| /* |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| /* |
| * This file is available under and governed by the GNU General Public |
| * License version 2 only, as published by the Free Software Foundation. |
| * However, the following notice accompanied the original version of this |
| * file: |
| * |
| * 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 |
| */ |
| |
| package 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; |
| |
| /** |
| * 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. |
| * |
| * <p>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}. 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. |
| * |
| * <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}. |
| * The efficiency of {@code ForkJoinTask}s stems from a set of |
| * restrictions (that are only partially statically enforceable) |
| * reflecting their intended use as computational tasks calculating |
| * pure functions or operating on purely isolated objects. The |
| * primary coordination mechanisms are {@link #fork}, that arranges |
| * asynchronous execution, and {@link #join}, that doesn't proceed |
| * until the task's result has been computed. Computations should |
| * avoid {@code synchronized} methods or blocks, and should minimize |
| * other blocking synchronization apart from joining other tasks or |
| * using synchronizers such as Phasers that are advertised to |
| * cooperate with fork/join scheduling. Tasks should also not perform |
| * blocking IO, and should ideally access variables that are |
| * completely independent of those accessed by other running |
| * tasks. Minor breaches of these restrictions, for example using |
| * shared output streams, may be tolerable in practice, but frequent |
| * use may result in poor performance, and the potential to |
| * indefinitely stall if the number of threads not waiting for IO or |
| * other external synchronization becomes exhausted. This usage |
| * restriction is in part enforced by not permitting checked |
| * exceptions such as {@code IOExceptions} to be thrown. However, |
| * computations may still encounter unchecked exceptions, that are |
| * rethrown to callers attempting to join them. These exceptions may |
| * additionally include {@link RejectedExecutionException} stemming |
| * from internal resource exhaustion, such as failure to allocate |
| * internal task queues. |
| * |
| * <p>The primary method for awaiting completion and extracting |
| * results of a task is {@link #join}, but there are several variants: |
| * The {@link Future#get} methods support interruptible and/or timed |
| * waits for completion and report results using {@code Future} |
| * conventions. Method {@link #helpJoin} enables callers to actively |
| * execute other tasks while awaiting joins, which is sometimes more |
| * efficient but only applies when all subtasks are known to be |
| * strictly tree-structured. Method {@link #invoke} is semantically |
| * equivalent to {@code fork(); join()} but always attempts to begin |
| * execution in the current thread. The "<em>quiet</em>" forms of |
| * these methods do not extract results or report exceptions. These |
| * may be useful when a set of tasks are being executed, and you need |
| * to delay processing of results or exceptions until all complete. |
| * Method {@code invokeAll} (available in multiple versions) |
| * performs the most common form of parallel invocation: forking a set |
| * of tasks and joining them all. |
| * |
| * <p>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}. |
| * |
| * <p>The ForkJoinTask class is not usually directly subclassed. |
| * Instead, you subclass one of the abstract classes that support a |
| * particular style of fork/join processing, typically {@link |
| * RecursiveAction} for computations that do not return results, or |
| * {@link RecursiveTask} for those that do. Normally, a concrete |
| * ForkJoinTask subclass declares fields comprising its parameters, |
| * established in a constructor, and then defines a {@code compute} |
| * method that somehow uses the control methods supplied by this base |
| * class. While these methods have {@code public} access (to allow |
| * instances of different task subclasses to call each other's |
| * methods), some of them may only be called from within other |
| * ForkJoinTasks (as may be determined using method {@link |
| * #inForkJoinPool}). Attempts to invoke them in other contexts |
| * result in exceptions or errors, possibly including |
| * ClassCastException. |
| * |
| * <p>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. |
| * |
| * <p>ForkJoinTasks should perform relatively small amounts of |
| * 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. |
| * |
| * <p>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}. |
| * |
| * <p>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<V> implements Future<V>, Serializable { |
| |
| /** |
| * Run control status bits packed into a single int to minimize |
| * footprint and to ensure atomicity (via CAS). Status is |
| * initially zero, and takes on nonnegative values until |
| * completed, upon which status holds COMPLETED. CANCELLED, or |
| * EXCEPTIONAL, which use the top 3 bits. Tasks undergoing |
| * blocking waits by other threads have SIGNAL_MASK bits set -- |
| * bit 15 for external (nonFJ) waits, and the rest a count of |
| * waiting FJ threads. (This representation relies on |
| * ForkJoinPool max thread limits). Completion of a stolen task |
| * with SIGNAL_MASK bits set awakens waiter via notifyAll. Even |
| * though suboptimal for some purposes, we use basic builtin |
| * wait/notify to take advantage of "monitor inflation" in JVMs |
| * that we would otherwise need to emulate to avoid adding further |
| * per-task bookkeeping overhead. Note that bits 16-28 are |
| * currently unused. Also value 0x80000000 is available as spare |
| * completion value. |
| */ |
| volatile int status; // accessed directly by pool and workers |
| |
| static final int COMPLETION_MASK = 0xe0000000; |
| static final int NORMAL = 0xe0000000; // == mask |
| static final int CANCELLED = 0xc0000000; |
| static final int EXCEPTIONAL = 0xa0000000; |
| static final int SIGNAL_MASK = 0x0000ffff; |
| static final int INTERNAL_SIGNAL_MASK = 0x00007fff; |
| static final int EXTERNAL_SIGNAL = 0x00008000; // top bit of low word |
| |
| /** |
| * Table of exceptions thrown by tasks, to enable reporting by |
| * callers. Because exceptions are rare, we don't directly keep |
| * them with task objects, but instead use a weak ref table. Note |
| * that cancellation exceptions don't appear in the table, but are |
| * instead recorded as status values. |
| * TODO: Use ConcurrentReferenceHashMap |
| */ |
| static final Map<ForkJoinTask<?>, Throwable> exceptionMap = |
| Collections.synchronizedMap |
| (new WeakHashMap<ForkJoinTask<?>, Throwable>()); |
| |
| // within-package utilities |
| |
| /** |
| * Gets current worker thread, or null if not a worker thread. |
| */ |
| static ForkJoinWorkerThread getWorker() { |
| Thread t = Thread.currentThread(); |
| return ((t instanceof ForkJoinWorkerThread) ? |
| (ForkJoinWorkerThread) t : null); |
| } |
| |
| final boolean casStatus(int cmp, int val) { |
| return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val); |
| } |
| |
| /** |
| * Workaround for not being able to rethrow unchecked exceptions. |
| */ |
| static void rethrowException(Throwable ex) { |
| if (ex != null) |
| UNSAFE.throwException(ex); |
| } |
| |
| // Setting completion status |
| |
| /** |
| * Marks completion and wakes up threads waiting to join this task. |
| * |
| * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL |
| */ |
| final void setCompletion(int completion) { |
| ForkJoinPool pool = getPool(); |
| if (pool != null) { |
| int s; // Clear signal bits while setting completion status |
| do {} while ((s = status) >= 0 && !casStatus(s, completion)); |
| |
| if ((s & SIGNAL_MASK) != 0) { |
| if ((s &= INTERNAL_SIGNAL_MASK) != 0) |
| pool.updateRunningCount(s); |
| synchronized (this) { notifyAll(); } |
| } |
| } |
| else |
| externallySetCompletion(completion); |
| } |
| |
| /** |
| * Version of setCompletion for non-FJ threads. Leaves signal |
| * bits for unblocked threads to adjust, and always notifies. |
| */ |
| private void externallySetCompletion(int completion) { |
| int s; |
| do {} while ((s = status) >= 0 && |
| !casStatus(s, (s & SIGNAL_MASK) | completion)); |
| synchronized (this) { notifyAll(); } |
| } |
| |
| /** |
| * Sets status to indicate normal completion. |
| */ |
| final void setNormalCompletion() { |
| // Try typical fast case -- single CAS, no signal, not already done. |
| // Manually expand casStatus to improve chances of inlining it |
| if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL)) |
| setCompletion(NORMAL); |
| } |
| |
| // internal waiting and notification |
| |
| /** |
| * Performs the actual monitor wait for awaitDone. |
| */ |
| private void doAwaitDone() { |
| // Minimize lock bias and in/de-flation effects by maximizing |
| // chances of waiting inside sync |
| try { |
| while (status >= 0) |
| synchronized (this) { if (status >= 0) wait(); } |
| } catch (InterruptedException ie) { |
| onInterruptedWait(); |
| } |
| } |
| |
| /** |
| * Performs the actual timed monitor wait for awaitDone. |
| */ |
| private void doAwaitDone(long startTime, long nanos) { |
| synchronized (this) { |
| try { |
| while (status >= 0) { |
| long nt = nanos - (System.nanoTime() - startTime); |
| if (nt <= 0) |
| break; |
| wait(nt / 1000000, (int) (nt % 1000000)); |
| } |
| } catch (InterruptedException ie) { |
| onInterruptedWait(); |
| } |
| } |
| } |
| |
| // Awaiting completion |
| |
| /** |
| * Sets status to indicate there is joiner, then waits for join, |
| * surrounded with pool notifications. |
| * |
| * @return status upon exit |
| */ |
| private int awaitDone(ForkJoinWorkerThread w, |
| boolean maintainParallelism) { |
| ForkJoinPool pool = (w == null) ? null : w.pool; |
| 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; |
| } |
| } |
| return s; |
| } |
| |
| /** |
| * Timed version of awaitDone |
| * |
| * @return status upon exit |
| */ |
| private int awaitDone(ForkJoinWorkerThread w, long nanos) { |
| ForkJoinPool pool = (w == null) ? null : w.pool; |
| int s; |
| while ((s = status) >= 0) { |
| if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) { |
| long startTime = System.nanoTime(); |
| if (pool == null || !pool.preJoin(this, false)) |
| doAwaitDone(startTime, nanos); |
| if ((s = status) >= 0) { |
| adjustPoolCountsOnCancelledWait(pool); |
| s = status; |
| } |
| if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0) |
| adjustPoolCountsOnUnblock(pool); |
| break; |
| } |
| } |
| return s; |
| } |
| |
| /** |
| * Notifies pool that thread is unblocked. Called by signalled |
| * threads when woken by non-FJ threads (which is atypical). |
| */ |
| private void adjustPoolCountsOnUnblock(ForkJoinPool pool) { |
| int s; |
| do {} while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK)); |
| if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0) |
| pool.updateRunningCount(s); |
| } |
| |
| /** |
| * Notifies pool to adjust counts on cancelled or timed out wait. |
| */ |
| private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) { |
| if (pool != null) { |
| int s; |
| while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) { |
| if (casStatus(s, s - 1)) { |
| pool.updateRunningCount(1); |
| break; |
| } |
| } |
| } |
| } |
| |
| /** |
| * Handles interruptions during waits. |
| */ |
| private void onInterruptedWait() { |
| ForkJoinWorkerThread w = getWorker(); |
| if (w == null) |
| Thread.currentThread().interrupt(); // re-interrupt |
| else if (w.isTerminating()) |
| cancelIgnoringExceptions(); |
| // else if FJworker, ignore interrupt |
| } |
| |
| // Recording and reporting exceptions |
| |
| private void setDoneExceptionally(Throwable rex) { |
| exceptionMap.put(this, rex); |
| setCompletion(EXCEPTIONAL); |
| } |
| |
| /** |
| * Throws the exception associated with status s. |
| * |
| * @throws the exception |
| */ |
| private void reportException(int s) { |
| if ((s &= COMPLETION_MASK) < NORMAL) { |
| if (s == CANCELLED) |
| throw new CancellationException(); |
| else |
| rethrowException(exceptionMap.get(this)); |
| } |
| } |
| |
| /** |
| * 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. |
| */ |
| 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); |
| } |
| return getRawResult(); |
| } |
| |
| /** |
| * Returns result or throws exception using j.u.c.Future conventions |
| * with timeouts. |
| */ |
| private V reportTimedFutureResult() |
| throws InterruptedException, ExecutionException, TimeoutException { |
| if (Thread.interrupted()) |
| throw new InterruptedException(); |
| Throwable ex; |
| int s = status & COMPLETION_MASK; |
| if (s == NORMAL) |
| return getRawResult(); |
| else if (s == CANCELLED) |
| throw new CancellationException(); |
| else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) |
| throw new ExecutionException(ex); |
| else |
| throw new TimeoutException(); |
| } |
| |
| // internal execution methods |
| |
| /** |
| * Calls exec, recording completion, and rethrowing exception if |
| * encountered. Caller should normally check status before calling. |
| * |
| * @return true if completed normally |
| */ |
| private boolean tryExec() { |
| try { // try block must contain only call to exec |
| if (!exec()) |
| return false; |
| } catch (Throwable rex) { |
| setDoneExceptionally(rex); |
| rethrowException(rex); |
| return false; // not reached |
| } |
| setNormalCompletion(); |
| return true; |
| } |
| |
| /** |
| * Main execution method used by worker threads. Invokes |
| * base computation unless already complete. |
| */ |
| final void quietlyExec() { |
| if (status >= 0) { |
| try { |
| if (!exec()) |
| return; |
| } catch (Throwable rex) { |
| setDoneExceptionally(rex); |
| return; |
| } |
| setNormalCompletion(); |
| } |
| } |
| |
| /** |
| * Calls exec(), recording but not rethrowing exception. |
| * Caller should normally check status before calling. |
| * |
| * @return true if completed normally |
| */ |
| private boolean tryQuietlyInvoke() { |
| try { |
| if (!exec()) |
| return false; |
| } catch (Throwable rex) { |
| setDoneExceptionally(rex); |
| return false; |
| } |
| setNormalCompletion(); |
| return true; |
| } |
| |
| /** |
| * Cancels, ignoring any exceptions it throws. |
| */ |
| final void cancelIgnoringExceptions() { |
| try { |
| cancel(false); |
| } catch (Throwable ignore) { |
| } |
| } |
| |
| /** |
| * Main implementation of helpJoin |
| */ |
| private int busyJoin(ForkJoinWorkerThread w) { |
| int s; |
| ForkJoinTask<?> t; |
| while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null) |
| t.quietlyExec(); |
| return (s >= 0) ? awaitDone(w, false) : s; // block if no work |
| } |
| |
| // public methods |
| |
| /** |
| * Arranges to asynchronously execute this task. While it is not |
| * necessarily enforced, it is a usage error to fork a task more |
| * than once unless it has completed and been reinitialized. |
| * Subsequent modifications to the state of this task or any data |
| * it operates on are not necessarily consistently observable by |
| * any thread other than the one executing it unless preceded by a |
| * call to {@link #join} or related methods, or a call to {@link |
| * #isDone} returning {@code true}. |
| * |
| * <p>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}. |
| * |
| * @return {@code this}, to simplify usage |
| */ |
| public final ForkJoinTask<V> fork() { |
| ((ForkJoinWorkerThread) Thread.currentThread()) |
| .pushTask(this); |
| return this; |
| } |
| |
| /** |
| * 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}. |
| * |
| * @return the computed result |
| */ |
| public final V join() { |
| ForkJoinWorkerThread w = getWorker(); |
| if (w == null || status < 0 || !w.unpushTask(this) || !tryExec()) |
| reportException(awaitDone(w, true)); |
| return getRawResult(); |
| } |
| |
| /** |
| * Commences performing this task, awaits its completion if |
| * necessary, and return its result, or throws an (unchecked) |
| * exception if the underlying computation did so. |
| * |
| * @return the computed result |
| */ |
| public final V invoke() { |
| if (status >= 0 && tryExec()) |
| return getRawResult(); |
| else |
| return join(); |
| } |
| |
| /** |
| * 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. |
| * |
| * <p>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 t1 the first task |
| * @param t2 the second task |
| * @throws NullPointerException if any task is null |
| */ |
| public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) { |
| t2.fork(); |
| t1.invoke(); |
| t2.join(); |
| } |
| |
| /** |
| * 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. |
| * |
| * <p>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 tasks the tasks |
| * @throws NullPointerException if any task is null |
| */ |
| public static void invokeAll(ForkJoinTask<?>... tasks) { |
| Throwable ex = null; |
| int last = tasks.length - 1; |
| for (int i = last; i >= 0; --i) { |
| ForkJoinTask<?> t = tasks[i]; |
| if (t == null) { |
| if (ex == null) |
| ex = new NullPointerException(); |
| } |
| else if (i != 0) |
| t.fork(); |
| else { |
| t.quietlyInvoke(); |
| if (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(); |
| } |
| } |
| } |
| if (ex != null) |
| rethrowException(ex); |
| } |
| |
| /** |
| * Forks all tasks in the specified collection, returning when |
| * {@code isDone} holds for each task or an (unchecked) exception |
| * is encountered. If any task encounters an exception, others |
| * may be, but are not guaranteed to be, cancelled. If more than |
| * one task encounters an exception, then this method throws any |
| * one of these exceptions. The individual status of each task |
| * may be checked using {@link #getException()} and related |
| * methods. The behavior of this operation is undefined if the |
| * specified collection is modified while the operation is in |
| * progress. |
| * |
| * <p>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 tasks the collection of tasks |
| * @return the tasks argument, to simplify usage |
| * @throws NullPointerException if tasks or any element are null |
| */ |
| public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) { |
| if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) { |
| invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()])); |
| return tasks; |
| } |
| @SuppressWarnings("unchecked") |
| List<? extends ForkJoinTask<?>> ts = |
| (List<? extends ForkJoinTask<?>>) tasks; |
| Throwable ex = null; |
| int last = ts.size() - 1; |
| for (int i = last; i >= 0; --i) { |
| ForkJoinTask<?> t = ts.get(i); |
| if (t == null) { |
| if (ex == null) |
| ex = new NullPointerException(); |
| } |
| else if (i != 0) |
| t.fork(); |
| else { |
| t.quietlyInvoke(); |
| if (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(); |
| } |
| } |
| } |
| if (ex != null) |
| rethrowException(ex); |
| return tasks; |
| } |
| |
| /** |
| * Attempts to cancel execution of this task. This attempt will |
| * fail if the task has already completed, has already been |
| * cancelled, or could not be cancelled for some other reason. If |
| * successful, and this task has not started when cancel is |
| * called, execution of this task is suppressed, {@link |
| * #isCancelled} will report true, and {@link #join} will result |
| * in a {@code CancellationException} being thrown. |
| * |
| * <p>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. |
| * |
| * <p>This method is designed to be invoked by <em>other</em> |
| * 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 |
| * |
| * @return {@code true} if this task is now cancelled |
| */ |
| public boolean cancel(boolean mayInterruptIfRunning) { |
| setCompletion(CANCELLED); |
| return (status & COMPLETION_MASK) == CANCELLED; |
| } |
| |
| public final boolean isDone() { |
| return status < 0; |
| } |
| |
| public final boolean isCancelled() { |
| return (status & COMPLETION_MASK) == CANCELLED; |
| } |
| |
| /** |
| * Returns {@code true} if this task threw an exception or was cancelled. |
| * |
| * @return {@code true} if this task threw an exception or was cancelled |
| */ |
| public final boolean isCompletedAbnormally() { |
| return (status & COMPLETION_MASK) < NORMAL; |
| } |
| |
| /** |
| * Returns {@code true} if this task completed without throwing an |
| * exception and was not cancelled. |
| * |
| * @return {@code true} if this task completed without throwing an |
| * exception and was not cancelled |
| */ |
| public final boolean isCompletedNormally() { |
| return (status & COMPLETION_MASK) == NORMAL; |
| } |
| |
| /** |
| * Returns the exception thrown by the base computation, or a |
| * {@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; |
| return ((s >= NORMAL) ? null : |
| (s == CANCELLED) ? new CancellationException() : |
| exceptionMap.get(this)); |
| } |
| |
| /** |
| * Completes this task abnormally, and if not already aborted or |
| * cancelled, causes it to throw the given exception upon |
| * {@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 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 |
| * {@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)); |
| } |
| |
| /** |
| * 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. |
| * |
| * @param value the result value for this task |
| */ |
| public void complete(V value) { |
| try { |
| setRawResult(value); |
| } catch (Throwable rex) { |
| setDoneExceptionally(rex); |
| return; |
| } |
| setNormalCompletion(); |
| } |
| |
| public final V get() throws InterruptedException, ExecutionException { |
| ForkJoinWorkerThread w = getWorker(); |
| if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke()) |
| awaitDone(w, true); |
| return reportFutureResult(); |
| } |
| |
| public final V get(long timeout, TimeUnit unit) |
| throws InterruptedException, ExecutionException, TimeoutException { |
| long nanos = unit.toNanos(timeout); |
| ForkJoinWorkerThread w = getWorker(); |
| if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke()) |
| awaitDone(w, nanos); |
| return reportTimedFutureResult(); |
| } |
| |
| /** |
| * 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). |
| * |
| * <p>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}. |
| * |
| * @return the computed result |
| */ |
| public final V helpJoin() { |
| ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread(); |
| if (status < 0 || !w.unpushTask(this) || !tryExec()) |
| reportException(busyJoin(w)); |
| 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. |
| * |
| * <p>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}. |
| */ |
| public final void quietlyHelpJoin() { |
| if (status >= 0) { |
| ForkJoinWorkerThread w = |
| (ForkJoinWorkerThread) Thread.currentThread(); |
| if (!w.unpushTask(this) || !tryQuietlyInvoke()) |
| busyJoin(w); |
| } |
| } |
| |
| /** |
| * Joins this task, 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. |
| */ |
| public final void quietlyJoin() { |
| if (status >= 0) { |
| ForkJoinWorkerThread w = getWorker(); |
| if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke()) |
| awaitDone(w, true); |
| } |
| } |
| |
| /** |
| * 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. |
| */ |
| public final void quietlyInvoke() { |
| if (status >= 0 && !tryQuietlyInvoke()) |
| quietlyJoin(); |
| } |
| |
| /** |
| * Possibly executes tasks until the pool hosting the current task |
| * {@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. |
| * |
| * <p>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}. |
| */ |
| public static void helpQuiesce() { |
| ((ForkJoinWorkerThread) Thread.currentThread()) |
| .helpQuiescePool(); |
| } |
| |
| /** |
| * Resets the internal bookkeeping state of this task, allowing a |
| * 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. |
| * This method may be useful when executing |
| * pre-constructed trees of subtasks in loops. |
| */ |
| public void reinitialize() { |
| if ((status & COMPLETION_MASK) == EXCEPTIONAL) |
| exceptionMap.remove(this); |
| status = 0; |
| } |
| |
| /** |
| * Returns the pool hosting the current task execution, or null |
| * if this task is executing outside of any ForkJoinPool. |
| * |
| * @see #inForkJoinPool |
| * @return the pool, or {@code null} if none |
| */ |
| public static ForkJoinPool getPool() { |
| Thread t = Thread.currentThread(); |
| return (t instanceof ForkJoinWorkerThread) ? |
| ((ForkJoinWorkerThread) t).pool : null; |
| } |
| |
| /** |
| * Returns {@code true} if the current thread is executing as a |
| * ForkJoinPool computation. |
| * |
| * @return {@code true} if the current thread is executing as a |
| * ForkJoinPool computation, or false otherwise |
| */ |
| public static boolean inForkJoinPool() { |
| return Thread.currentThread() instanceof ForkJoinWorkerThread; |
| } |
| |
| /** |
| * Tries to unschedule this task for execution. This method will |
| * typically succeed if this task is the most recently forked task |
| * 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. |
| * |
| * <p>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}. |
| * |
| * @return {@code true} if unforked |
| */ |
| public boolean tryUnfork() { |
| return ((ForkJoinWorkerThread) Thread.currentThread()) |
| .unpushTask(this); |
| } |
| |
| /** |
| * Returns an estimate of the number of tasks that have been |
| * forked by the current worker thread but not yet executed. This |
| * value may be useful for heuristic decisions about whether to |
| * fork other tasks. |
| * |
| * <p>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}. |
| * |
| * @return the number of tasks |
| */ |
| public static int getQueuedTaskCount() { |
| return ((ForkJoinWorkerThread) Thread.currentThread()) |
| .getQueueSize(); |
| } |
| |
| /** |
| * 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 |
| * usages of ForkJoinTasks, at steady state, each worker should |
| * aim to maintain a small constant surplus (for example, 3) of |
| * tasks, and to process computations locally if this threshold is |
| * exceeded. |
| * |
| * <p>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}. |
| * |
| * @return the surplus number of tasks, which may be negative |
| */ |
| public static int getSurplusQueuedTaskCount() { |
| return ((ForkJoinWorkerThread) Thread.currentThread()) |
| .getEstimatedSurplusTaskCount(); |
| } |
| |
| // Extension methods |
| |
| /** |
| * 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 {@code null} if not completed |
| */ |
| public abstract V getRawResult(); |
| |
| /** |
| * Forces the given value to be returned as a result. This method |
| * is designed to support extensions, and should not in general be |
| * called otherwise. |
| * |
| * @param value the value |
| */ |
| 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 |
| * asynchronous actions that require explicit invocations of |
| * {@link #complete} to become joinable. It may also throw an |
| * (unchecked) exception to indicate abnormal exit. |
| * |
| * @return {@code true} if completed normally |
| */ |
| protected abstract boolean exec(); |
| |
| /** |
| * 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. |
| * |
| * <p>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}. |
| * |
| * @return the next task, or {@code null} if none are available |
| */ |
| protected static ForkJoinTask<?> peekNextLocalTask() { |
| return ((ForkJoinWorkerThread) Thread.currentThread()) |
| .peekTask(); |
| } |
| |
| /** |
| * 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. |
| * |
| * <p>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}. |
| * |
| * @return the next task, or {@code null} if none are available |
| */ |
| protected static ForkJoinTask<?> pollNextLocalTask() { |
| return ((ForkJoinWorkerThread) Thread.currentThread()) |
| .pollLocalTask(); |
| } |
| |
| /** |
| * 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. |
| * |
| * <p>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}. |
| * |
| * @return a task, or {@code null} if none are available |
| */ |
| protected static ForkJoinTask<?> pollTask() { |
| return ((ForkJoinWorkerThread) Thread.currentThread()) |
| .pollTask(); |
| } |
| |
| /** |
| * Adaptor for Runnables. This implements RunnableFuture |
| * to be compliant with AbstractExecutorService constraints |
| * when used in ForkJoinPool. |
| */ |
| static final class AdaptedRunnable<T> extends ForkJoinTask<T> |
| implements RunnableFuture<T> { |
| final Runnable runnable; |
| final T resultOnCompletion; |
| T result; |
| AdaptedRunnable(Runnable runnable, T result) { |
| if (runnable == null) throw new NullPointerException(); |
| this.runnable = runnable; |
| this.resultOnCompletion = result; |
| } |
| public T getRawResult() { return result; } |
| public void setRawResult(T v) { result = v; } |
| public boolean exec() { |
| runnable.run(); |
| result = resultOnCompletion; |
| return true; |
| } |
| public void run() { invoke(); } |
| private static final long serialVersionUID = 5232453952276885070L; |
| } |
| |
| /** |
| * Adaptor for Callables |
| */ |
| static final class AdaptedCallable<T> extends ForkJoinTask<T> |
| implements RunnableFuture<T> { |
| final Callable<? extends T> callable; |
| T result; |
| AdaptedCallable(Callable<? extends T> callable) { |
| if (callable == null) throw new NullPointerException(); |
| this.callable = callable; |
| } |
| public T getRawResult() { return result; } |
| public void setRawResult(T v) { result = v; } |
| public boolean exec() { |
| try { |
| result = callable.call(); |
| return true; |
| } catch (Error err) { |
| throw err; |
| } catch (RuntimeException rex) { |
| throw rex; |
| } catch (Exception ex) { |
| throw new RuntimeException(ex); |
| } |
| } |
| public void run() { invoke(); } |
| private static final long serialVersionUID = 2838392045355241008L; |
| } |
| |
| /** |
| * Returns a new {@code ForkJoinTask} that performs the {@code run} |
| * method of the given {@code Runnable} as its action, and returns |
| * a null result upon {@link #join}. |
| * |
| * @param runnable the runnable action |
| * @return the task |
| */ |
| public static ForkJoinTask<?> adapt(Runnable runnable) { |
| return new AdaptedRunnable<Void>(runnable, null); |
| } |
| |
| /** |
| * 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 <T> ForkJoinTask<T> adapt(Runnable runnable, T result) { |
| return new AdaptedRunnable<T>(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 <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) { |
| return new AdaptedCallable<T>(callable); |
| } |
| |
| // Serialization support |
| |
| private static final long serialVersionUID = -7721805057305804111L; |
| |
| /** |
| * Saves the state to a stream. |
| * |
| * @serialData the current run status and the exception thrown |
| * during execution, or {@code null} if none |
| * @param s the stream |
| */ |
| private void writeObject(java.io.ObjectOutputStream s) |
| throws java.io.IOException { |
| s.defaultWriteObject(); |
| s.writeObject(getException()); |
| } |
| |
| /** |
| * Reconstitutes the instance from a stream. |
| * |
| * @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); |
| } |
| |
| // Unsafe mechanics |
| |
| private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe(); |
| private static final long statusOffset = |
| objectFieldOffset("status", ForkJoinTask.class); |
| |
| private static long objectFieldOffset(String field, Class<?> klazz) { |
| 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; |
| } |
| } |
| } |
