--- jsr166/src/jsr166y/ForkJoinPool.java 2009/01/07 19:12:36 1.3 +++ jsr166/src/jsr166y/ForkJoinPool.java 2009/08/03 00:53:15 1.40 @@ -5,55 +5,68 @@ */ 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. Normally a single {@code 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. * - *

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. + *

{@code ForkJoinPool}s differ from other kinds of {@link + * Executor}s 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 + * {@code ForkJoinTask}s), as well as the 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 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} 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 {@link ManagedBlocker} interface + * enables extension of the kinds of synchronization accommodated. + * The target parallelism level may also be changed dynamically + * ({@link #setParallelism}) and thread construction can be limited + * using methods {@link #setMaximumPoolSize} and/or {@link + * #setMaintainsParallelism}. * *

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. * *

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 +82,23 @@ 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 +144,11 @@ 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 +164,7 @@ public class ForkJoinPool extends Abstra /** * The uncaught exception handler used when any worker - * abrupty terminates + * abruptly terminates */ private Thread.UncaughtExceptionHandler ueh; @@ -179,9 +192,9 @@ 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 barrierStack; + private volatile WaitQueueNode syncStack; /** * The count for event barrier @@ -204,13 +217,18 @@ 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 +237,28 @@ 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)); } /** @@ -264,32 +284,41 @@ public class ForkJoinPool extends Abstra private static int runControlFor(int r, int a) { return (r << 16) + a; } /** - * Increment active count. Called by workers before/during - * executing tasks. + * Tries incrementing active count; fails on contention. + * Called by workers before/during executing tasks. + * + * @return true on success */ - final void incrementActiveCount() { - int c; - do;while (!casRunControl(c = runControl, c+1)); + final boolean tryIncrementActiveCount() { + int c = runControl; + return casRunControl(c, c+1); } /** - * Decrement active count; possibly trigger termination. + * 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 void decrementActiveCount() { - int c, nextc; - do;while (!casRunControl(c = runControl, nextc = c-1)); + final boolean tryDecrementActiveCount() { + int c = runControl; + int nextc = c - 1; + if (!casRunControl(c, nextc)) + return false; if (canTerminateOnShutdown(nextc)) terminateOnShutdown(); + return true; } /** - * 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; } /** @@ -315,12 +344,13 @@ public class ForkJoinPool extends Abstra /** * Creates a ForkJoinPool with a pool size equal to the number of - * processors available on the system and using the default - * ForkJoinWorkerThreadFactory, + * processors available on the system, using the default + * ForkJoinWorkerThreadFactory. + * * @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(), @@ -328,15 +358,16 @@ public class ForkJoinPool extends Abstra } /** - * Creates a ForkJoinPool with the indicated parellelism level - * threads, and using the default ForkJoinWorkerThreadFactory, + * Creates a ForkJoinPool with the indicated parallelism level + * threads and using the default ForkJoinWorkerThreadFactory. + * * @param parallelism the number of worker threads * @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); @@ -345,13 +376,14 @@ public class ForkJoinPool extends Abstra /** * Creates a ForkJoinPool with parallelism equal to the number of * processors available on the system and using the given - * ForkJoinWorkerThreadFactory, + * ForkJoinWorkerThreadFactory. + * * @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); @@ -363,12 +395,12 @@ public class ForkJoinPool extends Abstra * @param parallelism the targeted number of worker threads * @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) @@ -385,11 +417,12 @@ 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 */ @@ -399,6 +432,7 @@ 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); @@ -407,15 +441,18 @@ 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) { + return (poolSize <= 1) ? 1 : + (1 << (32 - Integer.numberOfLeadingZeros(poolSize-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) { @@ -429,39 +466,46 @@ 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(); } } @@ -505,14 +549,19 @@ 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(true); + 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 @@ -525,111 +574,89 @@ 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 */ @@ -640,7 +667,8 @@ 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; @@ -661,11 +689,11 @@ 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) { @@ -677,10 +705,12 @@ 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(); @@ -690,14 +720,15 @@ 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(); @@ -717,7 +748,7 @@ public class ForkJoinPool extends Abstra } finally { lock.unlock(); } - signalIdleWorkers(false); + signalIdleWorkers(); } /** @@ -732,7 +763,7 @@ 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 @@ -744,6 +775,7 @@ 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. + * * @return the maximum */ public int getMaximumPoolSize() { @@ -755,8 +787,9 @@ public class ForkJoinPool extends Abstra * 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. + * + * @throws IllegalArgumentException if negative or greater than + * internal implementation limit */ public void setMaximumPoolSize(int newMax) { if (newMax < 0 || newMax > MAX_THREADS) @@ -766,11 +799,11 @@ 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; @@ -780,13 +813,52 @@ 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. @@ -801,7 +873,8 @@ 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); @@ -811,22 +884,24 @@ 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; @@ -837,18 +912,19 @@ 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(); @@ -863,33 +939,38 @@ 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(); @@ -899,13 +980,44 @@ 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. @@ -949,16 +1061,31 @@ 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(); + } } /** @@ -966,13 +1093,16 @@ public class ForkJoinPool extends Abstra * 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. + * this method cancels rather than collects non-executed tasks + * upon termination, so always returns an empty list. However, you + * can use method {@link #drainTasksTo} before invoking this + * method to transfer unexecuted tasks to another collection. + * * @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(); @@ -981,28 +1111,28 @@ 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 + * Returns {@code true} if the process of termination has * commenced but possibly not yet completed. * - * @return true if terminating + * @return {@code true} if terminating */ public boolean isTerminating() { 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; @@ -1015,8 +1145,8 @@ public class ForkJoinPool extends Abstra * * @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) @@ -1040,9 +1170,10 @@ 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) { @@ -1052,41 +1183,43 @@ 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 (!isTerminating()) { + tryShrinkWorkerArray(); + tryResumeSpare(true); // allow replacement + } } } finally { lock.unlock(); } - signalIdleWorkers(false); + signalIdleWorkers(); } /** - * Initiate termination. + * Initiates termination. */ private void terminate() { if (transitionRunStateTo(TERMINATING)) { stopAllWorkers(); resumeAllSpares(); - signalIdleWorkers(true); + signalIdleWorkers(); cancelQueuedSubmissions(); cancelQueuedWorkerTasks(); interruptUnterminatedWorkers(); - signalIdleWorkers(true); // resignal after interrupt + signalIdleWorkers(); // resignal after interrupt } } /** - * Possibly terminate when on shutdown state + * Possibly terminates when on shutdown state. */ private void terminateOnShutdown() { if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl)) @@ -1094,7 +1227,7 @@ public class ForkJoinPool extends Abstra } /** - * Clear out and cancel submissions + * Clears out and cancels submissions. */ private void cancelQueuedSubmissions() { ForkJoinTask task; @@ -1103,17 +1236,19 @@ 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(); @@ -1121,18 +1256,20 @@ 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(); @@ -1140,7 +1277,7 @@ 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. */ @@ -1149,12 +1286,14 @@ 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) { + } } } } @@ -1165,75 +1304,93 @@ public class ForkJoinPool extends Abstra /* - * Nodes for event barrier to manage idle threads. + * 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 some, - * they may wait for next count. Synchronization events occur only - * in enough contexts to maintain overall liveness: + * 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 - * - Creation or termination of a worker + * - Resizes or other changes to the workers array * - pool termination * - A worker pushing a task on an empty queue * - * The last case (pushing a task) occurs often enough, and is - * heavy enough compared to simple stack pushes to require some - * special handling: Method signalNonEmptyWorkerQueue 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, a worker in sync - * rescans for tasks after being enqueued if it was the first to - * enqueue, and aborts the wait if finding one, also helping to - * signal others. This works well because the worker has nothing - * better to do anyway, and so might as well help alleviate the - * overhead and contention on the threads actually doing work. - * - * Queue nodes are basic Treiber stack nodes, also used for spare - * stack. + * 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(ForkJoinWorkerThread w, long c) { + + WaitQueueNode(long c, ForkJoinWorkerThread w) { count = c; thread = w; } - final boolean signal() { + + /** + * Wakes up waiter, returning false if known to already + */ + boolean signal() { ForkJoinWorkerThread t = thread; + if (t == null) + return false; thread = null; - if (t != null) { - LockSupport.unpark(t); - return true; + 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); } - return false; } } /** - * Release at least one thread waiting for event count to advance, - * if one exists. If initial attempt fails, release all threads. - * @param all if false, at first try to only release one thread - * @return current event + * 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 */ - private long releaseIdleWorkers(boolean all) { - long c; - for (;;) { - WaitQueueNode q = barrierStack; - c = eventCount; - long qc; - if (q == null || (qc = q.count) >= c) - break; - if (!all) { - if (casBarrierStack(q, q.next) && q.signal()) - break; - all = true; - } - else if (casBarrierStack(q, null)) { + final long ensureSync() { + long c = eventCount; + WaitQueueNode q; + while ((q = syncStack) != null && q.count < c) { + if (casBarrierStack(q, null)) { do { - q.signal(); + q.signal(); } while ((q = q.next) != null); break; } @@ -1242,94 +1399,111 @@ public class ForkJoinPool extends Abstra } /** - * Returns current barrier event count - * @return current barrier event count + * Increments event count and releases waiting threads. */ - final long getEventCount() { - long ec = eventCount; - releaseIdleWorkers(true); // release to ensure accurate result - return ec; - } - - /** - * Increment event count and release at least one waiting thread, - * if one exists (released threads will in turn wake up others). - * @param all if true, try to wake up all - */ - final void signalIdleWorkers(boolean all) { + private void signalIdleWorkers() { long c; - do;while (!casEventCount(c = eventCount, c+1)); - releaseIdleWorkers(all); + do {} while (!casEventCount(c = eventCount, c+1)); + ensureSync(); } /** - * Wake up threads waiting to steal a task. Because method - * sync rechecks availability, it is OK to only proceed if - * queue appears to be non-empty. + * 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 signalNonEmptyWorkerQueue() { - // If CAS fails another signaller must have succeeded + final void signalWork() { long c; - if (barrierStack != null && casEventCount(c = eventCount, c+1)) - releaseIdleWorkers(false); + 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 count, or some thread is - * waiting on a previous count, or there is stealable work - * available. Help wake up others on release. + * 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 - * @param prev previous value returned by sync (or 0) - * @return current event count */ - final long sync(ForkJoinWorkerThread w, long prev) { - updateStealCount(w); + final void sync(ForkJoinWorkerThread w) { + updateStealCount(w); // Transfer w's count while it is idle - while (!w.isShutdown() && !isTerminating() && - (parallelism >= runningCountOf(workerCounts) || - !suspendIfSpare(w))) { // prefer suspend to waiting here + while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) { + long prev = w.lastEventCount; WaitQueueNode node = null; - boolean queued = false; - for (;;) { - if (!queued) { - if (eventCount != prev) - break; - WaitQueueNode h = barrierStack; - if (h != null && h.count != prev) - break; // release below and maybe retry - if (node == null) - node = new WaitQueueNode(w, prev); - queued = casBarrierStack(node.next = h, node); - } - else if (Thread.interrupted() || - node.thread == null || - (node.next == null && w.prescan()) || - eventCount != prev) { - node.thread = null; - if (eventCount == prev) // help trigger - casEventCount(prev, prev+1); + 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; } - else - LockSupport.park(this); } + 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 (releaseIdleWorkers(false) != prev) - return ec; + if (prev <= ec) // help signal + casEventCount(ec, ec+1); } - return prev; // return old count if aborted + 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 /** - * 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 @@ -1343,7 +1517,7 @@ 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. * @@ -1352,12 +1526,14 @@ 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))) { + // CAS cheat if (!needSpare(counts, maintainParallelism)) break; if (joinMe.status < 0) @@ -1372,7 +1548,8 @@ 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)) { @@ -1390,12 +1567,13 @@ 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 */ @@ -1408,31 +1586,14 @@ public class ForkJoinPool extends Abstra return (tc < maxPoolSize && (rc == 0 || totalSurplus < 0 || (maintainParallelism && - runningDeficit > totalSurplus && mayHaveQueuedWork()))); + runningDeficit > totalSurplus && + ForkJoinWorkerThread.hasQueuedTasks(workers)))); } /** - * Returns true if at least one worker queue appears to be - * nonempty. This is expensive but not often called. It is not - * critical that this be accurate, but if not, more or fewer - * running threads than desired might be maintained. - */ - private boolean mayHaveQueuedWork() { - ForkJoinWorkerThread[] ws = workers; - int len = ws.length; - ForkJoinWorkerThread v; - for (int i = 0; i < len; ++i) { - if ((v = ws[i]) != null && v.getRawQueueSize() > 0) { - releaseIdleWorkers(false); // help wake up stragglers - return true; - } - } - return false; - } - - /** - * 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) { @@ -1465,7 +1626,7 @@ 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) { @@ -1483,15 +1644,16 @@ public class ForkJoinPool extends Abstra } else updateWorkerCount(-1); // adjust on failure - signalIdleWorkers(false); + signalIdleWorkers(); } /** - * 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) { @@ -1499,17 +1661,12 @@ public class ForkJoinPool extends Abstra int s; while (parallelism < runningCountOf(s = workerCounts)) { if (node == null) - node = new WaitQueueNode(w, 0); + 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 - while (node.thread != null) { - if (!Thread.interrupted()) - LockSupport.park(this); - } - w.activate(); // help warm up + node.awaitSpareRelease(); return true; } } @@ -1517,7 +1674,8 @@ 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 */ @@ -1535,8 +1693,8 @@ public class ForkJoinPool extends Abstra } /** - * Pop and resume all spare threads. Same idea as - * releaseIdleWorkers. + * Pops and resumes all spare threads. Same idea as ensureSync. + * * @return true if any spares released */ private boolean resumeAllSpares() { @@ -1554,7 +1712,7 @@ 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. @@ -1577,92 +1735,87 @@ public class ForkJoinPool extends Abstra } /** - * Returns approximate number of spares, just for diagnostics. - */ - private int countSpares() { - int sum = 0; - for (WaitQueueNode q = spareStack; q != null; q = q.next) - ++sum; - return sum; - } - - /** * 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 || @@ -1677,66 +1830,87 @@ 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 barrierStackOffset; - 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")); - barrierStackOffset = _unsafe.objectFieldOffset - (ForkJoinPool.class.getDeclaredField("barrierStack")); - 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, barrierStackOffset, 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()); + } + } } }