diff options
Diffstat (limited to 'src/forkjoin/scala/concurrent/forkjoin/ForkJoinTask.java')
| -rw-r--r-- | src/forkjoin/scala/concurrent/forkjoin/ForkJoinTask.java | 1488 |
1 files changed, 0 insertions, 1488 deletions
diff --git a/src/forkjoin/scala/concurrent/forkjoin/ForkJoinTask.java b/src/forkjoin/scala/concurrent/forkjoin/ForkJoinTask.java deleted file mode 100644 index fd1e132b07..0000000000 --- a/src/forkjoin/scala/concurrent/forkjoin/ForkJoinTask.java +++ /dev/null @@ -1,1488 +0,0 @@ -/* - * 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/publicdomain/zero/1.0/ - */ - -package scala.concurrent.forkjoin; - -import java.io.Serializable; -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 {@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 it is - * explicitly submitted to a {@link ForkJoinPool}, or, if not already - * engaged in a ForkJoin computation, commenced in the {@link - * ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or - * related methods. 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. - * - * <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 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 I/O, 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. - * - * <p>It is possible to define and use ForkJoinTasks that may block, - * but doing do requires three further considerations: (1) Completion - * of few if any <em>other</em> tasks should be dependent on a task - * that blocks on external synchronization or I/O. Event-style async - * tasks that are never joined (for example, those subclassing {@link - * CountedCompleter}) 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. - * - * <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 #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>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}. - * - * <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 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. - * - * <p>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 <em>tagged</em> 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. - * (Method names for tagging are bulky in part to encourage definition - * of methods that reflect their usage patterns.) - * - * <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, 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. - * - * <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 constructed in <em>asyncMode</em>. - * - * <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 { - - /* - * 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 - - /** - * Marks completion and wakes up threads waiting to join this - * task. - * - * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL - * @return completion status on exit - */ - 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; - } - } - } - - /** - * 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 - */ - 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; - } - - /** - * Tries to set SIGNAL status unless already completed. Used by - * ForkJoinPool. Other variants are directly incorporated into - * externalAwaitDone etc. - * - * @return true if successful - */ - final boolean trySetSignal() { - int s = status; - return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL); - } - - /** - * Blocks a non-worker-thread until completion. - * @return status upon completion - */ - private int externalAwaitDone() { - int s; - ForkJoinPool.externalHelpJoin(this); - boolean interrupted = false; - while ((s = status) >= 0) { - 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; - } - - /** - * Blocks a non-worker-thread until completion or interruption. - */ - private int externalInterruptibleAwaitDone() throws InterruptedException { - int s; - if (Thread.interrupted()) - throw new InterruptedException(); - ForkJoinPool.externalHelpJoin(this); - while ((s = status) >= 0) { - if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { - synchronized (this) { - if (status >= 0) - wait(); - else - notifyAll(); - } - } - } - return s; - } - - - /** - * 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 int doJoin() { - int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w; - return (s = status) < 0 ? s : - ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? - (w = (wt = (ForkJoinWorkerThread)t).workQueue). - tryUnpush(this) && (s = doExec()) < 0 ? s : - wt.pool.awaitJoin(w, this) : - externalAwaitDone(); - } - - /** - * Implementation for invoke, quietlyInvoke. - * - * @return status upon completion - */ - private int doInvoke() { - int s; Thread t; ForkJoinWorkerThread wt; - return (s = doExec()) < 0 ? s : - ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? - (wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue, this) : - externalAwaitDone(); - } - - // Exception table support - - /** - * Table of exceptions thrown by tasks, to enable reporting by - * callers. Because exceptions are rare, we don't directly keep - * them with task objects, but instead use a weak ref table. Note - * that cancellation exceptions don't appear in the table, but are - * instead recorded as status values. - * - * Note: These statics are initialized below in static block. - */ - private static final ExceptionNode[] exceptionTable; - private static final ReentrantLock exceptionTableLock; - private static final ReferenceQueue<Object> 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<ForkJoinTask<?>> { - final Throwable ex; - ExceptionNode next; - final long thrower; // use id not ref to avoid weak cycles - ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) { - super(task, exceptionTableRefQueue); - this.ex = ex; - this.next = next; - this.thrower = Thread.currentThread().getId(); - } - } - - /** - * Records exception and sets status. - * - * @return status on exit - */ - final int recordExceptionalCompletion(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 s; - } - - /** - * Records exception and possibly propagates. - * - * @return status on exit - */ - private int setExceptionalCompletion(Throwable ex) { - int s = recordExceptionalCompletion(ex); - if ((s & DONE_MASK) == EXCEPTIONAL) - internalPropagateException(ex); - return s; - } - - /** - * Hook for exception propagation support for tasks with completers. - */ - void internalPropagateException(Throwable ex) { - } - - /** - * 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) { - } - } - } - - /** - * Removes exception node and clears status. - */ - 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(); - } - } - - /** - * Returns a rethrowable exception for the given task, if - * available. To provide accurate stack traces, if the exception - * was not thrown by the current thread, we try to create a new - * exception of the same type as the one thrown, but with the - * recorded exception as its cause. If there is no such - * constructor, we instead try to use a no-arg constructor, - * followed by initCause, to the same effect. If none of these - * apply, or any fail due to other exceptions, we return the - * recorded exception, which is still correct, although it may - * contain a misleading stack trace. - * - * @return the exception, or null if none - */ - private Throwable getThrowableException() { - if ((status & 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<? extends Throwable> ec = ex.getClass(); - try { - Constructor<?> noArgCtor = null; - Constructor<?>[] cs = ec.getConstructors();// public ctors only - for (int i = 0; i < cs.length; ++i) { - Constructor<?> c = cs[i]; - Class<?>[] ps = c.getParameterTypes(); - if (ps.length == 0) - noArgCtor = c; - else if (ps.length == 1 && ps[0] == Throwable.class) - return (Throwable)(c.newInstance(ex)); - } - if (noArgCtor != null) { - Throwable wx = (Throwable)(noArgCtor.newInstance()); - wx.initCause(ex); - return wx; - } - } catch (Exception ignore) { - } - } - return ex; - } - - /** - * Poll stale refs and remove them. Call only while holding lock. - */ - 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; - } - } - } - } - - /** - * If lock is available, poll stale refs and remove them. - * Called from ForkJoinPool when pools become quiescent. - */ - static final void helpExpungeStaleExceptions() { - final ReentrantLock lock = exceptionTableLock; - if (lock.tryLock()) { - try { - expungeStaleExceptions(); - } finally { - lock.unlock(); - } - } - } - - /** - * A version of "sneaky throw" to relay exceptions - */ - static void rethrow(final Throwable ex) { - if (ex != null) { - if (ex instanceof Error) - throw (Error)ex; - if (ex instanceof RuntimeException) - throw (RuntimeException)ex; - ForkJoinTask.<RuntimeException>uncheckedThrow(ex); - } - } - - /** - * The sneaky part of sneaky throw, relying on generics - * limitations to evade compiler complaints about rethrowing - * unchecked exceptions - */ - @SuppressWarnings("unchecked") static <T extends Throwable> - void uncheckedThrow(Throwable t) throws T { - if (t != null) - throw (T)t; // rely on vacuous cast - } - - /** - * Throws exception, if any, associated with the given status. - */ - private void reportException(int s) { - if (s == CANCELLED) - throw new CancellationException(); - if (s == EXCEPTIONAL) - rethrow(getThrowableException()); - } - - // public methods - - /** - * Arranges to asynchronously execute this task in the pool the - * current task is running in, if applicable, or using the {@link - * ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}. 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}. - * - * @return {@code this}, to simplify usage - */ - public final ForkJoinTask<V> fork() { - Thread t; - if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) - ((ForkJoinWorkerThread)t).workQueue.push(this); - else - ForkJoinPool.common.externalPush(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}, and that - * interrupts of the calling thread do <em>not</em> cause the - * method to abruptly return by throwing {@code - * InterruptedException}. - * - * @return the computed result - */ - public final V join() { - int s; - if ((s = doJoin() & DONE_MASK) != NORMAL) - reportException(s); - return getRawResult(); - } - - /** - * Commences performing this task, awaits its completion if - * 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() { - int s; - if ((s = doInvoke() & DONE_MASK) != NORMAL) - reportException(s); - return getRawResult(); - } - - /** - * Forks the given tasks, returning when {@code isDone} holds for - * each task or an (unchecked) exception is encountered, in which - * case the exception is rethrown. If 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. - * - * @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) { - int s1, s2; - t2.fork(); - 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 {@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. - * - * @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 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 if (t.doJoin() < NORMAL) - ex = t.getException(); - } - } - if (ex != null) - rethrow(ex); - } - - /** - * 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. - * - * @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 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 if (t.doJoin() < NORMAL) - ex = t.getException(); - } - } - if (ex != null) - rethrow(ex); - return tasks; - } - - /** - * 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}. - * - * <p>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. - * - * <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 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; - } - - public final boolean isCancelled() { - return (status & DONE_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 < 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 & DONE_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 & 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 - * {@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) { - setExceptionalCompletion((ex instanceof RuntimeException) || - (ex instanceof Error) ? ex : - new RuntimeException(ex)); - } - - /** - * Completes this task, and if not already aborted or cancelled, - * 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 - */ - public void complete(V value) { - try { - setRawResult(value); - } catch (Throwable rex) { - setExceptionalCompletion(rex); - return; - } - setCompletion(NORMAL); - } - - /** - * 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); - } - - /** - * 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 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(); - } - - /** - * 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 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 ms; - long ns = unit.toNanos(timeout); - if ((s = status) >= 0 && ns > 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; - p.helpJoinOnce(w, this); // no retries on failure - } - else - ForkJoinPool.externalHelpJoin(this); - boolean canBlock = false; - boolean interrupted = false; - try { - while ((s = status) >= 0) { - if (w != null && w.qlock < 0) - cancelIgnoringExceptions(this); - else if (!canBlock) { - if (p == null || p.tryCompensate()) - 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 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() { - doJoin(); - } - - /** - * Commences performing this task and awaits its completion if - * necessary, without returning its result or throwing its - * exception. - */ - public final void quietlyInvoke() { - doInvoke(); - } - - /** - * 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. - */ - public static void helpQuiesce() { - Thread t; - if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) { - ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t; - wt.pool.helpQuiescePool(wt.workQueue); - } - else - ForkJoinPool.quiesceCommonPool(); - } - - /** - * 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. - * - * <p>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 & 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 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 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; - } - - /** - * Tries to unschedule this task for execution. This method will - * typically (but is not guaranteed to) 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. - * - * @return {@code true} if unforked - */ - public boolean tryUnfork() { - Thread t; - return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? - ((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) : - ForkJoinPool.tryExternalUnpush(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. - * - * @return the number of tasks - */ - public static int getQueuedTaskCount() { - Thread t; ForkJoinPool.WorkQueue q; - if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) - q = ((ForkJoinWorkerThread)t).workQueue; - else - q = ForkJoinPool.commonSubmitterQueue(); - return (q == null) ? 0 : q.queueSize(); - } - - /** - * 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, or zero if this thread is not - * operating in a ForkJoinPool. 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. - * - * @return the surplus number of tasks, which may be negative - */ - public static int getSurplusQueuedTaskCount() { - return ForkJoinPool.getSurplusQueuedTaskCount(); - } - - // 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 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 - * 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, 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. - * - * @return the next task, or {@code null} if none are available - */ - protected static ForkJoinTask<?> peekNextLocalTask() { - Thread t; ForkJoinPool.WorkQueue q; - if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) - q = ((ForkJoinWorkerThread)t).workQueue; - else - q = ForkJoinPool.commonSubmitterQueue(); - return (q == null) ? null : q.peek(); - } - - /** - * Unschedules and returns, without executing, the next task - * queued by the current thread but not yet executed, if the - * current thread is operating in a ForkJoinPool. This method is - * designed primarily to support extensions, and is unlikely to be - * useful otherwise. - * - * @return the next task, or {@code null} if none are available - */ - protected static ForkJoinTask<?> pollNextLocalTask() { - Thread t; - return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? - ((ForkJoinWorkerThread)t).workQueue.nextLocalTask() : - null; - } - - /** - * If the current thread is operating in a ForkJoinPool, - * 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. - * - * @return a task, or {@code null} if none are available - */ - protected static ForkJoinTask<?> pollTask() { - Thread t; ForkJoinWorkerThread wt; - return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? - (wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) : - null; - } - - // 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<T> extends ForkJoinTask<T> - implements RunnableFuture<T> { - 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<Void> - implements RunnableFuture<Void> { - 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<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 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 <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 this task to a stream (that is, serializes it). - * - * @serialData the current run status and the exception thrown - * during execution, or {@code null} if none - */ - private void writeObject(java.io.ObjectOutputStream s) - throws java.io.IOException { - s.defaultWriteObject(); - s.writeObject(getException()); - } - - /** - * Reconstitutes this task from a stream (that is, deserializes it). - */ - private void readObject(java.io.ObjectInputStream s) - throws java.io.IOException, ClassNotFoundException { - s.defaultReadObject(); - Object ex = s.readObject(); - if (ex != null) - setExceptionalCompletion((Throwable)ex); - } - - // Unsafe mechanics - private static final sun.misc.Unsafe U; - private static final long STATUS; - - static { - exceptionTableLock = new ReentrantLock(); - exceptionTableRefQueue = new ReferenceQueue<Object>(); - exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY]; - try { - U = getUnsafe(); - Class<?> k = ForkJoinTask.class; - STATUS = U.objectFieldOffset - (k.getDeclaredField("status")); - } 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() { - return scala.concurrent.util.Unsafe.instance; - } -} |