--- jsr166/src/jsr166y/ForkJoinTask.java 2010/04/18 12:51:18 1.47 +++ jsr166/src/jsr166y/ForkJoinTask.java 2011/03/15 19:47:02 1.77 @@ -1,20 +1,31 @@ /* * Written by Doug Lea with assistance from members of JCP JSR-166 * Expert Group and released to the public domain, as explained at - * http://creativecommons.org/licenses/publicdomain + * http://creativecommons.org/publicdomain/zero/1.0/ */ package jsr166y; -import java.util.concurrent.*; - import java.io.Serializable; import java.util.Collection; import java.util.Collections; import java.util.List; import java.util.RandomAccess; import java.util.Map; -import java.util.WeakHashMap; +import java.lang.ref.WeakReference; +import java.lang.ref.ReferenceQueue; +import java.util.concurrent.Callable; +import java.util.concurrent.CancellationException; +import java.util.concurrent.ExecutionException; +import java.util.concurrent.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}. @@ -28,10 +39,10 @@ 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 @@ -58,16 +69,17 @@ import java.util.WeakHashMap; * 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. + * 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 + * 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 @@ -103,7 +115,17 @@ 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 @@ -119,15 +141,15 @@ import java.util.WeakHashMap; * computation. Large tasks should be split into smaller subtasks, * usually via recursive decomposition. As a very rough rule of thumb, * a task should perform more than 100 and less than 10000 basic - * computational steps. If tasks are too big, then parallelism cannot - * improve throughput. If too small, then memory and internal task - * maintenance overhead may overwhelm processing. + * computational steps, and should avoid indefinite looping. If tasks + * are too big, then parallelism cannot improve throughput. If too + * small, then memory and internal task maintenance overhead may + * overwhelm processing. * *

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

ForkJoinTasks are {@code Serializable}, which enables them to be * used in extensions such as remote execution frameworks. It is @@ -151,299 +173,400 @@ public abstract class ForkJoinTask im * in a way that flows well in javadocs. */ - /** - * 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). Signal counts are not directly - * incremented by ForkJoinTask methods, but instead via a call to - * requestSignal within ForkJoinPool.preJoin, once their need is - * established. - * - * Completion of a stolen task with SIGNAL_MASK bits 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. - * - * 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 - - private static final int COMPLETION_MASK = 0xe0000000; - private static final int NORMAL = 0xe0000000; // == mask - private static final int CANCELLED = 0xc0000000; - private static final int EXCEPTIONAL = 0xa0000000; - private static final int SIGNAL_MASK = 0x0000ffff; - private static final int INTERNAL_SIGNAL_MASK = 0x00007fff; - private static final int EXTERNAL_SIGNAL = 0x00008000; - - /** - * 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 + /* + * 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>()); - // Maintaining 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, * also clearing signal request bits. * * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL + * @return completion status on exit */ - private void setCompletion(int completion) { - int s; - while ((s = status) >= 0) { + private int setCompletion(int completion) { + for (int s;;) { + if ((s = status) < 0) + return s; if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) { - if ((s & SIGNAL_MASK) != 0) { - Thread t = Thread.currentThread(); - if (t instanceof ForkJoinWorkerThread) - ((ForkJoinWorkerThread) t).pool.updateRunningCount - (s & INTERNAL_SIGNAL_MASK); + if (s != 0) synchronized (this) { notifyAll(); } - } - return; + return completion; } } } /** - * Record exception and set exceptional completion - */ - private void setDoneExceptionally(Throwable rex) { - exceptionMap.put(this, rex); - setCompletion(EXCEPTIONAL); - } - - /** - * Main internal execution method: Unless done, calls exec and - * records completion. + * Tries to block a worker thread until completed or timed out. + * Uses Object.wait time argument conventions. + * May fail on contention or interrupt. * - * @return true if ran and completed normally + * @param millis if > 0, wait time. */ - final boolean tryExec() { + final void tryAwaitDone(long millis) { + int s; try { - if (status < 0 || !exec()) - return false; - } catch (Throwable rex) { - setDoneExceptionally(rex); - return false; + if (((s = status) > 0 || + (s == 0 && + UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL))) && + status > 0) { + synchronized (this) { + if (status > 0) + wait(millis); + } + } + } catch (InterruptedException ie) { + // caller must check termination } - setCompletion(NORMAL); // must be outside try block - return true; } /** - * Increments internal signal count (thus requesting signal upon - * completion) unless already done. Call only once per join. - * Used by ForkJoinPool.preJoin. - * - * @return status + * Blocks a non-worker-thread until completion. + * @return status upon completion */ - final int requestSignal() { + private int externalAwaitDone() { int s; - do {} while ((s = status) >= 0 && - !UNSAFE.compareAndSwapInt(this, statusOffset, s, s + 1)); + 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; } /** - * Sets external signal request unless already done. - * - * @return status + * Blocks a non-worker-thread until completion or interruption or timeout. */ - private int requestExternalSignal() { + private int externalInterruptibleAwaitDone(long millis) + throws InterruptedException { int s; - do {} while ((s = status) >= 0 && - !UNSAFE.compareAndSwapInt(this, statusOffset, - s, s | EXTERNAL_SIGNAL)); + 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; + } + } + } + } return s; } - /* - * Awaiting completion. The four versions, internal vs external X - * untimed vs timed, have the same overall structure but differ - * from each other enough to defy simple integration. - */ - /** - * Blocks a worker until this task is done, also maintaining pool - * and signal counts + * Primary execution method for stolen tasks. Unless done, calls + * exec and records status if completed, but doesn't wait for + * completion otherwise. */ - private void awaitDone(ForkJoinWorkerThread w) { + final void doExec() { if (status >= 0) { - w.pool.preJoin(this); - while (status >= 0) { - try { // minimize lock scope - synchronized(this) { - if (status >= 0) - wait(); - else { // help release; also helps avoid lock-biasing - notifyAll(); - break; - } - } - } catch (InterruptedException ie) { - cancelIfTerminating(); - } + boolean completed; + try { + completed = exec(); + } catch (Throwable rex) { + setExceptionalCompletion(rex); + return; } + if (completed) + setCompletion(NORMAL); // must be outside try block } } /** - * Blocks a non-ForkJoin thread until this task is done. + * Primary mechanics for join, get, quietlyJoin. + * @return status upon completion */ - private void externalAwaitDone() { - if (requestExternalSignal() >= 0) { - boolean interrupted = false; - while (status >= 0) { + 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 { - synchronized(this) { - if (status >= 0) - wait(); - else { - notifyAll(); - break; - } - } - } catch (InterruptedException ie) { - interrupted = true; + completed = exec(); + } catch (Throwable rex) { + return setExceptionalCompletion(rex); } + if (completed) + return setCompletion(NORMAL); } - if (interrupted) - Thread.currentThread().interrupt(); + return w.joinTask(this); } + else + return externalAwaitDone(); } /** - * Blocks a worker until this task is done or timeout elapses + * Primary mechanics for invoke, quietlyInvoke. + * @return status upon completion */ - private void timedAwaitDone(ForkJoinWorkerThread w, long nanos) { - if (status >= 0) { - long startTime = System.nanoTime(); - ForkJoinPool pool = w.pool; - pool.preJoin(this); - while (status >= 0) { - long nt = nanos - (System.nanoTime() - startTime); - if (nt > 0) { - long ms = nt / 1000000; - int ns = (int) (nt % 1000000); - try { - synchronized(this) { if (status >= 0) wait(ms, ns); } - } catch (InterruptedException ie) { - cancelIfTerminating(); - } - } - else { - int s; // adjust running count on timeout - while ((s = status) >= 0 && - (s & INTERNAL_SIGNAL_MASK) != 0) { - if (UNSAFE.compareAndSwapInt(this, statusOffset, - s, s - 1)) { - pool.updateRunningCount(1); - break; - } - } + 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(); + } + + // Exception table support + + /** + * Table of exceptions thrown by tasks, to enable reporting by + * callers. Because exceptions are rare, we don't directly keep + * them with task objects, but instead use a weak ref table. Note + * that cancellation exceptions don't appear in the table, but are + * instead recorded as status values. + * + * Note: These statics are initialized below in static block. + */ + private static final ExceptionNode[] exceptionTable; + private static final ReentrantLock exceptionTableLock; + private static final ReferenceQueue exceptionTableRefQueue; + + /** + * Fixed capacity for exceptionTable. + */ + private static final int EXCEPTION_MAP_CAPACITY = 32; + + /** + * Key-value nodes for exception table. The chained hash table + * uses identity comparisons, full locking, and weak references + * for keys. The table has a fixed capacity because it only + * maintains task exceptions long enough for joiners to access + * them, so should never become very large for sustained + * periods. However, since we do not know when the last joiner + * completes, we must use weak references and expunge them. We do + * so on each operation (hence full locking). Also, some thread in + * any ForkJoinPool will call helpExpungeStaleExceptions when its + * pool becomes isQuiescent. + */ + static final class ExceptionNode extends WeakReference>{ + final Throwable ex; + ExceptionNode next; + final long thrower; // use id not ref to avoid weak cycles + ExceptionNode(ForkJoinTask task, Throwable ex, ExceptionNode next) { + super(task, exceptionTableRefQueue); + this.ex = ex; + this.next = next; + this.thrower = Thread.currentThread().getId(); + } + } + + /** + * Records exception and sets exceptional completion. + * + * @return status on exit + */ + private int setExceptionalCompletion(Throwable ex) { + int h = System.identityHashCode(this); + final ReentrantLock lock = exceptionTableLock; + lock.lock(); + try { + expungeStaleExceptions(); + ExceptionNode[] t = exceptionTable; + int i = h & (t.length - 1); + for (ExceptionNode e = t[i]; ; e = e.next) { + if (e == null) { + t[i] = new ExceptionNode(this, ex, t[i]); break; } + if (e.get() == this) // already present + break; } + } finally { + lock.unlock(); } + return setCompletion(EXCEPTIONAL); } /** - * Blocks a non-ForkJoin thread until this task is done or timeout elapses + * Removes exception node and clears status */ - private void externalTimedAwaitDone(long nanos) { - if (requestExternalSignal() >= 0) { - long startTime = System.nanoTime(); - boolean interrupted = false; - while (status >= 0) { - long nt = nanos - (System.nanoTime() - startTime); - if (nt <= 0) + private void clearExceptionalCompletion() { + int h = System.identityHashCode(this); + final ReentrantLock lock = exceptionTableLock; + lock.lock(); + try { + ExceptionNode[] t = exceptionTable; + int i = h & (t.length - 1); + ExceptionNode e = t[i]; + ExceptionNode pred = null; + while (e != null) { + ExceptionNode next = e.next; + if (e.get() == this) { + if (pred == null) + t[i] = next; + else + pred.next = next; break; - long ms = nt / 1000000; - int ns = (int) (nt % 1000000); - try { - synchronized(this) { if (status >= 0) wait(ms, ns); } - } catch (InterruptedException ie) { - interrupted = true; } + pred = e; + e = next; } - if (interrupted) - Thread.currentThread().interrupt(); + expungeStaleExceptions(); + status = 0; + } finally { + lock.unlock(); } } - // reporting results + /** + * Returns a rethrowable exception for the given task, if + * available. To provide accurate stack traces, if the exception + * was not thrown by the current thread, we try to create a new + * exception of the same type as the one thrown, but with the + * recorded exception as its cause. If there is no such + * constructor, we instead try to use a no-arg constructor, + * followed by initCause, to the same effect. If none of these + * apply, or any fail due to other exceptions, we return the + * recorded exception, which is still correct, although it may + * contain a misleading stack trace. + * + * @return the exception, or null if none + */ + private Throwable getThrowableException() { + if (status != EXCEPTIONAL) + return null; + int h = System.identityHashCode(this); + ExceptionNode e; + final ReentrantLock lock = exceptionTableLock; + lock.lock(); + try { + expungeStaleExceptions(); + ExceptionNode[] t = exceptionTable; + e = t[h & (t.length - 1)]; + while (e != null && e.get() != this) + e = e.next; + } finally { + lock.unlock(); + } + Throwable ex; + if (e == null || (ex = e.ex) == null) + return null; + if (e.thrower != Thread.currentThread().getId()) { + Class ec = ex.getClass(); + try { + 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; + } /** - * Returns result or throws the exception associated with status. - * Uses Unsafe as a workaround for javac not allowing rethrow of - * unchecked exceptions. + * Poll stale refs and remove them. Call only while holding lock. */ - private V reportResult() { - if ((status & COMPLETION_MASK) < NORMAL) { - Throwable ex = getException(); - if (ex != null) - UNSAFE.throwException(ex); + 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; + } + } } - return getRawResult(); } /** - * Returns result or throws exception using j.u.c.Future conventions. - * Only call when {@code isDone} known to be true or thread known - * to be interrupted. + * If lock is available, poll stale refs and remove them. + * Called from ForkJoinPool when pools become quiescent. */ - private V reportFutureResult() - throws InterruptedException, ExecutionException { - if (Thread.interrupted()) - throw new InterruptedException(); - int s = status & COMPLETION_MASK; - if (s < NORMAL) { - Throwable ex; - if (s == CANCELLED) - throw new CancellationException(); - if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) - throw new ExecutionException(ex); + static final void helpExpungeStaleExceptions() { + final ReentrantLock lock = exceptionTableLock; + if (lock.tryLock()) { + try { + expungeStaleExceptions(); + } finally { + lock.unlock(); + } } - return getRawResult(); } /** - * Returns result or throws exception using j.u.c.Future conventions - * with timeouts. + * Report the result of invoke or join; called only upon + * non-normal return of internal versions. */ - private V reportTimedFutureResult() - throws InterruptedException, ExecutionException, TimeoutException { - if (Thread.interrupted()) - throw new InterruptedException(); - Throwable ex; - int s = status & COMPLETION_MASK; - if (s == NORMAL) - return getRawResult(); - else if (s == CANCELLED) + private V reportResult() { + int s; Throwable ex; + if ((s = status) == CANCELLED) throw new CancellationException(); - else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) - throw new ExecutionException(ex); - else - throw new TimeoutException(); + if (s == EXCEPTIONAL && (ex = getThrowableException()) != null) + UNSAFE.throwException(ex); + return getRawResult(); } // public methods @@ -459,7 +582,7 @@ public abstract class ForkJoinTask im * #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}. @@ -473,42 +596,53 @@ public abstract class ForkJoinTask im } /** - * Returns the result of the computation when it {@link #isDone is done}. - * 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() { - quietlyJoin(); - return reportResult(); + if (doJoin() != NORMAL) + return reportResult(); + else + return getRawResult(); } /** * Commences performing this task, awaits its completion if - * necessary, and return its result, or throws an (unchecked) - * exception if the underlying computation did so. + * necessary, and returns its result, or throws an (unchecked) + * {@code RuntimeException} or {@code Error} if the underlying + * computation did so. * * @return the computed result */ public final V invoke() { - if (!tryExec()) - quietlyJoin(); - return reportResult(); + if (doInvoke() != NORMAL) + return reportResult(); + else + return getRawResult(); } /** * Forks the given tasks, returning when {@code isDone} holds for * each task or an (unchecked) exception is encountered, in which - * case the exception is rethrown. If either task encounters an - * exception, the other one may be, but is not guaranteed to be, - * cancelled. If both tasks throw an exception, then this method - * throws one of them. The individual status of each task may be - * checked using {@link #getException()} and related methods. + * case the exception is rethrown. If more than one task + * encounters an exception, then this method throws any one of + * these exceptions. If any task encounters an exception, the + * other may be cancelled. However, the execution status of + * individual tasks is not guaranteed upon exceptional return. The + * status of each task may be obtained using {@link + * #getException()} and related methods to check if they have been + * cancelled, completed normally or exceptionally, or left + * unprocessed. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -526,15 +660,17 @@ public abstract class ForkJoinTask im /** * Forks the given tasks, returning when {@code isDone} holds for * each task or an (unchecked) exception is encountered, in which - * case the exception is rethrown. If any task encounters an - * exception, others may be, but are not guaranteed to be, - * cancelled. If more than one task encounters an exception, then - * this method throws any one of these exceptions. The individual - * status of each task may be checked using {@link #getException()} - * and related methods. + * case the exception is rethrown. If more than one task + * encounters an exception, then this method throws any one of + * these exceptions. If any task encounters an exception, others + * may be cancelled. However, the execution status of individual + * tasks is not guaranteed upon exceptional return. The status of + * each task may be obtained using {@link #getException()} and + * related methods to check if they have been cancelled, completed + * normally or exceptionally, or left unprocessed. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -553,22 +689,16 @@ 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) @@ -578,17 +708,18 @@ public abstract class ForkJoinTask im /** * Forks all tasks in the specified collection, returning when * {@code isDone} holds for each task or an (unchecked) exception - * is encountered. If any task encounters an exception, others - * may be, but are not guaranteed to be, cancelled. If more than - * one task encounters an exception, then this method throws any - * one of these exceptions. The individual status of each task - * may be checked using {@link #getException()} and related - * methods. The behavior of this operation is undefined if the - * specified collection is modified while the operation is in - * progress. + * is encountered, in which case the exception is rethrown. If + * more than one task encounters an exception, then this method + * throws any one of these exceptions. If any task encounters an + * exception, others may be cancelled. However, the execution + * status of individual tasks is not guaranteed upon exceptional + * return. The status of each task may be obtained using {@link + * #getException()} and related methods to check if they have been + * cancelled, completed normally or exceptionally, or left + * unprocessed. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -615,22 +746,16 @@ 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) @@ -640,36 +765,40 @@ public abstract class ForkJoinTask im /** * Attempts to cancel execution of this task. This attempt will - * fail if the task has already completed, has already been - * cancelled, or could not be cancelled for some other reason. If - * successful, and this task has not started when cancel is - * called, execution of this task is suppressed, {@link - * #isCancelled} will report true, and {@link #join} will result - * in a {@code CancellationException} being thrown. + * fail if the task has already completed or could not be + * cancelled for some other reason. If successful, and this task + * has not started when {@code cancel} is called, execution of + * this task is suppressed. After this method returns + * successfully, unless there is an intervening call to {@link + * #reinitialize}, subsequent calls to {@link #isCancelled}, + * {@link #isDone}, and {@code cancel} will return {@code true} + * and calls to {@link #join} and related methods will result in + * {@code CancellationException}. * *

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

This method is designed to be invoked by other * tasks. To terminate the current task, you can just return or * throw an unchecked exception from its computation method, or * invoke {@link #completeExceptionally}. * - * @param mayInterruptIfRunning this value is ignored in the - * default implementation because tasks are not - * cancelled via interruption + * @param mayInterruptIfRunning this value has no effect in the + * default implementation because interrupts are not used to + * control cancellation. * * @return {@code true} if this task is now cancelled */ public boolean cancel(boolean mayInterruptIfRunning) { - setCompletion(CANCELLED); - return (status & COMPLETION_MASK) == CANCELLED; + return setCompletion(CANCELLED) == CANCELLED; } /** - * Cancels, ignoring any exceptions it throws. Used during worker - * and pool shutdown. + * 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 { @@ -678,26 +807,12 @@ public abstract class ForkJoinTask im } } - /** - * Cancels ignoring exceptions if worker is terminating - */ - private 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 & COMPLETION_MASK) == CANCELLED; + return status == CANCELLED; } /** @@ -706,7 +821,7 @@ public abstract class ForkJoinTask im * @return {@code true} if this task threw an exception or was cancelled */ public final boolean isCompletedAbnormally() { - return (status & COMPLETION_MASK) < NORMAL; + return status < NORMAL; } /** @@ -717,7 +832,7 @@ public abstract class ForkJoinTask im * exception and was not cancelled */ public final boolean isCompletedNormally() { - return (status & COMPLETION_MASK) == NORMAL; + return status == NORMAL; } /** @@ -728,10 +843,10 @@ public abstract class ForkJoinTask im * @return the exception, or {@code null} if none */ public final Throwable getException() { - int s = status & COMPLETION_MASK; + int s = status; return ((s >= NORMAL) ? null : (s == CANCELLED) ? new CancellationException() : - exceptionMap.get(this)); + getThrowableException()); } /** @@ -749,20 +864,21 @@ public abstract class ForkJoinTask im * 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 */ @@ -770,124 +886,104 @@ public abstract class ForkJoinTask im try { setRawResult(value); } catch (Throwable rex) { - setDoneExceptionally(rex); + setExceptionalCompletion(rex); return; } setCompletion(NORMAL); } - public final V get() throws InterruptedException, ExecutionException { - quietlyJoin(); - return reportFutureResult(); - } - - 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 w = (ForkJoinWorkerThread) t; - if (!w.unpushTask(this) || !tryExec()) - timedAwaitDone(w, nanos); - } - else - externalTimedAwaitDone(nanos); - return reportTimedFutureResult(); - } - /** - * Possibly executes other tasks until this task {@link #isDone is - * done}, 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() { - quietlyHelpJoin(); - return reportResult(); + 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 {@link #isDone is - * done}. 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() { - ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread(); - if (!w.unpushTask(this) || !tryExec()) { - for (;;) { - ForkJoinTask t; - if (status < 0) - return; - else if ((t = w.scanWhileJoining(this)) != null) - t.tryExec(); - else if (status < 0) - return; - else if (w.pool.preBlockHelpingJoin(this)) { - while (status >= 0) { // variant of awaitDone - try { - synchronized(this) { - if (status >= 0) - wait(); - else { - notifyAll(); - break; - } - } - } catch (InterruptedException ie) { - cancelIfTerminating(); - } + 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); } - return; } + 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() { - Thread t = Thread.currentThread(); - if (t instanceof ForkJoinWorkerThread) { - ForkJoinWorkerThread w = (ForkJoinWorkerThread) t; - if (!w.unpushTask(this) || !tryExec()) - awaitDone(w); - } - else - externalAwaitDone(); + 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 (!tryExec()) - quietlyJoin(); + doInvoke(); } /** @@ -898,7 +994,7 @@ public abstract class ForkJoinTask im * processed. * *

This method may be invoked only from within {@code - * ForkJoinTask} computations (as may be determined using method + * ForkJoinPool} computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including {@code * ClassCastException}. @@ -917,11 +1013,18 @@ public abstract class ForkJoinTask im * under any other usage conditions are not guaranteed. * This method may be useful when executing * pre-constructed trees of subtasks in loops. + * + *

Upon completion of this method, {@code isDone()} reports + * {@code false}, and {@code getException()} reports {@code + * null}. However, the value returned by {@code getRawResult} is + * unaffected. To clear this value, you can invoke {@code + * setRawResult(null)}. */ public void reinitialize() { - if ((status & COMPLETION_MASK) == EXCEPTIONAL) - exceptionMap.remove(this); - status = 0; + if (status == EXCEPTIONAL) + clearExceptionalCompletion(); + else + status = 0; } /** @@ -938,11 +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; @@ -957,7 +1061,7 @@ 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}. @@ -976,7 +1080,7 @@ 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}. @@ -999,7 +1103,7 @@ 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}. @@ -1057,7 +1161,7 @@ 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}. @@ -1076,7 +1180,7 @@ 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}. @@ -1099,7 +1203,7 @@ 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}. @@ -1209,7 +1313,7 @@ public abstract class ForkJoinTask im private static final long serialVersionUID = -7721805057305804111L; /** - * Saves 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 @@ -1222,34 +1326,31 @@ public abstract class ForkJoinTask im } /** - * Reconstitutes 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); } }