--- jsr166/src/jsr166y/ForkJoinTask.java 2009/01/07 19:12:36 1.3 +++ jsr166/src/jsr166y/ForkJoinTask.java 2012/04/09 13:11:44 1.89 @@ -1,470 +1,611 @@ /* * 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.io.Serializable; -import java.util.*; -import java.util.concurrent.*; -import java.util.concurrent.atomic.*; -import sun.misc.Unsafe; -import java.lang.reflect.*; +import java.util.Collection; +import java.util.List; +import java.util.RandomAccess; +import java.lang.ref.WeakReference; +import java.lang.ref.ReferenceQueue; +import java.util.concurrent.Callable; +import java.util.concurrent.CancellationException; +import java.util.concurrent.ExecutionException; +import java.util.concurrent.Future; +import java.util.concurrent.RejectedExecutionException; +import java.util.concurrent.RunnableFuture; +import java.util.concurrent.TimeUnit; +import java.util.concurrent.TimeoutException; +import java.util.concurrent.locks.ReentrantLock; +import java.lang.reflect.Constructor; /** - * Abstract base class for tasks that run within a {@link - * ForkJoinPool}. 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 fork - * and join, or derivatives such as - * 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 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 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 "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 {@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 main use as computational tasks calculating pure + * functions or operating on purely isolated objects. The primary + * coordination mechanisms are {@link #fork}, that arranges + * asynchronous execution, and {@link #join}, that doesn't proceed + * until the task's result has been computed. Computations should + * ideally avoid {@code synchronized} methods or blocks, and should + * minimize other blocking synchronization apart from joining other + * tasks or using synchronizers such as Phasers that are advertised to + * cooperate with fork/join scheduling. Subdividable tasks should also + * not perform blocking IO, and should ideally access variables that + * are completely independent of those accessed by other running + * tasks. These guidelines are loosely enforced by not permitting + * checked exceptions such as {@code IOExceptions} to be + * thrown. However, computations may still encounter unchecked + * exceptions, that are rethrown to callers attempting to join + * them. These exceptions may additionally include {@link + * RejectedExecutionException} stemming from internal resource + * exhaustion, such as failure to allocate internal task + * queues. Rethrown exceptions behave in the same way as regular + * exceptions, but, when possible, contain stack traces (as displayed + * for example using {@code ex.printStackTrace()}) of both the thread + * that initiated the computation as well as the thread actually + * encountering the exception; minimally only the latter. + * + *

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

The primary method for awaiting completion and extracting * results of a task is {@link #join}, but there are several variants: * The {@link Future#get} methods support interruptible and/or timed - * waits for completion and report results using 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 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 + * waits for completion and report results using {@code Future} + * 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 invokeAll (available in multiple versions) + * 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. + *

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

The execution status of tasks may be queried at several levels + * of detail: {@link #isDone} is true if a task completed in any way + * (including the case where a task was cancelled without executing); + * {@link #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 - * ForkJoinTask subclass declares fields comprising its parameters, - * established in a constructor, and then defines a compute - * method that somehow uses the control methods supplied by this base - * class. While these methods have public access (to allow - * instances of different task subclasses to call each others - * methods), some of them may only be called from within other - * ForkJoinTasks. Attempts to invoke them in other contexts result in - * exceptions or errors including ClassCastException. - * - *

Most base support methods are 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 protected methods - * exec, setRawResult, and - * getRawResult, while also introducing an abstract - * computational method that can be implemented in its subclasses, - * possibly relying on other protected methods provided - * by this class. + * particular style of fork/join processing, typically {@link + * RecursiveAction} for most computations that do not return results, + * {@link RecursiveTask} for those that do, and {@link + * CountedCompleter} for those in which completed actions trigger + * other actions. 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 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 {@code + * ClassCastException}. + * + *

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

Most base support methods are {@code final}, to prevent + * overriding of implementations that are intrinsically tied to the + * 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, othewise 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 - * parellelism cannot improve throughput. If too small, then memory - * and internal task maintenance overhead may overwhelm processing. - * - *

ForkJoinTasks are 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. + * 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 + * 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 directy 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 us a weak ref table. Note - * that cancellation exceptions don't appear in the table, but are - * instead recorded as status values. - * Todo: Use ConcurrentReferenceHashMap - */ - static final Map, Throwable> exceptionMap = - Collections.synchronizedMap - (new WeakHashMap, Throwable>()); - - // within-package utilities - - /** - * Get 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 + /* + * 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 (anded with + * DONE_MASK) 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, mainly by arranging that every synchronized + * block performs a wait, notifyAll or both. + * + * These control bits occupy only (some of) the upper half (16 + * bits) of status field. The lower bits are used for user-defined + * tags. + */ + + /** The run status of this task */ + volatile int status; // accessed directly by pool and workers + static final int DONE_MASK = 0xf0000000; // mask out non-completion bits + static final int NORMAL = 0xf0000000; // must be negative + static final int CANCELLED = 0xc0000000; // must be < NORMAL + static final int EXCEPTIONAL = 0x80000000; // must be < CANCELLED + static final int SIGNAL = 0x00010000; // must be >= 1 << 16 + static final int SMASK = 0x0000ffff; // short bits for tags /** - * Mark completion and wake up threads waiting to join this task. + * Marks completion and wakes up threads waiting to join this + * task. + * * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL + * @return completion status on exit */ - final void setCompletion(int completion) { - ForkJoinPool pool = getPool(); - if (pool != null) { - int s; // Clear signal bits while setting completion status - do;while ((s = status) >= 0 && !casStatus(s, completion)); - - if ((s & SIGNAL_MASK) != 0) { - if ((s &= INTERNAL_SIGNAL_MASK) != 0) - pool.updateRunningCount(s); - synchronized(this) { notifyAll(); } + private int setCompletion(int completion) { + for (int s;;) { + if ((s = status) < 0) + return s; + if (U.compareAndSwapInt(this, STATUS, s, s | completion)) { + if ((s >>> 16) != 0) + synchronized (this) { notifyAll(); } + return completion; } } - else - externallySetCompletion(completion); } /** - * Version of setCompletion for non-FJ threads. Leaves signal - * bits for unblocked threads to adjust, and always notifies. - */ - private void externallySetCompletion(int completion) { - int s; - do;while ((s = status) >= 0 && - !casStatus(s, (s & SIGNAL_MASK) | completion)); - synchronized(this) { notifyAll(); } - } - - /** - * Sets status to indicate normal completion - */ - final void setNormalCompletion() { - // Try typical fast case -- single CAS, no signal, not already done. - // Manually expand casStatus to improve chances of inlining it - if (!_unsafe.compareAndSwapInt(this, statusOffset, 0, NORMAL)) - setCompletion(NORMAL); - } - - // internal waiting and notification - - /** - * Performs the actual monitor wait for awaitDone + * Primary execution method for stolen tasks. Unless done, calls + * exec and records status if completed, but doesn't wait for + * completion otherwise. + * + * @return status on exit from this method */ - 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(); + final int doExec() { + int s; boolean completed; + if ((s = status) >= 0) { + try { + completed = exec(); + } catch (Throwable rex) { + return setExceptionalCompletion(rex); + } + if (completed) + s = setCompletion(NORMAL); } + return s; } /** - * Performs the actual monitor wait for awaitDone + * Tries to set SIGNAL status unless already completed. Used by + * ForkJoinPool. Other variants are directly incorporated into + * externalAwaitDone etc. + * + * @return true if successful */ - private void doAwaitDone(long startTime, long nanos) { - synchronized(this) { - try { - while (status >= 0) { - long nt = nanos - System.nanoTime() - startTime; - if (nt <= 0) - break; - wait(nt / 1000000, (int)(nt % 1000000)); - } - } catch (InterruptedException ie) { - onInterruptedWait(); - } - } + final boolean trySetSignal() { + int s = status; + return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL); } - // 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() { + boolean interrupted = false; 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 (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { + synchronized (this) { + if (status >= 0) { + try { + wait(); + } catch (InterruptedException ie) { + interrupted = true; + } + } + else + notifyAll(); + } } } + if (interrupted) + Thread.currentThread().interrupt(); return s; } /** - * Timed version of awaitDone - * @return status upon exit + * Blocks a non-worker-thread until completion or interruption. */ - private int awaitDone(ForkJoinWorkerThread w, long nanos) { - ForkJoinPool pool = w == null? null : w.pool; + private int externalInterruptibleAwaitDone() throws InterruptedException { int s; + if (Thread.interrupted()) + throw new InterruptedException(); 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 (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { + synchronized (this) { + if (status >= 0) + wait(); + else + notifyAll(); } - if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0) - adjustPoolCountsOnUnblock(pool); - break; } } return s; } /** - * Notify pool that thread is unblocked. Called by signalled - * threads when woken by non-FJ threads (which is atypical). - */ - private void adjustPoolCountsOnUnblock(ForkJoinPool pool) { - int s; - do;while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK)); - if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0) - pool.updateRunningCount(s); - } - - /** - * Notify pool to adjust counts on cancelled or timed out wait + * Implementation for join, get, quietlyJoin. Directly handles + * only cases of already-completed, external wait, and + * unfork+exec. Others are relayed to ForkJoinPool.awaitJoin. + * + * @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() { + int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w; + if ((s = status) >= 0) { + if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) { + if (!(w = (wt = (ForkJoinWorkerThread)t).workQueue). + tryUnpush(this) || (s = doExec()) >= 0) + s = wt.pool.awaitJoin(w, this); } + else + s = externalAwaitDone(); } + return s; } /** - * Handle interruptions during waits. + * Implementation 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; Thread t; ForkJoinWorkerThread wt; + if ((s = doExec()) >= 0) { + if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) + s = (wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue, + this); + else + s = externalAwaitDone(); + } + return s; } - // 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; - * @throws the exception + * Table of exceptions thrown by tasks, to enable reporting by + * callers. Because exceptions are rare, we don't directly keep + * them with task objects, but instead use a weak ref table. Note + * that cancellation exceptions don't appear in the table, but are + * instead recorded as status values. + * + * Note: These statics are initialized below in static block. */ - private void 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; + + /** + * 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(); } } /** - * Returns result or throws exception using j.u.c.Future conventions - * Only call when isDone known to be true. + * Records exception and sets exceptional completion. + * + * @return status on exit */ - private V reportFutureResult() - throws ExecutionException, InterruptedException { - int s = status & COMPLETION_MASK; - if (s < NORMAL) { - Throwable ex; - if (s == CANCELLED) - throw new CancellationException(); - if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) - throw new ExecutionException(ex); - if (Thread.interrupted()) - throw new InterruptedException(); + private int setExceptionalCompletion(Throwable ex) { + int s; + if ((s = status) >= 0) { + 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(); + } + s = setCompletion(EXCEPTIONAL); } - return getRawResult(); + ForkJoinTask p = internalGetCompleter(); // propagate + if (p != null && p.status >= 0) + p.setExceptionalCompletion(ex); + return s; } /** - * Returns result or throws exception using j.u.c.Future conventions - * with timeouts + * Exception propagation support for tasks with completers. */ - 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(); + ForkJoinTask internalGetCompleter() { + return null; } - // internal execution methods + /** + * 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. + */ + static final void cancelIgnoringExceptions(ForkJoinTask t) { + if (t != null && t.status >= 0) { + try { + t.cancel(false); + } catch (Throwable ignore) { + } + } + } /** - * Calls exec, recording completion, and rethrowing exception if - * encountered. Caller should normally check status before calling - * @return true if completed normally + * Removes exception node and clears status */ - private boolean tryExec() { - try { // try block must contain only call to exec - if (!exec()) - return false; - } catch (Throwable rex) { - setDoneExceptionally(rex); - rethrowException(rex); - return false; // not reached + private void clearExceptionalCompletion() { + int h = System.identityHashCode(this); + final ReentrantLock lock = exceptionTableLock; + lock.lock(); + try { + ExceptionNode[] t = exceptionTable; + int i = h & (t.length - 1); + ExceptionNode e = t[i]; + ExceptionNode pred = null; + while (e != null) { + ExceptionNode next = e.next; + if (e.get() == this) { + if (pred == null) + t[i] = next; + else + pred.next = next; + break; + } + pred = e; + e = next; + } + expungeStaleExceptions(); + status = 0; + } finally { + lock.unlock(); } - setNormalCompletion(); - return true; } /** - * Main execution method used by worker threads. Invokes - * base computation unless already complete + * 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 */ - final void quietlyExec() { - if (status >= 0) { + private Throwable getThrowableException() { + if ((status & DONE_MASK) != 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 (false && e.thrower != Thread.currentThread().getId()) { + Class ec = ex.getClass(); try { - if (!exec()) - return; - } catch(Throwable rex) { - setDoneExceptionally(rex); - return; + Constructor noArgCtor = null; + Constructor[] cs = ec.getConstructors();// public ctors only + for (int i = 0; i < cs.length; ++i) { + Constructor c = cs[i]; + Class[] ps = c.getParameterTypes(); + if (ps.length == 0) + noArgCtor = c; + else if (ps.length == 1 && ps[0] == Throwable.class) + return (Throwable)(c.newInstance(ex)); + } + if (noArgCtor != null) { + Throwable wx = (Throwable)(noArgCtor.newInstance()); + wx.initCause(ex); + return wx; + } + } catch (Exception ignore) { } - setNormalCompletion(); } + return ex; } /** - * Calls exec, recording but not rethrowing exception - * Caller should normally check status before calling - * @return true if completed normally + * Poll stale refs and remove them. Call only while holding lock. */ - private boolean tryQuietlyInvoke() { - try { - if (!exec()) - return false; - } catch (Throwable rex) { - setDoneExceptionally(rex); - return false; + private static void expungeStaleExceptions() { + for (Object x; (x = exceptionTableRefQueue.poll()) != null;) { + if (x instanceof ExceptionNode) { + ForkJoinTask key = ((ExceptionNode)x).get(); + ExceptionNode[] t = exceptionTable; + int i = System.identityHashCode(key) & (t.length - 1); + ExceptionNode e = t[i]; + ExceptionNode pred = null; + while (e != null) { + ExceptionNode next = e.next; + if (e == x) { + if (pred == null) + t[i] = next; + else + pred.next = next; + break; + } + pred = e; + e = next; + } + } } - setNormalCompletion(); - return true; } /** - * Cancel, ignoring any exceptions it throws + * If lock is available, poll stale refs and remove them. + * Called from ForkJoinPool when pools become quiescent. */ - final void cancelIgnoringExceptions() { - try { - cancel(false); - } catch(Throwable ignore) { + static final void helpExpungeStaleExceptions() { + final ReentrantLock lock = exceptionTableLock; + if (lock.tryLock()) { + try { + expungeStaleExceptions(); + } finally { + lock.unlock(); + } } } /** - * Main implementation of helpJoin + * Throws exception, if any, associated with the given status. */ - private int busyJoin(ForkJoinWorkerThread w) { - int s; - ForkJoinTask t; - while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null) - t.quietlyExec(); - return (s >= 0)? awaitDone(w, false) : s; // block if no work + private void reportException(int s) { + Throwable ex = ((s == CANCELLED) ? new CancellationException() : + (s == EXCEPTIONAL) ? getThrowableException() : + null); + if (ex != null) + U.throwException(ex); } // public methods @@ -472,70 +613,111 @@ 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. Attempts to invoke in other contexts result in - * exceptions or errors 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 */ - public final void fork() { - ((ForkJoinWorkerThread)(Thread.currentThread())).pushTask(this); + public final ForkJoinTask fork() { + ((ForkJoinWorkerThread)Thread.currentThread()).workQueue.push(this); + return this; } /** - * Returns the result of the computation when it is ready. - * This method differs from 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)); + int s; + if ((s = doJoin() & DONE_MASK) != NORMAL) + reportException(s); return getRawResult(); } /** * Commences performing this task, awaits its completion if - * necessary, and return its result. - * @throws Throwable (a RuntimeException, Error, or unchecked - * exception) if the underlying computation did so. + * necessary, and returns its result, or throws an (unchecked) + * {@code RuntimeException} or {@code Error} if the underlying + * computation did so. + * * @return the computed result */ public final V invoke() { - if (status >= 0 && tryExec()) - return getRawResult(); - else - return join(); + int s; + if ((s = doInvoke() & DONE_MASK) != NORMAL) + reportException(s); + return getRawResult(); } /** - * Forks both tasks, returning when isDone holds for - * both of them or an exception is encountered. This method may be - * invoked only from within ForkJoinTask computations. Attempts to - * invoke in other contexts result in exceptions or errors - * 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) { + int s1, s2; t2.fork(); - t1.invoke(); - t2.join(); + if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL) + t1.reportException(s1); + if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL) + t2.reportException(s2); } /** - * Forks the given tasks, returning when 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. Attempts to invoke in other contexts - * result in exceptions or errors including 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. + * 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 tasks + * @throws NullPointerException if any task is null */ public static void invokeAll(ForkJoinTask... tasks) { Throwable ex = null; @@ -548,46 +730,53 @@ public abstract class ForkJoinTask im } else if (i != 0) t.fork(); - else { - t.quietlyInvoke(); - if (ex == null) - ex = t.getException(); - } + else if (t.doInvoke() < NORMAL && ex == null) + ex = t.getException(); } for (int i = 1; i <= last; ++i) { ForkJoinTask t = tasks[i]; if (t != null) { if (ex != null) t.cancel(false); - else { - t.quietlyJoin(); - if (ex == null) - ex = t.getException(); - } + else if (t.doJoin() < NORMAL) + ex = t.getException(); } } if (ex != null) - rethrowException(ex); + U.throwException(ex); } /** - * Forks all tasks in the collection, returning when - * 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. Attempts to invoke in other contexts resul!t in - * exceptions or errors 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 - * @throws NullPointerException if tasks or any element are null. - * @throws RuntimeException or Error if any task did so. + * @return the tasks argument, to simplify usage + * @throws NullPointerException if tasks or any element are null */ - public static void invokeAll(Collection> tasks) { - if (!(tasks instanceof List)) { - invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()])); - return; + public static > Collection invokeAll(Collection tasks) { + if (!(tasks instanceof RandomAccess) || !(tasks instanceof List)) { + invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()])); + return tasks; } + @SuppressWarnings("unchecked") List> ts = - (List>)tasks; + (List>) tasks; Throwable ex = null; int last = ts.size() - 1; for (int i = last; i >= 0; --i) { @@ -598,253 +787,338 @@ public abstract class ForkJoinTask im } else if (i != 0) t.fork(); - else { - t.quietlyInvoke(); - if (ex == null) - ex = t.getException(); - } + else if (t.doInvoke() < NORMAL && ex == null) + ex = t.getException(); } for (int i = 1; i <= last; ++i) { ForkJoinTask t = ts.get(i); if (t != null) { if (ex != null) t.cancel(false); - else { - t.quietlyJoin(); - if (ex == null) - ex = t.getException(); - } + else if (t.doJoin() < NORMAL) + ex = t.getException(); } } if (ex != null) - rethrowException(ex); + U.throwException(ex); + return tasks; } /** - * Returns true if the computation performed by this task has - * completed (or has been cancelled). - * @return true if this computation has completed + * 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 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 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) { + return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED; + } + public final boolean isDone() { return status < 0; } - /** - * Returns true if this task was cancelled. - * @return true if this task was cancelled - */ public final boolean isCancelled() { - return (status & COMPLETION_MASK) == CANCELLED; + return (status & DONE_MASK) == CANCELLED; } /** - * Asserts that the results of this task's computation will not be - * used. If a cancellation occurs before atempting to execute this - * task, then execution will be suppressed, isCancelled - * will report true, and join will result in a - * CancellationException being thrown. Otherwise, when - * cancellation races with completion, there are no guarantees - * about whether isCancelled will report true, whether - * join will return normally or via an exception, or - * whether these behaviors will remain consistent upon repeated - * invocation. - * - *

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. + * Returns {@code true} if this task threw an exception or was cancelled. * - *

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 completeExceptionally. - * - * @param mayInterruptIfRunning this value is ignored in the - * default implementation because tasks are not in general - * cancelled via interruption. - * - * @return true if this task is now cancelled + * @return {@code true} if this task threw an exception or was cancelled */ - public boolean cancel(boolean mayInterruptIfRunning) { - setCompletion(CANCELLED); - return (status & COMPLETION_MASK) == CANCELLED; + public final boolean isCompletedAbnormally() { + return status < NORMAL; } /** - * Returns true if this task threw an exception or was cancelled - * @return true if this task threw an exception or was cancelled + * 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 isCompletedAbnormally() { - return (status & COMPLETION_MASK) < NORMAL; + public final boolean isCompletedNormally() { + return (status & DONE_MASK) == 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. - * @return the exception, or null if none + * {@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 & DONE_MASK; + return ((s >= NORMAL) ? null : + (s == CANCELLED) ? new CancellationException() : + getThrowableException()); } /** * Completes this task abnormally, and if not already aborted or * cancelled, causes it to throw the given exception upon - * join and related operations. This method may be used + * {@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 - * overridable, but overridden versions must invoke super + * 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 null result upon 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 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. + * @param value the result value for this task */ public void complete(V value) { try { setRawResult(value); - } catch(Throwable rex) { - setDoneExceptionally(rex); + } catch (Throwable rex) { + setExceptionalCompletion(rex); return; } - setNormalCompletion(); + setCompletion(NORMAL); } - 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(); + /** + * Completes this task normally without setting a value. The most + * recent value established by {@link #setRawResult} (or {@code + * null} by default) will be returned as the result of subsequent + * invocations of {@code join} and related operations. + * + * @since 1.8 + */ + public final void quietlyComplete() { + 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 join, but is only applicable when - * there are no potemtial 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. Attempts to invoke in other contexts - * resul!t in exceptions or errors 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(); + Throwable ex; + if ((s &= DONE_MASK) == 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. Attempts to invoke in other contexts resul!t in - * exceptions or errors 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 { + if (Thread.interrupted()) + throw new InterruptedException(); + // Messy in part because we measure in nanosecs, but wait in millisecs + int s; long ns, ms; + if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) { + long deadline = System.nanoTime() + ns; + ForkJoinPool p = null; + ForkJoinPool.WorkQueue w = null; + Thread t = Thread.currentThread(); + if (t instanceof ForkJoinWorkerThread) { + ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t; + p = wt.pool; + w = wt.workQueue; + s = p.helpJoinOnce(w, this); // no retries on failure + } + boolean canBlock = false; + boolean interrupted = false; + try { + while ((s = status) >= 0) { + if (w != null && w.runState < 0) + cancelIgnoringExceptions(this); + else if (!canBlock) { + if (p == null || p.tryCompensate(this, null)) + canBlock = true; + } + else { + if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L && + U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { + synchronized (this) { + if (status >= 0) { + try { + wait(ms); + } catch (InterruptedException ie) { + if (p == null) + interrupted = true; + } + } + else + notifyAll(); + } + } + if ((s = status) < 0 || interrupted || + (ns = deadline - System.nanoTime()) <= 0L) + break; + } + } + } finally { + if (p != null && canBlock) + p.incrementActiveCount(); + } + if (interrupted) + throw new InterruptedException(); + } + if ((s &= DONE_MASK) != 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())). - helpQuiescePool(); + ForkJoinWorkerThread wt = + (ForkJoinWorkerThread)Thread.currentThread(); + wt.pool.helpQuiescePool(wt.workQueue); } /** * Resets the internal bookkeeping state of this task, allowing a - * subsequent fork. This method allows repeated reuse of + * subsequent {@code fork}. This method allows repeated reuse of * 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 & DONE_MASK) == EXCEPTIONAL) + clearExceptionalCompletion(); + else + status = 0; } /** * Returns the pool hosting the current task execution, or null - * if this task is executing outside of any pool. - * @return the pool, or null if none. + * if this task is executing outside of any ForkJoinPool. + * + * @see #inForkJoinPool + * @return the pool, or {@code null} if none */ public static ForkJoinPool getPool() { Thread t = Thread.currentThread(); - return ((t instanceof ForkJoinWorkerThread)? - ((ForkJoinWorkerThread)t).pool : null); + return (t instanceof ForkJoinWorkerThread) ? + ((ForkJoinWorkerThread) t).pool : null; + } + + /** + * Returns {@code true} if the current thread is a {@link + * ForkJoinWorkerThread} executing as a ForkJoinPool computation. + * + * @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; } /** @@ -853,13 +1127,19 @@ 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. Attempts to invoke in other contexts - * result in exceptions or errors including ClassCastException. - * @return true if unforked + * 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 */ public boolean tryUnfork() { - return ((ForkJoinWorkerThread)(Thread.currentThread())).unpushTask(this); + return ((ForkJoinWorkerThread)Thread.currentThread()) + .workQueue.tryUnpush(this); } /** @@ -867,15 +1147,22 @@ public abstract class ForkJoinTask im * forked by the current worker thread but not yet executed. This * 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() { - return ((ForkJoinWorkerThread)(Thread.currentThread())). - getQueueSize(); + return ((ForkJoinWorkerThread) Thread.currentThread()) + .workQueue.queueSize(); } /** - * Returns a estimate of how many more locally queued tasks are + * Returns an estimate of how many more locally queued tasks are * held by the current worker thread than there are other worker * threads that might steal them. This value may be useful for * heuristic decisions about whether to fork other tasks. In many @@ -883,23 +1170,74 @@ public abstract class ForkJoinTask im * aim to maintain a small constant surplus (for example, 3) of * 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() { - return ((ForkJoinWorkerThread)(Thread.currentThread())) - .getEstimatedSurplusTaskCount(); + /* + * The aim of this method is to return a cheap heuristic guide + * for task partitioning when programmers, frameworks, tools, + * or languages have little or no idea about task granularity. + * In essence by offering this method, we ask users only about + * tradeoffs in overhead vs expected throughput and its + * variance, rather than how finely to partition tasks. + * + * In a steady state strict (tree-structured) computation, + * each thread makes available for stealing enough tasks for + * other threads to remain active. Inductively, if all threads + * play by the same rules, each thread should make available + * only a constant number of tasks. + * + * The minimum useful constant is just 1. But using a value of + * 1 would require immediate replenishment upon each steal to + * maintain enough tasks, which is infeasible. Further, + * partitionings/granularities of offered tasks should + * minimize steal rates, which in general means that threads + * nearer the top of computation tree should generate more + * than those nearer the bottom. In perfect steady state, each + * thread is at approximately the same level of computation + * tree. However, producing extra tasks amortizes the + * uncertainty of progress and diffusion assumptions. + * + * So, users will want to use values larger, but not much + * larger than 1 to both smooth over transient shortages and + * hedge against uneven progress; as traded off against the + * cost of extra task overhead. We leave the user to pick a + * threshold value to compare with the results of this call to + * guide decisions, but recommend values such as 3. + * + * When all threads are active, it is on average OK to + * estimate surplus strictly locally. In steady-state, if one + * thread is maintaining say 2 surplus tasks, then so are + * others. So we can just use estimated queue length. + * However, this strategy alone leads to serious mis-estimates + * in some non-steady-state conditions (ramp-up, ramp-down, + * other stalls). We can detect many of these by further + * considering the number of "idle" threads, that are known to + * have zero queued tasks, so compensate by a factor of + * (#idle/#active) threads. + */ + ForkJoinWorkerThread wt = + (ForkJoinWorkerThread)Thread.currentThread(); + return wt.workQueue.queueSize() - wt.pool.idlePerActive(); } // Extension methods /** - * Returns the result that would be returned by join, - * even if this task completed abnormally, or null if this task is - * not known to have been completed. This method is designed to - * aid debugging, as well as to support extensions. Its use in any - * other context is discouraged. + * Returns the result that would be returned by {@link #join}, even + * if this task completed abnormally, or {@code null} if this task + * is not known to have been completed. This method is designed + * to aid debugging, as well as to support extensions. Its use in + * any other context is discouraged. * - * @return the result, or null if not completed. + * @return the result, or {@code null} if not completed */ public abstract V getRawResult(); @@ -913,59 +1251,240 @@ public abstract class ForkJoinTask im protected abstract void setRawResult(V value); /** - * Immediately performs the base action of this task. This method - * is designed to support extensions, and should not in general be - * called otherwise. The return value controls whether this task - * is considered to be done normally. It may return false in + * Immediately performs the base action of this task and returns + * true if, upon return from this method, this task is guaranteed + * to have completed normally. This method may return false + * otherwise, to indicate that this task is not necessarily + * complete (or is not known to be complete), for example in * asynchronous actions that require explicit invocations of - * complete to become joinable. It may throw exceptions - * to indicate abnormal exit. - * @return true if completed normally - * @throws Error or RuntimeException if encountered during computation + * completion methods. This method may also throw an (unchecked) + * exception to indicate abnormal exit. This method is designed to + * support extensions, and should not in general be called + * otherwise. + * + * @return {@code true} if this task is known to have completed normally */ protected abstract boolean exec(); /** - * Returns, but does not unschedule or execute, the task most - * recently forked by the current thread but not yet executed, if - * one is 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. + * 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. 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 null if none are available + * @return the next task, or {@code null} if none are available */ protected static ForkJoinTask peekNextLocalTask() { - return ((ForkJoinWorkerThread)(Thread.currentThread())).peekTask(); + return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek(); } /** - * Unschedules and returns, without executing, the task most - * recently forked by the current thread but not yet executed. - * This method is designed primarily to support extensions, - * and is unlikely to be useful otherwise. + * 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. * - * @return the next task, or null if none are available + *

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 */ protected static ForkJoinTask pollNextLocalTask() { - return ((ForkJoinWorkerThread)(Thread.currentThread())).popTask(); + return ((ForkJoinWorkerThread) Thread.currentThread()) + .workQueue.nextLocalTask(); } /** - * Unschedules and returns, without executing, the task most - * recently forked by the current thread but not yet executed, if - * one is available, or if not available, a task that was forked - * by some other thread, if available. Availability may be - * transient, so a null result does not necessarily - * imply quiecence of the pool this task is operating in. - * This method is designed primarily to support extensions, - * and is unlikely to be useful otherwise. - * - * @return a task, or null if none are available + * Unschedules and returns, without executing, the next task + * queued by the current thread but not yet executed, if one is + * available, or if not available, a task that was forked by some + * other thread, if available. Availability may be transient, so a + * {@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 {@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 */ protected static ForkJoinTask pollTask() { - return ((ForkJoinWorkerThread)(Thread.currentThread())). - pollLocalOrStolenTask(); + ForkJoinWorkerThread wt = + (ForkJoinWorkerThread)Thread.currentThread(); + return wt.pool.nextTaskFor(wt.workQueue); + } + + // tag operations + + /** + * Returns the tag for this task. + * + * @return the tag for this task + * @since 1.8 + */ + public final short getForkJoinTaskTag() { + return (short)status; + } + + /** + * Atomically sets the tag value for this task. + * + * @param tag the tag value + * @return the previous value of the tag + * @since 1.8 + */ + public final short setForkJoinTaskTag(short tag) { + for (int s;;) { + if (U.compareAndSwapInt(this, STATUS, s = status, + (s & ~SMASK) | (tag & SMASK))) + return (short)s; + } + } + + /** + * Atomically conditionally sets the tag value for this task. + * Among other applications, tags can be used as visit markers + * in tasks operating on graphs, as in methods that check: {@code + * if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))} + * before processing, otherwise exiting because the node has + * already been visited. + * + * @param e the expected tag value + * @param tag the new tag value + * @return true if successful; i.e., the current value was + * equal to e and is now tag. + * @since 1.8 + */ + public final boolean compareAndSetForkJoinTaskTag(short e, short tag) { + for (int s;;) { + if ((short)(s = status) != e) + return false; + if (U.compareAndSwapInt(this, STATUS, s, + (s & ~SMASK) | (tag & SMASK))) + return true; + } + } + + /** + * 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; + T result; + AdaptedRunnable(Runnable runnable, T result) { + if (runnable == null) throw new NullPointerException(); + this.runnable = runnable; + this.result = result; // OK to set this even before completion + } + public final T getRawResult() { return result; } + public final void setRawResult(T v) { result = v; } + public final boolean exec() { runnable.run(); return true; } + public final void run() { invoke(); } + private static final long serialVersionUID = 5232453952276885070L; + } + + /** + * Adaptor for Runnables without results + */ + static final class AdaptedRunnableAction extends ForkJoinTask + implements RunnableFuture { + final Runnable runnable; + AdaptedRunnableAction(Runnable runnable) { + if (runnable == null) throw new NullPointerException(); + this.runnable = runnable; + } + public final Void getRawResult() { return null; } + public final void setRawResult(Void v) { } + public final boolean exec() { runnable.run(); return true; } + public final void run() { invoke(); } + private static final long serialVersionUID = 5232453952276885070L; + } + + /** + * 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 final T getRawResult() { return result; } + public final void setRawResult(T v) { result = v; } + public final 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 final 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 AdaptedRunnableAction(runnable); + } + + /** + * 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 AdaptedRunnable(runnable, result); + } + + /** + * 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 AdaptedCallable(callable); } // Serialization support @@ -973,11 +1492,10 @@ public abstract class ForkJoinTask im private static final long serialVersionUID = -7721805057305804111L; /** - * Save the state to a stream. + * Saves this task to a stream (that is, serializes it). * * @serialData the current run status and the exception thrown - * during execution, or null if none. - * @param s the stream + * during execution, or {@code null} if none */ private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { @@ -986,36 +1504,57 @@ public abstract class ForkJoinTask im } /** - * Reconstitute the instance from a stream. - * @param s the stream + * Reconstitutes this task from a stream (that is, deserializes it). */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { s.defaultReadObject(); - status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts - status |= EXTERNAL_SIGNAL; // conservatively set external signal Object ex = s.readObject(); if (ex != null) - setDoneExceptionally((Throwable)ex); + setExceptionalCompletion((Throwable)ex); } - // Temporary Unsafe mechanics for preliminary release - - static final Unsafe _unsafe; - static final long statusOffset; - + // Unsafe mechanics + private static final sun.misc.Unsafe U; + private static final long STATUS; static { + exceptionTableLock = new ReentrantLock(); + exceptionTableRefQueue = new ReferenceQueue(); + exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY]; try { - if (ForkJoinTask.class.getClassLoader() != null) { - Field f = Unsafe.class.getDeclaredField("theUnsafe"); - f.setAccessible(true); - _unsafe = (Unsafe)f.get(null); - } - else - _unsafe = Unsafe.getUnsafe(); - statusOffset = _unsafe.objectFieldOffset + U = getUnsafe(); + STATUS = U.objectFieldOffset (ForkJoinTask.class.getDeclaredField("status")); - } catch (Exception ex) { throw new Error(ex); } + } catch (Exception e) { + throw new Error(e); + } } + /** + * Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. + * Replace with a simple call to Unsafe.getUnsafe when integrating + * into a jdk. + * + * @return a sun.misc.Unsafe + */ + private static sun.misc.Unsafe getUnsafe() { + try { + return sun.misc.Unsafe.getUnsafe(); + } catch (SecurityException se) { + try { + return java.security.AccessController.doPrivileged + (new java.security + .PrivilegedExceptionAction() { + public sun.misc.Unsafe run() throws Exception { + java.lang.reflect.Field f = sun.misc + .Unsafe.class.getDeclaredField("theUnsafe"); + f.setAccessible(true); + return (sun.misc.Unsafe) f.get(null); + }}); + } catch (java.security.PrivilegedActionException e) { + throw new RuntimeException("Could not initialize intrinsics", + e.getCause()); + } + } + } }