--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/share/classes/java/util/concurrent/ForkJoinPool.java Mon Nov 02 17:25:38 2009 -0800
@@ -0,0 +1,1988 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent;
+
+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 {@code ForkJoinPool} provides the entry point for submissions
+ * from non-{@code ForkJoinTask}s, 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 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.
+ *
+ * <p>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 stalled 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.
+ *
+ * <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><b>Sample Usage.</b> 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 explicitly {@link
+ * #shutdown} such a pool upon program exit.
+ *
+ * <pre>
+ * static final ForkJoinPool mainPool = new ForkJoinPool();
+ * ...
+ * public void sort(long[] array) {
+ * mainPool.invoke(new SortTask(array, 0, array.length));
+ * }
+ * </pre>
+ *
+ * <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.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public class ForkJoinPool extends AbstractExecutorService {
+
+ /*
+ * See the extended comments interspersed below for design,
+ * rationale, and walkthroughs.
+ */
+
+ /** Mask for packing and unpacking shorts */
+ private static final int shortMask = 0xffff;
+
+ /** Max pool size -- must be a power of two minus 1 */
+ private static final int MAX_THREADS = 0x7FFF;
+
+ /**
+ * 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 class DefaultForkJoinWorkerThreadFactory
+ implements ForkJoinWorkerThreadFactory {
+ public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
+ try {
+ return new ForkJoinWorkerThread(pool);
+ } catch (OutOfMemoryError oom) {
+ return null;
+ }
+ }
+ }
+
+ /**
+ * Creates a new ForkJoinWorkerThread. This factory is used unless
+ * overridden in ForkJoinPool constructors.
+ */
+ public static final ForkJoinWorkerThreadFactory
+ defaultForkJoinWorkerThreadFactory =
+ new DefaultForkJoinWorkerThreadFactory();
+
+ /**
+ * Permission required for callers of methods that may start or
+ * kill threads.
+ */
+ private static final RuntimePermission modifyThreadPermission =
+ new RuntimePermission("modifyThread");
+
+ /**
+ * 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);
+ }
+
+ /**
+ * Generator for assigning sequence numbers as pool names.
+ */
+ private static final AtomicInteger poolNumberGenerator =
+ new AtomicInteger();
+
+ /**
+ * Array holding all worker threads in the pool. Initialized upon
+ * first use. Array size must be a power of two. Updates and
+ * replacements are protected by workerLock, but it is always kept
+ * in a consistent enough state to be randomly accessed without
+ * locking by workers performing work-stealing.
+ */
+ volatile ForkJoinWorkerThread[] workers;
+
+ /**
+ * Lock protecting access to workers.
+ */
+ private final ReentrantLock workerLock;
+
+ /**
+ * Condition for awaitTermination.
+ */
+ private final Condition termination;
+
+ /**
+ * The uncaught exception handler used when any worker
+ * abruptly terminates
+ */
+ private Thread.UncaughtExceptionHandler ueh;
+
+ /**
+ * Creation factory for worker threads.
+ */
+ private final ForkJoinWorkerThreadFactory factory;
+
+ /**
+ * Head of stack of threads that were created to maintain
+ * parallelism when other threads blocked, but have since
+ * suspended when the parallelism level rose.
+ */
+ private volatile WaitQueueNode spareStack;
+
+ /**
+ * Sum of per-thread steal counts, updated only when threads are
+ * idle or terminating.
+ */
+ private final AtomicLong stealCount;
+
+ /**
+ * Queue for external submissions.
+ */
+ private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
+
+ /**
+ * Head of Treiber stack for barrier sync. See below for explanation.
+ */
+ private volatile WaitQueueNode syncStack;
+
+ /**
+ * The count for event barrier
+ */
+ private volatile long eventCount;
+
+ /**
+ * Pool number, just for assigning useful names to worker threads
+ */
+ private final int poolNumber;
+
+ /**
+ * The maximum allowed pool size
+ */
+ private volatile int maxPoolSize;
+
+ /**
+ * The desired parallelism level, updated only under workerLock.
+ */
+ private volatile int parallelism;
+
+ /**
+ * True if use local fifo, not default lifo, for local polling
+ */
+ private volatile boolean locallyFifo;
+
+ /**
+ * Holds number of total (i.e., created and not yet terminated)
+ * and running (i.e., not blocked on joins or other managed sync)
+ * threads, packed into one int to ensure consistent snapshot when
+ * making decisions about creating and suspending spare
+ * threads. Updated only by CAS. Note: CASes in
+ * updateRunningCount and preJoin assume that running active count
+ * is in low word, so need to be modified if this changes.
+ */
+ private volatile int workerCounts;
+
+ private static int totalCountOf(int s) { return s >>> 16; }
+ private static int runningCountOf(int s) { return s & shortMask; }
+ private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
+
+ /**
+ * Adds delta (which may be negative) to running count. This must
+ * be called before (with negative arg) and after (with positive)
+ * any managed synchronization (i.e., mainly, joins).
+ *
+ * @param delta the number to add
+ */
+ final void updateRunningCount(int delta) {
+ int s;
+ do {} while (!casWorkerCounts(s = workerCounts, s + delta));
+ }
+
+ /**
+ * Adds delta (which may be negative) to both total and running
+ * count. This must be called upon creation and termination of
+ * worker threads.
+ *
+ * @param delta the number to add
+ */
+ private void updateWorkerCount(int delta) {
+ int d = delta + (delta << 16); // add to both lo and hi parts
+ int s;
+ do {} while (!casWorkerCounts(s = workerCounts, s + d));
+ }
+
+ /**
+ * Lifecycle control. High word contains runState, low word
+ * contains the number of workers that are (probably) executing
+ * tasks. This value is atomically incremented before a worker
+ * gets a task to run, and decremented when worker has no tasks
+ * and cannot find any. These two fields are bundled together to
+ * support correct termination triggering. Note: activeCount
+ * CAS'es cheat by assuming active count is in low word, so need
+ * to be modified if this changes
+ */
+ private volatile int runControl;
+
+ // RunState values. Order among values matters
+ private static final int RUNNING = 0;
+ private static final int SHUTDOWN = 1;
+ private static final int TERMINATING = 2;
+ private static final int TERMINATED = 3;
+
+ private static int runStateOf(int c) { return c >>> 16; }
+ private static int activeCountOf(int c) { return c & shortMask; }
+ private static int runControlFor(int r, int a) { return (r << 16) + a; }
+
+ /**
+ * Tries incrementing active count; fails on contention.
+ * Called by workers before/during executing tasks.
+ *
+ * @return true on success
+ */
+ final boolean tryIncrementActiveCount() {
+ int c = runControl;
+ return casRunControl(c, c+1);
+ }
+
+ /**
+ * Tries decrementing active count; fails on contention.
+ * Possibly triggers termination on success.
+ * Called by workers when they can't find tasks.
+ *
+ * @return true on success
+ */
+ final boolean tryDecrementActiveCount() {
+ int c = runControl;
+ int nextc = c - 1;
+ if (!casRunControl(c, nextc))
+ return false;
+ if (canTerminateOnShutdown(nextc))
+ terminateOnShutdown();
+ return true;
+ }
+
+ /**
+ * 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) {
+ // i.e. least bit is nonzero runState bit
+ return ((c & -c) >>> 16) != 0;
+ }
+
+ /**
+ * Transition run state to at least the given state. Return true
+ * if not already at least given state.
+ */
+ private boolean transitionRunStateTo(int state) {
+ for (;;) {
+ int c = runControl;
+ if (runStateOf(c) >= state)
+ return false;
+ if (casRunControl(c, runControlFor(state, activeCountOf(c))))
+ return true;
+ }
+ }
+
+ /**
+ * Controls whether to add spares to maintain parallelism
+ */
+ private volatile boolean maintainsParallelism;
+
+ // Constructors
+
+ /**
+ * 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
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
+ */
+ public ForkJoinPool() {
+ this(Runtime.getRuntime().availableProcessors(),
+ defaultForkJoinWorkerThreadFactory);
+ }
+
+ /**
+ * Creates a {@code ForkJoinPool} with the indicated parallelism
+ * level and using the {@linkplain
+ * #defaultForkJoinWorkerThreadFactory default thread factory}.
+ *
+ * @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);
+ }
+
+ /**
+ * 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 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(ForkJoinWorkerThreadFactory factory) {
+ this(Runtime.getRuntime().availableProcessors(), factory);
+ }
+
+ /**
+ * Creates a {@code ForkJoinPool} with the given parallelism and
+ * thread factory.
+ *
+ * @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
+ * @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) {
+ if (parallelism <= 0 || parallelism > MAX_THREADS)
+ throw new IllegalArgumentException();
+ if (factory == null)
+ throw new NullPointerException();
+ checkPermission();
+ this.factory = factory;
+ this.parallelism = parallelism;
+ this.maxPoolSize = MAX_THREADS;
+ this.maintainsParallelism = true;
+ this.poolNumber = poolNumberGenerator.incrementAndGet();
+ this.workerLock = new ReentrantLock();
+ this.termination = workerLock.newCondition();
+ this.stealCount = new AtomicLong();
+ this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
+ // worker array and workers are lazily constructed
+ }
+
+ /**
+ * Creates a new worker thread using factory.
+ *
+ * @param index the index to assign worker
+ * @return new worker, or null if factory failed
+ */
+ private ForkJoinWorkerThread createWorker(int index) {
+ Thread.UncaughtExceptionHandler h = ueh;
+ ForkJoinWorkerThread w = factory.newThread(this);
+ if (w != null) {
+ w.poolIndex = index;
+ w.setDaemon(true);
+ w.setAsyncMode(locallyFifo);
+ w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
+ if (h != null)
+ w.setUncaughtExceptionHandler(h);
+ }
+ return w;
+ }
+
+ /**
+ * Returns a good size for worker array given pool size.
+ * Currently requires size to be a power of two.
+ */
+ private static int arraySizeFor(int poolSize) {
+ 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;
+ }
+
+ /**
+ * Creates or resizes array if necessary to hold newLength.
+ * Call only under exclusion.
+ *
+ * @return the array
+ */
+ private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws == null)
+ return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
+ else if (newLength > ws.length)
+ return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
+ else
+ return ws;
+ }
+
+ /**
+ * Tries to shrink workers into smaller array after one or more terminate.
+ */
+ private void tryShrinkWorkerArray() {
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ int len = ws.length;
+ int last = len - 1;
+ while (last >= 0 && ws[last] == null)
+ --last;
+ int newLength = arraySizeFor(last+1);
+ if (newLength < len)
+ workers = Arrays.copyOf(ws, newLength);
+ }
+ }
+
+ /**
+ * Initializes workers if necessary.
+ */
+ final void ensureWorkerInitialization() {
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws == null) {
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ ws = workers;
+ if (ws == null) {
+ int ps = parallelism;
+ ws = ensureWorkerArrayCapacity(ps);
+ for (int i = 0; i < ps; ++i) {
+ ForkJoinWorkerThread w = createWorker(i);
+ if (w != null) {
+ ws[i] = w;
+ w.start();
+ updateWorkerCount(1);
+ }
+ }
+ }
+ } finally {
+ lock.unlock();
+ }
+ }
+ }
+
+ /**
+ * Worker creation and startup for threads added via setParallelism.
+ */
+ private void createAndStartAddedWorkers() {
+ resumeAllSpares(); // Allow spares to convert to nonspare
+ int ps = parallelism;
+ ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
+ int len = ws.length;
+ // Sweep through slots, to keep lowest indices most populated
+ int k = 0;
+ while (k < len) {
+ if (ws[k] != null) {
+ ++k;
+ continue;
+ }
+ int s = workerCounts;
+ int tc = totalCountOf(s);
+ int rc = runningCountOf(s);
+ if (rc >= ps || tc >= ps)
+ break;
+ if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
+ ForkJoinWorkerThread w = createWorker(k);
+ if (w != null) {
+ ws[k++] = w;
+ w.start();
+ }
+ else {
+ updateWorkerCount(-1); // back out on failed creation
+ break;
+ }
+ }
+ }
+ }
+
+ // Execution methods
+
+ /**
+ * Common code for execute, invoke and submit
+ */
+ private <T> void doSubmit(ForkJoinTask<T> task) {
+ if (task == null)
+ throw new NullPointerException();
+ if (isShutdown())
+ throw new RejectedExecutionException();
+ if (workers == null)
+ ensureWorkerInitialization();
+ submissionQueue.offer(task);
+ signalIdleWorkers();
+ }
+
+ /**
+ * Performs the given task, returning its result upon completion.
+ *
+ * @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) {
+ doSubmit(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) {
+ doSubmit(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) {
+ ForkJoinTask<?> job;
+ if (task instanceof ForkJoinTask<?>) // avoid re-wrap
+ job = (ForkJoinTask<?>) task;
+ else
+ job = ForkJoinTask.adapt(task, null);
+ doSubmit(job);
+ }
+
+ /**
+ * @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 = ForkJoinTask.adapt(task);
+ doSubmit(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 = ForkJoinTask.adapt(task, result);
+ doSubmit(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) {
+ ForkJoinTask<?> job;
+ if (task instanceof ForkJoinTask<?>) // avoid re-wrap
+ job = (ForkJoinTask<?>) task;
+ else
+ job = ForkJoinTask.adapt(task, null);
+ doSubmit(job);
+ return 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) {
+ doSubmit(task);
+ return task;
+ }
+
+
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ * @throws RejectedExecutionException {@inheritDoc}
+ */
+ public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
+ ArrayList<ForkJoinTask<T>> forkJoinTasks =
+ new ArrayList<ForkJoinTask<T>>(tasks.size());
+ for (Callable<T> task : tasks)
+ forkJoinTasks.add(ForkJoinTask.adapt(task));
+ invoke(new InvokeAll<T>(forkJoinTasks));
+
+ @SuppressWarnings({"unchecked", "rawtypes"})
+ List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
+ return futures;
+ }
+
+ static final class InvokeAll<T> extends RecursiveAction {
+ final ArrayList<ForkJoinTask<T>> tasks;
+ InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; }
+ public void compute() {
+ try { invokeAll(tasks); }
+ catch (Exception ignore) {}
+ }
+ private static final long serialVersionUID = -7914297376763021607L;
+ }
+
+ // Configuration and status settings and queries
+
+ /**
+ * 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() {
+ Thread.UncaughtExceptionHandler h;
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ h = ueh;
+ } finally {
+ lock.unlock();
+ }
+ return h;
+ }
+
+ /**
+ * Sets the handler for internal worker threads that terminate due
+ * to unrecoverable errors encountered while executing tasks.
+ * Unless set, the current default or ThreadGroup handler is used
+ * as handler.
+ *
+ * @param h the new handler
+ * @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
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
+ */
+ public Thread.UncaughtExceptionHandler
+ setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
+ checkPermission();
+ Thread.UncaughtExceptionHandler old = null;
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ old = ueh;
+ ueh = h;
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread w = ws[i];
+ if (w != null)
+ w.setUncaughtExceptionHandler(h);
+ }
+ }
+ } finally {
+ lock.unlock();
+ }
+ return old;
+ }
+
+
+ /**
+ * Sets the target parallelism level of this pool.
+ *
+ * @param parallelism the target parallelism
+ * @throws IllegalArgumentException if parallelism less than or
+ * equal to zero or greater than maximum size bounds
+ * @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 setParallelism(int parallelism) {
+ checkPermission();
+ if (parallelism <= 0 || parallelism > maxPoolSize)
+ throw new IllegalArgumentException();
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ if (isProcessingTasks()) {
+ int p = this.parallelism;
+ this.parallelism = parallelism;
+ if (parallelism > p)
+ createAndStartAddedWorkers();
+ else
+ trimSpares();
+ }
+ } finally {
+ lock.unlock();
+ }
+ signalIdleWorkers();
+ }
+
+ /**
+ * Returns the targeted parallelism level of this pool.
+ *
+ * @return the targeted parallelism level of this pool
+ */
+ public int getParallelism() {
+ return parallelism;
+ }
+
+ /**
+ * Returns the number of worker threads that have started but not
+ * yet terminated. This 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 totalCountOf(workerCounts);
+ }
+
+ /**
+ * Returns the maximum number of threads allowed to exist in the
+ * pool. Unless set using {@link #setMaximumPoolSize}, the
+ * maximum is an implementation-defined value designed only to
+ * prevent runaway growth.
+ *
+ * @return the maximum
+ */
+ public int getMaximumPoolSize() {
+ return maxPoolSize;
+ }
+
+ /**
+ * Sets the maximum number of threads allowed to exist in the
+ * pool. The given value should normally be greater than or equal
+ * to the {@link #getParallelism parallelism} level. Setting this
+ * value has no effect on current pool size. It controls
+ * construction of new threads.
+ *
+ * @throws IllegalArgumentException if negative or greater than
+ * internal implementation limit
+ */
+ public void setMaximumPoolSize(int newMax) {
+ if (newMax < 0 || newMax > MAX_THREADS)
+ throw new IllegalArgumentException();
+ maxPoolSize = newMax;
+ }
+
+
+ /**
+ * 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 {@code true} if maintains parallelism
+ */
+ public boolean getMaintainsParallelism() {
+ return maintainsParallelism;
+ }
+
+ /**
+ * Sets whether this pool dynamically maintains its target
+ * parallelism level. If false, new threads are added only to
+ * avoid possible starvation.
+ *
+ * @param enable {@code true} to maintain parallelism
+ */
+ public void setMaintainsParallelism(boolean enable) {
+ maintainsParallelism = enable;
+ }
+
+ /**
+ * 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 asynchronous tasks. This method is
+ * 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 {@code true}, use locally FIFO scheduling
+ * @return the previous mode
+ * @see #getAsyncMode
+ */
+ public boolean setAsyncMode(boolean async) {
+ boolean oldMode = locallyFifo;
+ locallyFifo = async;
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ t.setAsyncMode(async);
+ }
+ }
+ return oldMode;
+ }
+
+ /**
+ * 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
+ * @see #setAsyncMode
+ */
+ public boolean getAsyncMode() {
+ return locallyFifo;
+ }
+
+ /**
+ * Returns an estimate of the number of worker threads that are
+ * not blocked waiting to join tasks or for other managed
+ * synchronization.
+ *
+ * @return the number of worker threads
+ */
+ public int getRunningThreadCount() {
+ return runningCountOf(workerCounts);
+ }
+
+ /**
+ * 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() {
+ return activeCountOf(runControl);
+ }
+
+ /**
+ * Returns an estimate of the number of threads that are currently
+ * idle waiting for tasks. This method may underestimate the
+ * number of idle threads.
+ *
+ * @return the number of idle threads
+ */
+ final int getIdleThreadCount() {
+ int c = runningCountOf(workerCounts) - activeCountOf(runControl);
+ return (c <= 0) ? 0 : c;
+ }
+
+ /**
+ * 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 activeCountOf(runControl) == 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() {
+ return stealCount.get();
+ }
+
+ /**
+ * Accumulates steal count from a worker.
+ * Call only when worker known to be idle.
+ */
+ private void updateStealCount(ForkJoinWorkerThread w) {
+ int sc = w.getAndClearStealCount();
+ if (sc != 0)
+ stealCount.addAndGet(sc);
+ }
+
+ /**
+ * 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;
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ count += t.getQueueSize();
+ }
+ }
+ return count;
+ }
+
+ /**
+ * 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
+ */
+ public int getQueuedSubmissionCount() {
+ return submissionQueue.size();
+ }
+
+ /**
+ * 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() {
+ return !submissionQueue.isEmpty();
+ }
+
+ /**
+ * Removes and returns the next unexecuted submission if one is
+ * available. This method may be useful in extensions to this
+ * class that re-assign work in systems with multiple pools.
+ *
+ * @return the next submission, or {@code null} if none
+ */
+ protected ForkJoinTask<?> pollSubmission() {
+ return submissionQueue.poll();
+ }
+
+ /**
+ * 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 n = submissionQueue.drainTo(c);
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread w = ws[i];
+ if (w != null)
+ n += w.drainTasksTo(c);
+ }
+ }
+ return n;
+ }
+
+ /**
+ * 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() {
+ int ps = parallelism;
+ int wc = workerCounts;
+ int rc = runControl;
+ long st = getStealCount();
+ long qt = getQueuedTaskCount();
+ long qs = getQueuedSubmissionCount();
+ return super.toString() +
+ "[" + runStateToString(runStateOf(rc)) +
+ ", parallelism = " + ps +
+ ", size = " + totalCountOf(wc) +
+ ", active = " + activeCountOf(rc) +
+ ", running = " + runningCountOf(wc) +
+ ", steals = " + st +
+ ", tasks = " + qt +
+ ", submissions = " + qs +
+ "]";
+ }
+
+ private static String runStateToString(int rs) {
+ switch(rs) {
+ case RUNNING: return "Running";
+ case SHUTDOWN: return "Shutting down";
+ case TERMINATING: return "Terminating";
+ case TERMINATED: return "Terminated";
+ default: throw new Error("Unknown run state");
+ }
+ }
+
+ // lifecycle control
+
+ /**
+ * Initiates an orderly shutdown in which previously submitted
+ * tasks are executed, but no new tasks will be accepted.
+ * Invocation has 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();
+ transitionRunStateTo(SHUTDOWN);
+ 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 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
+ * the caller is not permitted to modify threads
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
+ */
+ public List<Runnable> shutdownNow() {
+ checkPermission();
+ terminate();
+ return Collections.emptyList();
+ }
+
+ /**
+ * Returns {@code true} if all tasks have completed following shut down.
+ *
+ * @return {@code true} if all tasks have completed following shut down
+ */
+ public boolean isTerminated() {
+ return runStateOf(runControl) == TERMINATED;
+ }
+
+ /**
+ * 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, causing this executor not
+ * to properly terminate.
+ *
+ * @return {@code true} if terminating but not yet terminated
+ */
+ public boolean isTerminating() {
+ return runStateOf(runControl) == TERMINATING;
+ }
+
+ /**
+ * Returns {@code true} if this pool has been shut down.
+ *
+ * @return {@code true} if this pool has been shut down
+ */
+ public boolean isShutdown() {
+ return runStateOf(runControl) >= SHUTDOWN;
+ }
+
+ /**
+ * 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.
+ *
+ * @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 {
+ long nanos = unit.toNanos(timeout);
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ for (;;) {
+ if (isTerminated())
+ return true;
+ if (nanos <= 0)
+ return false;
+ nanos = termination.awaitNanos(nanos);
+ }
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ // Shutdown and termination support
+
+ /**
+ * Callback from terminating worker. Nulls out the corresponding
+ * workers slot, and if terminating, tries to terminate; else
+ * tries to shrink workers array.
+ *
+ * @param w the worker
+ */
+ final void workerTerminated(ForkJoinWorkerThread w) {
+ updateStealCount(w);
+ updateWorkerCount(-1);
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ int idx = w.poolIndex;
+ if (idx >= 0 && idx < ws.length && ws[idx] == w)
+ ws[idx] = null;
+ if (totalCountOf(workerCounts) == 0) {
+ terminate(); // no-op if already terminating
+ transitionRunStateTo(TERMINATED);
+ termination.signalAll();
+ }
+ else if (isProcessingTasks()) {
+ tryShrinkWorkerArray();
+ tryResumeSpare(true); // allow replacement
+ }
+ }
+ } finally {
+ lock.unlock();
+ }
+ signalIdleWorkers();
+ }
+
+ /**
+ * Initiates termination.
+ */
+ private void terminate() {
+ if (transitionRunStateTo(TERMINATING)) {
+ stopAllWorkers();
+ resumeAllSpares();
+ signalIdleWorkers();
+ cancelQueuedSubmissions();
+ cancelQueuedWorkerTasks();
+ interruptUnterminatedWorkers();
+ signalIdleWorkers(); // resignal after interrupt
+ }
+ }
+
+ /**
+ * Possibly terminates when on shutdown state.
+ */
+ private void terminateOnShutdown() {
+ if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
+ terminate();
+ }
+
+ /**
+ * Clears out and cancels submissions.
+ */
+ private void cancelQueuedSubmissions() {
+ ForkJoinTask<?> task;
+ while ((task = pollSubmission()) != null)
+ task.cancel(false);
+ }
+
+ /**
+ * Cleans out worker queues.
+ */
+ private void cancelQueuedWorkerTasks() {
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ t.cancelTasks();
+ }
+ }
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * Sets each worker's status to terminating. Requires lock to avoid
+ * conflicts with add/remove.
+ */
+ private void stopAllWorkers() {
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ t.shutdownNow();
+ }
+ }
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * Interrupts all unterminated workers. This is not required for
+ * sake of internal control, but may help unstick user code during
+ * shutdown.
+ */
+ private void interruptUnterminatedWorkers() {
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null && !t.isTerminated()) {
+ try {
+ t.interrupt();
+ } catch (SecurityException ignore) {
+ }
+ }
+ }
+ }
+ } finally {
+ lock.unlock();
+ }
+ }
+
+
+ /*
+ * Nodes for event barrier to manage idle threads. Queue nodes
+ * are basic Treiber stack nodes, also used for spare stack.
+ *
+ * The event barrier has an event count and a wait queue (actually
+ * a Treiber stack). Workers are enabled to look for work when
+ * the eventCount is incremented. If they fail to find work, they
+ * may wait for next count. Upon release, threads help others wake
+ * up.
+ *
+ * Synchronization events occur only in enough contexts to
+ * maintain overall liveness:
+ *
+ * - Submission of a new task to the pool
+ * - Resizes or other changes to the workers array
+ * - pool termination
+ * - A worker pushing a task on an empty queue
+ *
+ * The case of pushing a task occurs often enough, and is heavy
+ * enough compared to simple stack pushes, to require special
+ * handling: Method signalWork returns without advancing count if
+ * the queue appears to be empty. This would ordinarily result in
+ * races causing some queued waiters not to be woken up. To avoid
+ * this, the first worker enqueued in method sync (see
+ * syncIsReleasable) rescans for tasks after being enqueued, and
+ * helps signal if any are found. This works well because the
+ * worker has nothing better to do, and so might as well help
+ * alleviate the overhead and contention on the threads actually
+ * doing work. Also, since event counts increments on task
+ * availability exist to maintain liveness (rather than to force
+ * refreshes etc), it is OK for callers to exit early if
+ * contending with another signaller.
+ */
+ static final class WaitQueueNode {
+ WaitQueueNode next; // only written before enqueued
+ volatile ForkJoinWorkerThread thread; // nulled to cancel wait
+ final long count; // unused for spare stack
+
+ WaitQueueNode(long c, ForkJoinWorkerThread w) {
+ count = c;
+ thread = w;
+ }
+
+ /**
+ * Wakes up waiter, returning false if known to already
+ */
+ boolean signal() {
+ ForkJoinWorkerThread t = thread;
+ if (t == null)
+ return false;
+ thread = null;
+ LockSupport.unpark(t);
+ return true;
+ }
+
+ /**
+ * Awaits release on sync.
+ */
+ void awaitSyncRelease(ForkJoinPool p) {
+ while (thread != null && !p.syncIsReleasable(this))
+ LockSupport.park(this);
+ }
+
+ /**
+ * Awaits resumption as spare.
+ */
+ void awaitSpareRelease() {
+ while (thread != null) {
+ if (!Thread.interrupted())
+ LockSupport.park(this);
+ }
+ }
+ }
+
+ /**
+ * Ensures that no thread is waiting for count to advance from the
+ * current value of eventCount read on entry to this method, by
+ * releasing waiting threads if necessary.
+ *
+ * @return the count
+ */
+ final long ensureSync() {
+ long c = eventCount;
+ WaitQueueNode q;
+ while ((q = syncStack) != null && q.count < c) {
+ if (casBarrierStack(q, null)) {
+ do {
+ q.signal();
+ } while ((q = q.next) != null);
+ break;
+ }
+ }
+ return c;
+ }
+
+ /**
+ * Increments event count and releases waiting threads.
+ */
+ private void signalIdleWorkers() {
+ long c;
+ do {} while (!casEventCount(c = eventCount, c+1));
+ ensureSync();
+ }
+
+ /**
+ * Signals threads waiting to poll a task. Because method sync
+ * rechecks availability, it is OK to only proceed if queue
+ * appears to be non-empty, and OK to skip under contention to
+ * increment count (since some other thread succeeded).
+ */
+ final void signalWork() {
+ long c;
+ WaitQueueNode q;
+ if (syncStack != null &&
+ casEventCount(c = eventCount, c+1) &&
+ (((q = syncStack) != null && q.count <= c) &&
+ (!casBarrierStack(q, q.next) || !q.signal())))
+ ensureSync();
+ }
+
+ /**
+ * Waits until event count advances from last value held by
+ * caller, or if excess threads, caller is resumed as spare, or
+ * caller or pool is terminating. Updates caller's event on exit.
+ *
+ * @param w the calling worker thread
+ */
+ final void sync(ForkJoinWorkerThread w) {
+ updateStealCount(w); // Transfer w's count while it is idle
+
+ while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
+ long prev = w.lastEventCount;
+ WaitQueueNode node = null;
+ WaitQueueNode h;
+ while (eventCount == prev &&
+ ((h = syncStack) == null || h.count == prev)) {
+ if (node == null)
+ node = new WaitQueueNode(prev, w);
+ if (casBarrierStack(node.next = h, node)) {
+ node.awaitSyncRelease(this);
+ break;
+ }
+ }
+ long ec = ensureSync();
+ if (ec != prev) {
+ w.lastEventCount = ec;
+ break;
+ }
+ }
+ }
+
+ /**
+ * 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
+ * - if the first queued node, we find work available
+ * If node was not signalled and event count not advanced on exit,
+ * then we also help advance event count.
+ *
+ * @return {@code true} if node can be released
+ */
+ final boolean syncIsReleasable(WaitQueueNode node) {
+ long prev = node.count;
+ if (!Thread.interrupted() && node.thread != null &&
+ (node.next != null ||
+ !ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
+ eventCount == prev)
+ return false;
+ if (node.thread != null) {
+ node.thread = null;
+ long ec = eventCount;
+ if (prev <= ec) // help signal
+ casEventCount(ec, ec+1);
+ }
+ return true;
+ }
+
+ /**
+ * 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;
+ long ec = ensureSync();
+ if (ec == lc)
+ return false;
+ w.lastEventCount = ec;
+ return true;
+ }
+
+ // Parallelism maintenance
+
+ /**
+ * Decrements running count; if too low, adds spare.
+ *
+ * Conceptually, all we need to do here is add or resume a
+ * spare thread when one is about to block (and remove or
+ * suspend it later when unblocked -- see suspendIfSpare).
+ * However, implementing this idea requires coping with
+ * several problems: we have imperfect information about the
+ * states of threads. Some count updates can and usually do
+ * lag run state changes, despite arrangements to keep them
+ * accurate (for example, when possible, updating counts
+ * before signalling or resuming), especially when running on
+ * dynamic JVMs that don't optimize the infrequent paths that
+ * update counts. Generating too many threads can make these
+ * problems become worse, because excess threads are more
+ * likely to be context-switched with others, slowing them all
+ * down, especially if there is no work available, so all are
+ * busy scanning or idling. Also, excess spare threads can
+ * only be suspended or removed when they are idle, not
+ * immediately when they aren't needed. So adding threads will
+ * raise parallelism level for longer than necessary. Also,
+ * FJ applications often encounter highly transient peaks when
+ * many threads are blocked joining, but for less time than it
+ * takes to create or resume spares.
+ *
+ * @param joinMe if non-null, return early if done
+ * @param maintainParallelism if true, try to stay within
+ * target counts, else create only to avoid starvation
+ * @return true if joinMe known to be done
+ */
+ final boolean preJoin(ForkJoinTask<?> joinMe,
+ boolean maintainParallelism) {
+ maintainParallelism &= maintainsParallelism; // overrride
+ boolean dec = false; // true when running count decremented
+ while (spareStack == null || !tryResumeSpare(dec)) {
+ int counts = workerCounts;
+ if (dec || (dec = casWorkerCounts(counts, --counts))) {
+ if (!needSpare(counts, maintainParallelism))
+ break;
+ if (joinMe.status < 0)
+ return true;
+ if (tryAddSpare(counts))
+ break;
+ }
+ }
+ return false;
+ }
+
+ /**
+ * Same idea as preJoin
+ */
+ final boolean preBlock(ManagedBlocker blocker,
+ boolean maintainParallelism) {
+ maintainParallelism &= maintainsParallelism;
+ boolean dec = false;
+ while (spareStack == null || !tryResumeSpare(dec)) {
+ int counts = workerCounts;
+ if (dec || (dec = casWorkerCounts(counts, --counts))) {
+ if (!needSpare(counts, maintainParallelism))
+ break;
+ if (blocker.isReleasable())
+ return true;
+ if (tryAddSpare(counts))
+ break;
+ }
+ }
+ return false;
+ }
+
+ /**
+ * 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
+ * less parallelism we will tolerate before adding another.
+ *
+ * @param counts current worker counts
+ * @param maintainParallelism try to maintain parallelism
+ */
+ private boolean needSpare(int counts, boolean maintainParallelism) {
+ int ps = parallelism;
+ int rc = runningCountOf(counts);
+ int tc = totalCountOf(counts);
+ int runningDeficit = ps - rc;
+ int totalSurplus = tc - ps;
+ return (tc < maxPoolSize &&
+ (rc == 0 || totalSurplus < 0 ||
+ (maintainParallelism &&
+ runningDeficit > totalSurplus &&
+ ForkJoinWorkerThread.hasQueuedTasks(workers))));
+ }
+
+ /**
+ * Adds a spare worker if lock available and no more than the
+ * expected numbers of threads exist.
+ *
+ * @return true if successful
+ */
+ private boolean tryAddSpare(int expectedCounts) {
+ final ReentrantLock lock = this.workerLock;
+ int expectedRunning = runningCountOf(expectedCounts);
+ int expectedTotal = totalCountOf(expectedCounts);
+ boolean success = false;
+ boolean locked = false;
+ // confirm counts while locking; CAS after obtaining lock
+ try {
+ for (;;) {
+ int s = workerCounts;
+ int tc = totalCountOf(s);
+ int rc = runningCountOf(s);
+ if (rc > expectedRunning || tc > expectedTotal)
+ break;
+ if (!locked && !(locked = lock.tryLock()))
+ break;
+ if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
+ createAndStartSpare(tc);
+ success = true;
+ break;
+ }
+ }
+ } finally {
+ if (locked)
+ lock.unlock();
+ }
+ return success;
+ }
+
+ /**
+ * Adds the kth spare worker. On entry, pool counts are already
+ * adjusted to reflect addition.
+ */
+ private void createAndStartSpare(int k) {
+ ForkJoinWorkerThread w = null;
+ ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
+ int len = ws.length;
+ // Probably, we can place at slot k. If not, find empty slot
+ if (k < len && ws[k] != null) {
+ for (k = 0; k < len && ws[k] != null; ++k)
+ ;
+ }
+ if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) {
+ ws[k] = w;
+ w.start();
+ }
+ else
+ updateWorkerCount(-1); // adjust on failure
+ signalIdleWorkers();
+ }
+
+ /**
+ * Suspends calling thread w if there are excess threads. Called
+ * only from sync. Spares are enqueued in a Treiber stack using
+ * the same WaitQueueNodes as barriers. They are resumed mainly
+ * in preJoin, but are also woken on pool events that require all
+ * threads to check run state.
+ *
+ * @param w the caller
+ */
+ private boolean suspendIfSpare(ForkJoinWorkerThread w) {
+ WaitQueueNode node = null;
+ int s;
+ while (parallelism < runningCountOf(s = workerCounts)) {
+ if (node == null)
+ node = new WaitQueueNode(0, w);
+ if (casWorkerCounts(s, s-1)) { // representation-dependent
+ // push onto stack
+ do {} while (!casSpareStack(node.next = spareStack, node));
+ // block until released by resumeSpare
+ node.awaitSpareRelease();
+ return true;
+ }
+ }
+ return false;
+ }
+
+ /**
+ * Tries to pop and resume a spare thread.
+ *
+ * @param updateCount if true, increment running count on success
+ * @return true if successful
+ */
+ private boolean tryResumeSpare(boolean updateCount) {
+ WaitQueueNode q;
+ while ((q = spareStack) != null) {
+ if (casSpareStack(q, q.next)) {
+ if (updateCount)
+ updateRunningCount(1);
+ q.signal();
+ return true;
+ }
+ }
+ return false;
+ }
+
+ /**
+ * Pops and resumes all spare threads. Same idea as ensureSync.
+ *
+ * @return true if any spares released
+ */
+ private boolean resumeAllSpares() {
+ WaitQueueNode q;
+ while ( (q = spareStack) != null) {
+ if (casSpareStack(q, null)) {
+ do {
+ updateRunningCount(1);
+ q.signal();
+ } while ((q = q.next) != null);
+ return true;
+ }
+ }
+ return false;
+ }
+
+ /**
+ * Pops and shuts down excessive spare threads. Call only while
+ * holding lock. This is not guaranteed to eliminate all excess
+ * threads, only those suspended as spares, which are the ones
+ * unlikely to be needed in the future.
+ */
+ private void trimSpares() {
+ int surplus = totalCountOf(workerCounts) - parallelism;
+ WaitQueueNode q;
+ while (surplus > 0 && (q = spareStack) != null) {
+ if (casSpareStack(q, null)) {
+ do {
+ updateRunningCount(1);
+ ForkJoinWorkerThread w = q.thread;
+ if (w != null && surplus > 0 &&
+ runningCountOf(workerCounts) > 0 && w.shutdown())
+ --surplus;
+ q.signal();
+ } while ((q = q.next) != null);
+ }
+ }
+ }
+
+ /**
+ * 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).
+ *
+ * <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>
+ */
+ 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 parallelism while the current thread is blocked.
+ *
+ * <p>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.
+ *
+ * <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
+ * @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,
+ boolean maintainParallelism)
+ throws InterruptedException {
+ Thread t = Thread.currentThread();
+ ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
+ ((ForkJoinWorkerThread) t).pool : null);
+ if (!blocker.isReleasable()) {
+ try {
+ if (pool == null ||
+ !pool.preBlock(blocker, maintainParallelism))
+ awaitBlocker(blocker);
+ } finally {
+ if (pool != null)
+ pool.updateRunningCount(1);
+ }
+ }
+ }
+
+ private static void awaitBlocker(ManagedBlocker blocker)
+ throws InterruptedException {
+ 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 (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
+ }
+
+ protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
+ return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
+ }
+
+ // Unsafe mechanics
+
+ private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe();
+ 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);
+ }
+ private boolean casWorkerCounts(int cmp, int val) {
+ return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
+ }
+ private boolean casRunControl(int cmp, int val) {
+ return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
+ }
+ private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
+ return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
+ }
+ 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;
+ }
+ }
+}