--- jsr166/src/jsr166y/ForkJoinPool.java 2009/01/12 17:16:18 1.4 +++ jsr166/src/jsr166y/ForkJoinPool.java 2009/08/04 14:19:00 1.46 @@ -5,55 +5,88 @@ */ package jsr166y; -import java.util.*; + import java.util.concurrent.*; -import java.util.concurrent.locks.*; -import java.util.concurrent.atomic.*; -import sun.misc.Unsafe; -import java.lang.reflect.*; + +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. 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 ManagedBlocker interface enables extension of - * the kinds of synchronization accommodated. The target parallelism - * level may also be changed dynamically (setParallelism) - * and dynamically thread construction can be limited using methods - * setMaximumPoolSize and/or - * 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 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. * *

In addition to execution and lifecycle control methods, this * class provides status check methods (for example - * 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 - * 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 explicitly {@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 */ public class ForkJoinPool extends AbstractExecutorService { @@ -69,23 +102,23 @@ 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 { /** * Returns a new worker thread operating in the given pool. * * @param pool the pool this thread works in - * @throws NullPointerException if pool is null; + * @throws NullPointerException if pool is null */ public ForkJoinWorkerThread newThread(ForkJoinPool pool); } /** - * Default ForkJoinWorkerThreadFactory implementation, creates a + * Default ForkJoinWorkerThreadFactory implementation; creates a * new ForkJoinWorkerThread. */ static class DefaultForkJoinWorkerThreadFactory @@ -131,11 +164,11 @@ public class ForkJoinPool extends Abstra new AtomicInteger(); /** - * Array holding all worker threads in the pool. 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. + * 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; @@ -151,7 +184,7 @@ public class ForkJoinPool extends Abstra /** * The uncaught exception handler used when any worker - * abrupty terminates + * abruptly terminates */ private Thread.UncaughtExceptionHandler ueh; @@ -179,7 +212,7 @@ public class ForkJoinPool extends Abstra private final LinkedTransferQueue> submissionQueue; /** - * Head of Treiber stack for barrier sync. See below for explanation + * Head of Treiber stack for barrier sync. See below for explanation. */ private volatile WaitQueueNode syncStack; @@ -204,13 +237,18 @@ public class ForkJoinPool extends Abstra 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 running active count is in low - * word, so need to be modified if this changes + * updateRunningCount and preJoin assume that running active count + * is in low word, so need to be modified if this changes. */ private volatile int workerCounts; @@ -219,26 +257,28 @@ public class ForkJoinPool extends Abstra private static int workerCountsFor(int t, int r) { return (t << 16) + r; } /** - * Add delta (which may be negative) to running count. This must + * 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) + * 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)); + do {} while (!casWorkerCounts(s = workerCounts, s + delta)); } /** - * Add delta (which may be negative) to both total and running + * 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)); + do {} while (!casWorkerCounts(s = workerCounts, s + d)); } /** @@ -264,9 +304,10 @@ public class ForkJoinPool extends Abstra private static int runControlFor(int r, int a) { return (r << 16) + a; } /** - * Try incrementing active count; fail on contention. Called by - * workers before/during executing tasks. - * @return true on success; + * Tries incrementing active count; fails on contention. + * Called by workers before/during executing tasks. + * + * @return true on success */ final boolean tryIncrementActiveCount() { int c = runControl; @@ -274,9 +315,10 @@ public class ForkJoinPool extends Abstra } /** - * Try decrementing active count; fail on contention. - * Possibly trigger termination on success + * 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() { @@ -290,12 +332,13 @@ public class ForkJoinPool extends Abstra } /** - * Return 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) { - return ((c & -c) >>> 16) != 0; // i.e. least bit is nonzero runState bit + // i.e. least bit is nonzero runState bit + return ((c & -c) >>> 16) != 0; } /** @@ -320,13 +363,14 @@ public class ForkJoinPool extends Abstra // Constructors /** - * Creates a ForkJoinPool with a pool size equal to the number of - * processors available on the system and 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 * because it does not hold {@link - * java.lang.RuntimePermission}("modifyThread"), + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public ForkJoinPool() { this(Runtime.getRuntime().availableProcessors(), @@ -334,47 +378,51 @@ public class ForkJoinPool extends Abstra } /** - * Creates a ForkJoinPool with the indicated parellelism level - * threads, and using the default ForkJoinWorkerThreadFactory, - * @param parallelism the number of worker threads + * 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 * @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}("modifyThread"), + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public ForkJoinPool(int parallelism) { this(parallelism, defaultForkJoinWorkerThreadFactory); } /** - * 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 * @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}("modifyThread"), + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public ForkJoinPool(ForkJoinWorkerThreadFactory factory) { this(Runtime.getRuntime().availableProcessors(), factory); } /** - * 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. + * equal to zero, or greater than implementation limit * @throws NullPointerException if 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}("modifyThread"), + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) { if (parallelism <= 0 || parallelism > MAX_THREADS) @@ -391,13 +439,14 @@ public class ForkJoinPool extends Abstra this.termination = workerLock.newCondition(); this.stealCount = new AtomicLong(); this.submissionQueue = new LinkedTransferQueue>(); - createAndStartInitialWorkers(parallelism); + // worker array and workers are lazily constructed } /** - * Create new worker using factory. + * 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; @@ -405,6 +454,7 @@ public class ForkJoinPool extends Abstra if (w != null) { w.poolIndex = index; w.setDaemon(true); + w.setAsyncMode(locallyFifo); w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index); if (h != null) w.setUncaughtExceptionHandler(h); @@ -413,15 +463,26 @@ public class ForkJoinPool extends Abstra } /** - * Return a good size for worker array given pool size. + * Returns a good size for worker array given pool size. * Currently requires size to be a power of two. */ - private static int arraySizeFor(int ps) { - return ps <= 1? 1 : (1 << (32 - Integer.numberOfLeadingZeros(ps-1))); + 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; } /** - * Create or resize array if necessary to hold newLength + * Creates or resizes array if necessary to hold newLength. + * Call only under exclusion. + * * @return the array */ private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) { @@ -435,39 +496,46 @@ public class ForkJoinPool extends Abstra } /** - * Try to shrink workers into smaller array after one or more terminate + * Tries to shrink workers into smaller array after one or more terminate. */ private void tryShrinkWorkerArray() { ForkJoinWorkerThread[] ws = workers; - 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); + 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); + } } /** - * Initial worker array and worker creation and startup. (This - * must be done under lock to avoid interference by some of the - * newly started threads while creating others.) + * Initializes workers if necessary. */ - private void createAndStartInitialWorkers(int ps) { - final ReentrantLock lock = this.workerLock; - lock.lock(); - try { - ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps); - for (int i = 0; i < ps; ++i) { - ForkJoinWorkerThread w = createWorker(i); - if (w != null) { - ws[i] = w; - w.start(); - updateWorkerCount(1); + 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(); } - } finally { - lock.unlock(); } } @@ -511,14 +579,19 @@ 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) + ensureWorkerInitialization(); submissionQueue.offer(task); signalIdleWorkers(); } /** - * Performs the given task; returning its result upon completion + * Performs the given task, returning its result upon completion. + * * @param task the task * @return the task's result * @throws NullPointerException if task is null @@ -531,111 +604,89 @@ public class ForkJoinPool extends Abstra /** * Arranges for (asynchronous) execution of the given task. + * * @param task the task * @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(); } + 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(); } - } public List> invokeAll(Collection> tasks) { - ArrayList> ts = + ArrayList> forkJoinTasks = new ArrayList>(tasks.size()); - for (Callable c : tasks) - ts.add(new AdaptedCallable(c)); - invoke(new InvokeAll(ts)); - return (List>)(List)ts; + for (Callable task : tasks) + forkJoinTasks.add(ForkJoinTask.adapt(task)); + invoke(new InvokeAll(forkJoinTasks)); + + @SuppressWarnings({"unchecked", "rawtypes"}) + List> futures = (List>) (List) forkJoinTasks; + return futures; } static final class InvokeAll extends RecursiveAction { final ArrayList> tasks; InvokeAll(ArrayList> tasks) { this.tasks = tasks; } public void compute() { - try { invokeAll(tasks); } catch(Exception ignore) {} + 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 + * Returns the factory used for constructing new workers. * * @return the factory used for constructing new workers */ @@ -646,7 +697,8 @@ 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; @@ -667,11 +719,11 @@ 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 - * java.lang.RuntimePermission}("modifyThread"), + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public Thread.UncaughtExceptionHandler setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) { @@ -683,10 +735,12 @@ public class ForkJoinPool extends Abstra old = ueh; ueh = h; ForkJoinWorkerThread[] ws = workers; - for (int i = 0; i < ws.length; ++i) { - ForkJoinWorkerThread w = ws[i]; - if (w != null) - w.setUncaughtExceptionHandler(h); + if (ws != null) { + for (int i = 0; i < ws.length; ++i) { + ForkJoinWorkerThread w = ws[i]; + if (w != null) + w.setUncaughtExceptionHandler(h); + } } } finally { lock.unlock(); @@ -696,14 +750,15 @@ public class ForkJoinPool extends Abstra /** - * Sets the target paralleism level of this pool. + * 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. + * 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}("modifyThread"), + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public void setParallelism(int parallelism) { checkPermission(); @@ -712,7 +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) @@ -727,9 +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; @@ -738,7 +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 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 @@ -749,7 +804,10 @@ 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 */ public int getMaximumPoolSize() { @@ -758,11 +816,13 @@ 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. - * @throws IllegalArgumentException if negative or greater then - * internal implementation limit. + * 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) @@ -772,11 +832,11 @@ 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; - * @return true if maintains parallelism + * 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; @@ -786,13 +846,52 @@ public class ForkJoinPool extends Abstra * Sets whether this pool dynamically maintains its target * 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; } /** + * 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. @@ -807,7 +906,8 @@ public class ForkJoinPool extends Abstra * 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. + * + * @return the number of active threads */ public int getActiveThreadCount() { return activeCountOf(runControl); @@ -817,22 +917,24 @@ public class ForkJoinPool extends Abstra * 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. + * + * @return the number of idle threads */ final int getIdleThreadCount() { int c = runningCountOf(workerCounts) - activeCountOf(runControl); - return (c <= 0)? 0 : c; + return (c <= 0) ? 0 : c; } /** - * 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. - * @return true if all threads are currently idle + * 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; @@ -843,18 +945,19 @@ public class ForkJoinPool extends Abstra * 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 + * 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. + * + * @return the number of steals */ public long getStealCount() { return stealCount.get(); } /** - * Accumulate steal count from a worker. Call only - * when worker known to be idle. + * Accumulates steal count from a worker. + * Call only when worker known to be idle. */ private void updateStealCount(ForkJoinWorkerThread w) { int sc = w.getAndClearStealCount(); @@ -869,33 +972,38 @@ public class ForkJoinPool extends Abstra * 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. + * + * @return the number of queued tasks */ public long getQueuedTaskCount() { long count = 0; ForkJoinWorkerThread[] ws = workers; - for (int i = 0; i < ws.length; ++i) { - ForkJoinWorkerThread t = ws[i]; - if (t != null) - count += t.getQueueSize(); + 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 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. + * + * @return the number of queued submissions */ public int getQueuedSubmissionCount() { return submissionQueue.size(); } /** - * Returns true if there are any tasks submitted to this pool - * that have not yet begun executing. - * @return true if there are any queued submissions. + * 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(); @@ -905,13 +1013,44 @@ public class ForkJoinPool extends Abstra * 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 null if none + * + * @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> 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. @@ -955,30 +1094,48 @@ public class ForkJoinPool extends Abstra * 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}("modifyThread"), + * java.lang.RuntimePermission}{@code ("modifyThread")} */ 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, - * so always returns an empty list. + * 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}("modifyThread"), + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public List shutdownNow() { checkPermission(); @@ -987,42 +1144,54 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if all tasks have completed following shut down. + * Returns {@code true} if all tasks have completed following shut down. * - * @return 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 true if the process of termination has - * commenced but possibly not yet completed. + * 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 true if terminating + * @return {@code true} if terminating but not yet terminated */ public boolean isTerminating() { - return runStateOf(runControl) >= TERMINATING; + return runStateOf(runControl) == TERMINATING; } /** - * Returns true if this pool has been shut down. + * Returns {@code true} if this pool has been shut down. * - * @return 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 true if this executor terminated and - * false if the timeout elapsed before termination + * @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) @@ -1046,9 +1215,10 @@ public class ForkJoinPool extends Abstra // Shutdown and termination support /** - * Callback from terminating worker. Null out the corresponding - * workers slot, and if terminating, try to terminate, else try to - * shrink workers array. + * 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) { @@ -1058,17 +1228,19 @@ public class ForkJoinPool extends Abstra lock.lock(); try { ForkJoinWorkerThread[] ws = workers; - 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 (!isTerminating()) { - tryShrinkWorkerArray(); - tryResumeSpare(true); // allow replacement + 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(); @@ -1077,7 +1249,7 @@ public class ForkJoinPool extends Abstra } /** - * Initiate termination. + * Initiates termination. */ private void terminate() { if (transitionRunStateTo(TERMINATING)) { @@ -1092,7 +1264,7 @@ public class ForkJoinPool extends Abstra } /** - * Possibly terminate when on shutdown state + * Possibly terminates when on shutdown state. */ private void terminateOnShutdown() { if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl)) @@ -1100,7 +1272,7 @@ public class ForkJoinPool extends Abstra } /** - * Clear out and cancel submissions + * Clears out and cancels submissions. */ private void cancelQueuedSubmissions() { ForkJoinTask task; @@ -1109,17 +1281,19 @@ public class ForkJoinPool extends Abstra } /** - * Clean out worker queues. + * Cleans out worker queues. */ private void cancelQueuedWorkerTasks() { final ReentrantLock lock = this.workerLock; lock.lock(); try { ForkJoinWorkerThread[] ws = workers; - for (int i = 0; i < ws.length; ++i) { - ForkJoinWorkerThread t = ws[i]; - if (t != null) - t.cancelTasks(); + if (ws != null) { + for (int i = 0; i < ws.length; ++i) { + ForkJoinWorkerThread t = ws[i]; + if (t != null) + t.cancelTasks(); + } } } finally { lock.unlock(); @@ -1127,18 +1301,20 @@ public class ForkJoinPool extends Abstra } /** - * Set each worker's status to terminating. Requires lock to avoid - * conflicts with add/remove + * 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; - for (int i = 0; i < ws.length; ++i) { - ForkJoinWorkerThread t = ws[i]; - if (t != null) - t.shutdownNow(); + if (ws != null) { + for (int i = 0; i < ws.length; ++i) { + ForkJoinWorkerThread t = ws[i]; + if (t != null) + t.shutdownNow(); + } } } finally { lock.unlock(); @@ -1146,7 +1322,7 @@ public class ForkJoinPool extends Abstra } /** - * Interrupt all unterminated workers. This is not required for + * Interrupts all unterminated workers. This is not required for * sake of internal control, but may help unstick user code during * shutdown. */ @@ -1155,12 +1331,14 @@ public class ForkJoinPool extends Abstra lock.lock(); try { ForkJoinWorkerThread[] ws = workers; - for (int i = 0; i < ws.length; ++i) { - ForkJoinWorkerThread t = ws[i]; - if (t != null && !t.isTerminated()) { - try { - t.interrupt(); - } catch (SecurityException ignore) { + 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) { + } } } } @@ -1214,7 +1392,7 @@ public class ForkJoinPool extends Abstra } /** - * Wake up waiter, returning false if known to already + * Wakes up waiter, returning false if known to already */ boolean signal() { ForkJoinWorkerThread t = thread; @@ -1226,7 +1404,7 @@ public class ForkJoinPool extends Abstra } /** - * Await release on sync + * Awaits release on sync. */ void awaitSyncRelease(ForkJoinPool p) { while (thread != null && !p.syncIsReleasable(this)) @@ -1234,7 +1412,7 @@ public class ForkJoinPool extends Abstra } /** - * Await resumption as spare + * Awaits resumption as spare. */ void awaitSpareRelease() { while (thread != null) { @@ -1248,6 +1426,7 @@ public class ForkJoinPool extends Abstra * 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() { @@ -1269,12 +1448,12 @@ public class ForkJoinPool extends Abstra */ private void signalIdleWorkers() { long c; - do;while (!casEventCount(c = eventCount, c+1)); + do {} while (!casEventCount(c = eventCount, c+1)); ensureSync(); } /** - * Signal threads waiting to poll a task. Because method sync + * 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). @@ -1293,16 +1472,17 @@ public class ForkJoinPool extends Abstra * 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() && !isTerminating() && !suspendIfSpare(w)) { + while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) { long prev = w.lastEventCount; WaitQueueNode node = null; WaitQueueNode h; - while (eventCount == prev && + while (eventCount == prev && ((h = syncStack) == null || h.count == prev)) { if (node == null) node = new WaitQueueNode(prev, w); @@ -1320,14 +1500,15 @@ 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 - * - if the first queued node, we find work available - * If node was not signalled and event count not advanced on exit, + * - 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 true if node can be released + * + * @return {@code true} if node can be released */ final boolean syncIsReleasable(WaitQueueNode node) { long prev = node.count; @@ -1346,8 +1527,8 @@ 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; @@ -1361,13 +1542,13 @@ public class ForkJoinPool extends Abstra // Parallelism maintenance /** - * Decrement running count; if too low, add spare. + * 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 + * 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 @@ -1381,7 +1562,7 @@ public class ForkJoinPool extends Abstra * 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 enounter highly transient peaks when + * 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. * @@ -1390,12 +1571,13 @@ public class ForkJoinPool extends Abstra * target counts, else create only to avoid starvation * @return true if joinMe known to be done */ - final boolean preJoin(ForkJoinTask joinMe, boolean maintainParallelism) { + 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))) { // CAS cheat + if (dec || (dec = casWorkerCounts(counts, --counts))) { if (!needSpare(counts, maintainParallelism)) break; if (joinMe.status < 0) @@ -1410,7 +1592,8 @@ public class ForkJoinPool extends Abstra /** * Same idea as preJoin */ - final boolean preBlock(ManagedBlocker blocker, boolean maintainParallelism){ + final boolean preBlock(ManagedBlocker blocker, + boolean maintainParallelism) { maintainParallelism &= maintainsParallelism; boolean dec = false; while (spareStack == null || !tryResumeSpare(dec)) { @@ -1428,12 +1611,13 @@ 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 * less parallelism we will tolerate before adding another. + * * @param counts current worker counts * @param maintainParallelism try to maintain parallelism */ @@ -1446,13 +1630,14 @@ public class ForkJoinPool extends Abstra return (tc < maxPoolSize && (rc == 0 || totalSurplus < 0 || (maintainParallelism && - runningDeficit > totalSurplus && + runningDeficit > totalSurplus && ForkJoinWorkerThread.hasQueuedTasks(workers)))); } - + /** - * Add a spare worker if lock available and no more than the - * expected numbers of threads exist + * 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) { @@ -1485,7 +1670,7 @@ public class ForkJoinPool extends Abstra } /** - * Add the kth spare worker. On entry, pool coounts are already + * Adds the kth spare worker. On entry, pool counts are already * adjusted to reflect addition. */ private void createAndStartSpare(int k) { @@ -1497,7 +1682,7 @@ 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(); } @@ -1507,11 +1692,12 @@ public class ForkJoinPool extends Abstra } /** - * Suspend 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. + * 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) { @@ -1522,7 +1708,7 @@ public class ForkJoinPool extends Abstra node = new WaitQueueNode(0, w); if (casWorkerCounts(s, s-1)) { // representation-dependent // push onto stack - do;while (!casSpareStack(node.next = spareStack, node)); + do {} while (!casSpareStack(node.next = spareStack, node)); // block until released by resumeSpare node.awaitSpareRelease(); return true; @@ -1532,7 +1718,8 @@ public class ForkJoinPool extends Abstra } /** - * Try to pop and resume a spare thread. + * Tries to pop and resume a spare thread. + * * @param updateCount if true, increment running count on success * @return true if successful */ @@ -1550,7 +1737,8 @@ public class ForkJoinPool extends Abstra } /** - * Pop and resume all spare threads. Same idea as ensureSync. + * Pops and resumes all spare threads. Same idea as ensureSync. + * * @return true if any spares released */ private boolean resumeAllSpares() { @@ -1568,7 +1756,7 @@ public class ForkJoinPool extends Abstra } /** - * Pop and shutdown excessive spare threads. Call only while + * 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. @@ -1592,81 +1780,86 @@ public class ForkJoinPool extends Abstra /** * Interface for extending managed parallelism for tasks running - * in ForkJoinPools. A ManagedBlocker provides two methods. - * Method isReleasable must return true if blocking is not - * necessary. Method block blocks the current thread - * if necessary (perhaps internally invoking 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: - * 

-     *   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());
-     *     }
+     *  
 {@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());
      *   }
-     * 

+     * }}
*/ public static interface ManagedBlocker { /** * 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 allowe to). + * (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 - * maintainParallelism is true and the pool supports - * it ({@link #getMaintainsParallelism}), this method attempts to - * maintain the pool's nominal parallelism. Otherwise if 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 - * 

-     *   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. + * 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 {@link ForkJoinTask}, this method is + * behaviorally equivalent to + * 

 {@code
+     * while (!blocker.isReleasable())
+     *   if (blocker.block())
+     *     return;
+     * }
+ * + * 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. - * @throws InterruptedException if blocker.block did so. + * @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); + ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ? + ((ForkJoinWorkerThread) t).pool : null); if (!blocker.isReleasable()) { try { if (pool == null || @@ -1681,66 +1874,87 @@ public class ForkJoinPool extends Abstra private static void awaitBlocker(ManagedBlocker blocker) throws InterruptedException { - do;while (!blocker.isReleasable() && !blocker.block()); + 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 - // Temporary Unsafe mechanics for preliminary release - - static final Unsafe _unsafe; - static final long eventCountOffset; - static final long workerCountsOffset; - static final long runControlOffset; - static final long syncStackOffset; - static final long spareStackOffset; - - static { - try { - if (ForkJoinPool.class.getClassLoader() != null) { - Field f = Unsafe.class.getDeclaredField("theUnsafe"); - f.setAccessible(true); - _unsafe = (Unsafe)f.get(null); - } - else - _unsafe = Unsafe.getUnsafe(); - eventCountOffset = _unsafe.objectFieldOffset - (ForkJoinPool.class.getDeclaredField("eventCount")); - workerCountsOffset = _unsafe.objectFieldOffset - (ForkJoinPool.class.getDeclaredField("workerCounts")); - runControlOffset = _unsafe.objectFieldOffset - (ForkJoinPool.class.getDeclaredField("runControl")); - syncStackOffset = _unsafe.objectFieldOffset - (ForkJoinPool.class.getDeclaredField("syncStack")); - spareStackOffset = _unsafe.objectFieldOffset - (ForkJoinPool.class.getDeclaredField("spareStack")); - } catch (Exception e) { - throw new RuntimeException("Could not initialize intrinsics", e); - } - } + private static final sun.misc.Unsafe 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); + return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val); } private boolean casWorkerCounts(int cmp, int val) { - return _unsafe.compareAndSwapInt(this, workerCountsOffset, cmp, val); + return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val); } private boolean casRunControl(int cmp, int val) { - return _unsafe.compareAndSwapInt(this, runControlOffset, cmp, val); + return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val); } private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) { - return _unsafe.compareAndSwapObject(this, spareStackOffset, cmp, val); + return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val); } private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) { - return _unsafe.compareAndSwapObject(this, syncStackOffset, cmp, 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()); + } + } } }