--- jsr166/src/jsr166y/ForkJoinTask.java 2009/08/19 17:44:45 1.44
+++ jsr166/src/jsr166y/ForkJoinTask.java 2010/11/28 21:21:03 1.73
@@ -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
@@ -139,33 +154,43 @@ import java.util.WeakHashMap;
*/
public abstract class ForkJoinTask implements Future, Serializable {
- /**
- * Run control status bits packed into a single int to minimize
- * footprint and to ensure atomicity (via CAS). Status is
- * initially zero, and takes on nonnegative values until
- * completed, upon which status holds COMPLETED. CANCELLED, or
- * EXCEPTIONAL, which use the top 3 bits. Tasks undergoing
- * blocking waits by other threads have SIGNAL_MASK bits set --
- * bit 15 for external (nonFJ) waits, and the rest a count of
- * waiting FJ threads. (This representation relies on
- * ForkJoinPool max thread limits). Completion of a stolen task
- * with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
- * though suboptimal for some purposes, we use basic builtin
- * wait/notify to take advantage of "monitor inflation" in JVMs
- * that we would otherwise need to emulate to avoid adding further
- * per-task bookkeeping overhead. Note that bits 16-28 are
- * currently unused. Also value 0x80000000 is available as spare
- * completion value.
+ /*
+ * See the internal documentation of class ForkJoinPool for a
+ * general implementation overview. ForkJoinTasks are mainly
+ * responsible for maintaining their "status" field amidst relays
+ * to methods in ForkJoinWorkerThread and ForkJoinPool. The
+ * methods of this class are more-or-less layered into (1) basic
+ * 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 particular, most
+ * join mechanics are in method quietlyJoin, below.
+ */
+
+ /*
+ * 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.
*/
+
+ /** The run status of this task */
volatile int status; // accessed directly by pool and workers
- static final int COMPLETION_MASK = 0xe0000000;
- static final int NORMAL = 0xe0000000; // == mask
- static final int CANCELLED = 0xc0000000;
- static final int EXCEPTIONAL = 0xa0000000;
- static final int SIGNAL_MASK = 0x0000ffff;
- static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
- static final int EXTERNAL_SIGNAL = 0x00008000; // top bit of low word
+ 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
@@ -179,330 +204,132 @@ public abstract class ForkJoinTask im
Collections.synchronizedMap
(new WeakHashMap, Throwable>());
- // within-package utilities
-
- /**
- * Gets current worker thread, or null if not a worker thread.
- */
- static ForkJoinWorkerThread getWorker() {
- Thread t = Thread.currentThread();
- return ((t instanceof ForkJoinWorkerThread) ?
- (ForkJoinWorkerThread) t : null);
- }
-
- final boolean casStatus(int cmp, int val) {
- return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val);
- }
-
- /**
- * Workaround for not being able to rethrow unchecked exceptions.
- */
- static void rethrowException(Throwable ex) {
- if (ex != null)
- UNSAFE.throwException(ex);
- }
-
- // Setting completion status
+ // Maintaining completion status
/**
- * Marks completion and wakes up threads waiting to join this task.
+ * Marks completion and wakes up threads waiting to join this task,
+ * also clearing signal request bits.
*
* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
*/
- final void setCompletion(int completion) {
- ForkJoinPool pool = getPool();
- if (pool != null) {
- int s; // Clear signal bits while setting completion status
- do {} while ((s = status) >= 0 && !casStatus(s, completion));
-
- if ((s & SIGNAL_MASK) != 0) {
- if ((s &= INTERNAL_SIGNAL_MASK) != 0)
- pool.updateRunningCount(s);
- synchronized (this) { notifyAll(); }
- }
- }
- else
- externallySetCompletion(completion);
- }
-
- /**
- * Version of setCompletion for non-FJ threads. Leaves signal
- * bits for unblocked threads to adjust, and always notifies.
- */
- private void externallySetCompletion(int completion) {
- int s;
- do {} while ((s = status) >= 0 &&
- !casStatus(s, (s & SIGNAL_MASK) | completion));
- synchronized (this) { notifyAll(); }
- }
-
- /**
- * Sets status to indicate normal completion.
- */
- final void setNormalCompletion() {
- // Try typical fast case -- single CAS, no signal, not already done.
- // Manually expand casStatus to improve chances of inlining it
- if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL))
- setCompletion(NORMAL);
- }
-
- // internal waiting and notification
-
- /**
- * Performs the actual monitor wait for awaitDone.
- */
- private void doAwaitDone() {
- // Minimize lock bias and in/de-flation effects by maximizing
- // chances of waiting inside sync
- try {
- while (status >= 0)
- synchronized (this) { if (status >= 0) wait(); }
- } catch (InterruptedException ie) {
- onInterruptedWait();
- }
- }
-
- /**
- * Performs the actual timed monitor wait for awaitDone.
- */
- private void doAwaitDone(long startTime, long nanos) {
- synchronized (this) {
- try {
- while (status >= 0) {
- long nt = nanos - (System.nanoTime() - startTime);
- if (nt <= 0)
- break;
- wait(nt / 1000000, (int) (nt % 1000000));
- }
- } catch (InterruptedException ie) {
- onInterruptedWait();
- }
- }
- }
-
- // Awaiting completion
-
- /**
- * Sets status to indicate there is joiner, then waits for join,
- * surrounded with pool notifications.
- *
- * @return status upon exit
- */
- private int awaitDone(ForkJoinWorkerThread w,
- boolean maintainParallelism) {
- ForkJoinPool pool = (w == null) ? null : w.pool;
+ private void setCompletion(int completion) {
int s;
while ((s = status) >= 0) {
- if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
- if (pool == null || !pool.preJoin(this, maintainParallelism))
- doAwaitDone();
- if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
- adjustPoolCountsOnUnblock(pool);
+ if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
+ if (s != 0)
+ synchronized (this) { notifyAll(); }
break;
}
}
- return s;
}
/**
- * Timed version of awaitDone
+ * Records exception and sets exceptional completion.
*
- * @return status upon exit
- */
- private int awaitDone(ForkJoinWorkerThread w, long nanos) {
- ForkJoinPool pool = (w == null) ? null : w.pool;
- int s;
- while ((s = status) >= 0) {
- if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
- long startTime = System.nanoTime();
- if (pool == null || !pool.preJoin(this, false))
- doAwaitDone(startTime, nanos);
- if ((s = status) >= 0) {
- adjustPoolCountsOnCancelledWait(pool);
- s = status;
- }
- if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
- adjustPoolCountsOnUnblock(pool);
- break;
- }
- }
- return s;
- }
-
- /**
- * Notifies pool that thread is unblocked. Called by signalled
- * threads when woken by non-FJ threads (which is atypical).
- */
- private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
- int s;
- do {} while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
- if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
- pool.updateRunningCount(s);
- }
-
- /**
- * Notifies pool to adjust counts on cancelled or timed out wait.
- */
- private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
- if (pool != null) {
- int s;
- while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
- if (casStatus(s, s - 1)) {
- pool.updateRunningCount(1);
- break;
- }
- }
- }
- }
-
- /**
- * Handles interruptions during waits.
+ * @return status on exit
*/
- private void onInterruptedWait() {
- ForkJoinWorkerThread w = getWorker();
- if (w == null)
- Thread.currentThread().interrupt(); // re-interrupt
- else if (w.isTerminating())
- cancelIgnoringExceptions();
- // else if FJworker, ignore interrupt
- }
-
- // Recording and reporting exceptions
-
- private void setDoneExceptionally(Throwable rex) {
+ private void setExceptionalCompletion(Throwable rex) {
exceptionMap.put(this, rex);
setCompletion(EXCEPTIONAL);
}
/**
- * Throws the exception associated with status s.
- *
- * @throws the exception
+ * Blocks a worker thread until completed or timed out. Called
+ * only by pool.
*/
- private void reportException(int s) {
- if ((s &= COMPLETION_MASK) < NORMAL) {
- if (s == CANCELLED)
- throw new CancellationException();
- else
- rethrowException(exceptionMap.get(this));
+ final void internalAwaitDone(long millis, int nanos) {
+ int s = status;
+ if ((s == 0 &&
+ UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL)) ||
+ s > 0) {
+ try { // the odd construction reduces lock bias effects
+ synchronized (this) {
+ if (status > 0)
+ wait(millis, nanos);
+ else
+ notifyAll();
+ }
+ } catch (InterruptedException ie) {
+ cancelIfTerminating();
+ }
}
}
/**
- * Returns result or throws exception using j.u.c.Future conventions.
- * Only call when {@code isDone} known to be true or thread known
- * to be interrupted.
+ * Blocks a non-worker-thread until completion.
*/
- private V reportFutureResult()
- throws InterruptedException, ExecutionException {
- if (Thread.interrupted())
- throw new InterruptedException();
- int s = status & COMPLETION_MASK;
- if (s < NORMAL) {
- Throwable ex;
- if (s == CANCELLED)
- throw new CancellationException();
- if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
- throw new ExecutionException(ex);
+ private void externalAwaitDone() {
+ if (status >= 0) {
+ boolean interrupted = false;
+ synchronized (this) {
+ for (;;) {
+ int s = status;
+ if (s == 0)
+ UNSAFE.compareAndSwapInt(this, statusOffset,
+ 0, SIGNAL);
+ else if (s < 0) {
+ notifyAll();
+ break;
+ }
+ else {
+ try {
+ wait();
+ } catch (InterruptedException ie) {
+ interrupted = true;
+ }
+ }
+ }
+ }
+ if (interrupted)
+ Thread.currentThread().interrupt();
}
- return getRawResult();
}
/**
- * Returns result or throws exception using j.u.c.Future conventions
- * with timeouts.
+ * Blocks a non-worker-thread until completion or interruption or timeout.
*/
- private V reportTimedFutureResult()
- throws InterruptedException, ExecutionException, TimeoutException {
+ private void externalInterruptibleAwaitDone(boolean timed, long nanos)
+ throws InterruptedException {
if (Thread.interrupted())
throw new InterruptedException();
- Throwable ex;
- int s = status & COMPLETION_MASK;
- if (s == NORMAL)
- return getRawResult();
- else if (s == CANCELLED)
- throw new CancellationException();
- else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
- throw new ExecutionException(ex);
- else
- throw new TimeoutException();
- }
-
- // internal execution methods
-
- /**
- * Calls exec, recording completion, and rethrowing exception if
- * encountered. Caller should normally check status before calling.
- *
- * @return true if completed normally
- */
- private boolean tryExec() {
- try { // try block must contain only call to exec
- if (!exec())
- return false;
- } catch (Throwable rex) {
- setDoneExceptionally(rex);
- rethrowException(rex);
- return false; // not reached
- }
- setNormalCompletion();
- return true;
- }
-
- /**
- * Main execution method used by worker threads. Invokes
- * base computation unless already complete.
- */
- final void quietlyExec() {
if (status >= 0) {
- try {
- if (!exec())
- return;
- } catch (Throwable rex) {
- setDoneExceptionally(rex);
- return;
+ long startTime = timed ? System.nanoTime() : 0L;
+ synchronized (this) {
+ for (;;) {
+ long nt;
+ int s = status;
+ if (s == 0)
+ UNSAFE.compareAndSwapInt(this, statusOffset,
+ 0, SIGNAL);
+ else if (s < 0) {
+ notifyAll();
+ break;
+ }
+ else if (!timed)
+ wait();
+ else if ((nt = nanos - (System.nanoTime()-startTime)) > 0L)
+ wait(nt / 1000000, (int)(nt % 1000000));
+ else
+ break;
+ }
}
- setNormalCompletion();
}
}
/**
- * Calls exec(), recording but not rethrowing exception.
- * Caller should normally check status before calling.
- *
- * @return true if completed normally
+ * Unless done, calls exec and records status if completed, but
+ * doesn't wait for completion otherwise. Primary execution method
+ * for ForkJoinWorkerThread.
*/
- private boolean tryQuietlyInvoke() {
+ final void quietlyExec() {
try {
- if (!exec())
- return false;
+ if (status < 0 || !exec())
+ return;
} catch (Throwable rex) {
- setDoneExceptionally(rex);
- return false;
- }
- setNormalCompletion();
- return true;
- }
-
- /**
- * Cancels, ignoring any exceptions it throws.
- */
- final void cancelIgnoringExceptions() {
- try {
- cancel(false);
- } catch (Throwable ignore) {
+ setExceptionalCompletion(rex);
+ return;
}
- }
-
- /**
- * Main implementation of helpJoin
- */
- private int busyJoin(ForkJoinWorkerThread w) {
- int s;
- ForkJoinTask t;
- while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
- t.quietlyExec();
- return (s >= 0) ? awaitDone(w, false) : s; // block if no work
+ setCompletion(NORMAL); // must be outside try block
}
// public methods
@@ -518,7 +345,7 @@ 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}.
@@ -532,45 +359,55 @@ 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() {
- ForkJoinWorkerThread w = getWorker();
- if (w == null || status < 0 || !w.unpushTask(this) || !tryExec())
- reportException(awaitDone(w, true));
+ 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() {
- if (status >= 0 && tryExec())
- return getRawResult();
- else
- return join();
+ 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}.
@@ -588,15 +425,17 @@ 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}.
@@ -617,7 +456,7 @@ public abstract class ForkJoinTask im
t.fork();
else {
t.quietlyInvoke();
- if (ex == null)
+ if (ex == null && t.status < NORMAL)
ex = t.getException();
}
}
@@ -628,29 +467,30 @@ public abstract class ForkJoinTask im
t.cancel(false);
else {
t.quietlyJoin();
- if (ex == null)
+ if (ex == null && t.status < NORMAL)
ex = t.getException();
}
}
}
if (ex != null)
- rethrowException(ex);
+ UNSAFE.throwException(ex);
}
/**
* 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}.
@@ -679,7 +519,7 @@ public abstract class ForkJoinTask im
t.fork();
else {
t.quietlyInvoke();
- if (ex == null)
+ if (ex == null && t.status < NORMAL)
ex = t.getException();
}
}
@@ -690,43 +530,74 @@ public abstract class ForkJoinTask im
t.cancel(false);
else {
t.quietlyJoin();
- if (ex == null)
+ if (ex == null && t.status < NORMAL)
ex = t.getException();
}
}
}
if (ex != null)
- rethrowException(ex);
+ UNSAFE.throwException(ex);
return tasks;
}
/**
* 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 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 {
+ cancel(false);
+ } catch (Throwable ignore) {
+ }
+ }
+
+ /**
+ * Cancels if current thread is a terminating worker thread,
+ * ignoring any exceptions thrown by cancel.
+ */
+ final void cancelIfTerminating() {
+ Thread t = Thread.currentThread();
+ if ((t instanceof ForkJoinWorkerThread) &&
+ ((ForkJoinWorkerThread) t).isTerminating()) {
+ try {
+ cancel(false);
+ } catch (Throwable ignore) {
+ }
+ }
}
public final boolean isDone() {
@@ -734,7 +605,7 @@ public abstract class ForkJoinTask im
}
public final boolean isCancelled() {
- return (status & COMPLETION_MASK) == CANCELLED;
+ return status == CANCELLED;
}
/**
@@ -743,7 +614,7 @@ 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;
}
/**
@@ -754,7 +625,7 @@ public abstract class ForkJoinTask im
* exception and was not cancelled
*/
public final boolean isCompletedNormally() {
- return (status & COMPLETION_MASK) == NORMAL;
+ return status == NORMAL;
}
/**
@@ -765,7 +636,7 @@ 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));
@@ -786,20 +657,21 @@ public abstract class ForkJoinTask im
* thrown will be a {@code RuntimeException} with cause {@code ex}.
*/
public void completeExceptionally(Throwable ex) {
- setDoneExceptionally((ex instanceof RuntimeException) ||
- (ex instanceof Error) ? ex :
- new RuntimeException(ex));
+ setExceptionalCompletion((ex instanceof RuntimeException) ||
+ (ex instanceof Error) ? ex :
+ new RuntimeException(ex));
}
/**
* 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
*/
@@ -807,97 +679,124 @@ public abstract class ForkJoinTask im
try {
setRawResult(value);
} catch (Throwable rex) {
- setDoneExceptionally(rex);
+ setExceptionalCompletion(rex);
return;
}
- setNormalCompletion();
- }
-
- public final V get() throws InterruptedException, ExecutionException {
- ForkJoinWorkerThread w = getWorker();
- if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
- awaitDone(w, true);
- return reportFutureResult();
- }
-
- public final V get(long timeout, TimeUnit unit)
- throws InterruptedException, ExecutionException, TimeoutException {
- long nanos = unit.toNanos(timeout);
- ForkJoinWorkerThread w = getWorker();
- if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
- awaitDone(w, nanos);
- return reportTimedFutureResult();
+ setCompletion(NORMAL);
}
/**
- * 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}.
+ * 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 helpJoin() {
- ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
- if (status < 0 || !w.unpushTask(this) || !tryExec())
- reportException(busyJoin(w));
+ public final V get() throws InterruptedException, ExecutionException {
+ 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();
+ if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
+ throw new ExecutionException(ex);
+ }
return getRawResult();
}
/**
- * 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.
+ * Waits if necessary for at most the given time for the computation
+ * to complete, and then retrieves its result, if available.
*
- *
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}.
+ * @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 void quietlyHelpJoin() {
- if (status >= 0) {
- ForkJoinWorkerThread w =
- (ForkJoinWorkerThread) Thread.currentThread();
- if (!w.unpushTask(this) || !tryQuietlyInvoke())
- busyJoin(w);
+ public final V get(long timeout, TimeUnit unit)
+ throws InterruptedException, ExecutionException, TimeoutException {
+ long nanos = unit.toNanos(timeout);
+ Thread t = Thread.currentThread();
+ if (t instanceof ForkJoinWorkerThread)
+ ((ForkJoinWorkerThread)t).joinTask(this, true, nanos);
+ else
+ externalInterruptibleAwaitDone(true, nanos);
+ int s = status;
+ if (s != NORMAL) {
+ Throwable ex;
+ if (s == CANCELLED)
+ throw new CancellationException();
+ if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
+ throw new ExecutionException(ex);
+ throw new TimeoutException();
}
+ return getRawResult();
}
/**
- * 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() {
- if (status >= 0) {
- ForkJoinWorkerThread w = getWorker();
- if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
- awaitDone(w, true);
+ 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() {
- if (status >= 0 && !tryQuietlyInvoke())
- quietlyJoin();
+ if (status >= 0) {
+ boolean completed;
+ try {
+ completed = exec();
+ } catch (Throwable rex) {
+ setExceptionalCompletion(rex);
+ return;
+ }
+ if (completed)
+ setCompletion(NORMAL);
+ else
+ quietlyJoin();
+ }
}
/**
@@ -908,7 +807,7 @@ 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}.
@@ -927,9 +826,15 @@ 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;
}
@@ -948,11 +853,12 @@ public abstract class ForkJoinTask im
}
/**
- * Returns {@code true} if the current thread is executing as a
- * ForkJoinPool computation.
+ * Returns {@code true} if the current thread is a {@link
+ * ForkJoinWorkerThread} executing as a ForkJoinPool computation.
*
- * @return {@code true} if the current thread is executing as a
- * ForkJoinPool computation, or false otherwise
+ * @return {@code true} if the current thread is a {@link
+ * ForkJoinWorkerThread} executing as a ForkJoinPool computation,
+ * or {@code false} otherwise
*/
public static boolean inForkJoinPool() {
return Thread.currentThread() instanceof ForkJoinWorkerThread;
@@ -967,7 +873,7 @@ 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}.
@@ -986,7 +892,7 @@ 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}.
@@ -1009,7 +915,7 @@ 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}.
@@ -1067,7 +973,7 @@ 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}.
@@ -1086,7 +992,7 @@ 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}.
@@ -1109,7 +1015,7 @@ 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}.
@@ -1219,7 +1125,7 @@ public abstract class ForkJoinTask im
private static final long serialVersionUID = -7721805057305804111L;
/**
- * Save 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
@@ -1232,18 +1138,16 @@ public abstract class ForkJoinTask im
}
/**
- * Reconstitute 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 &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
- status |= EXTERNAL_SIGNAL; // conservatively set external signal
Object ex = s.readObject();
if (ex != null)
- setDoneExceptionally((Throwable) ex);
+ setExceptionalCompletion((Throwable) ex);
}
// Unsafe mechanics