jaroslav@1890: /*
jaroslav@1890:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@1890:  *
jaroslav@1890:  * This code is free software; you can redistribute it and/or modify it
jaroslav@1890:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@1890:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@1890:  * particular file as subject to the "Classpath" exception as provided
jaroslav@1890:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@1890:  *
jaroslav@1890:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@1890:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@1890:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@1890:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@1890:  * accompanied this code).
jaroslav@1890:  *
jaroslav@1890:  * You should have received a copy of the GNU General Public License version
jaroslav@1890:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@1890:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@1890:  *
jaroslav@1890:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@1890:  * or visit www.oracle.com if you need additional information or have any
jaroslav@1890:  * questions.
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: /*
jaroslav@1890:  * This file is available under and governed by the GNU General Public
jaroslav@1890:  * License version 2 only, as published by the Free Software Foundation.
jaroslav@1890:  * However, the following notice accompanied the original version of this
jaroslav@1890:  * file:
jaroslav@1890:  *
jaroslav@1890:  * Written by Doug Lea with assistance from members of JCP JSR-166
jaroslav@1890:  * Expert Group and released to the public domain, as explained at
jaroslav@1890:  * http://creativecommons.org/publicdomain/zero/1.0/
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: package java.util.concurrent;
jaroslav@1890: 
jaroslav@1890: import java.io.Serializable;
jaroslav@1890: import java.util.Collection;
jaroslav@1890: import java.util.Collections;
jaroslav@1890: import java.util.List;
jaroslav@1890: import java.util.RandomAccess;
jaroslav@1890: import java.util.Map;
jaroslav@1890: import java.lang.ref.WeakReference;
jaroslav@1890: import java.lang.ref.ReferenceQueue;
jaroslav@1890: import java.util.concurrent.Callable;
jaroslav@1890: import java.util.concurrent.CancellationException;
jaroslav@1890: import java.util.concurrent.ExecutionException;
jaroslav@1890: import java.util.concurrent.Executor;
jaroslav@1890: import java.util.concurrent.ExecutorService;
jaroslav@1890: import java.util.concurrent.Future;
jaroslav@1890: import java.util.concurrent.RejectedExecutionException;
jaroslav@1890: import java.util.concurrent.RunnableFuture;
jaroslav@1890: import java.util.concurrent.TimeUnit;
jaroslav@1890: import java.util.concurrent.TimeoutException;
jaroslav@1890: import java.util.concurrent.locks.ReentrantLock;
jaroslav@1890: import java.lang.reflect.Constructor;
jaroslav@1890: 
jaroslav@1890: /**
jaroslav@1890:  * Abstract base class for tasks that run within a {@link ForkJoinPool}.
jaroslav@1890:  * A {@code ForkJoinTask} is a thread-like entity that is much
jaroslav@1890:  * lighter weight than a normal thread.  Huge numbers of tasks and
jaroslav@1890:  * subtasks may be hosted by a small number of actual threads in a
jaroslav@1890:  * ForkJoinPool, at the price of some usage limitations.
jaroslav@1890:  *
jaroslav@1890:  * <p>A "main" {@code ForkJoinTask} begins execution when submitted
jaroslav@1890:  * to a {@link ForkJoinPool}.  Once started, it will usually in turn
jaroslav@1890:  * start other subtasks.  As indicated by the name of this class,
jaroslav@1890:  * many programs using {@code ForkJoinTask} employ only methods
jaroslav@1890:  * {@link #fork} and {@link #join}, or derivatives such as {@link
jaroslav@1890:  * #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
jaroslav@1890:  * provides a number of other methods that can come into play in
jaroslav@1890:  * advanced usages, as well as extension mechanics that allow
jaroslav@1890:  * support of new forms of fork/join processing.
jaroslav@1890:  *
jaroslav@1890:  * <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
jaroslav@1890:  * The efficiency of {@code ForkJoinTask}s stems from a set of
jaroslav@1890:  * restrictions (that are only partially statically enforceable)
jaroslav@1890:  * reflecting their intended use as computational tasks calculating
jaroslav@1890:  * pure functions or operating on purely isolated objects.  The
jaroslav@1890:  * primary coordination mechanisms are {@link #fork}, that arranges
jaroslav@1890:  * asynchronous execution, and {@link #join}, that doesn't proceed
jaroslav@1890:  * until the task's result has been computed.  Computations should
jaroslav@1890:  * avoid {@code synchronized} methods or blocks, and should minimize
jaroslav@1890:  * other blocking synchronization apart from joining other tasks or
jaroslav@1890:  * using synchronizers such as Phasers that are advertised to
jaroslav@1890:  * cooperate with fork/join scheduling. Tasks should also not perform
jaroslav@1890:  * blocking IO, and should ideally access variables that are
jaroslav@1890:  * completely independent of those accessed by other running
jaroslav@1890:  * tasks. Minor breaches of these restrictions, for example using
jaroslav@1890:  * shared output streams, may be tolerable in practice, but frequent
jaroslav@1890:  * use may result in poor performance, and the potential to
jaroslav@1890:  * indefinitely stall if the number of threads not waiting for IO or
jaroslav@1890:  * other external synchronization becomes exhausted. This usage
jaroslav@1890:  * restriction is in part enforced by not permitting checked
jaroslav@1890:  * exceptions such as {@code IOExceptions} to be thrown. However,
jaroslav@1890:  * computations may still encounter unchecked exceptions, that are
jaroslav@1890:  * rethrown to callers attempting to join them. These exceptions may
jaroslav@1890:  * additionally include {@link RejectedExecutionException} stemming
jaroslav@1890:  * from internal resource exhaustion, such as failure to allocate
jaroslav@1890:  * internal task queues. Rethrown exceptions behave in the same way as
jaroslav@1890:  * regular exceptions, but, when possible, contain stack traces (as
jaroslav@1890:  * displayed for example using {@code ex.printStackTrace()}) of both
jaroslav@1890:  * the thread that initiated the computation as well as the thread
jaroslav@1890:  * actually encountering the exception; minimally only the latter.
jaroslav@1890:  *
jaroslav@1890:  * <p>The primary method for awaiting completion and extracting
jaroslav@1890:  * results of a task is {@link #join}, but there are several variants:
jaroslav@1890:  * The {@link Future#get} methods support interruptible and/or timed
jaroslav@1890:  * waits for completion and report results using {@code Future}
jaroslav@1890:  * conventions. Method {@link #invoke} is semantically
jaroslav@1890:  * equivalent to {@code fork(); join()} but always attempts to begin
jaroslav@1890:  * execution in the current thread. The "<em>quiet</em>" forms of
jaroslav@1890:  * these methods do not extract results or report exceptions. These
jaroslav@1890:  * may be useful when a set of tasks are being executed, and you need
jaroslav@1890:  * to delay processing of results or exceptions until all complete.
jaroslav@1890:  * Method {@code invokeAll} (available in multiple versions)
jaroslav@1890:  * performs the most common form of parallel invocation: forking a set
jaroslav@1890:  * of tasks and joining them all.
jaroslav@1890:  *
jaroslav@1890:  * <p>The execution status of tasks may be queried at several levels
jaroslav@1890:  * of detail: {@link #isDone} is true if a task completed in any way
jaroslav@1890:  * (including the case where a task was cancelled without executing);
jaroslav@1890:  * {@link #isCompletedNormally} is true if a task completed without
jaroslav@1890:  * cancellation or encountering an exception; {@link #isCancelled} is
jaroslav@1890:  * true if the task was cancelled (in which case {@link #getException}
jaroslav@1890:  * returns a {@link java.util.concurrent.CancellationException}); and
jaroslav@1890:  * {@link #isCompletedAbnormally} is true if a task was either
jaroslav@1890:  * cancelled or encountered an exception, in which case {@link
jaroslav@1890:  * #getException} will return either the encountered exception or
jaroslav@1890:  * {@link java.util.concurrent.CancellationException}.
jaroslav@1890:  *
jaroslav@1890:  * <p>The ForkJoinTask class is not usually directly subclassed.
jaroslav@1890:  * Instead, you subclass one of the abstract classes that support a
jaroslav@1890:  * particular style of fork/join processing, typically {@link
jaroslav@1890:  * RecursiveAction} for computations that do not return results, or
jaroslav@1890:  * {@link RecursiveTask} for those that do.  Normally, a concrete
jaroslav@1890:  * ForkJoinTask subclass declares fields comprising its parameters,
jaroslav@1890:  * established in a constructor, and then defines a {@code compute}
jaroslav@1890:  * method that somehow uses the control methods supplied by this base
jaroslav@1890:  * class. While these methods have {@code public} access (to allow
jaroslav@1890:  * instances of different task subclasses to call each other's
jaroslav@1890:  * methods), some of them may only be called from within other
jaroslav@1890:  * ForkJoinTasks (as may be determined using method {@link
jaroslav@1890:  * #inForkJoinPool}).  Attempts to invoke them in other contexts
jaroslav@1890:  * result in exceptions or errors, possibly including
jaroslav@1890:  * {@code ClassCastException}.
jaroslav@1890:  *
jaroslav@1890:  * <p>Method {@link #join} and its variants are appropriate for use
jaroslav@1890:  * only when completion dependencies are acyclic; that is, the
jaroslav@1890:  * parallel computation can be described as a directed acyclic graph
jaroslav@1890:  * (DAG). Otherwise, executions may encounter a form of deadlock as
jaroslav@1890:  * tasks cyclically wait for each other.  However, this framework
jaroslav@1890:  * supports other methods and techniques (for example the use of
jaroslav@1890:  * {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
jaroslav@1890:  * may be of use in constructing custom subclasses for problems that
jaroslav@1890:  * are not statically structured as DAGs.
jaroslav@1890:  *
jaroslav@1890:  * <p>Most base support methods are {@code final}, to prevent
jaroslav@1890:  * overriding of implementations that are intrinsically tied to the
jaroslav@1890:  * underlying lightweight task scheduling framework.  Developers
jaroslav@1890:  * creating new basic styles of fork/join processing should minimally
jaroslav@1890:  * implement {@code protected} methods {@link #exec}, {@link
jaroslav@1890:  * #setRawResult}, and {@link #getRawResult}, while also introducing
jaroslav@1890:  * an abstract computational method that can be implemented in its
jaroslav@1890:  * subclasses, possibly relying on other {@code protected} methods
jaroslav@1890:  * provided by this class.
jaroslav@1890:  *
jaroslav@1890:  * <p>ForkJoinTasks should perform relatively small amounts of
jaroslav@1890:  * computation. Large tasks should be split into smaller subtasks,
jaroslav@1890:  * usually via recursive decomposition. As a very rough rule of thumb,
jaroslav@1890:  * a task should perform more than 100 and less than 10000 basic
jaroslav@1890:  * computational steps, and should avoid indefinite looping. If tasks
jaroslav@1890:  * are too big, then parallelism cannot improve throughput. If too
jaroslav@1890:  * small, then memory and internal task maintenance overhead may
jaroslav@1890:  * overwhelm processing.
jaroslav@1890:  *
jaroslav@1890:  * <p>This class provides {@code adapt} methods for {@link Runnable}
jaroslav@1890:  * and {@link Callable}, that may be of use when mixing execution of
jaroslav@1890:  * {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
jaroslav@1890:  * of this form, consider using a pool constructed in <em>asyncMode</em>.
jaroslav@1890:  *
jaroslav@1890:  * <p>ForkJoinTasks are {@code Serializable}, which enables them to be
jaroslav@1890:  * used in extensions such as remote execution frameworks. It is
jaroslav@1890:  * sensible to serialize tasks only before or after, but not during,
jaroslav@1890:  * execution. Serialization is not relied on during execution itself.
jaroslav@1890:  *
jaroslav@1890:  * @since 1.7
jaroslav@1890:  * @author Doug Lea
jaroslav@1890:  */
jaroslav@1890: public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
jaroslav@1890: 
jaroslav@1890:     /*
jaroslav@1890:      * See the internal documentation of class ForkJoinPool for a
jaroslav@1890:      * general implementation overview.  ForkJoinTasks are mainly
jaroslav@1890:      * responsible for maintaining their "status" field amidst relays
jaroslav@1890:      * to methods in ForkJoinWorkerThread and ForkJoinPool. The
jaroslav@1890:      * methods of this class are more-or-less layered into (1) basic
jaroslav@1890:      * status maintenance (2) execution and awaiting completion (3)
jaroslav@1890:      * user-level methods that additionally report results. This is
jaroslav@1890:      * sometimes hard to see because this file orders exported methods
jaroslav@1890:      * in a way that flows well in javadocs.
jaroslav@1890:      */
jaroslav@1890: 
jaroslav@1890:     /*
jaroslav@1890:      * The status field holds run control status bits packed into a
jaroslav@1890:      * single int to minimize footprint and to ensure atomicity (via
jaroslav@1890:      * CAS).  Status is initially zero, and takes on nonnegative
jaroslav@1890:      * values until completed, upon which status holds value
jaroslav@1890:      * NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
jaroslav@1890:      * waits by other threads have the SIGNAL bit set.  Completion of
jaroslav@1890:      * a stolen task with SIGNAL set awakens any waiters via
jaroslav@1890:      * notifyAll. Even though suboptimal for some purposes, we use
jaroslav@1890:      * basic builtin wait/notify to take advantage of "monitor
jaroslav@1890:      * inflation" in JVMs that we would otherwise need to emulate to
jaroslav@1890:      * avoid adding further per-task bookkeeping overhead.  We want
jaroslav@1890:      * these monitors to be "fat", i.e., not use biasing or thin-lock
jaroslav@1890:      * techniques, so use some odd coding idioms that tend to avoid
jaroslav@1890:      * them.
jaroslav@1890:      */
jaroslav@1890: 
jaroslav@1890:     /** The run status of this task */
jaroslav@1890:     volatile int status; // accessed directly by pool and workers
jaroslav@1890:     private static final int NORMAL      = -1;
jaroslav@1890:     private static final int CANCELLED   = -2;
jaroslav@1890:     private static final int EXCEPTIONAL = -3;
jaroslav@1890:     private static final int SIGNAL      =  1;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Marks completion and wakes up threads waiting to join this task,
jaroslav@1890:      * also clearing signal request bits.
jaroslav@1890:      *
jaroslav@1890:      * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
jaroslav@1890:      * @return completion status on exit
jaroslav@1890:      */
jaroslav@1890:     private int setCompletion(int completion) {
jaroslav@1890:         for (int s;;) {
jaroslav@1890:             if ((s = status) < 0)
jaroslav@1890:                 return s;
jaroslav@1890:             if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
jaroslav@1890:                 if (s != 0)
jaroslav@1890:                     synchronized (this) { notifyAll(); }
jaroslav@1890:                 return completion;
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Tries to block a worker thread until completed or timed out.
jaroslav@1890:      * Uses Object.wait time argument conventions.
jaroslav@1890:      * May fail on contention or interrupt.
jaroslav@1890:      *
jaroslav@1890:      * @param millis if > 0, wait time.
jaroslav@1890:      */
jaroslav@1890:     final void tryAwaitDone(long millis) {
jaroslav@1890:         int s;
jaroslav@1890:         try {
jaroslav@1890:             if (((s = status) > 0 ||
jaroslav@1890:                  (s == 0 &&
jaroslav@1890:                   UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL))) &&
jaroslav@1890:                 status > 0) {
jaroslav@1890:                 synchronized (this) {
jaroslav@1890:                     if (status > 0)
jaroslav@1890:                         wait(millis);
jaroslav@1890:                 }
jaroslav@1890:             }
jaroslav@1890:         } catch (InterruptedException ie) {
jaroslav@1890:             // caller must check termination
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Blocks a non-worker-thread until completion.
jaroslav@1890:      * @return status upon completion
jaroslav@1890:      */
jaroslav@1890:     private int externalAwaitDone() {
jaroslav@1890:         int s;
jaroslav@1890:         if ((s = status) >= 0) {
jaroslav@1890:             boolean interrupted = false;
jaroslav@1890:             synchronized (this) {
jaroslav@1890:                 while ((s = status) >= 0) {
jaroslav@1890:                     if (s == 0)
jaroslav@1890:                         UNSAFE.compareAndSwapInt(this, statusOffset,
jaroslav@1890:                                                  0, SIGNAL);
jaroslav@1890:                     else {
jaroslav@1890:                         try {
jaroslav@1890:                             wait();
jaroslav@1890:                         } catch (InterruptedException ie) {
jaroslav@1890:                             interrupted = true;
jaroslav@1890:                         }
jaroslav@1890:                     }
jaroslav@1890:                 }
jaroslav@1890:             }
jaroslav@1890:             if (interrupted)
jaroslav@1890:                 Thread.currentThread().interrupt();
jaroslav@1890:         }
jaroslav@1890:         return s;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Blocks a non-worker-thread until completion or interruption or timeout.
jaroslav@1890:      */
jaroslav@1890:     private int externalInterruptibleAwaitDone(long millis)
jaroslav@1890:         throws InterruptedException {
jaroslav@1890:         int s;
jaroslav@1890:         if (Thread.interrupted())
jaroslav@1890:             throw new InterruptedException();
jaroslav@1890:         if ((s = status) >= 0) {
jaroslav@1890:             synchronized (this) {
jaroslav@1890:                 while ((s = status) >= 0) {
jaroslav@1890:                     if (s == 0)
jaroslav@1890:                         UNSAFE.compareAndSwapInt(this, statusOffset,
jaroslav@1890:                                                  0, SIGNAL);
jaroslav@1890:                     else {
jaroslav@1890:                         wait(millis);
jaroslav@1890:                         if (millis > 0L)
jaroslav@1890:                             break;
jaroslav@1890:                     }
jaroslav@1890:                 }
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890:         return s;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Primary execution method for stolen tasks. Unless done, calls
jaroslav@1890:      * exec and records status if completed, but doesn't wait for
jaroslav@1890:      * completion otherwise.
jaroslav@1890:      */
jaroslav@1890:     final void doExec() {
jaroslav@1890:         if (status >= 0) {
jaroslav@1890:             boolean completed;
jaroslav@1890:             try {
jaroslav@1890:                 completed = exec();
jaroslav@1890:             } catch (Throwable rex) {
jaroslav@1890:                 setExceptionalCompletion(rex);
jaroslav@1890:                 return;
jaroslav@1890:             }
jaroslav@1890:             if (completed)
jaroslav@1890:                 setCompletion(NORMAL); // must be outside try block
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Primary mechanics for join, get, quietlyJoin.
jaroslav@1890:      * @return status upon completion
jaroslav@1890:      */
jaroslav@1890:     private int doJoin() {
jaroslav@1890:         Thread t; ForkJoinWorkerThread w; int s; boolean completed;
jaroslav@1890:         if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
jaroslav@1890:             if ((s = status) < 0)
jaroslav@1890:                 return s;
jaroslav@1890:             if ((w = (ForkJoinWorkerThread)t).unpushTask(this)) {
jaroslav@1890:                 try {
jaroslav@1890:                     completed = exec();
jaroslav@1890:                 } catch (Throwable rex) {
jaroslav@1890:                     return setExceptionalCompletion(rex);
jaroslav@1890:                 }
jaroslav@1890:                 if (completed)
jaroslav@1890:                     return setCompletion(NORMAL);
jaroslav@1890:             }
jaroslav@1890:             return w.joinTask(this);
jaroslav@1890:         }
jaroslav@1890:         else
jaroslav@1890:             return externalAwaitDone();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Primary mechanics for invoke, quietlyInvoke.
jaroslav@1890:      * @return status upon completion
jaroslav@1890:      */
jaroslav@1890:     private int doInvoke() {
jaroslav@1890:         int s; boolean completed;
jaroslav@1890:         if ((s = status) < 0)
jaroslav@1890:             return s;
jaroslav@1890:         try {
jaroslav@1890:             completed = exec();
jaroslav@1890:         } catch (Throwable rex) {
jaroslav@1890:             return setExceptionalCompletion(rex);
jaroslav@1890:         }
jaroslav@1890:         if (completed)
jaroslav@1890:             return setCompletion(NORMAL);
jaroslav@1890:         else
jaroslav@1890:             return doJoin();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     // Exception table support
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Table of exceptions thrown by tasks, to enable reporting by
jaroslav@1890:      * callers. Because exceptions are rare, we don't directly keep
jaroslav@1890:      * them with task objects, but instead use a weak ref table.  Note
jaroslav@1890:      * that cancellation exceptions don't appear in the table, but are
jaroslav@1890:      * instead recorded as status values.
jaroslav@1890:      *
jaroslav@1890:      * Note: These statics are initialized below in static block.
jaroslav@1890:      */
jaroslav@1890:     private static final ExceptionNode[] exceptionTable;
jaroslav@1890:     private static final ReentrantLock exceptionTableLock;
jaroslav@1890:     private static final ReferenceQueue<Object> exceptionTableRefQueue;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Fixed capacity for exceptionTable.
jaroslav@1890:      */
jaroslav@1890:     private static final int EXCEPTION_MAP_CAPACITY = 32;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Key-value nodes for exception table.  The chained hash table
jaroslav@1890:      * uses identity comparisons, full locking, and weak references
jaroslav@1890:      * for keys. The table has a fixed capacity because it only
jaroslav@1890:      * maintains task exceptions long enough for joiners to access
jaroslav@1890:      * them, so should never become very large for sustained
jaroslav@1890:      * periods. However, since we do not know when the last joiner
jaroslav@1890:      * completes, we must use weak references and expunge them. We do
jaroslav@1890:      * so on each operation (hence full locking). Also, some thread in
jaroslav@1890:      * any ForkJoinPool will call helpExpungeStaleExceptions when its
jaroslav@1890:      * pool becomes isQuiescent.
jaroslav@1890:      */
jaroslav@1890:     static final class ExceptionNode extends WeakReference<ForkJoinTask<?>>{
jaroslav@1890:         final Throwable ex;
jaroslav@1890:         ExceptionNode next;
jaroslav@1890:         final long thrower;  // use id not ref to avoid weak cycles
jaroslav@1890:         ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
jaroslav@1890:             super(task, exceptionTableRefQueue);
jaroslav@1890:             this.ex = ex;
jaroslav@1890:             this.next = next;
jaroslav@1890:             this.thrower = Thread.currentThread().getId();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Records exception and sets exceptional completion.
jaroslav@1890:      *
jaroslav@1890:      * @return status on exit
jaroslav@1890:      */
jaroslav@1890:     private int setExceptionalCompletion(Throwable ex) {
jaroslav@1890:         int h = System.identityHashCode(this);
jaroslav@1890:         final ReentrantLock lock = exceptionTableLock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             expungeStaleExceptions();
jaroslav@1890:             ExceptionNode[] t = exceptionTable;
jaroslav@1890:             int i = h & (t.length - 1);
jaroslav@1890:             for (ExceptionNode e = t[i]; ; e = e.next) {
jaroslav@1890:                 if (e == null) {
jaroslav@1890:                     t[i] = new ExceptionNode(this, ex, t[i]);
jaroslav@1890:                     break;
jaroslav@1890:                 }
jaroslav@1890:                 if (e.get() == this) // already present
jaroslav@1890:                     break;
jaroslav@1890:             }
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:         return setCompletion(EXCEPTIONAL);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Removes exception node and clears status
jaroslav@1890:      */
jaroslav@1890:     private void clearExceptionalCompletion() {
jaroslav@1890:         int h = System.identityHashCode(this);
jaroslav@1890:         final ReentrantLock lock = exceptionTableLock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             ExceptionNode[] t = exceptionTable;
jaroslav@1890:             int i = h & (t.length - 1);
jaroslav@1890:             ExceptionNode e = t[i];
jaroslav@1890:             ExceptionNode pred = null;
jaroslav@1890:             while (e != null) {
jaroslav@1890:                 ExceptionNode next = e.next;
jaroslav@1890:                 if (e.get() == this) {
jaroslav@1890:                     if (pred == null)
jaroslav@1890:                         t[i] = next;
jaroslav@1890:                     else
jaroslav@1890:                         pred.next = next;
jaroslav@1890:                     break;
jaroslav@1890:                 }
jaroslav@1890:                 pred = e;
jaroslav@1890:                 e = next;
jaroslav@1890:             }
jaroslav@1890:             expungeStaleExceptions();
jaroslav@1890:             status = 0;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a rethrowable exception for the given task, if
jaroslav@1890:      * available. To provide accurate stack traces, if the exception
jaroslav@1890:      * was not thrown by the current thread, we try to create a new
jaroslav@1890:      * exception of the same type as the one thrown, but with the
jaroslav@1890:      * recorded exception as its cause. If there is no such
jaroslav@1890:      * constructor, we instead try to use a no-arg constructor,
jaroslav@1890:      * followed by initCause, to the same effect. If none of these
jaroslav@1890:      * apply, or any fail due to other exceptions, we return the
jaroslav@1890:      * recorded exception, which is still correct, although it may
jaroslav@1890:      * contain a misleading stack trace.
jaroslav@1890:      *
jaroslav@1890:      * @return the exception, or null if none
jaroslav@1890:      */
jaroslav@1890:     private Throwable getThrowableException() {
jaroslav@1890:         if (status != EXCEPTIONAL)
jaroslav@1890:             return null;
jaroslav@1890:         int h = System.identityHashCode(this);
jaroslav@1890:         ExceptionNode e;
jaroslav@1890:         final ReentrantLock lock = exceptionTableLock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             expungeStaleExceptions();
jaroslav@1890:             ExceptionNode[] t = exceptionTable;
jaroslav@1890:             e = t[h & (t.length - 1)];
jaroslav@1890:             while (e != null && e.get() != this)
jaroslav@1890:                 e = e.next;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:         Throwable ex;
jaroslav@1890:         if (e == null || (ex = e.ex) == null)
jaroslav@1890:             return null;
jaroslav@1890:         if (e.thrower != Thread.currentThread().getId()) {
jaroslav@1890:             Class ec = ex.getClass();
jaroslav@1890:             try {
jaroslav@1890:                 Constructor<?> noArgCtor = null;
jaroslav@1890:                 Constructor<?>[] cs = ec.getConstructors();// public ctors only
jaroslav@1890:                 for (int i = 0; i < cs.length; ++i) {
jaroslav@1890:                     Constructor<?> c = cs[i];
jaroslav@1890:                     Class<?>[] ps = c.getParameterTypes();
jaroslav@1890:                     if (ps.length == 0)
jaroslav@1890:                         noArgCtor = c;
jaroslav@1890:                     else if (ps.length == 1 && ps[0] == Throwable.class)
jaroslav@1890:                         return (Throwable)(c.newInstance(ex));
jaroslav@1890:                 }
jaroslav@1890:                 if (noArgCtor != null) {
jaroslav@1890:                     Throwable wx = (Throwable)(noArgCtor.newInstance());
jaroslav@1890:                     wx.initCause(ex);
jaroslav@1890:                     return wx;
jaroslav@1890:                 }
jaroslav@1890:             } catch (Exception ignore) {
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890:         return ex;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Poll stale refs and remove them. Call only while holding lock.
jaroslav@1890:      */
jaroslav@1890:     private static void expungeStaleExceptions() {
jaroslav@1890:         for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
jaroslav@1890:             if (x instanceof ExceptionNode) {
jaroslav@1890:                 ForkJoinTask<?> key = ((ExceptionNode)x).get();
jaroslav@1890:                 ExceptionNode[] t = exceptionTable;
jaroslav@1890:                 int i = System.identityHashCode(key) & (t.length - 1);
jaroslav@1890:                 ExceptionNode e = t[i];
jaroslav@1890:                 ExceptionNode pred = null;
jaroslav@1890:                 while (e != null) {
jaroslav@1890:                     ExceptionNode next = e.next;
jaroslav@1890:                     if (e == x) {
jaroslav@1890:                         if (pred == null)
jaroslav@1890:                             t[i] = next;
jaroslav@1890:                         else
jaroslav@1890:                             pred.next = next;
jaroslav@1890:                         break;
jaroslav@1890:                     }
jaroslav@1890:                     pred = e;
jaroslav@1890:                     e = next;
jaroslav@1890:                 }
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * If lock is available, poll stale refs and remove them.
jaroslav@1890:      * Called from ForkJoinPool when pools become quiescent.
jaroslav@1890:      */
jaroslav@1890:     static final void helpExpungeStaleExceptions() {
jaroslav@1890:         final ReentrantLock lock = exceptionTableLock;
jaroslav@1890:         if (lock.tryLock()) {
jaroslav@1890:             try {
jaroslav@1890:                 expungeStaleExceptions();
jaroslav@1890:             } finally {
jaroslav@1890:                 lock.unlock();
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Report the result of invoke or join; called only upon
jaroslav@1890:      * non-normal return of internal versions.
jaroslav@1890:      */
jaroslav@1890:     private V reportResult() {
jaroslav@1890:         int s; Throwable ex;
jaroslav@1890:         if ((s = status) == CANCELLED)
jaroslav@1890:             throw new CancellationException();
jaroslav@1890:         if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
jaroslav@1890:             UNSAFE.throwException(ex);
jaroslav@1890:         return getRawResult();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     // public methods
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Arranges to asynchronously execute this task.  While it is not
jaroslav@1890:      * necessarily enforced, it is a usage error to fork a task more
jaroslav@1890:      * than once unless it has completed and been reinitialized.
jaroslav@1890:      * Subsequent modifications to the state of this task or any data
jaroslav@1890:      * it operates on are not necessarily consistently observable by
jaroslav@1890:      * any thread other than the one executing it unless preceded by a
jaroslav@1890:      * call to {@link #join} or related methods, or a call to {@link
jaroslav@1890:      * #isDone} returning {@code true}.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method may be invoked only from within {@code
jaroslav@1890:      * ForkJoinPool} computations (as may be determined using method
jaroslav@1890:      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
jaroslav@1890:      * result in exceptions or errors, possibly including {@code
jaroslav@1890:      * ClassCastException}.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code this}, to simplify usage
jaroslav@1890:      */
jaroslav@1890:     public final ForkJoinTask<V> fork() {
jaroslav@1890:         ((ForkJoinWorkerThread) Thread.currentThread())
jaroslav@1890:             .pushTask(this);
jaroslav@1890:         return this;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns the result of the computation when it {@link #isDone is
jaroslav@1890:      * done}.  This method differs from {@link #get()} in that
jaroslav@1890:      * abnormal completion results in {@code RuntimeException} or
jaroslav@1890:      * {@code Error}, not {@code ExecutionException}, and that
jaroslav@1890:      * interrupts of the calling thread do <em>not</em> cause the
jaroslav@1890:      * method to abruptly return by throwing {@code
jaroslav@1890:      * InterruptedException}.
jaroslav@1890:      *
jaroslav@1890:      * @return the computed result
jaroslav@1890:      */
jaroslav@1890:     public final V join() {
jaroslav@1890:         if (doJoin() != NORMAL)
jaroslav@1890:             return reportResult();
jaroslav@1890:         else
jaroslav@1890:             return getRawResult();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Commences performing this task, awaits its completion if
jaroslav@1890:      * necessary, and returns its result, or throws an (unchecked)
jaroslav@1890:      * {@code RuntimeException} or {@code Error} if the underlying
jaroslav@1890:      * computation did so.
jaroslav@1890:      *
jaroslav@1890:      * @return the computed result
jaroslav@1890:      */
jaroslav@1890:     public final V invoke() {
jaroslav@1890:         if (doInvoke() != NORMAL)
jaroslav@1890:             return reportResult();
jaroslav@1890:         else
jaroslav@1890:             return getRawResult();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Forks the given tasks, returning when {@code isDone} holds for
jaroslav@1890:      * each task or an (unchecked) exception is encountered, in which
jaroslav@1890:      * case the exception is rethrown. If more than one task
jaroslav@1890:      * encounters an exception, then this method throws any one of
jaroslav@1890:      * these exceptions. If any task encounters an exception, the
jaroslav@1890:      * other may be cancelled. However, the execution status of
jaroslav@1890:      * individual tasks is not guaranteed upon exceptional return. The
jaroslav@1890:      * status of each task may be obtained using {@link
jaroslav@1890:      * #getException()} and related methods to check if they have been
jaroslav@1890:      * cancelled, completed normally or exceptionally, or left
jaroslav@1890:      * unprocessed.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method may be invoked only from within {@code
jaroslav@1890:      * ForkJoinPool} computations (as may be determined using method
jaroslav@1890:      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
jaroslav@1890:      * result in exceptions or errors, possibly including {@code
jaroslav@1890:      * ClassCastException}.
jaroslav@1890:      *
jaroslav@1890:      * @param t1 the first task
jaroslav@1890:      * @param t2 the second task
jaroslav@1890:      * @throws NullPointerException if any task is null
jaroslav@1890:      */
jaroslav@1890:     public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
jaroslav@1890:         t2.fork();
jaroslav@1890:         t1.invoke();
jaroslav@1890:         t2.join();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Forks the given tasks, returning when {@code isDone} holds for
jaroslav@1890:      * each task or an (unchecked) exception is encountered, in which
jaroslav@1890:      * case the exception is rethrown. If more than one task
jaroslav@1890:      * encounters an exception, then this method throws any one of
jaroslav@1890:      * these exceptions. If any task encounters an exception, others
jaroslav@1890:      * may be cancelled. However, the execution status of individual
jaroslav@1890:      * tasks is not guaranteed upon exceptional return. The status of
jaroslav@1890:      * each task may be obtained using {@link #getException()} and
jaroslav@1890:      * related methods to check if they have been cancelled, completed
jaroslav@1890:      * normally or exceptionally, or left unprocessed.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method may be invoked only from within {@code
jaroslav@1890:      * ForkJoinPool} computations (as may be determined using method
jaroslav@1890:      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
jaroslav@1890:      * result in exceptions or errors, possibly including {@code
jaroslav@1890:      * ClassCastException}.
jaroslav@1890:      *
jaroslav@1890:      * @param tasks the tasks
jaroslav@1890:      * @throws NullPointerException if any task is null
jaroslav@1890:      */
jaroslav@1890:     public static void invokeAll(ForkJoinTask<?>... tasks) {
jaroslav@1890:         Throwable ex = null;
jaroslav@1890:         int last = tasks.length - 1;
jaroslav@1890:         for (int i = last; i >= 0; --i) {
jaroslav@1890:             ForkJoinTask<?> t = tasks[i];
jaroslav@1890:             if (t == null) {
jaroslav@1890:                 if (ex == null)
jaroslav@1890:                     ex = new NullPointerException();
jaroslav@1890:             }
jaroslav@1890:             else if (i != 0)
jaroslav@1890:                 t.fork();
jaroslav@1890:             else if (t.doInvoke() < NORMAL && ex == null)
jaroslav@1890:                 ex = t.getException();
jaroslav@1890:         }
jaroslav@1890:         for (int i = 1; i <= last; ++i) {
jaroslav@1890:             ForkJoinTask<?> t = tasks[i];
jaroslav@1890:             if (t != null) {
jaroslav@1890:                 if (ex != null)
jaroslav@1890:                     t.cancel(false);
jaroslav@1890:                 else if (t.doJoin() < NORMAL && ex == null)
jaroslav@1890:                     ex = t.getException();
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890:         if (ex != null)
jaroslav@1890:             UNSAFE.throwException(ex);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Forks all tasks in the specified collection, returning when
jaroslav@1890:      * {@code isDone} holds for each task or an (unchecked) exception
jaroslav@1890:      * is encountered, in which case the exception is rethrown. If
jaroslav@1890:      * more than one task encounters an exception, then this method
jaroslav@1890:      * throws any one of these exceptions. If any task encounters an
jaroslav@1890:      * exception, others may be cancelled. However, the execution
jaroslav@1890:      * status of individual tasks is not guaranteed upon exceptional
jaroslav@1890:      * return. The status of each task may be obtained using {@link
jaroslav@1890:      * #getException()} and related methods to check if they have been
jaroslav@1890:      * cancelled, completed normally or exceptionally, or left
jaroslav@1890:      * unprocessed.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method may be invoked only from within {@code
jaroslav@1890:      * ForkJoinPool} computations (as may be determined using method
jaroslav@1890:      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
jaroslav@1890:      * result in exceptions or errors, possibly including {@code
jaroslav@1890:      * ClassCastException}.
jaroslav@1890:      *
jaroslav@1890:      * @param tasks the collection of tasks
jaroslav@1890:      * @return the tasks argument, to simplify usage
jaroslav@1890:      * @throws NullPointerException if tasks or any element are null
jaroslav@1890:      */
jaroslav@1890:     public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
jaroslav@1890:         if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
jaroslav@1890:             invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
jaroslav@1890:             return tasks;
jaroslav@1890:         }
jaroslav@1890:         @SuppressWarnings("unchecked")
jaroslav@1890:         List<? extends ForkJoinTask<?>> ts =
jaroslav@1890:             (List<? extends ForkJoinTask<?>>) tasks;
jaroslav@1890:         Throwable ex = null;
jaroslav@1890:         int last = ts.size() - 1;
jaroslav@1890:         for (int i = last; i >= 0; --i) {
jaroslav@1890:             ForkJoinTask<?> t = ts.get(i);
jaroslav@1890:             if (t == null) {
jaroslav@1890:                 if (ex == null)
jaroslav@1890:                     ex = new NullPointerException();
jaroslav@1890:             }
jaroslav@1890:             else if (i != 0)
jaroslav@1890:                 t.fork();
jaroslav@1890:             else if (t.doInvoke() < NORMAL && ex == null)
jaroslav@1890:                 ex = t.getException();
jaroslav@1890:         }
jaroslav@1890:         for (int i = 1; i <= last; ++i) {
jaroslav@1890:             ForkJoinTask<?> t = ts.get(i);
jaroslav@1890:             if (t != null) {
jaroslav@1890:                 if (ex != null)
jaroslav@1890:                     t.cancel(false);
jaroslav@1890:                 else if (t.doJoin() < NORMAL && ex == null)
jaroslav@1890:                     ex = t.getException();
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890:         if (ex != null)
jaroslav@1890:             UNSAFE.throwException(ex);
jaroslav@1890:         return tasks;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Attempts to cancel execution of this task. This attempt will
jaroslav@1890:      * fail if the task has already completed or could not be
jaroslav@1890:      * cancelled for some other reason. If successful, and this task
jaroslav@1890:      * has not started when {@code cancel} is called, execution of
jaroslav@1890:      * this task is suppressed. After this method returns
jaroslav@1890:      * successfully, unless there is an intervening call to {@link
jaroslav@1890:      * #reinitialize}, subsequent calls to {@link #isCancelled},
jaroslav@1890:      * {@link #isDone}, and {@code cancel} will return {@code true}
jaroslav@1890:      * and calls to {@link #join} and related methods will result in
jaroslav@1890:      * {@code CancellationException}.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method may be overridden in subclasses, but if so, must
jaroslav@1890:      * still ensure that these properties hold. In particular, the
jaroslav@1890:      * {@code cancel} method itself must not throw exceptions.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method is designed to be invoked by <em>other</em>
jaroslav@1890:      * tasks. To terminate the current task, you can just return or
jaroslav@1890:      * throw an unchecked exception from its computation method, or
jaroslav@1890:      * invoke {@link #completeExceptionally}.
jaroslav@1890:      *
jaroslav@1890:      * @param mayInterruptIfRunning this value has no effect in the
jaroslav@1890:      * default implementation because interrupts are not used to
jaroslav@1890:      * control cancellation.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if this task is now cancelled
jaroslav@1890:      */
jaroslav@1890:     public boolean cancel(boolean mayInterruptIfRunning) {
jaroslav@1890:         return setCompletion(CANCELLED) == CANCELLED;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Cancels, ignoring any exceptions thrown by cancel. Used during
jaroslav@1890:      * worker and pool shutdown. Cancel is spec'ed not to throw any
jaroslav@1890:      * exceptions, but if it does anyway, we have no recourse during
jaroslav@1890:      * shutdown, so guard against this case.
jaroslav@1890:      */
jaroslav@1890:     final void cancelIgnoringExceptions() {
jaroslav@1890:         try {
jaroslav@1890:             cancel(false);
jaroslav@1890:         } catch (Throwable ignore) {
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public final boolean isDone() {
jaroslav@1890:         return status < 0;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public final boolean isCancelled() {
jaroslav@1890:         return status == CANCELLED;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns {@code true} if this task threw an exception or was cancelled.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if this task threw an exception or was cancelled
jaroslav@1890:      */
jaroslav@1890:     public final boolean isCompletedAbnormally() {
jaroslav@1890:         return status < NORMAL;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns {@code true} if this task completed without throwing an
jaroslav@1890:      * exception and was not cancelled.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if this task completed without throwing an
jaroslav@1890:      * exception and was not cancelled
jaroslav@1890:      */
jaroslav@1890:     public final boolean isCompletedNormally() {
jaroslav@1890:         return status == NORMAL;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns the exception thrown by the base computation, or a
jaroslav@1890:      * {@code CancellationException} if cancelled, or {@code null} if
jaroslav@1890:      * none or if the method has not yet completed.
jaroslav@1890:      *
jaroslav@1890:      * @return the exception, or {@code null} if none
jaroslav@1890:      */
jaroslav@1890:     public final Throwable getException() {
jaroslav@1890:         int s = status;
jaroslav@1890:         return ((s >= NORMAL)    ? null :
jaroslav@1890:                 (s == CANCELLED) ? new CancellationException() :
jaroslav@1890:                 getThrowableException());
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Completes this task abnormally, and if not already aborted or
jaroslav@1890:      * cancelled, causes it to throw the given exception upon
jaroslav@1890:      * {@code join} and related operations. This method may be used
jaroslav@1890:      * to induce exceptions in asynchronous tasks, or to force
jaroslav@1890:      * completion of tasks that would not otherwise complete.  Its use
jaroslav@1890:      * in other situations is discouraged.  This method is
jaroslav@1890:      * overridable, but overridden versions must invoke {@code super}
jaroslav@1890:      * implementation to maintain guarantees.
jaroslav@1890:      *
jaroslav@1890:      * @param ex the exception to throw. If this exception is not a
jaroslav@1890:      * {@code RuntimeException} or {@code Error}, the actual exception
jaroslav@1890:      * thrown will be a {@code RuntimeException} with cause {@code ex}.
jaroslav@1890:      */
jaroslav@1890:     public void completeExceptionally(Throwable ex) {
jaroslav@1890:         setExceptionalCompletion((ex instanceof RuntimeException) ||
jaroslav@1890:                                  (ex instanceof Error) ? ex :
jaroslav@1890:                                  new RuntimeException(ex));
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Completes this task, and if not already aborted or cancelled,
jaroslav@1890:      * returning the given value as the result of subsequent
jaroslav@1890:      * invocations of {@code join} and related operations. This method
jaroslav@1890:      * may be used to provide results for asynchronous tasks, or to
jaroslav@1890:      * provide alternative handling for tasks that would not otherwise
jaroslav@1890:      * complete normally. Its use in other situations is
jaroslav@1890:      * discouraged. This method is overridable, but overridden
jaroslav@1890:      * versions must invoke {@code super} implementation to maintain
jaroslav@1890:      * guarantees.
jaroslav@1890:      *
jaroslav@1890:      * @param value the result value for this task
jaroslav@1890:      */
jaroslav@1890:     public void complete(V value) {
jaroslav@1890:         try {
jaroslav@1890:             setRawResult(value);
jaroslav@1890:         } catch (Throwable rex) {
jaroslav@1890:             setExceptionalCompletion(rex);
jaroslav@1890:             return;
jaroslav@1890:         }
jaroslav@1890:         setCompletion(NORMAL);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Waits if necessary for the computation to complete, and then
jaroslav@1890:      * retrieves its result.
jaroslav@1890:      *
jaroslav@1890:      * @return the computed result
jaroslav@1890:      * @throws CancellationException if the computation was cancelled
jaroslav@1890:      * @throws ExecutionException if the computation threw an
jaroslav@1890:      * exception
jaroslav@1890:      * @throws InterruptedException if the current thread is not a
jaroslav@1890:      * member of a ForkJoinPool and was interrupted while waiting
jaroslav@1890:      */
jaroslav@1890:     public final V get() throws InterruptedException, ExecutionException {
jaroslav@1890:         int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
jaroslav@1890:             doJoin() : externalInterruptibleAwaitDone(0L);
jaroslav@1890:         Throwable ex;
jaroslav@1890:         if (s == CANCELLED)
jaroslav@1890:             throw new CancellationException();
jaroslav@1890:         if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
jaroslav@1890:             throw new ExecutionException(ex);
jaroslav@1890:         return getRawResult();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Waits if necessary for at most the given time for the computation
jaroslav@1890:      * to complete, and then retrieves its result, if available.
jaroslav@1890:      *
jaroslav@1890:      * @param timeout the maximum time to wait
jaroslav@1890:      * @param unit the time unit of the timeout argument
jaroslav@1890:      * @return the computed result
jaroslav@1890:      * @throws CancellationException if the computation was cancelled
jaroslav@1890:      * @throws ExecutionException if the computation threw an
jaroslav@1890:      * exception
jaroslav@1890:      * @throws InterruptedException if the current thread is not a
jaroslav@1890:      * member of a ForkJoinPool and was interrupted while waiting
jaroslav@1890:      * @throws TimeoutException if the wait timed out
jaroslav@1890:      */
jaroslav@1890:     public final V get(long timeout, TimeUnit unit)
jaroslav@1890:         throws InterruptedException, ExecutionException, TimeoutException {
jaroslav@1890:         Thread t = Thread.currentThread();
jaroslav@1890:         if (t instanceof ForkJoinWorkerThread) {
jaroslav@1890:             ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
jaroslav@1890:             long nanos = unit.toNanos(timeout);
jaroslav@1890:             if (status >= 0) {
jaroslav@1890:                 boolean completed = false;
jaroslav@1890:                 if (w.unpushTask(this)) {
jaroslav@1890:                     try {
jaroslav@1890:                         completed = exec();
jaroslav@1890:                     } catch (Throwable rex) {
jaroslav@1890:                         setExceptionalCompletion(rex);
jaroslav@1890:                     }
jaroslav@1890:                 }
jaroslav@1890:                 if (completed)
jaroslav@1890:                     setCompletion(NORMAL);
jaroslav@1890:                 else if (status >= 0 && nanos > 0)
jaroslav@1890:                     w.pool.timedAwaitJoin(this, nanos);
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890:         else {
jaroslav@1890:             long millis = unit.toMillis(timeout);
jaroslav@1890:             if (millis > 0)
jaroslav@1890:                 externalInterruptibleAwaitDone(millis);
jaroslav@1890:         }
jaroslav@1890:         int s = status;
jaroslav@1890:         if (s != NORMAL) {
jaroslav@1890:             Throwable ex;
jaroslav@1890:             if (s == CANCELLED)
jaroslav@1890:                 throw new CancellationException();
jaroslav@1890:             if (s != EXCEPTIONAL)
jaroslav@1890:                 throw new TimeoutException();
jaroslav@1890:             if ((ex = getThrowableException()) != null)
jaroslav@1890:                 throw new ExecutionException(ex);
jaroslav@1890:         }
jaroslav@1890:         return getRawResult();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Joins this task, without returning its result or throwing its
jaroslav@1890:      * exception. This method may be useful when processing
jaroslav@1890:      * collections of tasks when some have been cancelled or otherwise
jaroslav@1890:      * known to have aborted.
jaroslav@1890:      */
jaroslav@1890:     public final void quietlyJoin() {
jaroslav@1890:         doJoin();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Commences performing this task and awaits its completion if
jaroslav@1890:      * necessary, without returning its result or throwing its
jaroslav@1890:      * exception.
jaroslav@1890:      */
jaroslav@1890:     public final void quietlyInvoke() {
jaroslav@1890:         doInvoke();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Possibly executes tasks until the pool hosting the current task
jaroslav@1890:      * {@link ForkJoinPool#isQuiescent is quiescent}. This method may
jaroslav@1890:      * be of use in designs in which many tasks are forked, but none
jaroslav@1890:      * are explicitly joined, instead executing them until all are
jaroslav@1890:      * processed.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method may be invoked only from within {@code
jaroslav@1890:      * ForkJoinPool} computations (as may be determined using method
jaroslav@1890:      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
jaroslav@1890:      * result in exceptions or errors, possibly including {@code
jaroslav@1890:      * ClassCastException}.
jaroslav@1890:      */
jaroslav@1890:     public static void helpQuiesce() {
jaroslav@1890:         ((ForkJoinWorkerThread) Thread.currentThread())
jaroslav@1890:             .helpQuiescePool();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Resets the internal bookkeeping state of this task, allowing a
jaroslav@1890:      * subsequent {@code fork}. This method allows repeated reuse of
jaroslav@1890:      * this task, but only if reuse occurs when this task has either
jaroslav@1890:      * never been forked, or has been forked, then completed and all
jaroslav@1890:      * outstanding joins of this task have also completed. Effects
jaroslav@1890:      * under any other usage conditions are not guaranteed.
jaroslav@1890:      * This method may be useful when executing
jaroslav@1890:      * pre-constructed trees of subtasks in loops.
jaroslav@1890:      *
jaroslav@1890:      * <p>Upon completion of this method, {@code isDone()} reports
jaroslav@1890:      * {@code false}, and {@code getException()} reports {@code
jaroslav@1890:      * null}. However, the value returned by {@code getRawResult} is
jaroslav@1890:      * unaffected. To clear this value, you can invoke {@code
jaroslav@1890:      * setRawResult(null)}.
jaroslav@1890:      */
jaroslav@1890:     public void reinitialize() {
jaroslav@1890:         if (status == EXCEPTIONAL)
jaroslav@1890:             clearExceptionalCompletion();
jaroslav@1890:         else
jaroslav@1890:             status = 0;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns the pool hosting the current task execution, or null
jaroslav@1890:      * if this task is executing outside of any ForkJoinPool.
jaroslav@1890:      *
jaroslav@1890:      * @see #inForkJoinPool
jaroslav@1890:      * @return the pool, or {@code null} if none
jaroslav@1890:      */
jaroslav@1890:     public static ForkJoinPool getPool() {
jaroslav@1890:         Thread t = Thread.currentThread();
jaroslav@1890:         return (t instanceof ForkJoinWorkerThread) ?
jaroslav@1890:             ((ForkJoinWorkerThread) t).pool : null;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns {@code true} if the current thread is a {@link
jaroslav@1890:      * ForkJoinWorkerThread} executing as a ForkJoinPool computation.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if the current thread is a {@link
jaroslav@1890:      * ForkJoinWorkerThread} executing as a ForkJoinPool computation,
jaroslav@1890:      * or {@code false} otherwise
jaroslav@1890:      */
jaroslav@1890:     public static boolean inForkJoinPool() {
jaroslav@1890:         return Thread.currentThread() instanceof ForkJoinWorkerThread;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Tries to unschedule this task for execution. This method will
jaroslav@1890:      * typically succeed if this task is the most recently forked task
jaroslav@1890:      * by the current thread, and has not commenced executing in
jaroslav@1890:      * another thread.  This method may be useful when arranging
jaroslav@1890:      * alternative local processing of tasks that could have been, but
jaroslav@1890:      * were not, stolen.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method may be invoked only from within {@code
jaroslav@1890:      * ForkJoinPool} computations (as may be determined using method
jaroslav@1890:      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
jaroslav@1890:      * result in exceptions or errors, possibly including {@code
jaroslav@1890:      * ClassCastException}.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if unforked
jaroslav@1890:      */
jaroslav@1890:     public boolean tryUnfork() {
jaroslav@1890:         return ((ForkJoinWorkerThread) Thread.currentThread())
jaroslav@1890:             .unpushTask(this);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an estimate of the number of tasks that have been
jaroslav@1890:      * forked by the current worker thread but not yet executed. This
jaroslav@1890:      * value may be useful for heuristic decisions about whether to
jaroslav@1890:      * fork other tasks.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method may be invoked only from within {@code
jaroslav@1890:      * ForkJoinPool} computations (as may be determined using method
jaroslav@1890:      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
jaroslav@1890:      * result in exceptions or errors, possibly including {@code
jaroslav@1890:      * ClassCastException}.
jaroslav@1890:      *
jaroslav@1890:      * @return the number of tasks
jaroslav@1890:      */
jaroslav@1890:     public static int getQueuedTaskCount() {
jaroslav@1890:         return ((ForkJoinWorkerThread) Thread.currentThread())
jaroslav@1890:             .getQueueSize();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an estimate of how many more locally queued tasks are
jaroslav@1890:      * held by the current worker thread than there are other worker
jaroslav@1890:      * threads that might steal them.  This value may be useful for
jaroslav@1890:      * heuristic decisions about whether to fork other tasks. In many
jaroslav@1890:      * usages of ForkJoinTasks, at steady state, each worker should
jaroslav@1890:      * aim to maintain a small constant surplus (for example, 3) of
jaroslav@1890:      * tasks, and to process computations locally if this threshold is
jaroslav@1890:      * exceeded.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method may be invoked only from within {@code
jaroslav@1890:      * ForkJoinPool} computations (as may be determined using method
jaroslav@1890:      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
jaroslav@1890:      * result in exceptions or errors, possibly including {@code
jaroslav@1890:      * ClassCastException}.
jaroslav@1890:      *
jaroslav@1890:      * @return the surplus number of tasks, which may be negative
jaroslav@1890:      */
jaroslav@1890:     public static int getSurplusQueuedTaskCount() {
jaroslav@1890:         return ((ForkJoinWorkerThread) Thread.currentThread())
jaroslav@1890:             .getEstimatedSurplusTaskCount();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     // Extension methods
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns the result that would be returned by {@link #join}, even
jaroslav@1890:      * if this task completed abnormally, or {@code null} if this task
jaroslav@1890:      * is not known to have been completed.  This method is designed
jaroslav@1890:      * to aid debugging, as well as to support extensions. Its use in
jaroslav@1890:      * any other context is discouraged.
jaroslav@1890:      *
jaroslav@1890:      * @return the result, or {@code null} if not completed
jaroslav@1890:      */
jaroslav@1890:     public abstract V getRawResult();
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Forces the given value to be returned as a result.  This method
jaroslav@1890:      * is designed to support extensions, and should not in general be
jaroslav@1890:      * called otherwise.
jaroslav@1890:      *
jaroslav@1890:      * @param value the value
jaroslav@1890:      */
jaroslav@1890:     protected abstract void setRawResult(V value);
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Immediately performs the base action of this task.  This method
jaroslav@1890:      * is designed to support extensions, and should not in general be
jaroslav@1890:      * called otherwise. The return value controls whether this task
jaroslav@1890:      * is considered to be done normally. It may return false in
jaroslav@1890:      * asynchronous actions that require explicit invocations of
jaroslav@1890:      * {@link #complete} to become joinable. It may also throw an
jaroslav@1890:      * (unchecked) exception to indicate abnormal exit.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if completed normally
jaroslav@1890:      */
jaroslav@1890:     protected abstract boolean exec();
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns, but does not unschedule or execute, a task queued by
jaroslav@1890:      * the current thread but not yet executed, if one is immediately
jaroslav@1890:      * available. There is no guarantee that this task will actually
jaroslav@1890:      * be polled or executed next. Conversely, this method may return
jaroslav@1890:      * null even if a task exists but cannot be accessed without
jaroslav@1890:      * contention with other threads.  This method is designed
jaroslav@1890:      * primarily to support extensions, and is unlikely to be useful
jaroslav@1890:      * otherwise.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method may be invoked only from within {@code
jaroslav@1890:      * ForkJoinPool} computations (as may be determined using method
jaroslav@1890:      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
jaroslav@1890:      * result in exceptions or errors, possibly including {@code
jaroslav@1890:      * ClassCastException}.
jaroslav@1890:      *
jaroslav@1890:      * @return the next task, or {@code null} if none are available
jaroslav@1890:      */
jaroslav@1890:     protected static ForkJoinTask<?> peekNextLocalTask() {
jaroslav@1890:         return ((ForkJoinWorkerThread) Thread.currentThread())
jaroslav@1890:             .peekTask();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Unschedules and returns, without executing, the next task
jaroslav@1890:      * queued by the current thread but not yet executed.  This method
jaroslav@1890:      * is designed primarily to support extensions, and is unlikely to
jaroslav@1890:      * be useful otherwise.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method may be invoked only from within {@code
jaroslav@1890:      * ForkJoinPool} computations (as may be determined using method
jaroslav@1890:      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
jaroslav@1890:      * result in exceptions or errors, possibly including {@code
jaroslav@1890:      * ClassCastException}.
jaroslav@1890:      *
jaroslav@1890:      * @return the next task, or {@code null} if none are available
jaroslav@1890:      */
jaroslav@1890:     protected static ForkJoinTask<?> pollNextLocalTask() {
jaroslav@1890:         return ((ForkJoinWorkerThread) Thread.currentThread())
jaroslav@1890:             .pollLocalTask();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Unschedules and returns, without executing, the next task
jaroslav@1890:      * queued by the current thread but not yet executed, if one is
jaroslav@1890:      * available, or if not available, a task that was forked by some
jaroslav@1890:      * other thread, if available. Availability may be transient, so a
jaroslav@1890:      * {@code null} result does not necessarily imply quiescence
jaroslav@1890:      * of the pool this task is operating in.  This method is designed
jaroslav@1890:      * primarily to support extensions, and is unlikely to be useful
jaroslav@1890:      * otherwise.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method may be invoked only from within {@code
jaroslav@1890:      * ForkJoinPool} computations (as may be determined using method
jaroslav@1890:      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
jaroslav@1890:      * result in exceptions or errors, possibly including {@code
jaroslav@1890:      * ClassCastException}.
jaroslav@1890:      *
jaroslav@1890:      * @return a task, or {@code null} if none are available
jaroslav@1890:      */
jaroslav@1890:     protected static ForkJoinTask<?> pollTask() {
jaroslav@1890:         return ((ForkJoinWorkerThread) Thread.currentThread())
jaroslav@1890:             .pollTask();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Adaptor for Runnables. This implements RunnableFuture
jaroslav@1890:      * to be compliant with AbstractExecutorService constraints
jaroslav@1890:      * when used in ForkJoinPool.
jaroslav@1890:      */
jaroslav@1890:     static final class AdaptedRunnable<T> extends ForkJoinTask<T>
jaroslav@1890:         implements RunnableFuture<T> {
jaroslav@1890:         final Runnable runnable;
jaroslav@1890:         final T resultOnCompletion;
jaroslav@1890:         T result;
jaroslav@1890:         AdaptedRunnable(Runnable runnable, T result) {
jaroslav@1890:             if (runnable == null) throw new NullPointerException();
jaroslav@1890:             this.runnable = runnable;
jaroslav@1890:             this.resultOnCompletion = result;
jaroslav@1890:         }
jaroslav@1890:         public T getRawResult() { return result; }
jaroslav@1890:         public void setRawResult(T v) { result = v; }
jaroslav@1890:         public boolean exec() {
jaroslav@1890:             runnable.run();
jaroslav@1890:             result = resultOnCompletion;
jaroslav@1890:             return true;
jaroslav@1890:         }
jaroslav@1890:         public void run() { invoke(); }
jaroslav@1890:         private static final long serialVersionUID = 5232453952276885070L;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Adaptor for Callables
jaroslav@1890:      */
jaroslav@1890:     static final class AdaptedCallable<T> extends ForkJoinTask<T>
jaroslav@1890:         implements RunnableFuture<T> {
jaroslav@1890:         final Callable<? extends T> callable;
jaroslav@1890:         T result;
jaroslav@1890:         AdaptedCallable(Callable<? extends T> callable) {
jaroslav@1890:             if (callable == null) throw new NullPointerException();
jaroslav@1890:             this.callable = callable;
jaroslav@1890:         }
jaroslav@1890:         public T getRawResult() { return result; }
jaroslav@1890:         public void setRawResult(T v) { result = v; }
jaroslav@1890:         public boolean exec() {
jaroslav@1890:             try {
jaroslav@1890:                 result = callable.call();
jaroslav@1890:                 return true;
jaroslav@1890:             } catch (Error err) {
jaroslav@1890:                 throw err;
jaroslav@1890:             } catch (RuntimeException rex) {
jaroslav@1890:                 throw rex;
jaroslav@1890:             } catch (Exception ex) {
jaroslav@1890:                 throw new RuntimeException(ex);
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890:         public void run() { invoke(); }
jaroslav@1890:         private static final long serialVersionUID = 2838392045355241008L;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a new {@code ForkJoinTask} that performs the {@code run}
jaroslav@1890:      * method of the given {@code Runnable} as its action, and returns
jaroslav@1890:      * a null result upon {@link #join}.
jaroslav@1890:      *
jaroslav@1890:      * @param runnable the runnable action
jaroslav@1890:      * @return the task
jaroslav@1890:      */
jaroslav@1890:     public static ForkJoinTask<?> adapt(Runnable runnable) {
jaroslav@1890:         return new AdaptedRunnable<Void>(runnable, null);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a new {@code ForkJoinTask} that performs the {@code run}
jaroslav@1890:      * method of the given {@code Runnable} as its action, and returns
jaroslav@1890:      * the given result upon {@link #join}.
jaroslav@1890:      *
jaroslav@1890:      * @param runnable the runnable action
jaroslav@1890:      * @param result the result upon completion
jaroslav@1890:      * @return the task
jaroslav@1890:      */
jaroslav@1890:     public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
jaroslav@1890:         return new AdaptedRunnable<T>(runnable, result);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a new {@code ForkJoinTask} that performs the {@code call}
jaroslav@1890:      * method of the given {@code Callable} as its action, and returns
jaroslav@1890:      * its result upon {@link #join}, translating any checked exceptions
jaroslav@1890:      * encountered into {@code RuntimeException}.
jaroslav@1890:      *
jaroslav@1890:      * @param callable the callable action
jaroslav@1890:      * @return the task
jaroslav@1890:      */
jaroslav@1890:     public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
jaroslav@1890:         return new AdaptedCallable<T>(callable);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     // Serialization support
jaroslav@1890: 
jaroslav@1890:     private static final long serialVersionUID = -7721805057305804111L;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Saves the state to a stream (that is, serializes it).
jaroslav@1890:      *
jaroslav@1890:      * @serialData the current run status and the exception thrown
jaroslav@1890:      * during execution, or {@code null} if none
jaroslav@1890:      * @param s the stream
jaroslav@1890:      */
jaroslav@1890:     private void writeObject(java.io.ObjectOutputStream s)
jaroslav@1890:         throws java.io.IOException {
jaroslav@1890:         s.defaultWriteObject();
jaroslav@1890:         s.writeObject(getException());
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Reconstitutes the instance from a stream (that is, deserializes it).
jaroslav@1890:      *
jaroslav@1890:      * @param s the stream
jaroslav@1890:      */
jaroslav@1890:     private void readObject(java.io.ObjectInputStream s)
jaroslav@1890:         throws java.io.IOException, ClassNotFoundException {
jaroslav@1890:         s.defaultReadObject();
jaroslav@1890:         Object ex = s.readObject();
jaroslav@1890:         if (ex != null)
jaroslav@1890:             setExceptionalCompletion((Throwable)ex);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     // Unsafe mechanics
jaroslav@1890:     private static final sun.misc.Unsafe UNSAFE;
jaroslav@1890:     private static final long statusOffset;
jaroslav@1890:     static {
jaroslav@1890:         exceptionTableLock = new ReentrantLock();
jaroslav@1890:         exceptionTableRefQueue = new ReferenceQueue<Object>();
jaroslav@1890:         exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
jaroslav@1890:         try {
jaroslav@1890:             UNSAFE = sun.misc.Unsafe.getUnsafe();
jaroslav@1890:             statusOffset = UNSAFE.objectFieldOffset
jaroslav@1890:                 (ForkJoinTask.class.getDeclaredField("status"));
jaroslav@1890:         } catch (Exception e) {
jaroslav@1890:             throw new Error(e);
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890: }