--- jsr166/src/jsr166y/ForkJoinTask.java 2010/05/27 16:46:48 1.48
+++ jsr166/src/jsr166y/ForkJoinTask.java 2010/08/11 18:45:12 1.53
@@ -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
@@ -148,36 +144,34 @@ 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 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.
*/
+
+ /** The 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
@@ -198,81 +192,74 @@ 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) != 0)
+ if (s != 0)
synchronized (this) { notifyAll(); }
- return completion;
+ break;
}
}
- return s;
}
/**
* Record exception and set 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.
*/
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();
}
}
}
/**
* 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) {
- if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
+ 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;
}
/**
* 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() {
+ final void quietlyExec() {
try {
if (status < 0 || !exec())
return;
@@ -283,88 +270,6 @@ 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 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)) {
- boolean completed;
- try {
- completed = exec();
- } catch (Throwable rex) {
- return setExceptionalCompletion(rex);
- }
- if (completed)
- return setCompletion(NORMAL);
- }
- return w.pool.awaitJoin(this);
- }
- else
- return externalAwaitDone();
- }
-
- /**
- * Unless done, calls exec and records status if completed, or
- * 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)) {
- boolean completed;
- try {
- completed = exec();
- } catch (Throwable rex) {
- return setExceptionalCompletion(rex);
- }
- if (completed)
- return setCompletion(NORMAL);
- }
- return w.execWhileJoining(this);
- }
-
- /**
- * 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
/**
@@ -400,7 +305,11 @@ public abstract class ForkJoinTask im
* @return the computed result
*/
public final V join() {
- return reportResult(waitingJoin());
+ quietlyJoin();
+ Throwable ex;
+ if (status < NORMAL && (ex = getException()) != null)
+ UNSAFE.throwException(ex);
+ return getRawResult();
}
/**
@@ -411,7 +320,11 @@ public abstract class ForkJoinTask im
* @return the computed result
*/
public final V invoke() {
- return reportResult(waitingInvoke());
+ quietlyInvoke();
+ Throwable ex;
+ if (status < NORMAL && (ex = getException()) != null)
+ UNSAFE.throwException(ex);
+ return getRawResult();
}
/**
@@ -469,16 +382,22 @@ public abstract class ForkJoinTask im
}
else if (i != 0)
t.fork();
- else if (t.waitingInvoke() < 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.waitingJoin() < NORMAL && ex == null)
- ex = t.getException();
+ else {
+ t.quietlyJoin();
+ if (ex == null && t.status < NORMAL)
+ ex = t.getException();
+ }
}
}
if (ex != null)
@@ -525,16 +444,22 @@ public abstract class ForkJoinTask im
}
else if (i != 0)
t.fork();
- else if (t.waitingInvoke() < 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.waitingJoin() < NORMAL && ex == null)
- ex = t.getException();
+ else {
+ t.quietlyJoin();
+ if (ex == null && t.status < NORMAL)
+ ex = t.getException();
+ }
}
}
if (ex != null)
@@ -568,12 +493,14 @@ public abstract class ForkJoinTask im
*/
public boolean cancel(boolean mayInterruptIfRunning) {
setCompletion(CANCELLED);
- return (status & COMPLETION_MASK) == 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 {
@@ -585,7 +512,7 @@ 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 +528,7 @@ public abstract class ForkJoinTask im
}
public final boolean isCancelled() {
- return (status & COMPLETION_MASK) == CANCELLED;
+ return status == CANCELLED;
}
/**
@@ -610,7 +537,7 @@ 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 +548,7 @@ public abstract class ForkJoinTask im
* exception and was not cancelled
*/
public final boolean isCompletedNormally() {
- return (status & COMPLETION_MASK) == NORMAL;
+ return status == NORMAL;
}
/**
@@ -632,7 +559,7 @@ 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));
@@ -681,9 +608,10 @@ public abstract class ForkJoinTask im
}
public final V get() throws InterruptedException, ExecutionException {
- int s = waitingJoin() & COMPLETION_MASK;
+ quietlyJoin();
if (Thread.interrupted())
throw new InterruptedException();
+ int s = status;
if (s < NORMAL) {
Throwable ex;
if (s == CANCELLED)
@@ -701,13 +629,13 @@ 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
@@ -723,8 +651,7 @@ 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 +681,10 @@ 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)
@@ -770,61 +697,57 @@ 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
+ * 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() {
- waitingJoin();
+ 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
+ * necessary, 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 quietlyInvoke() {
- waitingInvoke();
+ if (status >= 0) {
+ boolean completed;
+ try {
+ completed = exec();
+ } catch (Throwable rex) {
+ setExceptionalCompletion(rex);
+ return;
+ }
+ if (completed)
+ setCompletion(NORMAL);
+ else
+ quietlyJoin();
+ }
}
/**
@@ -856,7 +779,7 @@ 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 +1089,6 @@ 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);