--- jsr166/src/jsr166y/ForkJoinTask.java 2009/08/03 13:01:15 1.32 +++ jsr166/src/jsr166y/ForkJoinTask.java 2010/11/24 10:50:38 1.72 @@ -6,8 +6,6 @@ package jsr166y; -import java.util.concurrent.*; - import java.io.Serializable; import java.util.Collection; import java.util.Collections; @@ -15,6 +13,16 @@ import java.util.List; import java.util.RandomAccess; import java.util.Map; import java.util.WeakHashMap; +import java.util.concurrent.Callable; +import java.util.concurrent.CancellationException; +import java.util.concurrent.ExecutionException; +import java.util.concurrent.Executor; +import java.util.concurrent.ExecutorService; +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; /** * Abstract base class for tasks that run within a {@link ForkJoinPool}. @@ -28,10 +36,10 @@ 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 @@ -56,27 +64,36 @@ import java.util.WeakHashMap; * 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. + * additionally include {@link RejectedExecutionException} stemming + * from internal resource exhaustion, such as failure to allocate + * internal task queues. * *

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 - * 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 + * 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 * may be useful when a set of tasks are being executed, and you need * to delay processing of results or exceptions until all complete. * Method {@code invokeAll} (available in multiple versions) * performs the most common form of parallel invocation: forking a set * of tasks and joining them all. * + *

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 #isCompletedNormally} is true if a task completed without + * 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 * particular style of fork/join processing, typically {@link @@ -91,7 +108,17 @@ 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. * *

Most base support methods are {@code final}, to prevent * overriding of implementations that are intrinsically tied to the @@ -107,15 +134,15 @@ 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 - * java.lang.Runnable} and {@link java.util.concurrent.Callable}, that - * may be of use when mixing execution of ForkJoinTasks with other - * kinds of tasks. When all tasks are of this form, consider using a - * pool in {@link ForkJoinPool#setAsyncMode}. + *

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 constructed in asyncMode. * *

ForkJoinTasks are {@code Serializable}, which enables them to be * used in extensions such as remote execution frameworks. It is @@ -127,33 +154,43 @@ 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. + /* + * 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. In particular, most + * join mechanics are in method quietlyJoin, below. + */ + + /* + * 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. */ + + /** The run status of this task */ 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 + private static final int NORMAL = -1; + private static final int CANCELLED = -2; + private static final int EXCEPTIONAL = -3; + private static final int SIGNAL = 1; /** * Table of exceptions thrown by tasks, to enable reporting by @@ -167,328 +204,132 @@ public abstract class ForkJoinTask im Collections.synchronizedMap (new WeakHashMap, Throwable>()); - // within-package utilities - - /** - * Gets current worker thread, or null if not a worker thread. - */ - 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); - } + // Maintaining completion status /** - * Workaround for not being able to rethrow unchecked exceptions. - */ - static void rethrowException(Throwable ex) { - if (ex != null) - UNSAFE.throwException(ex); - } - - // Setting completion status - - /** - * 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. * * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL */ - 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(); } - } - } - 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); - } - - // internal waiting and notification - - /** - * Performs the actual monitor wait for awaitDone. - */ - 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(); - } - } - - /** - * Performs the actual timed monitor wait for awaitDone. - */ - 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)); - } - } catch (InterruptedException ie) { - onInterruptedWait(); - } - } - } - - // 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; + private void setCompletion(int completion) { 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); + if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) { + if (s != 0) + synchronized (this) { notifyAll(); } break; } } - return s; } /** - * Timed version of awaitDone + * Records exception and sets exceptional completion. * - * @return status upon exit - */ - private int awaitDone(ForkJoinWorkerThread w, long nanos) { - ForkJoinPool pool = (w == null) ? null : w.pool; - 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); - break; - } - } - 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. - */ - 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; - } - } - } - } - - /** - * Handles interruptions during waits. + * @return status on exit */ - private void onInterruptedWait() { - ForkJoinWorkerThread w = getWorker(); - if (w == null) - Thread.currentThread().interrupt(); // re-interrupt - else if (w.isTerminating()) - cancelIgnoringExceptions(); - // else if FJworker, ignore interrupt - } - - // Recording and reporting exceptions - - private void setDoneExceptionally(Throwable rex) { + private void setExceptionalCompletion(Throwable rex) { exceptionMap.put(this, rex); setCompletion(EXCEPTIONAL); } /** - * Throws the exception associated with status s. - * - * @throws the exception + * Blocks a worker thread until completed or timed out. Called + * only by pool. */ - private void reportException(int s) { - if ((s &= COMPLETION_MASK) < NORMAL) { - if (s == CANCELLED) - throw new CancellationException(); - else - rethrowException(exceptionMap.get(this)); + final void internalAwaitDone(long millis, int nanos) { + int s = status; + if ((s == 0 && + UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL)) || + s > 0) { + try { // the odd construction reduces lock bias effects + synchronized (this) { + if (status > 0) + wait(millis, nanos); + else + notifyAll(); + } + } catch (InterruptedException ie) { + cancelIfTerminating(); + } } } /** - * Returns result or throws exception using j.u.c.Future conventions. - * Only call when {@code isDone} known to be true. + * Blocks a non-worker-thread until completion. */ - private V reportFutureResult() - throws ExecutionException, 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); - if (Thread.interrupted()) - throw new InterruptedException(); + private void externalAwaitDone() { + if (status >= 0) { + boolean interrupted = false; + synchronized(this) { + for (;;) { + int s = status; + if (s == 0) + UNSAFE.compareAndSwapInt(this, statusOffset, + 0, SIGNAL); + else if (s < 0) { + notifyAll(); + break; + } + else { + try { + wait(); + } catch (InterruptedException ie) { + interrupted = true; + } + } + } + } + if (interrupted) + Thread.currentThread().interrupt(); } - return getRawResult(); } /** - * Returns result or throws exception using j.u.c.Future conventions - * with timeouts. + * Blocks a non-worker-thread until completion or interruption or timeout. */ - private V reportTimedFutureResult() - throws InterruptedException, ExecutionException, TimeoutException { - Throwable ex; - int s = status & COMPLETION_MASK; - if (s == NORMAL) - return getRawResult(); - if (s == CANCELLED) - throw new CancellationException(); - if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) - throw new ExecutionException(ex); + private void externalInterruptibleAwaitDone(boolean timed, long nanos) + throws InterruptedException { if (Thread.interrupted()) throw new InterruptedException(); - throw new TimeoutException(); - } - - // internal execution methods - - /** - * Calls exec, recording completion, and rethrowing exception if - * encountered. Caller should normally check status before calling. - * - * @return true if completed normally - */ - 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 - } - setNormalCompletion(); - return true; - } - - /** - * Main execution method used by worker threads. Invokes - * base computation unless already complete. - */ - final void quietlyExec() { if (status >= 0) { - try { - if (!exec()) - return; - } catch (Throwable rex) { - setDoneExceptionally(rex); - return; + long startTime = timed ? System.nanoTime() : 0L; + synchronized(this) { + for (;;) { + long nt; + int s = status; + if (s == 0) + UNSAFE.compareAndSwapInt(this, statusOffset, + 0, SIGNAL); + else if (s < 0) { + notifyAll(); + break; + } + else if (!timed) + wait(); + else if ((nt = nanos - (System.nanoTime()-startTime)) > 0L) + wait(nt / 1000000, (int)(nt % 1000000)); + else + break; + } } - setNormalCompletion(); } } /** - * Calls exec(), recording but not rethrowing exception. - * Caller should normally check status before calling. - * - * @return true if completed normally + * Unless done, calls exec and records status if completed, but + * doesn't wait for completion otherwise. Primary execution method + * for ForkJoinWorkerThread. */ - private boolean tryQuietlyInvoke() { + final void quietlyExec() { try { - if (!exec()) - return false; + if (status < 0 || !exec()) + return; } catch (Throwable rex) { - setDoneExceptionally(rex); - return false; - } - setNormalCompletion(); - return true; - } - - /** - * Cancels, ignoring any exceptions it throws. - */ - final void cancelIgnoringExceptions() { - try { - cancel(false); - } catch (Throwable ignore) { + setExceptionalCompletion(rex); + return; } - } - - /** - * Main implementation of helpJoin - */ - 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 + setCompletion(NORMAL); // must be outside try block } // public methods @@ -497,9 +338,14 @@ 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}. @@ -513,41 +359,55 @@ public abstract class ForkJoinTask im } /** - * 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)); + quietlyJoin(); + Throwable ex; + if (status < NORMAL && (ex = getException()) != null) + UNSAFE.throwException(ex); return getRawResult(); } /** * Commences performing this task, awaits its completion if - * necessary, and return its result. + * necessary, and returns its result, or throws an (unchecked) + * {@code RuntimeException} or {@code Error} if the underlying + * computation did so. * - * @throws Throwable (a RuntimeException, Error, or unchecked - * exception) if the underlying computation did so * @return the computed result */ public final V invoke() { - if (status >= 0 && tryExec()) - return getRawResult(); - else - return join(); + quietlyInvoke(); + Throwable ex; + if (status < NORMAL && (ex = getException()) != null) + UNSAFE.throwException(ex); + return getRawResult(); } /** - * Forks the given tasks, returning when {@code isDone} holds - * for each task or an exception is encountered. + * 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 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}. @@ -555,7 +415,6 @@ public abstract class ForkJoinTask im * @param t1 the first task * @param t2 the second task * @throws NullPointerException if any task is null - * @throws RuntimeException or Error if a task did so */ public static void invokeAll(ForkJoinTask t1, ForkJoinTask t2) { t2.fork(); @@ -565,19 +424,24 @@ public abstract class ForkJoinTask im /** * Forks the given tasks, returning when {@code isDone} holds for - * each task or an exception is encountered. If any task - * encounters an exception, others may be, but are not guaranteed - * to be, cancelled. + * each task or an (unchecked) exception 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}. * * @param tasks the tasks - * @throws NullPointerException if tasks or any element are null - * @throws RuntimeException or Error if any task did so + * @throws NullPointerException if any task is null */ public static void invokeAll(ForkJoinTask... tasks) { Throwable ex = null; @@ -592,7 +456,7 @@ public abstract class ForkJoinTask im t.fork(); else { t.quietlyInvoke(); - if (ex == null) + if (ex == null && t.status < NORMAL) ex = t.getException(); } } @@ -603,25 +467,30 @@ public abstract class ForkJoinTask im t.cancel(false); else { t.quietlyJoin(); - if (ex == null) + if (ex == null && t.status < NORMAL) ex = t.getException(); } } } if (ex != null) - rethrowException(ex); + UNSAFE.throwException(ex); } /** * Forks all tasks in the specified collection, returning when - * {@code isDone} holds for each task or an exception is - * encountered. If any task encounters an exception, others may - * be, but are not guaranteed to be, cancelled. The behavior of - * this operation is undefined if the specified collection is - * modified while the operation is in progress. + * {@code isDone} holds for each task or an (unchecked) exception + * 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}. @@ -629,7 +498,6 @@ public abstract class ForkJoinTask im * @param tasks the collection of tasks * @return the tasks argument, to simplify usage * @throws NullPointerException if tasks or any element are null - * @throws RuntimeException or Error if any task did so */ public static > Collection invokeAll(Collection tasks) { if (!(tasks instanceof RandomAccess) || !(tasks instanceof List)) { @@ -651,7 +519,7 @@ public abstract class ForkJoinTask im t.fork(); else { t.quietlyInvoke(); - if (ex == null) + if (ex == null && t.status < NORMAL) ex = t.getException(); } } @@ -662,65 +530,82 @@ public abstract class ForkJoinTask im t.cancel(false); else { t.quietlyJoin(); - if (ex == null) + if (ex == null && t.status < NORMAL) ex = t.getException(); } } } if (ex != null) - rethrowException(ex); + UNSAFE.throwException(ex); return tasks; } /** - * 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; - } - - /** - * Asserts that the results of this task's computation will not be - * used. If a cancellation occurs before attempting to execute this - * task, execution will be suppressed, {@link #isCancelled} - * will report true, and {@link #join} will result in a - * {@code CancellationException} being thrown. Otherwise, when - * cancellation races with completion, there are no guarantees - * about whether {@code isCancelled} will report {@code true}, - * whether {@code join} will return normally or via an exception, - * or whether these behaviors will remain consistent upon repeated - * invocation. + * Attempts to cancel execution of this task. This attempt will + * 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 in general - * 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 status == CANCELLED; + } + + /** + * 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. + */ + final void cancelIgnoringExceptions() { + try { + cancel(false); + } catch (Throwable ignore) { + } + } + + /** + * Cancels if current thread is a terminating worker thread, + * ignoring any exceptions thrown by cancel. + */ + final void cancelIfTerminating() { + Thread t = Thread.currentThread(); + if ((t instanceof ForkJoinWorkerThread) && + ((ForkJoinWorkerThread) t).isTerminating()) { + try { + cancel(false); + } catch (Throwable ignore) { + } + } + } + + public final boolean isDone() { + return status < 0; + } + + public final boolean isCancelled() { + return status == CANCELLED; } /** @@ -729,7 +614,18 @@ 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; + } + + /** + * Returns {@code true} if this task completed without throwing an + * exception and was not cancelled. + * + * @return {@code true} if this task completed without throwing an + * exception and was not cancelled + */ + public final boolean isCompletedNormally() { + return status == NORMAL; } /** @@ -740,12 +636,10 @@ public abstract class ForkJoinTask im * @return the exception, or {@code null} if none */ public final Throwable getException() { - int s = status & COMPLETION_MASK; - if (s >= NORMAL) - return null; - if (s == CANCELLED) - return new CancellationException(); - return exceptionMap.get(this); + int s = status; + return ((s >= NORMAL) ? null : + (s == CANCELLED) ? new CancellationException() : + exceptionMap.get(this)); } /** @@ -758,25 +652,26 @@ 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 */ @@ -784,106 +679,135 @@ 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 { + Thread t = Thread.currentThread(); + if (t instanceof ForkJoinWorkerThread) + quietlyJoin(); + else + externalInterruptibleAwaitDone(false, 0L); + int s = status; + if (s != NORMAL) { + Throwable ex; + if (s == CANCELLED) + throw new CancellationException(); + if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != 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 { + long nanos = unit.toNanos(timeout); + Thread t = Thread.currentThread(); + if (t instanceof ForkJoinWorkerThread) + ((ForkJoinWorkerThread)t).joinTask(this, true, nanos); + else + externalInterruptibleAwaitDone(true, nanos); + int s = status; + if (s != NORMAL) { + Throwable ex; + if (s == CANCELLED) + throw new CancellationException(); + if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) + throw new ExecutionException(ex); + throw new TimeoutException(); } + 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); + Thread t; + if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) { + ForkJoinWorkerThread w = (ForkJoinWorkerThread) t; + if (status >= 0) { + if (w.unpushTask(this)) { + boolean completed; + try { + completed = exec(); + } catch (Throwable rex) { + setExceptionalCompletion(rex); + return; + } + if (completed) { + setCompletion(NORMAL); + return; + } + } + w.joinTask(this, false, 0L); + } } + else + externalAwaitDone(); } /** * 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(); + if (status >= 0) { + boolean completed; + try { + completed = exec(); + } catch (Throwable rex) { + setExceptionalCompletion(rex); + return; + } + if (completed) + setCompletion(NORMAL); + else + quietlyJoin(); + } } /** * Possibly executes tasks until the pool hosting the current task - * {@link ForkJoinPool#isQuiescent}. This method may be of use in - * designs in which many tasks are forked, but none are explicitly - * joined, instead executing them until all are processed. + * {@link ForkJoinPool#isQuiescent is quiescent}. This method may + * be of use in designs in which many tasks are forked, but none + * are explicitly joined, instead executing them until all are + * 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}. @@ -902,9 +826,15 @@ 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) + if (status == EXCEPTIONAL) exceptionMap.remove(this); status = 0; } @@ -923,11 +853,12 @@ 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; @@ -942,7 +873,7 @@ 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}. @@ -961,7 +892,7 @@ 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}. @@ -984,7 +915,7 @@ 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}. @@ -1024,11 +955,10 @@ public abstract class ForkJoinTask im * called otherwise. The return value controls whether this task * is considered to be done normally. It may return false in * asynchronous actions that require explicit invocations of - * {@link #complete} to become joinable. It may throw exceptions - * to indicate abnormal exit. + * {@link #complete} to become joinable. It may also throw an + * (unchecked) exception to indicate abnormal exit. * * @return {@code true} if completed normally - * @throws Error or RuntimeException if encountered during computation */ protected abstract boolean exec(); @@ -1043,7 +973,7 @@ 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}. @@ -1062,7 +992,7 @@ 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}. @@ -1085,7 +1015,7 @@ 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}. @@ -1195,7 +1125,7 @@ public abstract class ForkJoinTask im private static final long serialVersionUID = -7721805057305804111L; /** - * Save the state to a stream. + * Saves the state to a stream (that is, serializes it). * * @serialData the current run status and the exception thrown * during execution, or {@code null} if none @@ -1208,18 +1138,16 @@ public abstract class ForkJoinTask im } /** - * Reconstitute the instance from a stream. + * Reconstitutes the instance from a stream (that is, deserializes it). * * @param s the stream */ 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