--- jsr166/src/jsr166y/ForkJoinTask.java 2010/05/27 16:46:48 1.48
+++ jsr166/src/jsr166y/ForkJoinTask.java 2010/11/23 00:10:39 1.70
@@ -6,8 +6,6 @@
package jsr166y;
-import java.util.concurrent.*;
-
import java.io.Serializable;
import java.util.Collection;
import java.util.Collections;
@@ -15,6 +13,16 @@ import java.util.List;
import java.util.RandomAccess;
import java.util.Map;
import java.util.WeakHashMap;
+import java.util.concurrent.Callable;
+import java.util.concurrent.CancellationException;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.RunnableFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
/**
* Abstract base class for tasks that run within a {@link ForkJoinPool}.
@@ -28,10 +36,10 @@ import java.util.WeakHashMap;
* start other subtasks. As indicated by the name of this class,
* many programs using {@code ForkJoinTask} employ only methods
* {@link #fork} and {@link #join}, or derivatives such as {@link
- * #invokeAll}. However, this class also provides a number of other
- * methods that can come into play in advanced usages, as well as
- * extension mechanics that allow support of new forms of fork/join
- * processing.
+ * #invokeAll(ForkJoinTask...) 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 {@code ForkJoinTask} is a lightweight form of {@link Future}.
* The efficiency of {@code ForkJoinTask}s stems from a set of
@@ -64,10 +72,7 @@ import java.util.WeakHashMap;
* results of a task is {@link #join}, but there are several variants:
* The {@link Future#get} methods support interruptible and/or timed
* waits for completion and report results using {@code Future}
- * conventions. Method {@link #helpJoin} enables callers to actively
- * execute other tasks while awaiting joins, which is sometimes more
- * efficient but only applies when all subtasks are known to be
- * strictly tree-structured. Method {@link #invoke} is semantically
+ * conventions. Method {@link #invoke} is semantically
* equivalent to {@code fork(); join()} but always attempts to begin
* execution in the current thread. The "quiet" forms of
* these methods do not extract results or report exceptions. These
@@ -103,7 +108,17 @@ import java.util.WeakHashMap;
* ForkJoinTasks (as may be determined using method {@link
* #inForkJoinPool}). Attempts to invoke them in other contexts
* result in exceptions or errors, possibly including
- * ClassCastException.
+ * {@code ClassCastException}.
+ *
+ *
Method {@link #join} and its variants are appropriate for use
+ * only when completion dependencies are acyclic; that is, the
+ * parallel computation can be described as a directed acyclic graph
+ * (DAG). Otherwise, executions may encounter a form of deadlock as
+ * tasks cyclically wait for each other. However, this framework
+ * supports other methods and techniques (for example the use of
+ * {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
+ * may be of use in constructing custom subclasses for problems that
+ * are not statically structured as DAGs.
*
*
Most base support methods are {@code final}, to prevent
* overriding of implementations that are intrinsically tied to the
@@ -119,15 +134,15 @@ import java.util.WeakHashMap;
* computation. Large tasks should be split into smaller subtasks,
* usually via recursive decomposition. 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 parallelism cannot
- * improve throughput. If too small, then memory and internal task
- * maintenance overhead may overwhelm processing.
+ * computational steps, and should avoid indefinite looping. If tasks
+ * are too big, then parallelism cannot improve throughput. If too
+ * small, then memory and internal task maintenance overhead may
+ * overwhelm processing.
*
*
This class provides {@code adapt} methods for {@link Runnable}
* and {@link Callable}, that may be of use when mixing execution of
- * {@code ForkJoinTasks} with other kinds of tasks. When all tasks
- * are of this form, consider using a pool in
- * {@linkplain ForkJoinPool#setAsyncMode async mode}.
+ * {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
+ * of this form, consider using a pool constructed in asyncMode.
*
*
ForkJoinTasks are {@code Serializable}, which enables them to be
* used in extensions such as remote execution frameworks. It is
@@ -148,36 +163,34 @@ public abstract class ForkJoinTask im
* status maintenance (2) execution and awaiting completion (3)
* user-level methods that additionally report results. This is
* sometimes hard to see because this file orders exported methods
- * in a way that flows well in javadocs.
+ * in a way that flows well in javadocs. In particular, most
+ * join mechanics are in method quietlyJoin, below.
*/
- /**
- * 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 the SIGNAL bit set.
- *
- * Completion of a stolen task with SIGNAL set awakens any waiters
- * via notifyAll. Even though suboptimal for some purposes, we use
+ /*
+ * The status field holds 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 value
+ * NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
+ * waits by other threads have the SIGNAL bit set. Completion of
+ * a stolen task with SIGNAL set awakens any waiters 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. We want
* these monitors to be "fat", i.e., not use biasing or thin-lock
* techniques, so use some odd coding idioms that tend to avoid
* them.
- *
- * Note that bits 1-28 are currently unused. Also value
- * 0x80000000 is available as spare completion value.
*/
+
+ /** The run status of this task */
volatile int status; // accessed directly by pool and workers
- private static final int COMPLETION_MASK = 0xe0000000;
- private static final int NORMAL = 0xe0000000; // == mask
- private static final int CANCELLED = 0xc0000000;
- private static final int EXCEPTIONAL = 0xa0000000;
- private static final int SIGNAL = 0x00000001;
+ private static final int NORMAL = -1;
+ private static final int CANCELLED = -2;
+ private static final int EXCEPTIONAL = -3;
+ private static final int SIGNAL = 1;
/**
* Table of exceptions thrown by tasks, to enable reporting by
@@ -198,171 +211,114 @@ public abstract class ForkJoinTask im
* also clearing signal request bits.
*
* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
- * @return status on exit
*/
- private int setCompletion(int completion) {
+ private void setCompletion(int completion) {
int s;
while ((s = status) >= 0) {
if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
- if ((s & SIGNAL) != 0)
+ if (s != 0)
synchronized (this) { notifyAll(); }
- return completion;
+ break;
}
}
- return s;
}
/**
- * Record exception and set exceptional completion
+ * Records exception and sets exceptional completion.
+ *
* @return status on exit
*/
- private int setExceptionalCompletion(Throwable rex) {
+ private void setExceptionalCompletion(Throwable rex) {
exceptionMap.put(this, rex);
- return setCompletion(EXCEPTIONAL);
+ setCompletion(EXCEPTIONAL);
}
/**
- * Blocks a worker thread until completion. Called only by pool.
+ * Blocks a worker thread until completed or timed out. Called
+ * only by pool.
*/
- final void internalAwaitDone() {
- int s;
- while ((s = status) >= 0) {
- synchronized(this) {
- if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
- do {
- try {
- wait();
- } catch (InterruptedException ie) {
- cancelIfTerminating();
- }
- } while (status >= 0);
- break;
+ final void internalAwaitDone(long millis, int nanos) {
+ if (status >= 0) {
+ try { // the odd construction reduces lock bias effects
+ synchronized (this) {
+ if (status > 0 ||
+ UNSAFE.compareAndSwapInt(this, statusOffset,
+ 0, SIGNAL))
+ wait(millis, nanos);
}
+ } catch (InterruptedException ie) {
+ cancelIfTerminating();
}
}
}
/**
* Blocks a non-worker-thread until completion.
- * @return status on exit
*/
- private int externalAwaitDone() {
- int s;
- while ((s = status) >= 0) {
+ private void externalAwaitDone() {
+ if (status >= 0) {
+ boolean interrupted = false;
synchronized(this) {
- if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
- boolean interrupted = false;
- do {
- try {
- wait();
- } catch (InterruptedException ie) {
- interrupted = true;
- }
- } while ((s = status) >= 0);
- if (interrupted)
- Thread.currentThread().interrupt();
- break;
+ int s;
+ while ((s = status) >= 0) {
+ if (s == 0 &&
+ !UNSAFE.compareAndSwapInt(this, statusOffset,
+ 0, SIGNAL))
+ continue;
+ try {
+ wait();
+ } catch (InterruptedException ie) {
+ interrupted = true;
+ }
}
}
+ if (interrupted)
+ Thread.currentThread().interrupt();
}
- return s;
- }
-
- /**
- * Unless done, calls exec and records status if completed, but
- * doesn't wait for completion otherwise.
- */
- final void tryExec() {
- try {
- if (status < 0 || !exec())
- return;
- } catch (Throwable rex) {
- setExceptionalCompletion(rex);
- return;
- }
- setCompletion(NORMAL); // must be outside try block
}
/**
- * If not done and this task is next in worker queue, runs it,
- * else waits for it.
- * @return status on exit
+ * Blocks a non-worker-thread until completion or interruption or timeout
*/
- private int waitingJoin() {
- int s = status;
- if (s < 0)
- return s;
- Thread t = Thread.currentThread();
- if (t instanceof ForkJoinWorkerThread) {
- ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
- if (w.unpushTask(this)) {
- boolean completed;
- try {
- completed = exec();
- } catch (Throwable rex) {
- return setExceptionalCompletion(rex);
+ private void externalInterruptibleAwaitDone(boolean timed, long nanos)
+ throws InterruptedException {
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ if (status >= 0) {
+ long startTime = timed ? System.nanoTime() : 0L;
+ synchronized(this) {
+ int s;
+ while ((s = status) >= 0) {
+ long nt;
+ if (s == 0 &&
+ !UNSAFE.compareAndSwapInt(this, statusOffset,
+ 0, SIGNAL))
+ continue;
+ else if (!timed)
+ wait();
+ else if ((nt = nanos - (System.nanoTime()-startTime)) > 0L)
+ wait(nt / 1000000, (int)(nt % 1000000));
+ else
+ break;
}
- if (completed)
- return setCompletion(NORMAL);
}
- return w.pool.awaitJoin(this);
}
- else
- return externalAwaitDone();
}
/**
- * Unless done, calls exec and records status if completed, or
- * waits for completion otherwise.
- * @return status on exit
+ * Unless done, calls exec and records status if completed, but
+ * doesn't wait for completion otherwise. Primary execution method
+ * for ForkJoinWorkerThread.
*/
- private int waitingInvoke() {
- int s = status;
- if (s < 0)
- return s;
- boolean completed;
+ final void quietlyExec() {
try {
- completed = exec();
+ if (status < 0 || !exec())
+ return;
} catch (Throwable rex) {
- return setExceptionalCompletion(rex);
- }
- if (completed)
- return setCompletion(NORMAL);
- return waitingJoin();
- }
-
- /**
- * If this task is next in worker queue, runs it, else processes other
- * tasks until complete.
- * @return status on exit
- */
- private int busyJoin() {
- int s = status;
- if (s < 0)
- return s;
- ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
- if (w.unpushTask(this)) {
- boolean completed;
- try {
- completed = exec();
- } catch (Throwable rex) {
- return setExceptionalCompletion(rex);
- }
- if (completed)
- return setCompletion(NORMAL);
+ setExceptionalCompletion(rex);
+ return;
}
- return w.execWhileJoining(this);
- }
-
- /**
- * Returns result or throws exception associated with given status.
- * @param s the status
- */
- private V reportResult(int s) {
- Throwable ex;
- if (s < NORMAL && (ex = getException()) != null)
- UNSAFE.throwException(ex);
- return getRawResult();
+ setCompletion(NORMAL); // must be outside try block
}
// public methods
@@ -378,7 +334,7 @@ public abstract class ForkJoinTask im
* #isDone} returning {@code true}.
*
* This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
+ * ForkJoinPool} computations (as may be determined using method
* {@link #inForkJoinPool}). Attempts to invoke in other contexts
* result in exceptions or errors, possibly including {@code
* ClassCastException}.
@@ -392,39 +348,55 @@ public abstract class ForkJoinTask im
}
/**
- * Returns the result of the computation when it {@link #isDone is done}.
- * This method differs from {@link #get()} in that
+ * Returns the result of the computation when it {@link #isDone is
+ * done}. This method differs from {@link #get()} in that
* abnormal completion results in {@code RuntimeException} or
- * {@code Error}, not {@code ExecutionException}.
+ * {@code Error}, not {@code ExecutionException}, and that
+ * interrupts of the calling thread do not cause the
+ * method to abruptly return by throwing {@code
+ * InterruptedException}.
*
* @return the computed result
*/
public final V join() {
- return reportResult(waitingJoin());
+ quietlyJoin();
+ Throwable ex;
+ if (status < NORMAL && (ex = getException()) != null)
+ UNSAFE.throwException(ex);
+ return getRawResult();
}
/**
* Commences performing this task, awaits its completion if
- * necessary, and return its result, or throws an (unchecked)
- * exception if the underlying computation did so.
+ * necessary, and returns its result, or throws an (unchecked)
+ * {@code RuntimeException} or {@code Error} if the underlying
+ * computation did so.
*
* @return the computed result
*/
public final V invoke() {
- return reportResult(waitingInvoke());
+ quietlyInvoke();
+ Throwable ex;
+ if (status < NORMAL && (ex = getException()) != null)
+ UNSAFE.throwException(ex);
+ return getRawResult();
}
/**
* Forks the given tasks, returning when {@code isDone} holds for
* each task or an (unchecked) exception is encountered, in which
- * case the exception is rethrown. If either task encounters an
- * exception, the other one may be, but is not guaranteed to be,
- * cancelled. If both tasks throw an exception, then this method
- * throws one of them. The individual status of each task may be
- * checked using {@link #getException()} and related methods.
+ * case the exception is rethrown. If more than one task
+ * encounters an exception, then this method throws any one of
+ * these exceptions. If any task encounters an exception, the
+ * other may be cancelled. However, the execution status of
+ * individual tasks is not guaranteed upon exceptional return. The
+ * status of each task may be obtained using {@link
+ * #getException()} and related methods to check if they have been
+ * cancelled, completed normally or exceptionally, or left
+ * unprocessed.
*
* This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
+ * ForkJoinPool} computations (as may be determined using method
* {@link #inForkJoinPool}). Attempts to invoke in other contexts
* result in exceptions or errors, possibly including {@code
* ClassCastException}.
@@ -442,15 +414,17 @@ public abstract class ForkJoinTask im
/**
* Forks the given tasks, returning when {@code isDone} holds for
* each task or an (unchecked) exception is encountered, in which
- * case the exception is rethrown. If any task encounters an
- * exception, others may be, but are not guaranteed to be,
- * cancelled. If more than one task encounters an exception, then
- * this method throws any one of these exceptions. The individual
- * status of each task may be checked using {@link #getException()}
- * and related methods.
+ * case the exception is rethrown. If more than one task
+ * encounters an exception, then this method throws any one of
+ * these exceptions. If any task encounters an exception, others
+ * may be cancelled. However, the execution status of individual
+ * tasks is not guaranteed upon exceptional return. The status of
+ * each task may be obtained using {@link #getException()} and
+ * related methods to check if they have been cancelled, completed
+ * normally or exceptionally, or left unprocessed.
*
* This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
+ * ForkJoinPool} computations (as may be determined using method
* {@link #inForkJoinPool}). Attempts to invoke in other contexts
* result in exceptions or errors, possibly including {@code
* ClassCastException}.
@@ -469,16 +443,22 @@ public abstract class ForkJoinTask im
}
else if (i != 0)
t.fork();
- else if (t.waitingInvoke() < NORMAL && ex == null)
- ex = t.getException();
+ else {
+ t.quietlyInvoke();
+ if (ex == null && t.status < NORMAL)
+ ex = t.getException();
+ }
}
for (int i = 1; i <= last; ++i) {
ForkJoinTask t = tasks[i];
if (t != null) {
if (ex != null)
t.cancel(false);
- else if (t.waitingJoin() < NORMAL && ex == null)
- ex = t.getException();
+ else {
+ t.quietlyJoin();
+ if (ex == null && t.status < NORMAL)
+ ex = t.getException();
+ }
}
}
if (ex != null)
@@ -488,17 +468,18 @@ public abstract class ForkJoinTask im
/**
* Forks all tasks in the specified collection, returning when
* {@code isDone} holds for each task or an (unchecked) exception
- * is encountered. If any task encounters an exception, others
- * may be, but are not guaranteed to be, cancelled. If more than
- * one task encounters an exception, then this method throws any
- * one of these exceptions. The individual status of each task
- * may be checked using {@link #getException()} and related
- * methods. The behavior of this operation is undefined if the
- * specified collection is modified while the operation is in
- * progress.
+ * is encountered, in which case the exception is rethrown. If
+ * more than one task encounters an exception, then this method
+ * throws any one of these exceptions. If any task encounters an
+ * exception, others may be cancelled. However, the execution
+ * status of individual tasks is not guaranteed upon exceptional
+ * return. The status of each task may be obtained using {@link
+ * #getException()} and related methods to check if they have been
+ * cancelled, completed normally or exceptionally, or left
+ * unprocessed.
*
* This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
+ * ForkJoinPool} computations (as may be determined using method
* {@link #inForkJoinPool}). Attempts to invoke in other contexts
* result in exceptions or errors, possibly including {@code
* ClassCastException}.
@@ -525,16 +506,22 @@ public abstract class ForkJoinTask im
}
else if (i != 0)
t.fork();
- else if (t.waitingInvoke() < NORMAL && ex == null)
- ex = t.getException();
+ else {
+ t.quietlyInvoke();
+ if (ex == null && t.status < NORMAL)
+ 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 if (t.waitingJoin() < NORMAL && ex == null)
- ex = t.getException();
+ else {
+ t.quietlyJoin();
+ if (ex == null && t.status < NORMAL)
+ ex = t.getException();
+ }
}
}
if (ex != null)
@@ -544,36 +531,41 @@ public abstract class ForkJoinTask im
/**
* Attempts to cancel execution of this task. This attempt will
- * fail if the task has already completed, has already been
- * cancelled, or could not be cancelled for some other reason. If
- * successful, and this task has not started when cancel is
- * called, execution of this task is suppressed, {@link
- * #isCancelled} will report true, and {@link #join} will result
- * in a {@code CancellationException} being thrown.
+ * fail if the task has already completed or could not be
+ * cancelled for some other reason. If successful, and this task
+ * has not started when {@code cancel} is called, execution of
+ * this task is suppressed. After this method returns
+ * successfully, unless there is an intervening call to {@link
+ * #reinitialize}, subsequent calls to {@link #isCancelled},
+ * {@link #isDone}, and {@code cancel} will return {@code true}
+ * and calls to {@link #join} and related methods will result in
+ * {@code CancellationException}.
*
* This method may be overridden in subclasses, but if so, must
- * still ensure that these minimal properties hold. In particular,
- * the {@code cancel} method itself must not throw exceptions.
+ * still ensure that these properties hold. In particular, the
+ * {@code 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 {@link #completeExceptionally}.
*
- * @param mayInterruptIfRunning this value is ignored in the
- * default implementation because tasks are not
- * cancelled via interruption
+ * @param mayInterruptIfRunning this value has no effect in the
+ * default implementation because interrupts are not used to
+ * control cancellation.
*
* @return {@code true} if this task is now cancelled
*/
public boolean cancel(boolean mayInterruptIfRunning) {
setCompletion(CANCELLED);
- return (status & COMPLETION_MASK) == CANCELLED;
+ return status == CANCELLED;
}
/**
- * Cancels, ignoring any exceptions it throws. Used during worker
- * and pool shutdown.
+ * Cancels, ignoring any exceptions thrown by cancel. Used during
+ * worker and pool shutdown. Cancel is spec'ed not to throw any
+ * exceptions, but if it does anyway, we have no recourse during
+ * shutdown, so guard against this case.
*/
final void cancelIgnoringExceptions() {
try {
@@ -583,9 +575,10 @@ public abstract class ForkJoinTask im
}
/**
- * Cancels ignoring exceptions if worker is terminating
+ * Cancels if current thread is a terminating worker thread,
+ * ignoring any exceptions thrown by cancel.
*/
- private void cancelIfTerminating() {
+ final void cancelIfTerminating() {
Thread t = Thread.currentThread();
if ((t instanceof ForkJoinWorkerThread) &&
((ForkJoinWorkerThread) t).isTerminating()) {
@@ -601,7 +594,7 @@ public abstract class ForkJoinTask im
}
public final boolean isCancelled() {
- return (status & COMPLETION_MASK) == CANCELLED;
+ return status == CANCELLED;
}
/**
@@ -610,7 +603,7 @@ public abstract class ForkJoinTask im
* @return {@code true} if this task threw an exception or was cancelled
*/
public final boolean isCompletedAbnormally() {
- return (status & COMPLETION_MASK) < NORMAL;
+ return status < NORMAL;
}
/**
@@ -621,7 +614,7 @@ public abstract class ForkJoinTask im
* exception and was not cancelled
*/
public final boolean isCompletedNormally() {
- return (status & COMPLETION_MASK) == NORMAL;
+ return status == NORMAL;
}
/**
@@ -632,7 +625,7 @@ public abstract class ForkJoinTask im
* @return the exception, or {@code null} if none
*/
public final Throwable getException() {
- int s = status & COMPLETION_MASK;
+ int s = status;
return ((s >= NORMAL) ? null :
(s == CANCELLED) ? new CancellationException() :
exceptionMap.get(this));
@@ -660,13 +653,14 @@ public abstract class ForkJoinTask im
/**
* Completes this task, and if not already aborted or cancelled,
- * returning a {@code null} result upon {@code join} and related
- * operations. This method may be used to provide results for
- * asynchronous tasks, or to provide alternative handling for
- * tasks that would not otherwise complete normally. Its use in
- * other situations is discouraged. This method is
- * overridable, but overridden versions must invoke {@code super}
- * implementation to maintain guarantees.
+ * returning the given value as the result of subsequent
+ * invocations of {@code join} and related operations. This method
+ * may be used to provide results for asynchronous tasks, or to
+ * provide alternative handling for tasks that would not otherwise
+ * complete normally. Its use in other situations is
+ * discouraged. This method is overridable, but overridden
+ * versions must invoke {@code super} implementation to maintain
+ * guarantees.
*
* @param value the result value for this task
*/
@@ -680,11 +674,25 @@ public abstract class ForkJoinTask im
setCompletion(NORMAL);
}
+ /**
+ * Waits if necessary for the computation to complete, and then
+ * retrieves its result.
+ *
+ * @return the computed result
+ * @throws CancellationException if the computation was cancelled
+ * @throws ExecutionException if the computation threw an
+ * exception
+ * @throws InterruptedException if the current thread is not a
+ * member of a ForkJoinPool and was interrupted while waiting
+ */
public final V get() throws InterruptedException, ExecutionException {
- int s = waitingJoin() & COMPLETION_MASK;
- if (Thread.interrupted())
- throw new InterruptedException();
- if (s < NORMAL) {
+ Thread t = Thread.currentThread();
+ if (t instanceof ForkJoinWorkerThread)
+ quietlyJoin();
+ else
+ externalInterruptibleAwaitDone(false, 0L);
+ int s = status;
+ if (s != NORMAL) {
Throwable ex;
if (s == CANCELLED)
throw new CancellationException();
@@ -694,75 +702,34 @@ public abstract class ForkJoinTask im
return getRawResult();
}
+ /**
+ * Waits if necessary for at most the given time for the computation
+ * to complete, and then retrieves its result, if available.
+ *
+ * @param timeout the maximum time to wait
+ * @param unit the time unit of the timeout argument
+ * @return the computed result
+ * @throws CancellationException if the computation was cancelled
+ * @throws ExecutionException if the computation threw an
+ * exception
+ * @throws InterruptedException if the current thread is not a
+ * member of a ForkJoinPool and was interrupted while waiting
+ * @throws TimeoutException if the wait timed out
+ */
public final V get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException {
+ long nanos = unit.toNanos(timeout);
Thread t = Thread.currentThread();
- ForkJoinPool pool;
- if (t instanceof ForkJoinWorkerThread) {
- ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
- if (status >= 0 && w.unpushTask(this))
- tryExec();
- pool = w.pool;
- }
+ if (t instanceof ForkJoinWorkerThread)
+ ((ForkJoinWorkerThread)t).joinTask(this, true, nanos);
else
- pool = null;
- /*
- * Timed wait loop intermixes cases for fj (pool != null) and
- * non FJ threads. For FJ, decrement pool count but don't try
- * for replacement; increment count on completion. For non-FJ,
- * deal with interrupts. This is messy, but a little less so
- * than is splitting the FJ and nonFJ cases.
- */
- boolean interrupted = false;
- boolean dec = false; // true if pool count decremented
- for (;;) {
- if (Thread.interrupted() && pool == null) {
- interrupted = true;
- break;
- }
- int s = status;
- if (s < 0)
- break;
- if (UNSAFE.compareAndSwapInt(this, statusOffset,
- s, s | SIGNAL)) {
- long startTime = System.nanoTime();
- long nanos = unit.toNanos(timeout);
- long nt; // wait time
- while (status >= 0 &&
- (nt = nanos - (System.nanoTime() - startTime)) > 0) {
- if (pool != null && !dec)
- dec = pool.tryDecrementRunningCount();
- else {
- long ms = nt / 1000000;
- int ns = (int) (nt % 1000000);
- try {
- synchronized(this) {
- if (status >= 0)
- wait(ms, ns);
- }
- } catch (InterruptedException ie) {
- if (pool != null)
- cancelIfTerminating();
- else {
- interrupted = true;
- break;
- }
- }
- }
- }
- break;
- }
- }
- if (pool != null && dec)
- pool.updateRunningCount(1);
- if (interrupted)
- throw new InterruptedException();
- int es = status & COMPLETION_MASK;
- if (es != NORMAL) {
+ externalInterruptibleAwaitDone(true, nanos);
+ int s = status;
+ if (s != NORMAL) {
Throwable ex;
- if (es == CANCELLED)
+ if (s == CANCELLED)
throw new CancellationException();
- if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
+ if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
throw new ExecutionException(ex);
throw new TimeoutException();
}
@@ -770,61 +737,55 @@ public abstract class ForkJoinTask im
}
/**
- * Possibly executes other tasks until this task {@link #isDone is
- * done}, then returns the result of the computation. This method
- * may be more efficient than {@code join}, but is only applicable
- * when there are no potential dependencies between continuation
- * of the current task and that of any other task that might be
- * executed while helping. (This usually holds for pure
- * divide-and-conquer tasks).
- *
- * This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
- * {@link #inForkJoinPool}). Attempts to invoke in other contexts
- * result in exceptions or errors, possibly including {@code
- * ClassCastException}.
- *
- * @return the computed result
- */
- public final V helpJoin() {
- return reportResult(busyJoin());
- }
-
- /**
- * Possibly executes other tasks until this task {@link #isDone is
- * done}. This method may be useful when processing collections
- * of tasks when some have been cancelled or otherwise known to
- * have aborted.
- *
- *
This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
- * {@link #inForkJoinPool}). Attempts to invoke in other contexts
- * result in exceptions or errors, possibly including {@code
- * ClassCastException}.
- */
- public final void quietlyHelpJoin() {
- busyJoin();
- }
-
- /**
- * Joins this task, without returning its result or throwing an
+ * Joins this task, without returning its result or throwing its
* 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() {
- waitingJoin();
+ Thread t;
+ if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
+ ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
+ if (status >= 0) {
+ if (w.unpushTask(this)) {
+ boolean completed;
+ try {
+ completed = exec();
+ } catch (Throwable rex) {
+ setExceptionalCompletion(rex);
+ return;
+ }
+ if (completed) {
+ setCompletion(NORMAL);
+ return;
+ }
+ }
+ w.joinTask(this, false, 0L);
+ }
+ }
+ else
+ externalAwaitDone();
}
/**
* 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.
+ * necessary, without returning its result or throwing its
+ * exception.
*/
public final void quietlyInvoke() {
- waitingInvoke();
+ if (status >= 0) {
+ boolean completed;
+ try {
+ completed = exec();
+ } catch (Throwable rex) {
+ setExceptionalCompletion(rex);
+ return;
+ }
+ if (completed)
+ setCompletion(NORMAL);
+ else
+ quietlyJoin();
+ }
}
/**
@@ -835,7 +796,7 @@ public abstract class ForkJoinTask im
* processed.
*
* This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
+ * ForkJoinPool} computations (as may be determined using method
* {@link #inForkJoinPool}). Attempts to invoke in other contexts
* result in exceptions or errors, possibly including {@code
* ClassCastException}.
@@ -854,9 +815,15 @@ public abstract class ForkJoinTask im
* under any other usage conditions are not guaranteed.
* This method may be useful when executing
* pre-constructed trees of subtasks in loops.
+ *
+ * Upon completion of this method, {@code isDone()} reports
+ * {@code false}, and {@code getException()} reports {@code
+ * null}. However, the value returned by {@code getRawResult} is
+ * unaffected. To clear this value, you can invoke {@code
+ * setRawResult(null)}.
*/
public void reinitialize() {
- if ((status & COMPLETION_MASK) == EXCEPTIONAL)
+ if (status == EXCEPTIONAL)
exceptionMap.remove(this);
status = 0;
}
@@ -894,7 +861,7 @@ public abstract class ForkJoinTask im
* were not, stolen.
*
* This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
+ * ForkJoinPool} computations (as may be determined using method
* {@link #inForkJoinPool}). Attempts to invoke in other contexts
* result in exceptions or errors, possibly including {@code
* ClassCastException}.
@@ -913,7 +880,7 @@ public abstract class ForkJoinTask im
* fork other tasks.
*
* This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
+ * ForkJoinPool} computations (as may be determined using method
* {@link #inForkJoinPool}). Attempts to invoke in other contexts
* result in exceptions or errors, possibly including {@code
* ClassCastException}.
@@ -936,7 +903,7 @@ public abstract class ForkJoinTask im
* exceeded.
*
* This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
+ * ForkJoinPool} computations (as may be determined using method
* {@link #inForkJoinPool}). Attempts to invoke in other contexts
* result in exceptions or errors, possibly including {@code
* ClassCastException}.
@@ -994,7 +961,7 @@ public abstract class ForkJoinTask im
* otherwise.
*
* This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
+ * ForkJoinPool} computations (as may be determined using method
* {@link #inForkJoinPool}). Attempts to invoke in other contexts
* result in exceptions or errors, possibly including {@code
* ClassCastException}.
@@ -1013,7 +980,7 @@ public abstract class ForkJoinTask im
* be useful otherwise.
*
* This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
+ * ForkJoinPool} computations (as may be determined using method
* {@link #inForkJoinPool}). Attempts to invoke in other contexts
* result in exceptions or errors, possibly including {@code
* ClassCastException}.
@@ -1036,7 +1003,7 @@ public abstract class ForkJoinTask im
* otherwise.
*
* This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
+ * ForkJoinPool} computations (as may be determined using method
* {@link #inForkJoinPool}). Attempts to invoke in other contexts
* result in exceptions or errors, possibly including {@code
* ClassCastException}.
@@ -1146,7 +1113,7 @@ public abstract class ForkJoinTask im
private static final long serialVersionUID = -7721805057305804111L;
/**
- * Saves the state to a stream.
+ * Saves the state to a stream (that is, serializes it).
*
* @serialData the current run status and the exception thrown
* during execution, or {@code null} if none
@@ -1159,14 +1126,13 @@ public abstract class ForkJoinTask im
}
/**
- * Reconstitutes the instance from a stream.
+ * Reconstitutes the instance from a stream (that is, deserializes it).
*
* @param s the stream
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
- status |= SIGNAL; // conservatively set external signal
Object ex = s.readObject();
if (ex != null)
setExceptionalCompletion((Throwable) ex);