--- jsr166/src/jsr166y/ForkJoinTask.java 2009/08/05 00:57:41 1.39 +++ jsr166/src/jsr166y/ForkJoinTask.java 2012/01/28 04:32:25 1.84 @@ -1,20 +1,26 @@ /* * Written by Doug Lea with assistance from members of JCP JSR-166 * Expert Group and released to the public domain, as explained at - * http://creativecommons.org/licenses/publicdomain + * http://creativecommons.org/publicdomain/zero/1.0/ */ package jsr166y; - -import java.util.concurrent.*; - import java.io.Serializable; import java.util.Collection; -import java.util.Collections; import java.util.List; import java.util.RandomAccess; -import java.util.Map; -import java.util.WeakHashMap; +import java.lang.ref.WeakReference; +import java.lang.ref.ReferenceQueue; +import java.util.concurrent.Callable; +import java.util.concurrent.CancellationException; +import java.util.concurrent.ExecutionException; +import java.util.concurrent.Future; +import java.util.concurrent.RejectedExecutionException; +import java.util.concurrent.RunnableFuture; +import java.util.concurrent.TimeUnit; +import java.util.concurrent.TimeoutException; +import java.util.concurrent.locks.ReentrantLock; +import java.lang.reflect.Constructor; /** * Abstract base class for tasks that run within a {@link ForkJoinPool}. @@ -28,46 +34,56 @@ import java.util.WeakHashMap; * start other subtasks. As indicated by the name of this class, * many programs using {@code ForkJoinTask} employ only methods * {@link #fork} and {@link #join}, or derivatives such as {@link - * #invokeAll}. However, this class also provides a number of other - * methods that can come into play in advanced usages, as well as - * extension mechanics that allow support of new forms of fork/join - * processing. + * #invokeAll(ForkJoinTask...) invokeAll}. However, this class also + * provides a number of other methods that can come into play in + * advanced usages, as well as extension mechanics that allow + * support of new forms of fork/join processing. * *

A {@code ForkJoinTask} is a lightweight form of {@link Future}. * The efficiency of {@code ForkJoinTask}s stems from a set of * restrictions (that are only partially statically enforceable) - * reflecting their intended use as computational tasks calculating - * pure functions or operating on purely isolated objects. The - * primary coordination mechanisms are {@link #fork}, that arranges + * reflecting their main use as computational tasks calculating pure + * functions or operating on purely isolated objects. The primary + * coordination mechanisms are {@link #fork}, that arranges * asynchronous execution, and {@link #join}, that doesn't proceed * until the task's result has been computed. Computations should - * avoid {@code synchronized} methods or blocks, and should minimize - * other blocking synchronization apart from joining other tasks or - * using synchronizers such as Phasers that are advertised to - * cooperate with fork/join scheduling. Tasks should also not perform - * blocking IO, and should ideally access variables that are - * completely independent of those accessed by other running - * tasks. Minor breaches of these restrictions, for example using - * shared output streams, may be tolerable in practice, but frequent - * use may result in poor performance, and the potential to - * indefinitely stall if the number of threads not waiting for IO or - * other external synchronization becomes exhausted. This usage - * restriction is in part enforced by not permitting checked - * exceptions such as {@code IOExceptions} to be thrown. However, - * computations may still encounter unchecked exceptions, that are - * rethrown to callers attempting to join them. These exceptions may - * additionally include RejectedExecutionExceptions stemming from - * internal resource exhaustion such as failure to allocate internal - * task queues. + * ideally avoid {@code synchronized} methods or blocks, and should + * minimize other blocking synchronization apart from joining other + * tasks or using synchronizers such as Phasers that are advertised to + * cooperate with fork/join scheduling. Subdividable tasks should also + * not perform blocking IO, and should ideally access variables that + * are completely independent of those accessed by other running + * tasks. These guidelines are loosely enforced by not permitting + * checked exceptions such as {@code IOExceptions} to be + * thrown. However, computations may still encounter unchecked + * exceptions, that are rethrown to callers attempting to join + * them. These exceptions may additionally include {@link + * RejectedExecutionException} stemming from internal resource + * exhaustion, such as failure to allocate internal task + * queues. Rethrown exceptions behave in the same way as regular + * exceptions, but, when possible, contain stack traces (as displayed + * for example using {@code ex.printStackTrace()}) of both the thread + * that initiated the computation as well as the thread actually + * encountering the exception; minimally only the latter. + * + *

It is possible to define and use ForkJoinTasks that may block, + * but doing do requires three further considerations: (1) Completion + * of few if any other tasks should be dependent on a task + * that blocks on external synchronization or IO. Event-style async + * tasks that are never joined often fall into this category. (2) To + * minimize resource impact, tasks should be small; ideally performing + * only the (possibly) blocking action. (3) Unless the {@link + * ForkJoinPool.ManagedBlocker} API is used, or the number of possibly + * blocked tasks is known to be less than the pool's {@link + * ForkJoinPool#getParallelism} level, the pool cannot guarantee that + * enough threads will be available to ensure progress or good + * performance. * *

The primary method for awaiting completion and extracting * results of a task is {@link #join}, but there are several variants: * The {@link Future#get} methods support interruptible and/or timed * waits for completion and report results using {@code Future} - * conventions. Method {@link #helpJoin} enables callers to actively - * execute other tasks while awaiting joins, which is sometimes more - * efficient but only applies when all subtasks are known to be - * strictly tree-structured. Method {@link #invoke} is semantically + * conventions. Method {@link #invoke} is semantically * equivalent to {@code fork(); join()} but always attempts to begin * execution in the current thread. The "quiet" forms of * these methods do not extract results or report exceptions. These @@ -77,19 +93,24 @@ import java.util.WeakHashMap; * performs the most common form of parallel invocation: forking a set * of tasks and joining them all. * + *

In the most typical usages, a fork-join pair act like a call + * (fork) and return (join) from a parallel recursive function. As is + * the case with other forms of recursive calls, returns (joins) + * should be performed innermost-first. For example, {@code a.fork(); + * b.fork(); b.join(); a.join();} is likely to be substantially more + * efficient than joining {@code a} before {@code b}. + * *

The execution status of tasks may be queried at several levels * of detail: {@link #isDone} is true if a task completed in any way * (including the case where a task was cancelled without executing); - * {@link #isCancelled} is true if completion was due to cancellation; * {@link #isCompletedNormally} is true if a task completed without - * cancellation or encountering an exception; {@link - * #isCompletedExceptionally} is true if if the task encountered an - * exception (in which case {@link #getException} returns the - * exception); {@link #isCancelled} is true if the task was cancelled - * (in which case {@link #getException} returns a {@link - * java.util.concurrent.CancellationException}); and {@link - * #isCompletedAbnormally} is true if a task was either cancelled or - * encountered an exception. + * cancellation or encountering an exception; {@link #isCancelled} is + * true if the task was cancelled (in which case {@link #getException} + * returns a {@link java.util.concurrent.CancellationException}); and + * {@link #isCompletedAbnormally} is true if a task was either + * cancelled or encountered an exception, in which case {@link + * #getException} will return either the encountered exception or + * {@link java.util.concurrent.CancellationException}. * *

The ForkJoinTask class is not usually directly subclassed. * Instead, you subclass one of the abstract classes that support a @@ -105,7 +126,28 @@ import java.util.WeakHashMap; * ForkJoinTasks (as may be determined using method {@link * #inForkJoinPool}). Attempts to invoke them in other contexts * result in exceptions or errors, possibly including - * ClassCastException. + * {@code ClassCastException}. + * + *

Method {@link #join} and its variants are appropriate for use + * only when completion dependencies are acyclic; that is, the + * parallel computation can be described as a directed acyclic graph + * (DAG). Otherwise, executions may encounter a form of deadlock as + * tasks cyclically wait for each other. However, this framework + * supports other methods and techniques (for example the use of + * {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that + * may be of use in constructing custom subclasses for problems that + * are not statically structured as DAGs. To support such usages a + * ForkJoinTask may be atomically marked using {@link + * #markForkJoinTask} and checked for marking using {@link + * #isMarkedForkJoinTask}. The ForkJoinTask implementation does not + * use these {@code protected} methods or marks for any purpose, but + * they may be of use in the construction of specialized subclasses. + * For example, parallel graph traversals can use the supplied methods + * to avoid revisiting nodes/tasks that have already been processed. + * Also, completion based designs can use them to record that one + * subtask has completed. (Method names for marking are bulky in part + * to encourage definition of methods that reflect their usage + * patterns.) * *

Most base support methods are {@code final}, to prevent * overriding of implementations that are intrinsically tied to the @@ -121,15 +163,15 @@ import java.util.WeakHashMap; * computation. Large tasks should be split into smaller subtasks, * usually via recursive decomposition. As a very rough rule of thumb, * a task should perform more than 100 and less than 10000 basic - * computational steps. If tasks are too big, then parallelism cannot - * improve throughput. If too small, then memory and internal task - * maintenance overhead may overwhelm processing. + * computational steps, and should avoid indefinite looping. If tasks + * are too big, then parallelism cannot improve throughput. If too + * small, then memory and internal task maintenance overhead may + * overwhelm processing. * *

This class provides {@code adapt} methods for {@link Runnable} * and {@link Callable}, that may be of use when mixing execution of - * {@code ForkJoinTasks} with other kinds of tasks. When all tasks - * are of this form, consider using a pool in - * {@linkplain ForkJoinPool#setAsyncMode async mode}. + * {@code ForkJoinTasks} with other kinds of tasks. When all tasks are + * of this form, consider using a pool constructed in asyncMode. * *

ForkJoinTasks are {@code Serializable}, which enables them to be * used in extensions such as remote execution frameworks. It is @@ -141,370 +183,457 @@ import java.util.WeakHashMap; */ public abstract class ForkJoinTask implements Future, Serializable { - /** - * Run control status bits packed into a single int to minimize - * footprint and to ensure atomicity (via CAS). Status is - * initially zero, and takes on nonnegative values until - * completed, upon which status holds COMPLETED. CANCELLED, or - * EXCEPTIONAL, which use the top 3 bits. Tasks undergoing - * blocking waits by other threads have SIGNAL_MASK bits set -- - * bit 15 for external (nonFJ) waits, and the rest a count of - * waiting FJ threads. (This representation relies on - * ForkJoinPool max thread limits). Completion of a stolen task - * with SIGNAL_MASK bits set awakens waiter via notifyAll. Even - * though suboptimal for some purposes, we use basic builtin - * wait/notify to take advantage of "monitor inflation" in JVMs - * that we would otherwise need to emulate to avoid adding further - * per-task bookkeeping overhead. Note that bits 16-28 are - * currently unused. Also value 0x80000000 is available as spare - * completion value. - */ - volatile int status; // accessed directly by pool and workers - - static final int COMPLETION_MASK = 0xe0000000; - static final int NORMAL = 0xe0000000; // == mask - static final int CANCELLED = 0xc0000000; - static final int EXCEPTIONAL = 0xa0000000; - static final int SIGNAL_MASK = 0x0000ffff; - static final int INTERNAL_SIGNAL_MASK = 0x00007fff; - static final int EXTERNAL_SIGNAL = 0x00008000; // top bit of low word - - /** - * Table of exceptions thrown by tasks, to enable reporting by - * callers. Because exceptions are rare, we don't directly keep - * them with task objects, but instead use a weak ref table. Note - * that cancellation exceptions don't appear in the table, but are - * instead recorded as status values. - * TODO: Use ConcurrentReferenceHashMap - */ - static final Map, Throwable> exceptionMap = - Collections.synchronizedMap - (new WeakHashMap, Throwable>()); - - // within-package utilities - - /** - * Gets current worker thread, or null if not a worker thread. + /* + * See the internal documentation of class ForkJoinPool for a + * general implementation overview. ForkJoinTasks are mainly + * responsible for maintaining their "status" field amidst relays + * to methods in ForkJoinWorkerThread and ForkJoinPool. + * + * The methods of this class are more-or-less layered into + * (1) basic status maintenance + * (2) execution and awaiting completion + * (3) user-level methods that additionally report results. + * This is sometimes hard to see because this file orders exported + * methods in a way that flows well in javadocs. */ - static ForkJoinWorkerThread getWorker() { - Thread t = Thread.currentThread(); - return ((t instanceof ForkJoinWorkerThread) ? - (ForkJoinWorkerThread) t : null); - } - - final boolean casStatus(int cmp, int val) { - return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val); - } /** - * Workaround for not being able to rethrow unchecked exceptions. + * The number of times to try to help join a task without any + * apparent progress before giving up and blocking. The value is + * arbitrary but should be large enough to cope with transient + * stalls (due to GC etc) that can cause helping methods not to be + * able to proceed because other workers have not progressed to + * the point where subtasks can be found or taken. + */ + private static final int HELP_RETRIES = 32; + + /* + * The status field holds run control status bits packed into a + * single int to minimize footprint and to ensure atomicity (via + * CAS). Status is initially zero, and takes on nonnegative + * values until completed, upon which status holds value + * NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking + * waits by other threads have the SIGNAL bit set. Completion of + * a stolen task with SIGNAL set awakens any waiters via + * notifyAll. Even though suboptimal for some purposes, we use + * basic builtin wait/notify to take advantage of "monitor + * inflation" in JVMs that we would otherwise need to emulate to + * avoid adding further per-task bookkeeping overhead. We want + * these monitors to be "fat", i.e., not use biasing or thin-lock + * techniques, so use some odd coding idioms that tend to avoid + * them. */ - static void rethrowException(Throwable ex) { - if (ex != null) - UNSAFE.throwException(ex); - } - // Setting completion status + /** The run status of this task */ + volatile int status; // accessed directly by pool and workers + static final int NORMAL = 0xfffffffc; // negative with low 2 bits 0 + static final int CANCELLED = 0xfffffff8; // must be < NORMAL + static final int EXCEPTIONAL = 0xfffffff4; // must be < CANCELLED + static final int SIGNAL = 0x00000001; + static final int MARKED = 0x00000002; /** - * Marks completion and wakes up threads waiting to join this task. + * Marks completion and wakes up threads waiting to join this + * task, also clearing signal request bits. A specialization for + * NORMAL completion is in method doExec. * * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL + * @return completion status on exit */ - final void setCompletion(int completion) { - ForkJoinPool pool = getPool(); - if (pool != null) { - int s; // Clear signal bits while setting completion status - do {} while ((s = status) >= 0 && !casStatus(s, completion)); - - if ((s & SIGNAL_MASK) != 0) { - if ((s &= INTERNAL_SIGNAL_MASK) != 0) - pool.updateRunningCount(s); - synchronized (this) { notifyAll(); } + private int setCompletion(int completion) { + for (int s;;) { + if ((s = status) < 0) + return s; + if (U.compareAndSwapInt(this, STATUS, s, (s & ~SIGNAL)|completion)) { + if ((s & SIGNAL) != 0) + synchronized (this) { notifyAll(); } + return completion; } } - else - externallySetCompletion(completion); - } - - /** - * Version of setCompletion for non-FJ threads. Leaves signal - * bits for unblocked threads to adjust, and always notifies. - */ - private void externallySetCompletion(int completion) { - int s; - do {} while ((s = status) >= 0 && - !casStatus(s, (s & SIGNAL_MASK) | completion)); - synchronized (this) { notifyAll(); } } /** - * Sets status to indicate normal completion. - */ - final void setNormalCompletion() { - // Try typical fast case -- single CAS, no signal, not already done. - // Manually expand casStatus to improve chances of inlining it - if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL)) - setCompletion(NORMAL); + * Primary execution method for stolen tasks. Unless done, calls + * exec and records status if completed, but doesn't wait for + * completion otherwise. + * + * @return status on exit from this method + */ + final int doExec() { + int s; boolean completed; + if ((s = status) >= 0) { + try { + completed = exec(); + } catch (Throwable rex) { + return setExceptionalCompletion(rex); + } + while ((s = status) >= 0 && completed) { + if (U.compareAndSwapInt(this, STATUS, s, (s & ~SIGNAL)|NORMAL)) { + if ((s & SIGNAL) != 0) + synchronized (this) { notifyAll(); } + return NORMAL; + } + } + } + return s; } - // internal waiting and notification - /** - * Performs the actual monitor wait for awaitDone. + * Blocks a non-worker-thread until completion. + * @return status upon completion */ - private void doAwaitDone() { - // Minimize lock bias and in/de-flation effects by maximizing - // chances of waiting inside sync - try { - while (status >= 0) - synchronized (this) { if (status >= 0) wait(); } - } catch (InterruptedException ie) { - onInterruptedWait(); + private int externalAwaitDone() { + int s; + if ((s = status) >= 0) { + boolean interrupted = false; + synchronized (this) { + while ((s = status) >= 0) { + if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { + try { + wait(); + } catch (InterruptedException ie) { + interrupted = true; + } + } + } + } + if (interrupted) + Thread.currentThread().interrupt(); } + return s; } /** - * Performs the actual timed monitor wait for awaitDone. + * Blocks a non-worker-thread until completion or interruption or timeout. */ - private void doAwaitDone(long startTime, long nanos) { - synchronized (this) { - try { - while (status >= 0) { - long nt = nanos - (System.nanoTime() - startTime); - if (nt <= 0) - break; - wait(nt / 1000000, (int) (nt % 1000000)); + private int externalInterruptibleAwaitDone(long millis) + throws InterruptedException { + int s; + if (Thread.interrupted()) + throw new InterruptedException(); + if ((s = status) >= 0) { + synchronized (this) { + while ((s = status) >= 0) { + if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { + wait(millis); + if (millis > 0L) + break; + } } - } catch (InterruptedException ie) { - onInterruptedWait(); } } + return s; } - // Awaiting completion /** - * Sets status to indicate there is joiner, then waits for join, - * surrounded with pool notifications. - * - * @return status upon exit - */ - private int awaitDone(ForkJoinWorkerThread w, - boolean maintainParallelism) { - ForkJoinPool pool = (w == null) ? null : w.pool; - int s; - while ((s = status) >= 0) { - if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) { - if (pool == null || !pool.preJoin(this, maintainParallelism)) - doAwaitDone(); - if (((s = status) & INTERNAL_SIGNAL_MASK) != 0) - adjustPoolCountsOnUnblock(pool); - break; - } + * Implementation for join, get, quietlyJoin. Directly handles + * only cases of already-completed, external wait, and + * unfork+exec. Others are relayed to awaitJoin. + * + * @return status upon completion + */ + private int doJoin() { + int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w; + if ((s = status) >= 0) { + if (!((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) + s = externalAwaitDone(); + else if (!(w = (wt = (ForkJoinWorkerThread)t).workQueue). + tryUnpush(this) || (s = doExec()) >= 0) + s = awaitJoin(w, wt.pool); } return s; } /** - * Timed version of awaitDone + * Helps and/or blocks until joined. * - * @return status upon exit + * @param w the joiner + * @param p the pool + * @return status upon completion */ - private int awaitDone(ForkJoinWorkerThread w, long nanos) { - ForkJoinPool pool = (w == null) ? null : w.pool; + private int awaitJoin(ForkJoinPool.WorkQueue w, ForkJoinPool p) { int s; - while ((s = status) >= 0) { - if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) { - long startTime = System.nanoTime(); - if (pool == null || !pool.preJoin(this, false)) - doAwaitDone(startTime, nanos); - if ((s = status) >= 0) { - adjustPoolCountsOnCancelledWait(pool); - s = status; - } - if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0) - adjustPoolCountsOnUnblock(pool); + ForkJoinTask prevJoin = w.currentJoin; + w.currentJoin = this; + for (int k = HELP_RETRIES; (s = status) >= 0;) { + if ((w.queueSize() > 0) ? + w.tryRemoveAndExec(this) : // self-help + p.tryHelpStealer(w, this)) // help process tasks + k = HELP_RETRIES; // reset if made progress + else if ((s = status) < 0) // recheck break; + else if (--k > 0) { + if ((k & 3) == 1) + Thread.yield(); // occasionally yield + } + else if (k == 0) + p.tryPollForAndExec(w, this); // uncommon self-help case + else if (p.tryCompensate()) { // true if can block + try { + int ss = status; + if (ss >= 0 && // assert need signal + U.compareAndSwapInt(this, STATUS, ss, ss | SIGNAL)) { + synchronized (this) { + if (status >= 0) // block + wait(); + } + } + } catch (InterruptedException ignore) { + } finally { + p.incrementActiveCount(); // re-activate + } } } + w.currentJoin = prevJoin; return s; } /** - * Notifies pool that thread is unblocked. Called by signalled - * threads when woken by non-FJ threads (which is atypical). - */ - private void adjustPoolCountsOnUnblock(ForkJoinPool pool) { - int s; - do {} while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK)); - if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0) - pool.updateRunningCount(s); - } - - /** - * Notifies pool to adjust counts on cancelled or timed out wait. + * Implementation for invoke, quietlyInvoke. + * + * @return status upon completion */ - private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) { - if (pool != null) { - int s; - while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) { - if (casStatus(s, s - 1)) { - pool.updateRunningCount(1); - break; - } + private int doInvoke() { + int s; Thread t; + if ((s = doExec()) >= 0) { + if (!((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) + s = externalAwaitDone(); + else { + ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t; + s = awaitJoin(wt.workQueue, wt.pool); } } + return s; } + // Exception table support + /** - * Handles interruptions during waits. + * Table of exceptions thrown by tasks, to enable reporting by + * callers. Because exceptions are rare, we don't directly keep + * them with task objects, but instead use a weak ref table. Note + * that cancellation exceptions don't appear in the table, but are + * instead recorded as status values. + * + * Note: These statics are initialized below in static block. */ - private void onInterruptedWait() { - ForkJoinWorkerThread w = getWorker(); - if (w == null) - Thread.currentThread().interrupt(); // re-interrupt - else if (w.isTerminating()) - cancelIgnoringExceptions(); - // else if FJworker, ignore interrupt - } + private static final ExceptionNode[] exceptionTable; + private static final ReentrantLock exceptionTableLock; + private static final ReferenceQueue exceptionTableRefQueue; - // Recording and reporting exceptions - - private void setDoneExceptionally(Throwable rex) { - exceptionMap.put(this, rex); - setCompletion(EXCEPTIONAL); - } + /** + * Fixed capacity for exceptionTable. + */ + private static final int EXCEPTION_MAP_CAPACITY = 32; /** - * Throws the exception associated with status s. - * - * @throws the exception + * Key-value nodes for exception table. The chained hash table + * uses identity comparisons, full locking, and weak references + * for keys. The table has a fixed capacity because it only + * maintains task exceptions long enough for joiners to access + * them, so should never become very large for sustained + * periods. However, since we do not know when the last joiner + * completes, we must use weak references and expunge them. We do + * so on each operation (hence full locking). Also, some thread in + * any ForkJoinPool will call helpExpungeStaleExceptions when its + * pool becomes isQuiescent. */ - private void reportException(int s) { - if ((s &= COMPLETION_MASK) < NORMAL) { - if (s == CANCELLED) - throw new CancellationException(); - else - rethrowException(exceptionMap.get(this)); + static final class ExceptionNode extends WeakReference>{ + final Throwable ex; + ExceptionNode next; + final long thrower; // use id not ref to avoid weak cycles + ExceptionNode(ForkJoinTask task, Throwable ex, ExceptionNode next) { + super(task, exceptionTableRefQueue); + this.ex = ex; + this.next = next; + this.thrower = Thread.currentThread().getId(); } } /** - * Returns result or throws exception using j.u.c.Future conventions. - * Only call when {@code isDone} known to be true or thread known - * to be interrupted. + * Records exception and sets exceptional completion. + * + * @return status on exit */ - private V reportFutureResult() - throws InterruptedException, ExecutionException { - if (Thread.interrupted()) - throw new InterruptedException(); - int s = status & COMPLETION_MASK; - if (s < NORMAL) { - Throwable ex; - if (s == CANCELLED) - throw new CancellationException(); - if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) - throw new ExecutionException(ex); + private int setExceptionalCompletion(Throwable ex) { + int h = System.identityHashCode(this); + final ReentrantLock lock = exceptionTableLock; + lock.lock(); + try { + expungeStaleExceptions(); + ExceptionNode[] t = exceptionTable; + int i = h & (t.length - 1); + for (ExceptionNode e = t[i]; ; e = e.next) { + if (e == null) { + t[i] = new ExceptionNode(this, ex, t[i]); + break; + } + if (e.get() == this) // already present + break; + } + } finally { + lock.unlock(); } - return getRawResult(); + return setCompletion(EXCEPTIONAL); } /** - * Returns result or throws exception using j.u.c.Future conventions - * with timeouts. + * Cancels, ignoring any exceptions thrown by cancel. Used during + * worker and pool shutdown. Cancel is spec'ed not to throw any + * exceptions, but if it does anyway, we have no recourse during + * shutdown, so guard against this case. */ - private V reportTimedFutureResult() - throws InterruptedException, ExecutionException, TimeoutException { - if (Thread.interrupted()) - throw new InterruptedException(); - Throwable ex; - int s = status & COMPLETION_MASK; - if (s == NORMAL) - return getRawResult(); - else if (s == CANCELLED) - throw new CancellationException(); - else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) - throw new ExecutionException(ex); - else - throw new TimeoutException(); + static final void cancelIgnoringExceptions(ForkJoinTask t) { + if (t != null && t.status >= 0) { + try { + t.cancel(false); + } catch (Throwable ignore) { + } + } } - // internal execution methods - /** - * Calls exec, recording completion, and rethrowing exception if - * encountered. Caller should normally check status before calling. - * - * @return true if completed normally + * Removes exception node and clears status */ - private boolean tryExec() { - try { // try block must contain only call to exec - if (!exec()) - return false; - } catch (Throwable rex) { - setDoneExceptionally(rex); - rethrowException(rex); - return false; // not reached + private void clearExceptionalCompletion() { + int h = System.identityHashCode(this); + final ReentrantLock lock = exceptionTableLock; + lock.lock(); + try { + ExceptionNode[] t = exceptionTable; + int i = h & (t.length - 1); + ExceptionNode e = t[i]; + ExceptionNode pred = null; + while (e != null) { + ExceptionNode next = e.next; + if (e.get() == this) { + if (pred == null) + t[i] = next; + else + pred.next = next; + break; + } + pred = e; + e = next; + } + expungeStaleExceptions(); + status = 0; + } finally { + lock.unlock(); } - setNormalCompletion(); - return true; } /** - * Main execution method used by worker threads. Invokes - * base computation unless already complete. - */ - final void quietlyExec() { - if (status >= 0) { + * Returns a rethrowable exception for the given task, if + * available. To provide accurate stack traces, if the exception + * was not thrown by the current thread, we try to create a new + * exception of the same type as the one thrown, but with the + * recorded exception as its cause. If there is no such + * constructor, we instead try to use a no-arg constructor, + * followed by initCause, to the same effect. If none of these + * apply, or any fail due to other exceptions, we return the + * recorded exception, which is still correct, although it may + * contain a misleading stack trace. + * + * @return the exception, or null if none + */ + private Throwable getThrowableException() { + if (status != EXCEPTIONAL) + return null; + int h = System.identityHashCode(this); + ExceptionNode e; + final ReentrantLock lock = exceptionTableLock; + lock.lock(); + try { + expungeStaleExceptions(); + ExceptionNode[] t = exceptionTable; + e = t[h & (t.length - 1)]; + while (e != null && e.get() != this) + e = e.next; + } finally { + lock.unlock(); + } + Throwable ex; + if (e == null || (ex = e.ex) == null) + return null; + if (e.thrower != Thread.currentThread().getId()) { + Class ec = ex.getClass(); try { - if (!exec()) - return; - } catch (Throwable rex) { - setDoneExceptionally(rex); - return; + Constructor noArgCtor = null; + Constructor[] cs = ec.getConstructors();// public ctors only + for (int i = 0; i < cs.length; ++i) { + Constructor c = cs[i]; + Class[] ps = c.getParameterTypes(); + if (ps.length == 0) + noArgCtor = c; + else if (ps.length == 1 && ps[0] == Throwable.class) + return (Throwable)(c.newInstance(ex)); + } + if (noArgCtor != null) { + Throwable wx = (Throwable)(noArgCtor.newInstance()); + wx.initCause(ex); + return wx; + } + } catch (Exception ignore) { } - setNormalCompletion(); } + return ex; } /** - * Calls exec(), recording but not rethrowing exception. - * Caller should normally check status before calling. - * - * @return true if completed normally + * Poll stale refs and remove them. Call only while holding lock. */ - private boolean tryQuietlyInvoke() { - try { - if (!exec()) - return false; - } catch (Throwable rex) { - setDoneExceptionally(rex); - return false; + private static void expungeStaleExceptions() { + for (Object x; (x = exceptionTableRefQueue.poll()) != null;) { + if (x instanceof ExceptionNode) { + ForkJoinTask key = ((ExceptionNode)x).get(); + ExceptionNode[] t = exceptionTable; + int i = System.identityHashCode(key) & (t.length - 1); + ExceptionNode e = t[i]; + ExceptionNode pred = null; + while (e != null) { + ExceptionNode next = e.next; + if (e == x) { + if (pred == null) + t[i] = next; + else + pred.next = next; + break; + } + pred = e; + e = next; + } + } } - setNormalCompletion(); - return true; } /** - * Cancels, ignoring any exceptions it throws. + * If lock is available, poll stale refs and remove them. + * Called from ForkJoinPool when pools become quiescent. */ - final void cancelIgnoringExceptions() { - try { - cancel(false); - } catch (Throwable ignore) { + static final void helpExpungeStaleExceptions() { + final ReentrantLock lock = exceptionTableLock; + if (lock.tryLock()) { + try { + expungeStaleExceptions(); + } finally { + lock.unlock(); + } } } /** - * Main implementation of helpJoin + * Report the result of invoke or join; called only upon + * non-normal return of internal versions. */ - private int busyJoin(ForkJoinWorkerThread w) { - int s; - ForkJoinTask t; - while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null) - t.quietlyExec(); - return (s >= 0) ? awaitDone(w, false) : s; // block if no work + private V reportResult() { + int s; Throwable ex; + if ((s = status) == CANCELLED) + throw new CancellationException(); + if (s == EXCEPTIONAL && (ex = getThrowableException()) != null) + U.throwException(ex); + return getRawResult(); } // public methods @@ -513,9 +642,14 @@ public abstract class ForkJoinTask im * Arranges to asynchronously execute this task. While it is not * necessarily enforced, it is a usage error to fork a task more * than once unless it has completed and been reinitialized. + * Subsequent modifications to the state of this task or any data + * it operates on are not necessarily consistently observable by + * any thread other than the one executing it unless preceded by a + * call to {@link #join} or related methods, or a call to {@link + * #isDone} returning {@code true}. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -523,51 +657,60 @@ public abstract class ForkJoinTask im * @return {@code this}, to simplify usage */ public final ForkJoinTask fork() { - ((ForkJoinWorkerThread) Thread.currentThread()) - .pushTask(this); + ForkJoinWorkerThread wt; + (wt = (ForkJoinWorkerThread)Thread.currentThread()). + workQueue.push(this, wt.pool); return this; } /** - * Returns the result of the computation when it is ready. - * This method differs from {@link #get()} in that + * Returns the result of the computation when it {@link #isDone is + * done}. This method differs from {@link #get()} in that * abnormal completion results in {@code RuntimeException} or - * {@code Error}, not {@code ExecutionException}. + * {@code Error}, not {@code ExecutionException}, and that + * interrupts of the calling thread do not cause the + * method to abruptly return by throwing {@code + * InterruptedException}. * * @return the computed result */ public final V join() { - ForkJoinWorkerThread w = getWorker(); - if (w == null || status < 0 || !w.unpushTask(this) || !tryExec()) - reportException(awaitDone(w, true)); - return getRawResult(); + if (doJoin() != NORMAL) + return reportResult(); + else + return getRawResult(); } /** * Commences performing this task, awaits its completion if - * necessary, and return its result, or throws an (unchecked) - * exception if the underlying computation did so. + * necessary, and returns its result, or throws an (unchecked) + * {@code RuntimeException} or {@code Error} if the underlying + * computation did so. * * @return the computed result */ public final V invoke() { - if (status >= 0 && tryExec()) - return getRawResult(); + if (doInvoke() != NORMAL) + return reportResult(); else - return join(); + return getRawResult(); } /** * Forks the given tasks, returning when {@code isDone} holds for * each task or an (unchecked) exception is encountered, in which - * case the exception is rethrown. If either task encounters an - * exception, the other one may be, but is not guaranteed to be, - * cancelled. If both tasks throw an exception, then this method - * throws one of them. The individual status of each task may be - * checked using {@link #getException()} and related methods. + * case the exception is rethrown. If more than one task + * encounters an exception, then this method throws any one of + * these exceptions. If any task encounters an exception, the + * other may be cancelled. However, the execution status of + * individual tasks is not guaranteed upon exceptional return. The + * status of each task may be obtained using {@link + * #getException()} and related methods to check if they have been + * cancelled, completed normally or exceptionally, or left + * unprocessed. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -585,15 +728,17 @@ public abstract class ForkJoinTask im /** * Forks the given tasks, returning when {@code isDone} holds for * each task or an (unchecked) exception is encountered, in which - * case the exception is rethrown. If any task encounters an - * exception, others may be, but are not guaranteed to be, - * cancelled. If more than one task encounters an exception, then - * this method throws any one of these exceptions. The individual - * status of each task may be checked using {@link #getException()} - * and related methods. + * case the exception is rethrown. If more than one task + * encounters an exception, then this method throws any one of + * these exceptions. If any task encounters an exception, others + * may be cancelled. However, the execution status of individual + * tasks is not guaranteed upon exceptional return. The status of + * each task may be obtained using {@link #getException()} and + * related methods to check if they have been cancelled, completed + * normally or exceptionally, or left unprocessed. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -612,42 +757,37 @@ public abstract class ForkJoinTask im } else if (i != 0) t.fork(); - else { - t.quietlyInvoke(); - if (ex == null) - ex = t.getException(); - } + else if (t.doInvoke() < NORMAL && ex == null) + ex = t.getException(); } for (int i = 1; i <= last; ++i) { ForkJoinTask t = tasks[i]; if (t != null) { if (ex != null) t.cancel(false); - else { - t.quietlyJoin(); - if (ex == null) - ex = t.getException(); - } + else if (t.doJoin() < NORMAL) + ex = t.getException(); } } if (ex != null) - rethrowException(ex); + U.throwException(ex); } /** * Forks all tasks in the specified collection, returning when * {@code isDone} holds for each task or an (unchecked) exception - * is encountered. If any task encounters an exception, others - * may be, but are not guaranteed to be, cancelled. If more than - * one task encounters an exception, then this method throws any - * one of these exceptions. The individual status of each task - * may be checked using {@link #getException()} and related - * methods. The behavior of this operation is undefined if the - * specified collection is modified while the operation is in - * progress. + * is encountered, in which case the exception is rethrown. If + * more than one task encounters an exception, then this method + * throws any one of these exceptions. If any task encounters an + * exception, others may be cancelled. However, the execution + * status of individual tasks is not guaranteed upon exceptional + * return. The status of each task may be obtained using {@link + * #getException()} and related methods to check if they have been + * cancelled, completed normally or exceptionally, or left + * unprocessed. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -674,75 +814,60 @@ public abstract class ForkJoinTask im } else if (i != 0) t.fork(); - else { - t.quietlyInvoke(); - if (ex == null) - ex = t.getException(); - } + else if (t.doInvoke() < NORMAL && ex == null) + ex = t.getException(); } for (int i = 1; i <= last; ++i) { ForkJoinTask t = ts.get(i); if (t != null) { if (ex != null) t.cancel(false); - else { - t.quietlyJoin(); - if (ex == null) - ex = t.getException(); - } + else if (t.doJoin() < NORMAL) + ex = t.getException(); } } if (ex != null) - rethrowException(ex); + U.throwException(ex); return tasks; } /** * Attempts to cancel execution of this task. This attempt will - * fail if the task has already completed, has already been - * cancelled, or could not be cancelled for some other reason. If - * successful, and this task has not started when cancel is - * called, execution of this task is suppressed, {@link - * #isCancelled} will report true, and {@link #join} will result - * in a {@code CancellationException} being thrown. + * fail if the task has already completed or could not be + * cancelled for some other reason. If successful, and this task + * has not started when {@code cancel} is called, execution of + * this task is suppressed. After this method returns + * successfully, unless there is an intervening call to {@link + * #reinitialize}, subsequent calls to {@link #isCancelled}, + * {@link #isDone}, and {@code cancel} will return {@code true} + * and calls to {@link #join} and related methods will result in + * {@code CancellationException}. * *

This method may be overridden in subclasses, but if so, must - * still ensure that these minimal properties hold. In particular, - * the {@code cancel} method itself must not throw exceptions. + * still ensure that these properties hold. In particular, the + * {@code cancel} method itself must not throw exceptions. * *

This method is designed to be invoked by other * tasks. To terminate the current task, you can just return or * throw an unchecked exception from its computation method, or * invoke {@link #completeExceptionally}. * - * @param mayInterruptIfRunning this value is ignored in the - * default implementation because tasks are not - * cancelled via interruption + * @param mayInterruptIfRunning this value has no effect in the + * default implementation because interrupts are not used to + * control cancellation. * * @return {@code true} if this task is now cancelled */ public boolean cancel(boolean mayInterruptIfRunning) { - setCompletion(CANCELLED); - return (status & COMPLETION_MASK) == CANCELLED; + return setCompletion(CANCELLED) == CANCELLED; } - /** - * Returns {@code true} if the computation performed by this task - * has completed (or has been cancelled). - * - * @return {@code true} if this computation has completed - */ public final boolean isDone() { return status < 0; } - /** - * Returns {@code true} if this task was cancelled. - * - * @return {@code true} if this task was cancelled - */ public final boolean isCancelled() { - return (status & COMPLETION_MASK) == CANCELLED; + return status == CANCELLED; } /** @@ -751,7 +876,7 @@ public abstract class ForkJoinTask im * @return {@code true} if this task threw an exception or was cancelled */ public final boolean isCompletedAbnormally() { - return (status & COMPLETION_MASK) < NORMAL; + return status < NORMAL; } /** @@ -762,16 +887,7 @@ public abstract class ForkJoinTask im * exception and was not cancelled */ public final boolean isCompletedNormally() { - return (status & COMPLETION_MASK) == NORMAL; - } - - /** - * Returns {@code true} if this task threw an exception. - * - * @return {@code true} if this task threw an exception - */ - public final boolean isCompletedExceptionally() { - return (status & COMPLETION_MASK) == EXCEPTIONAL; + return status == NORMAL; } /** @@ -782,10 +898,10 @@ public abstract class ForkJoinTask im * @return the exception, or {@code null} if none */ public final Throwable getException() { - int s = status & COMPLETION_MASK; + int s = status; return ((s >= NORMAL) ? null : (s == CANCELLED) ? new CancellationException() : - exceptionMap.get(this)); + getThrowableException()); } /** @@ -798,25 +914,26 @@ public abstract class ForkJoinTask im * overridable, but overridden versions must invoke {@code super} * implementation to maintain guarantees. * - * @param ex the exception to throw. If this exception is - * not a RuntimeException or Error, the actual exception thrown - * will be a RuntimeException with cause ex. + * @param ex the exception to throw. If this exception is not a + * {@code RuntimeException} or {@code Error}, the actual exception + * thrown will be a {@code RuntimeException} with cause {@code ex}. */ public void completeExceptionally(Throwable ex) { - setDoneExceptionally((ex instanceof RuntimeException) || - (ex instanceof Error) ? ex : - new RuntimeException(ex)); + setExceptionalCompletion((ex instanceof RuntimeException) || + (ex instanceof Error) ? ex : + new RuntimeException(ex)); } /** * Completes this task, and if not already aborted or cancelled, - * returning a {@code null} result upon {@code join} and related - * operations. This method may be used to provide results for - * asynchronous tasks, or to provide alternative handling for - * tasks that would not otherwise complete normally. Its use in - * other situations is discouraged. This method is - * overridable, but overridden versions must invoke {@code super} - * implementation to maintain guarantees. + * returning the given value as the result of subsequent + * invocations of {@code join} and related operations. This method + * may be used to provide results for asynchronous tasks, or to + * provide alternative handling for tasks that would not otherwise + * complete normally. Its use in other situations is + * discouraged. This method is overridable, but overridden + * versions must invoke {@code super} implementation to maintain + * guarantees. * * @param value the result value for this task */ @@ -824,96 +941,124 @@ public abstract class ForkJoinTask im try { setRawResult(value); } catch (Throwable rex) { - setDoneExceptionally(rex); + setExceptionalCompletion(rex); return; } - setNormalCompletion(); - } - - public final V get() throws InterruptedException, ExecutionException { - ForkJoinWorkerThread w = getWorker(); - if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke()) - awaitDone(w, true); - return reportFutureResult(); - } - - public final V get(long timeout, TimeUnit unit) - throws InterruptedException, ExecutionException, TimeoutException { - long nanos = unit.toNanos(timeout); - ForkJoinWorkerThread w = getWorker(); - if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke()) - awaitDone(w, nanos); - return reportTimedFutureResult(); + setCompletion(NORMAL); } /** - * Possibly executes other tasks until this task is ready, then - * returns the result of the computation. This method may be more - * efficient than {@code join}, but is only applicable when - * there are no potential dependencies between continuation of the - * current task and that of any other task that might be executed - * while helping. (This usually holds for pure divide-and-conquer - * tasks). - * - *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method - * {@link #inForkJoinPool}). Attempts to invoke in other contexts - * result in exceptions or errors, possibly including {@code - * ClassCastException}. + * Waits if necessary for the computation to complete, and then + * retrieves its result. * * @return the computed result + * @throws CancellationException if the computation was cancelled + * @throws ExecutionException if the computation threw an + * exception + * @throws InterruptedException if the current thread is not a + * member of a ForkJoinPool and was interrupted while waiting */ - public final V helpJoin() { - ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread(); - if (status < 0 || !w.unpushTask(this) || !tryExec()) - reportException(busyJoin(w)); + public final V get() throws InterruptedException, ExecutionException { + int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ? + doJoin() : externalInterruptibleAwaitDone(0L); + Throwable ex; + if (s == CANCELLED) + throw new CancellationException(); + if (s == EXCEPTIONAL && (ex = getThrowableException()) != null) + throw new ExecutionException(ex); return getRawResult(); } /** - * Possibly executes other tasks until this task is ready. This - * method may be useful when processing collections of tasks when - * some have been cancelled or otherwise known to have aborted. + * Waits if necessary for at most the given time for the computation + * to complete, and then retrieves its result, if available. * - *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method - * {@link #inForkJoinPool}). Attempts to invoke in other contexts - * result in exceptions or errors, possibly including {@code - * ClassCastException}. + * @param timeout the maximum time to wait + * @param unit the time unit of the timeout argument + * @return the computed result + * @throws CancellationException if the computation was cancelled + * @throws ExecutionException if the computation threw an + * exception + * @throws InterruptedException if the current thread is not a + * member of a ForkJoinPool and was interrupted while waiting + * @throws TimeoutException if the wait timed out */ - public final void quietlyHelpJoin() { - if (status >= 0) { - ForkJoinWorkerThread w = - (ForkJoinWorkerThread) Thread.currentThread(); - if (!w.unpushTask(this) || !tryQuietlyInvoke()) - busyJoin(w); + public final V get(long timeout, TimeUnit unit) + throws InterruptedException, ExecutionException, TimeoutException { + // Messy in part because we measure in nanos, but wait in millis + int s; long millis, nanos; + Thread t = Thread.currentThread(); + if (!(t instanceof ForkJoinWorkerThread)) { + if ((millis = unit.toMillis(timeout)) > 0L) + s = externalInterruptibleAwaitDone(millis); + else + s = status; + } + else if ((s = status) >= 0 && (nanos = unit.toNanos(timeout)) > 0L) { + long deadline = System.nanoTime() + nanos; + ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t; + ForkJoinPool.WorkQueue w = wt.workQueue; + ForkJoinPool p = wt.pool; + if (w.tryUnpush(this)) + doExec(); + boolean blocking = false; + try { + while ((s = status) >= 0) { + if (w.runState < 0) + cancelIgnoringExceptions(this); + else if (!blocking) + blocking = p.tryCompensate(); + else { + millis = TimeUnit.NANOSECONDS.toMillis(nanos); + if (millis > 0L && + U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { + try { + synchronized (this) { + if (status >= 0) + wait(millis); + } + } catch (InterruptedException ie) { + } + } + if ((s = status) < 0 || + (nanos = deadline - System.nanoTime()) <= 0L) + break; + } + } + } finally { + if (blocking) + p.incrementActiveCount(); + } + } + if (s != NORMAL) { + Throwable ex; + if (s == CANCELLED) + throw new CancellationException(); + if (s != EXCEPTIONAL) + throw new TimeoutException(); + if ((ex = getThrowableException()) != null) + throw new ExecutionException(ex); } + return getRawResult(); } /** - * Joins this task, without returning its result or throwing an + * Joins this task, without returning its result or throwing its * exception. This method may be useful when processing * collections of tasks when some have been cancelled or otherwise * known to have aborted. */ public final void quietlyJoin() { - if (status >= 0) { - ForkJoinWorkerThread w = getWorker(); - if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke()) - awaitDone(w, true); - } + doJoin(); } /** * Commences performing this task and awaits its completion if - * necessary, without returning its result or throwing an - * exception. This method may be useful when processing - * collections of tasks when some have been cancelled or otherwise - * known to have aborted. + * necessary, without returning its result or throwing its + * exception. */ public final void quietlyInvoke() { - if (status >= 0 && !tryQuietlyInvoke()) - quietlyJoin(); + doInvoke(); } /** @@ -924,14 +1069,15 @@ public abstract class ForkJoinTask im * processed. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. */ public static void helpQuiesce() { - ((ForkJoinWorkerThread) Thread.currentThread()) - .helpQuiescePool(); + ForkJoinWorkerThread wt = + (ForkJoinWorkerThread)Thread.currentThread(); + wt.pool.helpQuiescePool(wt.workQueue); } /** @@ -943,11 +1089,18 @@ public abstract class ForkJoinTask im * under any other usage conditions are not guaranteed. * This method may be useful when executing * pre-constructed trees of subtasks in loops. + * + *

Upon completion of this method, {@code isDone()} reports + * {@code false}, and {@code getException()} reports {@code + * null}. However, the value returned by {@code getRawResult} is + * unaffected. To clear this value, you can invoke {@code + * setRawResult(null)}. */ public void reinitialize() { - if ((status & COMPLETION_MASK) == EXCEPTIONAL) - exceptionMap.remove(this); - status = 0; + if (status == EXCEPTIONAL) + clearExceptionalCompletion(); + else + status = 0; } /** @@ -964,11 +1117,12 @@ public abstract class ForkJoinTask im } /** - * Returns {@code true} if the current thread is executing as a - * ForkJoinPool computation. + * Returns {@code true} if the current thread is a {@link + * ForkJoinWorkerThread} executing as a ForkJoinPool computation. * - * @return {@code true} if the current thread is executing as a - * ForkJoinPool computation, or false otherwise + * @return {@code true} if the current thread is a {@link + * ForkJoinWorkerThread} executing as a ForkJoinPool computation, + * or {@code false} otherwise */ public static boolean inForkJoinPool() { return Thread.currentThread() instanceof ForkJoinWorkerThread; @@ -983,7 +1137,7 @@ public abstract class ForkJoinTask im * were not, stolen. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -991,8 +1145,8 @@ public abstract class ForkJoinTask im * @return {@code true} if unforked */ public boolean tryUnfork() { - return ((ForkJoinWorkerThread) Thread.currentThread()) - .unpushTask(this); + return ((ForkJoinWorkerThread)Thread.currentThread()) + .workQueue.tryUnpush(this); } /** @@ -1002,7 +1156,7 @@ public abstract class ForkJoinTask im * fork other tasks. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -1011,7 +1165,7 @@ public abstract class ForkJoinTask im */ public static int getQueuedTaskCount() { return ((ForkJoinWorkerThread) Thread.currentThread()) - .getQueueSize(); + .workQueue.queueSize(); } /** @@ -1025,7 +1179,7 @@ public abstract class ForkJoinTask im * exceeded. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -1033,8 +1187,52 @@ public abstract class ForkJoinTask im * @return the surplus number of tasks, which may be negative */ public static int getSurplusQueuedTaskCount() { - return ((ForkJoinWorkerThread) Thread.currentThread()) - .getEstimatedSurplusTaskCount(); + /* + * The aim of this method is to return a cheap heuristic guide + * for task partitioning when programmers, frameworks, tools, + * or languages have little or no idea about task granularity. + * In essence by offering this method, we ask users only about + * tradeoffs in overhead vs expected throughput and its + * variance, rather than how finely to partition tasks. + * + * In a steady state strict (tree-structured) computation, + * each thread makes available for stealing enough tasks for + * other threads to remain active. Inductively, if all threads + * play by the same rules, each thread should make available + * only a constant number of tasks. + * + * The minimum useful constant is just 1. But using a value of + * 1 would require immediate replenishment upon each steal to + * maintain enough tasks, which is infeasible. Further, + * partitionings/granularities of offered tasks should + * minimize steal rates, which in general means that threads + * nearer the top of computation tree should generate more + * than those nearer the bottom. In perfect steady state, each + * thread is at approximately the same level of computation + * tree. However, producing extra tasks amortizes the + * uncertainty of progress and diffusion assumptions. + * + * So, users will want to use values larger, but not much + * larger than 1 to both smooth over transient shortages and + * hedge against uneven progress; as traded off against the + * cost of extra task overhead. We leave the user to pick a + * threshold value to compare with the results of this call to + * guide decisions, but recommend values such as 3. + * + * When all threads are active, it is on average OK to + * estimate surplus strictly locally. In steady-state, if one + * thread is maintaining say 2 surplus tasks, then so are + * others. So we can just use estimated queue length. + * However, this strategy alone leads to serious mis-estimates + * in some non-steady-state conditions (ramp-up, ramp-down, + * other stalls). We can detect many of these by further + * considering the number of "idle" threads, that are known to + * have zero queued tasks, so compensate by a factor of + * (#idle/#active) threads. + */ + ForkJoinWorkerThread wt = + (ForkJoinWorkerThread)Thread.currentThread(); + return wt.workQueue.queueSize() - wt.pool.idlePerActive(); } // Extension methods @@ -1083,7 +1281,7 @@ public abstract class ForkJoinTask im * otherwise. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -1091,8 +1289,7 @@ public abstract class ForkJoinTask im * @return the next task, or {@code null} if none are available */ protected static ForkJoinTask peekNextLocalTask() { - return ((ForkJoinWorkerThread) Thread.currentThread()) - .peekTask(); + return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek(); } /** @@ -1102,7 +1299,7 @@ public abstract class ForkJoinTask im * be useful otherwise. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -1111,7 +1308,7 @@ public abstract class ForkJoinTask im */ protected static ForkJoinTask pollNextLocalTask() { return ((ForkJoinWorkerThread) Thread.currentThread()) - .pollLocalTask(); + .workQueue.nextLocalTask(); } /** @@ -1125,7 +1322,7 @@ public abstract class ForkJoinTask im * otherwise. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -1133,8 +1330,51 @@ public abstract class ForkJoinTask im * @return a task, or {@code null} if none are available */ protected static ForkJoinTask pollTask() { - return ((ForkJoinWorkerThread) Thread.currentThread()) - .pollTask(); + ForkJoinWorkerThread wt = + (ForkJoinWorkerThread)Thread.currentThread(); + return wt.pool.nextTaskFor(wt.workQueue); + } + + // Mark-bit operations + + /** + * Returns true if this task is marked. + * + * @return true if this task is marked + * @since 1.8 + */ + public final boolean isMarkedForkJoinTask() { + return (status & MARKED) != 0; + } + + /** + * Atomically sets the mark on this task. + * + * @return true if this task was previously unmarked + * @since 1.8 + */ + public final boolean markForkJoinTask() { + for (int s;;) { + if (((s = status) & MARKED) != 0) + return false; + if (U.compareAndSwapInt(this, STATUS, s, s | MARKED)) + return true; + } + } + + /** + * Atomically clears the mark on this task. + * + * @return true if this task was previously marked + * @since 1.8 + */ + public final boolean unmarkForkJoinTask() { + for (int s;;) { + if (((s = status) & MARKED) == 0) + return false; + if (U.compareAndSwapInt(this, STATUS, s, s & ~MARKED)) + return true; + } } /** @@ -1235,11 +1475,10 @@ public abstract class ForkJoinTask im private static final long serialVersionUID = -7721805057305804111L; /** - * Save the state to a stream. + * Saves this task to a stream (that is, serializes it). * * @serialData the current run status and the exception thrown * during execution, or {@code null} if none - * @param s the stream */ private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { @@ -1248,34 +1487,29 @@ public abstract class ForkJoinTask im } /** - * Reconstitute the instance from a stream. - * - * @param s the stream + * Reconstitutes this task from a stream (that is, deserializes it). */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { s.defaultReadObject(); - status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts - status |= EXTERNAL_SIGNAL; // conservatively set external signal Object ex = s.readObject(); if (ex != null) - setDoneExceptionally((Throwable) ex); + setExceptionalCompletion((Throwable)ex); } // Unsafe mechanics - - private static final sun.misc.Unsafe UNSAFE = getUnsafe(); - private static final long statusOffset = - objectFieldOffset("status", ForkJoinTask.class); - - private static long objectFieldOffset(String field, Class klazz) { + private static final sun.misc.Unsafe U; + private static final long STATUS; + static { + exceptionTableLock = new ReentrantLock(); + exceptionTableRefQueue = new ReferenceQueue(); + exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY]; 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; + U = getUnsafe(); + STATUS = U.objectFieldOffset + (ForkJoinTask.class.getDeclaredField("status")); + } catch (Exception e) { + throw new Error(e); } }