--- jsr166/src/jsr166y/ForkJoinPool.java 2009/07/20 22:26:03 1.9 +++ jsr166/src/jsr166y/ForkJoinPool.java 2009/07/25 15:50:57 1.23 @@ -5,12 +5,19 @@ */ 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 @@ -56,6 +63,9 @@ import java.lang.reflect.*; * maximum number of running threads to 32767. Attempts to create * pools with greater than the maximum result in * IllegalArgumentExceptions. + * + * @since 1.7 + * @author Doug Lea */ public class ForkJoinPool extends AbstractExecutorService { @@ -81,13 +91,13 @@ public class ForkJoinPool extends Abstra * 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 @@ -181,7 +191,7 @@ 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; @@ -216,8 +226,8 @@ public class ForkJoinPool extends Abstra * 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; @@ -226,26 +236,28 @@ 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)); } /** @@ -271,9 +283,10 @@ 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; @@ -281,9 +294,10 @@ 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() { @@ -297,12 +311,13 @@ public class ForkJoinPool extends Abstra } /** - * Return true if argument represents zero active count and + * Returns 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; } /** @@ -328,12 +343,13 @@ 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}{@code ("modifyThread")}, + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public ForkJoinPool() { this(Runtime.getRuntime().availableProcessors(), @@ -342,14 +358,15 @@ public class ForkJoinPool extends Abstra /** * Creates a ForkJoinPool with the indicated parallelism level - * threads, and using the default ForkJoinWorkerThreadFactory, + * 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}{@code ("modifyThread")}, + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public ForkJoinPool(int parallelism) { this(parallelism, defaultForkJoinWorkerThreadFactory); @@ -358,13 +375,14 @@ 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}{@code ("modifyThread")}, + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public ForkJoinPool(ForkJoinWorkerThreadFactory factory) { this(Runtime.getRuntime().availableProcessors(), factory); @@ -376,12 +394,12 @@ 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}{@code ("modifyThread")}, + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) { if (parallelism <= 0 || parallelism > MAX_THREADS) @@ -402,7 +420,8 @@ public class ForkJoinPool extends Abstra } /** - * 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 */ @@ -421,16 +440,18 @@ 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. - * Call only under exclusion or lock + * Creates or resizes array if necessary to hold newLength. + * Call only under exclusion. + * * @return the array */ private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) { @@ -444,7 +465,7 @@ 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; @@ -460,7 +481,7 @@ public class ForkJoinPool extends Abstra } /** - * Initialize workers if necessary + * Initializes workers if necessary. */ final void ensureWorkerInitialization() { ForkJoinWorkerThread[] ws = workers; @@ -527,6 +548,8 @@ public class ForkJoinPool extends Abstra * Common code for execute, invoke and submit */ private void doSubmit(ForkJoinTask task) { + if (task == null) + throw new NullPointerException(); if (isShutdown()) throw new RejectedExecutionException(); if (workers == null) @@ -536,7 +559,8 @@ public class ForkJoinPool extends Abstra } /** - * 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 @@ -549,6 +573,7 @@ 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 @@ -560,7 +585,14 @@ public class ForkJoinPool extends Abstra // AbstractExecutorService methods public void execute(Runnable task) { - doSubmit(new AdaptedRunnable(task, null)); + ForkJoinTask job; + if (task instanceof AdaptedCallable) // avoid re-wrap + job = (AdaptedCallable)task; + else if (task instanceof AdaptedRunnable) + job = (AdaptedRunnable)task; + else + job = new AdaptedRunnable(task, null); + doSubmit(job); } public ForkJoinTask submit(Callable task) { @@ -576,14 +608,34 @@ public class ForkJoinPool extends Abstra } public ForkJoinTask submit(Runnable task) { - ForkJoinTask job = new AdaptedRunnable(task, null); + ForkJoinTask job; + if (task instanceof AdaptedCallable) // avoid re-wrap + job = (AdaptedCallable)task; + else if (task instanceof AdaptedRunnable) + job = (AdaptedRunnable)task; + else + job = new AdaptedRunnable(task, null); doSubmit(job); return job; } /** + * 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 + */ + public ForkJoinTask submit(ForkJoinTask task) { + doSubmit(task); + return task; + } + + /** * Adaptor for Runnables. This implements RunnableFuture - * to be compliant with AbstractExecutorService constraints + * to be compliant with AbstractExecutorService constraints. */ static final class AdaptedRunnable extends ForkJoinTask implements RunnableFuture { @@ -603,6 +655,7 @@ public class ForkJoinPool extends Abstra return true; } public void run() { invoke(); } + private static final long serialVersionUID = 5232453952276885070L; } /** @@ -631,29 +684,35 @@ public class ForkJoinPool extends Abstra } } public void run() { invoke(); } + private static final long serialVersionUID = 2838392045355241008L; } 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(new AdaptedCallable(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 */ @@ -664,6 +723,7 @@ public class ForkJoinPool extends Abstra /** * Returns the handler for internal worker threads that terminate * due to unrecoverable errors encountered while executing tasks. + * * @return the handler, or null if none */ public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { @@ -689,7 +749,7 @@ public class ForkJoinPool extends Abstra * @throws SecurityException if a security manager exists and * the caller is not permitted to modify threads * because it does not hold {@link - * java.lang.RuntimePermission}{@code ("modifyThread")}, + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public Thread.UncaughtExceptionHandler setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) { @@ -717,13 +777,14 @@ public class ForkJoinPool extends Abstra /** * 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}{@code ("modifyThread")}, + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public void setParallelism(int parallelism) { checkPermission(); @@ -770,6 +831,7 @@ 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() { @@ -781,8 +843,9 @@ 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. + * internal implementation limit */ public void setMaximumPoolSize(int newMax) { if (newMax < 0 || newMax > MAX_THREADS) @@ -795,7 +858,8 @@ 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; + * This setting is by default true. + * * @return true if maintains parallelism */ public boolean getMaintainsParallelism() { @@ -806,6 +870,7 @@ 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 */ public void setMaintainsParallelism(boolean enable) { @@ -822,7 +887,7 @@ public class ForkJoinPool extends Abstra * invocations at other times may be unpredictable. * * @param async if true, use locally FIFO scheduling - * @return the previous mode. + * @return the previous mode */ public boolean setAsyncMode(boolean async) { boolean oldMode = locallyFifo; @@ -842,7 +907,7 @@ public class ForkJoinPool extends Abstra * Returns true if this pool uses local first-in-first-out * scheduling mode for forked tasks that are never joined. * - * @return true if this pool uses async mode. + * @return true if this pool uses async mode */ public boolean getAsyncMode() { return locallyFifo; @@ -863,7 +928,8 @@ 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); @@ -873,21 +939,23 @@ 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 + * 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 */ public boolean isQuiescent() { @@ -899,18 +967,19 @@ 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(); @@ -925,7 +994,8 @@ 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; @@ -944,7 +1014,8 @@ public class ForkJoinPool extends Abstra * Returns an estimate of the number tasks submitted to this pool * that have not yet begun executing. This method takes time * proportional to the number of submissions. - * @return the number of queued submissions. + * + * @return the number of queued submissions */ public int getQueuedSubmissionCount() { return submissionQueue.size(); @@ -953,7 +1024,8 @@ public class ForkJoinPool extends Abstra /** * Returns 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. + * + * @return {@code true} if there are any queued submissions */ public boolean hasQueuedSubmissions() { return !submissionQueue.isEmpty(); @@ -963,6 +1035,7 @@ 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 */ protected ForkJoinTask pollSubmission() { @@ -982,6 +1055,7 @@ public class ForkJoinPool extends Abstra * 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 */ @@ -1042,10 +1116,11 @@ 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}{@code ("modifyThread")}, + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public void shutdown() { checkPermission(); @@ -1063,11 +1138,12 @@ public class ForkJoinPool extends Abstra * upon termination, so always returns an empty list. However, you * can use method {@code drainTasksTo} before invoking this * method to transfer unexecuted tasks to another collection. + * * @return an empty list * @throws SecurityException if a security manager exists and * the caller is not permitted to modify threads * because it does not hold {@link - * java.lang.RuntimePermission}{@code ("modifyThread")}, + * java.lang.RuntimePermission}{@code ("modifyThread")} */ public List shutdownNow() { checkPermission(); @@ -1135,9 +1211,10 @@ 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) { @@ -1168,7 +1245,7 @@ public class ForkJoinPool extends Abstra } /** - * Initiate termination. + * Initiates termination. */ private void terminate() { if (transitionRunStateTo(TERMINATING)) { @@ -1183,7 +1260,7 @@ public class ForkJoinPool extends Abstra } /** - * Possibly terminate when on shutdown state + * Possibly terminates when on shutdown state. */ private void terminateOnShutdown() { if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl)) @@ -1191,7 +1268,7 @@ public class ForkJoinPool extends Abstra } /** - * Clear out and cancel submissions + * Clears out and cancels submissions. */ private void cancelQueuedSubmissions() { ForkJoinTask task; @@ -1200,7 +1277,7 @@ public class ForkJoinPool extends Abstra } /** - * Clean out worker queues. + * Cleans out worker queues. */ private void cancelQueuedWorkerTasks() { final ReentrantLock lock = this.workerLock; @@ -1220,8 +1297,8 @@ 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; @@ -1241,7 +1318,7 @@ 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. */ @@ -1311,7 +1388,7 @@ 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; @@ -1323,7 +1400,7 @@ public class ForkJoinPool extends Abstra } /** - * Await release on sync + * Awaits release on sync. */ void awaitSyncRelease(ForkJoinPool p) { while (thread != null && !p.syncIsReleasable(this)) @@ -1331,7 +1408,7 @@ public class ForkJoinPool extends Abstra } /** - * Await resumption as spare + * Awaits resumption as spare. */ void awaitSpareRelease() { while (thread != null) { @@ -1345,6 +1422,7 @@ 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() { @@ -1366,12 +1444,12 @@ 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). @@ -1390,6 +1468,7 @@ 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) { @@ -1420,10 +1499,11 @@ public class ForkJoinPool extends Abstra * Returns true if worker waiting on sync can proceed: * - on signal (thread == null) * - on event count advance (winning race to notify vs signaller) - * - on Interrupt + * - 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 */ final boolean syncIsReleasable(WaitQueueNode node) { @@ -1458,13 +1538,13 @@ 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 @@ -1487,12 +1567,14 @@ 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) @@ -1507,7 +1589,8 @@ 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)) { @@ -1531,6 +1614,7 @@ public class ForkJoinPool extends Abstra * 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 */ @@ -1548,8 +1632,9 @@ public class ForkJoinPool extends Abstra } /** - * 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) { @@ -1582,7 +1667,7 @@ public class ForkJoinPool extends Abstra } /** - * Add the kth spare worker. On entry, pool counts are already + * Adds the kth spare worker. On entry, pool counts are already * adjusted to reflect addition. */ private void createAndStartSpare(int k) { @@ -1604,11 +1689,12 @@ 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) { @@ -1619,7 +1705,7 @@ 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; @@ -1629,7 +1715,8 @@ 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 */ @@ -1647,7 +1734,8 @@ 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() { @@ -1665,7 +1753,7 @@ 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. @@ -1691,35 +1779,36 @@ public class ForkJoinPool extends Abstra * Interface for extending managed parallelism for tasks running * in ForkJoinPools. A ManagedBlocker provides two methods. * Method {@code isReleasable} must return true if blocking is not - * necessary. Method {@code block} blocks the current thread - * if necessary (perhaps internally invoking isReleasable before - * actually blocking.). + * 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). + * if isReleasable would return true) * @throws InterruptedException if interrupted while waiting - * (the method is not required to do so, but is allowed to). + * (the method is not required to do so, but is allowed to) */ boolean block() throws InterruptedException; @@ -1736,18 +1825,18 @@ public class ForkJoinPool extends Abstra * while the current thread is blocked. If * {@code maintainParallelism} is true and the pool supports * it ({@link #getMaintainsParallelism}), this method attempts to - * maintain the pool's nominal parallelism. Otherwise if activates + * maintain the pool's nominal parallelism. Otherwise it activates * a thread only if necessary to avoid complete starvation. This * option may be preferable when blockages use timeouts, or are * almost always brief. * *

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

-     *   while (!blocker.isReleasable())
-     *      if (blocker.block())
-     *         return;
-     * 
+ *
 {@code
+     * while (!blocker.isReleasable())
+     *   if (blocker.block())
+     *     return;
+     * }
* If the caller is a ForkJoinTask, then the pool may first * be expanded to ensure parallelism, and later adjusted. * @@ -1756,14 +1845,14 @@ public class ForkJoinPool extends Abstra * 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. + * @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 || @@ -1778,83 +1867,82 @@ 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 protected RunnableFuture newTaskFor(Runnable runnable, T value) { - return new AdaptedRunnable(runnable, value); + return new AdaptedRunnable(runnable, value); } protected RunnableFuture newTaskFor(Callable callable) { - return new AdaptedCallable(callable); + return new AdaptedCallable(callable); } - // Temporary Unsafe mechanics for preliminary release - private static Unsafe getUnsafe() throws Throwable { + // Unsafe mechanics for jsr166y 3rd party package. + private static sun.misc.Unsafe getUnsafe() { try { - return Unsafe.getUnsafe(); + return sun.misc.Unsafe.getUnsafe(); } catch (SecurityException se) { try { return java.security.AccessController.doPrivileged - (new java.security.PrivilegedExceptionAction() { - public Unsafe run() throws Exception { - return getUnsafePrivileged(); + (new java.security.PrivilegedExceptionAction() { + public sun.misc.Unsafe run() throws Exception { + return getUnsafeByReflection(); }}); } catch (java.security.PrivilegedActionException e) { - throw e.getCause(); + throw new RuntimeException("Could not initialize intrinsics", + e.getCause()); } } } - private static Unsafe getUnsafePrivileged() + private static sun.misc.Unsafe getUnsafeByReflection() throws NoSuchFieldException, IllegalAccessException { - Field f = Unsafe.class.getDeclaredField("theUnsafe"); + java.lang.reflect.Field f = + sun.misc.Unsafe.class.getDeclaredField("theUnsafe"); f.setAccessible(true); - return (Unsafe) f.get(null); + return (sun.misc.Unsafe) f.get(null); } - private static long fieldOffset(String fieldName) - throws NoSuchFieldException { - return _unsafe.objectFieldOffset - (ForkJoinPool.class.getDeclaredField(fieldName)); - } - - 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 { + private static long fieldOffset(String fieldName, Class klazz) { try { - _unsafe = getUnsafe(); - eventCountOffset = fieldOffset("eventCount"); - workerCountsOffset = fieldOffset("workerCounts"); - runControlOffset = fieldOffset("runControl"); - syncStackOffset = fieldOffset("syncStack"); - spareStackOffset = fieldOffset("spareStack"); - } catch (Throwable e) { - throw new RuntimeException("Could not initialize intrinsics", e); + return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName)); + } catch (NoSuchFieldException e) { + // Convert Exception to Error + NoSuchFieldError error = new NoSuchFieldError(fieldName); + error.initCause(e); + throw error; } } + private static final sun.misc.Unsafe UNSAFE = getUnsafe(); + static final long eventCountOffset = + fieldOffset("eventCount", ForkJoinPool.class); + static final long workerCountsOffset = + fieldOffset("workerCounts", ForkJoinPool.class); + static final long runControlOffset = + fieldOffset("runControl", ForkJoinPool.class); + static final long syncStackOffset = + fieldOffset("syncStack",ForkJoinPool.class); + static final long spareStackOffset = + fieldOffset("spareStack", ForkJoinPool.class); + private 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); } }