--- jsr166/src/jsr166y/ForkJoinTask.java 2009/07/16 15:32:34 1.6 +++ jsr166/src/jsr166y/ForkJoinTask.java 2009/07/22 19:04:11 1.13 @@ -22,9 +22,9 @@ 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 fork - * and join, or derivatives such as - * invokeAll. However, this class also provides a number + * 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. @@ -36,7 +36,7 @@ import java.lang.reflect.*; * operating on purely isolated objects. The primary coordination * mechanisms are {@link #fork}, that arranges asynchronous execution, * and {@link #join}, that doesn't proceed until the task's result has - * been computed. Computations should avoid synchronized + * 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 @@ -48,7 +48,7 @@ import java.lang.reflect.*; * performance, and the potential to indefinitely stall if the number * of threads not waiting for IO or other external synchronization * becomes exhausted. This usage restriction is in part enforced by - * not permitting checked exceptions such as IOExceptions + * 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 @@ -58,17 +58,17 @@ import java.lang.reflect.*; *

The primary method for awaiting completion and extracting * results of a task is {@link #join}, but there are several variants: * The {@link Future#get} methods support interruptible and/or timed - * waits for completion and report results using Future + * waits for completion and report results using {@code Future} * conventions. Method {@link #helpJoin} enables callers to actively * execute other tasks while awaiting joins, which is sometimes more * efficient but only applies when all subtasks are known to be * strictly tree-structured. Method {@link #invoke} is semantically - * equivalent to fork(); join() but always attempts to + * equivalent to {@code fork(); join()} but always attempts to * begin execution in the current thread. The "quiet" forms * of these methods do not extract results or report exceptions. These * may be useful when a set of tasks are being executed, and you need * to delay processing of results or exceptions until all complete. - * Method invokeAll (available in multiple versions) + * Method {@code invokeAll} (available in multiple versions) * performs the most common form of parallel invocation: forking a set * of tasks and joining them all. * @@ -76,37 +76,42 @@ import java.lang.reflect.*; * Instead, you subclass one of the abstract classes that support a * particular style of fork/join processing. Normally, a concrete * ForkJoinTask subclass declares fields comprising its parameters, - * established in a constructor, and then defines a compute + * established in a constructor, and then defines a {@code compute} * method that somehow uses the control methods supplied by this base - * class. While these methods have public access (to allow + * class. While these methods have {@code public} access (to allow * instances of different task subclasses to call each others * methods), some of them may only be called from within other - * ForkJoinTasks. Attempts to invoke them in other contexts result in - * exceptions or errors possibly including ClassCastException. + * ForkJoinTasks (as may be determined using method {@link + * #inForkJoinPool}). Attempts to invoke them in other contexts + * result in exceptions or errors possibly including + * ClassCastException. * - *

Most base support methods are final because their + *

Most base support methods are {@code final} because their * implementations are intrinsically tied to the underlying * lightweight task scheduling framework, and so cannot be overridden. * Developers creating new basic styles of fork/join processing should - * minimally implement protected methods - * exec, setRawResult, and - * getRawResult, while also introducing an abstract + * minimally implement {@code protected} methods + * {@code exec}, {@code setRawResult}, and + * {@code getRawResult}, while also introducing an abstract * computational method that can be implemented in its subclasses, - * possibly relying on other protected methods provided + * possibly relying on other {@code protected} methods provided * by this class. * *

ForkJoinTasks should perform relatively small amounts of - * computations, othewise splitting into smaller tasks. As a very + * computations, otherwise splitting into smaller tasks. As a very * rough rule of thumb, a task should perform more than 100 and less * than 10000 basic computational steps. If tasks are too big, then - * parellelism cannot improve throughput. If too small, then memory + * parallelism cannot improve throughput. If too small, then memory * and internal task maintenance overhead may overwhelm processing. * - *

ForkJoinTasks are Serializable, which enables them + *

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 * not during execution. Serialization is not relied on during * execution itself. + * + * @since 1.7 + * @author Doug Lea */ public abstract class ForkJoinTask implements Future, Serializable { @@ -128,7 +133,7 @@ public abstract class ForkJoinTask im * currently unused. Also value 0x80000000 is available as spare * completion value. */ - volatile int status; // accessed directy by pool and workers + volatile int status; // accessed directly by pool and workers static final int COMPLETION_MASK = 0xe0000000; static final int NORMAL = 0xe0000000; // == mask @@ -141,10 +146,10 @@ public abstract class ForkJoinTask im /** * Table of exceptions thrown by tasks, to enable reporting by * callers. Because exceptions are rare, we don't directly keep - * them with task objects, but instead us a weak ref table. Note + * them with task objects, but instead use a weak ref table. Note * that cancellation exceptions don't appear in the table, but are * instead recorded as status values. - * Todo: Use ConcurrentReferenceHashMap + * TODO: Use ConcurrentReferenceHashMap */ static final Map, Throwable> exceptionMap = Collections.synchronizedMap @@ -153,7 +158,7 @@ public abstract class ForkJoinTask im // within-package utilities /** - * Get current worker thread, or null if not a worker thread + * Gets current worker thread, or null if not a worker thread. */ static ForkJoinWorkerThread getWorker() { Thread t = Thread.currentThread(); @@ -162,7 +167,7 @@ public abstract class ForkJoinTask im } final boolean casStatus(int cmp, int val) { - return _unsafe.compareAndSwapInt(this, statusOffset, cmp, val); + return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val); } /** @@ -170,13 +175,14 @@ public abstract class ForkJoinTask im */ static void rethrowException(Throwable ex) { if (ex != null) - _unsafe.throwException(ex); + UNSAFE.throwException(ex); } // Setting completion status /** - * Mark completion and wake up threads waiting to join this task. + * Marks completion and wakes up threads waiting to join this task. + * * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL */ final void setCompletion(int completion) { @@ -212,7 +218,7 @@ public abstract class ForkJoinTask im final void setNormalCompletion() { // Try typical fast case -- single CAS, no signal, not already done. // Manually expand casStatus to improve chances of inlining it - if (!_unsafe.compareAndSwapInt(this, statusOffset, 0, NORMAL)) + if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL)) setCompletion(NORMAL); } @@ -255,6 +261,7 @@ public abstract class ForkJoinTask im /** * Sets status to indicate there is joiner, then waits for join, * surrounded with pool notifications. + * * @return status upon exit */ private int awaitDone(ForkJoinWorkerThread w, boolean maintainParallelism) { @@ -297,7 +304,7 @@ public abstract class ForkJoinTask im } /** - * Notify pool that thread is unblocked. Called by signalled + * Notifies pool that thread is unblocked. Called by signalled * threads when woken by non-FJ threads (which is atypical). */ private void adjustPoolCountsOnUnblock(ForkJoinPool pool) { @@ -308,7 +315,7 @@ public abstract class ForkJoinTask im } /** - * Notify pool to adjust counts on cancelled or timed out wait + * Notifies pool to adjust counts on cancelled or timed out wait. */ private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) { if (pool != null) { @@ -323,7 +330,7 @@ public abstract class ForkJoinTask im } /** - * Handle interruptions during waits. + * Handles interruptions during waits. */ private void onInterruptedWait() { ForkJoinWorkerThread w = getWorker(); @@ -342,7 +349,8 @@ public abstract class ForkJoinTask im } /** - * Throws the exception associated with status s; + * Throws the exception associated with status s. + * * @throws the exception */ private void reportException(int s) { @@ -355,7 +363,7 @@ public abstract class ForkJoinTask im } /** - * Returns result or throws exception using j.u.c.Future conventions + * Returns result or throws exception using j.u.c.Future conventions. * Only call when isDone known to be true. */ private V reportFutureResult() @@ -375,7 +383,7 @@ public abstract class ForkJoinTask im /** * Returns result or throws exception using j.u.c.Future conventions - * with timeouts + * with timeouts. */ private V reportTimedFutureResult() throws InterruptedException, ExecutionException, TimeoutException { @@ -396,7 +404,8 @@ public abstract class ForkJoinTask im /** * Calls exec, recording completion, and rethrowing exception if - * encountered. Caller should normally check status before calling + * encountered. Caller should normally check status before calling. + * * @return true if completed normally */ private boolean tryExec() { @@ -414,7 +423,7 @@ public abstract class ForkJoinTask im /** * Main execution method used by worker threads. Invokes - * base computation unless already complete + * base computation unless already complete. */ final void quietlyExec() { if (status >= 0) { @@ -430,8 +439,9 @@ public abstract class ForkJoinTask im } /** - * Calls exec, recording but not rethrowing exception - * Caller should normally check status before calling + * Calls exec(), recording but not rethrowing exception. + * Caller should normally check status before calling. + * * @return true if completed normally */ private boolean tryQuietlyInvoke() { @@ -447,7 +457,7 @@ public abstract class ForkJoinTask im } /** - * Cancel, ignoring any exceptions it throws + * Cancels, ignoring any exceptions it throws. */ final void cancelIgnoringExceptions() { try { @@ -474,8 +484,9 @@ public abstract class ForkJoinTask im * necessarily enforced, it is a usage error to fork a task more * than once unless it has completed and been reinitialized. This * method may be invoked only from within ForkJoinTask - * computations. Attempts to invoke in other contexts result in - * exceptions or errors possibly including ClassCastException. + * computations (as may be determined using method {@link + * #inForkJoinPool}). Attempts to invoke in other contexts result + * in exceptions or errors possibly including ClassCastException. */ public final void fork() { ((ForkJoinWorkerThread)(Thread.currentThread())).pushTask(this); @@ -483,7 +494,7 @@ public abstract class ForkJoinTask im /** * Returns the result of the computation when it is ready. - * This method differs from get in that abnormal + * This method differs from {@code get} in that abnormal * completion results in RuntimeExceptions or Errors, not * ExecutionExceptions. * @@ -499,8 +510,9 @@ public abstract class ForkJoinTask im /** * Commences performing this task, awaits its completion if * necessary, and return its result. + * * @throws Throwable (a RuntimeException, Error, or unchecked - * exception) if the underlying computation did so. + * exception) if the underlying computation did so * @return the computed result */ public final V invoke() { @@ -511,15 +523,17 @@ public abstract class ForkJoinTask im } /** - * Forks both tasks, returning when isDone holds for + * Forks both tasks, returning when {@code isDone} holds for * both of them or an exception is encountered. This method may be - * invoked only from within ForkJoinTask computations. Attempts to + * 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. + * @throws RuntimeException or Error if either task did so */ public static void invokeAll(ForkJoinTaskt1, ForkJoinTask t2) { t2.fork(); @@ -528,14 +542,16 @@ public abstract class ForkJoinTask im } /** - * Forks the given tasks, returning when isDone holds + * 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 - * ForkJoinTask computations. Attempts to invoke in other contexts - * result in exceptions or errors possibly including ClassCastException. + * 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 - * @throws NullPointerException if tasks or any element are null. - * @throws RuntimeException or Error if any task did so. + * @throws NullPointerException if tasks or any element are null + * @throws RuntimeException or Error if any task did so */ public static void invokeAll(ForkJoinTask... tasks) { Throwable ex = null; @@ -572,14 +588,16 @@ public abstract class ForkJoinTask im /** * Forks all tasks in the collection, returning when - * isDone holds for all of them. If any task + * {@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. Attempts to invoke in other contexts resul!t in - * exceptions or errors possibly including ClassCastException. + * may be invoked only from within ForkJoinTask computations (as + * may be determined using method {@link + * #inForkJoinPool}). Attempts to invoke in other contexts resul!t + * in exceptions or errors possibly including ClassCastException. + * * @param tasks the collection of tasks - * @throws NullPointerException if tasks or any element are null. - * @throws RuntimeException or Error if any task did so. + * @throws NullPointerException if tasks or any element are null + * @throws RuntimeException or Error if any task did so */ public static void invokeAll(Collection> tasks) { if (!(tasks instanceof List)) { @@ -623,6 +641,7 @@ public abstract class ForkJoinTask im /** * Returns true if the computation performed by this task has * completed (or has been cancelled). + * * @return true if this computation has completed */ public final boolean isDone() { @@ -631,6 +650,7 @@ public abstract class ForkJoinTask im /** * Returns true if this task was cancelled. + * * @return true if this task was cancelled */ public final boolean isCancelled() { @@ -639,13 +659,13 @@ public abstract class ForkJoinTask im /** * Asserts that the results of this task's computation will not be - * used. If a cancellation occurs before atempting to execute this - * task, then execution will be suppressed, isCancelled - * will report true, and join will result in a - * CancellationException being thrown. Otherwise, when + * 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 + * {@code CancellationException} being thrown. Otherwise, when * cancellation races with completion, there are no guarantees - * about whether isCancelled will report true, whether - * join will return normally or via an exception, or + * 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 * invocation. * @@ -656,7 +676,7 @@ 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 completeExceptionally. + * invoke {@code completeExceptionally}. * * @param mayInterruptIfRunning this value is ignored in the * default implementation because tasks are not in general @@ -670,7 +690,8 @@ public abstract class ForkJoinTask im } /** - * Returns true if this task threw an exception or was cancelled + * Returns true if this task threw an exception or was cancelled. + * * @return true if this task threw an exception or was cancelled */ public final boolean isCompletedAbnormally() { @@ -681,6 +702,7 @@ 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. + * * @return the exception, or null if none */ public final Throwable getException() { @@ -695,11 +717,11 @@ public abstract class ForkJoinTask im /** * Completes this task abnormally, and if not already aborted or * cancelled, causes it to throw the given exception upon - * join and related operations. This method may be used + * {@code join} and related operations. This method may be used * to induce exceptions in asynchronous tasks, or to force * completion of tasks that would not otherwise complete. Its use * in other situations is likely to be wrong. This method is - * overridable, but overridden versions must invoke super + * overridable, but overridden versions must invoke {@code super} * implementation to maintain guarantees. * * @param ex the exception to throw. If this exception is @@ -714,15 +736,15 @@ public abstract class ForkJoinTask im /** * Completes this task, and if not already aborted or cancelled, - * returning a null result upon join and related + * returning a {@code null} result upon {@code join} and related * operations. This method may be used to provide results for * asynchronous tasks, or to provide alternative handling for * tasks that would not otherwise complete normally. Its use in * other situations is likely to be wrong. This method is - * overridable, but overridden versions must invoke super + * overridable, but overridden versions must invoke {@code super} * implementation to maintain guarantees. * - * @param value the result value for this task. + * @param value the result value for this task */ public void complete(V value) { try { @@ -752,13 +774,16 @@ public abstract class ForkJoinTask im /** * Possibly executes other tasks until this task is ready, then * returns the result of the computation. This method may be more - * efficient than join, but is only applicable when - * there are no potemtial dependencies between continuation of the + * efficient than {@code join}, but is only applicable when + * there are no potential dependencies between continuation of the * current task and that of any other task that might be executed * while helping. (This usually holds for pure divide-and-conquer * tasks). This method may be invoked only from within - * ForkJoinTask computations. Attempts to invoke in other contexts - * resul!t in exceptions or errors possibly including ClassCastException. + * ForkJoinTask computations (as may be determined using method + * {@link #inForkJoinPool}). Attempts to invoke in other contexts + * resul!t in exceptions or errors possibly including + * ClassCastException. + * * @return the computed result */ public final V helpJoin() { @@ -771,8 +796,9 @@ public abstract class ForkJoinTask im /** * Possibly executes other tasks until this task is ready. This * method may be invoked only from within ForkJoinTask - * computations. Attempts to invoke in other contexts resul!t in - * exceptions or errors possibly including ClassCastException. + * computations (as may be determined using method {@link + * #inForkJoinPool}). Attempts to invoke in other contexts resul!t + * in exceptions or errors possibly including ClassCastException. */ public final void quietlyHelpJoin() { if (status >= 0) { @@ -822,7 +848,7 @@ public abstract class ForkJoinTask im /** * Resets the internal bookkeeping state of this task, allowing a - * subsequent fork. This method allows repeated reuse of + * subsequent {@code fork}. This method allows repeated reuse of * this task, but only if reuse occurs when this task has either * never been forked, or has been forked, then completed and all * outstanding joins of this task have also completed. Effects @@ -838,7 +864,8 @@ public abstract class ForkJoinTask im /** * Returns the pool hosting the current task execution, or null - * if this task is executing outside of any pool. + * if this task is executing outside of any ForkJoinPool. + * * @return the pool, or null if none. */ public static ForkJoinPool getPool() { @@ -848,14 +875,27 @@ public abstract class ForkJoinTask im } /** + * Returns true if the current thread is executing as a + * ForkJoinPool computation. + * @return true if the current thread is executing as a + * ForkJoinPool computation, or false otherwise + */ + public static boolean inForkJoinPool() { + return Thread.currentThread() instanceof ForkJoinWorkerThread; + } + + /** * Tries to unschedule this task for execution. This method will * typically succeed if this task is the most recently forked task * by the current thread, and has not commenced executing in * another thread. This method may be useful when arranging * alternative local processing of tasks that could have been, but * were not, stolen. This method may be invoked only from within - * ForkJoinTask computations. Attempts to invoke in other contexts - * result in exceptions or errors possibly including ClassCastException. + * 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 true if unforked */ public boolean tryUnfork() { @@ -867,6 +907,7 @@ public abstract class ForkJoinTask im * forked by the current worker thread but not yet executed. This * value may be useful for heuristic decisions about whether to * fork other tasks. + * * @return the number of tasks */ public static int getQueuedTaskCount() { @@ -875,7 +916,7 @@ public abstract class ForkJoinTask im } /** - * Returns a estimate of how many more locally queued tasks are + * Returns an estimate of how many more locally queued tasks are * held by the current worker thread than there are other worker * threads that might steal them. This value may be useful for * heuristic decisions about whether to fork other tasks. In many @@ -883,6 +924,7 @@ public abstract class ForkJoinTask im * aim to maintain a small constant surplus (for example, 3) of * tasks, and to process computations locally if this threshold is * exceeded. + * * @return the surplus number of tasks, which may be negative */ public static int getSurplusQueuedTaskCount() { @@ -893,13 +935,13 @@ public abstract class ForkJoinTask im // Extension methods /** - * Returns the result that would be returned by join, + * 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. * - * @return the result, or null if not completed. + * @return the result, or null if not completed */ public abstract V getRawResult(); @@ -918,8 +960,9 @@ 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 - * complete to become joinable. It may throw exceptions + * {@code complete} to become joinable. It may throw exceptions * to indicate abnormal exit. + * * @return true if completed normally * @throws Error or RuntimeException if encountered during computation */ @@ -932,8 +975,9 @@ public abstract class ForkJoinTask im * 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. Attempts to invoke in other contexts result in - * exceptions or errors possibly including ClassCastException. + * 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 */ @@ -946,7 +990,8 @@ public abstract class ForkJoinTask im * queued by the current thread but not yet executed. 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. Attempts to invoke in other + * 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. * @@ -955,17 +1000,18 @@ public abstract class ForkJoinTask im protected static ForkJoinTask pollNextLocalTask() { return ((ForkJoinWorkerThread)(Thread.currentThread())).pollLocalTask(); } - + /** * Unschedules and returns, without executing, the next task * queued by the current thread but not yet executed, if one is * available, or if not available, a task that was forked by some * other thread, if available. Availability may be transient, so a - * null result does not necessarily imply quiecence + * {@code null} result does not necessarily imply quiescence * of the pool this task is operating in. This method is designed * primarily to support extensions, and is unlikely to be useful * otherwise. This method may be invoked only from within - * ForkJoinTask computations. Attempts to invoke in other contexts + * ForkJoinTask computations (as may be determined using method + * {@link #inForkJoinPool}). Attempts to invoke in other contexts * result in exceptions or errors possibly including * ClassCastException. * @@ -984,7 +1030,7 @@ 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 null if none * @param s the stream */ private void writeObject(java.io.ObjectOutputStream s) @@ -995,6 +1041,7 @@ public abstract class ForkJoinTask im /** * Reconstitute the instance from a stream. + * * @param s the stream */ private void readObject(java.io.ObjectInputStream s) @@ -1033,16 +1080,16 @@ public abstract class ForkJoinTask im private static long fieldOffset(String fieldName) throws NoSuchFieldException { - return _unsafe.objectFieldOffset + return UNSAFE.objectFieldOffset (ForkJoinTask.class.getDeclaredField(fieldName)); } - static final Unsafe _unsafe; + static final Unsafe UNSAFE; static final long statusOffset; static { try { - _unsafe = getUnsafe(); + UNSAFE = getUnsafe(); statusOffset = fieldOffset("status"); } catch (Throwable e) { throw new RuntimeException("Could not initialize intrinsics", e);