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Diffstat (limited to 'src/forkjoin/scala/concurrent/forkjoin/ForkJoinPool.java')
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diff --git a/src/forkjoin/scala/concurrent/forkjoin/ForkJoinPool.java b/src/forkjoin/scala/concurrent/forkjoin/ForkJoinPool.java deleted file mode 100644 index 6578504155..0000000000 --- a/src/forkjoin/scala/concurrent/forkjoin/ForkJoinPool.java +++ /dev/null @@ -1,3759 +0,0 @@ -/* - * 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 scala.concurrent.forkjoin; - -import java.util.ArrayList; -import java.util.Arrays; -import java.util.Collection; -import java.util.Collections; -import java.util.List; -import java.util.concurrent.AbstractExecutorService; -import java.util.concurrent.Callable; -import java.util.concurrent.ExecutorService; -import java.util.concurrent.Future; -import java.util.concurrent.RejectedExecutionException; -import java.util.concurrent.RunnableFuture; -import java.util.concurrent.TimeUnit; - -/** - * @since 1.8 - * @author Doug Lea - */ -/*public*/ abstract class CountedCompleter<T> extends ForkJoinTask<T> { - private static final long serialVersionUID = 5232453752276485070L; - - /** This task's completer, or null if none */ - final CountedCompleter<?> completer; - /** The number of pending tasks until completion */ - volatile int pending; - - /** - * Creates a new CountedCompleter with the given completer - * and initial pending count. - * - * @param completer this task's completer, or {@code null} if none - * @param initialPendingCount the initial pending count - */ - protected CountedCompleter(CountedCompleter<?> completer, - int initialPendingCount) { - this.completer = completer; - this.pending = initialPendingCount; - } - - /** - * Creates a new CountedCompleter with the given completer - * and an initial pending count of zero. - * - * @param completer this task's completer, or {@code null} if none - */ - protected CountedCompleter(CountedCompleter<?> completer) { - this.completer = completer; - } - - /** - * Creates a new CountedCompleter with no completer - * and an initial pending count of zero. - */ - protected CountedCompleter() { - this.completer = null; - } - - /** - * The main computation performed by this task. - */ - public abstract void compute(); - - /** - * Performs an action when method {@link #tryComplete} is invoked - * and the pending count is zero, or when the unconditional - * method {@link #complete} is invoked. By default, this method - * does nothing. You can distinguish cases by checking the - * identity of the given caller argument. If not equal to {@code - * this}, then it is typically a subtask that may contain results - * (and/or links to other results) to combine. - * - * @param caller the task invoking this method (which may - * be this task itself) - */ - public void onCompletion(CountedCompleter<?> caller) { - } - - /** - * Performs an action when method {@link #completeExceptionally} - * is invoked or method {@link #compute} throws an exception, and - * this task has not otherwise already completed normally. On - * entry to this method, this task {@link - * ForkJoinTask#isCompletedAbnormally}. The return value of this - * method controls further propagation: If {@code true} and this - * task has a completer, then this completer is also completed - * exceptionally. The default implementation of this method does - * nothing except return {@code true}. - * - * @param ex the exception - * @param caller the task invoking this method (which may - * be this task itself) - * @return true if this exception should be propagated to this - * task's completer, if one exists - */ - public boolean onExceptionalCompletion(Throwable ex, CountedCompleter<?> caller) { - return true; - } - - /** - * Returns the completer established in this task's constructor, - * or {@code null} if none. - * - * @return the completer - */ - public final CountedCompleter<?> getCompleter() { - return completer; - } - - /** - * Returns the current pending count. - * - * @return the current pending count - */ - public final int getPendingCount() { - return pending; - } - - /** - * Sets the pending count to the given value. - * - * @param count the count - */ - public final void setPendingCount(int count) { - pending = count; - } - - /** - * Adds (atomically) the given value to the pending count. - * - * @param delta the value to add - */ - public final void addToPendingCount(int delta) { - int c; // note: can replace with intrinsic in jdk8 - do {} while (!U.compareAndSwapInt(this, PENDING, c = pending, c+delta)); - } - - /** - * Sets (atomically) the pending count to the given count only if - * it currently holds the given expected value. - * - * @param expected the expected value - * @param count the new value - * @return true if successful - */ - public final boolean compareAndSetPendingCount(int expected, int count) { - return U.compareAndSwapInt(this, PENDING, expected, count); - } - - /** - * If the pending count is nonzero, (atomically) decrements it. - * - * @return the initial (undecremented) pending count holding on entry - * to this method - */ - public final int decrementPendingCountUnlessZero() { - int c; - do {} while ((c = pending) != 0 && - !U.compareAndSwapInt(this, PENDING, c, c - 1)); - return c; - } - - /** - * Returns the root of the current computation; i.e., this - * task if it has no completer, else its completer's root. - * - * @return the root of the current computation - */ - public final CountedCompleter<?> getRoot() { - CountedCompleter<?> a = this, p; - while ((p = a.completer) != null) - a = p; - return a; - } - - /** - * If the pending count is nonzero, decrements the count; - * otherwise invokes {@link #onCompletion} and then similarly - * tries to complete this task's completer, if one exists, - * else marks this task as complete. - */ - public final void tryComplete() { - CountedCompleter<?> a = this, s = a; - for (int c;;) { - if ((c = a.pending) == 0) { - a.onCompletion(s); - if ((a = (s = a).completer) == null) { - s.quietlyComplete(); - return; - } - } - else if (U.compareAndSwapInt(a, PENDING, c, c - 1)) - return; - } - } - - /** - * Equivalent to {@link #tryComplete} but does not invoke {@link - * #onCompletion} along the completion path: If the pending count - * is nonzero, decrements the count; otherwise, similarly tries to - * complete this task's completer, if one exists, else marks this - * task as complete. This method may be useful in cases where - * {@code onCompletion} should not, or need not, be invoked for - * each completer in a computation. - */ - public final void propagateCompletion() { - CountedCompleter<?> a = this, s = a; - for (int c;;) { - if ((c = a.pending) == 0) { - if ((a = (s = a).completer) == null) { - s.quietlyComplete(); - return; - } - } - else if (U.compareAndSwapInt(a, PENDING, c, c - 1)) - return; - } - } - - /** - * Regardless of pending count, invokes {@link #onCompletion}, - * marks this task as complete and further triggers {@link - * #tryComplete} on this task's completer, if one exists. The - * given rawResult is used as an argument to {@link #setRawResult} - * before invoking {@link #onCompletion} or marking this task as - * complete; its value is meaningful only for classes overriding - * {@code setRawResult}. - * - * <p>This method may be useful when forcing completion as soon as - * any one (versus all) of several subtask results are obtained. - * However, in the common (and recommended) case in which {@code - * setRawResult} is not overridden, this effect can be obtained - * more simply using {@code quietlyCompleteRoot();}. - * - * @param rawResult the raw result - */ - public void complete(T rawResult) { - CountedCompleter<?> p; - setRawResult(rawResult); - onCompletion(this); - quietlyComplete(); - if ((p = completer) != null) - p.tryComplete(); - } - - - /** - * If this task's pending count is zero, returns this task; - * otherwise decrements its pending count and returns {@code - * null}. This method is designed to be used with {@link - * #nextComplete} in completion traversal loops. - * - * @return this task, if pending count was zero, else {@code null} - */ - public final CountedCompleter<?> firstComplete() { - for (int c;;) { - if ((c = pending) == 0) - return this; - else if (U.compareAndSwapInt(this, PENDING, c, c - 1)) - return null; - } - } - - /** - * If this task does not have a completer, invokes {@link - * ForkJoinTask#quietlyComplete} and returns {@code null}. Or, if - * this task's pending count is non-zero, decrements its pending - * count and returns {@code null}. Otherwise, returns the - * completer. This method can be used as part of a completion - * traversal loop for homogeneous task hierarchies: - * - * <pre> {@code - * for (CountedCompleter<?> c = firstComplete(); - * c != null; - * c = c.nextComplete()) { - * // ... process c ... - * }}</pre> - * - * @return the completer, or {@code null} if none - */ - public final CountedCompleter<?> nextComplete() { - CountedCompleter<?> p; - if ((p = completer) != null) - return p.firstComplete(); - else { - quietlyComplete(); - return null; - } - } - - /** - * Equivalent to {@code getRoot().quietlyComplete()}. - */ - public final void quietlyCompleteRoot() { - for (CountedCompleter<?> a = this, p;;) { - if ((p = a.completer) == null) { - a.quietlyComplete(); - return; - } - a = p; - } - } - - /** - * Supports ForkJoinTask exception propagation. - */ - void internalPropagateException(Throwable ex) { - CountedCompleter<?> a = this, s = a; - while (a.onExceptionalCompletion(ex, s) && - (a = (s = a).completer) != null && a.status >= 0) - a.recordExceptionalCompletion(ex); - } - - /** - * Implements execution conventions for CountedCompleters. - */ - protected final boolean exec() { - compute(); - return false; - } - - /** - * Returns the result of the computation. By default - * returns {@code null}, which is appropriate for {@code Void} - * actions, but in other cases should be overridden, almost - * always to return a field or function of a field that - * holds the result upon completion. - * - * @return the result of the computation - */ - public T getRawResult() { return null; } - - /** - * A method that result-bearing CountedCompleters may optionally - * use to help maintain result data. By default, does nothing. - * Overrides are not recommended. However, if this method is - * overridden to update existing objects or fields, then it must - * in general be defined to be thread-safe. - */ - protected void setRawResult(T t) { } - - // Unsafe mechanics - private static final sun.misc.Unsafe U; - private static final long PENDING; - static { - try { - U = getUnsafe(); - PENDING = U.objectFieldOffset - (CountedCompleter.class.getDeclaredField("pending")); - } catch (Exception e) { - throw new Error(e); - } - } - - /** - * Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. - * Replace with a simple call to Unsafe.getUnsafe when integrating - * into a jdk. - * - * @return a sun.misc.Unsafe - */ - private static sun.misc.Unsafe getUnsafe() { - return scala.concurrent.util.Unsafe.instance; - } -} - -/** - * An {@link ExecutorService} for running {@link ForkJoinTask}s. - * A {@code ForkJoinPool} provides the entry point for submissions - * from non-{@code ForkJoinTask} clients, as well as management and - * monitoring operations. - * - * <p>A {@code ForkJoinPool} differs from other kinds of {@link - * ExecutorService} mainly by virtue of employing - * <em>work-stealing</em>: all threads in the pool attempt to find and - * execute tasks submitted to the pool and/or created by other active - * tasks (eventually blocking waiting for work if none exist). This - * enables efficient processing when most tasks spawn other subtasks - * (as do most {@code ForkJoinTask}s), as well as when many small - * tasks are submitted to the pool from external clients. Especially - * when setting <em>asyncMode</em> to true in constructors, {@code - * ForkJoinPool}s may also be appropriate for use with event-style - * tasks that are never joined. - * - * <p>A static {@link #commonPool()} is available and appropriate for - * most applications. The common pool is used by any ForkJoinTask that - * is not explicitly submitted to a specified pool. Using the common - * pool normally reduces resource usage (its threads are slowly - * reclaimed during periods of non-use, and reinstated upon subsequent - * use). - * - * <p>For applications that require separate or custom pools, a {@code - * ForkJoinPool} may be constructed with a given target parallelism - * level; by default, equal to the number of available processors. The - * pool attempts to maintain enough active (or available) threads by - * dynamically adding, suspending, or resuming internal worker - * threads, even if some tasks are stalled waiting to join - * others. However, no such adjustments are guaranteed in the face of - * blocked I/O or other unmanaged synchronization. The nested {@link - * ManagedBlocker} interface enables extension of the kinds of - * synchronization accommodated. - * - * <p>In addition to execution and lifecycle control methods, this - * class provides status check methods (for example - * {@link #getStealCount}) that are intended to aid in developing, - * tuning, and monitoring fork/join applications. Also, method - * {@link #toString} returns indications of pool state in a - * convenient form for informal monitoring. - * - * <p>As is the case with other ExecutorServices, there are three - * main task execution methods summarized in the following table. - * These are designed to be used primarily by clients not already - * engaged in fork/join computations in the current pool. The main - * forms of these methods accept instances of {@code ForkJoinTask}, - * but overloaded forms also allow mixed execution of plain {@code - * Runnable}- or {@code Callable}- based activities as well. However, - * tasks that are already executing in a pool should normally instead - * use the within-computation forms listed in the table unless using - * async event-style tasks that are not usually joined, in which case - * there is little difference among choice of methods. - * - * <table BORDER CELLPADDING=3 CELLSPACING=1> - * <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</td> - * <td> {@link #execute(ForkJoinTask)}</td> - * <td> {@link ForkJoinTask#fork}</td> - * </tr> - * <tr> - * <td> <b>Await and obtain result</td> - * <td> {@link #invoke(ForkJoinTask)}</td> - * <td> {@link ForkJoinTask#invoke}</td> - * </tr> - * <tr> - * <td> <b>Arrange exec and obtain Future</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 {@link - * System#getProperty system properties} with prefix {@code - * java.util.concurrent.ForkJoinPool.common}: {@code parallelism} -- - * an integer greater than zero, {@code threadFactory} -- the class - * name of a {@link ForkJoinWorkerThreadFactory}, and {@code - * exceptionHandler} -- the class name of a {@link - * java.lang.Thread.UncaughtExceptionHandler - * Thread.UncaughtExceptionHandler}. Upon any error in establishing - * these settings, default parameters are used. - * - * <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). - * 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 - * ThreadLocal Submitter class contains a value initially used as - * a hash code for choosing existing queues, but may be randomly - * repositioned upon contention with other submitters. In - * essence, submitters act like workers except that they are - * restricted to executing local tasks that they submitted (or in - * the case of CountedCompleters, others with the same root task). - * 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. During a rescan, the worker might release - * some other queued worker rather than itself, which has the same - * net effect. 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. However, many other threads may notice the same task - * and each signal to wake up a thread that might take it. So in - * general, pools will be over-signalled. 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), and may leave a hint to the unparked worker to - * help signal others upon wakeup). These primary signals are - * buttressed by others (see method helpSignal) whenever other - * threads scan for work or do not have a task to process. 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. - * - * 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. - * - * Helping actions for CountedCompleters are much simpler: Method - * helpComplete can take and execute any task with the same root - * as the task being waited on. However, this still entails some - * traversal of completer chains, so is less efficient than using - * CountedCompleters without explicit joins. - * - * 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 some subtask processing (see externalHelpJoin and - * related methods). We do not need to record whether these - * 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 - */ - - // 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 - * @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); - } - } - - /** - * 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; } - } - - /** - * 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). Unfortunately, because they are recorded - * in a common array, WorkQueue instances are often moved to be - * adjacent by garbage collectors. To reduce impact, we use field - * padding that works OK on common platforms; this effectively - * trades off slightly slower average field access for the sake of - * avoiding really bad worst-case access. (Until better JVM - * support is in place, this padding is dependent on transient - * properties of JVM field layout rules.) We also take care in - * allocating, sizing and resizing the array. Non-shared queue - * arrays are initialized by workers before use. Others are - * allocated on first use. - */ - 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; - - int seed; // for random scanning; initialize nonzero - volatile int eventCount; // encoded inactivation count; < 0 if inactive - int nextWait; // encoded record of next event waiter - int hint; // steal or signal hint (index) - int poolIndex; // index of this queue in pool (or 0) - final int mode; // 0: lifo, > 0: fifo, < 0: shared - int nsteals; // number of steals - 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 = mode; - this.seed = seed; - // 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, m, n; - if ((a = array) != null) { // ignore if queue removed - int j = (((m = a.length - 1) & s) << ASHIFT) + ABASE; - U.putOrderedObject(a, j, task); - if ((n = (top = s + 1) - base) <= 2) { - if ((p = pool) != null) - p.signalWork(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)) { - base = b + 1; - return t; - } - } - return null; - } - - /** - * Takes next task, if one exists, in FIFO order. - */ - final ForkJoinTask<?> poll() { - ForkJoinTask<?>[] a; int b; ForkJoinTask<?> t; - while ((b = base) - top < 0 && (a = array) != null) { - int j = (((a.length - 1) & b) << ASHIFT) + ABASE; - t = (ForkJoinTask<?>)U.getObjectVolatile(a, j); - if (t != null) { - if (base == b && - U.compareAndSwapObject(a, j, t, null)) { - base = 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); - } - - /** - * Computes next value for random probes. Scans don't require - * a very high quality generator, but also not a crummy one. - * Marsaglia xor-shift is cheap and works well enough. Note: - * This is manually inlined in its usages in ForkJoinPool to - * avoid writes inside busy scan loops. - */ - final int nextSeed() { - int r = seed; - r ^= r << 13; - r ^= r >>> 17; - return seed = r ^= r << 5; - } - - // Specialized execution methods - - /** - * Pops and runs tasks until empty. - */ - private void popAndExecAll() { - // A bit faster than repeated pop calls - ForkJoinTask<?>[] a; int m, s; long j; ForkJoinTask<?> t; - while ((a = array) != null && (m = a.length - 1) >= 0 && - (s = top - 1) - base >= 0 && - (t = ((ForkJoinTask<?>) - U.getObject(a, j = ((m & s) << ASHIFT) + ABASE))) - != null) { - if (U.compareAndSwapObject(a, j, t, null)) { - top = s; - t.doExec(); - } - } - } - - /** - * Polls and runs tasks until empty. - */ - private void pollAndExecAll() { - for (ForkJoinTask<?> t; (t = poll()) != null;) - 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 = true, removed = false, empty = true; - ForkJoinTask<?>[] a; int m, s, b, n; - if ((a = array) != null && (m = a.length - 1) >= 0 && - (n = (s = top) - (b = base)) > 0) { - for (ForkJoinTask<?> t;;) { // traverse from s to b - int j = ((--s & m) << ASHIFT) + ABASE; - t = (ForkJoinTask<?>)U.getObjectVolatile(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(); - return stat; - } - - /** - * Polls for and executes the given task or any other task in - * its CountedCompleter computation. - */ - final boolean pollAndExecCC(ForkJoinTask<?> root) { - ForkJoinTask<?>[] a; int b; Object o; - outer: while ((b = base) - top < 0 && (a = array) != null) { - long j = (((a.length - 1) & b) << ASHIFT) + ABASE; - if ((o = U.getObject(a, j)) == null || - !(o instanceof CountedCompleter)) - break; - for (CountedCompleter<?> t = (CountedCompleter<?>)o, r = t;;) { - if (r == root) { - if (base == b && - U.compareAndSwapObject(a, j, t, null)) { - base = b + 1; - t.doExec(); - return true; - } - else - break; // restart - } - if ((r = r.completer) == null) - break outer; // not part of root computation - } - } - return false; - } - - /** - * Executes a top-level task and any local tasks remaining - * after execution. - */ - final void runTask(ForkJoinTask<?> t) { - if (t != null) { - (currentSteal = t).doExec(); - currentSteal = null; - ++nsteals; - if (base - top < 0) { // process remaining local tasks - if (mode == 0) - popAndExecAll(); - else - pollAndExecAll(); - } - } - } - - /** - * Executes a non-top-level (stolen) task. - */ - final void runSubtask(ForkJoinTask<?> t) { - if (t != null) { - ForkJoinTask<?> ps = currentSteal; - (currentSteal = t).doExec(); - currentSteal = ps; - } - } - - /** - * 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 QLOCK; - private static final int ABASE; - private static final int ASHIFT; - static { - try { - U = getUnsafe(); - Class<?> k = WorkQueue.class; - Class<?> ak = ForkJoinTask[].class; - 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) - - /** - * Creates a new ForkJoinWorkerThread. This factory is used unless - * overridden in ForkJoinPool constructors. - */ - public static final ForkJoinWorkerThreadFactory - defaultForkJoinWorkerThreadFactory; - - /** - * 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; - - /** - * 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. Must equal common.parallelism. - */ - 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; - - // bounds for #steps in scan loop -- must be power 2 minus 1 - private static final int MIN_SCAN = 0x1ff; // cover estimation slop - private static final int MAX_SCAN = 0x1ffff; // 4 * max workers - - // Instance fields - - /* - * Field layout of this class tends to matter more than one would - * like. Runtime layout order is only loosely related to - * declaration order and may differ across JVMs, but the following - * empirically works OK on current JVMs. - */ - - // Heuristic padding to ameliorate unfortunate memory placements - volatile long pad00, pad01, pad02, pad03, pad04, pad05, pad06; - - 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 int config; // mode and parallelism level - WorkQueue[] workQueues; // main registry - final ForkJoinWorkerThreadFactory factory; - final Thread.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, r = 0, ps, nps; - for (;;) { - if (((ps = plock) & PL_LOCK) == 0 && - U.compareAndSwapInt(this, PLOCK, ps, nps = ps + PL_LOCK)) - return nps; - else if (r == 0) { // randomize spins if possible - Thread t = Thread.currentThread(); WorkQueue w; Submitter z; - if ((t instanceof ForkJoinWorkerThread) && - (w = ((ForkJoinWorkerThread)t).workQueue) != null) - r = w.seed; - else if ((z = submitters.get()) != null) - r = z.seed; - else - r = 1; - } - else if (spins >= 0) { - r ^= r << 1; r ^= r >>> 3; r ^= r << 10; // xorshift - if (r >= 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; - while ((u = (int)((c = ctl) >>> 32)) < 0 && - (u & SHORT_SIGN) != 0 && (int)c == 0) { - long nc = (long)(((u + UTC_UNIT) & UTC_MASK) | - ((u + UAC_UNIT) & UAC_MASK)) << 32; - 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 e) { - ex = e; - } - 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) { - Thread.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, config >>> 16, 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.eventCount = w.poolIndex = 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))); - 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; - w.qlock = -1; // ensure set - long ns = w.nsteals, sc; // collect steal count - do {} while (!U.compareAndSwapLong(this, STEALCOUNT, - sc = stealCount, sc + ns)); - 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 - - /** - * 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) { - WorkQueue[] ws; WorkQueue q; Submitter z; int m; ForkJoinTask<?>[] a; - if ((z = submitters.get()) != null && plock > 0 && - (ws = workQueues) != null && (m = (ws.length - 1)) >= 0 && - (q = ws[m & z.seed & SQMASK]) != null && - U.compareAndSwapInt(q, QLOCK, 0, 1)) { // lock - int b = q.base, s = q.top, n, an; - if ((a = q.array) != null && (an = a.length) > (n = s + 1 - b)) { - int j = (((an - 1) & s) << ASHIFT) + ABASE; - U.putOrderedObject(a, j, task); - q.top = s + 1; // push on to deque - q.qlock = 0; - if (n <= 2) - signalWork(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); - } - else if ((ps = plock) < 0) - throw new RejectedExecutionException(); - else if (ps == 0 || (ws = workQueues) == null || - (m = ws.length - 1) < 0) { // initialize workQueues - int p = config & SMASK; // 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(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); - 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; // try elsewhere while lock held - } - } - - // 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_UNIT)); - } - - /** - * Tries to create or activate a worker if too few are active. - * - * @param q the (non-null) queue holding tasks to be signalled - */ - final void signalWork(WorkQueue q) { - int hint = q.poolIndex; - long c; int e, u, i, n; WorkQueue[] ws; WorkQueue w; Thread p; - while ((u = (int)((c = ctl) >>> 32)) < 0) { - if ((e = (int)c) > 0) { - if ((ws = workQueues) != null && ws.length > (i = e & SMASK) && - (w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) { - long nc = (((long)(w.nextWait & E_MASK)) | - ((long)(u + UAC_UNIT) << 32)); - if (U.compareAndSwapLong(this, CTL, c, nc)) { - w.hint = hint; - w.eventCount = (e + E_SEQ) & E_MASK; - if ((p = w.parker) != null) - U.unpark(p); - break; - } - if (q.top - q.base <= 0) - break; - } - else - break; - } - else { - if ((short)u < 0) - tryAddWorker(); - break; - } - } - } - - // Scanning for tasks - - /** - * Top-level runloop for workers, called by ForkJoinWorkerThread.run. - */ - final void runWorker(WorkQueue w) { - w.growArray(); // allocate queue - do { w.runTask(scan(w)); } while (w.qlock >= 0); - } - - /** - * Scans for and, if found, returns 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, and relying on registerWorker to irregularly scatter - * them within array to avoid bias), 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 returns a task from this queue. Otherwise, if not - * activated, it signals workers (that may include itself) and - * returns so caller can retry. Also returns for true if the - * worker array may have changed during an empty scan. On failure - * to find a task, we take one of the following actions, after - * which the caller will retry calling this method unless - * terminated. - * - * * If pool is terminating, terminate the worker. - * - * * If not already enqueued, try to inactivate and enqueue the - * worker on wait queue. Or, if inactivating has caused the pool - * to be quiescent, relay to idleAwaitWork to possibly shrink - * pool. - * - * * If already enqueued and none of the above apply, possibly - * park awaiting signal, else lingering to help scan and signal. - * - * * If a non-empty queue discovered or left as a hint, - * help wake up other workers before return. - * - * @param w the worker (via its WorkQueue) - * @return a task or null if none found - */ - private final ForkJoinTask<?> scan(WorkQueue w) { - WorkQueue[] ws; int m; - int ps = plock; // read plock before ws - if (w != null && (ws = workQueues) != null && (m = ws.length - 1) >= 0) { - int ec = w.eventCount; // ec is negative if inactive - int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5; - w.hint = -1; // update seed and clear hint - int j = ((m + m + 1) | MIN_SCAN) & MAX_SCAN; - do { - WorkQueue q; ForkJoinTask<?>[] a; int b; - if ((q = ws[(r + j) & m]) != null && (b = q.base) - q.top < 0 && - (a = q.array) != null) { // probably nonempty - int i = (((a.length - 1) & b) << ASHIFT) + ABASE; - ForkJoinTask<?> t = (ForkJoinTask<?>) - U.getObjectVolatile(a, i); - if (q.base == b && ec >= 0 && t != null && - U.compareAndSwapObject(a, i, t, null)) { - if ((q.base = b + 1) - q.top < 0) - signalWork(q); - return t; // taken - } - else if ((ec < 0 || j < m) && (int)(ctl >> AC_SHIFT) <= 0) { - w.hint = (r + j) & m; // help signal below - break; // cannot take - } - } - } while (--j >= 0); - - int h, e, ns; long c, sc; WorkQueue q; - if ((ns = w.nsteals) != 0) { - if (U.compareAndSwapLong(this, STEALCOUNT, - sc = stealCount, sc + ns)) - w.nsteals = 0; // collect steals and rescan - } - else if (plock != ps) // consistency check - ; // skip - else if ((e = (int)(c = ctl)) < 0) - w.qlock = -1; // pool is terminating - else { - if ((h = w.hint) < 0) { - if (ec >= 0) { // try to enqueue/inactivate - long nc = (((long)ec | - ((c - AC_UNIT) & (AC_MASK|TC_MASK)))); - w.nextWait = e; // link and mark inactive - w.eventCount = ec | INT_SIGN; - if (ctl != c || !U.compareAndSwapLong(this, CTL, c, nc)) - w.eventCount = ec; // unmark on CAS failure - else if ((int)(c >> AC_SHIFT) == 1 - (config & SMASK)) - idleAwaitWork(w, nc, c); - } - else if (w.eventCount < 0 && ctl == c) { - Thread wt = Thread.currentThread(); - Thread.interrupted(); // clear status - U.putObject(wt, PARKBLOCKER, this); - w.parker = wt; // emulate LockSupport.park - if (w.eventCount < 0) // recheck - U.park(false, 0L); // block - w.parker = null; - U.putObject(wt, PARKBLOCKER, null); - } - } - if ((h >= 0 || (h = w.hint) >= 0) && - (ws = workQueues) != null && h < ws.length && - (q = ws[h]) != null) { // signal others before retry - WorkQueue v; Thread p; int u, i, s; - for (int n = (config & SMASK) - 1;;) { - int idleCount = (w.eventCount < 0) ? 0 : -1; - if (((s = idleCount - q.base + q.top) <= n && - (n = s) <= 0) || - (u = (int)((c = ctl) >>> 32)) >= 0 || - (e = (int)c) <= 0 || m < (i = e & SMASK) || - (v = ws[i]) == null) - break; - long nc = (((long)(v.nextWait & E_MASK)) | - ((long)(u + UAC_UNIT) << 32)); - if (v.eventCount != (e | INT_SIGN) || - !U.compareAndSwapLong(this, CTL, c, nc)) - break; - v.hint = h; - v.eventCount = (e + E_SEQ) & E_MASK; - if ((p = v.parker) != null) - U.unpark(p); - if (--n <= 0) - break; - } - } - } - } - return null; - } - - /** - * If inactivating worker 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 currentCtl the ctl value triggering possible quiescence - * @param prevCtl the ctl value to restore if thread is terminated - */ - private void idleAwaitWork(WorkQueue w, long currentCtl, long prevCtl) { - if (w != null && w.eventCount < 0 && - !tryTerminate(false, false) && (int)prevCtl != 0 && - ctl == currentCtl) { - int dc = -(short)(currentCtl >>> TC_SHIFT); - long parkTime = dc < 0 ? FAST_IDLE_TIMEOUT: (dc + 1) * IDLE_TIMEOUT; - long deadline = System.nanoTime() + parkTime - TIMEOUT_SLOP; - Thread wt = Thread.currentThread(); - while (ctl == currentCtl) { - Thread.interrupted(); // timed variant of version in scan() - U.putObject(wt, PARKBLOCKER, this); - w.parker = wt; - if (ctl == currentCtl) - U.park(false, parkTime); - w.parker = null; - U.putObject(wt, PARKBLOCKER, null); - if (ctl != currentCtl) - break; - if (deadline - System.nanoTime() <= 0L && - U.compareAndSwapLong(this, CTL, currentCtl, prevCtl)) { - w.eventCount = (w.eventCount + E_SEQ) | E_MASK; - w.hint = -1; - w.qlock = -1; // shrink - break; - } - } - } - } - - /** - * Scans through queues looking for work while joining a task; if - * any present, signals. May return early if more signalling is - * detectably unneeded. - * - * @param task return early if done - * @param origin an index to start scan - */ - private void helpSignal(ForkJoinTask<?> task, int origin) { - WorkQueue[] ws; WorkQueue w; Thread p; long c; int m, u, e, i, s; - if (task != null && task.status >= 0 && - (u = (int)(ctl >>> 32)) < 0 && (u >> UAC_SHIFT) < 0 && - (ws = workQueues) != null && (m = ws.length - 1) >= 0) { - outer: for (int k = origin, j = m; j >= 0; --j) { - WorkQueue q = ws[k++ & m]; - for (int n = m;;) { // limit to at most m signals - if (task.status < 0) - break outer; - if (q == null || - ((s = -q.base + q.top) <= n && (n = s) <= 0)) - break; - if ((u = (int)((c = ctl) >>> 32)) >= 0 || - (e = (int)c) <= 0 || m < (i = e & SMASK) || - (w = ws[i]) == null) - break outer; - long nc = (((long)(w.nextWait & E_MASK)) | - ((long)(u + UAC_UNIT) << 32)); - if (w.eventCount != (e | INT_SIGN)) - break outer; - if (U.compareAndSwapLong(this, CTL, c, nc)) { - w.eventCount = (e + E_SEQ) & E_MASK; - if ((p = w.parker) != null) - U.unpark(p); - if (--n <= 0) - break; - } - } - } - } - } - - /** - * 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 (joiner != null && task != null) { // hoist null 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 (t != null && v.base == b && - U.compareAndSwapObject(a, i, t, null)) { - v.base = b + 1; // help stealer - joiner.runSubtask(t); - } - else if (v.base == b && ++steps == MAX_HELP) - break restart; // v apparently stalled - } - 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 - * @param mode if shared, exit upon completing any task - * if all workers are active - */ - private int helpComplete(ForkJoinTask<?> task, int mode) { - WorkQueue[] ws; WorkQueue q; int m, n, s, u; - if (task != null && (ws = workQueues) != null && - (m = ws.length - 1) >= 0) { - for (int j = 1, origin = j;;) { - if ((s = task.status) < 0) - return s; - if ((q = ws[j & m]) != null && q.pollAndExecCC(task)) { - origin = j; - if (mode == SHARED_QUEUE && - ((u = (int)(ctl >>> 32)) >= 0 || (u >> UAC_SHIFT) >= 0)) - break; - } - else if ((j = (j + 2) & m) == origin) - break; - } - } - return 0; - } - - /** - * 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. - */ - final boolean tryCompensate() { - int pc = config & SMASK, e, i, tc; long c; - WorkQueue[] ws; WorkQueue w; Thread p; - if ((ws = workQueues) != null && (e = (int)(c = ctl)) >= 0) { - if (e != 0 && (i = e & SMASK) < ws.length && - (w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) { - long nc = ((long)(w.nextWait & E_MASK) | - (c & (AC_MASK|TC_MASK))); - if (U.compareAndSwapLong(this, CTL, c, nc)) { - w.eventCount = (e + E_SEQ) & E_MASK; - 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 (joiner != null && task != null && (s = task.status) >= 0) { - ForkJoinTask<?> prevJoin = joiner.currentJoin; - joiner.currentJoin = task; - do {} while ((s = task.status) >= 0 && !joiner.isEmpty() && - joiner.tryRemoveAndExec(task)); // process local tasks - if (s >= 0 && (s = task.status) >= 0) { - helpSignal(task, joiner.poolIndex); - if ((s = task.status) >= 0 && - (task instanceof CountedCompleter)) - s = helpComplete(task, LIFO_QUEUE); - } - while (s >= 0 && (s = task.status) >= 0) { - if ((!joiner.isEmpty() || // try helping - (s = tryHelpStealer(joiner, task)) == 0) && - (s = task.status) >= 0) { - helpSignal(task, joiner.poolIndex); - if ((s = task.status) >= 0 && tryCompensate()) { - 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; // re-activate - do {} while (!U.compareAndSwapLong - (this, CTL, c = ctl, c + 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 ((s = task.status) >= 0 && !joiner.isEmpty() && - joiner.tryRemoveAndExec(task)); - if (s >= 0 && (s = task.status) >= 0) { - helpSignal(task, joiner.poolIndex); - if ((s = task.status) >= 0 && - (task instanceof CountedCompleter)) - s = helpComplete(task, LIFO_QUEUE); - } - if (s >= 0 && joiner.isEmpty()) { - 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. - * @param r a (random) seed for scanning - */ - private WorkQueue findNonEmptyStealQueue(int r) { - 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) { - for (boolean active = true;;) { - long c; WorkQueue q; ForkJoinTask<?> t; int b; - while ((t = w.nextLocalTask()) != null) { - if (w.base - w.top < 0) - signalWork(w); - t.doExec(); - } - if ((q = findNonEmptyStealQueue(w.nextSeed())) != null) { - if (!active) { // re-establish active count - active = true; - do {} while (!U.compareAndSwapLong - (this, CTL, c = ctl, c + AC_UNIT)); - } - if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null) { - if (q.base - q.top < 0) - signalWork(q); - w.runSubtask(t); - } - } - else if (active) { // decrement active count without queuing - long nc = (c = ctl) - AC_UNIT; - if ((int)(nc >> AC_SHIFT) + (config & SMASK) == 0) - return; // bypass decrement-then-increment - if (U.compareAndSwapLong(this, CTL, c, nc)) - active = false; - } - else if ((int)((c = ctl) >> AC_SHIFT) + (config & SMASK) == 0 && - U.compareAndSwapLong(this, CTL, c, c + AC_UNIT)) - return; - } - } - - /** - * 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(w.nextSeed())) == null) - return null; - if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null) { - if (q.base - q.top < 0) - signalWork(q); - 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).config & SMASK; - int n = (q = wt.workQueue).top - q.base; - int a = (int)(pool.ctl >> AC_SHIFT) + p; - return n - (a > (p >>>= 1) ? 0 : - a > (p >>>= 1) ? 1 : - a > (p >>>= 1) ? 2 : - a > (p >>>= 1) ? 4 : - 8); - } - return 0; - } - - // Termination - - /** - * Possibly initiates and/or completes termination. 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) == -(config & SMASK)) { - 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) != -(config & SMASK)) - return false; - if ((ws = workQueues) != null) { - for (int i = 0; i < ws.length; ++i) { - if ((w = ws[i]) != null) { - if (!w.isEmpty()) { // signal unprocessed tasks - signalWork(w); - return false; - } - if ((i & 1) != 0 && w.eventCount >= 0) - return false; // unqueued inactive worker - } - } - } - } - 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() { - ForkJoinPool p; WorkQueue[] ws; int m; Submitter z; - 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. - */ - static boolean tryExternalUnpush(ForkJoinTask<?> t) { - ForkJoinPool p; WorkQueue[] ws; WorkQueue q; Submitter z; - ForkJoinTask<?>[] a; int m, s; - if (t != null && - (z = submitters.get()) != null && - (p = common) != null && - (ws = p.workQueues) != null && - (m = ws.length - 1) >= 0 && - (q = ws[m & z.seed & SQMASK]) != null && - (s = q.top) != q.base && - (a = q.array) != null) { - long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE; - if (U.getObject(a, j) == t && - U.compareAndSwapInt(q, QLOCK, 0, 1)) { - if (q.array == a && q.top == s && // recheck - U.compareAndSwapObject(a, j, t, null)) { - q.top = s - 1; - q.qlock = 0; - return true; - } - q.qlock = 0; - } - } - return false; - } - - /** - * Tries to pop and run local tasks within the same computation - * as the given root. On failure, tries to help complete from - * other queues via helpComplete. - */ - private void externalHelpComplete(WorkQueue q, ForkJoinTask<?> root) { - ForkJoinTask<?>[] a; int m; - if (q != null && (a = q.array) != null && (m = (a.length - 1)) >= 0 && - root != null && root.status >= 0) { - for (;;) { - int s, u; Object o; CountedCompleter<?> task = null; - if ((s = q.top) - q.base > 0) { - long j = ((m & (s - 1)) << ASHIFT) + ABASE; - if ((o = U.getObject(a, j)) != null && - (o instanceof CountedCompleter)) { - CountedCompleter<?> t = (CountedCompleter<?>)o, r = t; - do { - if (r == root) { - if (U.compareAndSwapInt(q, QLOCK, 0, 1)) { - if (q.array == a && q.top == s && - U.compareAndSwapObject(a, j, t, null)) { - q.top = s - 1; - task = t; - } - q.qlock = 0; - } - break; - } - } while ((r = r.completer) != null); - } - } - if (task != null) - task.doExec(); - if (root.status < 0 || - (u = (int)(ctl >>> 32)) >= 0 || (u >> UAC_SHIFT) >= 0) - break; - if (task == null) { - helpSignal(root, q.poolIndex); - if (root.status >= 0) - helpComplete(root, SHARED_QUEUE); - break; - } - } - } - } - - /** - * Tries to help execute or signal availability of the given task - * from submitter's queue in common pool. - */ - static void externalHelpJoin(ForkJoinTask<?> t) { - // Some hard-to-avoid overlap with tryExternalUnpush - ForkJoinPool p; WorkQueue[] ws; WorkQueue q, w; Submitter z; - ForkJoinTask<?>[] a; int m, s, n; - if (t != null && - (z = submitters.get()) != null && - (p = common) != null && - (ws = p.workQueues) != null && - (m = ws.length - 1) >= 0 && - (q = ws[m & z.seed & SQMASK]) != null && - (a = q.array) != null) { - int am = a.length - 1; - if ((s = q.top) != q.base) { - long j = ((am & (s - 1)) << ASHIFT) + ABASE; - if (U.getObject(a, j) == t && - U.compareAndSwapInt(q, QLOCK, 0, 1)) { - if (q.array == a && q.top == s && - U.compareAndSwapObject(a, j, t, null)) { - q.top = s - 1; - q.qlock = 0; - t.doExec(); - } - else - q.qlock = 0; - } - } - if (t.status >= 0) { - if (t instanceof CountedCompleter) - p.externalHelpComplete(q, t); - else - p.helpSignal(t, q.poolIndex); - } - } - } - - // Exported methods - - // Constructors - - /** - * Creates a {@code ForkJoinPool} with parallelism equal to {@link - * java.lang.Runtime#availableProcessors}, using the {@linkplain - * #defaultForkJoinWorkerThreadFactory default thread factory}, - * no UncaughtExceptionHandler, and non-async LIFO processing mode. - * - * @throws SecurityException if a security manager exists and - * the caller is not permitted to modify threads - * because it does not hold {@link - * java.lang.RuntimePermission}{@code ("modifyThread")} - */ - public ForkJoinPool() { - this(Math.min(MAX_CAP, Runtime.getRuntime().availableProcessors()), - defaultForkJoinWorkerThreadFactory, null, false); - } - - /** - * Creates a {@code ForkJoinPool} with the indicated parallelism - * level, the {@linkplain - * #defaultForkJoinWorkerThreadFactory default thread factory}, - * no UncaughtExceptionHandler, and non-async LIFO processing mode. - * - * @param parallelism the parallelism level - * @throws IllegalArgumentException if parallelism less than or - * equal to zero, or greater than implementation limit - * @throws SecurityException if a security manager exists and - * the caller is not permitted to modify threads - * because it does not hold {@link - * java.lang.RuntimePermission}{@code ("modifyThread")} - */ - public ForkJoinPool(int parallelism) { - this(parallelism, defaultForkJoinWorkerThreadFactory, null, false); - } - - /** - * Creates a {@code ForkJoinPool} with the given parameters. - * - * @param parallelism the parallelism level. For default value, - * use {@link java.lang.Runtime#availableProcessors}. - * @param factory the factory for creating new threads. For default value, - * use {@link #defaultForkJoinWorkerThreadFactory}. - * @param handler the handler for internal worker threads that - * terminate due to unrecoverable errors encountered while executing - * tasks. For default value, use {@code null}. - * @param asyncMode if true, - * establishes local first-in-first-out scheduling mode for forked - * tasks that are never joined. This mode may be more appropriate - * than default locally stack-based mode in applications in which - * worker threads only process event-style asynchronous tasks. - * For default value, use {@code false}. - * @throws IllegalArgumentException if parallelism less than or - * equal to zero, or greater than implementation limit - * @throws NullPointerException if the factory is null - * @throws SecurityException if a security manager exists and - * the caller is not permitted to modify threads - * because it does not hold {@link - * java.lang.RuntimePermission}{@code ("modifyThread")} - */ - public ForkJoinPool(int parallelism, - ForkJoinWorkerThreadFactory factory, - Thread.UncaughtExceptionHandler handler, - boolean asyncMode) { - checkPermission(); - if (factory == null) - throw new NullPointerException(); - if (parallelism <= 0 || parallelism > MAX_CAP) - throw new IllegalArgumentException(); - this.factory = factory; - this.ueh = handler; - this.config = parallelism | (asyncMode ? (FIFO_QUEUE << 16) : 0); - long np = (long)(-parallelism); // offset ctl counts - this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK); - int pn = nextPoolId(); - StringBuilder sb = new StringBuilder("ForkJoinPool-"); - sb.append(Integer.toString(pn)); - sb.append("-worker-"); - this.workerNamePrefix = sb.toString(); - } - - /** - * Constructor for common pool, suitable only for static initialization. - * Basically the same as above, but uses smallest possible initial footprint. - */ - ForkJoinPool(int parallelism, long ctl, - ForkJoinWorkerThreadFactory factory, - Thread.UncaughtExceptionHandler handler) { - this.config = parallelism; - this.ctl = ctl; - this.factory = factory; - this.ueh = handler; - this.workerNamePrefix = "ForkJoinPool.commonPool-worker-"; - } - - /** - * 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}, before - * exit. - * - * @return the common pool instance - * @since 1.8 - */ - public static ForkJoinPool commonPool() { - // assert common != null : "static init error"; - return common; - } - - // Execution methods - - /** - * Performs the given task, returning its result upon completion. - * If the computation encounters an unchecked Exception or Error, - * it is rethrown as the outcome of this invocation. Rethrown - * exceptions behave in the same way as regular exceptions, but, - * when possible, contain stack traces (as displayed for example - * using {@code ex.printStackTrace()}) of both the current thread - * as well as the thread actually encountering the exception; - * minimally only the latter. - * - * @param task the task - * @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.AdaptedRunnableAction(task); - externalPush(job); - } - - /** - * Submits a ForkJoinTask for execution. - * - * @param task the task to submit - * @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 Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { - return ueh; - } - - /** - * Returns the targeted parallelism level of this pool. - * - * @return the targeted parallelism level of this pool - */ - public int getParallelism() { - return config & SMASK; - } - - /** - * Returns the targeted parallelism level of the common pool. - * - * @return the targeted parallelism level of the common pool - * @since 1.8 - */ - public static int getCommonPoolParallelism() { - return commonParallelism; - } - - /** - * Returns the number of worker threads that have started but not - * yet terminated. The result returned by this method may differ - * from {@link #getParallelism} when threads are created to - * maintain parallelism when others are cooperatively blocked. - * - * @return the number of worker threads - */ - public int getPoolSize() { - return (config & SMASK) + (short)(ctl >>> TC_SHIFT); - } - - /** - * Returns {@code true} if this pool uses local first-in-first-out - * scheduling mode for forked tasks that are never joined. - * - * @return {@code true} if this pool uses async mode - */ - public boolean getAsyncMode() { - return (config >>> 16) == 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 = (config & SMASK) + (int)(ctl >> AC_SHIFT); - return (r <= 0) ? 0 : r; // suppress momentarily negative values - } - - /** - * Returns {@code true} if all worker threads are currently idle. - * An idle worker is one that cannot obtain a task to execute - * because none are available to steal from other threads, and - * there are no pending submissions to the pool. This method is - * conservative; it might not return {@code true} immediately upon - * idleness of all threads, but will eventually become true if - * threads remain inactive. - * - * @return {@code true} if all threads are currently idle - */ - public boolean isQuiescent() { - return (int)(ctl >> AC_SHIFT) + (config & SMASK) == 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 = (config & SMASK); - 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 {@link #commonPool()}, and no additional effect if - * already shut down. Tasks that are in the process of being - * submitted concurrently during the course of this method may or - * may not be rejected. - * - * @throws SecurityException if a security manager exists and - * the caller is not permitted to modify threads - * because it does not hold {@link - * java.lang.RuntimePermission}{@code ("modifyThread")} - */ - public void shutdown() { - checkPermission(); - tryTerminate(false, true); - } - - /** - * Possibly attempts to cancel and/or stop all tasks, and reject - * all subsequently submitted tasks. Invocation has no effect on - * execution state if this is the {@link #commonPool()}, and no - * additional effect if already shut down. Otherwise, tasks that - * are in the process of being submitted or executed concurrently - * during the course of this method may or may not be - * rejected. This method cancels both existing and unexecuted - * tasks, in order to permit termination in the presence of task - * dependencies. So the method always returns an empty list - * (unlike the case for some other Executors). - * - * @return an empty list - * @throws SecurityException if a security manager exists and - * the caller is not permitted to modify threads - * because it does not hold {@link - * java.lang.RuntimePermission}{@code ("modifyThread")} - */ - public List<Runnable> shutdownNow() { - checkPermission(); - tryTerminate(true, true); - return Collections.emptyList(); - } - - /** - * Returns {@code true} if all tasks have completed following shut down. - * - * @return {@code true} if all tasks have completed following shut down - */ - public boolean isTerminated() { - long c = ctl; - return ((c & STOP_BIT) != 0L && - (short)(c >>> TC_SHIFT) == -(config & SMASK)); - } - - /** - * 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) != -(config & SMASK)); - } - - /** - * 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 {@link - * #commonPool()} never terminates until program shutdown, when - * applied to the common pool, this method is equivalent to {@link - * #awaitQuiescence} 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; - long startTime = System.nanoTime(); - boolean terminated = false; - synchronized (this) { - for (long waitTime = nanos, millis = 0L;;) { - if (terminated = isTerminated() || - waitTime <= 0L || - (millis = unit.toMillis(waitTime)) <= 0L) - break; - wait(millis); - waitTime = nanos - (System.nanoTime() - startTime); - } - } - return terminated; - } - - /** - * 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) { - if (q.base - q.top < 0) - signalWork(q); - t.doExec(); - } - break; - } - } - } - return true; - } - - /** - * Waits and/or attempts to assist performing tasks indefinitely - * until the {@link #commonPool()} {@link #isQuiescent}. - */ - static void quiesceCommonPool() { - common.awaitQuiescence(Long.MAX_VALUE, TimeUnit.NANOSECONDS); - } - - /** - * Interface for extending managed parallelism for tasks running - * in {@link ForkJoinPool}s. - * - * <p>A {@code ManagedBlocker} provides two methods. Method - * {@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}. 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. - */ - 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()) { // variant of helpSignal - WorkQueue[] ws; WorkQueue q; int m, u; - if ((ws = p.workQueues) != null && (m = ws.length - 1) >= 0) { - for (int i = 0; i <= m; ++i) { - if (blocker.isReleasable()) - return; - if ((q = ws[i]) != null && q.base - q.top < 0) { - p.signalWork(q); - if ((u = (int)(p.ctl >>> 32)) >= 0 || - (u >> UAC_SHIFT) >= 0) - break; - } - } - } - if (p.tryCompensate()) { - 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 QLOCK; - - static { - // initialize field offsets for CAS etc - try { - U = 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; - 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>(); - ForkJoinWorkerThreadFactory fac = defaultForkJoinWorkerThreadFactory = - new DefaultForkJoinWorkerThreadFactory(); - modifyThreadPermission = new RuntimePermission("modifyThread"); - - /* - * Establish common pool parameters. For extra caution, - * computations to set up common pool state are here; the - * constructor just assigns these values to fields. - */ - - int par = 0; - Thread.UncaughtExceptionHandler handler = null; - try { // TBD: limit or report ignored exceptions? - String pp = System.getProperty - ("java.util.concurrent.ForkJoinPool.common.parallelism"); - String hp = System.getProperty - ("java.util.concurrent.ForkJoinPool.common.exceptionHandler"); - String fp = System.getProperty - ("java.util.concurrent.ForkJoinPool.common.threadFactory"); - if (fp != null) - fac = ((ForkJoinWorkerThreadFactory)ClassLoader. - getSystemClassLoader().loadClass(fp).newInstance()); - if (hp != null) - handler = ((Thread.UncaughtExceptionHandler)ClassLoader. - getSystemClassLoader().loadClass(hp).newInstance()); - if (pp != null) - par = Integer.parseInt(pp); - } catch (Exception ignore) { - } - - if (par <= 0) - par = Runtime.getRuntime().availableProcessors(); - if (par > MAX_CAP) - par = MAX_CAP; - commonParallelism = par; - long np = (long)(-par); // precompute initial ctl value - long ct = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK); - - common = new ForkJoinPool(par, ct, fac, handler); - } - - /** - * Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. - * Replace with a simple call to Unsafe.getUnsafe when integrating - * into a jdk. - * - * @return a sun.misc.Unsafe - */ - private static sun.misc.Unsafe getUnsafe() { - return scala.concurrent.util.Unsafe.instance; - } -} |