--- jsr166/src/jsr166y/ForkJoinTask.java 2009/07/27 21:41:53 1.24 +++ jsr166/src/jsr166y/ForkJoinTask.java 2011/02/22 10:50:51 1.75 @@ -6,479 +6,567 @@ 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.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; +import java.util.concurrent.locks.ReentrantLock; +import java.lang.reflect.Constructor; /** - * Abstract base class for tasks that run within a {@link - * ForkJoinPool}. A ForkJoinTask is a thread-like entity that is much + * Abstract base class for tasks that run within a {@link ForkJoinPool}. + * A {@code ForkJoinTask} is a thread-like entity that is much * lighter weight than a normal thread. Huge numbers of tasks and * subtasks may be hosted by a small number of actual threads in a * ForkJoinPool, at the price of some usage limitations. * - *

A "main" ForkJoinTask begins execution when submitted to a - * {@link ForkJoinPool}. Once started, it will usually in turn start - * other subtasks. As indicated by the name of this class, many - * programs using ForkJoinTasks employ only methods {@code fork} and - * {@code join}, or derivatives such as {@code 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 "main" {@code ForkJoinTask} begins execution when submitted + * to a {@link ForkJoinPool}. Once started, it will usually in turn + * 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(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 ForkJoinTask is a lightweight form of {@link Future}. The - * efficiency of ForkJoinTasks 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 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 join - * them. These exceptions may additionally include - * RejectedExecutionExceptions stemming from internal resource - * exhaustion such as failure to allocate internal task queues. + *

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 + * 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 {@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. * *

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 ForkJoinTask class is not usually directly subclassed. + *

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. Normally, a concrete + * particular style of fork/join processing, typically {@link + * RecursiveAction} for computations that do not return results, or + * {@link RecursiveTask} for those that do. Normally, a concrete * ForkJoinTask subclass declares fields comprising its parameters, * established in a constructor, and then defines a {@code compute} * method that somehow uses the control methods supplied by this base * class. While these methods have {@code public} access (to allow - * instances of different task subclasses to call each others + * instances of different task subclasses to call each other's * methods), some of them may only be called from within other * 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}. * - *

Most base support methods are {@code final} because their - * implementations are intrinsically tied to the underlying - * lightweight task scheduling framework, and so cannot be overridden. - * Developers creating new basic styles of fork/join processing should - * minimally implement {@code protected} methods - * {@link #exec}, {@link #setRawResult}, and - * {@link #getRawResult}, while also introducing an abstract - * computational method that can be implemented in its subclasses, - * possibly relying on other {@code protected} methods provided - * by this class. + *

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 + * underlying lightweight task scheduling framework. Developers + * creating new basic styles of fork/join processing should minimally + * implement {@code protected} methods {@link #exec}, {@link + * #setRawResult}, and {@link #getRawResult}, while also introducing + * an abstract computational method that can be implemented in its + * subclasses, possibly relying on other {@code protected} methods + * provided by this class. * *

ForkJoinTasks should perform relatively small amounts of - * computations, otherwise splitting into smaller tasks. 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. + * 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, 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 constructed in asyncMode. * - *

ForkJoinTasks are {@code Serializable}, which enables them - * to be used in extensions such as remote execution frameworks. It is - * in general sensible to serialize tasks only before or after, but - * not during execution. Serialization is not relied on during - * execution itself. + *

ForkJoinTasks are {@code Serializable}, which enables them to be + * used in extensions such as remote execution frameworks. It is + * sensible to serialize tasks only before or after, but not during, + * execution. Serialization is not relied on during execution itself. * * @since 1.7 * @author Doug Lea */ 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 + /* + * 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. + */ + + /* + * 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 final Map, Throwable> exceptionMap = - 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); - } - - /** - * Workaround for not being able to rethrow unchecked exceptions. - */ - 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 + private static final int NORMAL = -1; + private static final int CANCELLED = -2; + private static final int EXCEPTIONAL = -3; + private static final int SIGNAL = 1; /** - * 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 + * @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 (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) { + if (s != 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. + * Tries to block a worker thread until completed or timed out. + * Uses Object.wait time argument conventions. + * May fail on contention or interrupt. + * + * @param millis if > 0, wait time. */ - private void externallySetCompletion(int completion) { + final void tryAwaitDone(long millis) { 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)); + if (((s = status) > 0 || + (s == 0 && + UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL))) && + status > 0) { + synchronized (this) { + if (status > 0) + wait(millis); } - } catch (InterruptedException ie) { - onInterruptedWait(); } + } catch (InterruptedException ie) { + // caller must check termination } } - // Awaiting completion - /** - * Sets status to indicate there is joiner, then waits for join, - * surrounded with pool notifications. - * - * @return status upon exit + * Blocks a non-worker-thread until completion. + * @return status upon completion */ - private int awaitDone(ForkJoinWorkerThread w, - boolean maintainParallelism) { - ForkJoinPool pool = (w == null) ? null : w.pool; + private int externalAwaitDone() { 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; + if ((s = status) >= 0) { + boolean interrupted = false; + synchronized (this) { + while ((s = status) >= 0) { + if (s == 0) + UNSAFE.compareAndSwapInt(this, statusOffset, + 0, SIGNAL); + else { + try { + wait(); + } catch (InterruptedException ie) { + interrupted = true; + } + } + } } + if (interrupted) + Thread.currentThread().interrupt(); } return s; } /** - * Timed version of awaitDone - * - * @return status upon exit + * Blocks a non-worker-thread until completion or interruption or timeout. */ - private int awaitDone(ForkJoinWorkerThread w, long nanos) { - ForkJoinPool pool = (w == null) ? null : w.pool; + private int externalInterruptibleAwaitDone(long millis) + throws InterruptedException { 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 (Thread.interrupted()) + throw new InterruptedException(); + if ((s = status) >= 0) { + synchronized (this) { + while ((s = status) >= 0) { + if (s == 0) + UNSAFE.compareAndSwapInt(this, statusOffset, + 0, SIGNAL); + else { + wait(millis); + if (millis > 0L) + break; + } } - 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). + * Primary execution method for stolen tasks. Unless done, calls + * exec and records status if completed, but doesn't wait for + * completion otherwise. */ - 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); + final void doExec() { + if (status >= 0) { + boolean completed; + try { + completed = exec(); + } catch (Throwable rex) { + setExceptionalCompletion(rex); + return; + } + if (completed) + setCompletion(NORMAL); // must be outside try block + } } /** - * Notifies pool to adjust counts on cancelled or timed out wait. + * Primary mechanics for join, get, quietlyJoin. + * @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 doJoin() { + Thread t; ForkJoinWorkerThread w; int s; boolean completed; + if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) { + if ((s = status) < 0) + return s; + if ((w = (ForkJoinWorkerThread)t).unpushTask(this)) { + try { + completed = exec(); + } catch (Throwable rex) { + return setExceptionalCompletion(rex); } + if (completed) + return setCompletion(NORMAL); } + return w.joinTask(this); } + else + return externalAwaitDone(); } /** - * Handles interruptions during waits. + * Primary mechanics for invoke, quietlyInvoke. + * @return status upon completion */ - 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 int doInvoke() { + int s; boolean completed; + if ((s = status) < 0) + return s; + try { + completed = exec(); + } catch (Throwable rex) { + return setExceptionalCompletion(rex); + } + if (completed) + return setCompletion(NORMAL); + else + return doJoin(); } - // Recording and reporting exceptions - - private void setDoneExceptionally(Throwable rex) { - exceptionMap.put(this, rex); - setCompletion(EXCEPTIONAL); - } + // Exception table support /** - * Throws the exception associated with status s. + * 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. * - * @throws the exception + * Note: These statics are initialized below in static block. */ - private void reportException(int s) { - if ((s &= COMPLETION_MASK) < NORMAL) { - if (s == CANCELLED) - throw new CancellationException(); - else - rethrowException(exceptionMap.get(this)); - } - } + private static final ExceptionNode[] exceptionTable; + private static final ReentrantLock exceptionTableLock; + private static final ReferenceQueue exceptionTableRefQueue; /** - * Returns result or throws exception using j.u.c.Future conventions. - * Only call when {@code isDone} known to be true. + * Fixed capacity for exceptionTable. */ - 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(); - } - return getRawResult(); - } + private static final int EXCEPTION_MAP_CAPACITY = 32; /** - * Returns result or throws exception using j.u.c.Future conventions - * with timeouts. + * 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 helpExpunge when its pool becomes + * isQuiescent. */ - 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); - if (Thread.interrupted()) - throw new InterruptedException(); - throw new TimeoutException(); + static final class ExceptionNode extends WeakReference>{ + final Throwable ex; + ExceptionNode next; + final long thrower; + ExceptionNode(ForkJoinTask task, Throwable ex, ExceptionNode next) { + super(task, exceptionTableRefQueue); + this.ex = ex; + this.next = next; + this.thrower = Thread.currentThread().getId(); + } } - // internal execution methods - /** - * Calls exec, recording completion, and rethrowing exception if - * encountered. Caller should normally check status before calling. + * Records exception and sets exceptional completion. * - * @return true if completed normally + * @return status on exit */ - 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 int setExceptionalCompletion(Throwable ex) { + int h = System.identityHashCode(this); + 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(); } - setNormalCompletion(); - return true; + return setCompletion(EXCEPTIONAL); } /** - * Main execution method used by worker threads. Invokes - * base computation unless already complete. + * Removes exception node and clears status */ - final void quietlyExec() { - if (status >= 0) { - try { - if (!exec()) - return; - } catch (Throwable rex) { - setDoneExceptionally(rex); - return; + private void clearExceptionalCompletion() { + int h = System.identityHashCode(this); + 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; } - setNormalCompletion(); + expungeStaleExceptions(); + status = 0; + } finally { + lock.unlock(); } } /** - * Calls exec(), recording but not rethrowing exception. - * Caller should normally check status before calling. + * 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 true if completed normally + * @return the exception, or null if none */ - private boolean tryQuietlyInvoke() { + private Throwable getThrowableException() { + if (status != EXCEPTIONAL) + return null; + int h = System.identityHashCode(this); + ExceptionNode e; + ReentrantLock lock = exceptionTableLock; + lock.lock(); try { - if (!exec()) - return false; - } catch (Throwable rex) { - setDoneExceptionally(rex); - return false; + expungeStaleExceptions(); + ExceptionNode[] t = exceptionTable; + e = t[h & (t.length - 1)]; + while (e != null && e.get() != this) + e = e.next; + } finally { + lock.unlock(); } - setNormalCompletion(); - return true; + Throwable ex; + if (e == null || (ex = e.ex) == null) + return null; + if (e.thrower != Thread.currentThread().getId()) { + Class ec = ex.getClass(); + try { + 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) { + } + } + return ex; } /** - * Cancels, ignoring any exceptions it throws. + * Poll stale refs and remove them. Call only while holding lock. */ - final void cancelIgnoringExceptions() { - try { - cancel(false); - } catch (Throwable ignore) { + 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; + } + } } } /** - * Main implementation of helpJoin + * If lock is available, poll any stale refs and remove them. + * Called from ForkJoinPool when pools become quiescent. */ - 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 + static final void helpExpungeStaleExceptions() { + ReentrantLock lock = exceptionTableLock; + if (lock.tryLock()) { + try { + expungeStaleExceptions(); + } finally { + lock.unlock(); + } + } + } + + /** + * Report the result of invoke or join; called only upon + * non-normal return of internal versions. + */ + private V reportResult() { + int s; Throwable ex; + if ((s = status) == CANCELLED) + throw new CancellationException(); + if (s == EXCEPTIONAL && (ex = getThrowableException()) != null) + UNSAFE.throwException(ex); + return getRawResult(); } // public methods @@ -486,13 +574,20 @@ 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. This - * method may be invoked only from within ForkJoinTask - * computations (as may be determined using method {@link - * #inForkJoinPool}). Attempts to invoke in other contexts result - * in exceptions or errors, possibly including ClassCastException. + * 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 + * 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}. * - * @return {@code this}, to simplify usage. + * @return {@code this}, to simplify usage */ public final ForkJoinTask fork() { ((ForkJoinWorkerThread) Thread.currentThread()) @@ -501,66 +596,87 @@ public abstract class ForkJoinTask im } /** - * Returns the result of the computation when it is ready. - * This method differs from {@code get} in that abnormal - * completion results in RuntimeExceptions or Errors, not - * ExecutionExceptions. + * 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}, 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. + * 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(); + if (doInvoke() != NORMAL) + return reportResult(); else - return join(); + return getRawResult(); } /** - * Forks both tasks, returning when {@code isDone} holds for - * both of them or an exception is encountered. This method may be - * invoked only from within ForkJoinTask computations (as may be - * determined using method {@link #inForkJoinPool}). Attempts to - * invoke in other contexts result in exceptions or errors, - * possibly including ClassCastException. - * - * @param t1 one task - * @param t2 the other task - * @throws NullPointerException if t1 or t2 are null - * @throws RuntimeException or Error if either task did so + * 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 + * 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 t1 the first task + * @param t2 the second task + * @throws NullPointerException if any task is null */ - public static void invokeAll(ForkJoinTaskt1, ForkJoinTask t2) { + public static void invokeAll(ForkJoinTask t1, ForkJoinTask t2) { t2.fork(); t1.invoke(); t2.join(); } /** - * Forks the given tasks, returning when {@code isDone} holds - * for all of them. If any task encounters an exception, others - * may be cancelled. This method may be invoked only from within - * ForkJoinTask computations (as may be determined using method - * {@link #inForkJoinPool}). Attempts to invoke in other contexts - * result in exceptions or errors, possibly including - * ClassCastException. + * 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, 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 + * 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 array of tasks - * @throws NullPointerException if tasks or any element are null - * @throws RuntimeException or Error if any task did so + * @param tasks the tasks + * @throws NullPointerException if any task is null */ public static void invokeAll(ForkJoinTask... tasks) { Throwable ex = null; @@ -573,44 +689,47 @@ 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 == null) + ex = t.getException(); } } if (ex != null) - rethrowException(ex); + UNSAFE.throwException(ex); } /** - * Forks all tasks in the collection, returning when - * {@code isDone} holds for all of them. If any task - * encounters an exception, others may be cancelled. This method - * may be invoked only from within ForkJoinTask computations (as - * may be determined using method {@link - * #inForkJoinPool}). Attempts to invoke in other contexts result - * in exceptions or errors, possibly including ClassCastException. + * Forks all tasks in the specified collection, 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, 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 + * 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 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 List)) { + if (!(tasks instanceof RandomAccess) || !(tasks instanceof List)) { invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()])); return tasks; } @@ -627,78 +746,73 @@ 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 == null) + 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 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 + *

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 setCompletion(CANCELLED) == 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) { + } + } + + public final boolean isDone() { + return status < 0; + } + + public final boolean isCancelled() { + return status == CANCELLED; } /** @@ -707,23 +821,32 @@ 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; } /** * Returns the exception thrown by the base computation, or a - * CancellationException if cancelled, or null if none or if the - * method has not yet completed. + * {@code CancellationException} if cancelled, or {@code null} if + * none or if the method has not yet completed. * * @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() : + getThrowableException()); } /** @@ -732,29 +855,30 @@ public abstract class ForkJoinTask im * {@code join} and related operations. This method may be used * to induce exceptions in asynchronous tasks, or to force * completion of tasks that would not otherwise complete. Its use - * in other situations is likely to be wrong. This method is + * in other situations is discouraged. This method is * 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 likely to be wrong. 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 */ @@ -762,96 +886,118 @@ 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 { - ForkJoinWorkerThread w = getWorker(); - if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke()) - awaitDone(w, unit.toNanos(timeout)); - 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 - * ForkJoinTask computations (as may be determined using method - * {@link #inForkJoinPool}). Attempts to invoke in other contexts - * result in exceptions or errors, possibly including - * 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 invoked only from within ForkJoinTask - * computations (as may be determined using method {@link - * #inForkJoinPool}). Attempts to invoke in other contexts result - * in exceptions or errors, possibly including ClassCastException. + * Waits if necessary for at most the given time for the computation + * to complete, and then retrieves its result, if available. + * + * @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 { + Thread t = Thread.currentThread(); + if (t instanceof ForkJoinWorkerThread) { + ForkJoinWorkerThread w = (ForkJoinWorkerThread) t; + long nanos = unit.toNanos(timeout); + if (status >= 0) { + boolean completed = false; + if (w.unpushTask(this)) { + try { + completed = exec(); + } catch (Throwable rex) { + setExceptionalCompletion(rex); + } + } + if (completed) + setCompletion(NORMAL); + else if (status >= 0 && nanos > 0) + w.pool.timedAwaitJoin(this, nanos); + } + } + else { + long millis = unit.toMillis(timeout); + if (millis > 0) + externalInterruptibleAwaitDone(millis); } + int s = status; + 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(); } /** * 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 + * 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()) @@ -864,20 +1010,28 @@ public abstract class ForkJoinTask im * this task, but only if reuse occurs when this task has either * never been forked, or has been forked, then completed and all * outstanding joins of this task have also completed. Effects - * under any other usage conditions are not guaranteed, and are - * almost surely wrong. This method may be useful when executing + * 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; } /** * Returns the pool hosting the current task execution, or null * if this task is executing outside of any ForkJoinPool. * + * @see #inForkJoinPool * @return the pool, or {@code null} if none */ public static ForkJoinPool getPool() { @@ -887,11 +1041,12 @@ 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; @@ -903,11 +1058,13 @@ public abstract class ForkJoinTask im * by the current thread, and has not commenced executing in * another thread. This method may be useful when arranging * alternative local processing of tasks that could have been, but - * were not, stolen. This method may be invoked only from within - * ForkJoinTask computations (as may be determined using method - * {@link #inForkJoinPool}). Attempts to invoke in other contexts - * result in exceptions or errors, possibly including - * ClassCastException. + * were not, stolen. + * + *

This method may be invoked only from within {@code + * 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}. * * @return {@code true} if unforked */ @@ -922,6 +1079,12 @@ public abstract class ForkJoinTask im * value may be useful for heuristic decisions about whether to * fork other tasks. * + *

This method may be invoked only from within {@code + * 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}. + * * @return the number of tasks */ public static int getQueuedTaskCount() { @@ -939,6 +1102,12 @@ public abstract class ForkJoinTask im * tasks, and to process computations locally if this threshold is * exceeded. * + *

This method may be invoked only from within {@code + * 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}. + * * @return the surplus number of tasks, which may be negative */ public static int getSurplusQueuedTaskCount() { @@ -974,24 +1143,28 @@ 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(); /** - * Returns, but does not unschedule or execute, the task queued by - * the current thread but not yet executed, if one is + * Returns, but does not unschedule or execute, a task queued by + * the current thread but not yet executed, if one is immediately * available. There is no guarantee that this task will actually - * be polled or executed next. This method is designed primarily - * to support extensions, and is unlikely to be useful otherwise. - * This method may be invoked only from within ForkJoinTask - * computations (as may be determined using method {@link - * #inForkJoinPool}). Attempts to invoke in other contexts result - * in exceptions or errors, possibly including ClassCastException. + * be polled or executed next. Conversely, this method may return + * null even if a task exists but cannot be accessed without + * contention with other threads. This method is designed + * primarily to support extensions, and is unlikely to be useful + * otherwise. + * + *

This method may be invoked only from within {@code + * 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}. * * @return the next task, or {@code null} if none are available */ @@ -1004,11 +1177,13 @@ public abstract class ForkJoinTask im * Unschedules and returns, without executing, the next task * queued by the current thread but not yet executed. This method * is designed primarily to support extensions, and is unlikely to - * be useful otherwise. This method may be invoked only from - * within ForkJoinTask computations (as may be determined using - * method {@link #inForkJoinPool}). Attempts to invoke in other - * contexts result in exceptions or errors, possibly including - * ClassCastException. + * be useful otherwise. + * + *

This method may be invoked only from within {@code + * 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}. * * @return the next task, or {@code null} if none are available */ @@ -1025,11 +1200,13 @@ public abstract class ForkJoinTask im * {@code null} result does not necessarily imply quiescence * of the pool this task is operating in. This method is designed * primarily to support extensions, and is unlikely to be useful - * otherwise. This method may be invoked only from within - * ForkJoinTask computations (as may be determined using method - * {@link #inForkJoinPool}). Attempts to invoke in other contexts - * result in exceptions or errors, possibly including - * ClassCastException. + * otherwise. + * + *

This method may be invoked only from within {@code + * 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}. * * @return a task, or {@code null} if none are available */ @@ -1038,44 +1215,97 @@ public abstract class ForkJoinTask im .pollTask(); } - // adaptors + /** + * Adaptor for Runnables. This implements RunnableFuture + * to be compliant with AbstractExecutorService constraints + * when used in ForkJoinPool. + */ + static final class AdaptedRunnable extends ForkJoinTask + implements RunnableFuture { + final Runnable runnable; + final T resultOnCompletion; + T result; + AdaptedRunnable(Runnable runnable, T result) { + if (runnable == null) throw new NullPointerException(); + this.runnable = runnable; + this.resultOnCompletion = result; + } + public T getRawResult() { return result; } + public void setRawResult(T v) { result = v; } + public boolean exec() { + runnable.run(); + result = resultOnCompletion; + return true; + } + public void run() { invoke(); } + private static final long serialVersionUID = 5232453952276885070L; + } /** - * Returns a new ForkJoinTask that performs the {@code run} - * method of the given Runnable as its action, and returns a null - * result upon {@code join}. + * Adaptor for Callables + */ + static final class AdaptedCallable extends ForkJoinTask + implements RunnableFuture { + final Callable callable; + T result; + AdaptedCallable(Callable callable) { + if (callable == null) throw new NullPointerException(); + this.callable = callable; + } + public T getRawResult() { return result; } + public void setRawResult(T v) { result = v; } + public boolean exec() { + try { + result = callable.call(); + return true; + } catch (Error err) { + throw err; + } catch (RuntimeException rex) { + throw rex; + } catch (Exception ex) { + throw new RuntimeException(ex); + } + } + public void run() { invoke(); } + private static final long serialVersionUID = 2838392045355241008L; + } + + /** + * Returns a new {@code ForkJoinTask} that performs the {@code run} + * method of the given {@code Runnable} as its action, and returns + * a null result upon {@link #join}. * * @param runnable the runnable action * @return the task */ - public static ForkJoinTask adapt(Runnable runnable) { - return new ForkJoinPool.AdaptedRunnable(runnable, null); + public static ForkJoinTask adapt(Runnable runnable) { + return new AdaptedRunnable(runnable, null); } /** - * Returns a new ForkJoinTask that performs the {@code run} - * method of the given Runnable as its action, and returns the - * given result upon {@code join}. + * Returns a new {@code ForkJoinTask} that performs the {@code run} + * method of the given {@code Runnable} as its action, and returns + * the given result upon {@link #join}. * * @param runnable the runnable action * @param result the result upon completion * @return the task */ public static ForkJoinTask adapt(Runnable runnable, T result) { - return new ForkJoinPool.AdaptedRunnable(runnable, result); + return new AdaptedRunnable(runnable, result); } /** - * Returns a new ForkJoinTask that performs the {@code call} - * method of the given Callable as its action, and returns its - * result upon {@code join}, translating any checked - * exceptions encountered into {@code RuntimeException}. + * Returns a new {@code ForkJoinTask} that performs the {@code call} + * method of the given {@code Callable} as its action, and returns + * its result upon {@link #join}, translating any checked exceptions + * encountered into {@code RuntimeException}. * * @param callable the callable action * @return the task */ - public static ForkJoinTask adapt(Callable callable) { - return new ForkJoinPool.AdaptedCallable(callable); + public static ForkJoinTask adapt(Callable callable) { + return new AdaptedCallable(callable); } // Serialization support @@ -1083,7 +1313,7 @@ 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 @@ -1096,34 +1326,31 @@ 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 - - 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 UNSAFE; + private static final long statusOffset; + 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; + UNSAFE = getUnsafe(); + statusOffset = UNSAFE.objectFieldOffset + (ForkJoinTask.class.getDeclaredField("status")); + } catch (Exception e) { + throw new Error(e); } }