--- jsr166/src/jsr166y/ForkJoinTask.java 2010/07/23 16:49:11 1.51
+++ jsr166/src/jsr166y/ForkJoinTask.java 2010/10/16 16:37:30 1.65
@@ -7,7 +7,6 @@
package jsr166y;
import java.util.concurrent.*;
-
import java.io.Serializable;
import java.util.Collection;
import java.util.Collections;
@@ -28,10 +27,10 @@ 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
@@ -100,7 +99,7 @@ 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}.
*
*
Most base support methods are {@code final}, to prevent
* overriding of implementations that are intrinsically tied to the
@@ -144,7 +143,8 @@ 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.
*/
/*
@@ -152,7 +152,7 @@ public abstract class ForkJoinTask im
* 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
- * COMPLETED. CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
+ * 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
@@ -164,7 +164,7 @@ public abstract class ForkJoinTask im
* them.
*/
- /** Run status of this task */
+ /** The run status of this task */
volatile int status; // accessed directly by pool and workers
private static final int NORMAL = -1;
@@ -191,37 +191,38 @@ 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 != 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 completion. Called only by
+ * pool. Currently unused -- pool-based waits use timeout
+ * version below.
*/
final void internalAwaitDone() {
int s; // the odd construction reduces lock bias effects
while ((s = status) >= 0) {
try {
- synchronized(this) {
+ synchronized (this) {
if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
wait();
}
@@ -232,16 +233,37 @@ public abstract class ForkJoinTask im
}
/**
- * Blocks a non-worker-thread until completion.
+ * Blocks a worker thread until completed or timed out. Called
+ * only by pool.
+ *
* @return status on exit
*/
- private int externalAwaitDone() {
+ final int internalAwaitDone(long millis) {
+ int s;
+ if ((s = status) >= 0) {
+ try {
+ synchronized (this) {
+ if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
+ wait(millis, 0);
+ }
+ } catch (InterruptedException ie) {
+ cancelIfTerminating();
+ }
+ s = status;
+ }
+ return s;
+ }
+
+ /**
+ * Blocks a non-worker-thread until completion.
+ */
+ private void externalAwaitDone() {
int s;
while ((s = status) >= 0) {
- synchronized(this) {
- if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
+ synchronized (this) {
+ if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
boolean interrupted = false;
- while ((s = status) >= 0) {
+ while (status >= 0) {
try {
wait();
} catch (InterruptedException ie) {
@@ -254,7 +276,6 @@ public abstract class ForkJoinTask im
}
}
}
- return s;
}
/**
@@ -262,7 +283,7 @@ public abstract class ForkJoinTask im
* doesn't wait for completion otherwise. Primary execution method
* for ForkJoinWorkerThread.
*/
- final void tryExec() {
+ final void quietlyExec() {
try {
if (status < 0 || !exec())
return;
@@ -273,63 +294,6 @@ public abstract class ForkJoinTask im
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
- */
- private int doJoin() {
- int stat;
- if ((stat = status) < 0)
- return stat;
- Thread t = Thread.currentThread();
- ForkJoinWorkerThread w;
- if (t instanceof ForkJoinWorkerThread) {
- if ((w = (ForkJoinWorkerThread) t).unpushTask(this)) {
- boolean completed;
- try {
- completed = exec();
- } catch (Throwable rex) {
- return setExceptionalCompletion(rex);
- }
- if (completed)
- return setCompletion(NORMAL);
- }
- return w.joinTask(this);
- }
- return externalAwaitDone();
- }
-
- /**
- * Unless done, calls exec and records status if completed, or
- * waits for completion otherwise.
- * @return status on exit
- */
- private int doInvoke() {
- int stat;
- if ((stat = status) >= 0) {
- boolean completed;
- try {
- completed = exec();
- } catch (Throwable rex) {
- return setExceptionalCompletion(rex);
- }
- stat = completed ? setCompletion(NORMAL) : doJoin();
- }
- return stat;
- }
-
- /**
- * 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();
- }
-
// public methods
/**
@@ -365,28 +329,41 @@ public abstract class ForkJoinTask im
* @return the computed result
*/
public final V join() {
- return reportResult(doJoin());
+ 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(doInvoke());
+ 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
@@ -407,12 +384,14 @@ 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
@@ -434,16 +413,22 @@ public abstract class ForkJoinTask im
}
else if (i != 0)
t.fork();
- else if (t.doInvoke() < 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.doJoin() < NORMAL && ex == null)
- ex = t.getException();
+ else {
+ t.quietlyJoin();
+ if (ex == null && t.status < NORMAL)
+ ex = t.getException();
+ }
}
}
if (ex != null)
@@ -453,14 +438,15 @@ 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
@@ -490,16 +476,22 @@ public abstract class ForkJoinTask im
}
else if (i != 0)
t.fork();
- else if (t.doInvoke() < 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.doJoin() < NORMAL && ex == null)
- ex = t.getException();
+ else {
+ t.quietlyJoin();
+ if (ex == null && t.status < NORMAL)
+ ex = t.getException();
+ }
}
}
if (ex != null)
@@ -532,12 +524,15 @@ public abstract class ForkJoinTask im
* @return {@code true} if this task is now cancelled
*/
public boolean cancel(boolean mayInterruptIfRunning) {
- return setCompletion(CANCELLED) == CANCELLED;
+ setCompletion(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 {
@@ -547,7 +542,8 @@ 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.
*/
final void cancelIfTerminating() {
Thread t = Thread.currentThread();
@@ -624,13 +620,14 @@ 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
*/
@@ -644,10 +641,34 @@ 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 = doJoin();
- if (Thread.interrupted())
- throw new InterruptedException();
+ int s;
+ if (Thread.currentThread() instanceof ForkJoinWorkerThread) {
+ quietlyJoin();
+ s = status;
+ }
+ else {
+ while ((s = status) >= 0) {
+ synchronized (this) { // interruptible form of awaitDone
+ if (UNSAFE.compareAndSwapInt(this, statusOffset,
+ s, SIGNAL)) {
+ while (status >= 0)
+ wait();
+ }
+ }
+ }
+ }
if (s < NORMAL) {
Throwable ex;
if (s == CANCELLED)
@@ -658,6 +679,20 @@ 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 {
Thread t = Thread.currentThread();
@@ -665,13 +700,13 @@ public abstract class ForkJoinTask im
if (t instanceof ForkJoinWorkerThread) {
ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
if (status >= 0 && w.unpushTask(this))
- tryExec();
+ quietlyExec();
pool = w.pool;
}
else
pool = null;
/*
- * Timed wait loop intermixes cases for fj (pool != null) and
+ * 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
@@ -679,18 +714,17 @@ public abstract class ForkJoinTask im
*/
boolean interrupted = false;
boolean dec = false; // true if pool count decremented
+ long nanos = unit.toNanos(timeout);
for (;;) {
- if (Thread.interrupted() && pool == null) {
+ if (pool == null && Thread.interrupted()) {
interrupted = true;
break;
}
int s = status;
if (s < 0)
break;
- if (UNSAFE.compareAndSwapInt(this, statusOffset,
- s, s | SIGNAL)) {
+ if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
long startTime = System.nanoTime();
- long nanos = unit.toNanos(timeout);
long nt; // wait time
while (status >= 0 &&
(nt = nanos - (System.nanoTime() - startTime)) > 0) {
@@ -700,7 +734,7 @@ public abstract class ForkJoinTask im
long ms = nt / 1000000;
int ns = (int) (nt % 1000000);
try {
- synchronized(this) {
+ synchronized (this) {
if (status >= 0)
wait(ms, ns);
}
@@ -734,24 +768,55 @@ public abstract class ForkJoinTask im
}
/**
- * 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() {
- doJoin();
+ 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);
+ }
+ }
+ 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() {
- doInvoke();
+ if (status >= 0) {
+ boolean completed;
+ try {
+ completed = exec();
+ } catch (Throwable rex) {
+ setExceptionalCompletion(rex);
+ return;
+ }
+ if (completed)
+ setCompletion(NORMAL);
+ else
+ quietlyJoin();
+ }
}
/**
@@ -1073,7 +1138,7 @@ 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
@@ -1086,7 +1151,7 @@ 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
*/