--- jsr166/src/jsr166y/ForkJoinTask.java 2010/07/07 19:52:31 1.49
+++ jsr166/src/jsr166y/ForkJoinTask.java 2010/09/17 14:24:56 1.62
@@ -28,10 +28,10 @@ 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 +100,7 @@ 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
@@ -144,24 +144,28 @@ 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 value COMPLETED. 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 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
private static final int NORMAL = -1;
@@ -188,75 +192,91 @@ 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)
+ 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 int internalAwaitDone() {
- int s;
+ final void internalAwaitDone() {
+ int s; // the odd construction reduces lock bias effects
while ((s = status) >= 0) {
- synchronized(this) {
- if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
- do {
- try {
- wait();
- } catch (InterruptedException ie) {
- cancelIfTerminating();
- }
- } while ((s = status) >= 0);
- break;
+ try {
+ synchronized (this) {
+ if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
+ wait();
}
+ } catch (InterruptedException ie) {
+ cancelIfTerminating();
}
}
+ }
+
+ /**
+ * Blocks a worker thread until completed or timed out. Called
+ * only by pool.
+ *
+ * @return status on exit
+ */
+ 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.
- * @return status on exit
*/
- private int externalAwaitDone() {
+ private void externalAwaitDone() {
int s;
while ((s = status) >= 0) {
- synchronized(this) {
+ synchronized (this) {
if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
boolean interrupted = false;
- do {
+ while (status >= 0) {
try {
wait();
} catch (InterruptedException ie) {
interrupted = true;
}
- } while ((s = status) >= 0);
+ }
if (interrupted)
Thread.currentThread().interrupt();
break;
}
}
}
- return s;
}
/**
@@ -264,7 +284,7 @@ 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;
@@ -275,67 +295,6 @@ 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);
- }
- w.joinTask(this);
- return status;
- }
- 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);
- }
- if (completed)
- stat = setCompletion(NORMAL);
- else
- stat = 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
/**
@@ -371,28 +330,41 @@ 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
@@ -413,12 +385,14 @@ 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
@@ -440,16 +414,22 @@ 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)
@@ -459,14 +439,15 @@ 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
@@ -496,16 +477,22 @@ 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)
@@ -543,8 +530,10 @@ public abstract class ForkJoinTask im
}
/**
- * 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 {
@@ -554,9 +543,10 @@ 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()) {
@@ -631,13 +621,14 @@ 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
*/
@@ -651,10 +642,26 @@ public abstract class ForkJoinTask im
setCompletion(NORMAL);
}
+ /**
+ * @throws CancellationException {@inheritDoc}
+ */
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)
@@ -665,6 +672,9 @@ public abstract class ForkJoinTask im
return getRawResult();
}
+ /**
+ * @throws CancellationException {@inheritDoc}
+ */
public final V get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException {
Thread t = Thread.currentThread();
@@ -672,13 +682,13 @@ 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
@@ -686,18 +696,17 @@ 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) {
@@ -707,7 +716,7 @@ 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);
}
@@ -741,24 +750,55 @@ 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();
+ }
}
/**
@@ -1080,7 +1120,7 @@ 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
@@ -1093,7 +1133,7 @@ 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
*/
@@ -1103,8 +1143,6 @@ public abstract class ForkJoinTask im
Object ex = s.readObject();
if (ex != null)
setExceptionalCompletion((Throwable) ex);
- if (status < 0)
- synchronized (this) { notifyAll(); }
}
// Unsafe mechanics