--- jsr166/src/jsr166y/ForkJoinTask.java 2010/04/18 12:51:18 1.47
+++ jsr166/src/jsr166y/ForkJoinTask.java 2010/07/23 13:07:43 1.50
@@ -64,10 +64,7 @@ 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
@@ -125,9 +122,8 @@ import java.util.WeakHashMap;
*
* 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
@@ -151,41 +147,30 @@ public abstract class ForkJoinTask im
* in a way that flows well in javadocs.
*/
- /**
- * 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). Signal counts are not directly
- * incremented by ForkJoinTask methods, but instead via a call to
- * requestSignal within ForkJoinPool.preJoin, once their need is
- * established.
- *
- * Completion of a stolen task with SIGNAL_MASK bits 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 16-28 are currently unused. Also value
- * 0x80000000 is available as spare completion value.
+ /*
+ * 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
+ * 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.
*/
+
+ /** 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_MASK = 0x0000ffff;
- private static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
- private static final int EXTERNAL_SIGNAL = 0x00008000;
+ 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
@@ -206,244 +191,143 @@ public abstract class ForkJoinTask im
* also clearing signal request bits.
*
* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
+ * @return status on exit
*/
- private void setCompletion(int completion) {
+ private int setCompletion(int completion) {
int s;
while ((s = status) >= 0) {
if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
- if ((s & SIGNAL_MASK) != 0) {
- Thread t = Thread.currentThread();
- if (t instanceof ForkJoinWorkerThread)
- ((ForkJoinWorkerThread) t).pool.updateRunningCount
- (s & INTERNAL_SIGNAL_MASK);
+ if (s == SIGNAL)
synchronized (this) { notifyAll(); }
- }
- return;
+ return completion;
}
}
+ return s;
}
/**
* Record exception and set exceptional completion
+ * @return status on exit
*/
- private void setDoneExceptionally(Throwable rex) {
+ private int setExceptionalCompletion(Throwable rex) {
exceptionMap.put(this, rex);
- setCompletion(EXCEPTIONAL);
- }
-
- /**
- * Main internal execution method: Unless done, calls exec and
- * records completion.
- *
- * @return true if ran and completed normally
- */
- final boolean tryExec() {
- try {
- if (status < 0 || !exec())
- return false;
- } catch (Throwable rex) {
- setDoneExceptionally(rex);
- return false;
- }
- setCompletion(NORMAL); // must be outside try block
- return true;
- }
-
- /**
- * Increments internal signal count (thus requesting signal upon
- * completion) unless already done. Call only once per join.
- * Used by ForkJoinPool.preJoin.
- *
- * @return status
- */
- final int requestSignal() {
- int s;
- do {} while ((s = status) >= 0 &&
- !UNSAFE.compareAndSwapInt(this, statusOffset, s, s + 1));
- return s;
+ return setCompletion(EXCEPTIONAL);
}
/**
- * Sets external signal request unless already done.
- *
- * @return status
- */
- private int requestExternalSignal() {
- int s;
- do {} while ((s = status) >= 0 &&
- !UNSAFE.compareAndSwapInt(this, statusOffset,
- s, s | EXTERNAL_SIGNAL));
- return s;
- }
-
- /*
- * Awaiting completion. The four versions, internal vs external X
- * untimed vs timed, have the same overall structure but differ
- * from each other enough to defy simple integration.
+ * Blocks a worker thread until completion. Called only by pool.
*/
-
- /**
- * Blocks a worker until this task is done, also maintaining pool
- * and signal counts
- */
- private void awaitDone(ForkJoinWorkerThread w) {
- if (status >= 0) {
- w.pool.preJoin(this);
- while (status >= 0) {
- try { // minimize lock scope
- synchronized(this) {
- if (status >= 0)
- wait();
- else { // help release; also helps avoid lock-biasing
- notifyAll();
- break;
- }
- }
- } catch (InterruptedException ie) {
- cancelIfTerminating();
+ final void internalAwaitDone() {
+ int s; // the odd construction reduces lock bias effects
+ while ((s = status) >= 0) {
+ try {
+ synchronized(this) {
+ if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
+ wait();
}
+ } catch (InterruptedException ie) {
+ cancelIfTerminating();
}
}
}
/**
- * Blocks a non-ForkJoin thread until this task is done.
+ * Blocks a non-worker-thread until completion.
+ * @return status on exit
*/
- private void externalAwaitDone() {
- if (requestExternalSignal() >= 0) {
- boolean interrupted = false;
- while (status >= 0) {
- try {
- synchronized(this) {
- if (status >= 0)
+ private int externalAwaitDone() {
+ int s;
+ while ((s = status) >= 0) {
+ synchronized(this) {
+ if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
+ boolean interrupted = false;
+ while ((s = status) >= 0) {
+ try {
wait();
- else {
- notifyAll();
- break;
+ } catch (InterruptedException ie) {
+ interrupted = true;
}
}
- } catch (InterruptedException ie) {
- interrupted = true;
+ if (interrupted)
+ Thread.currentThread().interrupt();
+ break;
}
}
- if (interrupted)
- Thread.currentThread().interrupt();
}
+ return s;
}
/**
- * Blocks a worker until this task is done or timeout elapses
+ * Unless done, calls exec and records status if completed, but
+ * doesn't wait for completion otherwise. Primary execution method
+ * for ForkJoinWorkerThread.
*/
- private void timedAwaitDone(ForkJoinWorkerThread w, long nanos) {
- if (status >= 0) {
- long startTime = System.nanoTime();
- ForkJoinPool pool = w.pool;
- pool.preJoin(this);
- while (status >= 0) {
- long nt = nanos - (System.nanoTime() - startTime);
- if (nt > 0) {
- long ms = nt / 1000000;
- int ns = (int) (nt % 1000000);
- try {
- synchronized(this) { if (status >= 0) wait(ms, ns); }
- } catch (InterruptedException ie) {
- cancelIfTerminating();
- }
- }
- else {
- int s; // adjust running count on timeout
- while ((s = status) >= 0 &&
- (s & INTERNAL_SIGNAL_MASK) != 0) {
- if (UNSAFE.compareAndSwapInt(this, statusOffset,
- s, s - 1)) {
- pool.updateRunningCount(1);
- break;
- }
- }
- break;
- }
- }
+ final void tryExec() {
+ try {
+ if (status < 0 || !exec())
+ return;
+ } catch (Throwable rex) {
+ setExceptionalCompletion(rex);
+ return;
}
+ setCompletion(NORMAL); // must be outside try block
}
/**
- * Blocks a non-ForkJoin thread until this task is done or timeout elapses
- */
- private void externalTimedAwaitDone(long nanos) {
- if (requestExternalSignal() >= 0) {
- long startTime = System.nanoTime();
- boolean interrupted = false;
- while (status >= 0) {
- long nt = nanos - (System.nanoTime() - startTime);
- if (nt <= 0)
- break;
- long ms = nt / 1000000;
- int ns = (int) (nt % 1000000);
+ * 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 {
- synchronized(this) { if (status >= 0) wait(ms, ns); }
- } catch (InterruptedException ie) {
- interrupted = true;
+ completed = exec();
+ } catch (Throwable rex) {
+ return setExceptionalCompletion(rex);
}
+ if (completed)
+ return setCompletion(NORMAL);
}
- if (interrupted)
- Thread.currentThread().interrupt();
- }
- }
-
- // reporting results
-
- /**
- * Returns result or throws the exception associated with status.
- * Uses Unsafe as a workaround for javac not allowing rethrow of
- * unchecked exceptions.
- */
- private V reportResult() {
- if ((status & COMPLETION_MASK) < NORMAL) {
- Throwable ex = getException();
- if (ex != null)
- UNSAFE.throwException(ex);
+ return w.joinTask(this);
}
- return getRawResult();
+ return externalAwaitDone();
}
/**
- * 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.
+ * Unless done, calls exec and records status if completed, or
+ * waits for completion otherwise.
+ * @return status on exit
*/
- 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 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 getRawResult();
+ return stat;
}
/**
- * Returns result or throws exception using j.u.c.Future conventions
- * with timeouts.
+ * Returns result or throws exception associated with given status.
+ * @param s the status
*/
- private V reportTimedFutureResult()
- throws InterruptedException, ExecutionException, TimeoutException {
- if (Thread.interrupted())
- throw new InterruptedException();
+ private V reportResult(int s) {
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();
+ if (s < NORMAL && (ex = getException()) != null)
+ UNSAFE.throwException(ex);
+ return getRawResult();
}
// public methods
@@ -481,8 +365,7 @@ public abstract class ForkJoinTask im
* @return the computed result
*/
public final V join() {
- quietlyJoin();
- return reportResult();
+ return reportResult(doJoin());
}
/**
@@ -493,9 +376,7 @@ public abstract class ForkJoinTask im
* @return the computed result
*/
public final V invoke() {
- if (!tryExec())
- quietlyJoin();
- return reportResult();
+ return reportResult(doInvoke());
}
/**
@@ -553,22 +434,16 @@ public abstract class ForkJoinTask im
}
else if (i != 0)
t.fork();
- else {
- t.quietlyInvoke();
- if (ex == null)
- ex = t.getException();
- }
+ else if (t.doInvoke() < NORMAL && ex == null)
+ ex = t.getException();
}
for (int i = 1; i <= last; ++i) {
ForkJoinTask t = tasks[i];
if (t != null) {
if (ex != null)
t.cancel(false);
- else {
- t.quietlyJoin();
- if (ex == null)
- ex = t.getException();
- }
+ else if (t.doJoin() < NORMAL && ex == null)
+ ex = t.getException();
}
}
if (ex != null)
@@ -615,22 +490,16 @@ public abstract class ForkJoinTask im
}
else if (i != 0)
t.fork();
- else {
- t.quietlyInvoke();
- if (ex == null)
- ex = t.getException();
- }
+ else if (t.doInvoke() < NORMAL && ex == null)
+ 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 {
- t.quietlyJoin();
- if (ex == null)
- ex = t.getException();
- }
+ else if (t.doJoin() < NORMAL && ex == null)
+ ex = t.getException();
}
}
if (ex != null)
@@ -663,8 +532,7 @@ public abstract class ForkJoinTask im
* @return {@code true} if this task is now cancelled
*/
public boolean cancel(boolean mayInterruptIfRunning) {
- setCompletion(CANCELLED);
- return (status & COMPLETION_MASK) == CANCELLED;
+ return setCompletion(CANCELLED) == CANCELLED;
}
/**
@@ -681,7 +549,7 @@ public abstract class ForkJoinTask im
/**
* Cancels ignoring exceptions if worker is terminating
*/
- private void cancelIfTerminating() {
+ final void cancelIfTerminating() {
Thread t = Thread.currentThread();
if ((t instanceof ForkJoinWorkerThread) &&
((ForkJoinWorkerThread) t).isTerminating()) {
@@ -697,7 +565,7 @@ public abstract class ForkJoinTask im
}
public final boolean isCancelled() {
- return (status & COMPLETION_MASK) == CANCELLED;
+ return status == CANCELLED;
}
/**
@@ -706,7 +574,7 @@ 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;
}
/**
@@ -717,7 +585,7 @@ public abstract class ForkJoinTask im
* exception and was not cancelled
*/
public final boolean isCompletedNormally() {
- return (status & COMPLETION_MASK) == NORMAL;
+ return status == NORMAL;
}
/**
@@ -728,7 +596,7 @@ 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));
@@ -749,9 +617,9 @@ 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));
}
/**
@@ -770,95 +638,99 @@ public abstract class ForkJoinTask im
try {
setRawResult(value);
} catch (Throwable rex) {
- setDoneExceptionally(rex);
+ setExceptionalCompletion(rex);
return;
}
setCompletion(NORMAL);
}
public final V get() throws InterruptedException, ExecutionException {
- quietlyJoin();
- return reportFutureResult();
+ int s = doJoin();
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ 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();
}
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 (!w.unpushTask(this) || !tryExec())
- timedAwaitDone(w, nanos);
+ if (status >= 0 && w.unpushTask(this))
+ tryExec();
+ pool = w.pool;
}
else
- externalTimedAwaitDone(nanos);
- return reportTimedFutureResult();
- }
-
- /**
- * 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() {
- quietlyHelpJoin();
- return reportResult();
- }
-
- /**
- * 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() {
- ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
- if (!w.unpushTask(this) || !tryExec()) {
- for (;;) {
- ForkJoinTask t;
- if (status < 0)
- return;
- else if ((t = w.scanWhileJoining(this)) != null)
- t.tryExec();
- else if (status < 0)
- return;
- else if (w.pool.preBlockHelpingJoin(this)) {
- while (status >= 0) { // variant of awaitDone
+ 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();
- else {
- notifyAll();
- break;
- }
+ wait(ms, ns);
}
} catch (InterruptedException ie) {
- cancelIfTerminating();
+ if (pool != null)
+ cancelIfTerminating();
+ else {
+ interrupted = true;
+ break;
+ }
}
}
- return;
}
+ break;
}
}
+ if (pool != null && dec)
+ pool.incrementRunningCount();
+ if (interrupted)
+ throw new InterruptedException();
+ int es = status;
+ if (es != NORMAL) {
+ Throwable ex;
+ if (es == CANCELLED)
+ throw new CancellationException();
+ if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
+ throw new ExecutionException(ex);
+ throw new TimeoutException();
+ }
+ return getRawResult();
}
/**
@@ -868,14 +740,7 @@ public abstract class ForkJoinTask im
* known to have aborted.
*/
public final void quietlyJoin() {
- Thread t = Thread.currentThread();
- if (t instanceof ForkJoinWorkerThread) {
- ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
- if (!w.unpushTask(this) || !tryExec())
- awaitDone(w);
- }
- else
- externalAwaitDone();
+ doJoin();
}
/**
@@ -886,8 +751,7 @@ public abstract class ForkJoinTask im
* known to have aborted.
*/
public final void quietlyInvoke() {
- if (!tryExec())
- quietlyJoin();
+ doInvoke();
}
/**
@@ -919,7 +783,7 @@ public abstract class ForkJoinTask im
* pre-constructed trees of subtasks in loops.
*/
public void reinitialize() {
- if ((status & COMPLETION_MASK) == EXCEPTIONAL)
+ if (status == EXCEPTIONAL)
exceptionMap.remove(this);
status = 0;
}
@@ -1229,11 +1093,9 @@ public abstract class ForkJoinTask im
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