1 |
/* |
2 |
* Written by Doug Lea with assistance from members of JCP JSR-166 |
3 |
* Expert Group and released to the public domain. Use, modify, and |
4 |
* redistribute this code in any way without acknowledgement. |
5 |
*/ |
6 |
|
7 |
package java.util.concurrent; |
8 |
import java.util.concurrent.atomic.*; |
9 |
import java.util.*; |
10 |
|
11 |
/** |
12 |
* A {@link ThreadPoolExecutor} that can schedule commands to run |
13 |
* after a given delay, or to execute periodically. This class is |
14 |
* preferable to {@link java.util.Timer} when multiple worker threads |
15 |
* are needed, or when the additional flexibility or capabilities of |
16 |
* {@link ThreadPoolExecutor} (which this class extends) are required. |
17 |
* |
18 |
* <p> Delayed tasks execute no sooner than they are enabled, but |
19 |
* without any real-time guarantees about when, after they are enabled, |
20 |
* they will commence. Tasks tied for the same execution time are |
21 |
* enabled in first-in-first-out (FIFO) order of submission. |
22 |
* |
23 |
* <p>While this class inherits from {@link ThreadPoolExecutor}, a few |
24 |
* of the inherited tuning methods are not especially useful for |
25 |
* it. In particular, because a <tt>ScheduledExecutor</tt> always acts |
26 |
* as a fixed-sized pool using <tt>corePoolSize</tt> threads and an |
27 |
* unbounded queue, adjustments to <tt>maximumPoolSize</tt> have no |
28 |
* useful effect. |
29 |
* |
30 |
* @since 1.5 |
31 |
* @author Doug Lea |
32 |
*/ |
33 |
public class ScheduledThreadPoolExecutor |
34 |
extends ThreadPoolExecutor |
35 |
implements ScheduledExecutorService { |
36 |
|
37 |
/** |
38 |
* False if should cancel/suppress periodic tasks on shutdown. |
39 |
*/ |
40 |
private volatile boolean continueExistingPeriodicTasksAfterShutdown; |
41 |
|
42 |
/** |
43 |
* False if should cancel non-periodic tasks on shutdown. |
44 |
*/ |
45 |
private volatile boolean executeExistingDelayedTasksAfterShutdown = true; |
46 |
|
47 |
|
48 |
/** |
49 |
* Sequence number to break scheduling ties, and in turn to |
50 |
* guarantee FIFO order among tied entries. |
51 |
*/ |
52 |
private static final AtomicLong sequencer = new AtomicLong(0); |
53 |
|
54 |
private class ScheduledFutureTask<V> |
55 |
extends FutureTask<V> implements ScheduledFuture<V> { |
56 |
|
57 |
/** Sequence number to break ties FIFO */ |
58 |
private final long sequenceNumber; |
59 |
/** The time the task is enabled to execute in nanoTime units */ |
60 |
private long time; |
61 |
/** The delay following next time, or <= 0 if non-periodic */ |
62 |
private final long period; |
63 |
/** true if at fixed rate; false if fixed delay */ |
64 |
private final boolean rateBased; |
65 |
|
66 |
/** |
67 |
* Creates a one-shot action with given nanoTime-based trigger time |
68 |
*/ |
69 |
ScheduledFutureTask(Runnable r, V result, long ns) { |
70 |
super(r, result); |
71 |
this.time = ns; |
72 |
this.period = 0; |
73 |
rateBased = false; |
74 |
this.sequenceNumber = sequencer.getAndIncrement(); |
75 |
} |
76 |
|
77 |
/** |
78 |
* Creates a periodic action with given nano time and period |
79 |
*/ |
80 |
ScheduledFutureTask(Runnable r, V result, long ns, long period, boolean rateBased) { |
81 |
super(r, result); |
82 |
this.time = ns; |
83 |
this.period = period; |
84 |
this.rateBased = rateBased; |
85 |
this.sequenceNumber = sequencer.getAndIncrement(); |
86 |
} |
87 |
|
88 |
/** |
89 |
* Creates a one-shot action with given nanoTime-based trigger |
90 |
*/ |
91 |
ScheduledFutureTask(Callable<V> callable, long ns) { |
92 |
super(callable); |
93 |
this.time = ns; |
94 |
this.period = 0; |
95 |
rateBased = false; |
96 |
this.sequenceNumber = sequencer.getAndIncrement(); |
97 |
} |
98 |
|
99 |
|
100 |
public long getDelay(TimeUnit unit) { |
101 |
long d = unit.convert(time - System.nanoTime(), |
102 |
TimeUnit.NANOSECONDS); |
103 |
return d; |
104 |
} |
105 |
|
106 |
public int compareTo(Object other) { |
107 |
if (other == this) // compare zero ONLY if same object |
108 |
return 0; |
109 |
ScheduledFutureTask<?> x = (ScheduledFutureTask<?>)other; |
110 |
long diff = time - x.time; |
111 |
if (diff < 0) |
112 |
return -1; |
113 |
else if (diff > 0) |
114 |
return 1; |
115 |
else if (sequenceNumber < x.sequenceNumber) |
116 |
return -1; |
117 |
else |
118 |
return 1; |
119 |
} |
120 |
|
121 |
/** |
122 |
* Return true if this is a periodic (not a one-shot) action. |
123 |
* @return true if periodic |
124 |
*/ |
125 |
public boolean isPeriodic() { |
126 |
return period > 0; |
127 |
} |
128 |
|
129 |
/** |
130 |
* Returns the period, or zero if non-periodic. |
131 |
* |
132 |
* @return the period |
133 |
*/ |
134 |
public long getPeriod(TimeUnit unit) { |
135 |
return unit.convert(period, TimeUnit.NANOSECONDS); |
136 |
} |
137 |
|
138 |
/** |
139 |
* Overrides FutureTask version so as to reset/requeue if periodic. |
140 |
*/ |
141 |
public void run() { |
142 |
if (!isPeriodic()) |
143 |
ScheduledFutureTask.super.run(); |
144 |
else { |
145 |
ScheduledFutureTask.super.runAndReset(); |
146 |
if (isCancelled()) |
147 |
return; |
148 |
boolean down = isShutdown(); |
149 |
if (!down || |
150 |
(getContinueExistingPeriodicTasksAfterShutdownPolicy() && |
151 |
!isTerminating())) { |
152 |
time = period + (rateBased ? time : System.nanoTime()); |
153 |
ScheduledThreadPoolExecutor.super.getQueue().add(this); |
154 |
} |
155 |
// This might have been the final executed delayed |
156 |
// task. Wake up threads to check. |
157 |
else if (down) |
158 |
interruptIdleWorkers(); |
159 |
} |
160 |
} |
161 |
} |
162 |
|
163 |
/** |
164 |
* An annoying wrapper class to convince generics compiler to |
165 |
* use a DelayQueue<ScheduledFutureTask> as a BlockingQueue<Runnable> |
166 |
*/ |
167 |
private static class DelayedWorkQueue |
168 |
extends AbstractCollection<Runnable> implements BlockingQueue<Runnable> { |
169 |
|
170 |
private final DelayQueue<ScheduledFutureTask> dq = new DelayQueue<ScheduledFutureTask>(); |
171 |
public Runnable poll() { return dq.poll(); } |
172 |
public Runnable peek() { return dq.peek(); } |
173 |
public Runnable take() throws InterruptedException { return dq.take(); } |
174 |
public Runnable poll(long timeout, TimeUnit unit) throws InterruptedException { |
175 |
return dq.poll(timeout, unit); |
176 |
} |
177 |
|
178 |
public boolean add(Runnable x) { return dq.add((ScheduledFutureTask)x); } |
179 |
public boolean offer(Runnable x) { return dq.offer((ScheduledFutureTask)x); } |
180 |
public void put(Runnable x) { |
181 |
dq.put((ScheduledFutureTask)x); |
182 |
} |
183 |
public boolean offer(Runnable x, long timeout, TimeUnit unit) { |
184 |
return dq.offer((ScheduledFutureTask)x, timeout, unit); |
185 |
} |
186 |
|
187 |
public Runnable remove() { return dq.remove(); } |
188 |
public Runnable element() { return dq.element(); } |
189 |
public void clear() { dq.clear(); } |
190 |
public int drainTo(Collection<? super Runnable> c) { return dq.drainTo(c); } |
191 |
public int drainTo(Collection<? super Runnable> c, int maxElements) { |
192 |
return dq.drainTo(c, maxElements); |
193 |
} |
194 |
|
195 |
public int remainingCapacity() { return dq.remainingCapacity(); } |
196 |
public boolean remove(Object x) { return dq.remove(x); } |
197 |
public boolean contains(Object x) { return dq.contains(x); } |
198 |
public int size() { return dq.size(); } |
199 |
public boolean isEmpty() { return dq.isEmpty(); } |
200 |
public Object[] toArray() { return dq.toArray(); } |
201 |
public <T> T[] toArray(T[] array) { return dq.toArray(array); } |
202 |
public Iterator<Runnable> iterator() { |
203 |
return new Iterator<Runnable>() { |
204 |
private Iterator<ScheduledFutureTask> it = dq.iterator(); |
205 |
public boolean hasNext() { return it.hasNext(); } |
206 |
public Runnable next() { return it.next(); } |
207 |
public void remove() { it.remove(); } |
208 |
}; |
209 |
} |
210 |
} |
211 |
|
212 |
/** |
213 |
* Creates a new ScheduledThreadPoolExecutor with the given core pool size. |
214 |
* |
215 |
* @param corePoolSize the number of threads to keep in the pool, |
216 |
* even if they are idle. |
217 |
* @throws IllegalArgumentException if corePoolSize less than or |
218 |
* equal to zero |
219 |
*/ |
220 |
public ScheduledThreadPoolExecutor(int corePoolSize) { |
221 |
super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, |
222 |
new DelayedWorkQueue()); |
223 |
} |
224 |
|
225 |
/** |
226 |
* Creates a new ScheduledThreadPoolExecutor with the given initial parameters. |
227 |
* |
228 |
* @param corePoolSize the number of threads to keep in the pool, |
229 |
* even if they are idle. |
230 |
* @param threadFactory the factory to use when the executor |
231 |
* creates a new thread. |
232 |
* @throws NullPointerException if threadFactory is null |
233 |
*/ |
234 |
public ScheduledThreadPoolExecutor(int corePoolSize, |
235 |
ThreadFactory threadFactory) { |
236 |
super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, |
237 |
new DelayedWorkQueue(), threadFactory); |
238 |
} |
239 |
|
240 |
/** |
241 |
* Creates a new ScheduledThreadPoolExecutor with the given initial parameters. |
242 |
* |
243 |
* @param corePoolSize the number of threads to keep in the pool, |
244 |
* even if they are idle. |
245 |
* @param handler the handler to use when execution is blocked |
246 |
* because the thread bounds and queue capacities are reached. |
247 |
* @throws NullPointerException if handler is null |
248 |
*/ |
249 |
public ScheduledThreadPoolExecutor(int corePoolSize, |
250 |
RejectedExecutionHandler handler) { |
251 |
super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, |
252 |
new DelayedWorkQueue(), handler); |
253 |
} |
254 |
|
255 |
/** |
256 |
* Creates a new ScheduledThreadPoolExecutor with the given initial parameters. |
257 |
* |
258 |
* @param corePoolSize the number of threads to keep in the pool, |
259 |
* even if they are idle. |
260 |
* @param threadFactory the factory to use when the executor |
261 |
* creates a new thread. |
262 |
* @param handler the handler to use when execution is blocked |
263 |
* because the thread bounds and queue capacities are reached. |
264 |
* @throws NullPointerException if threadFactory or handler is null |
265 |
*/ |
266 |
public ScheduledThreadPoolExecutor(int corePoolSize, |
267 |
ThreadFactory threadFactory, |
268 |
RejectedExecutionHandler handler) { |
269 |
super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, |
270 |
new DelayedWorkQueue(), threadFactory, handler); |
271 |
} |
272 |
|
273 |
/** |
274 |
* Specialized variant of ThreadPoolExecutor.execute for delayed tasks. |
275 |
*/ |
276 |
private void delayedExecute(Runnable command) { |
277 |
if (isShutdown()) { |
278 |
reject(command); |
279 |
return; |
280 |
} |
281 |
// Prestart a thread if necessary. We cannot prestart it |
282 |
// running the task because the task (probably) shouldn't be |
283 |
// run yet, so thread will just idle until delay elapses. |
284 |
if (getPoolSize() < getCorePoolSize()) |
285 |
prestartCoreThread(); |
286 |
|
287 |
super.getQueue().add(command); |
288 |
} |
289 |
|
290 |
/** |
291 |
* Creates and executes a one-shot action that becomes enabled after |
292 |
* the given delay. |
293 |
* @param command the task to execute. |
294 |
* @param delay the time from now to delay execution. |
295 |
* @param unit the time unit of the delay parameter. |
296 |
* @return a Future representing pending completion of the task, |
297 |
* and whose <tt>get()</tt> method will return <tt>null</tt> |
298 |
* upon completion. |
299 |
* @throws RejectedExecutionException if task cannot be scheduled |
300 |
* for execution because the executor has been shut down. |
301 |
* @throws NullPointerException if command is null |
302 |
*/ |
303 |
|
304 |
public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) { |
305 |
if (command == null) |
306 |
throw new NullPointerException(); |
307 |
long triggerTime = System.nanoTime() + unit.toNanos(delay); |
308 |
ScheduledFutureTask<?> t = new ScheduledFutureTask<Boolean>(command, null, triggerTime); |
309 |
delayedExecute(t); |
310 |
return t; |
311 |
} |
312 |
|
313 |
/** |
314 |
* Creates and executes a ScheduledFuture that becomes enabled after the |
315 |
* given delay. |
316 |
* @param callable the function to execute. |
317 |
* @param delay the time from now to delay execution. |
318 |
* @param unit the time unit of the delay parameter. |
319 |
* @return a ScheduledFuture that can be used to extract result or cancel. |
320 |
* @throws RejectedExecutionException if task cannot be scheduled |
321 |
* for execution because the executor has been shut down. |
322 |
* @throws NullPointerException if callable is null |
323 |
*/ |
324 |
public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) { |
325 |
if (callable == null) |
326 |
throw new NullPointerException(); |
327 |
long triggerTime = System.nanoTime() + unit.toNanos(delay); |
328 |
ScheduledFutureTask<V> t = new ScheduledFutureTask<V>(callable, triggerTime); |
329 |
delayedExecute(t); |
330 |
return t; |
331 |
} |
332 |
|
333 |
/** |
334 |
* Creates and executes a periodic action that becomes enabled first |
335 |
* after the given initial delay, and subsequently with the given |
336 |
* period; that is executions will commence after |
337 |
* <tt>initialDelay</tt> then <tt>initialDelay+period</tt>, then |
338 |
* <tt>initialDelay + 2 * period</tt>, and so on. The |
339 |
* task will only terminate via cancellation. |
340 |
* @param command the task to execute. |
341 |
* @param initialDelay the time to delay first execution. |
342 |
* @param period the period between successive executions. |
343 |
* @param unit the time unit of the delay and period parameters |
344 |
* @return a Future representing pending completion of the task, |
345 |
* and whose <tt>get()</tt> method will throw an exception upon |
346 |
* cancellation. |
347 |
* @throws RejectedExecutionException if task cannot be scheduled |
348 |
* for execution because the executor has been shut down. |
349 |
* @throws NullPointerException if command is null |
350 |
* @throws IllegalArgumentException if period less than or equal to zero. |
351 |
*/ |
352 |
public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) { |
353 |
if (command == null) |
354 |
throw new NullPointerException(); |
355 |
if (period <= 0) |
356 |
throw new IllegalArgumentException(); |
357 |
long triggerTime = System.nanoTime() + unit.toNanos(initialDelay); |
358 |
ScheduledFutureTask<?> t = new ScheduledFutureTask<Object> |
359 |
(command, null, |
360 |
triggerTime, |
361 |
unit.toNanos(period), |
362 |
true); |
363 |
delayedExecute(t); |
364 |
return t; |
365 |
} |
366 |
|
367 |
/** |
368 |
* Creates and executes a periodic action that becomes enabled first |
369 |
* after the given initial delay, and subsequently with the |
370 |
* given delay between the termination of one execution and the |
371 |
* commencement of the next. |
372 |
* The task will only terminate via cancellation. |
373 |
* @param command the task to execute. |
374 |
* @param initialDelay the time to delay first execution. |
375 |
* @param delay the delay between the termination of one |
376 |
* execution and the commencement of the next. |
377 |
* @param unit the time unit of the delay and delay parameters |
378 |
* @return a Future representing pending completion of the task, |
379 |
* and whose <tt>get()</tt> method will throw an exception upon |
380 |
* cancellation. |
381 |
* @throws RejectedExecutionException if task cannot be scheduled |
382 |
* for execution because the executor has been shut down. |
383 |
* @throws NullPointerException if command is null |
384 |
* @throws IllegalArgumentException if delay less than or equal to zero. |
385 |
*/ |
386 |
public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) { |
387 |
if (command == null) |
388 |
throw new NullPointerException(); |
389 |
if (delay <= 0) |
390 |
throw new IllegalArgumentException(); |
391 |
long triggerTime = System.nanoTime() + unit.toNanos(initialDelay); |
392 |
ScheduledFutureTask<?> t = new ScheduledFutureTask<Boolean> |
393 |
(command, |
394 |
null, |
395 |
triggerTime, |
396 |
unit.toNanos(delay), |
397 |
false); |
398 |
delayedExecute(t); |
399 |
return t; |
400 |
} |
401 |
|
402 |
|
403 |
/** |
404 |
* Execute command with zero required delay. This has effect |
405 |
* equivalent to <tt>schedule(command, 0, anyUnit)</tt>. Note |
406 |
* that inspections of the queue and of the list returned by |
407 |
* <tt>shutdownNow</tt> will access the zero-delayed |
408 |
* {@link ScheduledFuture}, not the <tt>command</tt> itself. |
409 |
* |
410 |
* @param command the task to execute |
411 |
* @throws RejectedExecutionException at discretion of |
412 |
* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted |
413 |
* for execution because the executor has been shut down. |
414 |
* @throws NullPointerException if command is null |
415 |
*/ |
416 |
public void execute(Runnable command) { |
417 |
if (command == null) |
418 |
throw new NullPointerException(); |
419 |
schedule(command, 0, TimeUnit.NANOSECONDS); |
420 |
} |
421 |
|
422 |
|
423 |
/** |
424 |
* Set policy on whether to continue executing existing periodic |
425 |
* tasks even when this executor has been <tt>shutdown</tt>. In |
426 |
* this case, these tasks will only terminate upon |
427 |
* <tt>shutdownNow</tt>, or after setting the policy to |
428 |
* <tt>false</tt> when already shutdown. This value is by default |
429 |
* false. |
430 |
* @param value if true, continue after shutdown, else don't. |
431 |
*/ |
432 |
public void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value) { |
433 |
continueExistingPeriodicTasksAfterShutdown = value; |
434 |
if (!value && isShutdown()) |
435 |
cancelUnwantedTasks(); |
436 |
} |
437 |
|
438 |
/** |
439 |
* Get the policy on whether to continue executing existing |
440 |
* periodic tasks even when this executor has been |
441 |
* <tt>shutdown</tt>. In this case, these tasks will only |
442 |
* terminate upon <tt>shutdownNow</tt> or after setting the policy |
443 |
* to <tt>false</tt> when already shutdown. This value is by |
444 |
* default false. |
445 |
* @return true if will continue after shutdown. |
446 |
*/ |
447 |
public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy() { |
448 |
return continueExistingPeriodicTasksAfterShutdown; |
449 |
} |
450 |
|
451 |
/** |
452 |
* Set policy on whether to execute existing delayed |
453 |
* tasks even when this executor has been <tt>shutdown</tt>. In |
454 |
* this case, these tasks will only terminate upon |
455 |
* <tt>shutdownNow</tt>, or after setting the policy to |
456 |
* <tt>false</tt> when already shutdown. This value is by default |
457 |
* true. |
458 |
* @param value if true, execute after shutdown, else don't. |
459 |
*/ |
460 |
public void setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value) { |
461 |
executeExistingDelayedTasksAfterShutdown = value; |
462 |
if (!value && isShutdown()) |
463 |
cancelUnwantedTasks(); |
464 |
} |
465 |
|
466 |
/** |
467 |
* Get policy on whether to execute existing delayed |
468 |
* tasks even when this executor has been <tt>shutdown</tt>. In |
469 |
* this case, these tasks will only terminate upon |
470 |
* <tt>shutdownNow</tt>, or after setting the policy to |
471 |
* <tt>false</tt> when already shutdown. This value is by default |
472 |
* true. |
473 |
* @return true if will execute after shutdown. |
474 |
*/ |
475 |
public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy() { |
476 |
return executeExistingDelayedTasksAfterShutdown; |
477 |
} |
478 |
|
479 |
/** |
480 |
* Cancel and clear the queue of all tasks that should not be run |
481 |
* due to shutdown policy. |
482 |
*/ |
483 |
private void cancelUnwantedTasks() { |
484 |
boolean keepDelayed = getExecuteExistingDelayedTasksAfterShutdownPolicy(); |
485 |
boolean keepPeriodic = getContinueExistingPeriodicTasksAfterShutdownPolicy(); |
486 |
if (!keepDelayed && !keepPeriodic) |
487 |
super.getQueue().clear(); |
488 |
else if (keepDelayed || keepPeriodic) { |
489 |
Object[] entries = super.getQueue().toArray(); |
490 |
for (int i = 0; i < entries.length; ++i) { |
491 |
ScheduledFutureTask<?> t = (ScheduledFutureTask<?>)entries[i]; |
492 |
if (t.isPeriodic()? !keepPeriodic : !keepDelayed) |
493 |
t.cancel(false); |
494 |
} |
495 |
entries = null; |
496 |
purge(); |
497 |
} |
498 |
} |
499 |
|
500 |
/** |
501 |
* Initiates an orderly shutdown in which previously submitted |
502 |
* tasks are executed, but no new tasks will be accepted. If the |
503 |
* <tt>ExecuteExistingDelayedTasksAfterShutdownPolicy</tt> has |
504 |
* been set <tt>false</tt>, existing delayed tasks whose delays |
505 |
* have not yet elapsed are cancelled. And unless the |
506 |
* <tt>ContinueExistingPeriodicTasksAfterShutdownPolicy</tt> has |
507 |
* been set <tt>true</tt>, future executions of existing periodic |
508 |
* tasks will be cancelled. |
509 |
*/ |
510 |
public void shutdown() { |
511 |
cancelUnwantedTasks(); |
512 |
super.shutdown(); |
513 |
} |
514 |
|
515 |
/** |
516 |
* Attempts to stop all actively executing tasks, halts the |
517 |
* processing of waiting tasks, and returns a list of the tasks that were |
518 |
* awaiting execution. |
519 |
* |
520 |
* <p>There are no guarantees beyond best-effort attempts to stop |
521 |
* processing actively executing tasks. This implementations |
522 |
* cancels via {@link Thread#interrupt}, so if any tasks mask or |
523 |
* fail to respond to interrupts, they may never terminate. |
524 |
* |
525 |
* @return list of tasks that never commenced execution. Each |
526 |
* element of this list is a {@link ScheduledFuture}, |
527 |
* including those tasks submitted using <tt>execute</tt> which |
528 |
* are for scheduling purposes used as the basis of a zero-delay |
529 |
* <tt>ScheduledFuture</tt>. |
530 |
*/ |
531 |
public List<Runnable> shutdownNow() { |
532 |
return super.shutdownNow(); |
533 |
} |
534 |
|
535 |
/** |
536 |
* Removes this task from internal queue if it is present, thus |
537 |
* causing it not to be run if it has not already started. This |
538 |
* method may be useful as one part of a cancellation scheme. |
539 |
* |
540 |
* @param task the task to remove |
541 |
* @return true if the task was removed |
542 |
*/ |
543 |
public boolean remove(Runnable task) { |
544 |
if (task instanceof ScheduledFuture) |
545 |
return super.remove(task); |
546 |
|
547 |
// The task might actually have been wrapped as a ScheduledFuture |
548 |
// in execute(), in which case we need to manually traverse |
549 |
// looking for it. |
550 |
|
551 |
ScheduledFuture wrap = null; |
552 |
Object[] entries = super.getQueue().toArray(); |
553 |
for (int i = 0; i < entries.length; ++i) { |
554 |
ScheduledFutureTask<?> t = (ScheduledFutureTask<?>)entries[i]; |
555 |
Object r = t.getTask(); |
556 |
if (task.equals(r)) { |
557 |
wrap = t; |
558 |
break; |
559 |
} |
560 |
} |
561 |
entries = null; |
562 |
return wrap != null && super.getQueue().remove(wrap); |
563 |
} |
564 |
|
565 |
|
566 |
/** |
567 |
* Returns the task queue used by this executor. Each element of |
568 |
* this queue is a {@link ScheduledFuture}, including those |
569 |
* tasks submitted using <tt>execute</tt> which are for scheduling |
570 |
* purposes used as the basis of a zero-delay |
571 |
* <tt>ScheduledFuture</tt>. Iteration over this queue is |
572 |
* </em>not</em> guaranteed to traverse tasks in the order in |
573 |
* which they will execute. |
574 |
* |
575 |
* @return the task queue |
576 |
*/ |
577 |
public BlockingQueue<Runnable> getQueue() { |
578 |
return super.getQueue(); |
579 |
} |
580 |
|
581 |
} |