = (ForkJoinTask<?>)U.getObject(a, j)) == null) |
| break; |
| if (U.compareAndSwapObject(a, j, t, null)) { |
| top = s; |
| return t; |
| } |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Takes a task in FIFO order if b is base of queue and a task |
| * can be claimed without contention. Specialized versions |
| * appear in ForkJoinPool methods scan and tryHelpStealer. |
| */ |
| final ForkJoinTask<?> pollAt(int b) { |
| ForkJoinTask<?> t; ForkJoinTask<?>[] a; |
| if ((a = array) != null) { |
| int j = (((a.length - 1) & b) << ASHIFT) + ABASE; |
| if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null && |
| base == b && U.compareAndSwapObject(a, j, t, null)) { |
| U.putOrderedInt(this, QBASE, b + 1); |
| return t; |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Takes next task, if one exists, in FIFO order. |
| */ |
| final ForkJoinTask<?> poll() { |
| ForkJoinTask<?>[] a; int b; ForkJoinTask<?> t; |
| while ((b = base) - top < 0 && (a = array) != null) { |
| int j = (((a.length - 1) & b) << ASHIFT) + ABASE; |
| t = (ForkJoinTask<?>)U.getObjectVolatile(a, j); |
| if (t != null) { |
| if (U.compareAndSwapObject(a, j, t, null)) { |
| U.putOrderedInt(this, QBASE, b + 1); |
| return t; |
| } |
| } |
| else if (base == b) { |
| if (b + 1 == top) |
| break; |
| Thread.yield(); // wait for lagging update (very rare) |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Takes next task, if one exists, in order specified by mode. |
| */ |
| final ForkJoinTask<?> nextLocalTask() { |
| return mode == 0 ? pop() : poll(); |
| } |
| |
| /** |
| * Returns next task, if one exists, in order specified by mode. |
| */ |
| final ForkJoinTask<?> peek() { |
| ForkJoinTask<?>[] a = array; int m; |
| if (a == null || (m = a.length - 1) < 0) |
| return null; |
| int i = mode == 0 ? top - 1 : base; |
| int j = ((i & m) << ASHIFT) + ABASE; |
| return (ForkJoinTask<?>)U.getObjectVolatile(a, j); |
| } |
| |
| /** |
| * Pops the given task only if it is at the current top. |
| * (A shared version is available only via FJP.tryExternalUnpush) |
| */ |
| final boolean tryUnpush(ForkJoinTask<?> t) { |
| ForkJoinTask<?>[] a; int s; |
| if ((a = array) != null && (s = top) != base && |
| U.compareAndSwapObject |
| (a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) { |
| top = s; |
| return true; |
| } |
| return false; |
| } |
| |
| /** |
| * Removes and cancels all known tasks, ignoring any exceptions. |
| */ |
| final void cancelAll() { |
| ForkJoinTask.cancelIgnoringExceptions(currentJoin); |
| ForkJoinTask.cancelIgnoringExceptions(currentSteal); |
| for (ForkJoinTask<?> t; (t = poll()) != null; ) |
| ForkJoinTask.cancelIgnoringExceptions(t); |
| } |
| |
| // Specialized execution methods |
| |
| /** |
| * Polls and runs tasks until empty. |
| */ |
| final void pollAndExecAll() { |
| for (ForkJoinTask<?> t; (t = poll()) != null;) |
| t.doExec(); |
| } |
| |
| /** |
| * Executes a top-level task and any local tasks remaining |
| * after execution. |
| */ |
| final void runTask(ForkJoinTask<?> task) { |
| if ((currentSteal = task) != null) { |
| task.doExec(); |
| ForkJoinTask<?>[] a = array; |
| int md = mode; |
| ++nsteals; |
| currentSteal = null; |
| if (md != 0) |
| pollAndExecAll(); |
| else if (a != null) { |
| int s, m = a.length - 1; |
| while ((s = top - 1) - base >= 0) { |
| long i = ((m & s) << ASHIFT) + ABASE; |
| ForkJoinTask<?> t = (ForkJoinTask<?>)U.getObject(a, i); |
| if (t == null) |
| break; |
| if (U.compareAndSwapObject(a, i, t, null)) { |
| top = s; |
| t.doExec(); |
| } |
| } |
| } |
| } |
| } |
| |
| /** |
| * If present, removes from queue and executes the given task, |
| * or any other cancelled task. Returns (true) on any CAS |
| * or consistency check failure so caller can retry. |
| * |
| * @return false if no progress can be made, else true |
| */ |
| final boolean tryRemoveAndExec(ForkJoinTask<?> task) { |
| boolean stat; |
| ForkJoinTask<?>[] a; int m, s, b, n; |
| if (task != null && (a = array) != null && (m = a.length - 1) >= 0 && |
| (n = (s = top) - (b = base)) > 0) { |
| boolean removed = false, empty = true; |
| stat = true; |
| for (ForkJoinTask<?> t;;) { // traverse from s to b |
| long j = ((--s & m) << ASHIFT) + ABASE; |
| t = (ForkJoinTask<?>)U.getObject(a, j); |
| if (t == null) // inconsistent length |
| break; |
| else if (t == task) { |
| if (s + 1 == top) { // pop |
| if (!U.compareAndSwapObject(a, j, task, null)) |
| break; |
| top = s; |
| removed = true; |
| } |
| else if (base == b) // replace with proxy |
| removed = U.compareAndSwapObject(a, j, task, |
| new EmptyTask()); |
| break; |
| } |
| else if (t.status >= 0) |
| empty = false; |
| else if (s + 1 == top) { // pop and throw away |
| if (U.compareAndSwapObject(a, j, t, null)) |
| top = s; |
| break; |
| } |
| if (--n == 0) { |
| if (!empty && base == b) |
| stat = false; |
| break; |
| } |
| } |
| if (removed) |
| task.doExec(); |
| } |
| else |
| stat = false; |
| return stat; |
| } |
| |
| /** |
| * Tries to poll for and execute the given task or any other |
| * task in its CountedCompleter computation. |
| */ |
| final boolean pollAndExecCC(CountedCompleter<?> root) { |
| ForkJoinTask<?>[] a; int b; Object o; CountedCompleter<?> t, r; |
| if ((b = base) - top < 0 && (a = array) != null) { |
| long j = (((a.length - 1) & b) << ASHIFT) + ABASE; |
| if ((o = U.getObjectVolatile(a, j)) == null) |
| return true; // retry |
| if (o instanceof CountedCompleter) { |
| for (t = (CountedCompleter<?>)o, r = t;;) { |
| if (r == root) { |
| if (base == b && |
| U.compareAndSwapObject(a, j, t, null)) { |
| U.putOrderedInt(this, QBASE, b + 1); |
| t.doExec(); |
| } |
| return true; |
| } |
| else if ((r = r.completer) == null) |
| break; // not part of root computation |
| } |
| } |
| } |
| return false; |
| } |
| |
| /** |
| * Tries to pop and execute the given task or any other task |
| * in its CountedCompleter computation. |
| */ |
| final boolean externalPopAndExecCC(CountedCompleter<?> root) { |
| ForkJoinTask<?>[] a; int s; Object o; CountedCompleter<?> t, r; |
| if (base - (s = top) < 0 && (a = array) != null) { |
| long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE; |
| if ((o = U.getObject(a, j)) instanceof CountedCompleter) { |
| for (t = (CountedCompleter<?>)o, r = t;;) { |
| if (r == root) { |
| if (U.compareAndSwapInt(this, QLOCK, 0, 1)) { |
| if (top == s && array == a && |
| U.compareAndSwapObject(a, j, t, null)) { |
| top = s - 1; |
| qlock = 0; |
| t.doExec(); |
| } |
| else |
| qlock = 0; |
| } |
| return true; |
| } |
| else if ((r = r.completer) == null) |
| break; |
| } |
| } |
| } |
| return false; |
| } |
| |
| /** |
| * Internal version |
| */ |
| final boolean internalPopAndExecCC(CountedCompleter<?> root) { |
| ForkJoinTask<?>[] a; int s; Object o; CountedCompleter<?> t, r; |
| if (base - (s = top) < 0 && (a = array) != null) { |
| long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE; |
| if ((o = U.getObject(a, j)) instanceof CountedCompleter) { |
| for (t = (CountedCompleter<?>)o, r = t;;) { |
| if (r == root) { |
| if (U.compareAndSwapObject(a, j, t, null)) { |
| top = s - 1; |
| t.doExec(); |
| } |
| return true; |
| } |
| else if ((r = r.completer) == null) |
| break; |
| } |
| } |
| } |
| return false; |
| } |
| |
| /** |
| * Returns true if owned and not known to be blocked. |
| */ |
| final boolean isApparentlyUnblocked() { |
| Thread wt; Thread.State s; |
| return (eventCount >= 0 && |
| (wt = owner) != null && |
| (s = wt.getState()) != Thread.State.BLOCKED && |
| s != Thread.State.WAITING && |
| s != Thread.State.TIMED_WAITING); |
| } |
| |
| // Unsafe mechanics |
| private static final sun.misc.Unsafe U; |
| private static final long QBASE; |
| private static final long QLOCK; |
| private static final int ABASE; |
| private static final int ASHIFT; |
| static { |
| try { |
| U = sun.misc.Unsafe.getUnsafe(); |
| Class<?> k = WorkQueue.class; |
| Class<?> ak = ForkJoinTask[].class; |
| QBASE = U.objectFieldOffset |
| (k.getDeclaredField("base")); |
| QLOCK = U.objectFieldOffset |
| (k.getDeclaredField("qlock")); |
| ABASE = U.arrayBaseOffset(ak); |
| int scale = U.arrayIndexScale(ak); |
| if ((scale & (scale - 1)) != 0) |
| throw new Error("data type scale not a power of two"); |
| ASHIFT = 31 - Integer.numberOfLeadingZeros(scale); |
| } catch (Exception e) { |
| throw new Error(e); |
| } |
| } |
| } |
| |
| // static fields (initialized in static initializer below) |
| |
| /** |
| * Per-thread submission bookkeeping. Shared across all pools |
| * to reduce ThreadLocal pollution and because random motion |
| * to avoid contention in one pool is likely to hold for others. |
| * Lazily initialized on first submission (but null-checked |
| * in other contexts to avoid unnecessary initialization). |
| */ |
| static final ThreadLocal<Submitter> submitters; |
| |
| /** |
| * Creates a new ForkJoinWorkerThread. This factory is used unless |
| * overridden in ForkJoinPool constructors. |
| */ |
| public static final ForkJoinWorkerThreadFactory |
| defaultForkJoinWorkerThreadFactory; |
| |
| /** |
| * Permission required for callers of methods that may start or |
| * kill threads. |
| */ |
| private static final RuntimePermission modifyThreadPermission; |
| |
| /** |
| * Common (static) pool. Non-null for public use unless a static |
| * construction exception, but internal usages null-check on use |
| * to paranoically avoid potential initialization circularities |
| * as well as to simplify generated code. |
| */ |
| static final ForkJoinPool common; |
| |
| /** |
| * Common pool parallelism. To allow simpler use and management |
| * when common pool threads are disabled, we allow the underlying |
| * common.parallelism field to be zero, but in that case still report |
| * parallelism as 1 to reflect resulting caller-runs mechanics. |
| */ |
| static final int commonParallelism; |
| |
| /** |
| * 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 constants |
| |
| /** |
| * Initial timeout value (in nanoseconds) for the thread |
| * triggering quiescence to park waiting for new work. On timeout, |
| * the thread will instead try to shrink the number of |
| * workers. The value should be large enough to avoid overly |
| * aggressive shrinkage during most transient stalls (long GCs |
| * etc). |
| */ |
| private static final long IDLE_TIMEOUT = 2000L * 1000L * 1000L; // 2sec |
| |
| /** |
| * Timeout value when there are more threads than parallelism level |
| */ |
| private static final long FAST_IDLE_TIMEOUT = 200L * 1000L * 1000L; |
| |
| /** |
| * Tolerance for idle timeouts, to cope with timer undershoots |
| */ |
| private static final long TIMEOUT_SLOP = 2000000L; |
| |
| /** |
| * The maximum stolen->joining link depth allowed in method |
| * tryHelpStealer. Must be a power of two. Depths for legitimate |
| * chains are unbounded, but we use a fixed constant to avoid |
| * (otherwise unchecked) cycles and to bound staleness of |
| * traversal parameters at the expense of sometimes blocking when |
| * we could be helping. |
| */ |
| private static final int MAX_HELP = 64; |
| |
| /** |
| * Increment for seed generators. See class ThreadLocal for |
| * explanation. |
| */ |
| private static final int SEED_INCREMENT = 0x61c88647; |
| |
| /* |
| * Bits and masks for control variables |
| * |
| * Field ctl is a long packed with: |
| * AC: Number of active running workers minus target parallelism (16 bits) |
| * TC: Number of total workers minus target parallelism (16 bits) |
| * ST: true if pool is terminating (1 bit) |
| * EC: the wait count of top waiting thread (15 bits) |
| * ID: poolIndex of top of Treiber stack of waiters (16 bits) |
| * |
| * When convenient, we can extract the upper 32 bits of counts and |
| * the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e = |
| * (int)ctl. The ec field is never accessed alone, but always |
| * together with id and st. The offsets of counts by the target |
| * parallelism and the positionings of fields makes it possible to |
| * perform the most common checks via sign tests of fields: When |
| * ac is negative, there are not enough active workers, when tc is |
| * negative, there are not enough total workers, and when e is |
| * negative, the pool is terminating. To deal with these possibly |
| * negative fields, we use casts in and out of "short" and/or |
| * signed shifts to maintain signedness. |
| * |
| * When a thread is queued (inactivated), its eventCount field is |
| * set negative, which is the only way to tell if a worker is |
| * prevented from executing tasks, even though it must continue to |
| * scan for them to avoid queuing races. Note however that |
| * eventCount updates lag releases so usage requires care. |
| * |
| * Field plock is an int packed with: |
| * SHUTDOWN: true if shutdown is enabled (1 bit) |
| * SEQ: a sequence lock, with PL_LOCK bit set if locked (30 bits) |
| * SIGNAL: set when threads may be waiting on the lock (1 bit) |
| * |
| * The sequence number enables simple consistency checks: |
| * Staleness of read-only operations on the workQueues array can |
| * be checked by comparing plock before vs after the reads. |
| */ |
| |
| // bit positions/shifts for fields |
| private static final int AC_SHIFT = 48; |
| private static final int TC_SHIFT = 32; |
| private static final int ST_SHIFT = 31; |
| private static final int EC_SHIFT = 16; |
| |
| // bounds |
| private static final int SMASK = 0xffff; // short bits |
| private static final int MAX_CAP = 0x7fff; // max #workers - 1 |
| private static final int EVENMASK = 0xfffe; // even short bits |
| private static final int SQMASK = 0x007e; // max 64 (even) slots |
| private static final int SHORT_SIGN = 1 << 15; |
| private static final int INT_SIGN = 1 << 31; |
| |
| // masks |
| private static final long STOP_BIT = 0x0001L << ST_SHIFT; |
| private static final long AC_MASK = ((long)SMASK) << AC_SHIFT; |
| private static final long TC_MASK = ((long)SMASK) << TC_SHIFT; |
| |
| // units for incrementing and decrementing |
| private static final long TC_UNIT = 1L << TC_SHIFT; |
| private static final long AC_UNIT = 1L << AC_SHIFT; |
| |
| // masks and units for dealing with u = (int)(ctl >>> 32) |
| private static final int UAC_SHIFT = AC_SHIFT - 32; |
| private static final int UTC_SHIFT = TC_SHIFT - 32; |
| private static final int UAC_MASK = SMASK << UAC_SHIFT; |
| private static final int UTC_MASK = SMASK << UTC_SHIFT; |
| private static final int UAC_UNIT = 1 << UAC_SHIFT; |
| private static final int UTC_UNIT = 1 << UTC_SHIFT; |
| |
| // masks and units for dealing with e = (int)ctl |
| private static final int E_MASK = 0x7fffffff; // no STOP_BIT |
| private static final int E_SEQ = 1 << EC_SHIFT; |
| |
| // plock bits |
| private static final int SHUTDOWN = 1 << 31; |
| private static final int PL_LOCK = 2; |
| private static final int PL_SIGNAL = 1; |
| private static final int PL_SPINS = 1 << 8; |
| |
| // access mode for WorkQueue |
| static final int LIFO_QUEUE = 0; |
| static final int FIFO_QUEUE = 1; |
| static final int SHARED_QUEUE = -1; |
| |
| // Heuristic padding to ameliorate unfortunate memory placements |
| volatile long pad00, pad01, pad02, pad03, pad04, pad05, pad06; |
| |
| // Instance fields |
| volatile long stealCount; // collects worker counts |
| volatile long ctl; // main pool control |
| volatile int plock; // shutdown status and seqLock |
| volatile int indexSeed; // worker/submitter index seed |
| final short parallelism; // parallelism level |
| final short mode; // LIFO/FIFO |
| WorkQueue[] workQueues; // main registry |
| final ForkJoinWorkerThreadFactory factory; |
| final UncaughtExceptionHandler ueh; // per-worker UEH |
| final String workerNamePrefix; // to create worker name string |
| |
| volatile Object pad10, pad11, pad12, pad13, pad14, pad15, pad16, pad17; |
| volatile Object pad18, pad19, pad1a, pad1b; |
| |
| /** |
| * Acquires the plock lock to protect worker array and related |
| * updates. This method is called only if an initial CAS on plock |
| * fails. This acts as a spinlock for normal cases, but falls back |
| * to builtin monitor to block when (rarely) needed. This would be |
| * a terrible idea for a highly contended lock, but works fine as |
| * a more conservative alternative to a pure spinlock. |
| */ |
| private int acquirePlock() { |
| int spins = PL_SPINS, ps, nps; |
| for (;;) { |
| if (((ps = plock) & PL_LOCK) == 0 && |
| U.compareAndSwapInt(this, PLOCK, ps, nps = ps + PL_LOCK)) |
| return nps; |
| else if (spins >= 0) { |
| if (ThreadLocalRandom.current().nextInt() >= 0) |
| --spins; |
| } |
| else if (U.compareAndSwapInt(this, PLOCK, ps, ps | PL_SIGNAL)) { |
| synchronized (this) { |
| if ((plock & PL_SIGNAL) != 0) { |
| try { |
| wait(); |
| } catch (InterruptedException ie) { |
| try { |
| Thread.currentThread().interrupt(); |
| } catch (SecurityException ignore) { |
| } |
| } |
| } |
| else |
| notifyAll(); |
| } |
| } |
| } |
| } |
| |
| /** |
| * Unlocks and signals any thread waiting for plock. Called only |
| * when CAS of seq value for unlock fails. |
| */ |
| private void releasePlock(int ps) { |
| plock = ps; |
| synchronized (this) { notifyAll(); } |
| } |
| |
| /** |
| * Tries to create and start one worker if fewer than target |
| * parallelism level exist. Adjusts counts etc on failure. |
| */ |
| private void tryAddWorker() { |
| long c; int u, e; |
| while ((u = (int)((c = ctl) >>> 32)) < 0 && |
| (u & SHORT_SIGN) != 0 && (e = (int)c) >= 0) { |
| long nc = ((long)(((u + UTC_UNIT) & UTC_MASK) | |
| ((u + UAC_UNIT) & UAC_MASK)) << 32) | (long)e; |
| if (U.compareAndSwapLong(this, CTL, c, nc)) { |
| ForkJoinWorkerThreadFactory fac; |
| Throwable ex = null; |
| ForkJoinWorkerThread wt = null; |
| try { |
| if ((fac = factory) != null && |
| (wt = fac.newThread(this)) != null) { |
| wt.start(); |
| break; |
| } |
| } catch (Throwable rex) { |
| ex = rex; |
| } |
| deregisterWorker(wt, ex); |
| break; |
| } |
| } |
| } |
| |
| // Registering and deregistering workers |
| |
| /** |
| * Callback from ForkJoinWorkerThread to establish and record its |
| * WorkQueue. To avoid scanning bias due to packing entries in |
| * front of the workQueues array, we treat the array as a simple |
| * power-of-two hash table using per-thread seed as hash, |
| * expanding as needed. |
| * |
| * @param wt the worker thread |
| * @return the worker's queue |
| */ |
| final WorkQueue registerWorker(ForkJoinWorkerThread wt) { |
| UncaughtExceptionHandler handler; WorkQueue[] ws; int s, ps; |
| wt.setDaemon(true); |
| if ((handler = ueh) != null) |
| wt.setUncaughtExceptionHandler(handler); |
| do {} while (!U.compareAndSwapInt(this, INDEXSEED, s = indexSeed, |
| s += SEED_INCREMENT) || |
| s == 0); // skip 0 |
| WorkQueue w = new WorkQueue(this, wt, mode, s); |
| if (((ps = plock) & PL_LOCK) != 0 || |
| !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK)) |
| ps = acquirePlock(); |
| int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN); |
| try { |
| if ((ws = workQueues) != null) { // skip if shutting down |
| int n = ws.length, m = n - 1; |
| int r = (s << 1) | 1; // use odd-numbered indices |
| if (ws[r &= m] != null) { // collision |
| int probes = 0; // step by approx half size |
| int step = (n <= 4) ? 2 : ((n >>> 1) & EVENMASK) + 2; |
| while (ws[r = (r + step) & m] != null) { |
| if (++probes >= n) { |
| workQueues = ws = Arrays.copyOf(ws, n <<= 1); |
| m = n - 1; |
| probes = 0; |
| } |
| } |
| } |
| w.poolIndex = (short)r; |
| w.eventCount = r; // volatile write orders |
| ws[r] = w; |
| } |
| } finally { |
| if (!U.compareAndSwapInt(this, PLOCK, ps, nps)) |
| releasePlock(nps); |
| } |
| wt.setName(workerNamePrefix.concat(Integer.toString(w.poolIndex >>> 1))); |
| return w; |
| } |
| |
| /** |
| * Final callback from terminating worker, as well as upon failure |
| * to construct or start a worker. Removes record of worker from |
| * array, and adjusts counts. If pool is shutting down, tries to |
| * complete termination. |
| * |
| * @param wt the worker thread, or null if construction failed |
| * @param ex the exception causing failure, or null if none |
| */ |
| final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) { |
| WorkQueue w = null; |
| if (wt != null && (w = wt.workQueue) != null) { |
| int ps; long sc; |
| w.qlock = -1; // ensure set |
| do {} while (!U.compareAndSwapLong(this, STEALCOUNT, |
| sc = stealCount, |
| sc + w.nsteals)); |
| if (((ps = plock) & PL_LOCK) != 0 || |
| !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK)) |
| ps = acquirePlock(); |
| int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN); |
| try { |
| int idx = w.poolIndex; |
| WorkQueue[] ws = workQueues; |
| if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w) |
| ws[idx] = null; |
| } finally { |
| if (!U.compareAndSwapInt(this, PLOCK, ps, nps)) |
| releasePlock(nps); |
| } |
| } |
| |
| long c; // adjust ctl counts |
| do {} while (!U.compareAndSwapLong |
| (this, CTL, c = ctl, (((c - AC_UNIT) & AC_MASK) | |
| ((c - TC_UNIT) & TC_MASK) | |
| (c & ~(AC_MASK|TC_MASK))))); |
| |
| if (!tryTerminate(false, false) && w != null && w.array != null) { |
| w.cancelAll(); // cancel remaining tasks |
| WorkQueue[] ws; WorkQueue v; Thread p; int u, i, e; |
| while ((u = (int)((c = ctl) >>> 32)) < 0 && (e = (int)c) >= 0) { |
| if (e > 0) { // activate or create replacement |
| if ((ws = workQueues) == null || |
| (i = e & SMASK) >= ws.length || |
| (v = ws[i]) == null) |
| break; |
| long nc = (((long)(v.nextWait & E_MASK)) | |
| ((long)(u + UAC_UNIT) << 32)); |
| if (v.eventCount != (e | INT_SIGN)) |
| break; |
| if (U.compareAndSwapLong(this, CTL, c, nc)) { |
| v.eventCount = (e + E_SEQ) & E_MASK; |
| if ((p = v.parker) != null) |
| U.unpark(p); |
| break; |
| } |
| } |
| else { |
| if ((short)u < 0) |
| tryAddWorker(); |
| break; |
| } |
| } |
| } |
| if (ex == null) // help clean refs on way out |
| ForkJoinTask.helpExpungeStaleExceptions(); |
| else // rethrow |
| ForkJoinTask.rethrow(ex); |
| } |
| |
| // Submissions |
| |
| /** |
| * Per-thread records for threads that submit to pools. Currently |
| * holds only pseudo-random seed / index that is used to choose |
| * submission queues in method externalPush. In the future, this may |
| * also incorporate a means to implement different task rejection |
| * and resubmission policies. |
| * |
| * Seeds for submitters and workers/workQueues work in basically |
| * the same way but are initialized and updated using slightly |
| * different mechanics. Both are initialized using the same |
| * approach as in class ThreadLocal, where successive values are |
| * unlikely to collide with previous values. Seeds are then |
| * randomly modified upon collisions using xorshifts, which |
| * requires a non-zero seed. |
| */ |
| static final class Submitter { |
| int seed; |
| Submitter(int s) { seed = s; } |
| } |
| |
| /** |
| * Unless shutting down, adds the given task to a submission queue |
| * at submitter's current queue index (modulo submission |
| * range). Only the most common path is directly handled in this |
| * method. All others are relayed to fullExternalPush. |
| * |
| * @param task the task. Caller must ensure non-null. |
| */ |
| final void externalPush(ForkJoinTask<?> task) { |
| Submitter z = submitters.get(); |
| WorkQueue q; int r, m, s, n, am; ForkJoinTask<?>[] a; |
| int ps = plock; |
| WorkQueue[] ws = workQueues; |
| if (z != null && ps > 0 && ws != null && (m = (ws.length - 1)) >= 0 && |
| (q = ws[m & (r = z.seed) & SQMASK]) != null && r != 0 && |
| U.compareAndSwapInt(q, QLOCK, 0, 1)) { // lock |
| if ((a = q.array) != null && |
| (am = a.length - 1) > (n = (s = q.top) - q.base)) { |
| int j = ((am & s) << ASHIFT) + ABASE; |
| U.putOrderedObject(a, j, task); |
| q.top = s + 1; // push on to deque |
| q.qlock = 0; |
| if (n <= 1) |
| signalWork(ws, q); |
| return; |
| } |
| q.qlock = 0; |
| } |
| fullExternalPush(task); |
| } |
| |
| /** |
| * Full version of externalPush. This method is called, among |
| * other times, upon the first submission of the first task to the |
| * pool, so must perform secondary initialization. It also |
| * detects first submission by an external thread by looking up |
| * its ThreadLocal, and creates a new shared queue if the one at |
| * index if empty or contended. The plock lock body must be |
| * exception-free (so no try/finally) so we optimistically |
| * allocate new queues outside the lock and throw them away if |
| * (very rarely) not needed. |
| * |
| * Secondary initialization occurs when plock is zero, to create |
| * workQueue array and set plock to a valid value. This lock body |
| * must also be exception-free. Because the plock seq value can |
| * eventually wrap around zero, this method harmlessly fails to |
| * reinitialize if workQueues exists, while still advancing plock. |
| */ |
| private void fullExternalPush(ForkJoinTask<?> task) { |
| int r = 0; // random index seed |
| for (Submitter z = submitters.get();;) { |
| WorkQueue[] ws; WorkQueue q; int ps, m, k; |
| if (z == null) { |
| if (U.compareAndSwapInt(this, INDEXSEED, r = indexSeed, |
| r += SEED_INCREMENT) && r != 0) |
| submitters.set(z = new Submitter(r)); |
| } |
| else if (r == 0) { // move to a different index |
| r = z.seed; |
| r ^= r << 13; // same xorshift as WorkQueues |
| r ^= r >>> 17; |
| z.seed = r ^= (r << 5); |
| } |
| if ((ps = plock) < 0) |
| throw new RejectedExecutionException(); |
| else if (ps == 0 || (ws = workQueues) == null || |
| (m = ws.length - 1) < 0) { // initialize workQueues |
| int p = parallelism; // find power of two table size |
| int n = (p > 1) ? p - 1 : 1; // ensure at least 2 slots |
| n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; |
| n |= n >>> 8; n |= n >>> 16; n = (n + 1) << 1; |
| WorkQueue[] nws = ((ws = workQueues) == null || ws.length == 0 ? |
| new WorkQueue[n] : null); |
| if (((ps = plock) & PL_LOCK) != 0 || |
| !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK)) |
| ps = acquirePlock(); |
| if (((ws = workQueues) == null || ws.length == 0) && nws != null) |
| workQueues = nws; |
| int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN); |
| if (!U.compareAndSwapInt(this, PLOCK, ps, nps)) |
| releasePlock(nps); |
| } |
| else if ((q = ws[k = r & m & SQMASK]) != null) { |
| if (q.qlock == 0 && U.compareAndSwapInt(q, QLOCK, 0, 1)) { |
| ForkJoinTask<?>[] a = q.array; |
| int s = q.top; |
| boolean submitted = false; |
| try { // locked version of push |
| if ((a != null && a.length > s + 1 - q.base) || |
| (a = q.growArray()) != null) { // must presize |
| int j = (((a.length - 1) & s) << ASHIFT) + ABASE; |
| U.putOrderedObject(a, j, task); |
| q.top = s + 1; |
| submitted = true; |
| } |
| } finally { |
| q.qlock = 0; // unlock |
| } |
| if (submitted) { |
| signalWork(ws, q); |
| return; |
| } |
| } |
| r = 0; // move on failure |
| } |
| else if (((ps = plock) & PL_LOCK) == 0) { // create new queue |
| q = new WorkQueue(this, null, SHARED_QUEUE, r); |
| q.poolIndex = (short)k; |
| if (((ps = plock) & PL_LOCK) != 0 || |
| !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK)) |
| ps = acquirePlock(); |
| if ((ws = workQueues) != null && k < ws.length && ws[k] == null) |
| ws[k] = q; |
| int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN); |
| if (!U.compareAndSwapInt(this, PLOCK, ps, nps)) |
| releasePlock(nps); |
| } |
| else |
| r = 0; |
| } |
| } |
| |
| // Maintaining ctl counts |
| |
| /** |
| * Increments active count; mainly called upon return from blocking. |
| */ |
| final void incrementActiveCount() { |
| long c; |
| do {} while (!U.compareAndSwapLong |
| (this, CTL, c = ctl, ((c & ~AC_MASK) | |
| ((c & AC_MASK) + AC_UNIT)))); |
| } |
| |
| /** |
| * Tries to create or activate a worker if too few are active. |
| * |
| * @param ws the worker array to use to find signallees |
| * @param q if non-null, the queue holding tasks to be processed |
| */ |
| final void signalWork(WorkQueue[] ws, WorkQueue q) { |
| for (;;) { |
| long c; int e, u, i; WorkQueue w; Thread p; |
| if ((u = (int)((c = ctl) >>> 32)) >= 0) |
| break; |
| if ((e = (int)c) <= 0) { |
| if ((short)u < 0) |
| tryAddWorker(); |
| break; |
| } |
| if (ws == null || ws.length <= (i = e & SMASK) || |
| (w = ws[i]) == null) |
| break; |
| long nc = (((long)(w.nextWait & E_MASK)) | |
| ((long)(u + UAC_UNIT)) << 32); |
| int ne = (e + E_SEQ) & E_MASK; |
| if (w.eventCount == (e | INT_SIGN) && |
| U.compareAndSwapLong(this, CTL, c, nc)) { |
| w.eventCount = ne; |
| if ((p = w.parker) != null) |
| U.unpark(p); |
| break; |
| } |
| if (q != null && q.base >= q.top) |
| break; |
| } |
| } |
| |
| // Scanning for tasks |
| |
| /** |
| * Top-level runloop for workers, called by ForkJoinWorkerThread.run. |
| */ |
| final void runWorker(WorkQueue w) { |
| w.growArray(); // allocate queue |
| for (int r = w.hint; scan(w, r) == 0; ) { |
| r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // xorshift |
| } |
| } |
| |
| /** |
| * Scans for and, if found, runs one task, else possibly |
| * inactivates the worker. This method operates on single reads of |
| * volatile state and is designed to be re-invoked continuously, |
| * in part because it returns upon detecting inconsistencies, |
| * contention, or state changes that indicate possible success on |
| * re-invocation. |
| * |
| * The scan searches for tasks across queues starting at a random |
| * index, checking each at least twice. The scan terminates upon |
| * either finding a non-empty queue, or completing the sweep. If |
| * the worker is not inactivated, it takes and runs a task from |
| * this queue. Otherwise, if not activated, it tries to activate |
| * itself or some other worker by signalling. On failure to find a |
| * task, returns (for retry) if pool state may have changed during |
| * an empty scan, or tries to inactivate if active, else possibly |
| * blocks or terminates via method awaitWork. |
| * |
| * @param w the worker (via its WorkQueue) |
| * @param r a random seed |
| * @return worker qlock status if would have waited, else 0 |
| */ |
| private final int scan(WorkQueue w, int r) { |
| WorkQueue[] ws; int m; |
| long c = ctl; // for consistency check |
| if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 && w != null) { |
| for (int j = m + m + 1, ec = w.eventCount;;) { |
| WorkQueue q; int b, e; ForkJoinTask<?>[] a; ForkJoinTask<?> t; |
| if ((q = ws[(r - j) & m]) != null && |
| (b = q.base) - q.top < 0 && (a = q.array) != null) { |
| long i = (((a.length - 1) & b) << ASHIFT) + ABASE; |
| if ((t = ((ForkJoinTask<?>) |
| U.getObjectVolatile(a, i))) != null) { |
| if (ec < 0) |
| helpRelease(c, ws, w, q, b); |
| else if (q.base == b && |
| U.compareAndSwapObject(a, i, t, null)) { |
| U.putOrderedInt(q, QBASE, b + 1); |
| if ((b + 1) - q.top < 0) |
| signalWork(ws, q); |
| w.runTask(t); |
| } |
| } |
| break; |
| } |
| else if (--j < 0) { |
| if ((ec | (e = (int)c)) < 0) // inactive or terminating |
| return awaitWork(w, c, ec); |
| else if (ctl == c) { // try to inactivate and enqueue |
| long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK)); |
| w.nextWait = e; |
| w.eventCount = ec | INT_SIGN; |
| if (!U.compareAndSwapLong(this, CTL, c, nc)) |
| w.eventCount = ec; // back out |
| } |
| break; |
| } |
| } |
| } |
| return 0; |
| } |
| |
| /** |
| * A continuation of scan(), possibly blocking or terminating |
| * worker w. Returns without blocking if pool state has apparently |
| * changed since last invocation. Also, if inactivating w has |
| * caused the pool to become quiescent, checks for pool |
| * termination, and, so long as this is not the only worker, waits |
| * for event for up to a given duration. On timeout, if ctl has |
| * not changed, terminates the worker, which will in turn wake up |
| * another worker to possibly repeat this process. |
| * |
| * @param w the calling worker |
| * @param c the ctl value on entry to scan |
| * @param ec the worker's eventCount on entry to scan |
| */ |
| private final int awaitWork(WorkQueue w, long c, int ec) { |
| int stat, ns; long parkTime, deadline; |
| if ((stat = w.qlock) >= 0 && w.eventCount == ec && ctl == c && |
| !Thread.interrupted()) { |
| int e = (int)c; |
| int u = (int)(c >>> 32); |
| int d = (u >> UAC_SHIFT) + parallelism; // active count |
| |
| if (e < 0 || (d <= 0 && tryTerminate(false, false))) |
| stat = w.qlock = -1; // pool is terminating |
| else if ((ns = w.nsteals) != 0) { // collect steals and retry |
| long sc; |
| w.nsteals = 0; |
| do {} while (!U.compareAndSwapLong(this, STEALCOUNT, |
| sc = stealCount, sc + ns)); |
| } |
| else { |
| long pc = ((d > 0 || ec != (e | INT_SIGN)) ? 0L : |
| ((long)(w.nextWait & E_MASK)) | // ctl to restore |
| ((long)(u + UAC_UNIT)) << 32); |
| if (pc != 0L) { // timed wait if last waiter |
| int dc = -(short)(c >>> TC_SHIFT); |
| parkTime = (dc < 0 ? FAST_IDLE_TIMEOUT: |
| (dc + 1) * IDLE_TIMEOUT); |
| deadline = System.nanoTime() + parkTime - TIMEOUT_SLOP; |
| } |
| else |
| parkTime = deadline = 0L; |
| if (w.eventCount == ec && ctl == c) { |
| Thread wt = Thread.currentThread(); |
| U.putObject(wt, PARKBLOCKER, this); |
| w.parker = wt; // emulate LockSupport.park |
| if (w.eventCount == ec && ctl == c) |
| U.park(false, parkTime); // must recheck before park |
| w.parker = null; |
| U.putObject(wt, PARKBLOCKER, null); |
| if (parkTime != 0L && ctl == c && |
| deadline - System.nanoTime() <= 0L && |
| U.compareAndSwapLong(this, CTL, c, pc)) |
| stat = w.qlock = -1; // shrink pool |
| } |
| } |
| } |
| return stat; |
| } |
| |
| /** |
| * Possibly releases (signals) a worker. Called only from scan() |
| * when a worker with apparently inactive status finds a non-empty |
| * queue. This requires revalidating all of the associated state |
| * from caller. |
| */ |
| private final void helpRelease(long c, WorkQueue[] ws, WorkQueue w, |
| WorkQueue q, int b) { |
| WorkQueue v; int e, i; Thread p; |
| if (w != null && w.eventCount < 0 && (e = (int)c) > 0 && |
| ws != null && ws.length > (i = e & SMASK) && |
| (v = ws[i]) != null && ctl == c) { |
| long nc = (((long)(v.nextWait & E_MASK)) | |
| ((long)((int)(c >>> 32) + UAC_UNIT)) << 32); |
| int ne = (e + E_SEQ) & E_MASK; |
| if (q != null && q.base == b && w.eventCount < 0 && |
| v.eventCount == (e | INT_SIGN) && |
| U.compareAndSwapLong(this, CTL, c, nc)) { |
| v.eventCount = ne; |
| if ((p = v.parker) != null) |
| U.unpark(p); |
| } |
| } |
| } |
| |
| /** |
| * Tries to locate and execute tasks for a stealer of the given |
| * task, or in turn one of its stealers, Traces currentSteal -> |
| * currentJoin links looking for a thread working on a descendant |
| * of the given task and with a non-empty queue to steal back and |
| * execute tasks from. The first call to this method upon a |
| * waiting join will often entail scanning/search, (which is OK |
| * because the joiner has nothing better to do), but this method |
| * leaves hints in workers to speed up subsequent calls. The |
| * implementation is very branchy to cope with potential |
| * inconsistencies or loops encountering chains that are stale, |
| * unknown, or so long that they are likely cyclic. |
| * |
| * @param joiner the joining worker |
| * @param task the task to join |
| * @return 0 if no progress can be made, negative if task |
| * known complete, else positive |
| */ |
| private int tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) { |
| int stat = 0, steps = 0; // bound to avoid cycles |
| if (task != null && joiner != null && |
| joiner.base - joiner.top >= 0) { // hoist checks |
| restart: for (;;) { |
| ForkJoinTask<?> subtask = task; // current target |
| for (WorkQueue j = joiner, v;;) { // v is stealer of subtask |
| WorkQueue[] ws; int m, s, h; |
| if ((s = task.status) < 0) { |
| stat = s; |
| break restart; |
| } |
| if ((ws = workQueues) == null || (m = ws.length - 1) <= 0) |
| break restart; // shutting down |
| if ((v = ws[h = (j.hint | 1) & m]) == null || |
| v.currentSteal != subtask) { |
| for (int origin = h;;) { // find stealer |
| if (((h = (h + 2) & m) & 15) == 1 && |
| (subtask.status < 0 || j.currentJoin != subtask)) |
| continue restart; // occasional staleness check |
| if ((v = ws[h]) != null && |
| v.currentSteal == subtask) { |
| j.hint = h; // save hint |
| break; |
| } |
| if (h == origin) |
| break restart; // cannot find stealer |
| } |
| } |
| for (;;) { // help stealer or descend to its stealer |
| ForkJoinTask[] a; int b; |
| if (subtask.status < 0) // surround probes with |
| continue restart; // consistency checks |
| if ((b = v.base) - v.top < 0 && (a = v.array) != null) { |
| int i = (((a.length - 1) & b) << ASHIFT) + ABASE; |
| ForkJoinTask<?> t = |
| (ForkJoinTask<?>)U.getObjectVolatile(a, i); |
| if (subtask.status < 0 || j.currentJoin != subtask || |
| v.currentSteal != subtask) |
| continue restart; // stale |
| stat = 1; // apparent progress |
| if (v.base == b) { |
| if (t == null) |
| break restart; |
| if (U.compareAndSwapObject(a, i, t, null)) { |
| U.putOrderedInt(v, QBASE, b + 1); |
| ForkJoinTask<?> ps = joiner.currentSteal; |
| int jt = joiner.top; |
| do { |
| joiner.currentSteal = t; |
| t.doExec(); // clear local tasks too |
| } while (task.status >= 0 && |
| joiner.top != jt && |
| (t = joiner.pop()) != null); |
| joiner.currentSteal = ps; |
| break restart; |
| } |
| } |
| } |
| else { // empty -- try to descend |
| ForkJoinTask<?> next = v.currentJoin; |
| if (subtask.status < 0 || j.currentJoin != subtask || |
| v.currentSteal != subtask) |
| continue restart; // stale |
| else if (next == null || ++steps == MAX_HELP) |
| break restart; // dead-end or maybe cyclic |
| else { |
| subtask = next; |
| j = v; |
| break; |
| } |
| } |
| } |
| } |
| } |
| } |
| return stat; |
| } |
| |
| /** |
| * Analog of tryHelpStealer for CountedCompleters. Tries to steal |
| * and run tasks within the target's computation. |
| * |
| * @param task the task to join |
| */ |
| private int helpComplete(WorkQueue joiner, CountedCompleter<?> task) { |
| WorkQueue[] ws; int m; |
| int s = 0; |
| if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 && |
| joiner != null && task != null) { |
| int j = joiner.poolIndex; |
| int scans = m + m + 1; |
| long c = 0L; // for stability check |
| for (int k = scans; ; j += 2) { |
| WorkQueue q; |
| if ((s = task.status) < 0) |
| break; |
| else if (joiner.internalPopAndExecCC(task)) |
| k = scans; |
| else if ((s = task.status) < 0) |
| break; |
| else if ((q = ws[j & m]) != null && q.pollAndExecCC(task)) |
| k = scans; |
| else if (--k < 0) { |
| if (c == (c = ctl)) |
| break; |
| k = scans; |
| } |
| } |
| } |
| return s; |
| } |
| |
| /** |
| * Tries to decrement active count (sometimes implicitly) and |
| * possibly release or create a compensating worker in preparation |
| * for blocking. Fails on contention or termination. Otherwise, |
| * adds a new thread if no idle workers are available and pool |
| * may become starved. |
| * |
| * @param c the assumed ctl value |
| */ |
| final boolean tryCompensate(long c) { |
| WorkQueue[] ws = workQueues; |
| int pc = parallelism, e = (int)c, m, tc; |
| if (ws != null && (m = ws.length - 1) >= 0 && e >= 0 && ctl == c) { |
| WorkQueue w = ws[e & m]; |
| if (e != 0 && w != null) { |
| Thread p; |
| long nc = ((long)(w.nextWait & E_MASK) | |
| (c & (AC_MASK|TC_MASK))); |
| int ne = (e + E_SEQ) & E_MASK; |
| if (w.eventCount == (e | INT_SIGN) && |
| U.compareAndSwapLong(this, CTL, c, nc)) { |
| w.eventCount = ne; |
| if ((p = w.parker) != null) |
| U.unpark(p); |
| return true; // replace with idle worker |
| } |
| } |
| else if ((tc = (short)(c >>> TC_SHIFT)) >= 0 && |
| (int)(c >> AC_SHIFT) + pc > 1) { |
| long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK); |
| if (U.compareAndSwapLong(this, CTL, c, nc)) |
| return true; // no compensation |
| } |
| else if (tc + pc < MAX_CAP) { |
| long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK); |
| if (U.compareAndSwapLong(this, CTL, c, nc)) { |
| ForkJoinWorkerThreadFactory fac; |
| Throwable ex = null; |
| ForkJoinWorkerThread wt = null; |
| try { |
| if ((fac = factory) != null && |
| (wt = fac.newThread(this)) != null) { |
| wt.start(); |
| return true; |
| } |
| } catch (Throwable rex) { |
| ex = rex; |
| } |
| deregisterWorker(wt, ex); // clean up and return false |
| } |
| } |
| } |
| return false; |
| } |
| |
| /** |
| * Helps and/or blocks until the given task is done. |
| * |
| * @param joiner the joining worker |
| * @param task the task |
| * @return task status on exit |
| */ |
| final int awaitJoin(WorkQueue joiner, ForkJoinTask<?> task) { |
| int s = 0; |
| if (task != null && (s = task.status) >= 0 && joiner != null) { |
| ForkJoinTask<?> prevJoin = joiner.currentJoin; |
| joiner.currentJoin = task; |
| do {} while (joiner.tryRemoveAndExec(task) && // process local tasks |
| (s = task.status) >= 0); |
| if (s >= 0 && (task instanceof CountedCompleter)) |
| s = helpComplete(joiner, (CountedCompleter<?>)task); |
| long cc = 0; // for stability checks |
| while (s >= 0 && (s = task.status) >= 0) { |
| if ((s = tryHelpStealer(joiner, task)) == 0 && |
| (s = task.status) >= 0) { |
| if (!tryCompensate(cc)) |
| cc = ctl; |
| else { |
| if (task.trySetSignal() && (s = task.status) >= 0) { |
| synchronized (task) { |
| if (task.status >= 0) { |
| try { // see ForkJoinTask |
| task.wait(); // for explanation |
| } catch (InterruptedException ie) { |
| } |
| } |
| else |
| task.notifyAll(); |
| } |
| } |
| long c; // reactivate |
| do {} while (!U.compareAndSwapLong |
| (this, CTL, c = ctl, |
| ((c & ~AC_MASK) | |
| ((c & AC_MASK) + AC_UNIT)))); |
| } |
| } |
| } |
| joiner.currentJoin = prevJoin; |
| } |
| return s; |
| } |
| |
| /** |
| * Stripped-down variant of awaitJoin used by timed joins. Tries |
| * to help join only while there is continuous progress. (Caller |
| * will then enter a timed wait.) |
| * |
| * @param joiner the joining worker |
| * @param task the task |
| */ |
| final void helpJoinOnce(WorkQueue joiner, ForkJoinTask<?> task) { |
| int s; |
| if (joiner != null && task != null && (s = task.status) >= 0) { |
| ForkJoinTask<?> prevJoin = joiner.currentJoin; |
| joiner.currentJoin = task; |
| do {} while (joiner.tryRemoveAndExec(task) && // process local tasks |
| (s = task.status) >= 0); |
| if (s >= 0) { |
| if (task instanceof CountedCompleter) |
| helpComplete(joiner, (CountedCompleter<?>)task); |
| do {} while (task.status >= 0 && |
| tryHelpStealer(joiner, task) > 0); |
| } |
| joiner.currentJoin = prevJoin; |
| } |
| } |
| |
| /** |
| * Returns a (probably) non-empty steal queue, if one is found |
| * during a scan, else null. This method must be retried by |
| * caller if, by the time it tries to use the queue, it is empty. |
| */ |
| private WorkQueue findNonEmptyStealQueue() { |
| int r = ThreadLocalRandom.current().nextInt(); |
| for (;;) { |
| int ps = plock, m; WorkQueue[] ws; WorkQueue q; |
| if ((ws = workQueues) != null && (m = ws.length - 1) >= 0) { |
| for (int j = (m + 1) << 2; j >= 0; --j) { |
| if ((q = ws[(((r - j) << 1) | 1) & m]) != null && |
| q.base - q.top < 0) |
| return q; |
| } |
| } |
| if (plock == ps) |
| return null; |
| } |
| } |
| |
| /** |
| * Runs tasks until {@code isQuiescent()}. We piggyback on |
| * active count ctl maintenance, but rather than blocking |
| * when tasks cannot be found, we rescan until all others cannot |
| * find tasks either. |
| */ |
| final void helpQuiescePool(WorkQueue w) { |
| ForkJoinTask<?> ps = w.currentSteal; |
| for (boolean active = true;;) { |
| long c; WorkQueue q; ForkJoinTask<?> t; int b; |
| while ((t = w.nextLocalTask()) != null) |
| t.doExec(); |
| if ((q = findNonEmptyStealQueue()) != null) { |
| if (!active) { // re-establish active count |
| active = true; |
| do {} while (!U.compareAndSwapLong |
| (this, CTL, c = ctl, |
| ((c & ~AC_MASK) | |
| ((c & AC_MASK) + AC_UNIT)))); |
| } |
| if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null) { |
| (w.currentSteal = t).doExec(); |
| w.currentSteal = ps; |
| } |
| } |
| else if (active) { // decrement active count without queuing |
| long nc = ((c = ctl) & ~AC_MASK) | ((c & AC_MASK) - AC_UNIT); |
| if ((int)(nc >> AC_SHIFT) + parallelism == 0) |
| break; // bypass decrement-then-increment |
| if (U.compareAndSwapLong(this, CTL, c, nc)) |
| active = false; |
| } |
| else if ((int)((c = ctl) >> AC_SHIFT) + parallelism <= 0 && |
| U.compareAndSwapLong |
| (this, CTL, c, ((c & ~AC_MASK) | |
| ((c & AC_MASK) + AC_UNIT)))) |
| break; |
| } |
| } |
| |
| /** |
| * Gets and removes a local or stolen task for the given worker. |
| * |
| * @return a task, if available |
| */ |
| final ForkJoinTask<?> nextTaskFor(WorkQueue w) { |
| for (ForkJoinTask<?> t;;) { |
| WorkQueue q; int b; |
| if ((t = w.nextLocalTask()) != null) |
| return t; |
| if ((q = findNonEmptyStealQueue()) == null) |
| return null; |
| if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null) |
| return t; |
| } |
| } |
| |
| /** |
| * Returns a cheap heuristic guide for task partitioning when |
| * programmers, frameworks, tools, or languages have little or no |
| * idea about task granularity. In essence by offering this |
| * method, we ask users only about tradeoffs in overhead vs |
| * expected throughput and its variance, rather than how finely to |
| * partition tasks. |
| * |
| * In a steady state strict (tree-structured) computation, each |
| * thread makes available for stealing enough tasks for other |
| * threads to remain active. Inductively, if all threads play by |
| * the same rules, each thread should make available only a |
| * constant number of tasks. |
| * |
| * The minimum useful constant is just 1. But using a value of 1 |
| * would require immediate replenishment upon each steal to |
| * maintain enough tasks, which is infeasible. Further, |
| * partitionings/granularities of offered tasks should minimize |
| * steal rates, which in general means that threads nearer the top |
| * of computation tree should generate more than those nearer the |
| * bottom. In perfect steady state, each thread is at |
| * approximately the same level of computation tree. However, |
| * producing extra tasks amortizes the uncertainty of progress and |
| * diffusion assumptions. |
| * |
| * So, users will want to use values larger (but not much larger) |
| * than 1 to both smooth over transient shortages and hedge |
| * against uneven progress; as traded off against the cost of |
| * extra task overhead. We leave the user to pick a threshold |
| * value to compare with the results of this call to guide |
| * decisions, but recommend values such as 3. |
| * |
| * When all threads are active, it is on average OK to estimate |
| * surplus strictly locally. In steady-state, if one thread is |
| * maintaining say 2 surplus tasks, then so are others. So we can |
| * just use estimated queue length. However, this strategy alone |
| * leads to serious mis-estimates in some non-steady-state |
| * conditions (ramp-up, ramp-down, other stalls). We can detect |
| * many of these by further considering the number of "idle" |
| * threads, that are known to have zero queued tasks, so |
| * compensate by a factor of (#idle/#active) threads. |
| * |
| * Note: The approximation of #busy workers as #active workers is |
| * not very good under current signalling scheme, and should be |
| * improved. |
| */ |
| static int getSurplusQueuedTaskCount() { |
| Thread t; ForkJoinWorkerThread wt; ForkJoinPool pool; WorkQueue q; |
| if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) { |
| int p = (pool = (wt = (ForkJoinWorkerThread)t).pool).parallelism; |
| int n = (q = wt.workQueue).top - q.base; |
| int a = (int)(pool.ctl >> AC_SHIFT) + p; |
| return n - (a > (p >>>= 1) ? 0 : |
| a > (p >>>= 1) ? 1 : |
| a > (p >>>= 1) ? 2 : |
| a > (p >>>= 1) ? 4 : |
| 8); |
| } |
| return 0; |
| } |
| |
| // Termination |
| |
| /** |
| * Possibly initiates and/or completes termination. The caller |
| * triggering termination runs three passes through workQueues: |
| * (0) Setting termination status, followed by wakeups of queued |
| * workers; (1) cancelling all tasks; (2) interrupting lagging |
| * threads (likely in external tasks, but possibly also blocked in |
| * joins). Each pass repeats previous steps because of potential |
| * lagging thread creation. |
| * |
| * @param now if true, unconditionally terminate, else only |
| * if no work and no active workers |
| * @param enable if true, enable shutdown when next possible |
| * @return true if now terminating or terminated |
| */ |
| private boolean tryTerminate(boolean now, boolean enable) { |
| int ps; |
| if (this == common) // cannot shut down |
| return false; |
| if ((ps = plock) >= 0) { // enable by setting plock |
| if (!enable) |
| return false; |
| if ((ps & PL_LOCK) != 0 || |
| !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK)) |
| ps = acquirePlock(); |
| int nps = ((ps + PL_LOCK) & ~SHUTDOWN) | SHUTDOWN; |
| if (!U.compareAndSwapInt(this, PLOCK, ps, nps)) |
| releasePlock(nps); |
| } |
| for (long c;;) { |
| if (((c = ctl) & STOP_BIT) != 0) { // already terminating |
| if ((short)(c >>> TC_SHIFT) + parallelism <= 0) { |
| synchronized (this) { |
| notifyAll(); // signal when 0 workers |
| } |
| } |
| return true; |
| } |
| if (!now) { // check if idle & no tasks |
| WorkQueue[] ws; WorkQueue w; |
| if ((int)(c >> AC_SHIFT) + parallelism > 0) |
| return false; |
| if ((ws = workQueues) != null) { |
| for (int i = 0; i < ws.length; ++i) { |
| if ((w = ws[i]) != null && |
| (!w.isEmpty() || |
| ((i & 1) != 0 && w.eventCount >= 0))) { |
| signalWork(ws, w); |
| return false; |
| } |
| } |
| } |
| } |
| if (U.compareAndSwapLong(this, CTL, c, c | STOP_BIT)) { |
| for (int pass = 0; pass < 3; ++pass) { |
| WorkQueue[] ws; WorkQueue w; Thread wt; |
| if ((ws = workQueues) != null) { |
| int n = ws.length; |
| for (int i = 0; i < n; ++i) { |
| if ((w = ws[i]) != null) { |
| w.qlock = -1; |
| if (pass > 0) { |
| w.cancelAll(); |
| if (pass > 1 && (wt = w.owner) != null) { |
| if (!wt.isInterrupted()) { |
| try { |
| wt.interrupt(); |
| } catch (Throwable ignore) { |
| } |
| } |
| U.unpark(wt); |
| } |
| } |
| } |
| } |
| // Wake up workers parked on event queue |
| int i, e; long cc; Thread p; |
| while ((e = (int)(cc = ctl) & E_MASK) != 0 && |
| (i = e & SMASK) < n && i >= 0 && |
| (w = ws[i]) != null) { |
| long nc = ((long)(w.nextWait & E_MASK) | |
| ((cc + AC_UNIT) & AC_MASK) | |
| (cc & (TC_MASK|STOP_BIT))); |
| if (w.eventCount == (e | INT_SIGN) && |
| U.compareAndSwapLong(this, CTL, cc, nc)) { |
| w.eventCount = (e + E_SEQ) & E_MASK; |
| w.qlock = -1; |
| if ((p = w.parker) != null) |
| U.unpark(p); |
| } |
| } |
| } |
| } |
| } |
| } |
| } |
| |
| // external operations on common pool |
| |
| /** |
| * Returns common pool queue for a thread that has submitted at |
| * least one task. |
| */ |
| static WorkQueue commonSubmitterQueue() { |
| Submitter z; ForkJoinPool p; WorkQueue[] ws; int m, r; |
| return ((z = submitters.get()) != null && |
| (p = common) != null && |
| (ws = p.workQueues) != null && |
| (m = ws.length - 1) >= 0) ? |
| ws[m & z.seed & SQMASK] : null; |
| } |
| |
| /** |
| * Tries to pop the given task from submitter's queue in common pool. |
| */ |
| final boolean tryExternalUnpush(ForkJoinTask<?> task) { |
| WorkQueue joiner; ForkJoinTask<?>[] a; int m, s; |
| Submitter z = submitters.get(); |
| WorkQueue[] ws = workQueues; |
| boolean popped = false; |
| if (z != null && ws != null && (m = ws.length - 1) >= 0 && |
| (joiner = ws[z.seed & m & SQMASK]) != null && |
| joiner.base != (s = joiner.top) && |
| (a = joiner.array) != null) { |
| long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE; |
| if (U.getObject(a, j) == task && |
| U.compareAndSwapInt(joiner, QLOCK, 0, 1)) { |
| if (joiner.top == s && joiner.array == a && |
| U.compareAndSwapObject(a, j, task, null)) { |
| joiner.top = s - 1; |
| popped = true; |
| } |
| joiner.qlock = 0; |
| } |
| } |
| return popped; |
| } |
| |
| final int externalHelpComplete(CountedCompleter<?> task) { |
| WorkQueue joiner; int m, j; |
| Submitter z = submitters.get(); |
| WorkQueue[] ws = workQueues; |
| int s = 0; |
| if (z != null && ws != null && (m = ws.length - 1) >= 0 && |
| (joiner = ws[(j = z.seed) & m & SQMASK]) != null && task != null) { |
| int scans = m + m + 1; |
| long c = 0L; // for stability check |
| j |= 1; // poll odd queues |
| for (int k = scans; ; j += 2) { |
| WorkQueue q; |
| if ((s = task.status) < 0) |
| break; |
| else if (joiner.externalPopAndExecCC(task)) |
| k = scans; |
| else if ((s = task.status) < 0) |
| break; |
| else if ((q = ws[j & m]) != null && q.pollAndExecCC(task)) |
| k = scans; |
| else if (--k < 0) { |
| if (c == (c = ctl)) |
| break; |
| k = scans; |
| } |
| } |
| } |
| return s; |
| } |
| |
| // Exported methods |
| |
| // Constructors |
| |
| /** |
| * Creates a {@code ForkJoinPool} with parallelism equal to {@link |
| * java.lang.Runtime#availableProcessors}, using the {@linkplain |
| * #defaultForkJoinWorkerThreadFactory default thread factory}, |
| * no UncaughtExceptionHandler, and non-async LIFO processing mode. |
| */ |
| public ForkJoinPool() { |
| this(Math.min(MAX_CAP, Runtime.getRuntime().availableProcessors()), |
| defaultForkJoinWorkerThreadFactory, null, false); |
| } |
| |
| /** |
| * Creates a {@code ForkJoinPool} with the indicated parallelism |
| * level, the {@linkplain |
| * #defaultForkJoinWorkerThreadFactory default thread factory}, |
| * no UncaughtExceptionHandler, and non-async LIFO processing mode. |
| * |
| * @param parallelism the parallelism level |
| * @throws IllegalArgumentException if parallelism less than or |
| * equal to zero, or greater than implementation limit |
| */ |
| public ForkJoinPool(int parallelism) { |
| this(parallelism, defaultForkJoinWorkerThreadFactory, null, false); |
| } |
| |
| /** |
| * Creates a {@code ForkJoinPool} with the given parameters. |
| * |
| * @param parallelism the parallelism level. For default value, |
| * use {@link java.lang.Runtime#availableProcessors}. |
| * @param factory the factory for creating new threads. For default value, |
| * use {@link #defaultForkJoinWorkerThreadFactory}. |
| * @param handler the handler for internal worker threads that |
| * terminate due to unrecoverable errors encountered while executing |
| * tasks. For default value, use {@code null}. |
| * @param asyncMode if true, |
| * establishes local first-in-first-out scheduling mode for forked |
| * tasks that are never joined. This mode may be more appropriate |
| * than default locally stack-based mode in applications in which |
| * worker threads only process event-style asynchronous tasks. |
| * For default value, use {@code false}. |
| * @throws IllegalArgumentException if parallelism less than or |
| * equal to zero, or greater than implementation limit |
| * @throws NullPointerException if the factory is null |
| */ |
| public ForkJoinPool(int parallelism, |
| ForkJoinWorkerThreadFactory factory, |
| UncaughtExceptionHandler handler, |
| boolean asyncMode) { |
| this(checkParallelism(parallelism), |
| checkFactory(factory), |
| handler, |
| (asyncMode ? FIFO_QUEUE : LIFO_QUEUE), |
| "ForkJoinPool-" + nextPoolId() + "-worker-"); |
| checkPermission(); |
| } |
| |
| private static int checkParallelism(int parallelism) { |
| if (parallelism <= 0 || parallelism > MAX_CAP) |
| throw new IllegalArgumentException(); |
| return parallelism; |
| } |
| |
| private static ForkJoinWorkerThreadFactory checkFactory |
| (ForkJoinWorkerThreadFactory factory) { |
| if (factory == null) |
| throw new NullPointerException(); |
| return factory; |
| } |
| |
| /** |
| * Creates a {@code ForkJoinPool} with the given parameters, without |
| * any security checks or parameter validation. Invoked directly by |
| * makeCommonPool. |
| */ |
| private ForkJoinPool(int parallelism, |
| ForkJoinWorkerThreadFactory factory, |
| UncaughtExceptionHandler handler, |
| int mode, |
| String workerNamePrefix) { |
| this.workerNamePrefix = workerNamePrefix; |
| this.factory = factory; |
| this.ueh = handler; |
| this.mode = (short)mode; |
| this.parallelism = (short)parallelism; |
| long np = (long)(-parallelism); // offset ctl counts |
| this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK); |
| } |
| |
| /** |
| * Returns the common pool instance. This pool is statically |
| * constructed; its run state is unaffected by attempts to {@link |
| * #shutdown} or {@link #shutdownNow}. However this pool and any |
| * ongoing processing are automatically terminated upon program |
| * {@link System#exit}. Any program that relies on asynchronous |
| * task processing to complete before program termination should |
| * invoke {@code commonPool().}{@link #awaitQuiescence awaitQuiescence}, |
| * before exit. |
| * |
| * @return the common pool instance |
| * @since 1.8 |
| * @hide |
| */ |
| public static ForkJoinPool commonPool() { |
| // assert common != null : "static init error"; |
| return common; |
| } |
| |
| // Execution methods |
| |
| /** |
| * Performs the given task, returning its result upon completion. |
| * If the computation encounters an unchecked Exception or Error, |
| * it is rethrown as the outcome of this invocation. Rethrown |
| * exceptions behave in the same way as regular exceptions, but, |
| * when possible, contain stack traces (as displayed for example |
| * using {@code ex.printStackTrace()}) of both the current thread |
| * as well as the thread actually encountering the exception; |
| * minimally only the latter. |
| * |
| * @param task the task |
| * @param <T> the type of the task's result |
| * @return the task's result |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public <T> T invoke(ForkJoinTask<T> task) { |
| if (task == null) |
| throw new NullPointerException(); |
| externalPush(task); |
| return task.join(); |
| } |
| |
| /** |
| * Arranges for (asynchronous) execution of the given task. |
| * |
| * @param task the task |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public void execute(ForkJoinTask<?> task) { |
| if (task == null) |
| throw new NullPointerException(); |
| externalPush(task); |
| } |
| |
| // AbstractExecutorService methods |
| |
| /** |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public void execute(Runnable task) { |
| if (task == null) |
| throw new NullPointerException(); |
| ForkJoinTask<?> job; |
| if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
| job = (ForkJoinTask<?>) task; |
| else |
| job = new ForkJoinTask.RunnableExecuteAction(task); |
| externalPush(job); |
| } |
| |
| /** |
| * Submits a ForkJoinTask for execution. |
| * |
| * @param task the task to submit |
| * @param <T> the type of the task's result |
| * @return the task |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) { |
| if (task == null) |
| throw new NullPointerException(); |
| externalPush(task); |
| return task; |
| } |
| |
| /** |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public <T> ForkJoinTask<T> submit(Callable<T> task) { |
| ForkJoinTask<T> job = new ForkJoinTask.AdaptedCallable<T>(task); |
| externalPush(job); |
| return job; |
| } |
| |
| /** |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public <T> ForkJoinTask<T> submit(Runnable task, T result) { |
| ForkJoinTask<T> job = new ForkJoinTask.AdaptedRunnable<T>(task, result); |
| externalPush(job); |
| return job; |
| } |
| |
| /** |
| * @throws NullPointerException if the task is null |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| */ |
| public ForkJoinTask<?> submit(Runnable task) { |
| if (task == null) |
| throw new NullPointerException(); |
| ForkJoinTask<?> job; |
| if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
| job = (ForkJoinTask<?>) task; |
| else |
| job = new ForkJoinTask.AdaptedRunnableAction(task); |
| externalPush(job); |
| return job; |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| * @throws RejectedExecutionException {@inheritDoc} |
| */ |
| public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) { |
| // In previous versions of this class, this method constructed |
| // a task to run ForkJoinTask.invokeAll, but now external |
| // invocation of multiple tasks is at least as efficient. |
| ArrayList<Future<T>> futures = new ArrayList<Future<T>>(tasks.size()); |
| |
| boolean done = false; |
| try { |
| for (Callable<T> t : tasks) { |
| ForkJoinTask<T> f = new ForkJoinTask.AdaptedCallable<T>(t); |
| futures.add(f); |
| externalPush(f); |
| } |
| for (int i = 0, size = futures.size(); i < size; i++) |
| ((ForkJoinTask<?>)futures.get(i)).quietlyJoin(); |
| done = true; |
| return futures; |
| } finally { |
| if (!done) |
| for (int i = 0, size = futures.size(); i < size; i++) |
| futures.get(i).cancel(false); |
| } |
| } |
| |
| /** |
| * Returns the factory used for constructing new workers. |
| * |
| * @return the factory used for constructing new workers |
| */ |
| public ForkJoinWorkerThreadFactory getFactory() { |
| return factory; |
| } |
| |
| /** |
| * Returns the handler for internal worker threads that terminate |
| * due to unrecoverable errors encountered while executing tasks. |
| * |
| * @return the handler, or {@code null} if none |
| */ |
| public UncaughtExceptionHandler getUncaughtExceptionHandler() { |
| return ueh; |
| } |
| |
| /** |
| * Returns the targeted parallelism level of this pool. |
| * |
| * @return the targeted parallelism level of this pool |
| */ |
| public int getParallelism() { |
| int par; |
| return ((par = parallelism) > 0) ? par : 1; |
| } |
| |
| /** |
| * Returns the targeted parallelism level of the common pool. |
| * |
| * @return the targeted parallelism level of the common pool |
| * @since 1.8 |
| * @hide |
| */ |
| public static int getCommonPoolParallelism() { |
| return commonParallelism; |
| } |
| |
| /** |
| * Returns the number of worker threads that have started but not |
| * yet terminated. The result returned by this method may differ |
| * from {@link #getParallelism} when threads are created to |
| * maintain parallelism when others are cooperatively blocked. |
| * |
| * @return the number of worker threads |
| */ |
| public int getPoolSize() { |
| return parallelism + (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_QUEUE; |
| } |
| |
| /** |
| * 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 = parallelism + (int)(ctl >> AC_SHIFT); |
| return (r <= 0) ? 0 : r; // suppress momentarily negative values |
| } |
| |
| /** |
| * Returns {@code true} if all worker threads are currently idle. |
| * An idle worker is one that cannot obtain a task to execute |
| * because none are available to steal from other threads, and |
| * there are no pending submissions to the pool. This method is |
| * conservative; it might not return {@code true} immediately upon |
| * idleness of all threads, but will eventually become true if |
| * threads remain inactive. |
| * |
| * @return {@code true} if all threads are currently idle |
| */ |
| public boolean isQuiescent() { |
| return parallelism + (int)(ctl >> AC_SHIFT) <= 0; |
| } |
| |
| /** |
| * Returns an estimate of the total number of tasks stolen from |
| * one thread's work queue by another. The reported value |
| * underestimates the actual total number of steals when the pool |
| * is not quiescent. This value may be useful for monitoring and |
| * tuning fork/join programs: in general, steal counts should be |
| * high enough to keep threads busy, but low enough to avoid |
| * overhead and contention across threads. |
| * |
| * @return the number of steals |
| */ |
| public long getStealCount() { |
| 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 += w.nsteals; |
| } |
| } |
| return count; |
| } |
| |
| /** |
| * Returns an estimate of the total number of tasks currently held |
| * in queues by worker threads (but not including tasks submitted |
| * to the pool that have not begun executing). This value is only |
| * an approximation, obtained by iterating across all threads in |
| * the pool. This method may be useful for tuning task |
| * granularities. |
| * |
| * @return the number of queued tasks |
| */ |
| public long getQueuedTaskCount() { |
| long count = 0; |
| WorkQueue[] ws; WorkQueue w; |
| if ((ws = workQueues) != null) { |
| for (int i = 1; i < ws.length; i += 2) { |
| if ((w = ws[i]) != null) |
| count += w.queueSize(); |
| } |
| } |
| return count; |
| } |
| |
| /** |
| * Returns an estimate of the number of tasks submitted to this |
| * pool that have not yet begun executing. This method may take |
| * time proportional to the number of submissions. |
| * |
| * @return the number of queued submissions |
| */ |
| public int getQueuedSubmissionCount() { |
| int count = 0; |
| WorkQueue[] ws; WorkQueue w; |
| if ((ws = workQueues) != null) { |
| for (int i = 0; i < ws.length; i += 2) { |
| if ((w = ws[i]) != null) |
| count += w.queueSize(); |
| } |
| } |
| return count; |
| } |
| |
| /** |
| * Returns {@code true} if there are any tasks submitted to this |
| * pool that have not yet begun executing. |
| * |
| * @return {@code true} if there are any queued submissions |
| */ |
| public boolean hasQueuedSubmissions() { |
| WorkQueue[] ws; WorkQueue w; |
| if ((ws = workQueues) != null) { |
| for (int i = 0; i < ws.length; i += 2) { |
| if ((w = ws[i]) != null && !w.isEmpty()) |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| /** |
| * Removes and returns the next unexecuted submission if one is |
| * available. This method may be useful in extensions to this |
| * class that re-assign work in systems with multiple pools. |
| * |
| * @return the next submission, or {@code null} if none |
| */ |
| protected ForkJoinTask<?> pollSubmission() { |
| WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t; |
| if ((ws = workQueues) != null) { |
| for (int i = 0; i < ws.length; i += 2) { |
| if ((w = ws[i]) != null && (t = w.poll()) != null) |
| return t; |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Removes all available unexecuted submitted and forked tasks |
| * from scheduling queues and adds them to the given collection, |
| * without altering their execution status. These may include |
| * artificially generated or wrapped tasks. This method is |
| * designed to be invoked only when the pool is known to be |
| * quiescent. Invocations at other times may not remove all |
| * tasks. A failure encountered while attempting to add elements |
| * to collection {@code c} may result in elements being in |
| * neither, either or both collections when the associated |
| * exception is thrown. The behavior of this operation is |
| * undefined if the specified collection is modified while the |
| * operation is in progress. |
| * |
| * @param c the collection to transfer elements into |
| * @return the number of elements transferred |
| */ |
| protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { |
| int count = 0; |
| WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t; |
| if ((ws = workQueues) != null) { |
| for (int i = 0; i < ws.length; ++i) { |
| if ((w = ws[i]) != null) { |
| while ((t = w.poll()) != null) { |
| c.add(t); |
| ++count; |
| } |
| } |
| } |
| } |
| return count; |
| } |
| |
| /** |
| * Returns a string identifying this pool, as well as its state, |
| * including indications of run state, parallelism level, and |
| * worker and task counts. |
| * |
| * @return a string identifying this pool, as well as its state |
| */ |
| public String toString() { |
| // Use a single pass through workQueues to collect counts |
| long qt = 0L, qs = 0L; int rc = 0; |
| long st = stealCount; |
| long c = ctl; |
| WorkQueue[] ws; WorkQueue w; |
| if ((ws = workQueues) != null) { |
| for (int i = 0; i < ws.length; ++i) { |
| if ((w = ws[i]) != null) { |
| int size = w.queueSize(); |
| if ((i & 1) == 0) |
| qs += size; |
| else { |
| qt += size; |
| st += w.nsteals; |
| if (w.isApparentlyUnblocked()) |
| ++rc; |
| } |
| } |
| } |
| } |
| int pc = parallelism; |
| int tc = pc + (short)(c >>> TC_SHIFT); |
| int ac = pc + (int)(c >> AC_SHIFT); |
| if (ac < 0) // ignore transient negative |
| ac = 0; |
| String level; |
| if ((c & STOP_BIT) != 0) |
| level = (tc == 0) ? "Terminated" : "Terminating"; |
| else |
| level = plock < 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 {@code 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. |
| */ |
| 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 {@code 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 |
| */ |
| 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() { |
| long c = ctl; |
| return ((c & STOP_BIT) != 0L && |
| (short)(c >>> TC_SHIFT) + parallelism <= 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() { |
| long c = ctl; |
| return ((c & STOP_BIT) != 0L && |
| (short)(c >>> TC_SHIFT) + parallelism > 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 plock < 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 {@code |
| * commonPool()} never terminates until program shutdown, when |
| * applied to the common pool, this method is equivalent to {@link |
| * #awaitQuiescence(long, TimeUnit)} but always returns {@code false}. |
| * |
| * @param timeout the maximum time to wait |
| * @param unit the time unit of the timeout argument |
| * @return {@code true} if this executor terminated and |
| * {@code false} if the timeout elapsed before termination |
| * @throws InterruptedException if interrupted while waiting |
| */ |
| public boolean awaitTermination(long timeout, TimeUnit unit) |
| throws InterruptedException { |
| if (Thread.interrupted()) |
| throw new InterruptedException(); |
| if (this == common) { |
| awaitQuiescence(timeout, unit); |
| return false; |
| } |
| long nanos = unit.toNanos(timeout); |
| if (isTerminated()) |
| return true; |
| if (nanos <= 0L) |
| return false; |
| long deadline = System.nanoTime() + nanos; |
| synchronized (this) { |
| for (;;) { |
| if (isTerminated()) |
| return true; |
| if (nanos <= 0L) |
| return false; |
| long millis = TimeUnit.NANOSECONDS.toMillis(nanos); |
| wait(millis > 0L ? millis : 1L); |
| nanos = deadline - System.nanoTime(); |
| } |
| } |
| } |
| |
| /** |
| * If called by a ForkJoinTask operating in this pool, equivalent |
| * in effect to {@link ForkJoinTask#helpQuiesce}. Otherwise, |
| * waits and/or attempts to assist performing tasks until this |
| * pool {@link #isQuiescent} or the indicated timeout elapses. |
| * |
| * @param timeout the maximum time to wait |
| * @param unit the time unit of the timeout argument |
| * @return {@code true} if quiescent; {@code false} if the |
| * timeout elapsed. |
| */ |
| public boolean awaitQuiescence(long timeout, TimeUnit unit) { |
| long nanos = unit.toNanos(timeout); |
| ForkJoinWorkerThread wt; |
| Thread thread = Thread.currentThread(); |
| if ((thread instanceof ForkJoinWorkerThread) && |
| (wt = (ForkJoinWorkerThread)thread).pool == this) { |
| helpQuiescePool(wt.workQueue); |
| return true; |
| } |
| long startTime = System.nanoTime(); |
| WorkQueue[] ws; |
| int r = 0, m; |
| boolean found = true; |
| while (!isQuiescent() && (ws = workQueues) != null && |
| (m = ws.length - 1) >= 0) { |
| if (!found) { |
| if ((System.nanoTime() - startTime) > nanos) |
| return false; |
| Thread.yield(); // cannot block |
| } |
| found = false; |
| for (int j = (m + 1) << 2; j >= 0; --j) { |
| ForkJoinTask<?> t; WorkQueue q; int b; |
| if ((q = ws[r++ & m]) != null && (b = q.base) - q.top < 0) { |
| found = true; |
| if ((t = q.pollAt(b)) != null) |
| t.doExec(); |
| break; |
| } |
| } |
| } |
| return true; |
| } |
| |
| /** |
| * Waits and/or attempts to assist performing tasks indefinitely |
| * until the {@code 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 |
| * {@code isReleasable} must return {@code true} if blocking is |
| * not necessary. Method {@code 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(); |
| } |
| |
| /** |
| * Blocks in accord with the given blocker. If the current thread |
| * is a {@link ForkJoinWorkerThread}, this method possibly |
| * arranges for a spare thread to be activated if necessary to |
| * ensure sufficient parallelism while the current thread is blocked. |
| * |
| * <p>If the caller is not a {@link ForkJoinTask}, this method is |
| * behaviorally equivalent to |
| * <pre> {@code |
| * while (!blocker.isReleasable()) |
| * if (blocker.block()) |
| * return; |
| * }</pre> |
| * |
| * If the caller is a {@code ForkJoinTask}, then the pool may |
| * first be expanded to ensure parallelism, and later adjusted. |
| * |
| * @param blocker the blocker |
| * @throws InterruptedException if blocker.block did so |
| */ |
| public static void managedBlock(ManagedBlocker blocker) |
| throws InterruptedException { |
| Thread t = Thread.currentThread(); |
| if (t instanceof ForkJoinWorkerThread) { |
| ForkJoinPool p = ((ForkJoinWorkerThread)t).pool; |
| while (!blocker.isReleasable()) { |
| if (p.tryCompensate(p.ctl)) { |
| try { |
| do {} while (!blocker.isReleasable() && |
| !blocker.block()); |
| } finally { |
| p.incrementActiveCount(); |
| } |
| break; |
| } |
| } |
| } |
| else { |
| do {} while (!blocker.isReleasable() && |
| !blocker.block()); |
| } |
| } |
| |
| // AbstractExecutorService overrides. These rely on undocumented |
| // fact that ForkJoinTask.adapt returns ForkJoinTasks that also |
| // implement RunnableFuture. |
| |
| protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) { |
| return new ForkJoinTask.AdaptedRunnable<T>(runnable, value); |
| } |
| |
| protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) { |
| return new ForkJoinTask.AdaptedCallable<T>(callable); |
| } |
| |
| // Unsafe mechanics |
| private static final sun.misc.Unsafe U; |
| private static final long CTL; |
| private static final long PARKBLOCKER; |
| private static final int ABASE; |
| private static final int ASHIFT; |
| private static final long STEALCOUNT; |
| private static final long PLOCK; |
| private static final long INDEXSEED; |
| private static final long QBASE; |
| private static final long QLOCK; |
| |
| static { |
| // initialize field offsets for CAS etc |
| try { |
| U = sun.misc.Unsafe.getUnsafe(); |
| Class<?> k = ForkJoinPool.class; |
| CTL = U.objectFieldOffset |
| (k.getDeclaredField("ctl")); |
| STEALCOUNT = U.objectFieldOffset |
| (k.getDeclaredField("stealCount")); |
| PLOCK = U.objectFieldOffset |
| (k.getDeclaredField("plock")); |
| INDEXSEED = U.objectFieldOffset |
| (k.getDeclaredField("indexSeed")); |
| Class<?> tk = Thread.class; |
| PARKBLOCKER = U.objectFieldOffset |
| (tk.getDeclaredField("parkBlocker")); |
| Class<?> wk = WorkQueue.class; |
| QBASE = U.objectFieldOffset |
| (wk.getDeclaredField("base")); |
| QLOCK = U.objectFieldOffset |
| (wk.getDeclaredField("qlock")); |
| Class<?> ak = ForkJoinTask[].class; |
| ABASE = U.arrayBaseOffset(ak); |
| int scale = U.arrayIndexScale(ak); |
| if ((scale & (scale - 1)) != 0) |
| throw new Error("data type scale not a power of two"); |
| ASHIFT = 31 - Integer.numberOfLeadingZeros(scale); |
| } catch (Exception e) { |
| throw new Error(e); |
| } |
| |
| submitters = new ThreadLocal<Submitter>(); |
| defaultForkJoinWorkerThreadFactory = |
| new DefaultForkJoinWorkerThreadFactory(); |
| modifyThreadPermission = new RuntimePermission("modifyThread"); |
| |
| common = java.security.AccessController.doPrivileged |
| (new java.security.PrivilegedAction<ForkJoinPool>() { |
| public ForkJoinPool run() { return makeCommonPool(); }}); |
| int par = common.parallelism; // report 1 even if threads disabled |
| commonParallelism = par > 0 ? par : 1; |
| } |
| |
| /** |
| * Creates and returns the common pool, respecting user settings |
| * specified via system properties. |
| */ |
| private static ForkJoinPool makeCommonPool() { |
| int parallelism = -1; |
| ForkJoinWorkerThreadFactory factory |
| = defaultForkJoinWorkerThreadFactory; |
| UncaughtExceptionHandler handler = null; |
| try { // ignore exceptions in accessing/parsing properties |
| String pp = System.getProperty |
| ("java.util.concurrent.ForkJoinPool.common.parallelism"); |
| String fp = System.getProperty |
| ("java.util.concurrent.ForkJoinPool.common.threadFactory"); |
| String hp = System.getProperty |
| ("java.util.concurrent.ForkJoinPool.common.exceptionHandler"); |
| if (pp != null) |
| parallelism = Integer.parseInt(pp); |
| if (fp != null) |
| factory = ((ForkJoinWorkerThreadFactory)ClassLoader. |
| getSystemClassLoader().loadClass(fp).newInstance()); |
| if (hp != null) |
| handler = ((UncaughtExceptionHandler)ClassLoader. |
| getSystemClassLoader().loadClass(hp).newInstance()); |
| } catch (Exception ignore) { |
| } |
| |
| if (parallelism < 0 && // default 1 less than #cores |
| (parallelism = Runtime.getRuntime().availableProcessors() - 1) < 0) |
| parallelism = 0; |
| if (parallelism > MAX_CAP) |
| parallelism = MAX_CAP; |
| return new ForkJoinPool(parallelism, factory, handler, LIFO_QUEUE, |
| "ForkJoinPool.commonPool-worker-"); |
| } |
| |
| } |