33 |
|
* <p>A "main" {@code ForkJoinTask} begins execution when it is |
34 |
|
* explicitly submitted to a {@link ForkJoinPool}, or, if not already |
35 |
|
* engaged in a ForkJoin computation, commenced in the {@link |
36 |
< |
* ForkJoinPool#commonPool} via {@link #fork}, {@link #invoke}, or |
36 |
> |
* ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or |
37 |
|
* related methods. Once started, it will usually in turn start other |
38 |
|
* subtasks. As indicated by the name of this class, many programs |
39 |
|
* using {@code ForkJoinTask} employ only methods {@link #fork} and |
55 |
|
* minimize other blocking synchronization apart from joining other |
56 |
|
* tasks or using synchronizers such as Phasers that are advertised to |
57 |
|
* cooperate with fork/join scheduling. Subdividable tasks should also |
58 |
< |
* not perform blocking IO, and should ideally access variables that |
58 |
> |
* not perform blocking I/O, and should ideally access variables that |
59 |
|
* are completely independent of those accessed by other running |
60 |
|
* tasks. These guidelines are loosely enforced by not permitting |
61 |
|
* checked exceptions such as {@code IOExceptions} to be |
73 |
|
* <p>It is possible to define and use ForkJoinTasks that may block, |
74 |
|
* but doing do requires three further considerations: (1) Completion |
75 |
|
* of few if any <em>other</em> tasks should be dependent on a task |
76 |
< |
* that blocks on external synchronization or IO. Event-style async |
76 |
> |
* that blocks on external synchronization or I/O. Event-style async |
77 |
|
* tasks that are never joined (for example, those subclassing {@link |
78 |
|
* CountedCompleter}) often fall into this category. (2) To minimize |
79 |
|
* resource impact, tasks should be small; ideally performing only the |
136 |
|
* supports other methods and techniques (for example the use of |
137 |
|
* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that |
138 |
|
* may be of use in constructing custom subclasses for problems that |
139 |
< |
* are not statically structured as DAGs. To support such usages a |
139 |
> |
* are not statically structured as DAGs. To support such usages, a |
140 |
|
* ForkJoinTask may be atomically <em>tagged</em> with a {@code short} |
141 |
|
* value using {@link #setForkJoinTaskTag} or {@link |
142 |
|
* #compareAndSetForkJoinTaskTag} and checked using {@link |
285 |
|
*/ |
286 |
|
private int externalAwaitDone() { |
287 |
|
int s; |
288 |
< |
boolean interrupted = false; |
289 |
< |
if ((s = status) >= 0 && ForkJoinPool.tryUnsubmitFromCommonPool(this)) |
290 |
< |
s = doExec(); |
291 |
< |
while (s >= 0) { |
292 |
< |
if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { |
293 |
< |
synchronized (this) { |
294 |
< |
if (status >= 0) { |
295 |
< |
try { |
296 |
< |
wait(); |
297 |
< |
} catch (InterruptedException ie) { |
298 |
< |
interrupted = true; |
288 |
> |
ForkJoinPool cp = ForkJoinPool.common; |
289 |
> |
if ((s = status) >= 0) { |
290 |
> |
if (cp != null) { |
291 |
> |
if (this instanceof CountedCompleter) |
292 |
> |
s = cp.externalHelpComplete((CountedCompleter<?>)this); |
293 |
> |
else if (cp.tryExternalUnpush(this)) |
294 |
> |
s = doExec(); |
295 |
> |
} |
296 |
> |
if (s >= 0 && (s = status) >= 0) { |
297 |
> |
boolean interrupted = false; |
298 |
> |
do { |
299 |
> |
if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { |
300 |
> |
synchronized (this) { |
301 |
> |
if (status >= 0) { |
302 |
> |
try { |
303 |
> |
wait(); |
304 |
> |
} catch (InterruptedException ie) { |
305 |
> |
interrupted = true; |
306 |
> |
} |
307 |
> |
} |
308 |
> |
else |
309 |
> |
notifyAll(); |
310 |
|
} |
311 |
|
} |
312 |
< |
else |
313 |
< |
notifyAll(); |
314 |
< |
} |
312 |
> |
} while ((s = status) >= 0); |
313 |
> |
if (interrupted) |
314 |
> |
Thread.currentThread().interrupt(); |
315 |
|
} |
305 |
– |
s = status; |
316 |
|
} |
307 |
– |
if (interrupted) |
308 |
– |
Thread.currentThread().interrupt(); |
317 |
|
return s; |
318 |
|
} |
319 |
|
|
321 |
|
* Blocks a non-worker-thread until completion or interruption. |
322 |
|
*/ |
323 |
|
private int externalInterruptibleAwaitDone() throws InterruptedException { |
324 |
+ |
int s; |
325 |
+ |
ForkJoinPool cp = ForkJoinPool.common; |
326 |
|
if (Thread.interrupted()) |
327 |
|
throw new InterruptedException(); |
328 |
< |
int s; |
329 |
< |
if ((s = status) >= 0 && ForkJoinPool.tryUnsubmitFromCommonPool(this)) |
330 |
< |
s = doExec(); |
331 |
< |
while (s >= 0) { |
328 |
> |
if ((s = status) >= 0 && cp != null) { |
329 |
> |
if (this instanceof CountedCompleter) |
330 |
> |
cp.externalHelpComplete((CountedCompleter<?>)this); |
331 |
> |
else if (cp.tryExternalUnpush(this)) |
332 |
> |
doExec(); |
333 |
> |
} |
334 |
> |
while ((s = status) >= 0) { |
335 |
|
if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { |
336 |
|
synchronized (this) { |
337 |
|
if (status >= 0) |
340 |
|
notifyAll(); |
341 |
|
} |
342 |
|
} |
330 |
– |
s = status; |
343 |
|
} |
344 |
|
return s; |
345 |
|
} |
346 |
|
|
347 |
+ |
|
348 |
|
/** |
349 |
|
* Implementation for join, get, quietlyJoin. Directly handles |
350 |
|
* only cases of already-completed, external wait, and |
451 |
|
} |
452 |
|
|
453 |
|
/** |
454 |
< |
* Records exception and possibly propagates |
454 |
> |
* Records exception and possibly propagates. |
455 |
|
* |
456 |
|
* @return status on exit |
457 |
|
*/ |
484 |
|
} |
485 |
|
|
486 |
|
/** |
487 |
< |
* Removes exception node and clears status |
487 |
> |
* Removes exception node and clears status. |
488 |
|
*/ |
489 |
|
private void clearExceptionalCompletion() { |
490 |
|
int h = System.identityHashCode(this); |
614 |
|
} |
615 |
|
|
616 |
|
/** |
617 |
+ |
* A version of "sneaky throw" to relay exceptions |
618 |
+ |
*/ |
619 |
+ |
static void rethrow(Throwable ex) { |
620 |
+ |
if (ex != null) |
621 |
+ |
ForkJoinTask.<RuntimeException>uncheckedThrow(ex); |
622 |
+ |
} |
623 |
+ |
|
624 |
+ |
/** |
625 |
+ |
* The sneaky part of sneaky throw, relying on generics |
626 |
+ |
* limitations to evade compiler complaints about rethrowing |
627 |
+ |
* unchecked exceptions |
628 |
+ |
*/ |
629 |
+ |
@SuppressWarnings("unchecked") static <T extends Throwable> |
630 |
+ |
void uncheckedThrow(Throwable t) throws T { |
631 |
+ |
throw (T)t; // rely on vacuous cast |
632 |
+ |
} |
633 |
+ |
|
634 |
+ |
/** |
635 |
|
* Throws exception, if any, associated with the given status. |
636 |
|
*/ |
637 |
|
private void reportException(int s) { |
638 |
< |
Throwable ex = ((s == CANCELLED) ? new CancellationException() : |
639 |
< |
(s == EXCEPTIONAL) ? getThrowableException() : |
640 |
< |
null); |
641 |
< |
if (ex != null) |
611 |
< |
U.throwException(ex); |
638 |
> |
if (s == CANCELLED) |
639 |
> |
throw new CancellationException(); |
640 |
> |
if (s == EXCEPTIONAL) |
641 |
> |
rethrow(getThrowableException()); |
642 |
|
} |
643 |
|
|
644 |
|
// public methods |
646 |
|
/** |
647 |
|
* Arranges to asynchronously execute this task in the pool the |
648 |
|
* current task is running in, if applicable, or using the {@link |
649 |
< |
* ForkJoinPool#commonPool} if not {@link #inForkJoinPool}. While |
649 |
> |
* ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}. While |
650 |
|
* it is not necessarily enforced, it is a usage error to fork a |
651 |
|
* task more than once unless it has completed and been |
652 |
|
* reinitialized. Subsequent modifications to the state of this |
663 |
|
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) |
664 |
|
((ForkJoinWorkerThread)t).workQueue.push(this); |
665 |
|
else |
666 |
< |
ForkJoinPool.submitToCommonPool(this); |
666 |
> |
ForkJoinPool.common.externalPush(this); |
667 |
|
return this; |
668 |
|
} |
669 |
|
|
765 |
|
} |
766 |
|
} |
767 |
|
if (ex != null) |
768 |
< |
U.throwException(ex); |
768 |
> |
rethrow(ex); |
769 |
|
} |
770 |
|
|
771 |
|
/** |
816 |
|
} |
817 |
|
} |
818 |
|
if (ex != null) |
819 |
< |
U.throwException(ex); |
819 |
> |
rethrow(ex); |
820 |
|
return tasks; |
821 |
|
} |
822 |
|
|
839 |
|
* <p>This method is designed to be invoked by <em>other</em> |
840 |
|
* tasks. To terminate the current task, you can just return or |
841 |
|
* throw an unchecked exception from its computation method, or |
842 |
< |
* invoke {@link #completeExceptionally}. |
842 |
> |
* invoke {@link #completeExceptionally(Throwable)}. |
843 |
|
* |
844 |
|
* @param mayInterruptIfRunning this value has no effect in the |
845 |
|
* default implementation because interrupts are not used to |
989 |
|
if (Thread.interrupted()) |
990 |
|
throw new InterruptedException(); |
991 |
|
// Messy in part because we measure in nanosecs, but wait in millisecs |
992 |
< |
int s; long ns, ms; |
993 |
< |
if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) { |
992 |
> |
int s; long ms; |
993 |
> |
long ns = unit.toNanos(timeout); |
994 |
> |
ForkJoinPool cp; |
995 |
> |
if ((s = status) >= 0 && ns > 0L) { |
996 |
|
long deadline = System.nanoTime() + ns; |
997 |
|
ForkJoinPool p = null; |
998 |
|
ForkJoinPool.WorkQueue w = null; |
1001 |
|
ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t; |
1002 |
|
p = wt.pool; |
1003 |
|
w = wt.workQueue; |
1004 |
< |
s = p.helpJoinOnce(w, this); // no retries on failure |
1004 |
> |
p.helpJoinOnce(w, this); // no retries on failure |
1005 |
> |
} |
1006 |
> |
else if ((cp = ForkJoinPool.common) != null) { |
1007 |
> |
if (this instanceof CountedCompleter) |
1008 |
> |
cp.externalHelpComplete((CountedCompleter<?>)this); |
1009 |
> |
else if (cp.tryExternalUnpush(this)) |
1010 |
> |
doExec(); |
1011 |
|
} |
1012 |
|
boolean canBlock = false; |
1013 |
|
boolean interrupted = false; |
1014 |
|
try { |
1015 |
|
while ((s = status) >= 0) { |
1016 |
< |
if (w != null && w.runState < 0) |
1016 |
> |
if (w != null && w.qlock < 0) |
1017 |
|
cancelIgnoringExceptions(this); |
1018 |
|
else if (!canBlock) { |
1019 |
< |
if (p == null || p.tryCompensate(this, null)) |
1019 |
> |
if (p == null || p.tryCompensate(p.ctl)) |
1020 |
|
canBlock = true; |
1021 |
|
} |
1022 |
|
else { |
1092 |
|
wt.pool.helpQuiescePool(wt.workQueue); |
1093 |
|
} |
1094 |
|
else |
1095 |
< |
ForkJoinPool.externalHelpQuiescePool(); |
1095 |
> |
ForkJoinPool.quiesceCommonPool(); |
1096 |
|
} |
1097 |
|
|
1098 |
|
/** |
1155 |
|
*/ |
1156 |
|
public boolean tryUnfork() { |
1157 |
|
Thread t; |
1158 |
< |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1159 |
< |
((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) : |
1160 |
< |
ForkJoinPool.tryUnsubmitFromCommonPool(this); |
1158 |
> |
return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1159 |
> |
((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) : |
1160 |
> |
ForkJoinPool.common.tryExternalUnpush(this)); |
1161 |
|
} |
1162 |
|
|
1163 |
|
/** |
1169 |
|
* @return the number of tasks |
1170 |
|
*/ |
1171 |
|
public static int getQueuedTaskCount() { |
1172 |
< |
Thread t; |
1173 |
< |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1174 |
< |
((ForkJoinWorkerThread)t).workQueue.queueSize() : |
1175 |
< |
ForkJoinPool.getEstimatedSubmitterQueueLength(); |
1172 |
> |
Thread t; ForkJoinPool.WorkQueue q; |
1173 |
> |
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) |
1174 |
> |
q = ((ForkJoinWorkerThread)t).workQueue; |
1175 |
> |
else |
1176 |
> |
q = ForkJoinPool.commonSubmitterQueue(); |
1177 |
> |
return (q == null) ? 0 : q.queueSize(); |
1178 |
|
} |
1179 |
|
|
1180 |
|
/** |
1191 |
|
* @return the surplus number of tasks, which may be negative |
1192 |
|
*/ |
1193 |
|
public static int getSurplusQueuedTaskCount() { |
1194 |
< |
/* |
1155 |
< |
* The aim of this method is to return a cheap heuristic guide |
1156 |
< |
* for task partitioning when programmers, frameworks, tools, |
1157 |
< |
* or languages have little or no idea about task granularity. |
1158 |
< |
* In essence by offering this method, we ask users only about |
1159 |
< |
* tradeoffs in overhead vs expected throughput and its |
1160 |
< |
* variance, rather than how finely to partition tasks. |
1161 |
< |
* |
1162 |
< |
* In a steady state strict (tree-structured) computation, |
1163 |
< |
* each thread makes available for stealing enough tasks for |
1164 |
< |
* other threads to remain active. Inductively, if all threads |
1165 |
< |
* play by the same rules, each thread should make available |
1166 |
< |
* only a constant number of tasks. |
1167 |
< |
* |
1168 |
< |
* The minimum useful constant is just 1. But using a value of |
1169 |
< |
* 1 would require immediate replenishment upon each steal to |
1170 |
< |
* maintain enough tasks, which is infeasible. Further, |
1171 |
< |
* partitionings/granularities of offered tasks should |
1172 |
< |
* minimize steal rates, which in general means that threads |
1173 |
< |
* nearer the top of computation tree should generate more |
1174 |
< |
* than those nearer the bottom. In perfect steady state, each |
1175 |
< |
* thread is at approximately the same level of computation |
1176 |
< |
* tree. However, producing extra tasks amortizes the |
1177 |
< |
* uncertainty of progress and diffusion assumptions. |
1178 |
< |
* |
1179 |
< |
* So, users will want to use values larger, but not much |
1180 |
< |
* larger than 1 to both smooth over transient shortages and |
1181 |
< |
* hedge against uneven progress; as traded off against the |
1182 |
< |
* cost of extra task overhead. We leave the user to pick a |
1183 |
< |
* threshold value to compare with the results of this call to |
1184 |
< |
* guide decisions, but recommend values such as 3. |
1185 |
< |
* |
1186 |
< |
* When all threads are active, it is on average OK to |
1187 |
< |
* estimate surplus strictly locally. In steady-state, if one |
1188 |
< |
* thread is maintaining say 2 surplus tasks, then so are |
1189 |
< |
* others. So we can just use estimated queue length. |
1190 |
< |
* However, this strategy alone leads to serious mis-estimates |
1191 |
< |
* in some non-steady-state conditions (ramp-up, ramp-down, |
1192 |
< |
* other stalls). We can detect many of these by further |
1193 |
< |
* considering the number of "idle" threads, that are known to |
1194 |
< |
* have zero queued tasks, so compensate by a factor of |
1195 |
< |
* (#idle/#active) threads. |
1196 |
< |
*/ |
1197 |
< |
Thread t; ForkJoinWorkerThread wt; |
1198 |
< |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1199 |
< |
(wt = (ForkJoinWorkerThread)t).workQueue.queueSize() - wt.pool.idlePerActive() : |
1200 |
< |
0; |
1194 |
> |
return ForkJoinPool.getSurplusQueuedTaskCount(); |
1195 |
|
} |
1196 |
|
|
1197 |
|
// Extension methods |
1235 |
|
/** |
1236 |
|
* Returns, but does not unschedule or execute, a task queued by |
1237 |
|
* the current thread but not yet executed, if one is immediately |
1238 |
< |
* available and the current thread is operating in a |
1239 |
< |
* ForkJoinPool. There is no guarantee that this task will |
1240 |
< |
* actually be polled or executed next. Conversely, this method |
1241 |
< |
* may return null even if a task exists but cannot be accessed |
1248 |
< |
* without contention with other threads. This method is designed |
1238 |
> |
* available. There is no guarantee that this task will actually |
1239 |
> |
* be polled or executed next. Conversely, this method may return |
1240 |
> |
* null even if a task exists but cannot be accessed without |
1241 |
> |
* contention with other threads. This method is designed |
1242 |
|
* primarily to support extensions, and is unlikely to be useful |
1243 |
|
* otherwise. |
1244 |
|
* |
1245 |
|
* @return the next task, or {@code null} if none are available |
1246 |
|
*/ |
1247 |
|
protected static ForkJoinTask<?> peekNextLocalTask() { |
1248 |
< |
Thread t; |
1249 |
< |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1250 |
< |
((ForkJoinWorkerThread)t).workQueue.peek() : |
1251 |
< |
null; |
1248 |
> |
Thread t; ForkJoinPool.WorkQueue q; |
1249 |
> |
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) |
1250 |
> |
q = ((ForkJoinWorkerThread)t).workQueue; |
1251 |
> |
else |
1252 |
> |
q = ForkJoinPool.commonSubmitterQueue(); |
1253 |
> |
return (q == null) ? null : q.peek(); |
1254 |
|
} |
1255 |
|
|
1256 |
|
/** |
1326 |
|
* |
1327 |
|
* @param e the expected tag value |
1328 |
|
* @param tag the new tag value |
1329 |
< |
* @return true if successful; i.e., the current value was |
1329 |
> |
* @return {@code true} if successful; i.e., the current value was |
1330 |
|
* equal to e and is now tag. |
1331 |
|
* @since 1.8 |
1332 |
|
*/ |
1379 |
|
} |
1380 |
|
|
1381 |
|
/** |
1382 |
+ |
* Adaptor for Runnables in which failure forces worker exception |
1383 |
+ |
*/ |
1384 |
+ |
static final class RunnableExecuteAction extends ForkJoinTask<Void> { |
1385 |
+ |
final Runnable runnable; |
1386 |
+ |
RunnableExecuteAction(Runnable runnable) { |
1387 |
+ |
if (runnable == null) throw new NullPointerException(); |
1388 |
+ |
this.runnable = runnable; |
1389 |
+ |
} |
1390 |
+ |
public final Void getRawResult() { return null; } |
1391 |
+ |
public final void setRawResult(Void v) { } |
1392 |
+ |
public final boolean exec() { runnable.run(); return true; } |
1393 |
+ |
void internalPropagateException(Throwable ex) { |
1394 |
+ |
rethrow(ex); // rethrow outside exec() catches. |
1395 |
+ |
} |
1396 |
+ |
private static final long serialVersionUID = 5232453952276885070L; |
1397 |
+ |
} |
1398 |
+ |
|
1399 |
+ |
/** |
1400 |
|
* Adaptor for Callables |
1401 |
|
*/ |
1402 |
|
static final class AdaptedCallable<T> extends ForkJoinTask<T> |
1493 |
|
// Unsafe mechanics |
1494 |
|
private static final sun.misc.Unsafe U; |
1495 |
|
private static final long STATUS; |
1496 |
+ |
|
1497 |
|
static { |
1498 |
|
exceptionTableLock = new ReentrantLock(); |
1499 |
|
exceptionTableRefQueue = new ReferenceQueue<Object>(); |
1500 |
|
exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY]; |
1501 |
|
try { |
1502 |
|
U = getUnsafe(); |
1503 |
+ |
Class<?> k = ForkJoinTask.class; |
1504 |
|
STATUS = U.objectFieldOffset |
1505 |
< |
(ForkJoinTask.class.getDeclaredField("status")); |
1505 |
> |
(k.getDeclaredField("status")); |
1506 |
|
} catch (Exception e) { |
1507 |
|
throw new Error(e); |
1508 |
|
} |
1518 |
|
private static sun.misc.Unsafe getUnsafe() { |
1519 |
|
try { |
1520 |
|
return sun.misc.Unsafe.getUnsafe(); |
1521 |
< |
} catch (SecurityException se) { |
1522 |
< |
try { |
1523 |
< |
return java.security.AccessController.doPrivileged |
1524 |
< |
(new java.security |
1525 |
< |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1526 |
< |
public sun.misc.Unsafe run() throws Exception { |
1527 |
< |
java.lang.reflect.Field f = sun.misc |
1528 |
< |
.Unsafe.class.getDeclaredField("theUnsafe"); |
1529 |
< |
f.setAccessible(true); |
1530 |
< |
return (sun.misc.Unsafe) f.get(null); |
1531 |
< |
}}); |
1532 |
< |
} catch (java.security.PrivilegedActionException e) { |
1533 |
< |
throw new RuntimeException("Could not initialize intrinsics", |
1534 |
< |
e.getCause()); |
1535 |
< |
} |
1521 |
> |
} catch (SecurityException tryReflectionInstead) {} |
1522 |
> |
try { |
1523 |
> |
return java.security.AccessController.doPrivileged |
1524 |
> |
(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1525 |
> |
public sun.misc.Unsafe run() throws Exception { |
1526 |
> |
Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class; |
1527 |
> |
for (java.lang.reflect.Field f : k.getDeclaredFields()) { |
1528 |
> |
f.setAccessible(true); |
1529 |
> |
Object x = f.get(null); |
1530 |
> |
if (k.isInstance(x)) |
1531 |
> |
return k.cast(x); |
1532 |
> |
} |
1533 |
> |
throw new NoSuchFieldError("the Unsafe"); |
1534 |
> |
}}); |
1535 |
> |
} catch (java.security.PrivilegedActionException e) { |
1536 |
> |
throw new RuntimeException("Could not initialize intrinsics", |
1537 |
> |
e.getCause()); |
1538 |
|
} |
1539 |
|
} |
1540 |
|
} |