1 |
/* |
2 |
* Written by Doug Lea with assistance from members of JCP JSR-166 |
3 |
* Expert Group and released to the public domain, as explained at |
4 |
* http://creativecommons.org/publicdomain/zero/1.0/ |
5 |
*/ |
6 |
|
7 |
package jsr166e; |
8 |
|
9 |
import java.io.Serializable; |
10 |
import java.util.Collection; |
11 |
import java.util.List; |
12 |
import java.util.RandomAccess; |
13 |
import java.lang.ref.WeakReference; |
14 |
import java.lang.ref.ReferenceQueue; |
15 |
import java.util.concurrent.Callable; |
16 |
import java.util.concurrent.CancellationException; |
17 |
import java.util.concurrent.ExecutionException; |
18 |
import java.util.concurrent.Future; |
19 |
import java.util.concurrent.RejectedExecutionException; |
20 |
import java.util.concurrent.RunnableFuture; |
21 |
import java.util.concurrent.TimeUnit; |
22 |
import java.util.concurrent.TimeoutException; |
23 |
import java.util.concurrent.locks.ReentrantLock; |
24 |
import java.lang.reflect.Constructor; |
25 |
|
26 |
/** |
27 |
* Abstract base class for tasks that run within a {@link ForkJoinPool}. |
28 |
* A {@code ForkJoinTask} is a thread-like entity that is much |
29 |
* lighter weight than a normal thread. Huge numbers of tasks and |
30 |
* subtasks may be hosted by a small number of actual threads in a |
31 |
* ForkJoinPool, at the price of some usage limitations. |
32 |
* |
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 |
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 |
40 |
* {@link #join}, or derivatives such as {@link |
41 |
* #invokeAll(ForkJoinTask...) invokeAll}. However, this class also |
42 |
* provides a number of other methods that can come into play in |
43 |
* advanced usages, as well as extension mechanics that allow support |
44 |
* of new forms of fork/join processing. |
45 |
* |
46 |
* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}. |
47 |
* The efficiency of {@code ForkJoinTask}s stems from a set of |
48 |
* restrictions (that are only partially statically enforceable) |
49 |
* reflecting their main use as computational tasks calculating pure |
50 |
* functions or operating on purely isolated objects. The primary |
51 |
* coordination mechanisms are {@link #fork}, that arranges |
52 |
* asynchronous execution, and {@link #join}, that doesn't proceed |
53 |
* until the task's result has been computed. Computations should |
54 |
* ideally avoid {@code synchronized} methods or blocks, and should |
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 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 |
62 |
* thrown. However, computations may still encounter unchecked |
63 |
* exceptions, that are rethrown to callers attempting to join |
64 |
* them. These exceptions may additionally include {@link |
65 |
* RejectedExecutionException} stemming from internal resource |
66 |
* exhaustion, such as failure to allocate internal task |
67 |
* queues. Rethrown exceptions behave in the same way as regular |
68 |
* exceptions, but, when possible, contain stack traces (as displayed |
69 |
* for example using {@code ex.printStackTrace()}) of both the thread |
70 |
* that initiated the computation as well as the thread actually |
71 |
* encountering the exception; minimally only the latter. |
72 |
* |
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 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 |
80 |
* (possibly) blocking action. (3) Unless the {@link |
81 |
* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly |
82 |
* blocked tasks is known to be less than the pool's {@link |
83 |
* ForkJoinPool#getParallelism} level, the pool cannot guarantee that |
84 |
* enough threads will be available to ensure progress or good |
85 |
* performance. |
86 |
* |
87 |
* <p>The primary method for awaiting completion and extracting |
88 |
* results of a task is {@link #join}, but there are several variants: |
89 |
* The {@link Future#get} methods support interruptible and/or timed |
90 |
* waits for completion and report results using {@code Future} |
91 |
* conventions. Method {@link #invoke} is semantically |
92 |
* equivalent to {@code fork(); join()} but always attempts to begin |
93 |
* execution in the current thread. The "<em>quiet</em>" forms of |
94 |
* these methods do not extract results or report exceptions. These |
95 |
* may be useful when a set of tasks are being executed, and you need |
96 |
* to delay processing of results or exceptions until all complete. |
97 |
* Method {@code invokeAll} (available in multiple versions) |
98 |
* performs the most common form of parallel invocation: forking a set |
99 |
* of tasks and joining them all. |
100 |
* |
101 |
* <p>In the most typical usages, a fork-join pair act like a call |
102 |
* (fork) and return (join) from a parallel recursive function. As is |
103 |
* the case with other forms of recursive calls, returns (joins) |
104 |
* should be performed innermost-first. For example, {@code a.fork(); |
105 |
* b.fork(); b.join(); a.join();} is likely to be substantially more |
106 |
* efficient than joining {@code a} before {@code b}. |
107 |
* |
108 |
* <p>The execution status of tasks may be queried at several levels |
109 |
* of detail: {@link #isDone} is true if a task completed in any way |
110 |
* (including the case where a task was cancelled without executing); |
111 |
* {@link #isCompletedNormally} is true if a task completed without |
112 |
* cancellation or encountering an exception; {@link #isCancelled} is |
113 |
* true if the task was cancelled (in which case {@link #getException} |
114 |
* returns a {@link java.util.concurrent.CancellationException}); and |
115 |
* {@link #isCompletedAbnormally} is true if a task was either |
116 |
* cancelled or encountered an exception, in which case {@link |
117 |
* #getException} will return either the encountered exception or |
118 |
* {@link java.util.concurrent.CancellationException}. |
119 |
* |
120 |
* <p>The ForkJoinTask class is not usually directly subclassed. |
121 |
* Instead, you subclass one of the abstract classes that support a |
122 |
* particular style of fork/join processing, typically {@link |
123 |
* RecursiveAction} for most computations that do not return results, |
124 |
* {@link RecursiveTask} for those that do, and {@link |
125 |
* CountedCompleter} for those in which completed actions trigger |
126 |
* other actions. Normally, a concrete ForkJoinTask subclass declares |
127 |
* fields comprising its parameters, established in a constructor, and |
128 |
* then defines a {@code compute} method that somehow uses the control |
129 |
* methods supplied by this base class. |
130 |
* |
131 |
* <p>Method {@link #join} and its variants are appropriate for use |
132 |
* only when completion dependencies are acyclic; that is, the |
133 |
* parallel computation can be described as a directed acyclic graph |
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 |
138 |
* may be of use in constructing custom subclasses for problems that |
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 |
143 |
* #getForkJoinTaskTag}. The ForkJoinTask implementation does not use |
144 |
* these {@code protected} methods or tags for any purpose, but they |
145 |
* may be of use in the construction of specialized subclasses. For |
146 |
* example, parallel graph traversals can use the supplied methods to |
147 |
* avoid revisiting nodes/tasks that have already been processed. |
148 |
* (Method names for tagging are bulky in part to encourage definition |
149 |
* of methods that reflect their usage patterns.) |
150 |
* |
151 |
* <p>Most base support methods are {@code final}, to prevent |
152 |
* overriding of implementations that are intrinsically tied to the |
153 |
* underlying lightweight task scheduling framework. Developers |
154 |
* creating new basic styles of fork/join processing should minimally |
155 |
* implement {@code protected} methods {@link #exec}, {@link |
156 |
* #setRawResult}, and {@link #getRawResult}, while also introducing |
157 |
* an abstract computational method that can be implemented in its |
158 |
* subclasses, possibly relying on other {@code protected} methods |
159 |
* provided by this class. |
160 |
* |
161 |
* <p>ForkJoinTasks should perform relatively small amounts of |
162 |
* computation. Large tasks should be split into smaller subtasks, |
163 |
* usually via recursive decomposition. As a very rough rule of thumb, |
164 |
* a task should perform more than 100 and less than 10000 basic |
165 |
* computational steps, and should avoid indefinite looping. If tasks |
166 |
* are too big, then parallelism cannot improve throughput. If too |
167 |
* small, then memory and internal task maintenance overhead may |
168 |
* overwhelm processing. |
169 |
* |
170 |
* <p>This class provides {@code adapt} methods for {@link Runnable} |
171 |
* and {@link Callable}, that may be of use when mixing execution of |
172 |
* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are |
173 |
* of this form, consider using a pool constructed in <em>asyncMode</em>. |
174 |
* |
175 |
* <p>ForkJoinTasks are {@code Serializable}, which enables them to be |
176 |
* used in extensions such as remote execution frameworks. It is |
177 |
* sensible to serialize tasks only before or after, but not during, |
178 |
* execution. Serialization is not relied on during execution itself. |
179 |
* |
180 |
* @since 1.7 |
181 |
* @author Doug Lea |
182 |
*/ |
183 |
public abstract class ForkJoinTask<V> implements Future<V>, Serializable { |
184 |
|
185 |
/* |
186 |
* See the internal documentation of class ForkJoinPool for a |
187 |
* general implementation overview. ForkJoinTasks are mainly |
188 |
* responsible for maintaining their "status" field amidst relays |
189 |
* to methods in ForkJoinWorkerThread and ForkJoinPool. |
190 |
* |
191 |
* The methods of this class are more-or-less layered into |
192 |
* (1) basic status maintenance |
193 |
* (2) execution and awaiting completion |
194 |
* (3) user-level methods that additionally report results. |
195 |
* This is sometimes hard to see because this file orders exported |
196 |
* methods in a way that flows well in javadocs. |
197 |
*/ |
198 |
|
199 |
/* |
200 |
* The status field holds run control status bits packed into a |
201 |
* single int to minimize footprint and to ensure atomicity (via |
202 |
* CAS). Status is initially zero, and takes on nonnegative |
203 |
* values until completed, upon which status (anded with |
204 |
* DONE_MASK) holds value NORMAL, CANCELLED, or EXCEPTIONAL. Tasks |
205 |
* undergoing blocking waits by other threads have the SIGNAL bit |
206 |
* set. Completion of a stolen task with SIGNAL set awakens any |
207 |
* waiters via notifyAll. Even though suboptimal for some |
208 |
* purposes, we use basic builtin wait/notify to take advantage of |
209 |
* "monitor inflation" in JVMs that we would otherwise need to |
210 |
* emulate to avoid adding further per-task bookkeeping overhead. |
211 |
* We want these monitors to be "fat", i.e., not use biasing or |
212 |
* thin-lock techniques, so use some odd coding idioms that tend |
213 |
* to avoid them, mainly by arranging that every synchronized |
214 |
* block performs a wait, notifyAll or both. |
215 |
* |
216 |
* These control bits occupy only (some of) the upper half (16 |
217 |
* bits) of status field. The lower bits are used for user-defined |
218 |
* tags. |
219 |
*/ |
220 |
|
221 |
/** The run status of this task */ |
222 |
volatile int status; // accessed directly by pool and workers |
223 |
static final int DONE_MASK = 0xf0000000; // mask out non-completion bits |
224 |
static final int NORMAL = 0xf0000000; // must be negative |
225 |
static final int CANCELLED = 0xc0000000; // must be < NORMAL |
226 |
static final int EXCEPTIONAL = 0x80000000; // must be < CANCELLED |
227 |
static final int SIGNAL = 0x00010000; // must be >= 1 << 16 |
228 |
static final int SMASK = 0x0000ffff; // short bits for tags |
229 |
|
230 |
/** |
231 |
* Marks completion and wakes up threads waiting to join this |
232 |
* task. |
233 |
* |
234 |
* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL |
235 |
* @return completion status on exit |
236 |
*/ |
237 |
private int setCompletion(int completion) { |
238 |
for (int s;;) { |
239 |
if ((s = status) < 0) |
240 |
return s; |
241 |
if (U.compareAndSwapInt(this, STATUS, s, s | completion)) { |
242 |
if ((s >>> 16) != 0) |
243 |
synchronized (this) { notifyAll(); } |
244 |
return completion; |
245 |
} |
246 |
} |
247 |
} |
248 |
|
249 |
/** |
250 |
* Primary execution method for stolen tasks. Unless done, calls |
251 |
* exec and records status if completed, but doesn't wait for |
252 |
* completion otherwise. |
253 |
* |
254 |
* @return status on exit from this method |
255 |
*/ |
256 |
final int doExec() { |
257 |
int s; boolean completed; |
258 |
if ((s = status) >= 0) { |
259 |
try { |
260 |
completed = exec(); |
261 |
} catch (Throwable rex) { |
262 |
return setExceptionalCompletion(rex); |
263 |
} |
264 |
if (completed) |
265 |
s = setCompletion(NORMAL); |
266 |
} |
267 |
return s; |
268 |
} |
269 |
|
270 |
/** |
271 |
* Tries to set SIGNAL status unless already completed. Used by |
272 |
* ForkJoinPool. Other variants are directly incorporated into |
273 |
* externalAwaitDone etc. |
274 |
* |
275 |
* @return true if successful |
276 |
*/ |
277 |
final boolean trySetSignal() { |
278 |
int s = status; |
279 |
return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL); |
280 |
} |
281 |
|
282 |
/** |
283 |
* Blocks a non-worker-thread until completion. |
284 |
* @return status upon completion |
285 |
*/ |
286 |
private int externalAwaitDone() { |
287 |
int s; |
288 |
ForkJoinPool.externalHelpJoin(this); |
289 |
boolean interrupted = false; |
290 |
while ((s = status) >= 0) { |
291 |
if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { |
292 |
synchronized (this) { |
293 |
if (status >= 0) { |
294 |
try { |
295 |
wait(); |
296 |
} catch (InterruptedException ie) { |
297 |
interrupted = true; |
298 |
} |
299 |
} |
300 |
else |
301 |
notifyAll(); |
302 |
} |
303 |
} |
304 |
} |
305 |
if (interrupted) |
306 |
Thread.currentThread().interrupt(); |
307 |
return s; |
308 |
} |
309 |
|
310 |
/** |
311 |
* Blocks a non-worker-thread until completion or interruption. |
312 |
*/ |
313 |
private int externalInterruptibleAwaitDone() throws InterruptedException { |
314 |
int s; |
315 |
if (Thread.interrupted()) |
316 |
throw new InterruptedException(); |
317 |
ForkJoinPool.externalHelpJoin(this); |
318 |
while ((s = status) >= 0) { |
319 |
if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { |
320 |
synchronized (this) { |
321 |
if (status >= 0) |
322 |
wait(); |
323 |
else |
324 |
notifyAll(); |
325 |
} |
326 |
} |
327 |
} |
328 |
return s; |
329 |
} |
330 |
|
331 |
|
332 |
/** |
333 |
* Implementation for join, get, quietlyJoin. Directly handles |
334 |
* only cases of already-completed, external wait, and |
335 |
* unfork+exec. Others are relayed to ForkJoinPool.awaitJoin. |
336 |
* |
337 |
* @return status upon completion |
338 |
*/ |
339 |
private int doJoin() { |
340 |
int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w; |
341 |
return (s = status) < 0 ? s : |
342 |
((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
343 |
(w = (wt = (ForkJoinWorkerThread)t).workQueue). |
344 |
tryUnpush(this) && (s = doExec()) < 0 ? s : |
345 |
wt.pool.awaitJoin(w, this) : |
346 |
externalAwaitDone(); |
347 |
} |
348 |
|
349 |
/** |
350 |
* Implementation for invoke, quietlyInvoke. |
351 |
* |
352 |
* @return status upon completion |
353 |
*/ |
354 |
private int doInvoke() { |
355 |
int s; Thread t; ForkJoinWorkerThread wt; |
356 |
return (s = doExec()) < 0 ? s : |
357 |
((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
358 |
(wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue, this) : |
359 |
externalAwaitDone(); |
360 |
} |
361 |
|
362 |
// Exception table support |
363 |
|
364 |
/** |
365 |
* Table of exceptions thrown by tasks, to enable reporting by |
366 |
* callers. Because exceptions are rare, we don't directly keep |
367 |
* them with task objects, but instead use a weak ref table. Note |
368 |
* that cancellation exceptions don't appear in the table, but are |
369 |
* instead recorded as status values. |
370 |
* |
371 |
* Note: These statics are initialized below in static block. |
372 |
*/ |
373 |
private static final ExceptionNode[] exceptionTable; |
374 |
private static final ReentrantLock exceptionTableLock; |
375 |
private static final ReferenceQueue<Object> exceptionTableRefQueue; |
376 |
|
377 |
/** |
378 |
* Fixed capacity for exceptionTable. |
379 |
*/ |
380 |
private static final int EXCEPTION_MAP_CAPACITY = 32; |
381 |
|
382 |
/** |
383 |
* Key-value nodes for exception table. The chained hash table |
384 |
* uses identity comparisons, full locking, and weak references |
385 |
* for keys. The table has a fixed capacity because it only |
386 |
* maintains task exceptions long enough for joiners to access |
387 |
* them, so should never become very large for sustained |
388 |
* periods. However, since we do not know when the last joiner |
389 |
* completes, we must use weak references and expunge them. We do |
390 |
* so on each operation (hence full locking). Also, some thread in |
391 |
* any ForkJoinPool will call helpExpungeStaleExceptions when its |
392 |
* pool becomes isQuiescent. |
393 |
*/ |
394 |
static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> { |
395 |
final Throwable ex; |
396 |
ExceptionNode next; |
397 |
final long thrower; // use id not ref to avoid weak cycles |
398 |
ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) { |
399 |
super(task, exceptionTableRefQueue); |
400 |
this.ex = ex; |
401 |
this.next = next; |
402 |
this.thrower = Thread.currentThread().getId(); |
403 |
} |
404 |
} |
405 |
|
406 |
/** |
407 |
* Records exception and sets status. |
408 |
* |
409 |
* @return status on exit |
410 |
*/ |
411 |
final int recordExceptionalCompletion(Throwable ex) { |
412 |
int s; |
413 |
if ((s = status) >= 0) { |
414 |
int h = System.identityHashCode(this); |
415 |
final ReentrantLock lock = exceptionTableLock; |
416 |
lock.lock(); |
417 |
try { |
418 |
expungeStaleExceptions(); |
419 |
ExceptionNode[] t = exceptionTable; |
420 |
int i = h & (t.length - 1); |
421 |
for (ExceptionNode e = t[i]; ; e = e.next) { |
422 |
if (e == null) { |
423 |
t[i] = new ExceptionNode(this, ex, t[i]); |
424 |
break; |
425 |
} |
426 |
if (e.get() == this) // already present |
427 |
break; |
428 |
} |
429 |
} finally { |
430 |
lock.unlock(); |
431 |
} |
432 |
s = setCompletion(EXCEPTIONAL); |
433 |
} |
434 |
return s; |
435 |
} |
436 |
|
437 |
/** |
438 |
* Records exception and possibly propagates |
439 |
* |
440 |
* @return status on exit |
441 |
*/ |
442 |
private int setExceptionalCompletion(Throwable ex) { |
443 |
int s = recordExceptionalCompletion(ex); |
444 |
if ((s & DONE_MASK) == EXCEPTIONAL) |
445 |
internalPropagateException(ex); |
446 |
return s; |
447 |
} |
448 |
|
449 |
/** |
450 |
* Hook for exception propagation support for tasks with completers. |
451 |
*/ |
452 |
void internalPropagateException(Throwable ex) { |
453 |
} |
454 |
|
455 |
/** |
456 |
* Cancels, ignoring any exceptions thrown by cancel. Used during |
457 |
* worker and pool shutdown. Cancel is spec'ed not to throw any |
458 |
* exceptions, but if it does anyway, we have no recourse during |
459 |
* shutdown, so guard against this case. |
460 |
*/ |
461 |
static final void cancelIgnoringExceptions(ForkJoinTask<?> t) { |
462 |
if (t != null && t.status >= 0) { |
463 |
try { |
464 |
t.cancel(false); |
465 |
} catch (Throwable ignore) { |
466 |
} |
467 |
} |
468 |
} |
469 |
|
470 |
/** |
471 |
* Removes exception node and clears status |
472 |
*/ |
473 |
private void clearExceptionalCompletion() { |
474 |
int h = System.identityHashCode(this); |
475 |
final ReentrantLock lock = exceptionTableLock; |
476 |
lock.lock(); |
477 |
try { |
478 |
ExceptionNode[] t = exceptionTable; |
479 |
int i = h & (t.length - 1); |
480 |
ExceptionNode e = t[i]; |
481 |
ExceptionNode pred = null; |
482 |
while (e != null) { |
483 |
ExceptionNode next = e.next; |
484 |
if (e.get() == this) { |
485 |
if (pred == null) |
486 |
t[i] = next; |
487 |
else |
488 |
pred.next = next; |
489 |
break; |
490 |
} |
491 |
pred = e; |
492 |
e = next; |
493 |
} |
494 |
expungeStaleExceptions(); |
495 |
status = 0; |
496 |
} finally { |
497 |
lock.unlock(); |
498 |
} |
499 |
} |
500 |
|
501 |
/** |
502 |
* Returns a rethrowable exception for the given task, if |
503 |
* available. To provide accurate stack traces, if the exception |
504 |
* was not thrown by the current thread, we try to create a new |
505 |
* exception of the same type as the one thrown, but with the |
506 |
* recorded exception as its cause. If there is no such |
507 |
* constructor, we instead try to use a no-arg constructor, |
508 |
* followed by initCause, to the same effect. If none of these |
509 |
* apply, or any fail due to other exceptions, we return the |
510 |
* recorded exception, which is still correct, although it may |
511 |
* contain a misleading stack trace. |
512 |
* |
513 |
* @return the exception, or null if none |
514 |
*/ |
515 |
private Throwable getThrowableException() { |
516 |
if ((status & DONE_MASK) != EXCEPTIONAL) |
517 |
return null; |
518 |
int h = System.identityHashCode(this); |
519 |
ExceptionNode e; |
520 |
final ReentrantLock lock = exceptionTableLock; |
521 |
lock.lock(); |
522 |
try { |
523 |
expungeStaleExceptions(); |
524 |
ExceptionNode[] t = exceptionTable; |
525 |
e = t[h & (t.length - 1)]; |
526 |
while (e != null && e.get() != this) |
527 |
e = e.next; |
528 |
} finally { |
529 |
lock.unlock(); |
530 |
} |
531 |
Throwable ex; |
532 |
if (e == null || (ex = e.ex) == null) |
533 |
return null; |
534 |
if (false && e.thrower != Thread.currentThread().getId()) { |
535 |
Class<? extends Throwable> ec = ex.getClass(); |
536 |
try { |
537 |
Constructor<?> noArgCtor = null; |
538 |
Constructor<?>[] cs = ec.getConstructors();// public ctors only |
539 |
for (int i = 0; i < cs.length; ++i) { |
540 |
Constructor<?> c = cs[i]; |
541 |
Class<?>[] ps = c.getParameterTypes(); |
542 |
if (ps.length == 0) |
543 |
noArgCtor = c; |
544 |
else if (ps.length == 1 && ps[0] == Throwable.class) |
545 |
return (Throwable)(c.newInstance(ex)); |
546 |
} |
547 |
if (noArgCtor != null) { |
548 |
Throwable wx = (Throwable)(noArgCtor.newInstance()); |
549 |
wx.initCause(ex); |
550 |
return wx; |
551 |
} |
552 |
} catch (Exception ignore) { |
553 |
} |
554 |
} |
555 |
return ex; |
556 |
} |
557 |
|
558 |
/** |
559 |
* Poll stale refs and remove them. Call only while holding lock. |
560 |
*/ |
561 |
private static void expungeStaleExceptions() { |
562 |
for (Object x; (x = exceptionTableRefQueue.poll()) != null;) { |
563 |
if (x instanceof ExceptionNode) { |
564 |
ForkJoinTask<?> key = ((ExceptionNode)x).get(); |
565 |
ExceptionNode[] t = exceptionTable; |
566 |
int i = System.identityHashCode(key) & (t.length - 1); |
567 |
ExceptionNode e = t[i]; |
568 |
ExceptionNode pred = null; |
569 |
while (e != null) { |
570 |
ExceptionNode next = e.next; |
571 |
if (e == x) { |
572 |
if (pred == null) |
573 |
t[i] = next; |
574 |
else |
575 |
pred.next = next; |
576 |
break; |
577 |
} |
578 |
pred = e; |
579 |
e = next; |
580 |
} |
581 |
} |
582 |
} |
583 |
} |
584 |
|
585 |
/** |
586 |
* If lock is available, poll stale refs and remove them. |
587 |
* Called from ForkJoinPool when pools become quiescent. |
588 |
*/ |
589 |
static final void helpExpungeStaleExceptions() { |
590 |
final ReentrantLock lock = exceptionTableLock; |
591 |
if (lock.tryLock()) { |
592 |
try { |
593 |
expungeStaleExceptions(); |
594 |
} finally { |
595 |
lock.unlock(); |
596 |
} |
597 |
} |
598 |
} |
599 |
|
600 |
/** |
601 |
* A version of "sneaky throw" to relay exceptions |
602 |
*/ |
603 |
static void rethrow(final Throwable ex) { |
604 |
if (ex != null) { |
605 |
if (ex instanceof Error) |
606 |
throw (Error)ex; |
607 |
if (ex instanceof RuntimeException) |
608 |
throw (RuntimeException)ex; |
609 |
throw uncheckedThrowable(ex, RuntimeException.class); |
610 |
} |
611 |
} |
612 |
|
613 |
/** |
614 |
* The sneaky part of sneaky throw, relying on generics |
615 |
* limitations to evade compiler complaints about rethrowing |
616 |
* unchecked exceptions |
617 |
*/ |
618 |
@SuppressWarnings("unchecked") static <T extends Throwable> |
619 |
T uncheckedThrowable(final Throwable t, final Class<T> c) { |
620 |
return (T)t; // rely on vacuous cast |
621 |
} |
622 |
|
623 |
/** |
624 |
* Throws exception, if any, associated with the given status. |
625 |
*/ |
626 |
private void reportException(int s) { |
627 |
if (s == CANCELLED) |
628 |
throw new CancellationException(); |
629 |
if (s == EXCEPTIONAL) |
630 |
rethrow(getThrowableException()); |
631 |
} |
632 |
|
633 |
// public methods |
634 |
|
635 |
/** |
636 |
* Arranges to asynchronously execute this task in the pool the |
637 |
* current task is running in, if applicable, or using the {@link |
638 |
* ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}. While |
639 |
* it is not necessarily enforced, it is a usage error to fork a |
640 |
* task more than once unless it has completed and been |
641 |
* reinitialized. Subsequent modifications to the state of this |
642 |
* task or any data it operates on are not necessarily |
643 |
* consistently observable by any thread other than the one |
644 |
* executing it unless preceded by a call to {@link #join} or |
645 |
* related methods, or a call to {@link #isDone} returning {@code |
646 |
* true}. |
647 |
* |
648 |
* @return {@code this}, to simplify usage |
649 |
*/ |
650 |
public final ForkJoinTask<V> fork() { |
651 |
Thread t; |
652 |
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) |
653 |
((ForkJoinWorkerThread)t).workQueue.push(this); |
654 |
else |
655 |
ForkJoinPool.commonPool.externalPush(this); |
656 |
return this; |
657 |
} |
658 |
|
659 |
/** |
660 |
* Returns the result of the computation when it {@link #isDone is |
661 |
* done}. This method differs from {@link #get()} in that |
662 |
* abnormal completion results in {@code RuntimeException} or |
663 |
* {@code Error}, not {@code ExecutionException}, and that |
664 |
* interrupts of the calling thread do <em>not</em> cause the |
665 |
* method to abruptly return by throwing {@code |
666 |
* InterruptedException}. |
667 |
* |
668 |
* @return the computed result |
669 |
*/ |
670 |
public final V join() { |
671 |
int s; |
672 |
if ((s = doJoin() & DONE_MASK) != NORMAL) |
673 |
reportException(s); |
674 |
return getRawResult(); |
675 |
} |
676 |
|
677 |
/** |
678 |
* Commences performing this task, awaits its completion if |
679 |
* necessary, and returns its result, or throws an (unchecked) |
680 |
* {@code RuntimeException} or {@code Error} if the underlying |
681 |
* computation did so. |
682 |
* |
683 |
* @return the computed result |
684 |
*/ |
685 |
public final V invoke() { |
686 |
int s; |
687 |
if ((s = doInvoke() & DONE_MASK) != NORMAL) |
688 |
reportException(s); |
689 |
return getRawResult(); |
690 |
} |
691 |
|
692 |
/** |
693 |
* Forks the given tasks, returning when {@code isDone} holds for |
694 |
* each task or an (unchecked) exception is encountered, in which |
695 |
* case the exception is rethrown. If more than one task |
696 |
* encounters an exception, then this method throws any one of |
697 |
* these exceptions. If any task encounters an exception, the |
698 |
* other may be cancelled. However, the execution status of |
699 |
* individual tasks is not guaranteed upon exceptional return. The |
700 |
* status of each task may be obtained using {@link |
701 |
* #getException()} and related methods to check if they have been |
702 |
* cancelled, completed normally or exceptionally, or left |
703 |
* unprocessed. |
704 |
* |
705 |
* @param t1 the first task |
706 |
* @param t2 the second task |
707 |
* @throws NullPointerException if any task is null |
708 |
*/ |
709 |
public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) { |
710 |
int s1, s2; |
711 |
t2.fork(); |
712 |
if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL) |
713 |
t1.reportException(s1); |
714 |
if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL) |
715 |
t2.reportException(s2); |
716 |
} |
717 |
|
718 |
/** |
719 |
* Forks the given tasks, returning when {@code isDone} holds for |
720 |
* each task or an (unchecked) exception is encountered, in which |
721 |
* case the exception is rethrown. If more than one task |
722 |
* encounters an exception, then this method throws any one of |
723 |
* these exceptions. If any task encounters an exception, others |
724 |
* may be cancelled. However, the execution status of individual |
725 |
* tasks is not guaranteed upon exceptional return. The status of |
726 |
* each task may be obtained using {@link #getException()} and |
727 |
* related methods to check if they have been cancelled, completed |
728 |
* normally or exceptionally, or left unprocessed. |
729 |
* |
730 |
* @param tasks the tasks |
731 |
* @throws NullPointerException if any task is null |
732 |
*/ |
733 |
public static void invokeAll(ForkJoinTask<?>... tasks) { |
734 |
Throwable ex = null; |
735 |
int last = tasks.length - 1; |
736 |
for (int i = last; i >= 0; --i) { |
737 |
ForkJoinTask<?> t = tasks[i]; |
738 |
if (t == null) { |
739 |
if (ex == null) |
740 |
ex = new NullPointerException(); |
741 |
} |
742 |
else if (i != 0) |
743 |
t.fork(); |
744 |
else if (t.doInvoke() < NORMAL && ex == null) |
745 |
ex = t.getException(); |
746 |
} |
747 |
for (int i = 1; i <= last; ++i) { |
748 |
ForkJoinTask<?> t = tasks[i]; |
749 |
if (t != null) { |
750 |
if (ex != null) |
751 |
t.cancel(false); |
752 |
else if (t.doJoin() < NORMAL) |
753 |
ex = t.getException(); |
754 |
} |
755 |
} |
756 |
if (ex != null) |
757 |
rethrow(ex); |
758 |
} |
759 |
|
760 |
/** |
761 |
* Forks all tasks in the specified collection, returning when |
762 |
* {@code isDone} holds for each task or an (unchecked) exception |
763 |
* is encountered, in which case the exception is rethrown. If |
764 |
* more than one task encounters an exception, then this method |
765 |
* throws any one of these exceptions. If any task encounters an |
766 |
* exception, others may be cancelled. However, the execution |
767 |
* status of individual tasks is not guaranteed upon exceptional |
768 |
* return. The status of each task may be obtained using {@link |
769 |
* #getException()} and related methods to check if they have been |
770 |
* cancelled, completed normally or exceptionally, or left |
771 |
* unprocessed. |
772 |
* |
773 |
* @param tasks the collection of tasks |
774 |
* @return the tasks argument, to simplify usage |
775 |
* @throws NullPointerException if tasks or any element are null |
776 |
*/ |
777 |
public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) { |
778 |
if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) { |
779 |
invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()])); |
780 |
return tasks; |
781 |
} |
782 |
@SuppressWarnings("unchecked") |
783 |
List<? extends ForkJoinTask<?>> ts = |
784 |
(List<? extends ForkJoinTask<?>>) tasks; |
785 |
Throwable ex = null; |
786 |
int last = ts.size() - 1; |
787 |
for (int i = last; i >= 0; --i) { |
788 |
ForkJoinTask<?> t = ts.get(i); |
789 |
if (t == null) { |
790 |
if (ex == null) |
791 |
ex = new NullPointerException(); |
792 |
} |
793 |
else if (i != 0) |
794 |
t.fork(); |
795 |
else if (t.doInvoke() < NORMAL && ex == null) |
796 |
ex = t.getException(); |
797 |
} |
798 |
for (int i = 1; i <= last; ++i) { |
799 |
ForkJoinTask<?> t = ts.get(i); |
800 |
if (t != null) { |
801 |
if (ex != null) |
802 |
t.cancel(false); |
803 |
else if (t.doJoin() < NORMAL) |
804 |
ex = t.getException(); |
805 |
} |
806 |
} |
807 |
if (ex != null) |
808 |
rethrow(ex); |
809 |
return tasks; |
810 |
} |
811 |
|
812 |
/** |
813 |
* Attempts to cancel execution of this task. This attempt will |
814 |
* fail if the task has already completed or could not be |
815 |
* cancelled for some other reason. If successful, and this task |
816 |
* has not started when {@code cancel} is called, execution of |
817 |
* this task is suppressed. After this method returns |
818 |
* successfully, unless there is an intervening call to {@link |
819 |
* #reinitialize}, subsequent calls to {@link #isCancelled}, |
820 |
* {@link #isDone}, and {@code cancel} will return {@code true} |
821 |
* and calls to {@link #join} and related methods will result in |
822 |
* {@code CancellationException}. |
823 |
* |
824 |
* <p>This method may be overridden in subclasses, but if so, must |
825 |
* still ensure that these properties hold. In particular, the |
826 |
* {@code cancel} method itself must not throw exceptions. |
827 |
* |
828 |
* <p>This method is designed to be invoked by <em>other</em> |
829 |
* tasks. To terminate the current task, you can just return or |
830 |
* throw an unchecked exception from its computation method, or |
831 |
* invoke {@link #completeExceptionally}. |
832 |
* |
833 |
* @param mayInterruptIfRunning this value has no effect in the |
834 |
* default implementation because interrupts are not used to |
835 |
* control cancellation. |
836 |
* |
837 |
* @return {@code true} if this task is now cancelled |
838 |
*/ |
839 |
public boolean cancel(boolean mayInterruptIfRunning) { |
840 |
return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED; |
841 |
} |
842 |
|
843 |
public final boolean isDone() { |
844 |
return status < 0; |
845 |
} |
846 |
|
847 |
public final boolean isCancelled() { |
848 |
return (status & DONE_MASK) == CANCELLED; |
849 |
} |
850 |
|
851 |
/** |
852 |
* Returns {@code true} if this task threw an exception or was cancelled. |
853 |
* |
854 |
* @return {@code true} if this task threw an exception or was cancelled |
855 |
*/ |
856 |
public final boolean isCompletedAbnormally() { |
857 |
return status < NORMAL; |
858 |
} |
859 |
|
860 |
/** |
861 |
* Returns {@code true} if this task completed without throwing an |
862 |
* exception and was not cancelled. |
863 |
* |
864 |
* @return {@code true} if this task completed without throwing an |
865 |
* exception and was not cancelled |
866 |
*/ |
867 |
public final boolean isCompletedNormally() { |
868 |
return (status & DONE_MASK) == NORMAL; |
869 |
} |
870 |
|
871 |
/** |
872 |
* Returns the exception thrown by the base computation, or a |
873 |
* {@code CancellationException} if cancelled, or {@code null} if |
874 |
* none or if the method has not yet completed. |
875 |
* |
876 |
* @return the exception, or {@code null} if none |
877 |
*/ |
878 |
public final Throwable getException() { |
879 |
int s = status & DONE_MASK; |
880 |
return ((s >= NORMAL) ? null : |
881 |
(s == CANCELLED) ? new CancellationException() : |
882 |
getThrowableException()); |
883 |
} |
884 |
|
885 |
/** |
886 |
* Completes this task abnormally, and if not already aborted or |
887 |
* cancelled, causes it to throw the given exception upon |
888 |
* {@code join} and related operations. This method may be used |
889 |
* to induce exceptions in asynchronous tasks, or to force |
890 |
* completion of tasks that would not otherwise complete. Its use |
891 |
* in other situations is discouraged. This method is |
892 |
* overridable, but overridden versions must invoke {@code super} |
893 |
* implementation to maintain guarantees. |
894 |
* |
895 |
* @param ex the exception to throw. If this exception is not a |
896 |
* {@code RuntimeException} or {@code Error}, the actual exception |
897 |
* thrown will be a {@code RuntimeException} with cause {@code ex}. |
898 |
*/ |
899 |
public void completeExceptionally(Throwable ex) { |
900 |
setExceptionalCompletion((ex instanceof RuntimeException) || |
901 |
(ex instanceof Error) ? ex : |
902 |
new RuntimeException(ex)); |
903 |
} |
904 |
|
905 |
/** |
906 |
* Completes this task, and if not already aborted or cancelled, |
907 |
* returning the given value as the result of subsequent |
908 |
* invocations of {@code join} and related operations. This method |
909 |
* may be used to provide results for asynchronous tasks, or to |
910 |
* provide alternative handling for tasks that would not otherwise |
911 |
* complete normally. Its use in other situations is |
912 |
* discouraged. This method is overridable, but overridden |
913 |
* versions must invoke {@code super} implementation to maintain |
914 |
* guarantees. |
915 |
* |
916 |
* @param value the result value for this task |
917 |
*/ |
918 |
public void complete(V value) { |
919 |
try { |
920 |
setRawResult(value); |
921 |
} catch (Throwable rex) { |
922 |
setExceptionalCompletion(rex); |
923 |
return; |
924 |
} |
925 |
setCompletion(NORMAL); |
926 |
} |
927 |
|
928 |
/** |
929 |
* Completes this task normally without setting a value. The most |
930 |
* recent value established by {@link #setRawResult} (or {@code |
931 |
* null} by default) will be returned as the result of subsequent |
932 |
* invocations of {@code join} and related operations. |
933 |
* |
934 |
* @since 1.8 |
935 |
*/ |
936 |
public final void quietlyComplete() { |
937 |
setCompletion(NORMAL); |
938 |
} |
939 |
|
940 |
/** |
941 |
* Waits if necessary for the computation to complete, and then |
942 |
* retrieves its result. |
943 |
* |
944 |
* @return the computed result |
945 |
* @throws CancellationException if the computation was cancelled |
946 |
* @throws ExecutionException if the computation threw an |
947 |
* exception |
948 |
* @throws InterruptedException if the current thread is not a |
949 |
* member of a ForkJoinPool and was interrupted while waiting |
950 |
*/ |
951 |
public final V get() throws InterruptedException, ExecutionException { |
952 |
int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ? |
953 |
doJoin() : externalInterruptibleAwaitDone(); |
954 |
Throwable ex; |
955 |
if ((s &= DONE_MASK) == CANCELLED) |
956 |
throw new CancellationException(); |
957 |
if (s == EXCEPTIONAL && (ex = getThrowableException()) != null) |
958 |
throw new ExecutionException(ex); |
959 |
return getRawResult(); |
960 |
} |
961 |
|
962 |
/** |
963 |
* Waits if necessary for at most the given time for the computation |
964 |
* to complete, and then retrieves its result, if available. |
965 |
* |
966 |
* @param timeout the maximum time to wait |
967 |
* @param unit the time unit of the timeout argument |
968 |
* @return the computed result |
969 |
* @throws CancellationException if the computation was cancelled |
970 |
* @throws ExecutionException if the computation threw an |
971 |
* exception |
972 |
* @throws InterruptedException if the current thread is not a |
973 |
* member of a ForkJoinPool and was interrupted while waiting |
974 |
* @throws TimeoutException if the wait timed out |
975 |
*/ |
976 |
public final V get(long timeout, TimeUnit unit) |
977 |
throws InterruptedException, ExecutionException, TimeoutException { |
978 |
if (Thread.interrupted()) |
979 |
throw new InterruptedException(); |
980 |
// Messy in part because we measure in nanosecs, but wait in millisecs |
981 |
int s; long ms; |
982 |
long ns = unit.toNanos(timeout); |
983 |
if ((s = status) >= 0 && ns > 0L) { |
984 |
long deadline = System.nanoTime() + ns; |
985 |
ForkJoinPool p = null; |
986 |
ForkJoinPool.WorkQueue w = null; |
987 |
Thread t = Thread.currentThread(); |
988 |
if (t instanceof ForkJoinWorkerThread) { |
989 |
ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t; |
990 |
p = wt.pool; |
991 |
w = wt.workQueue; |
992 |
p.helpJoinOnce(w, this); // no retries on failure |
993 |
} |
994 |
else |
995 |
ForkJoinPool.externalHelpJoin(this); |
996 |
boolean canBlock = false; |
997 |
boolean interrupted = false; |
998 |
try { |
999 |
while ((s = status) >= 0) { |
1000 |
if (w != null && w.qlock < 0) |
1001 |
cancelIgnoringExceptions(this); |
1002 |
else if (!canBlock) { |
1003 |
if (p == null || p.tryCompensate()) |
1004 |
canBlock = true; |
1005 |
} |
1006 |
else { |
1007 |
if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L && |
1008 |
U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { |
1009 |
synchronized (this) { |
1010 |
if (status >= 0) { |
1011 |
try { |
1012 |
wait(ms); |
1013 |
} catch (InterruptedException ie) { |
1014 |
if (p == null) |
1015 |
interrupted = true; |
1016 |
} |
1017 |
} |
1018 |
else |
1019 |
notifyAll(); |
1020 |
} |
1021 |
} |
1022 |
if ((s = status) < 0 || interrupted || |
1023 |
(ns = deadline - System.nanoTime()) <= 0L) |
1024 |
break; |
1025 |
} |
1026 |
} |
1027 |
} finally { |
1028 |
if (p != null && canBlock) |
1029 |
p.incrementActiveCount(); |
1030 |
} |
1031 |
if (interrupted) |
1032 |
throw new InterruptedException(); |
1033 |
} |
1034 |
if ((s &= DONE_MASK) != NORMAL) { |
1035 |
Throwable ex; |
1036 |
if (s == CANCELLED) |
1037 |
throw new CancellationException(); |
1038 |
if (s != EXCEPTIONAL) |
1039 |
throw new TimeoutException(); |
1040 |
if ((ex = getThrowableException()) != null) |
1041 |
throw new ExecutionException(ex); |
1042 |
} |
1043 |
return getRawResult(); |
1044 |
} |
1045 |
|
1046 |
/** |
1047 |
* Joins this task, without returning its result or throwing its |
1048 |
* exception. This method may be useful when processing |
1049 |
* collections of tasks when some have been cancelled or otherwise |
1050 |
* known to have aborted. |
1051 |
*/ |
1052 |
public final void quietlyJoin() { |
1053 |
doJoin(); |
1054 |
} |
1055 |
|
1056 |
/** |
1057 |
* Commences performing this task and awaits its completion if |
1058 |
* necessary, without returning its result or throwing its |
1059 |
* exception. |
1060 |
*/ |
1061 |
public final void quietlyInvoke() { |
1062 |
doInvoke(); |
1063 |
} |
1064 |
|
1065 |
/** |
1066 |
* Possibly executes tasks until the pool hosting the current task |
1067 |
* {@link ForkJoinPool#isQuiescent is quiescent}. This method may |
1068 |
* be of use in designs in which many tasks are forked, but none |
1069 |
* are explicitly joined, instead executing them until all are |
1070 |
* processed. |
1071 |
*/ |
1072 |
public static void helpQuiesce() { |
1073 |
Thread t; |
1074 |
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) { |
1075 |
ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t; |
1076 |
wt.pool.helpQuiescePool(wt.workQueue); |
1077 |
} |
1078 |
else |
1079 |
ForkJoinPool.externalHelpQuiescePool(); |
1080 |
} |
1081 |
|
1082 |
/** |
1083 |
* Resets the internal bookkeeping state of this task, allowing a |
1084 |
* subsequent {@code fork}. This method allows repeated reuse of |
1085 |
* this task, but only if reuse occurs when this task has either |
1086 |
* never been forked, or has been forked, then completed and all |
1087 |
* outstanding joins of this task have also completed. Effects |
1088 |
* under any other usage conditions are not guaranteed. |
1089 |
* This method may be useful when executing |
1090 |
* pre-constructed trees of subtasks in loops. |
1091 |
* |
1092 |
* <p>Upon completion of this method, {@code isDone()} reports |
1093 |
* {@code false}, and {@code getException()} reports {@code |
1094 |
* null}. However, the value returned by {@code getRawResult} is |
1095 |
* unaffected. To clear this value, you can invoke {@code |
1096 |
* setRawResult(null)}. |
1097 |
*/ |
1098 |
public void reinitialize() { |
1099 |
if ((status & DONE_MASK) == EXCEPTIONAL) |
1100 |
clearExceptionalCompletion(); |
1101 |
else |
1102 |
status = 0; |
1103 |
} |
1104 |
|
1105 |
/** |
1106 |
* Returns the pool hosting the current task execution, or null |
1107 |
* if this task is executing outside of any ForkJoinPool. |
1108 |
* |
1109 |
* @see #inForkJoinPool |
1110 |
* @return the pool, or {@code null} if none |
1111 |
*/ |
1112 |
public static ForkJoinPool getPool() { |
1113 |
Thread t = Thread.currentThread(); |
1114 |
return (t instanceof ForkJoinWorkerThread) ? |
1115 |
((ForkJoinWorkerThread) t).pool : null; |
1116 |
} |
1117 |
|
1118 |
/** |
1119 |
* Returns {@code true} if the current thread is a {@link |
1120 |
* ForkJoinWorkerThread} executing as a ForkJoinPool computation. |
1121 |
* |
1122 |
* @return {@code true} if the current thread is a {@link |
1123 |
* ForkJoinWorkerThread} executing as a ForkJoinPool computation, |
1124 |
* or {@code false} otherwise |
1125 |
*/ |
1126 |
public static boolean inForkJoinPool() { |
1127 |
return Thread.currentThread() instanceof ForkJoinWorkerThread; |
1128 |
} |
1129 |
|
1130 |
/** |
1131 |
* Tries to unschedule this task for execution. This method will |
1132 |
* typically (but is not guaranteed to) succeed if this task is |
1133 |
* the most recently forked task by the current thread, and has |
1134 |
* not commenced executing in another thread. This method may be |
1135 |
* useful when arranging alternative local processing of tasks |
1136 |
* that could have been, but were not, stolen. |
1137 |
* |
1138 |
* @return {@code true} if unforked |
1139 |
*/ |
1140 |
public boolean tryUnfork() { |
1141 |
Thread t; |
1142 |
return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1143 |
((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) : |
1144 |
ForkJoinPool.tryExternalUnpush(this)); |
1145 |
} |
1146 |
|
1147 |
/** |
1148 |
* Returns an estimate of the number of tasks that have been |
1149 |
* forked by the current worker thread but not yet executed. This |
1150 |
* value may be useful for heuristic decisions about whether to |
1151 |
* fork other tasks. |
1152 |
* |
1153 |
* @return the number of tasks |
1154 |
*/ |
1155 |
public static int getQueuedTaskCount() { |
1156 |
Thread t; ForkJoinPool.WorkQueue q; |
1157 |
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) |
1158 |
q = ((ForkJoinWorkerThread)t).workQueue; |
1159 |
else |
1160 |
q = ForkJoinPool.commonSubmitterQueue(); |
1161 |
return (q == null) ? 0 : q.queueSize(); |
1162 |
} |
1163 |
|
1164 |
/** |
1165 |
* Returns an estimate of how many more locally queued tasks are |
1166 |
* held by the current worker thread than there are other worker |
1167 |
* threads that might steal them, or zero if this thread is not |
1168 |
* operating in a ForkJoinPool. This value may be useful for |
1169 |
* heuristic decisions about whether to fork other tasks. In many |
1170 |
* usages of ForkJoinTasks, at steady state, each worker should |
1171 |
* aim to maintain a small constant surplus (for example, 3) of |
1172 |
* tasks, and to process computations locally if this threshold is |
1173 |
* exceeded. |
1174 |
* |
1175 |
* @return the surplus number of tasks, which may be negative |
1176 |
*/ |
1177 |
public static int getSurplusQueuedTaskCount() { |
1178 |
return ForkJoinPool.getSurplusQueuedTaskCount(); |
1179 |
} |
1180 |
|
1181 |
// Extension methods |
1182 |
|
1183 |
/** |
1184 |
* Returns the result that would be returned by {@link #join}, even |
1185 |
* if this task completed abnormally, or {@code null} if this task |
1186 |
* is not known to have been completed. This method is designed |
1187 |
* to aid debugging, as well as to support extensions. Its use in |
1188 |
* any other context is discouraged. |
1189 |
* |
1190 |
* @return the result, or {@code null} if not completed |
1191 |
*/ |
1192 |
public abstract V getRawResult(); |
1193 |
|
1194 |
/** |
1195 |
* Forces the given value to be returned as a result. This method |
1196 |
* is designed to support extensions, and should not in general be |
1197 |
* called otherwise. |
1198 |
* |
1199 |
* @param value the value |
1200 |
*/ |
1201 |
protected abstract void setRawResult(V value); |
1202 |
|
1203 |
/** |
1204 |
* Immediately performs the base action of this task and returns |
1205 |
* true if, upon return from this method, this task is guaranteed |
1206 |
* to have completed normally. This method may return false |
1207 |
* otherwise, to indicate that this task is not necessarily |
1208 |
* complete (or is not known to be complete), for example in |
1209 |
* asynchronous actions that require explicit invocations of |
1210 |
* completion methods. This method may also throw an (unchecked) |
1211 |
* exception to indicate abnormal exit. This method is designed to |
1212 |
* support extensions, and should not in general be called |
1213 |
* otherwise. |
1214 |
* |
1215 |
* @return {@code true} if this task is known to have completed normally |
1216 |
*/ |
1217 |
protected abstract boolean exec(); |
1218 |
|
1219 |
/** |
1220 |
* Returns, but does not unschedule or execute, a task queued by |
1221 |
* the current thread but not yet executed, if one is immediately |
1222 |
* available. There is no guarantee that this task will actually |
1223 |
* be polled or executed next. Conversely, this method may return |
1224 |
* null even if a task exists but cannot be accessed without |
1225 |
* contention with other threads. This method is designed |
1226 |
* primarily to support extensions, and is unlikely to be useful |
1227 |
* otherwise. |
1228 |
* |
1229 |
* @return the next task, or {@code null} if none are available |
1230 |
*/ |
1231 |
protected static ForkJoinTask<?> peekNextLocalTask() { |
1232 |
Thread t; ForkJoinPool.WorkQueue q; |
1233 |
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) |
1234 |
q = ((ForkJoinWorkerThread)t).workQueue; |
1235 |
else |
1236 |
q = ForkJoinPool.commonSubmitterQueue(); |
1237 |
return (q == null) ? null : q.peek(); |
1238 |
} |
1239 |
|
1240 |
/** |
1241 |
* Unschedules and returns, without executing, the next task |
1242 |
* queued by the current thread but not yet executed, if the |
1243 |
* current thread is operating in a ForkJoinPool. This method is |
1244 |
* designed primarily to support extensions, and is unlikely to be |
1245 |
* useful otherwise. |
1246 |
* |
1247 |
* @return the next task, or {@code null} if none are available |
1248 |
*/ |
1249 |
protected static ForkJoinTask<?> pollNextLocalTask() { |
1250 |
Thread t; |
1251 |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1252 |
((ForkJoinWorkerThread)t).workQueue.nextLocalTask() : |
1253 |
null; |
1254 |
} |
1255 |
|
1256 |
/** |
1257 |
* If the current thread is operating in a ForkJoinPool, |
1258 |
* unschedules and returns, without executing, the next task |
1259 |
* queued by the current thread but not yet executed, if one is |
1260 |
* available, or if not available, a task that was forked by some |
1261 |
* other thread, if available. Availability may be transient, so a |
1262 |
* {@code null} result does not necessarily imply quiescence of |
1263 |
* the pool this task is operating in. This method is designed |
1264 |
* primarily to support extensions, and is unlikely to be useful |
1265 |
* otherwise. |
1266 |
* |
1267 |
* @return a task, or {@code null} if none are available |
1268 |
*/ |
1269 |
protected static ForkJoinTask<?> pollTask() { |
1270 |
Thread t; ForkJoinWorkerThread wt; |
1271 |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1272 |
(wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) : |
1273 |
null; |
1274 |
} |
1275 |
|
1276 |
// tag operations |
1277 |
|
1278 |
/** |
1279 |
* Returns the tag for this task. |
1280 |
* |
1281 |
* @return the tag for this task |
1282 |
* @since 1.8 |
1283 |
*/ |
1284 |
public final short getForkJoinTaskTag() { |
1285 |
return (short)status; |
1286 |
} |
1287 |
|
1288 |
/** |
1289 |
* Atomically sets the tag value for this task. |
1290 |
* |
1291 |
* @param tag the tag value |
1292 |
* @return the previous value of the tag |
1293 |
* @since 1.8 |
1294 |
*/ |
1295 |
public final short setForkJoinTaskTag(short tag) { |
1296 |
for (int s;;) { |
1297 |
if (U.compareAndSwapInt(this, STATUS, s = status, |
1298 |
(s & ~SMASK) | (tag & SMASK))) |
1299 |
return (short)s; |
1300 |
} |
1301 |
} |
1302 |
|
1303 |
/** |
1304 |
* Atomically conditionally sets the tag value for this task. |
1305 |
* Among other applications, tags can be used as visit markers |
1306 |
* in tasks operating on graphs, as in methods that check: {@code |
1307 |
* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))} |
1308 |
* before processing, otherwise exiting because the node has |
1309 |
* already been visited. |
1310 |
* |
1311 |
* @param e the expected tag value |
1312 |
* @param tag the new tag value |
1313 |
* @return true if successful; i.e., the current value was |
1314 |
* equal to e and is now tag. |
1315 |
* @since 1.8 |
1316 |
*/ |
1317 |
public final boolean compareAndSetForkJoinTaskTag(short e, short tag) { |
1318 |
for (int s;;) { |
1319 |
if ((short)(s = status) != e) |
1320 |
return false; |
1321 |
if (U.compareAndSwapInt(this, STATUS, s, |
1322 |
(s & ~SMASK) | (tag & SMASK))) |
1323 |
return true; |
1324 |
} |
1325 |
} |
1326 |
|
1327 |
/** |
1328 |
* Adaptor for Runnables. This implements RunnableFuture |
1329 |
* to be compliant with AbstractExecutorService constraints |
1330 |
* when used in ForkJoinPool. |
1331 |
*/ |
1332 |
static final class AdaptedRunnable<T> extends ForkJoinTask<T> |
1333 |
implements RunnableFuture<T> { |
1334 |
final Runnable runnable; |
1335 |
T result; |
1336 |
AdaptedRunnable(Runnable runnable, T result) { |
1337 |
if (runnable == null) throw new NullPointerException(); |
1338 |
this.runnable = runnable; |
1339 |
this.result = result; // OK to set this even before completion |
1340 |
} |
1341 |
public final T getRawResult() { return result; } |
1342 |
public final void setRawResult(T v) { result = v; } |
1343 |
public final boolean exec() { runnable.run(); return true; } |
1344 |
public final void run() { invoke(); } |
1345 |
private static final long serialVersionUID = 5232453952276885070L; |
1346 |
} |
1347 |
|
1348 |
/** |
1349 |
* Adaptor for Runnables without results |
1350 |
*/ |
1351 |
static final class AdaptedRunnableAction extends ForkJoinTask<Void> |
1352 |
implements RunnableFuture<Void> { |
1353 |
final Runnable runnable; |
1354 |
AdaptedRunnableAction(Runnable runnable) { |
1355 |
if (runnable == null) throw new NullPointerException(); |
1356 |
this.runnable = runnable; |
1357 |
} |
1358 |
public final Void getRawResult() { return null; } |
1359 |
public final void setRawResult(Void v) { } |
1360 |
public final boolean exec() { runnable.run(); return true; } |
1361 |
public final void run() { invoke(); } |
1362 |
private static final long serialVersionUID = 5232453952276885070L; |
1363 |
} |
1364 |
|
1365 |
/** |
1366 |
* Adaptor for Callables |
1367 |
*/ |
1368 |
static final class AdaptedCallable<T> extends ForkJoinTask<T> |
1369 |
implements RunnableFuture<T> { |
1370 |
final Callable<? extends T> callable; |
1371 |
T result; |
1372 |
AdaptedCallable(Callable<? extends T> callable) { |
1373 |
if (callable == null) throw new NullPointerException(); |
1374 |
this.callable = callable; |
1375 |
} |
1376 |
public final T getRawResult() { return result; } |
1377 |
public final void setRawResult(T v) { result = v; } |
1378 |
public final boolean exec() { |
1379 |
try { |
1380 |
result = callable.call(); |
1381 |
return true; |
1382 |
} catch (Error err) { |
1383 |
throw err; |
1384 |
} catch (RuntimeException rex) { |
1385 |
throw rex; |
1386 |
} catch (Exception ex) { |
1387 |
throw new RuntimeException(ex); |
1388 |
} |
1389 |
} |
1390 |
public final void run() { invoke(); } |
1391 |
private static final long serialVersionUID = 2838392045355241008L; |
1392 |
} |
1393 |
|
1394 |
/** |
1395 |
* Returns a new {@code ForkJoinTask} that performs the {@code run} |
1396 |
* method of the given {@code Runnable} as its action, and returns |
1397 |
* a null result upon {@link #join}. |
1398 |
* |
1399 |
* @param runnable the runnable action |
1400 |
* @return the task |
1401 |
*/ |
1402 |
public static ForkJoinTask<?> adapt(Runnable runnable) { |
1403 |
return new AdaptedRunnableAction(runnable); |
1404 |
} |
1405 |
|
1406 |
/** |
1407 |
* Returns a new {@code ForkJoinTask} that performs the {@code run} |
1408 |
* method of the given {@code Runnable} as its action, and returns |
1409 |
* the given result upon {@link #join}. |
1410 |
* |
1411 |
* @param runnable the runnable action |
1412 |
* @param result the result upon completion |
1413 |
* @return the task |
1414 |
*/ |
1415 |
public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) { |
1416 |
return new AdaptedRunnable<T>(runnable, result); |
1417 |
} |
1418 |
|
1419 |
/** |
1420 |
* Returns a new {@code ForkJoinTask} that performs the {@code call} |
1421 |
* method of the given {@code Callable} as its action, and returns |
1422 |
* its result upon {@link #join}, translating any checked exceptions |
1423 |
* encountered into {@code RuntimeException}. |
1424 |
* |
1425 |
* @param callable the callable action |
1426 |
* @return the task |
1427 |
*/ |
1428 |
public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) { |
1429 |
return new AdaptedCallable<T>(callable); |
1430 |
} |
1431 |
|
1432 |
// Serialization support |
1433 |
|
1434 |
private static final long serialVersionUID = -7721805057305804111L; |
1435 |
|
1436 |
/** |
1437 |
* Saves this task to a stream (that is, serializes it). |
1438 |
* |
1439 |
* @serialData the current run status and the exception thrown |
1440 |
* during execution, or {@code null} if none |
1441 |
*/ |
1442 |
private void writeObject(java.io.ObjectOutputStream s) |
1443 |
throws java.io.IOException { |
1444 |
s.defaultWriteObject(); |
1445 |
s.writeObject(getException()); |
1446 |
} |
1447 |
|
1448 |
/** |
1449 |
* Reconstitutes this task from a stream (that is, deserializes it). |
1450 |
*/ |
1451 |
private void readObject(java.io.ObjectInputStream s) |
1452 |
throws java.io.IOException, ClassNotFoundException { |
1453 |
s.defaultReadObject(); |
1454 |
Object ex = s.readObject(); |
1455 |
if (ex != null) |
1456 |
setExceptionalCompletion((Throwable)ex); |
1457 |
} |
1458 |
|
1459 |
// Unsafe mechanics |
1460 |
private static final sun.misc.Unsafe U; |
1461 |
private static final long STATUS; |
1462 |
|
1463 |
static { |
1464 |
exceptionTableLock = new ReentrantLock(); |
1465 |
exceptionTableRefQueue = new ReferenceQueue<Object>(); |
1466 |
exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY]; |
1467 |
try { |
1468 |
U = getUnsafe(); |
1469 |
Class<?> k = ForkJoinTask.class; |
1470 |
STATUS = U.objectFieldOffset |
1471 |
(k.getDeclaredField("status")); |
1472 |
} catch (Exception e) { |
1473 |
throw new Error(e); |
1474 |
} |
1475 |
} |
1476 |
|
1477 |
/** |
1478 |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
1479 |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
1480 |
* into a jdk. |
1481 |
* |
1482 |
* @return a sun.misc.Unsafe |
1483 |
*/ |
1484 |
private static sun.misc.Unsafe getUnsafe() { |
1485 |
try { |
1486 |
return sun.misc.Unsafe.getUnsafe(); |
1487 |
} catch (SecurityException se) { |
1488 |
try { |
1489 |
return java.security.AccessController.doPrivileged |
1490 |
(new java.security |
1491 |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1492 |
public sun.misc.Unsafe run() throws Exception { |
1493 |
java.lang.reflect.Field f = sun.misc |
1494 |
.Unsafe.class.getDeclaredField("theUnsafe"); |
1495 |
f.setAccessible(true); |
1496 |
return (sun.misc.Unsafe) f.get(null); |
1497 |
}}); |
1498 |
} catch (java.security.PrivilegedActionException e) { |
1499 |
throw new RuntimeException("Could not initialize intrinsics", |
1500 |
e.getCause()); |
1501 |
} |
1502 |
} |
1503 |
} |
1504 |
|
1505 |
} |