| 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 |
| 134 |
|
* (DAG). Otherwise, executions may encounter a form of deadlock as |
| 135 |
|
* tasks cyclically wait for each other. However, this framework |
| 136 |
|
* supports other methods and techniques (for example the use of |
| 137 |
< |
* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that |
| 137 |
> |
* {@link java.util.concurrent.Phaser}, {@link #helpQuiesce}, and |
| 138 |
> |
* {@link #complete}) that |
| 139 |
|
* may be of use in constructing custom subclasses for problems that |
| 140 |
|
* are not statically structured as DAGs. To support such usages a |
| 141 |
|
* ForkJoinTask may be atomically <em>tagged</em> with a {@code short} |
| 286 |
|
*/ |
| 287 |
|
private int externalAwaitDone() { |
| 288 |
|
int s; |
| 289 |
+ |
ForkJoinPool.externalHelpJoin(this); |
| 290 |
|
boolean interrupted = false; |
| 291 |
< |
if ((s = status) >= 0 && ForkJoinPool.tryUnsubmitFromCommonPool(this)) |
| 290 |
< |
s = doExec(); |
| 291 |
< |
while (s >= 0) { |
| 291 |
> |
while ((s = status) >= 0) { |
| 292 |
|
if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { |
| 293 |
|
synchronized (this) { |
| 294 |
|
if (status >= 0) { |
| 302 |
|
notifyAll(); |
| 303 |
|
} |
| 304 |
|
} |
| 305 |
– |
s = status; |
| 305 |
|
} |
| 306 |
|
if (interrupted) |
| 307 |
|
Thread.currentThread().interrupt(); |
| 312 |
|
* Blocks a non-worker-thread until completion or interruption. |
| 313 |
|
*/ |
| 314 |
|
private int externalInterruptibleAwaitDone() throws InterruptedException { |
| 315 |
+ |
int s; |
| 316 |
|
if (Thread.interrupted()) |
| 317 |
|
throw new InterruptedException(); |
| 318 |
< |
int s; |
| 319 |
< |
if ((s = status) >= 0 && ForkJoinPool.tryUnsubmitFromCommonPool(this)) |
| 320 |
< |
s = doExec(); |
| 321 |
< |
while (s >= 0) { |
| 318 |
> |
ForkJoinPool.externalHelpJoin(this); |
| 319 |
> |
while ((s = status) >= 0) { |
| 320 |
|
if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { |
| 321 |
|
synchronized (this) { |
| 322 |
|
if (status >= 0) |
| 325 |
|
notifyAll(); |
| 326 |
|
} |
| 327 |
|
} |
| 330 |
– |
s = status; |
| 328 |
|
} |
| 329 |
|
return s; |
| 330 |
|
} |
| 331 |
|
|
| 332 |
+ |
|
| 333 |
|
/** |
| 334 |
|
* Implementation for join, get, quietlyJoin. Directly handles |
| 335 |
|
* only cases of already-completed, external wait, and |
| 436 |
|
} |
| 437 |
|
|
| 438 |
|
/** |
| 439 |
< |
* Records exception and possibly propagates |
| 439 |
> |
* Records exception and possibly propagates. |
| 440 |
|
* |
| 441 |
|
* @return status on exit |
| 442 |
|
*/ |
| 607 |
|
throw (Error)ex; |
| 608 |
|
if (ex instanceof RuntimeException) |
| 609 |
|
throw (RuntimeException)ex; |
| 610 |
< |
throw uncheckedThrowable(ex, RuntimeException.class); |
| 610 |
> |
ForkJoinTask.<RuntimeException>uncheckedThrow(ex); |
| 611 |
|
} |
| 612 |
|
} |
| 613 |
|
|
| 617 |
|
* unchecked exceptions |
| 618 |
|
*/ |
| 619 |
|
@SuppressWarnings("unchecked") static <T extends Throwable> |
| 620 |
< |
T uncheckedThrowable(final Throwable t, final Class<T> c) { |
| 621 |
< |
return (T)t; // rely on vacuous cast |
| 620 |
> |
void uncheckedThrow(Throwable t) throws T { |
| 621 |
> |
if (t != null) |
| 622 |
> |
throw (T)t; // rely on vacuous cast |
| 623 |
|
} |
| 624 |
|
|
| 625 |
|
/** |
| 637 |
|
/** |
| 638 |
|
* Arranges to asynchronously execute this task in the pool the |
| 639 |
|
* current task is running in, if applicable, or using the {@link |
| 640 |
< |
* ForkJoinPool#commonPool} if not {@link #inForkJoinPool}. While |
| 640 |
> |
* ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}. While |
| 641 |
|
* it is not necessarily enforced, it is a usage error to fork a |
| 642 |
|
* task more than once unless it has completed and been |
| 643 |
|
* reinitialized. Subsequent modifications to the state of this |
| 654 |
|
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) |
| 655 |
|
((ForkJoinWorkerThread)t).workQueue.push(this); |
| 656 |
|
else |
| 657 |
< |
ForkJoinPool.submitToCommonPool(this); |
| 657 |
> |
ForkJoinPool.common.externalPush(this); |
| 658 |
|
return this; |
| 659 |
|
} |
| 660 |
|
|
| 980 |
|
if (Thread.interrupted()) |
| 981 |
|
throw new InterruptedException(); |
| 982 |
|
// Messy in part because we measure in nanosecs, but wait in millisecs |
| 983 |
< |
int s; long ns, ms; |
| 984 |
< |
if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) { |
| 983 |
> |
int s; long ms; |
| 984 |
> |
long ns = unit.toNanos(timeout); |
| 985 |
> |
if ((s = status) >= 0 && ns > 0L) { |
| 986 |
|
long deadline = System.nanoTime() + ns; |
| 987 |
|
ForkJoinPool p = null; |
| 988 |
|
ForkJoinPool.WorkQueue w = null; |
| 991 |
|
ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t; |
| 992 |
|
p = wt.pool; |
| 993 |
|
w = wt.workQueue; |
| 994 |
< |
s = p.helpJoinOnce(w, this); // no retries on failure |
| 994 |
> |
p.helpJoinOnce(w, this); // no retries on failure |
| 995 |
|
} |
| 996 |
+ |
else |
| 997 |
+ |
ForkJoinPool.externalHelpJoin(this); |
| 998 |
|
boolean canBlock = false; |
| 999 |
|
boolean interrupted = false; |
| 1000 |
|
try { |
| 1001 |
|
while ((s = status) >= 0) { |
| 1002 |
< |
if (w != null && w.runState < 0) |
| 1002 |
> |
if (w != null && w.qlock < 0) |
| 1003 |
|
cancelIgnoringExceptions(this); |
| 1004 |
|
else if (!canBlock) { |
| 1005 |
< |
if (p == null || p.tryCompensate(this, null)) |
| 1005 |
> |
if (p == null || p.tryCompensate()) |
| 1006 |
|
canBlock = true; |
| 1007 |
|
} |
| 1008 |
|
else { |
| 1078 |
|
wt.pool.helpQuiescePool(wt.workQueue); |
| 1079 |
|
} |
| 1080 |
|
else |
| 1081 |
< |
ForkJoinPool.externalHelpQuiescePool(); |
| 1081 |
> |
ForkJoinPool.quiesceCommonPool(); |
| 1082 |
|
} |
| 1083 |
|
|
| 1084 |
|
/** |
| 1141 |
|
*/ |
| 1142 |
|
public boolean tryUnfork() { |
| 1143 |
|
Thread t; |
| 1144 |
< |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
| 1145 |
< |
((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) : |
| 1146 |
< |
ForkJoinPool.tryUnsubmitFromCommonPool(this); |
| 1144 |
> |
return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
| 1145 |
> |
((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) : |
| 1146 |
> |
ForkJoinPool.tryExternalUnpush(this)); |
| 1147 |
|
} |
| 1148 |
|
|
| 1149 |
|
/** |
| 1155 |
|
* @return the number of tasks |
| 1156 |
|
*/ |
| 1157 |
|
public static int getQueuedTaskCount() { |
| 1158 |
< |
Thread t; |
| 1159 |
< |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
| 1160 |
< |
((ForkJoinWorkerThread)t).workQueue.queueSize() : |
| 1161 |
< |
ForkJoinPool.getEstimatedSubmitterQueueLength(); |
| 1158 |
> |
Thread t; ForkJoinPool.WorkQueue q; |
| 1159 |
> |
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) |
| 1160 |
> |
q = ((ForkJoinWorkerThread)t).workQueue; |
| 1161 |
> |
else |
| 1162 |
> |
q = ForkJoinPool.commonSubmitterQueue(); |
| 1163 |
> |
return (q == null) ? 0 : q.queueSize(); |
| 1164 |
|
} |
| 1165 |
|
|
| 1166 |
|
/** |
| 1177 |
|
* @return the surplus number of tasks, which may be negative |
| 1178 |
|
*/ |
| 1179 |
|
public static int getSurplusQueuedTaskCount() { |
| 1180 |
< |
/* |
| 1177 |
< |
* The aim of this method is to return a cheap heuristic guide |
| 1178 |
< |
* for task partitioning when programmers, frameworks, tools, |
| 1179 |
< |
* or languages have little or no idea about task granularity. |
| 1180 |
< |
* In essence by offering this method, we ask users only about |
| 1181 |
< |
* tradeoffs in overhead vs expected throughput and its |
| 1182 |
< |
* variance, rather than how finely to partition tasks. |
| 1183 |
< |
* |
| 1184 |
< |
* In a steady state strict (tree-structured) computation, |
| 1185 |
< |
* each thread makes available for stealing enough tasks for |
| 1186 |
< |
* other threads to remain active. Inductively, if all threads |
| 1187 |
< |
* play by the same rules, each thread should make available |
| 1188 |
< |
* only a constant number of tasks. |
| 1189 |
< |
* |
| 1190 |
< |
* The minimum useful constant is just 1. But using a value of |
| 1191 |
< |
* 1 would require immediate replenishment upon each steal to |
| 1192 |
< |
* maintain enough tasks, which is infeasible. Further, |
| 1193 |
< |
* partitionings/granularities of offered tasks should |
| 1194 |
< |
* minimize steal rates, which in general means that threads |
| 1195 |
< |
* nearer the top of computation tree should generate more |
| 1196 |
< |
* than those nearer the bottom. In perfect steady state, each |
| 1197 |
< |
* thread is at approximately the same level of computation |
| 1198 |
< |
* tree. However, producing extra tasks amortizes the |
| 1199 |
< |
* uncertainty of progress and diffusion assumptions. |
| 1200 |
< |
* |
| 1201 |
< |
* So, users will want to use values larger, but not much |
| 1202 |
< |
* larger than 1 to both smooth over transient shortages and |
| 1203 |
< |
* hedge against uneven progress; as traded off against the |
| 1204 |
< |
* cost of extra task overhead. We leave the user to pick a |
| 1205 |
< |
* threshold value to compare with the results of this call to |
| 1206 |
< |
* guide decisions, but recommend values such as 3. |
| 1207 |
< |
* |
| 1208 |
< |
* When all threads are active, it is on average OK to |
| 1209 |
< |
* estimate surplus strictly locally. In steady-state, if one |
| 1210 |
< |
* thread is maintaining say 2 surplus tasks, then so are |
| 1211 |
< |
* others. So we can just use estimated queue length. |
| 1212 |
< |
* However, this strategy alone leads to serious mis-estimates |
| 1213 |
< |
* in some non-steady-state conditions (ramp-up, ramp-down, |
| 1214 |
< |
* other stalls). We can detect many of these by further |
| 1215 |
< |
* considering the number of "idle" threads, that are known to |
| 1216 |
< |
* have zero queued tasks, so compensate by a factor of |
| 1217 |
< |
* (#idle/#active) threads. |
| 1218 |
< |
*/ |
| 1219 |
< |
Thread t; ForkJoinWorkerThread wt; |
| 1220 |
< |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
| 1221 |
< |
(wt = (ForkJoinWorkerThread)t).workQueue.queueSize() - wt.pool.idlePerActive() : |
| 1222 |
< |
0; |
| 1180 |
> |
return ForkJoinPool.getSurplusQueuedTaskCount(); |
| 1181 |
|
} |
| 1182 |
|
|
| 1183 |
|
// Extension methods |
| 1221 |
|
/** |
| 1222 |
|
* Returns, but does not unschedule or execute, a task queued by |
| 1223 |
|
* the current thread but not yet executed, if one is immediately |
| 1224 |
< |
* available and the current thread is operating in a |
| 1225 |
< |
* ForkJoinPool. There is no guarantee that this task will |
| 1226 |
< |
* actually be polled or executed next. Conversely, this method |
| 1227 |
< |
* may return null even if a task exists but cannot be accessed |
| 1270 |
< |
* without contention with other threads. This method is designed |
| 1224 |
> |
* available. There is no guarantee that this task will actually |
| 1225 |
> |
* be polled or executed next. Conversely, this method may return |
| 1226 |
> |
* null even if a task exists but cannot be accessed without |
| 1227 |
> |
* contention with other threads. This method is designed |
| 1228 |
|
* primarily to support extensions, and is unlikely to be useful |
| 1229 |
|
* otherwise. |
| 1230 |
|
* |
| 1231 |
|
* @return the next task, or {@code null} if none are available |
| 1232 |
|
*/ |
| 1233 |
|
protected static ForkJoinTask<?> peekNextLocalTask() { |
| 1234 |
< |
Thread t; |
| 1235 |
< |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
| 1236 |
< |
((ForkJoinWorkerThread)t).workQueue.peek() : |
| 1237 |
< |
null; |
| 1234 |
> |
Thread t; ForkJoinPool.WorkQueue q; |
| 1235 |
> |
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) |
| 1236 |
> |
q = ((ForkJoinWorkerThread)t).workQueue; |
| 1237 |
> |
else |
| 1238 |
> |
q = ForkJoinPool.commonSubmitterQueue(); |
| 1239 |
> |
return (q == null) ? null : q.peek(); |
| 1240 |
|
} |
| 1241 |
|
|
| 1242 |
|
/** |
| 1461 |
|
// Unsafe mechanics |
| 1462 |
|
private static final sun.misc.Unsafe U; |
| 1463 |
|
private static final long STATUS; |
| 1464 |
+ |
|
| 1465 |
|
static { |
| 1466 |
|
exceptionTableLock = new ReentrantLock(); |
| 1467 |
|
exceptionTableRefQueue = new ReferenceQueue<Object>(); |
| 1468 |
|
exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY]; |
| 1469 |
|
try { |
| 1470 |
|
U = getUnsafe(); |
| 1471 |
+ |
Class<?> k = ForkJoinTask.class; |
| 1472 |
|
STATUS = U.objectFieldOffset |
| 1473 |
< |
(ForkJoinTask.class.getDeclaredField("status")); |
| 1473 |
> |
(k.getDeclaredField("status")); |
| 1474 |
|
} catch (Exception e) { |
| 1475 |
|
throw new Error(e); |
| 1476 |
|
} |
| 1486 |
|
private static sun.misc.Unsafe getUnsafe() { |
| 1487 |
|
try { |
| 1488 |
|
return sun.misc.Unsafe.getUnsafe(); |
| 1489 |
< |
} catch (SecurityException se) { |
| 1490 |
< |
try { |
| 1491 |
< |
return java.security.AccessController.doPrivileged |
| 1492 |
< |
(new java.security |
| 1493 |
< |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
| 1494 |
< |
public sun.misc.Unsafe run() throws Exception { |
| 1495 |
< |
java.lang.reflect.Field f = sun.misc |
| 1496 |
< |
.Unsafe.class.getDeclaredField("theUnsafe"); |
| 1497 |
< |
f.setAccessible(true); |
| 1498 |
< |
return (sun.misc.Unsafe) f.get(null); |
| 1499 |
< |
}}); |
| 1500 |
< |
} catch (java.security.PrivilegedActionException e) { |
| 1501 |
< |
throw new RuntimeException("Could not initialize intrinsics", |
| 1502 |
< |
e.getCause()); |
| 1503 |
< |
} |
| 1489 |
> |
} catch (SecurityException tryReflectionInstead) {} |
| 1490 |
> |
try { |
| 1491 |
> |
return java.security.AccessController.doPrivileged |
| 1492 |
> |
(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
| 1493 |
> |
public sun.misc.Unsafe run() throws Exception { |
| 1494 |
> |
Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class; |
| 1495 |
> |
for (java.lang.reflect.Field f : k.getDeclaredFields()) { |
| 1496 |
> |
f.setAccessible(true); |
| 1497 |
> |
Object x = f.get(null); |
| 1498 |
> |
if (k.isInstance(x)) |
| 1499 |
> |
return k.cast(x); |
| 1500 |
> |
} |
| 1501 |
> |
throw new NoSuchFieldError("the Unsafe"); |
| 1502 |
> |
}}); |
| 1503 |
> |
} catch (java.security.PrivilegedActionException e) { |
| 1504 |
> |
throw new RuntimeException("Could not initialize intrinsics", |
| 1505 |
> |
e.getCause()); |
| 1506 |
|
} |
| 1507 |
|
} |
| 1508 |
|
} |
