/* * Written by Doug Lea with assistance from members of JCP JSR-166 * Expert Group and released to the public domain, as explained at * http://creativecommons.org/licenses/publicdomain */ package jsr166y; import java.io.Serializable; import java.util.*; import java.util.concurrent.*; import java.util.concurrent.atomic.*; import sun.misc.Unsafe; import java.lang.reflect.*; /** * 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. * *

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 * 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 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 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: * The {@link Future#get} methods support interruptible and/or timed * waits for completion and report results using 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 * 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) * 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 compute * method that somehow uses the control methods supplied by this base * class. While these methods have 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 including ClassCastException. * *

Most base support methods are 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, * possibly relying on other protected methods provided * by this class. * *

ForkJoinTasks should perform relatively small amounts of * computations, othewise 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 * and internal task maintenance overhead may overwhelm processing. * *

ForkJoinTasks are 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 { /** * 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 -- * bit 15 for external (nonFJ) waits, and the rest a count of * waiting FJ threads. (This representation relies on * ForkJoinPool max thread limits). Completion of a stolen task * with SIGNAL_MASK bits set awakens waiter via notifyAll. Even * though suboptimal for some purposes, we use basic builtin * wait/notify to take advantage of "monitor inflation" in JVMs * that we would otherwise need to emulate to avoid adding further * per-task bookkeeping overhead. Note that bits 16-28 are * currently unused. Also value 0x80000000 is available as spare * completion value. */ volatile int status; // accessed directy by pool and workers static final int COMPLETION_MASK = 0xe0000000; static final int NORMAL = 0xe0000000; // == mask static final int CANCELLED = 0xc0000000; static final int EXCEPTIONAL = 0xa0000000; static final int SIGNAL_MASK = 0x0000ffff; static final int INTERNAL_SIGNAL_MASK = 0x00007fff; static final int EXTERNAL_SIGNAL = 0x00008000; // top bit of low word /** * 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 * that cancellation exceptions don't appear in the table, but are * instead recorded as status values. * Todo: Use ConcurrentReferenceHashMap */ static final Map, Throwable> exceptionMap = Collections.synchronizedMap (new WeakHashMap, Throwable>()); // within-package utilities /** * Get current worker thread, or null if not a worker thread */ static ForkJoinWorkerThread getWorker() { Thread t = Thread.currentThread(); return ((t instanceof ForkJoinWorkerThread)? (ForkJoinWorkerThread)t : null); } final boolean casStatus(int cmp, int val) { return _unsafe.compareAndSwapInt(this, statusOffset, cmp, val); } /** * Workaround for not being able to rethrow unchecked exceptions. */ static void rethrowException(Throwable ex) { if (ex != null) _unsafe.throwException(ex); } // Setting completion status /** * Mark completion and wake up threads waiting to join this task. * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL */ final void setCompletion(int completion) { ForkJoinPool pool = getPool(); if (pool != null) { int s; // Clear signal bits while setting completion status do;while ((s = status) >= 0 && !casStatus(s, completion)); if ((s & SIGNAL_MASK) != 0) { if ((s &= INTERNAL_SIGNAL_MASK) != 0) pool.updateRunningCount(s); synchronized(this) { notifyAll(); } } } else externallySetCompletion(completion); } /** * Version of setCompletion for non-FJ threads. Leaves signal * bits for unblocked threads to adjust, and always notifies. */ private void externallySetCompletion(int completion) { int s; do;while ((s = status) >= 0 && !casStatus(s, (s & SIGNAL_MASK) | completion)); synchronized(this) { notifyAll(); } } /** * Sets status to indicate normal completion */ 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)) setCompletion(NORMAL); } // internal waiting and notification /** * Performs the actual monitor wait for awaitDone */ private void doAwaitDone() { // Minimize lock bias and in/de-flation effects by maximizing // chances of waiting inside sync try { while (status >= 0) synchronized(this) { if (status >= 0) wait(); } } catch (InterruptedException ie) { onInterruptedWait(); } } /** * Performs the actual monitor wait for awaitDone */ private void doAwaitDone(long startTime, long nanos) { synchronized(this) { try { while (status >= 0) { long nt = nanos - System.nanoTime() - startTime; if (nt <= 0) break; wait(nt / 1000000, (int)(nt % 1000000)); } } catch (InterruptedException ie) { onInterruptedWait(); } } } // Awaiting completion /** * 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) { ForkJoinPool pool = w == null? null : w.pool; int s; while ((s = status) >= 0) { if (casStatus(s, pool == null? s|EXTERNAL_SIGNAL : s+1)) { if (pool == null || !pool.preJoin(this, maintainParallelism)) doAwaitDone(); if (((s = status) & INTERNAL_SIGNAL_MASK) != 0) adjustPoolCountsOnUnblock(pool); break; } } return s; } /** * Timed version of awaitDone * @return status upon exit */ final int awaitDone(ForkJoinWorkerThread w, long nanos) { ForkJoinPool pool = w == null? null : w.pool; int s; while ((s = status) >= 0) { if (casStatus(s, pool == null? s|EXTERNAL_SIGNAL : s+1)) { long startTime = System.nanoTime(); if (pool == null || !pool.preJoin(this, false)) doAwaitDone(startTime, nanos); if ((s = status) >= 0) { adjustPoolCountsOnCancelledWait(pool); s = status; } if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0) adjustPoolCountsOnUnblock(pool); break; } } return s; } /** * Notify pool that thread is unblocked. Called by signalled * threads when woken by non-FJ threads (which is atypical). */ private void adjustPoolCountsOnUnblock(ForkJoinPool pool) { int s; do;while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK)); if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0) pool.updateRunningCount(s); } /** * Notify pool to adjust counts on cancelled or timed out wait */ private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) { if (pool != null) { int s; while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) { if (casStatus(s, s - 1)) { pool.updateRunningCount(1); break; } } } } /** * Handle interruptions during waits. */ private void onInterruptedWait() { ForkJoinWorkerThread w = getWorker(); if (w == null) Thread.currentThread().interrupt(); // re-interrupt else if (w.isTerminating()) cancelIgnoreExceptions(); // else if FJworker, ignore interrupt } // Recording and reporting exceptions private void setDoneExceptionally(Throwable rex) { exceptionMap.put(this, rex); setCompletion(EXCEPTIONAL); } /** * Throws the exception associated with status s; * @throws the exception */ private void reportException(int s) { if ((s &= COMPLETION_MASK) < NORMAL) { if (s == CANCELLED) throw new CancellationException(); else rethrowException(exceptionMap.get(this)); } } /** * Returns result or throws exception using j.u.c.Future conventions * Only call when isDone known to be true. */ private V reportFutureResult() throws ExecutionException, InterruptedException { int s = status & COMPLETION_MASK; if (s < NORMAL) { Throwable ex; if (s == CANCELLED) throw new CancellationException(); if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) throw new ExecutionException(ex); if (Thread.interrupted()) throw new InterruptedException(); } return getRawResult(); } /** * Returns result or throws exception using j.u.c.Future conventions * with timeouts */ private V reportTimedFutureResult() throws InterruptedException, ExecutionException, TimeoutException { Throwable ex; int s = status & COMPLETION_MASK; if (s == NORMAL) return getRawResult(); if (s == CANCELLED) throw new CancellationException(); if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) throw new ExecutionException(ex); if (Thread.interrupted()) throw new InterruptedException(); throw new TimeoutException(); } // internal execution methods /** * Calls exec, recording completion, and rethrowing exception if * encountered. Caller should normally check status before calling * @return true if completed normally */ private boolean tryExec() { try { // try block must contain only call to exec if (!exec()) return false; } catch (Throwable rex) { setDoneExceptionally(rex); rethrowException(rex); return false; // not reached } setNormalCompletion(); return true; } /** * Main execution method used by worker threads. Invokes * base computation unless already complete */ final void quietlyExec() { if (status >= 0) { try { if (!exec()) return; } catch(Throwable rex) { setDoneExceptionally(rex); return; } setNormalCompletion(); } } /** * Calls exec, recording but not rethrowing exception * Caller should normally check status before calling * @return true if completed normally */ private boolean tryQuietlyInvoke() { try { if (!exec()) return false; } catch (Throwable rex) { setDoneExceptionally(rex); return false; } setNormalCompletion(); return true; } /** * Cancel, ignoring any exceptions it throws */ final void cancelIgnoreExceptions() { try { cancel(false); } catch(Throwable ignore) { } } // 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 ForkJoinTask * computations. Attempts to invoke in other contexts result in * exceptions or errors including ClassCastException. */ public final void fork() { ((ForkJoinWorkerThread)(Thread.currentThread())).pushTask(this); } /** * Returns the result of the computation when it is ready. * This method differs from get in that abnormal * completion results in RuntimeExceptions or Errors, not * ExecutionExceptions. * * @return the computed result */ public final V join() { ForkJoinWorkerThread w = getWorker(); if (w == null || status < 0 || !w.unpushTask(this) || !tryExec()) reportException(awaitDone(w, true)); 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(); } /** * 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. * @return the computed result */ public final V invoke() { if (status >= 0 && tryExec()) return getRawResult(); else return join(); } /** * Forks both tasks, returning when 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 * 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 static void invokeAll(ForkJoinTaskt1, ForkJoinTask t2) { t2.fork(); t1.invoke(); t2.join(); } /** * 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 * 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. */ 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); } /** * 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 ForkJoinTask * computations. Attempts to invoke in other contexts resul!t 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. */ 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() { return status < 0; } /** * Returns true if this task was cancelled. * @return true if this task was cancelled */ public final boolean isCancelled() { return (status & COMPLETION_MASK) == 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() { 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 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 * cancellation races with completion, there are no guarantees * about whether isCancelled will report true, whether * 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. * *

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. * * @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 */ public boolean cancel(boolean mayInterruptIfRunning) { setCompletion(CANCELLED); return (status & COMPLETION_MASK) == CANCELLED; } /** * 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 * 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 * 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. */ public void completeExceptionally(Throwable ex) { setDoneExceptionally((ex instanceof RuntimeException) || (ex instanceof Error)? ex : new RuntimeException(ex)); } /** * Completes this task, and if not already aborted or cancelled, * returning a null result upon 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 * implementation to maintain guarantees. * * @param value the result value for this task. */ public void complete(V value) { try { setRawResult(value); } catch(Throwable rex) { setDoneExceptionally(rex); return; } setNormalCompletion(); } /** * 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). This method may be invoked only from within * ForkJoinTask computations. Attempts to invoke in other contexts * resul!t in exceptions or errors including ClassCastException. * @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(); } /** * 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 including ClassCastException. */ public final void quietlyHelpJoin() { if (status >= 0) { ForkJoinWorkerThread w = (ForkJoinWorkerThread)(Thread.currentThread()); if (!w.unpushTask(this) || !tryQuietlyInvoke()) w.helpJoinTask(this); } } /** * 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 final void quietlyJoin() { if (status >= 0) { ForkJoinWorkerThread w = getWorker(); if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke()) awaitDone(w, true); } } /** * 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 final void quietlyInvoke() { if (status >= 0 && !tryQuietlyInvoke()) quietlyJoin(); } /** * 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; } /** * 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 including ClassCastException. * @return true if unforked */ public boolean tryUnfork() { return ((ForkJoinWorkerThread)(Thread.currentThread())).unpushTask(this); } /** * 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. */ public static void helpQuiesce() { ((ForkJoinWorkerThread)(Thread.currentThread())). helpQuiescePool(); } /** * 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 a 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 * usages of ForkJoinTasks, at steady state, each worker should * aim to maintain a small constant surplus (for example, 3) of * tasks, and to process computations locally if this threshold is * exceeded. * @return the surplus number of tasks, which may be negative */ public static int getSurplusQueuedTaskCount() { return ((ForkJoinWorkerThread)(Thread.currentThread())) .getEstimatedSurplusTaskCount(); } // Extension methods /** * Returns the result that would be returned by 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. */ public abstract V getRawResult(); /** * Forces the given value to be returned as a result. This method * is designed to support extensions, and should not in general be * called otherwise. * * @param value the value */ protected abstract void setRawResult(V value); /** * Immediately performs the base action of this task. This method * is designed to support extensions, and should not in general be * 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 * 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 most * recently forked 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. * * @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 task most * recently forked by the current thread but not yet executed. * This method is designed primarily to support extensions, * and is unlikely to be useful otherwise. * * @return the next task, or null if none are available */ protected static ForkJoinTask pollNextLocalTask() { return ((ForkJoinWorkerThread)(Thread.currentThread())).popTask(); } /** * Unschedules and returns, without executing, the task most * recently forked 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 of the pool this task is operating in. * This method is designed primarily to support extensions, * and is unlikely to be useful otherwise. * * @return a task, or null if none are available */ protected static ForkJoinTask pollTask() { return ((ForkJoinWorkerThread)(Thread.currentThread())). getLocalOrStolenTask(); } // Serialization support private static final long serialVersionUID = -7721805057305804111L; /** * Save the state to a stream. * * @serialData the current run status and the exception thrown * during execution, or null if none. * @param s the stream */ private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { s.defaultWriteObject(); s.writeObject(getException()); } /** * 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; // 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 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); } } }