--- jsr166/src/jsr166y/ForkJoinTask.java 2009/07/24 22:05:22 1.15 +++ jsr166/src/jsr166y/ForkJoinTask.java 2009/08/02 11:54:31 1.27 @@ -5,16 +5,19 @@ */ package jsr166y; -import java.io.Serializable; -import java.util.*; + import java.util.concurrent.*; -import java.util.concurrent.atomic.*; -import sun.misc.Unsafe; -import java.lang.reflect.*; + +import java.io.Serializable; +import java.util.Collection; +import java.util.Collections; +import java.util.List; +import java.util.Map; +import java.util.WeakHashMap; /** - * Abstract base class for tasks that run within a {@link - * ForkJoinPool}. A ForkJoinTask is a thread-like entity that is much + * Abstract base class for tasks that run within a {@link ForkJoinPool}. + * A {@code ForkJoinTask} is a thread-like entity that is much * lighter weight than a normal thread. Huge numbers of tasks and * subtasks may be hosted by a small number of actual threads in a * ForkJoinPool, at the price of some usage limitations. @@ -22,12 +25,11 @@ import java.lang.reflect.*; *

A "main" ForkJoinTask begins execution when submitted to a * {@link ForkJoinPool}. Once started, it will usually in turn start * other subtasks. As indicated by the name of this class, many - * programs using ForkJoinTasks employ only methods {@code fork} - * and {@code join}, or derivatives such as - * {@code invokeAll}. However, this class also provides a number - * of other methods that can come into play in advanced usages, as - * well as extension mechanics that allow support of new forms of - * fork/join processing. + * programs using ForkJoinTasks employ only methods {@code fork} and + * {@code join}, or derivatives such as {@code invokeAll}. However, + * this class also provides a number of other methods that can come + * into play in advanced usages, as well as extension mechanics that + * allow support of new forms of fork/join processing. * *

A ForkJoinTask is a lightweight form of {@link Future}. The * efficiency of ForkJoinTasks stems from a set of restrictions (that @@ -74,7 +76,9 @@ import java.lang.reflect.*; * *

The ForkJoinTask class is not usually directly subclassed. * Instead, you subclass one of the abstract classes that support a - * particular style of fork/join processing. Normally, a concrete + * particular style of fork/join processing, typically {@link + * RecursiveAction} for computations that do not return results, or + * {@link RecursiveTask} for those that do. Normally, a concrete * ForkJoinTask subclass declares fields comprising its parameters, * established in a constructor, and then defines a {@code compute} * method that somehow uses the control methods supplied by this base @@ -91,8 +95,8 @@ import java.lang.reflect.*; * lightweight task scheduling framework, and so cannot be overridden. * Developers creating new basic styles of fork/join processing should * minimally implement {@code protected} methods - * {@code exec}, {@code setRawResult}, and - * {@code getRawResult}, while also introducing an abstract + * {@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. @@ -104,6 +108,12 @@ import java.lang.reflect.*; * parallelism cannot improve throughput. If too small, then memory * and internal task maintenance overhead may overwhelm processing. * + *

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

ForkJoinTasks are {@code Serializable}, which enables them * to be used in extensions such as remote execution frameworks. It is * in general sensible to serialize tasks only before or after, but @@ -245,7 +255,7 @@ public abstract class ForkJoinTask im synchronized (this) { try { while (status >= 0) { - long nt = nanos - System.nanoTime() - startTime; + long nt = nanos - (System.nanoTime() - startTime); if (nt <= 0) break; wait(nt / 1000000, (int) (nt % 1000000)); @@ -489,10 +499,13 @@ public abstract class ForkJoinTask im * computations (as may be determined using method {@link * #inForkJoinPool}). Attempts to invoke in other contexts result * in exceptions or errors, possibly including ClassCastException. + * + * @return {@code this}, to simplify usage. */ - public final void fork() { + public final ForkJoinTask fork() { ((ForkJoinWorkerThread) Thread.currentThread()) .pushTask(this); + return this; } /** @@ -526,17 +539,17 @@ public abstract class ForkJoinTask im } /** - * Forks both tasks, returning when {@code isDone} holds for - * both of them or an exception is encountered. This method may be + * Forks the given tasks, returning when {@code isDone} holds for + * each task or an exception is encountered. This method may be * invoked only from within ForkJoinTask computations (as may be * determined using method {@link #inForkJoinPool}). Attempts to * invoke in other contexts result in exceptions or errors, * possibly including ClassCastException. * - * @param t1 one task - * @param t2 the other task - * @throws NullPointerException if t1 or t2 are null - * @throws RuntimeException or Error if either task did so + * @param t1 the first task + * @param t2 the second task + * @throws NullPointerException if any task is null + * @throws RuntimeException or Error if a task did so */ public static void invokeAll(ForkJoinTaskt1, ForkJoinTask t2) { t2.fork(); @@ -545,15 +558,19 @@ public abstract class ForkJoinTask im } /** - * Forks the given tasks, returning when {@code isDone} holds - * for all of them. If any task encounters an exception, others - * may be cancelled. This method may be invoked only from within + * Forks the given tasks, returning when {@code isDone} holds for + * each task or an exception is encountered. If any task + * encounters an exception, others may be, but are not guaranteed + * to be, cancelled. This method may be invoked only from within * ForkJoinTask computations (as may be determined using method * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors, possibly including * ClassCastException. * - * @param tasks the array of tasks + * Overloadings of this method exist for the special cases + * of one to four arguments. + * + * @param tasks the tasks * @throws NullPointerException if tasks or any element are null * @throws RuntimeException or Error if any task did so */ @@ -591,22 +608,24 @@ public abstract class ForkJoinTask im } /** - * Forks all tasks in the collection, returning when - * {@code isDone} holds for all of them. If any task - * encounters an exception, others may be cancelled. This method - * may be invoked only from within ForkJoinTask computations (as - * may be determined using method {@link - * #inForkJoinPool}). Attempts to invoke in other contexts result - * in exceptions or errors, possibly including ClassCastException. + * Forks all tasks in the collection, returning when {@code + * isDone} holds for each task or an exception is encountered. If + * any task encounters an exception, others may be, but are not + * guaranteed to be, cancelled. This method may be invoked only + * from within ForkJoinTask computations (as may be determined + * using method {@link #inForkJoinPool}). Attempts to invoke in + * other contexts result in exceptions or errors, possibly + * including ClassCastException. * * @param tasks the collection of tasks + * @return the tasks argument, to simplify usage * @throws NullPointerException if tasks or any element are null * @throws RuntimeException or Error if any task did so */ - public static void invokeAll(Collection> tasks) { + public static > Collection invokeAll(Collection tasks) { if (!(tasks instanceof List)) { invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()])); - return; + return tasks; } @SuppressWarnings("unchecked") List> ts = @@ -641,22 +660,23 @@ public abstract class ForkJoinTask im } if (ex != null) rethrowException(ex); + return tasks; } /** - * Returns true if the computation performed by this task has - * completed (or has been cancelled). + * Returns {@code true} if the computation performed by this task + * has completed (or has been cancelled). * - * @return true if this computation has completed + * @return {@code true} if this computation has completed */ public final boolean isDone() { return status < 0; } /** - * Returns true if this task was cancelled. + * Returns {@code true} if this task was cancelled. * - * @return true if this task was cancelled + * @return {@code true} if this task was cancelled */ public final boolean isCancelled() { return (status & COMPLETION_MASK) == CANCELLED; @@ -665,13 +685,13 @@ public abstract class ForkJoinTask im /** * Asserts that the results of this task's computation will not be * used. If a cancellation occurs before attempting to execute this - * task, then execution will be suppressed, {@code isCancelled} - * will report true, and {@code join} will result in a + * task, execution will be suppressed, {@link #isCancelled} + * will report true, and {@link #join} will result in a * {@code CancellationException} being thrown. Otherwise, when * cancellation races with completion, there are no guarantees - * about whether {@code isCancelled} will report true, whether - * {@code join} will return normally or via an exception, or - * whether these behaviors will remain consistent upon repeated + * about whether {@code isCancelled} will report {@code true}, + * whether {@code join} will return normally or via an exception, + * or whether these behaviors will remain consistent upon repeated * invocation. * *

This method may be overridden in subclasses, but if so, must @@ -681,13 +701,13 @@ public abstract class ForkJoinTask im *

This method is designed to be invoked by other * tasks. To terminate the current task, you can just return or * throw an unchecked exception from its computation method, or - * invoke {@code completeExceptionally}. + * invoke {@link #completeExceptionally}. * * @param mayInterruptIfRunning this value is ignored in the * default implementation because tasks are not in general * cancelled via interruption * - * @return true if this task is now cancelled + * @return {@code true} if this task is now cancelled */ public boolean cancel(boolean mayInterruptIfRunning) { setCompletion(CANCELLED); @@ -695,9 +715,9 @@ public abstract class ForkJoinTask im } /** - * Returns true if this task threw an exception or was cancelled. + * Returns {@code true} if this task threw an exception or was cancelled. * - * @return 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; @@ -708,7 +728,7 @@ public abstract class ForkJoinTask im * CancellationException if cancelled, or null if none or if the * method has not yet completed. * - * @return the exception, or null if none + * @return the exception, or {@code null} if none */ public final Throwable getException() { int s = status & COMPLETION_MASK; @@ -725,7 +745,7 @@ public abstract class ForkJoinTask im * {@code join} and related operations. This method may be used * to induce exceptions in asynchronous tasks, or to force * completion of tasks that would not otherwise complete. Its use - * in other situations is likely to be wrong. This method is + * in other situations is discouraged. This method is * overridable, but overridden versions must invoke {@code super} * implementation to maintain guarantees. * @@ -745,7 +765,7 @@ public abstract class ForkJoinTask im * operations. This method may be used to provide results for * asynchronous tasks, or to provide alternative handling for * tasks that would not otherwise complete normally. Its use in - * other situations is likely to be wrong. This method is + * other situations is discouraged. This method is * overridable, but overridden versions must invoke {@code super} * implementation to maintain guarantees. * @@ -770,9 +790,10 @@ public abstract class ForkJoinTask im 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, unit.toNanos(timeout)); + awaitDone(w, nanos); return reportTimedFutureResult(); } @@ -844,7 +865,11 @@ public abstract class ForkJoinTask im * Possibly executes tasks until the pool hosting the current task * {@link ForkJoinPool#isQuiescent}. This method may be of use in * designs in which many tasks are forked, but none are explicitly - * joined, instead executing them until all are processed. + * joined, instead executing them until all are processed. This + * method may be invoked only from within ForkJoinTask + * computations (as may be determined using method {@link + * #inForkJoinPool}). Attempts to invoke in other contexts result + * in exceptions or errors, possibly including ClassCastException. */ public static void helpQuiesce() { ((ForkJoinWorkerThread) Thread.currentThread()) @@ -858,7 +883,7 @@ public abstract class ForkJoinTask im * never been forked, or has been forked, then completed and all * outstanding joins of this task have also completed. Effects * under any other usage conditions are not guaranteed, and are - * almost surely wrong. This method may be useful when executing + * discouraged. This method may be useful when executing * pre-constructed trees of subtasks in loops. */ public void reinitialize() { @@ -871,7 +896,8 @@ public abstract class ForkJoinTask im * Returns the pool hosting the current task execution, or null * if this task is executing outside of any ForkJoinPool. * - * @return the pool, or null if none + * @see #inForkJoinPool + * @return the pool, or {@code null} if none */ public static ForkJoinPool getPool() { Thread t = Thread.currentThread(); @@ -902,7 +928,7 @@ public abstract class ForkJoinTask im * result in exceptions or errors, possibly including * ClassCastException. * - * @return true if unforked + * @return {@code true} if unforked */ public boolean tryUnfork() { return ((ForkJoinWorkerThread) Thread.currentThread()) @@ -913,8 +939,11 @@ public abstract class ForkJoinTask im * 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. - * + * fork other tasks. This method may be invoked only from within + * ForkJoinTask computations (as may be determined using method + * {@link #inForkJoinPool}). Attempts to invoke in other contexts + * result in exceptions or errors, possibly including + * ClassCastException. * @return the number of tasks */ public static int getQueuedTaskCount() { @@ -930,8 +959,11 @@ public abstract class ForkJoinTask im * 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. - * + * exceeded. This method may be invoked only from within + * ForkJoinTask computations (as may be determined using method + * {@link #inForkJoinPool}). Attempts to invoke in other contexts + * result in exceptions or errors, possibly including + * ClassCastException. * * @return the surplus number of tasks, which may be negative */ public static int getSurplusQueuedTaskCount() { @@ -942,13 +974,13 @@ public abstract class ForkJoinTask im // Extension methods /** - * Returns the result that would be returned by {@code join}, - * even if this task completed abnormally, or null if this task is - * not known to have been completed. This method is designed to - * aid debugging, as well as to support extensions. Its use in any - * other context is discouraged. + * Returns the result that would be returned by {@link #join}, even + * if this task completed abnormally, or {@code null} if this task + * is not known to have been completed. This method is designed + * to aid debugging, as well as to support extensions. Its use in + * any other context is discouraged. * - * @return the result, or null if not completed + * @return the result, or {@code null} if not completed */ public abstract V getRawResult(); @@ -967,26 +999,29 @@ public abstract class ForkJoinTask im * called otherwise. The return value controls whether this task * is considered to be done normally. It may return false in * asynchronous actions that require explicit invocations of - * {@code complete} to become joinable. It may throw exceptions + * {@link #complete} to become joinable. It may throw exceptions * to indicate abnormal exit. * - * @return true if completed normally + * @return {@code true} if completed normally * @throws Error or RuntimeException if encountered during computation */ protected abstract boolean exec(); /** - * Returns, but does not unschedule or execute, the task queued by - * the current thread but not yet executed, if one is + * Returns, but does not unschedule or execute, a task queued by + * the current thread but not yet executed, if one is immediately * available. There is no guarantee that this task will actually - * be polled or executed next. This method is designed primarily - * to support extensions, and is unlikely to be useful otherwise. - * This method may be invoked only from within ForkJoinTask - * computations (as may be determined using method {@link - * #inForkJoinPool}). Attempts to invoke in other contexts result - * in exceptions or errors, possibly including ClassCastException. + * be polled or executed next. Conversely, this method may return + * null even if a task exists but cannot be accessed without + * contention with other threads. This method is designed + * primarily to support extensions, and is unlikely to be useful + * otherwise. This method may be invoked only from within + * ForkJoinTask computations (as may be determined using method + * {@link #inForkJoinPool}). Attempts to invoke in other contexts + * result in exceptions or errors, possibly including + * ClassCastException. * - * @return the next task, or null if none are available + * @return the next task, or {@code null} if none are available */ protected static ForkJoinTask peekNextLocalTask() { return ((ForkJoinWorkerThread) Thread.currentThread()) @@ -1003,7 +1038,7 @@ public abstract class ForkJoinTask im * contexts result in exceptions or errors, possibly including * ClassCastException. * - * @return the next task, or null if none are available + * @return the next task, or {@code null} if none are available */ protected static ForkJoinTask pollNextLocalTask() { return ((ForkJoinWorkerThread) Thread.currentThread()) @@ -1024,13 +1059,106 @@ public abstract class ForkJoinTask im * result in exceptions or errors, possibly including * ClassCastException. * - * @return a task, or null if none are available + * @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 extends ForkJoinTask + implements RunnableFuture { + final Runnable runnable; + final T resultOnCompletion; + T result; + AdaptedRunnable(Runnable runnable, T result) { + if (runnable == null) throw new NullPointerException(); + this.runnable = runnable; + this.resultOnCompletion = result; + } + public T getRawResult() { return result; } + public void setRawResult(T v) { result = v; } + public boolean exec() { + runnable.run(); + result = resultOnCompletion; + return true; + } + public void run() { invoke(); } + private static final long serialVersionUID = 5232453952276885070L; + } + + /** + * Adaptor for Callables + */ + static final class AdaptedCallable extends ForkJoinTask + implements RunnableFuture { + final Callable callable; + T result; + AdaptedCallable(Callable callable) { + if (callable == null) throw new NullPointerException(); + this.callable = callable; + } + public T getRawResult() { return result; } + public void setRawResult(T v) { result = v; } + public boolean exec() { + try { + result = callable.call(); + return true; + } catch (Error err) { + throw err; + } catch (RuntimeException rex) { + throw rex; + } catch (Exception ex) { + throw new RuntimeException(ex); + } + } + public void run() { invoke(); } + private static final long serialVersionUID = 2838392045355241008L; + } + + /** + * Returns a new ForkJoinTask that performs the {@code run} + * method of the given Runnable as its action, and returns a null + * result upon {@code join}. + * + * @param runnable the runnable action + * @return the task + */ + public static ForkJoinTask adapt(Runnable runnable) { + return new AdaptedRunnable(runnable, null); + } + + /** + * Returns a new ForkJoinTask that performs the {@code run} + * method of the given Runnable as its action, and returns the + * given result upon {@code join}. + * + * @param runnable the runnable action + * @param result the result upon completion + * @return the task + */ + public static ForkJoinTask adapt(Runnable runnable, T result) { + return new AdaptedRunnable(runnable, result); + } + + /** + * Returns a new ForkJoinTask that performs the {@code call} + * method of the given Callable as its action, and returns its + * result upon {@code join}, translating any checked + * exceptions encountered into {@code RuntimeException}. + * + * @param callable the callable action + * @return the task + */ + public static ForkJoinTask adapt(Callable callable) { + return new AdaptedCallable(callable); + } + // Serialization support private static final long serialVersionUID = -7721805057305804111L; @@ -1039,7 +1167,7 @@ public abstract class ForkJoinTask im * Save the state to a stream. * * @serialData the current run status and the exception thrown - * during execution, or null if none + * during execution, or {@code null} if none * @param s the stream */ private void writeObject(java.io.ObjectOutputStream s) @@ -1063,46 +1191,48 @@ public abstract class ForkJoinTask im setDoneExceptionally((Throwable) ex); } - // Temporary Unsafe mechanics for preliminary release - private static Unsafe getUnsafe() throws Throwable { + // Unsafe mechanics + + private static final sun.misc.Unsafe UNSAFE = getUnsafe(); + private static final long statusOffset = + objectFieldOffset("status", ForkJoinTask.class); + + private static long objectFieldOffset(String field, Class klazz) { + 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; + } + } + + /** + * Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. + * Replace with a simple call to Unsafe.getUnsafe when integrating + * into a jdk. + * + * @return a sun.misc.Unsafe + */ + private static sun.misc.Unsafe getUnsafe() { try { - return Unsafe.getUnsafe(); + return sun.misc.Unsafe.getUnsafe(); } catch (SecurityException se) { try { return java.security.AccessController.doPrivileged - (new java.security.PrivilegedExceptionAction() { - public Unsafe run() throws Exception { - return getUnsafePrivileged(); + (new java.security + .PrivilegedExceptionAction() { + public sun.misc.Unsafe run() throws Exception { + java.lang.reflect.Field f = sun.misc + .Unsafe.class.getDeclaredField("theUnsafe"); + f.setAccessible(true); + return (sun.misc.Unsafe) f.get(null); }}); } catch (java.security.PrivilegedActionException e) { - throw e.getCause(); + throw new RuntimeException("Could not initialize intrinsics", + e.getCause()); } } } - - private static Unsafe getUnsafePrivileged() - throws NoSuchFieldException, IllegalAccessException { - Field f = Unsafe.class.getDeclaredField("theUnsafe"); - f.setAccessible(true); - return (Unsafe) f.get(null); - } - - private static long fieldOffset(String fieldName) - throws NoSuchFieldException { - return UNSAFE.objectFieldOffset - (ForkJoinTask.class.getDeclaredField(fieldName)); - } - - static final Unsafe UNSAFE; - static final long statusOffset; - - static { - try { - UNSAFE = getUnsafe(); - statusOffset = fieldOffset("status"); - } catch (Throwable e) { - throw new RuntimeException("Could not initialize intrinsics", e); - } - } - }