--- jsr166/src/jsr166y/ForkJoinPool.java 2009/07/24 23:47:01 1.21 +++ jsr166/src/jsr166y/ForkJoinPool.java 2009/08/03 13:01:15 1.42 @@ -5,55 +5,85 @@ */ package jsr166y; -import java.util.*; + import java.util.concurrent.*; -import java.util.concurrent.locks.*; -import java.util.concurrent.atomic.*; + +import java.util.ArrayList; +import java.util.Arrays; +import java.util.Collection; +import java.util.Collections; +import java.util.List; +import java.util.concurrent.locks.Condition; +import java.util.concurrent.locks.LockSupport; +import java.util.concurrent.locks.ReentrantLock; +import java.util.concurrent.atomic.AtomicInteger; +import java.util.concurrent.atomic.AtomicLong; /** - * An {@link ExecutorService} for running {@link ForkJoinTask}s. A - * ForkJoinPool provides the entry point for submissions from - * non-ForkJoinTasks, as well as management and monitoring operations. - * Normally a single ForkJoinPool is used for a large number of - * submitted tasks. Otherwise, use would not usually outweigh the - * construction and bookkeeping overhead of creating a large set of - * threads. + * An {@link ExecutorService} for running {@link ForkJoinTask}s. + * A {@code ForkJoinPool} provides the entry point for submissions + * from non-{@code ForkJoinTask}s, as well as management and + * monitoring operations. * - *

ForkJoinPools differ from other kinds of Executors mainly in - * that they provide work-stealing: all threads in the pool - * attempt to find and execute subtasks created by other active tasks - * (eventually blocking if none exist). This makes them efficient when - * most tasks spawn other subtasks (as do most ForkJoinTasks), as well - * as the mixed execution of some plain Runnable- or Callable- based - * activities along with ForkJoinTasks. When setting - * {@code setAsyncMode}, a ForkJoinPools may also be appropriate for - * use with fine-grained tasks that are never joined. Otherwise, other - * ExecutorService implementations are typically more appropriate - * choices. + *

A {@code ForkJoinPool} differs from other kinds of {@link + * ExecutorService} mainly by virtue of employing + * work-stealing: all threads in the pool attempt to find and + * execute subtasks 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). A {@code ForkJoinPool} may also be used for mixed + * execution of some plain {@code Runnable}- or {@code Callable}- + * based activities along with {@code ForkJoinTask}s. When setting + * {@linkplain #setAsyncMode async mode}, a {@code ForkJoinPool} may + * also be appropriate for use with fine-grained tasks of any form + * that are never joined. Otherwise, other {@code ExecutorService} + * implementations are typically more appropriate choices. * - *

A ForkJoinPool may be constructed with a given parallelism level - * (target pool size), which it attempts to maintain by dynamically - * adding, suspending, or resuming threads, even if some tasks are - * waiting to join others. However, no such adjustments are performed - * in the face of blocked IO or other unmanaged synchronization. The - * nested {@code ManagedBlocker} interface enables extension of - * the kinds of synchronization accommodated. The target parallelism - * level may also be changed dynamically ({@code setParallelism}) - * and thread construction can be limited using methods - * {@code setMaximumPoolSize} and/or - * {@code setMaintainsParallelism}. + *

A {@code ForkJoinPool} is constructed with a given target + * parallelism level; by default, equal to the number of available + * processors. Unless configured otherwise via {@link + * #setMaintainsParallelism}, the pool attempts to maintain this + * number of active (or available) threads by dynamically adding, + * suspending, or resuming internal worker threads, even if some tasks + * are waiting to join others. However, no such adjustments are + * performed in the face of blocked IO or other unmanaged + * synchronization. The nested {@link ManagedBlocker} interface + * enables extension of the kinds of synchronization accommodated. + * The target parallelism level may also be changed dynamically + * ({@link #setParallelism}). The total number of threads may be + * limited using method {@link #setMaximumPoolSize}, in which case it + * may become possible for the activities of a pool to stall due to + * the lack of available threads to process new tasks. * *

In addition to execution and lifecycle control methods, this * class provides status check methods (for example - * {@code getStealCount}) that are intended to aid in developing, + * {@link #getStealCount}) that are intended to aid in developing, * tuning, and monitoring fork/join applications. Also, method - * {@code toString} returns indications of pool state in a + * {@link #toString} returns indications of pool state in a * convenient form for informal monitoring. * + *

Sample Usage. Normally a single {@code ForkJoinPool} is + * used for all parallel task execution in a program or subsystem. + * Otherwise, use would not usually outweigh the construction and + * bookkeeping overhead of creating a large set of threads. For + * example a common pool could be used for the {@code SortTasks} + * illustrated in {@link RecursiveAction}. Because {@code + * ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon + * daemon} mode, there is typically no need to explictly {@link + * #shutdown} such a pool upon program exit. + * + * 

+ * static final ForkJoinPool mainPool = new ForkJoinPool();
+ * ...
+ * public void sort(long[] array) {
+ *   mainPool.invoke(new SortTask(array, 0, array.length));
+ * }
+ *
+ * *

Implementation notes: This implementation restricts the * maximum number of running threads to 32767. Attempts to create * pools with greater than the maximum result in - * IllegalArgumentExceptions. + * {@code IllegalArgumentException}. * * @since 1.7 * @author Doug Lea @@ -72,10 +102,10 @@ public class ForkJoinPool extends Abstra private static final int MAX_THREADS = 0x7FFF; /** - * Factory for creating new ForkJoinWorkerThreads. A - * ForkJoinWorkerThreadFactory must be defined and used for - * ForkJoinWorkerThread subclasses that extend base functionality - * or initialize threads with different contexts. + * 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 { /** @@ -302,8 +332,8 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if argument represents zero active count and - * nonzero runstate, which is the triggering condition for + * Returns {@code true} if argument represents zero active count + * and nonzero runstate, which is the triggering condition for * terminating on shutdown. */ private static boolean canTerminateOnShutdown(int c) { @@ -333,9 +363,9 @@ public class ForkJoinPool extends Abstra // Constructors /** - * Creates a ForkJoinPool with a pool size equal to the number of - * processors available on the system, using the default - * ForkJoinWorkerThreadFactory. + * Creates a {@code ForkJoinPool} with parallelism equal to {@link + * java.lang.Runtime#availableProcessors}, and using the {@linkplain + * #defaultForkJoinWorkerThreadFactory default thread factory}. * * @throws SecurityException if a security manager exists and * the caller is not permitted to modify threads @@ -348,10 +378,11 @@ public class ForkJoinPool extends Abstra } /** - * Creates a ForkJoinPool with the indicated parallelism level - * threads and using the default ForkJoinWorkerThreadFactory. + * Creates a {@code ForkJoinPool} with the indicated parallelism + * level and using the {@linkplain + * #defaultForkJoinWorkerThreadFactory default thread factory}. * - * @param parallelism the number of worker threads + * @param parallelism the parallelism level * @throws IllegalArgumentException if parallelism less than or * equal to zero * @throws SecurityException if a security manager exists and @@ -364,9 +395,9 @@ public class ForkJoinPool extends Abstra } /** - * Creates a ForkJoinPool with parallelism equal to the number of - * processors available on the system and using the given - * ForkJoinWorkerThreadFactory. + * Creates a {@code ForkJoinPool} with parallelism equal to {@link + * java.lang.Runtime#availableProcessors}, and using the given + * thread factory. * * @param factory the factory for creating new threads * @throws NullPointerException if factory is null @@ -380,9 +411,10 @@ public class ForkJoinPool extends Abstra } /** - * Creates a ForkJoinPool with the given parallelism and factory. + * Creates a {@code ForkJoinPool} with the given parallelism and + * thread factory. * - * @param parallelism the targeted number of worker threads + * @param parallelism the parallelism level * @param factory the factory for creating new threads * @throws IllegalArgumentException if parallelism less than or * equal to zero, or greater than implementation limit @@ -414,7 +446,7 @@ public class ForkJoinPool extends Abstra * Creates a new worker thread using factory. * * @param index the index to assign worker - * @return new worker, or null of factory failed + * @return new worker, or null if factory failed */ private ForkJoinWorkerThread createWorker(int index) { Thread.UncaughtExceptionHandler h = ueh; @@ -435,8 +467,16 @@ public class ForkJoinPool extends Abstra * Currently requires size to be a power of two. */ private static int arraySizeFor(int poolSize) { - return (poolSize <= 1) ? 1 : - (1 << (32 - Integer.numberOfLeadingZeros(poolSize-1))); + if (poolSize <= 1) + return 1; + // See Hackers Delight, sec 3.2 + int c = poolSize >= MAX_THREADS ? MAX_THREADS : (poolSize - 1); + c |= c >>> 1; + c |= c >>> 2; + c |= c >>> 4; + c |= c >>> 8; + c |= c >>> 16; + return c + 1; } /** @@ -539,6 +579,8 @@ public class ForkJoinPool extends Abstra * Common code for execute, invoke and submit */ private void doSubmit(ForkJoinTask task) { + if (task == null) + throw new NullPointerException(); if (isShutdown()) throw new RejectedExecutionException(); if (workers == null) @@ -567,93 +609,63 @@ public class ForkJoinPool extends Abstra * @throws NullPointerException if task is null * @throws RejectedExecutionException if pool is shut down */ - public void execute(ForkJoinTask task) { + public void execute(ForkJoinTask task) { doSubmit(task); } // AbstractExecutorService methods public void execute(Runnable task) { - doSubmit(new AdaptedRunnable(task, null)); + ForkJoinTask job; + if (task instanceof ForkJoinTask) // avoid re-wrap + job = (ForkJoinTask) task; + else + job = ForkJoinTask.adapt(task, null); + doSubmit(job); } public ForkJoinTask submit(Callable task) { - ForkJoinTask job = new AdaptedCallable(task); + ForkJoinTask job = ForkJoinTask.adapt(task); doSubmit(job); return job; } public ForkJoinTask submit(Runnable task, T result) { - ForkJoinTask job = new AdaptedRunnable(task, result); + ForkJoinTask job = ForkJoinTask.adapt(task, result); doSubmit(job); return job; } public ForkJoinTask submit(Runnable task) { - ForkJoinTask job = new AdaptedRunnable(task, null); + ForkJoinTask job; + if (task instanceof ForkJoinTask) // avoid re-wrap + job = (ForkJoinTask) task; + else + job = ForkJoinTask.adapt(task, null); doSubmit(job); return job; } /** - * Adaptor for Runnables. This implements RunnableFuture - * to be compliant with AbstractExecutorService constraints. + * Submits a ForkJoinTask for execution. + * + * @param task the task to submit + * @return the task + * @throws RejectedExecutionException if the task cannot be + * scheduled for execution + * @throws NullPointerException if the task is null */ - static final class AdaptedRunnable extends ForkJoinTask - implements RunnableFuture { - final Runnable runnable; - final T resultOnCompletion; - T result; - AdaptedRunnable(Runnable runnable, T result) { - if (runnable == null) throw new NullPointerException(); - this.runnable = runnable; - this.resultOnCompletion = result; - } - public T getRawResult() { return result; } - public void setRawResult(T v) { result = v; } - public boolean exec() { - runnable.run(); - result = resultOnCompletion; - return true; - } - public void run() { invoke(); } - private static final long serialVersionUID = 5232453952276885070L; + public ForkJoinTask submit(ForkJoinTask task) { + doSubmit(task); + return task; } - /** - * Adaptor for Callables - */ - static final class AdaptedCallable extends ForkJoinTask - implements RunnableFuture { - final Callable callable; - T result; - AdaptedCallable(Callable callable) { - if (callable == null) throw new NullPointerException(); - this.callable = callable; - } - public T getRawResult() { return result; } - public void setRawResult(T v) { result = v; } - public boolean exec() { - try { - result = callable.call(); - return true; - } catch (Error err) { - throw err; - } catch (RuntimeException rex) { - throw rex; - } catch (Exception ex) { - throw new RuntimeException(ex); - } - } - public void run() { invoke(); } - private static final long serialVersionUID = 2838392045355241008L; - } public List> invokeAll(Collection> tasks) { ArrayList> forkJoinTasks = new ArrayList>(tasks.size()); for (Callable task : tasks) - forkJoinTasks.add(new AdaptedCallable(task)); + forkJoinTasks.add(ForkJoinTask.adapt(task)); invoke(new InvokeAll(forkJoinTasks)); @SuppressWarnings({"unchecked", "rawtypes"}) @@ -686,7 +698,7 @@ public class ForkJoinPool extends Abstra * Returns the handler for internal worker threads that terminate * due to unrecoverable errors encountered while executing tasks. * - * @return the handler, or null if none + * @return the handler, or {@code null} if none */ public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { Thread.UncaughtExceptionHandler h; @@ -707,7 +719,7 @@ public class ForkJoinPool extends Abstra * as handler. * * @param h the new handler - * @return the old handler, or null if none + * @return the old handler, or {@code null} if none * @throws SecurityException if a security manager exists and * the caller is not permitted to modify threads * because it does not hold {@link @@ -755,7 +767,7 @@ public class ForkJoinPool extends Abstra final ReentrantLock lock = this.workerLock; lock.lock(); try { - if (!isTerminating()) { + if (isProcessingTasks()) { int p = this.parallelism; this.parallelism = parallelism; if (parallelism > p) @@ -770,9 +782,9 @@ public class ForkJoinPool extends Abstra } /** - * Returns the targeted number of worker threads in this pool. + * Returns the targeted parallelism level of this pool. * - * @return the targeted number of worker threads in this pool + * @return the targeted parallelism level of this pool */ public int getParallelism() { return parallelism; @@ -781,7 +793,7 @@ public class ForkJoinPool extends Abstra /** * Returns the number of worker threads that have started but not * yet terminated. This result returned by this method may differ - * from {@code getParallelism} when threads are created to + * from {@link #getParallelism} when threads are created to * maintain parallelism when others are cooperatively blocked. * * @return the number of worker threads @@ -792,7 +804,9 @@ public class ForkJoinPool extends Abstra /** * Returns the maximum number of threads allowed to exist in the - * pool, even if there are insufficient unblocked running threads. + * pool. Unless set using {@link #setMaximumPoolSize}, the + * maximum is an implementation-defined value designed only to + * prevent runaway growth. * * @return the maximum */ @@ -802,11 +816,10 @@ public class ForkJoinPool extends Abstra /** * Sets the maximum number of threads allowed to exist in the - * pool, even if there are insufficient unblocked running threads. - * Setting this value has no effect on current pool size. It - * controls construction of new threads. + * pool. Setting this value has no effect on current pool + * size. It controls construction of new threads. * - * @throws IllegalArgumentException if negative or greater then + * @throws IllegalArgumentException if negative or greater than * internal implementation limit */ public void setMaximumPoolSize(int newMax) { @@ -817,12 +830,11 @@ public class ForkJoinPool extends Abstra /** - * Returns true if this pool dynamically maintains its target - * parallelism level. If false, new threads are added only to - * avoid possible starvation. - * This setting is by default true. + * Returns {@code true} if this pool dynamically maintains its + * target parallelism level. If false, new threads are added only + * to avoid possible starvation. This setting is by default true. * - * @return true if maintains parallelism + * @return {@code true} if maintains parallelism */ public boolean getMaintainsParallelism() { return maintainsParallelism; @@ -833,7 +845,7 @@ public class ForkJoinPool extends Abstra * parallelism level. If false, new threads are added only to * avoid possible starvation. * - * @param enable true to maintains parallelism + * @param enable {@code true} to maintain parallelism */ public void setMaintainsParallelism(boolean enable) { maintainsParallelism = enable; @@ -844,12 +856,13 @@ public class ForkJoinPool extends Abstra * 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 asynchronous tasks. This method is - * designed to be invoked only when pool is quiescent, and + * designed to be invoked only when the pool is quiescent, and * typically only before any tasks are submitted. The effects of * invocations at other times may be unpredictable. * - * @param async if true, use locally FIFO scheduling + * @param async if {@code true}, use locally FIFO scheduling * @return the previous mode + * @see #getAsyncMode */ public boolean setAsyncMode(boolean async) { boolean oldMode = locallyFifo; @@ -866,10 +879,11 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if this pool uses local first-in-first-out + * Returns {@code true} if this pool uses local first-in-first-out * scheduling mode for forked tasks that are never joined. * - * @return true if this pool uses async mode + * @return {@code true} if this pool uses async mode + * @see #setAsyncMode */ public boolean getAsyncMode() { return locallyFifo; @@ -910,15 +924,15 @@ public class ForkJoinPool extends Abstra } /** - * Returns 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 true immediately upon idleness of all - * threads, but will eventually become true if threads remain - * inactive. + * 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 true if all threads are currently idle + * @return {@code true} if all threads are currently idle */ public boolean isQuiescent() { return activeCountOf(runControl) == 0; @@ -973,8 +987,8 @@ public class ForkJoinPool extends Abstra } /** - * Returns an estimate of the number tasks submitted to this pool - * that have not yet begun executing. This method takes time + * Returns an estimate of the number of tasks submitted to this + * pool that have not yet begun executing. This method takes time * proportional to the number of submissions. * * @return the number of queued submissions @@ -984,8 +998,8 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if there are any tasks submitted to this pool - * that have not yet begun executing. + * 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 */ @@ -998,7 +1012,7 @@ public class ForkJoinPool extends Abstra * 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 null if none + * @return the next submission, or {@code null} if none */ protected ForkJoinTask pollSubmission() { return submissionQueue.poll(); @@ -1008,8 +1022,8 @@ public class ForkJoinPool extends Abstra * 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 + * 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 @@ -1021,7 +1035,7 @@ public class ForkJoinPool extends Abstra * @param c the collection to transfer elements into * @return the number of elements transferred */ - protected int drainTasksTo(Collection> c) { + protected int drainTasksTo(Collection> c) { int n = submissionQueue.drainTo(c); ForkJoinWorkerThread[] ws = workers; if (ws != null) { @@ -1087,19 +1101,33 @@ public class ForkJoinPool extends Abstra public void shutdown() { checkPermission(); transitionRunStateTo(SHUTDOWN); - if (canTerminateOnShutdown(runControl)) + if (canTerminateOnShutdown(runControl)) { + if (workers == null) { // shutting down before workers created + final ReentrantLock lock = this.workerLock; + lock.lock(); + try { + if (workers == null) { + terminate(); + transitionRunStateTo(TERMINATED); + termination.signalAll(); + } + } finally { + lock.unlock(); + } + } terminateOnShutdown(); + } } /** - * Attempts to stop all actively executing tasks, and cancels all - * waiting tasks. Tasks that are in the process of being - * submitted or executed concurrently during the course of this - * method may or may not be rejected. Unlike some other executors, - * this method cancels rather than collects non-executed tasks - * upon termination, so always returns an empty list. However, you - * can use method {@code drainTasksTo} before invoking this - * method to transfer unexecuted tasks to another collection. + * Attempts to cancel and/or stop all tasks, and reject all + * subsequently submitted tasks. 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 @@ -1124,12 +1152,16 @@ public class ForkJoinPool extends Abstra /** * Returns {@code true} if the process of termination has - * commenced but possibly not yet completed. + * 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, causing this executor not + * to properly terminate. * - * @return {@code true} if terminating + * @return {@code true} if terminating but not yet terminated */ public boolean isTerminating() { - return runStateOf(runControl) >= TERMINATING; + return runStateOf(runControl) == TERMINATING; } /** @@ -1142,6 +1174,14 @@ public class ForkJoinPool extends Abstra } /** + * Returns true if pool is not terminating or terminated. + * Used internally to suppress execution when terminating. + */ + final boolean isProcessingTasks() { + return runStateOf(runControl) < TERMINATING; + } + + /** * Blocks until all tasks have completed execution after a shutdown * request, or the timeout occurs, or the current thread is * interrupted, whichever happens first. @@ -1195,7 +1235,7 @@ public class ForkJoinPool extends Abstra transitionRunStateTo(TERMINATED); termination.signalAll(); } - else if (!isTerminating()) { + else if (isProcessingTasks()) { tryShrinkWorkerArray(); tryResumeSpare(true); // allow replacement } @@ -1436,7 +1476,7 @@ public class ForkJoinPool extends Abstra final void sync(ForkJoinWorkerThread w) { updateStealCount(w); // Transfer w's count while it is idle - while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) { + while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) { long prev = w.lastEventCount; WaitQueueNode node = null; WaitQueueNode h; @@ -1458,7 +1498,7 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if worker waiting on sync can proceed: + * Returns {@code true} if worker waiting on sync can proceed: * - on signal (thread == null) * - on event count advance (winning race to notify vs signaller) * - on interrupt @@ -1466,7 +1506,7 @@ public class ForkJoinPool extends Abstra * If node was not signalled and event count not advanced on exit, * then we also help advance event count. * - * @return true if node can be released + * @return {@code true} if node can be released */ final boolean syncIsReleasable(WaitQueueNode node) { long prev = node.count; @@ -1485,8 +1525,8 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if a new sync event occurred since last call to - * sync or this method, if so, updating caller's count. + * Returns {@code true} if a new sync event occurred since last + * call to sync or this method, if so, updating caller's count. */ final boolean hasNewSyncEvent(ForkJoinWorkerThread w) { long lc = w.lastEventCount; @@ -1570,8 +1610,8 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if a spare thread appears to be needed. If - * maintaining parallelism, returns true when the deficit in + * Returns {@code true} if a spare thread appears to be needed. + * If maintaining parallelism, returns true when the deficit in * running threads is more than the surplus of total threads, and * there is apparently some work to do. This self-limiting rule * means that the more threads that have already been added, the @@ -1641,7 +1681,7 @@ public class ForkJoinPool extends Abstra for (k = 0; k < len && ws[k] != null; ++k) ; } - if (k < len && !isTerminating() && (w = createWorker(k)) != null) { + if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) { ws[k] = w; w.start(); } @@ -1739,11 +1779,13 @@ public class ForkJoinPool extends Abstra /** * Interface for extending managed parallelism for tasks running - * in ForkJoinPools. A ManagedBlocker provides two methods. - * Method {@code isReleasable} must return true if blocking is not - * necessary. Method {@code block} blocks the current thread if - * necessary (perhaps internally invoking {@code isReleasable} - * before actually blocking.). + * in {@link ForkJoinPool}s. + * + *

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). * *

For example, here is a ManagedBlocker based on a * ReentrantLock: @@ -1767,46 +1809,48 @@ public class ForkJoinPool extends Abstra * Possibly blocks the current thread, for example waiting for * a lock or condition. * - * @return true if no additional blocking is necessary (i.e., - * if isReleasable would return true) + * @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 true if blocking is unnecessary. + * Returns {@code true} if blocking is unnecessary. */ boolean isReleasable(); } /** * Blocks in accord with the given blocker. If the current thread - * is a ForkJoinWorkerThread, this method possibly arranges for a - * spare thread to be activated if necessary to ensure parallelism - * while the current thread is blocked. If - * {@code maintainParallelism} is true and the pool supports - * it ({@link #getMaintainsParallelism}), this method attempts to - * maintain the pool's nominal parallelism. Otherwise it activates - * a thread only if necessary to avoid complete starvation. This - * option may be preferable when blockages use timeouts, or are - * almost always brief. + * is a {@link ForkJoinWorkerThread}, this method possibly + * arranges for a spare thread to be activated if necessary to + * ensure parallelism while the current thread is blocked. + * + *

If {@code maintainParallelism} is {@code true} and the pool + * supports it ({@link #getMaintainsParallelism}), this method + * attempts to maintain the pool's nominal parallelism. Otherwise + * it activates a thread only if necessary to avoid complete + * starvation. This option may be preferable when blockages use + * timeouts, or are almost always brief. * - *

If the caller is not a ForkJoinTask, this method is behaviorally - * equivalent to + *

If the caller is not a {@link ForkJoinTask}, this method is + * behaviorally equivalent to * 

 {@code
      * while (!blocker.isReleasable())
      *   if (blocker.block())
      *     return;
      * }
- * If the caller is a ForkJoinTask, then the pool may first - * be expanded to ensure parallelism, and later adjusted. + * + * If the caller is a {@code ForkJoinTask}, then the pool may + * first be expanded to ensure parallelism, and later adjusted. * * @param blocker the blocker - * @param maintainParallelism if true and supported by this pool, - * attempt to maintain the pool's nominal parallelism; otherwise - * activate a thread only if necessary to avoid complete - * starvation. + * @param maintainParallelism if {@code true} and supported by + * this pool, attempt to maintain the pool's nominal parallelism; + * otherwise activate a thread only if necessary to avoid + * complete starvation. * @throws InterruptedException if blocker.block did so */ public static void managedBlock(ManagedBlocker blocker, @@ -1832,65 +1876,31 @@ public class ForkJoinPool extends Abstra do {} while (!blocker.isReleasable() && !blocker.block()); } - // AbstractExecutorService overrides + // AbstractExecutorService overrides. These rely on undocumented + // fact that ForkJoinTask.adapt returns ForkJoinTasks that also + // implement RunnableFuture. protected RunnableFuture newTaskFor(Runnable runnable, T value) { - return new AdaptedRunnable(runnable, value); + return (RunnableFuture) ForkJoinTask.adapt(runnable, value); } protected RunnableFuture newTaskFor(Callable callable) { - return new AdaptedCallable(callable); + return (RunnableFuture) ForkJoinTask.adapt(callable); } - - // Unsafe mechanics for jsr166y 3rd party package. - private static sun.misc.Unsafe getUnsafe() { - try { - return sun.misc.Unsafe.getUnsafe(); - } catch (SecurityException se) { - try { - return java.security.AccessController.doPrivileged - (new java.security.PrivilegedExceptionAction() { - public sun.misc.Unsafe run() throws Exception { - return getUnsafeByReflection(); - }}); - } catch (java.security.PrivilegedActionException e) { - throw new RuntimeException("Could not initialize intrinsics", - e.getCause()); - } - } - } - - private static sun.misc.Unsafe getUnsafeByReflection() - throws NoSuchFieldException, IllegalAccessException { - java.lang.reflect.Field f = - sun.misc.Unsafe.class.getDeclaredField("theUnsafe"); - f.setAccessible(true); - return (sun.misc.Unsafe) f.get(null); - } - - private static long fieldOffset(String fieldName, Class klazz) { - try { - return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName)); - } catch (NoSuchFieldException e) { - // Convert Exception to Error - NoSuchFieldError error = new NoSuchFieldError(fieldName); - error.initCause(e); - throw error; - } - } + // Unsafe mechanics private static final sun.misc.Unsafe UNSAFE = getUnsafe(); - static final long eventCountOffset = - fieldOffset("eventCount", ForkJoinPool.class); - static final long workerCountsOffset = - fieldOffset("workerCounts", ForkJoinPool.class); - static final long runControlOffset = - fieldOffset("runControl", ForkJoinPool.class); - static final long syncStackOffset = - fieldOffset("syncStack",ForkJoinPool.class); - static final long spareStackOffset = - fieldOffset("spareStack", ForkJoinPool.class); + private static final long eventCountOffset = + objectFieldOffset("eventCount", ForkJoinPool.class); + private static final long workerCountsOffset = + objectFieldOffset("workerCounts", ForkJoinPool.class); + private static final long runControlOffset = + objectFieldOffset("runControl", ForkJoinPool.class); + private static final long syncStackOffset = + objectFieldOffset("syncStack",ForkJoinPool.class); + private static final long spareStackOffset = + objectFieldOffset("spareStack", ForkJoinPool.class); private boolean casEventCount(long cmp, long val) { return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val); @@ -1907,4 +1917,43 @@ public class ForkJoinPool extends Abstra private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) { return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val); } + + private static long objectFieldOffset(String field, Class klazz) { + try { + return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); + } catch (NoSuchFieldException e) { + // Convert Exception to corresponding Error + NoSuchFieldError error = new NoSuchFieldError(field); + error.initCause(e); + throw error; + } + } + + /** + * 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() { + try { + return sun.misc.Unsafe.getUnsafe(); + } catch (SecurityException se) { + try { + return java.security.AccessController.doPrivileged + (new java.security + .PrivilegedExceptionAction() { + public sun.misc.Unsafe run() throws Exception { + java.lang.reflect.Field f = sun.misc + .Unsafe.class.getDeclaredField("theUnsafe"); + f.setAccessible(true); + return (sun.misc.Unsafe) f.get(null); + }}); + } catch (java.security.PrivilegedActionException e) { + throw new RuntimeException("Could not initialize intrinsics", + e.getCause()); + } + } + } }