--- jsr166/src/jsr166y/ForkJoinTask.java 2009/01/06 14:30:31 1.1 +++ jsr166/src/jsr166y/ForkJoinTask.java 2009/07/21 00:15:13 1.10 @@ -13,24 +13,32 @@ import sun.misc.Unsafe; import java.lang.reflect.*; /** - * Abstract base class for tasks that run within a ForkJoinPool. A - * 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. + * Abstract base class for tasks that run within a {@link + * ForkJoinPool}. A 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. * - *

ForkJoinTasks are forms of Futures supporting a - * limited range of use. The "lightness" of ForkJoinTasks is due to 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 supported for ForkJoinTasks are - * fork, that arranges asynchronous execution, and - * join, that doesn't proceed until the task's result has - * been computed. (Cancellation is also supported). The computation - * defined in the compute method should avoid - * synchronized methods or blocks, and should minimize - * blocking synchronization apart from joining other tasks or using + *

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 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 @@ -38,65 +46,74 @@ import java.lang.reflect.*; * 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 external synchronization becomes - * exhausted. This usage restriction is in part enforced by not - * permitting checked exceptions such as IOExceptions to be - * thrown. However, computations may still encounter unchecked + * 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 ForkJoinTask class is not usually directly - * subclassed. Instead, you subclass one of the abstract classes that - * support different styles of fork/join processing. Normally, a - * concrete ForkJoinTask subclass declares fields comprising its - * parameters, established in a constructor, and then defines a - * compute method that somehow uses the control methods - * supplied by this base class. While these methods have - * public access, some of them may only be called from within - * other ForkJoinTasks. Attempts to invoke them in other contexts - * result in exceptions or errors including ClassCastException. The - * only way to invoke a "main" driver task is to submit it to a - * ForkJoinPool. Once started, this will usually in turn start other - * subtasks. + *

The primary method for awaiting completion and extracting + * results of a task is {@link #join}, but there are several variants: + * The {@link Future#get} methods support interruptible and/or timed + * waits for completion and report results using {@code Future} + * conventions. Method {@link #helpJoin} enables callers to actively + * execute other tasks while awaiting joins, which is sometimes more + * efficient but only applies when all subtasks are known to be + * strictly tree-structured. Method {@link #invoke} is semantically + * equivalent to {@code fork(); join()} but always attempts to + * begin execution in the current thread. The "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 {@code invokeAll} (available in multiple versions) + * 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. + * 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 {@code compute} + * method that somehow uses the control methods supplied by this base + * class. While these methods have {@code public} access (to allow + * instances of different task subclasses to call each 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. * - *

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 computational method that can be - * implemented in its subclasses. To support such extensions, - * instances of ForkJoinTasks maintain an atomically updated - * short representing user-defined control state. Control - * state is guaranteed initially to be zero, and to be negative upon - * completion, but may otherwise be used for any other control - * purposes, such as maintaining join counts. The {@link - * ForkJoinWorkerThread} class supports additional inspection and - * tuning methods that can be useful when developing extensions. + * 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 {@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 to - * be used in extensions such as remote execution frameworks. However, - * it is in general safe to serialize tasks only before or after, but + *

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. */ public abstract class ForkJoinTask implements Future, Serializable { + /** - * Status field holding all run status. We pack this into a single - * int both to minimize footprint overhead and to ensure atomicity - * (updates are via CAS). - * - * Status is initially zero, and takes on nonnegative values until + * Run control status bits packed into a single int to minimize + * footprint and to ensure atomicity (via CAS). Status is + * initially zero, and takes on nonnegative values until * completed, upon which status holds COMPLETED. CANCELLED, or * EXCEPTIONAL, which use the top 3 bits. Tasks undergoing * blocking waits by other threads have SIGNAL_MASK bits set -- @@ -111,7 +128,7 @@ 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 @@ -124,10 +141,10 @@ 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 @@ -136,7 +153,7 @@ 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(); @@ -144,15 +161,6 @@ public abstract class ForkJoinTask im (ForkJoinWorkerThread)t : null); } - /** - * Get pool of current worker thread, or null if not a worker thread - */ - static ForkJoinPool getWorkerPool() { - Thread t = Thread.currentThread(); - return ((t instanceof ForkJoinWorkerThread)? - ((ForkJoinWorkerThread)t).pool : null); - } - final boolean casStatus(int cmp, int val) { return _unsafe.compareAndSwapInt(this, statusOffset, cmp, val); } @@ -168,11 +176,12 @@ public abstract class ForkJoinTask im // 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) { - ForkJoinPool pool = getWorkerPool(); + ForkJoinPool pool = getPool(); if (pool != null) { int s; // Clear signal bits while setting completion status do;while ((s = status) >= 0 && !casStatus(s, completion)); @@ -247,9 +256,10 @@ public abstract class ForkJoinTask im /** * Sets status to indicate there is joiner, then waits for join, * surrounded with pool notifications. + * * @return status upon exit */ - final int awaitDone(ForkJoinWorkerThread w, boolean maintainParallelism) { + private int awaitDone(ForkJoinWorkerThread w, boolean maintainParallelism) { ForkJoinPool pool = w == null? null : w.pool; int s; while ((s = status) >= 0) { @@ -268,7 +278,7 @@ public abstract class ForkJoinTask im * Timed version of awaitDone * @return status upon exit */ - final int awaitDone(ForkJoinWorkerThread w, long nanos) { + private int awaitDone(ForkJoinWorkerThread w, long nanos) { ForkJoinPool pool = w == null? null : w.pool; int s; while ((s = status) >= 0) { @@ -289,7 +299,7 @@ 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) { @@ -300,7 +310,7 @@ 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) { @@ -314,19 +324,16 @@ public abstract class ForkJoinTask im } } + /** + * Handles interruptions during waits. + */ private void onInterruptedWait() { - Thread t = Thread.currentThread(); - if (t instanceof ForkJoinWorkerThread) { - ForkJoinWorkerThread w = (ForkJoinWorkerThread)t; - if (w.isTerminating()) - cancelIgnoreExceptions(); - } - else { // re-interrupt - try { - t.interrupt(); - } catch (SecurityException ignore) { - } - } + ForkJoinWorkerThread w = getWorker(); + if (w == null) + Thread.currentThread().interrupt(); // re-interrupt + else if (w.isTerminating()) + cancelIgnoringExceptions(); + // else if FJworker, ignore interrupt } // Recording and reporting exceptions @@ -337,7 +344,8 @@ 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) { @@ -350,7 +358,7 @@ 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() @@ -370,7 +378,7 @@ 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 { @@ -391,7 +399,8 @@ 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() { @@ -409,7 +418,7 @@ 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) { @@ -425,8 +434,9 @@ 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() { @@ -442,24 +452,35 @@ public abstract class ForkJoinTask im } /** - * Cancel, ignoring any exceptions it throws + * Cancels, ignoring any exceptions it throws. */ - final void cancelIgnoreExceptions() { + final void cancelIgnoringExceptions() { try { cancel(false); } catch(Throwable ignore) { } } + /** + * Main implementation of helpJoin + */ + private int busyJoin(ForkJoinWorkerThread w) { + int s; + ForkJoinTask t; + while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null) + t.quietlyExec(); + return (s >= 0)? awaitDone(w, false) : s; // block if no work + } + // public methods /** * Arranges to asynchronously execute this task. While it is not * necessarily enforced, it is a usage error to fork a task more * than once unless it has completed and been reinitialized. This - * method may be invoked only from within other ForkJoinTask + * method may be invoked only from within ForkJoinTask * computations. Attempts to invoke in other contexts result in - * exceptions or errors including ClassCastException. + * exceptions or errors possibly including ClassCastException. */ public final void fork() { ((ForkJoinWorkerThread)(Thread.currentThread())).pushTask(this); @@ -467,7 +488,7 @@ 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. * @@ -480,43 +501,12 @@ public abstract class ForkJoinTask im return getRawResult(); } - public final V get() throws InterruptedException, ExecutionException { - ForkJoinWorkerThread w = getWorker(); - if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke()) - awaitDone(w, true); - return reportFutureResult(); - } - - public final V get(long timeout, TimeUnit unit) - throws InterruptedException, ExecutionException, TimeoutException { - ForkJoinWorkerThread w = getWorker(); - if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke()) - awaitDone(w, unit.toNanos(timeout)); - return reportTimedFutureResult(); - } - /** - * 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 - * current task and that of any other task that might be executed - * while helping. (This usually holds for pure divide-and-conquer - * tasks). - * @return the computed result - */ - public final V helpJoin() { - ForkJoinWorkerThread w = (ForkJoinWorkerThread)(Thread.currentThread()); - if (status < 0 || !w.unpushTask(this) || !tryExec()) - reportException(w.helpJoinTask(this)); - return getRawResult(); - } - - /** - * Performs this task, awaits its completion if necessary, and - * return its result. + * 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() { @@ -527,45 +517,122 @@ public abstract class ForkJoinTask im } /** - * Joins this task, without returning its result or throwing an - * exception. This method may be useful when processing - * collections of tasks when some have been cancelled or otherwise - * known to have aborted. + * 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 + * 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 */ - public final void quietlyJoin() { - if (status >= 0) { - ForkJoinWorkerThread w = getWorker(); - if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke()) - awaitDone(w, true); - } + public static void invokeAll(ForkJoinTaskt1, ForkJoinTask t2) { + t2.fork(); + t1.invoke(); + t2.join(); } /** - * Possibly executes other tasks until this task is ready. + * 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. + * + * @param tasks the array of tasks + * @throws NullPointerException if tasks or any element are null + * @throws RuntimeException or Error if any task did so */ - public final void quietlyHelpJoin() { - if (status >= 0) { - ForkJoinWorkerThread w = - (ForkJoinWorkerThread)(Thread.currentThread()); - if (!w.unpushTask(this) || !tryQuietlyInvoke()) - w.helpJoinTask(this); + public static void invokeAll(ForkJoinTask... tasks) { + Throwable ex = null; + int last = tasks.length - 1; + for (int i = last; i >= 0; --i) { + ForkJoinTask t = tasks[i]; + if (t == null) { + if (ex == null) + ex = new NullPointerException(); + } + else if (i != 0) + t.fork(); + else { + t.quietlyInvoke(); + if (ex == null) + ex = t.getException(); + } } + for (int i = 1; i <= last; ++i) { + ForkJoinTask t = tasks[i]; + if (t != null) { + if (ex != null) + t.cancel(false); + else { + t.quietlyJoin(); + if (ex == null) + ex = t.getException(); + } + } + } + if (ex != null) + rethrowException(ex); } /** - * Performs this task and awaits its completion if necessary, - * without returning its result or throwing an exception. This - * method may be useful when processing collections of tasks when - * some have been cancelled or otherwise known to have aborted. + * 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. Attempts to invoke in other contexts result 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 */ - public final void quietlyInvoke() { - if (status >= 0 && !tryQuietlyInvoke()) - quietlyJoin(); + public static void invokeAll(Collection> tasks) { + if (!(tasks instanceof List)) { + invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()])); + return; + } + List> ts = + (List>)tasks; + Throwable ex = null; + int last = ts.size() - 1; + for (int i = last; i >= 0; --i) { + ForkJoinTask t = ts.get(i); + if (t == null) { + if (ex == null) + ex = new NullPointerException(); + } + else if (i != 0) + t.fork(); + else { + t.quietlyInvoke(); + if (ex == null) + ex = t.getException(); + } + } + for (int i = 1; i <= last; ++i) { + ForkJoinTask t = ts.get(i); + if (t != null) { + if (ex != null) + t.cancel(false); + else { + t.quietlyJoin(); + if (ex == null) + ex = t.getException(); + } + } + } + if (ex != null) + rethrowException(ex); } /** * 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() { @@ -574,6 +641,7 @@ public abstract class ForkJoinTask im /** * Returns true if this task was cancelled. + * * @return true if this task was cancelled */ public final boolean isCancelled() { @@ -581,37 +649,14 @@ public abstract class ForkJoinTask im } /** - * 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 completedAbnormally() { - return (status & COMPLETION_MASK) < NORMAL; - } - - /** - * 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() { - int s = status & COMPLETION_MASK; - if (s >= NORMAL) - return null; - if (s == CANCELLED) - return new CancellationException(); - return exceptionMap.get(this); - } - - /** * Asserts that the results of this task's computation will not be - * used. If a cancellation occurs before this task is processed, - * then its compute method will not be executed, - * 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. * @@ -622,7 +667,7 @@ 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(someException). + * invoke {@code completeExceptionally}. * * @param mayInterruptIfRunning this value is ignored in the * default implementation because tasks are not in general @@ -636,13 +681,40 @@ public abstract class ForkJoinTask im } /** + * 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() { + return (status & COMPLETION_MASK) < NORMAL; + } + + /** + * 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() { + int s = status & COMPLETION_MASK; + if (s >= NORMAL) + return null; + if (s == CANCELLED) + return new CancellationException(); + return exceptionMap.get(this); + } + + /** * 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. This - * method is overridable, but overridden versions must invoke - * super implementation to maintain guarantees. + * 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 {@code super} + * implementation to maintain guarantees. + * * @param ex the exception to throw. If this exception is * not a RuntimeException or Error, the actual exception thrown * will be a RuntimeException with cause ex. @@ -655,12 +727,15 @@ 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. + * 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 {@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 { @@ -672,143 +747,80 @@ public abstract class ForkJoinTask im setNormalCompletion(); } - /** - * Resets the internal bookkeeping state of this task, allowing a - * subsequent 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, and are - * almost surely wrong. This method may be useful when executing - * pre-constructed trees of subtasks in loops. - */ - public void reinitialize() { - if ((status & COMPLETION_MASK) == EXCEPTIONAL) - exceptionMap.remove(this); - status = 0; + public final V get() throws InterruptedException, ExecutionException { + ForkJoinWorkerThread w = getWorker(); + if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke()) + awaitDone(w, true); + return reportFutureResult(); + } + + public final V get(long timeout, TimeUnit unit) + throws InterruptedException, ExecutionException, TimeoutException { + ForkJoinWorkerThread w = getWorker(); + if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke()) + awaitDone(w, unit.toNanos(timeout)); + return reportTimedFutureResult(); } /** - * Tries to unschedule this task for execution. This method will - * typically succeed if this task is the next task that would be - * executed by the current thread, and will typically fail (return - * false) otherwise. This method may be useful when arranging - * faster local processing of tasks that could have been, but were - * not, stolen. - * @return true if unforked + * Possibly executes other tasks until this task is ready, then + * returns the result of the computation. This method may be more + * efficient than {@code join}, but is only applicable when + * there are no potential dependencies between continuation of the + * current task and that of any other task that might be executed + * while helping. (This usually holds for pure divide-and-conquer + * tasks). This method may be invoked only from within + * ForkJoinTask computations. Attempts to invoke in other contexts + * result in exceptions or errors possibly including ClassCastException. + * + * @return the computed result */ - public boolean tryUnfork() { - return ((ForkJoinWorkerThread)(Thread.currentThread())).unpushTask(this); + public final V helpJoin() { + ForkJoinWorkerThread w = (ForkJoinWorkerThread)(Thread.currentThread()); + if (status < 0 || !w.unpushTask(this) || !tryExec()) + reportException(busyJoin(w)); + return getRawResult(); } /** - * Forks both tasks, returning when isDone holds for both - * of them or an exception is encountered. This method may be - * invoked only from within other ForkJoinTask + * 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 result in - * exceptions or errors 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. + * exceptions or errors possibly including ClassCastException. */ - public static void invokeAll(ForkJoinTaskt1, ForkJoinTask t2) { - t2.fork(); - t1.invoke(); - t2.join(); + public final void quietlyHelpJoin() { + if (status >= 0) { + ForkJoinWorkerThread w = + (ForkJoinWorkerThread)(Thread.currentThread()); + if (!w.unpushTask(this) || !tryQuietlyInvoke()) + busyJoin(w); + } } /** - * Forks the given tasks, returning when isDone holds for - * all of them. If any task encounters an exception, others may be - * cancelled. This method may be invoked only from within other - * ForkJoinTask computations. Attempts to invoke in other contexts - * result in exceptions or errors 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. + * Joins this task, without returning its result or throwing an + * exception. This method may be useful when processing + * collections of tasks when some have been cancelled or otherwise + * known to have aborted. */ - public static void invokeAll(ForkJoinTask... tasks) { - Throwable ex = null; - int last = tasks.length - 1; - for (int i = last; i >= 0; --i) { - ForkJoinTask t = tasks[i]; - if (t == null) { - if (ex == null) - ex = new NullPointerException(); - } - else if (i != 0) - t.fork(); - else { - t.quietlyInvoke(); - if (ex == null) - ex = t.getException(); - } - } - for (int i = 1; i <= last; ++i) { - ForkJoinTask t = tasks[i]; - if (t != null) { - if (ex != null) - t.cancel(false); - else { - t.quietlyJoin(); - if (ex == null) - ex = t.getException(); - } - } + public final void quietlyJoin() { + if (status >= 0) { + ForkJoinWorkerThread w = getWorker(); + if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke()) + awaitDone(w, true); } - if (ex != null) - rethrowException(ex); } /** - * Forks all tasks in the collection, returning when - * isDone holds for all of them. If any task encounters - * an exception, others may be cancelled. This method may be - * invoked only from within other ForkJoinTask - * computations. Attempts to invoke in other contexts result in - * exceptions or errors 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. + * Commences performing this task and awaits its completion if + * necessary, without returning its result or throwing an + * exception. This method may be useful when processing + * collections of tasks when some have been cancelled or otherwise + * known to have aborted. */ - public static void invokeAll(Collection> tasks) { - if (!(tasks instanceof List)) { - invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()])); - return; - } - List> ts = - (List>)tasks; - Throwable ex = null; - int last = ts.size() - 1; - for (int i = last; i >= 0; --i) { - ForkJoinTask t = ts.get(i); - if (t == null) { - if (ex == null) - ex = new NullPointerException(); - } - else if (i != 0) - t.fork(); - else { - t.quietlyInvoke(); - if (ex == null) - ex = t.getException(); - } - } - for (int i = 1; i <= last; ++i) { - ForkJoinTask t = ts.get(i); - if (t != null) { - if (ex != null) - t.cancel(false); - else { - t.quietlyJoin(); - if (ex == null) - ex = t.getException(); - } - } - } - if (ex != null) - rethrowException(ex); + public final void quietlyInvoke() { + if (status >= 0 && !tryQuietlyInvoke()) + quietlyJoin(); } /** @@ -823,30 +835,89 @@ public abstract class ForkJoinTask im } /** - * Returns a estimate of how many more locally queued tasks are + * 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, and are + * almost surely wrong. This method may be useful when executing + * pre-constructed trees of subtasks in loops. + */ + public void reinitialize() { + if ((status & COMPLETION_MASK) == EXCEPTIONAL) + exceptionMap.remove(this); + status = 0; + } + + /** + * Returns the pool hosting the current task execution, or null + * if this task is executing outside of any pool. + * + * @return the pool, or null if none + */ + public static ForkJoinPool getPool() { + Thread t = Thread.currentThread(); + return ((t instanceof ForkJoinWorkerThread)? + ((ForkJoinWorkerThread)t).pool : null); + } + + /** + * 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. + * + * @return true if unforked + */ + public boolean tryUnfork() { + return ((ForkJoinWorkerThread)(Thread.currentThread())).unpushTask(this); + } + + /** + * Returns an estimate of the number of tasks that have been + * forked by the current worker thread but not yet executed. This + * value may be useful for heuristic decisions about whether to + * fork other tasks. + * + * @return the number of tasks + */ + public static int getQueuedTaskCount() { + return ((ForkJoinWorkerThread)(Thread.currentThread())). + getQueueSize(); + } + + /** + * Returns an estimate of how many more locally queued tasks are * held by the current worker thread than there are other worker - * threads that might want to steal them. This value may be - * useful for heuristic decisions about whether to fork other - * tasks. In many usages of ForkJoinTasks, at steady state, each - * worker should aim to maintain a small constant surplus (for - * example, 3) of tasks, and to process computations locally if - * this threshold is exceeded. + * threads that might steal them. This value may be useful for + * heuristic decisions about whether to fork other tasks. In many + * usages of ForkJoinTasks, at steady state, each worker should + * aim to maintain a small constant surplus (for example, 3) of + * tasks, and to process computations locally if this threshold is + * exceeded. + * * @return the surplus number of tasks, which may be negative */ - public static int surplus() { + public static int getSurplusQueuedTaskCount() { return ((ForkJoinWorkerThread)(Thread.currentThread())) .getEstimatedSurplusTaskCount(); } - // Extension kit + // Extension methods /** - * Returns the result that would be returned by join, 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 {@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(); @@ -865,13 +936,65 @@ 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 */ 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 + * 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. Attempts to invoke in other contexts result in + * exceptions or errors possibly including ClassCastException. + * + * @return the next task, or null if none are available + */ + protected static ForkJoinTask peekNextLocalTask() { + return ((ForkJoinWorkerThread)(Thread.currentThread())).peekTask(); + } + + /** + * Unschedules and returns, without executing, the next task + * queued by the current thread but not yet executed. This method + * is designed primarily to support extensions, and is unlikely to + * be useful otherwise. This method may be invoked only from + * within ForkJoinTask computations. Attempts to invoke in other + * contexts result in exceptions or errors possibly including + * ClassCastException. + * + * @return the next task, or null if none are available + */ + protected static ForkJoinTask pollNextLocalTask() { + return ((ForkJoinWorkerThread)(Thread.currentThread())).pollLocalTask(); + } + + /** + * Unschedules and returns, without executing, the next task + * queued by the current thread but not yet executed, if one is + * available, or if not available, a task that was forked by some + * other thread, if available. Availability may be transient, so a + * {@code null} result does not necessarily imply quiescence + * of the pool this task is operating in. This method is designed + * primarily to support extensions, and is unlikely to be useful + * otherwise. This method may be invoked only from within + * ForkJoinTask computations. Attempts to invoke in other contexts + * result in exceptions or errors possibly including + * ClassCastException. + * + * @return a task, or null if none are available + */ + protected static ForkJoinTask pollTask() { + return ((ForkJoinWorkerThread)(Thread.currentThread())). + pollTask(); + } + // Serialization support private static final long serialVersionUID = -7721805057305804111L; @@ -880,7 +1003,7 @@ 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) @@ -891,34 +1014,59 @@ public abstract class ForkJoinTask im /** * Reconstitute the instance from a stream. + * * @param s the stream */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { s.defaultReadObject(); - // status &= ~INTERNAL_SIGNAL_MASK; // todo: define policy + status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts + status |= EXTERNAL_SIGNAL; // conservatively set external signal Object ex = s.readObject(); if (ex != null) setDoneExceptionally((Throwable)ex); } // Temporary Unsafe mechanics for preliminary release + private static Unsafe getUnsafe() throws Throwable { + try { + return Unsafe.getUnsafe(); + } catch (SecurityException se) { + try { + return java.security.AccessController.doPrivileged + (new java.security.PrivilegedExceptionAction() { + public Unsafe run() throws Exception { + return getUnsafePrivileged(); + }}); + } catch (java.security.PrivilegedActionException e) { + throw 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 { - if (ForkJoinTask.class.getClassLoader() != null) { - Field f = Unsafe.class.getDeclaredField("theUnsafe"); - f.setAccessible(true); - _unsafe = (Unsafe)f.get(null); - } - else - _unsafe = Unsafe.getUnsafe(); - statusOffset = _unsafe.objectFieldOffset - (ForkJoinTask.class.getDeclaredField("status")); - } catch (Exception ex) { throw new Error(ex); } + _unsafe = getUnsafe(); + statusOffset = fieldOffset("status"); + } catch (Throwable e) { + throw new RuntimeException("Could not initialize intrinsics", e); + } } }