--- jsr166/src/jsr166y/ForkJoinTask.java 2010/05/27 16:46:48 1.48
+++ jsr166/src/jsr166y/ForkJoinTask.java 2010/07/24 20:28:18 1.52
@@ -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
@@ -151,33 +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 the SIGNAL bit set.
- *
- * Completion of a stolen task with SIGNAL set awakens any waiters
- * via notifyAll. Even though suboptimal for some purposes, we use
+ /*
+ * The status field holds run control status bits packed into a
+ * single int to minimize footprint and to ensure atomicity (via
+ * CAS). Status is initially zero, and takes on nonnegative
+ * values until completed, upon which status holds value
+ * 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.
- *
- * Note that bits 1-28 are currently unused. Also value
- * 0x80000000 is available as spare completion value.
*/
+
+ /** Run status of this task */
volatile int status; // accessed directly by pool and workers
- private static final int COMPLETION_MASK = 0xe0000000;
- private static final int NORMAL = 0xe0000000; // == mask
- private static final int CANCELLED = 0xc0000000;
- private static final int EXCEPTIONAL = 0xa0000000;
- private static final int SIGNAL = 0x00000001;
+ private static final int NORMAL = -1;
+ private static final int CANCELLED = -2;
+ private static final int EXCEPTIONAL = -3;
+ private static final int SIGNAL = 1;
/**
* Table of exceptions thrown by tasks, to enable reporting by
@@ -204,7 +197,7 @@ public abstract class ForkJoinTask im
int s;
while ((s = status) >= 0) {
if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
- if ((s & SIGNAL) != 0)
+ if (s != 0)
synchronized (this) { notifyAll(); }
return completion;
}
@@ -225,19 +218,15 @@ public abstract class ForkJoinTask im
* Blocks a worker thread until completion. Called only by pool.
*/
final void internalAwaitDone() {
- int s;
+ int s; // the odd construction reduces lock bias effects
while ((s = status) >= 0) {
- synchronized(this) {
- if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
- do {
- try {
- wait();
- } catch (InterruptedException ie) {
- cancelIfTerminating();
- }
- } while (status >= 0);
- break;
+ try {
+ synchronized(this) {
+ if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
+ wait();
}
+ } catch (InterruptedException ie) {
+ cancelIfTerminating();
}
}
}
@@ -250,15 +239,15 @@ public abstract class ForkJoinTask im
int s;
while ((s = status) >= 0) {
synchronized(this) {
- if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
+ if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
boolean interrupted = false;
- do {
+ while ((s = status) >= 0) {
try {
wait();
} catch (InterruptedException ie) {
interrupted = true;
}
- } while ((s = status) >= 0);
+ }
if (interrupted)
Thread.currentThread().interrupt();
break;
@@ -270,7 +259,8 @@ public abstract class ForkJoinTask im
/**
* Unless done, calls exec and records status if completed, but
- * doesn't wait for completion otherwise.
+ * doesn't wait for completion otherwise. Primary execution method
+ * for ForkJoinWorkerThread.
*/
final void tryExec() {
try {
@@ -288,14 +278,14 @@ public abstract class ForkJoinTask im
* else waits for it.
* @return status on exit
*/
- private int waitingJoin() {
- int s = status;
- if (s < 0)
- return s;
- Thread t = Thread.currentThread();
- if (t instanceof ForkJoinWorkerThread) {
- ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
- if (w.unpushTask(this)) {
+ private int doJoin() {
+ int stat;
+ Thread t;
+ ForkJoinWorkerThread w;
+ if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
+ if ((stat = status) < 0)
+ return stat;
+ if ((w = (ForkJoinWorkerThread) t).unpushTask(this)) {
boolean completed;
try {
completed = exec();
@@ -305,10 +295,9 @@ public abstract class ForkJoinTask im
if (completed)
return setCompletion(NORMAL);
}
- return w.pool.awaitJoin(this);
+ return w.joinTask(this);
}
- else
- return externalAwaitDone();
+ return externalAwaitDone();
}
/**
@@ -316,42 +305,18 @@ public abstract class ForkJoinTask im
* waits for completion otherwise.
* @return status on exit
*/
- private int waitingInvoke() {
- int s = status;
- if (s < 0)
- return s;
- boolean completed;
- try {
- completed = exec();
- } catch (Throwable rex) {
- return setExceptionalCompletion(rex);
- }
- if (completed)
- return setCompletion(NORMAL);
- return waitingJoin();
- }
-
- /**
- * If this task is next in worker queue, runs it, else processes other
- * tasks until complete.
- * @return status on exit
- */
- private int busyJoin() {
- int s = status;
- if (s < 0)
- return s;
- ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
- if (w.unpushTask(this)) {
+ private int doInvoke() {
+ int stat;
+ if ((stat = status) >= 0) {
boolean completed;
try {
completed = exec();
} catch (Throwable rex) {
return setExceptionalCompletion(rex);
}
- if (completed)
- return setCompletion(NORMAL);
+ stat = completed ? setCompletion(NORMAL) : doJoin();
}
- return w.execWhileJoining(this);
+ return stat;
}
/**
@@ -400,7 +365,7 @@ public abstract class ForkJoinTask im
* @return the computed result
*/
public final V join() {
- return reportResult(waitingJoin());
+ return reportResult(doJoin());
}
/**
@@ -411,7 +376,7 @@ public abstract class ForkJoinTask im
* @return the computed result
*/
public final V invoke() {
- return reportResult(waitingInvoke());
+ return reportResult(doInvoke());
}
/**
@@ -469,7 +434,7 @@ public abstract class ForkJoinTask im
}
else if (i != 0)
t.fork();
- else if (t.waitingInvoke() < NORMAL && ex == null)
+ else if (t.doInvoke() < NORMAL && ex == null)
ex = t.getException();
}
for (int i = 1; i <= last; ++i) {
@@ -477,7 +442,7 @@ public abstract class ForkJoinTask im
if (t != null) {
if (ex != null)
t.cancel(false);
- else if (t.waitingJoin() < NORMAL && ex == null)
+ else if (t.doJoin() < NORMAL && ex == null)
ex = t.getException();
}
}
@@ -525,7 +490,7 @@ public abstract class ForkJoinTask im
}
else if (i != 0)
t.fork();
- else if (t.waitingInvoke() < NORMAL && ex == null)
+ else if (t.doInvoke() < NORMAL && ex == null)
ex = t.getException();
}
for (int i = 1; i <= last; ++i) {
@@ -533,7 +498,7 @@ public abstract class ForkJoinTask im
if (t != null) {
if (ex != null)
t.cancel(false);
- else if (t.waitingJoin() < NORMAL && ex == null)
+ else if (t.doJoin() < NORMAL && ex == null)
ex = t.getException();
}
}
@@ -567,13 +532,14 @@ 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;
}
/**
- * 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 {
@@ -585,7 +551,7 @@ 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()) {
@@ -601,7 +567,7 @@ public abstract class ForkJoinTask im
}
public final boolean isCancelled() {
- return (status & COMPLETION_MASK) == CANCELLED;
+ return status == CANCELLED;
}
/**
@@ -610,7 +576,7 @@ public abstract class ForkJoinTask im
* @return {@code true} if this task threw an exception or was cancelled
*/
public final boolean isCompletedAbnormally() {
- return (status & COMPLETION_MASK) < NORMAL;
+ return status < NORMAL;
}
/**
@@ -621,7 +587,7 @@ public abstract class ForkJoinTask im
* exception and was not cancelled
*/
public final boolean isCompletedNormally() {
- return (status & COMPLETION_MASK) == NORMAL;
+ return status == NORMAL;
}
/**
@@ -632,7 +598,7 @@ 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));
@@ -681,7 +647,7 @@ public abstract class ForkJoinTask im
}
public final V get() throws InterruptedException, ExecutionException {
- int s = waitingJoin() & COMPLETION_MASK;
+ int s = doJoin();
if (Thread.interrupted())
throw new InterruptedException();
if (s < NORMAL) {
@@ -707,7 +673,7 @@ public abstract class ForkJoinTask im
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
@@ -723,8 +689,7 @@ public abstract class ForkJoinTask im
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
@@ -754,10 +719,10 @@ public abstract class ForkJoinTask im
}
}
if (pool != null && dec)
- pool.updateRunningCount(1);
+ pool.incrementRunningCount();
if (interrupted)
throw new InterruptedException();
- int es = status & COMPLETION_MASK;
+ int es = status;
if (es != NORMAL) {
Throwable ex;
if (es == CANCELLED)
@@ -770,50 +735,13 @@ public abstract class ForkJoinTask im
}
/**
- * Possibly executes other tasks until this task {@link #isDone is
- * done}, then returns the result of the computation. This method
- * may be more efficient than {@code join}, but is only applicable
- * when there are no potential dependencies between continuation
- * of the current task and that of any other task that might be
- * executed while helping. (This usually holds for pure
- * divide-and-conquer tasks).
- *
- * This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
- * {@link #inForkJoinPool}). Attempts to invoke in other contexts
- * result in exceptions or errors, possibly including {@code
- * ClassCastException}.
- *
- * @return the computed result
- */
- public final V helpJoin() {
- return reportResult(busyJoin());
- }
-
- /**
- * Possibly executes other tasks until this task {@link #isDone is
- * done}. This method may be useful when processing collections
- * of tasks when some have been cancelled or otherwise known to
- * have aborted.
- *
- *
This method may be invoked only from within {@code
- * ForkJoinTask} computations (as may be determined using method
- * {@link #inForkJoinPool}). Attempts to invoke in other contexts
- * result in exceptions or errors, possibly including {@code
- * ClassCastException}.
- */
- public final void quietlyHelpJoin() {
- busyJoin();
- }
-
- /**
* Joins this task, without returning its result or throwing an
* exception. This method may be useful when processing
* collections of tasks when some have been cancelled or otherwise
* known to have aborted.
*/
public final void quietlyJoin() {
- waitingJoin();
+ doJoin();
}
/**
@@ -824,7 +752,7 @@ public abstract class ForkJoinTask im
* known to have aborted.
*/
public final void quietlyInvoke() {
- waitingInvoke();
+ doInvoke();
}
/**
@@ -856,7 +784,7 @@ 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;
}
@@ -1166,7 +1094,6 @@ public abstract class ForkJoinTask im
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
- status |= SIGNAL; // conservatively set external signal
Object ex = s.readObject();
if (ex != null)
setExceptionalCompletion((Throwable) ex);