--- jsr166/src/jsr166y/ForkJoinTask.java 2009/07/26 06:26:37 1.21 +++ jsr166/src/jsr166y/ForkJoinTask.java 2009/08/02 17:19:24 1.29 @@ -16,47 +16,48 @@ 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. * - *

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. + *

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. * - *

A ForkJoinTask is a lightweight form of {@link Future}. The - * efficiency of ForkJoinTasks stems from a set of restrictions (that - * are only partially statically enforceable) reflecting their - * intended use as computational tasks calculating pure functions or - * operating on purely isolated objects. The primary coordination - * mechanisms are {@link #fork}, that arranges asynchronous execution, - * and {@link #join}, that doesn't proceed until the task's result has - * been computed. Computations should avoid {@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 join - * them. These exceptions may additionally include - * RejectedExecutionExceptions stemming from internal resource - * exhaustion such as failure to allocate internal task queues. + *

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 join them. These exceptions may + * additionally include RejectedExecutionExceptions stemming from + * internal resource exhaustion such as failure to allocate internal + * task queues. * *

The primary method for awaiting completion and extracting * results of a task is {@link #join}, but there are several variants: @@ -75,9 +76,11 @@ import java.util.WeakHashMap; * performs the most common form of parallel invocation: forking a set * of tasks and joining them all. * - *

The ForkJoinTask class is not usually directly subclassed. + *

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 @@ -94,8 +97,8 @@ import java.util.WeakHashMap; * 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. @@ -107,6 +110,12 @@ import java.util.WeakHashMap; * 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 @@ -248,7 +257,7 @@ 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)); @@ -532,17 +541,17 @@ 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(); @@ -551,15 +560,19 @@ 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 */ @@ -597,13 +610,14 @@ 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 @@ -652,19 +666,19 @@ public abstract class ForkJoinTask im } /** - * 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; @@ -673,29 +687,29 @@ 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 * still ensure that these minimal properties hold. In particular, - * the cancel method itself must not throw exceptions. + * the {@code cancel} method itself must not throw exceptions. * - *

This method is designed to be invoked by other + *

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); @@ -703,9 +717,9 @@ 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; @@ -713,10 +727,10 @@ public abstract class ForkJoinTask im /** * Returns the exception thrown by the base computation, or a - * CancellationException if cancelled, or null if none or if the - * method has not yet completed. + * {@code CancellationException} if cancelled, or {@code 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; @@ -733,7 +747,7 @@ 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. * @@ -753,7 +767,7 @@ 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. * @@ -778,9 +792,10 @@ 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(); } @@ -852,7 +867,11 @@ 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()) @@ -866,7 +885,7 @@ 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() { @@ -879,7 +898,8 @@ 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(); @@ -910,7 +930,7 @@ 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()) @@ -921,8 +941,11 @@ 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() { @@ -938,8 +961,11 @@ 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() { @@ -950,13 +976,13 @@ 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(); @@ -975,26 +1001,29 @@ 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()) @@ -1011,7 +1040,7 @@ 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()) @@ -1032,14 +1061,67 @@ 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(); } - // adaptors + /** + * 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} @@ -1049,8 +1131,8 @@ public abstract class ForkJoinTask im * @param runnable the runnable action * @return the task */ - public static ForkJoinTask adapt(Runnable runnable) { - return new ForkJoinPool.AdaptedRunnable(runnable, null); + public static ForkJoinTask adapt(Runnable runnable) { + return new AdaptedRunnable(runnable, null); } /** @@ -1063,7 +1145,7 @@ public abstract class ForkJoinTask im * @return the task */ public static ForkJoinTask adapt(Runnable runnable, T result) { - return new ForkJoinPool.AdaptedRunnable(runnable, result); + return new AdaptedRunnable(runnable, result); } /** @@ -1075,8 +1157,8 @@ public abstract class ForkJoinTask im * @param callable the callable action * @return the task */ - public static ForkJoinTask adapt(Callable callable) { - return new ForkJoinPool.AdaptedCallable(callable); + public static ForkJoinTask adapt(Callable callable) { + return new AdaptedCallable(callable); } // Serialization support @@ -1087,7 +1169,7 @@ 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) @@ -1111,16 +1193,43 @@ public abstract class ForkJoinTask im setDoneExceptionally((Throwable) ex); } - // Unsafe mechanics for jsr166y 3rd party package. + // 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 sun.misc.Unsafe.getUnsafe(); } catch (SecurityException se) { try { return java.security.AccessController.doPrivileged - (new java.security.PrivilegedExceptionAction() { + (new java.security + .PrivilegedExceptionAction() { public sun.misc.Unsafe run() throws Exception { - return getUnsafeByReflection(); + java.lang.reflect.Field f = sun.misc + .Unsafe.class.getDeclaredField("theUnsafe"); + f.setAccessible(true); + return (sun.misc.Unsafe) f.get(null); }}); } catch (java.security.PrivilegedActionException e) { throw new RuntimeException("Could not initialize intrinsics", @@ -1128,28 +1237,4 @@ public abstract class ForkJoinTask im } } } - - private static sun.misc.Unsafe getUnsafeByReflection() - throws NoSuchFieldException, IllegalAccessException { - java.lang.reflect.Field f = - sun.misc.Unsafe.class.getDeclaredField("theUnsafe"); - f.setAccessible(true); - return (sun.misc.Unsafe) f.get(null); - } - - private static long fieldOffset(String fieldName, Class klazz) { - try { - return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName)); - } catch (NoSuchFieldException e) { - // Convert Exception to Error - NoSuchFieldError error = new NoSuchFieldError(fieldName); - error.initCause(e); - throw error; - } - } - - private static final sun.misc.Unsafe UNSAFE = getUnsafe(); - private static final long statusOffset = - fieldOffset("status", ForkJoinTask.class); - }