001 /*
002 * Copyright 1999-2007 Sun Microsystems, Inc. All Rights Reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation. Sun designates this
008 * particular file as subject to the "Classpath" exception as provided
009 * by Sun in the LICENSE file that accompanied this code.
010 *
011 * This code is distributed in the hope that it will be useful, but WITHOUT
012 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014 * version 2 for more details (a copy is included in the LICENSE file that
015 * accompanied this code).
016 *
017 * You should have received a copy of the GNU General Public License version
018 * 2 along with this work; if not, write to the Free Software Foundation,
019 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020 *
021 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022 * CA 95054 USA or visit www.sun.com if you need additional information or
023 * have any questions.
024 */
025
026 package java.util;
027
028 import java.util.Date;
029
030 /**
031 * A facility for threads to schedule tasks for future execution in a
032 * background thread. Tasks may be scheduled for one-time execution, or for
033 * repeated execution at regular intervals.
034 *
035 * <p>Corresponding to each <tt>Timer</tt> object is a single background
036 * thread that is used to execute all of the timer's tasks, sequentially.
037 * Timer tasks should complete quickly. If a timer task takes excessive time
038 * to complete, it "hogs" the timer's task execution thread. This can, in
039 * turn, delay the execution of subsequent tasks, which may "bunch up" and
040 * execute in rapid succession when (and if) the offending task finally
041 * completes.
042 *
043 * <p>After the last live reference to a <tt>Timer</tt> object goes away
044 * <i>and</i> all outstanding tasks have completed execution, the timer's task
045 * execution thread terminates gracefully (and becomes subject to garbage
046 * collection). However, this can take arbitrarily long to occur. By
047 * default, the task execution thread does not run as a <i>daemon thread</i>,
048 * so it is capable of keeping an application from terminating. If a caller
049 * wants to terminate a timer's task execution thread rapidly, the caller
050 * should invoke the timer's <tt>cancel</tt> method.
051 *
052 * <p>If the timer's task execution thread terminates unexpectedly, for
053 * example, because its <tt>stop</tt> method is invoked, any further
054 * attempt to schedule a task on the timer will result in an
055 * <tt>IllegalStateException</tt>, as if the timer's <tt>cancel</tt>
056 * method had been invoked.
057 *
058 * <p>This class is thread-safe: multiple threads can share a single
059 * <tt>Timer</tt> object without the need for external synchronization.
060 *
061 * <p>This class does <i>not</i> offer real-time guarantees: it schedules
062 * tasks using the <tt>Object.wait(long)</tt> method.
063 *
064 * <p>Java 5.0 introduced the {@code java.util.concurrent} package and
065 * one of the concurrency utilities therein is the {@link
066 * java.util.concurrent.ScheduledThreadPoolExecutor
067 * ScheduledThreadPoolExecutor} which is a thread pool for repeatedly
068 * executing tasks at a given rate or delay. It is effectively a more
069 * versatile replacement for the {@code Timer}/{@code TimerTask}
070 * combination, as it allows multiple service threads, accepts various
071 * time units, and doesn't require subclassing {@code TimerTask} (just
072 * implement {@code Runnable}). Configuring {@code
073 * ScheduledThreadPoolExecutor} with one thread makes it equivalent to
074 * {@code Timer}.
075 *
076 * <p>Implementation note: This class scales to large numbers of concurrently
077 * scheduled tasks (thousands should present no problem). Internally,
078 * it uses a binary heap to represent its task queue, so the cost to schedule
079 * a task is O(log n), where n is the number of concurrently scheduled tasks.
080 *
081 * <p>Implementation note: All constructors start a timer thread.
082 *
083 * @author Josh Bloch
084 * @version 1.28, 06/27/07
085 * @see TimerTask
086 * @see Object#wait(long)
087 * @since 1.3
088 */
089
090 public class Timer {
091 /**
092 * The timer task queue. This data structure is shared with the timer
093 * thread. The timer produces tasks, via its various schedule calls,
094 * and the timer thread consumes, executing timer tasks as appropriate,
095 * and removing them from the queue when they're obsolete.
096 */
097 private TaskQueue queue = new TaskQueue();
098
099 /**
100 * The timer thread.
101 */
102 private TimerThread thread = new TimerThread(queue);
103
104 /**
105 * This object causes the timer's task execution thread to exit
106 * gracefully when there are no live references to the Timer object and no
107 * tasks in the timer queue. It is used in preference to a finalizer on
108 * Timer as such a finalizer would be susceptible to a subclass's
109 * finalizer forgetting to call it.
110 */
111 private Object threadReaper = new Object() {
112 protected void finalize() throws Throwable {
113 synchronized (queue) {
114 thread.newTasksMayBeScheduled = false;
115 queue.notify(); // In case queue is empty.
116 }
117 }
118 };
119
120 /**
121 * This ID is used to generate thread names. (It could be replaced
122 * by an AtomicInteger as soon as they become available.)
123 */
124 private static int nextSerialNumber = 0;
125
126 private static synchronized int serialNumber() {
127 return nextSerialNumber++;
128 }
129
130 /**
131 * Creates a new timer. The associated thread does <i>not</i>
132 * {@linkplain Thread#setDaemon run as a daemon}.
133 */
134 public Timer() {
135 this ("Timer-" + serialNumber());
136 }
137
138 /**
139 * Creates a new timer whose associated thread may be specified to
140 * {@linkplain Thread#setDaemon run as a daemon}.
141 * A daemon thread is called for if the timer will be used to
142 * schedule repeating "maintenance activities", which must be
143 * performed as long as the application is running, but should not
144 * prolong the lifetime of the application.
145 *
146 * @param isDaemon true if the associated thread should run as a daemon.
147 */
148 public Timer(boolean isDaemon) {
149 this ("Timer-" + serialNumber(), isDaemon);
150 }
151
152 /**
153 * Creates a new timer whose associated thread has the specified name.
154 * The associated thread does <i>not</i>
155 * {@linkplain Thread#setDaemon run as a daemon}.
156 *
157 * @param name the name of the associated thread
158 * @throws NullPointerException if name is null
159 * @since 1.5
160 */
161 public Timer(String name) {
162 thread.setName(name);
163 thread.start();
164 }
165
166 /**
167 * Creates a new timer whose associated thread has the specified name,
168 * and may be specified to
169 * {@linkplain Thread#setDaemon run as a daemon}.
170 *
171 * @param name the name of the associated thread
172 * @param isDaemon true if the associated thread should run as a daemon
173 * @throws NullPointerException if name is null
174 * @since 1.5
175 */
176 public Timer(String name, boolean isDaemon) {
177 thread.setName(name);
178 thread.setDaemon(isDaemon);
179 thread.start();
180 }
181
182 /**
183 * Schedules the specified task for execution after the specified delay.
184 *
185 * @param task task to be scheduled.
186 * @param delay delay in milliseconds before task is to be executed.
187 * @throws IllegalArgumentException if <tt>delay</tt> is negative, or
188 * <tt>delay + System.currentTimeMillis()</tt> is negative.
189 * @throws IllegalStateException if task was already scheduled or
190 * cancelled, timer was cancelled, or timer thread terminated.
191 */
192 public void schedule(TimerTask task, long delay) {
193 if (delay < 0)
194 throw new IllegalArgumentException("Negative delay.");
195 sched(task, System.currentTimeMillis() + delay, 0);
196 }
197
198 /**
199 * Schedules the specified task for execution at the specified time. If
200 * the time is in the past, the task is scheduled for immediate execution.
201 *
202 * @param task task to be scheduled.
203 * @param time time at which task is to be executed.
204 * @throws IllegalArgumentException if <tt>time.getTime()</tt> is negative.
205 * @throws IllegalStateException if task was already scheduled or
206 * cancelled, timer was cancelled, or timer thread terminated.
207 */
208 public void schedule(TimerTask task, Date time) {
209 sched(task, time.getTime(), 0);
210 }
211
212 /**
213 * Schedules the specified task for repeated <i>fixed-delay execution</i>,
214 * beginning after the specified delay. Subsequent executions take place
215 * at approximately regular intervals separated by the specified period.
216 *
217 * <p>In fixed-delay execution, each execution is scheduled relative to
218 * the actual execution time of the previous execution. If an execution
219 * is delayed for any reason (such as garbage collection or other
220 * background activity), subsequent executions will be delayed as well.
221 * In the long run, the frequency of execution will generally be slightly
222 * lower than the reciprocal of the specified period (assuming the system
223 * clock underlying <tt>Object.wait(long)</tt> is accurate).
224 *
225 * <p>Fixed-delay execution is appropriate for recurring activities
226 * that require "smoothness." In other words, it is appropriate for
227 * activities where it is more important to keep the frequency accurate
228 * in the short run than in the long run. This includes most animation
229 * tasks, such as blinking a cursor at regular intervals. It also includes
230 * tasks wherein regular activity is performed in response to human
231 * input, such as automatically repeating a character as long as a key
232 * is held down.
233 *
234 * @param task task to be scheduled.
235 * @param delay delay in milliseconds before task is to be executed.
236 * @param period time in milliseconds between successive task executions.
237 * @throws IllegalArgumentException if {@code delay < 0}, or
238 * {@code delay + System.currentTimeMillis() < 0}, or
239 * {@code period <= 0}
240 * @throws IllegalStateException if task was already scheduled or
241 * cancelled, timer was cancelled, or timer thread terminated.
242 */
243 public void schedule(TimerTask task, long delay, long period) {
244 if (delay < 0)
245 throw new IllegalArgumentException("Negative delay.");
246 if (period <= 0)
247 throw new IllegalArgumentException("Non-positive period.");
248 sched(task, System.currentTimeMillis() + delay, -period);
249 }
250
251 /**
252 * Schedules the specified task for repeated <i>fixed-delay execution</i>,
253 * beginning at the specified time. Subsequent executions take place at
254 * approximately regular intervals, separated by the specified period.
255 *
256 * <p>In fixed-delay execution, each execution is scheduled relative to
257 * the actual execution time of the previous execution. If an execution
258 * is delayed for any reason (such as garbage collection or other
259 * background activity), subsequent executions will be delayed as well.
260 * In the long run, the frequency of execution will generally be slightly
261 * lower than the reciprocal of the specified period (assuming the system
262 * clock underlying <tt>Object.wait(long)</tt> is accurate). As a
263 * consequence of the above, if the scheduled first time is in the past,
264 * it is scheduled for immediate execution.
265 *
266 * <p>Fixed-delay execution is appropriate for recurring activities
267 * that require "smoothness." In other words, it is appropriate for
268 * activities where it is more important to keep the frequency accurate
269 * in the short run than in the long run. This includes most animation
270 * tasks, such as blinking a cursor at regular intervals. It also includes
271 * tasks wherein regular activity is performed in response to human
272 * input, such as automatically repeating a character as long as a key
273 * is held down.
274 *
275 * @param task task to be scheduled.
276 * @param firstTime First time at which task is to be executed.
277 * @param period time in milliseconds between successive task executions.
278 * @throws IllegalArgumentException if {@code firstTime.getTime() < 0}, or
279 * {@code period <= 0}
280 * @throws IllegalStateException if task was already scheduled or
281 * cancelled, timer was cancelled, or timer thread terminated.
282 */
283 public void schedule(TimerTask task, Date firstTime, long period) {
284 if (period <= 0)
285 throw new IllegalArgumentException("Non-positive period.");
286 sched(task, firstTime.getTime(), -period);
287 }
288
289 /**
290 * Schedules the specified task for repeated <i>fixed-rate execution</i>,
291 * beginning after the specified delay. Subsequent executions take place
292 * at approximately regular intervals, separated by the specified period.
293 *
294 * <p>In fixed-rate execution, each execution is scheduled relative to the
295 * scheduled execution time of the initial execution. If an execution is
296 * delayed for any reason (such as garbage collection or other background
297 * activity), two or more executions will occur in rapid succession to
298 * "catch up." In the long run, the frequency of execution will be
299 * exactly the reciprocal of the specified period (assuming the system
300 * clock underlying <tt>Object.wait(long)</tt> is accurate).
301 *
302 * <p>Fixed-rate execution is appropriate for recurring activities that
303 * are sensitive to <i>absolute</i> time, such as ringing a chime every
304 * hour on the hour, or running scheduled maintenance every day at a
305 * particular time. It is also appropriate for recurring activities
306 * where the total time to perform a fixed number of executions is
307 * important, such as a countdown timer that ticks once every second for
308 * ten seconds. Finally, fixed-rate execution is appropriate for
309 * scheduling multiple repeating timer tasks that must remain synchronized
310 * with respect to one another.
311 *
312 * @param task task to be scheduled.
313 * @param delay delay in milliseconds before task is to be executed.
314 * @param period time in milliseconds between successive task executions.
315 * @throws IllegalArgumentException if {@code delay < 0}, or
316 * {@code delay + System.currentTimeMillis() < 0}, or
317 * {@code period <= 0}
318 * @throws IllegalStateException if task was already scheduled or
319 * cancelled, timer was cancelled, or timer thread terminated.
320 */
321 public void scheduleAtFixedRate(TimerTask task, long delay,
322 long period) {
323 if (delay < 0)
324 throw new IllegalArgumentException("Negative delay.");
325 if (period <= 0)
326 throw new IllegalArgumentException("Non-positive period.");
327 sched(task, System.currentTimeMillis() + delay, period);
328 }
329
330 /**
331 * Schedules the specified task for repeated <i>fixed-rate execution</i>,
332 * beginning at the specified time. Subsequent executions take place at
333 * approximately regular intervals, separated by the specified period.
334 *
335 * <p>In fixed-rate execution, each execution is scheduled relative to the
336 * scheduled execution time of the initial execution. If an execution is
337 * delayed for any reason (such as garbage collection or other background
338 * activity), two or more executions will occur in rapid succession to
339 * "catch up." In the long run, the frequency of execution will be
340 * exactly the reciprocal of the specified period (assuming the system
341 * clock underlying <tt>Object.wait(long)</tt> is accurate). As a
342 * consequence of the above, if the scheduled first time is in the past,
343 * then any "missed" executions will be scheduled for immediate "catch up"
344 * execution.
345 *
346 * <p>Fixed-rate execution is appropriate for recurring activities that
347 * are sensitive to <i>absolute</i> time, such as ringing a chime every
348 * hour on the hour, or running scheduled maintenance every day at a
349 * particular time. It is also appropriate for recurring activities
350 * where the total time to perform a fixed number of executions is
351 * important, such as a countdown timer that ticks once every second for
352 * ten seconds. Finally, fixed-rate execution is appropriate for
353 * scheduling multiple repeating timer tasks that must remain synchronized
354 * with respect to one another.
355 *
356 * @param task task to be scheduled.
357 * @param firstTime First time at which task is to be executed.
358 * @param period time in milliseconds between successive task executions.
359 * @throws IllegalArgumentException if {@code firstTime.getTime() < 0} or
360 * {@code period <= 0}
361 * @throws IllegalStateException if task was already scheduled or
362 * cancelled, timer was cancelled, or timer thread terminated.
363 */
364 public void scheduleAtFixedRate(TimerTask task, Date firstTime,
365 long period) {
366 if (period <= 0)
367 throw new IllegalArgumentException("Non-positive period.");
368 sched(task, firstTime.getTime(), period);
369 }
370
371 /**
372 * Schedule the specified timer task for execution at the specified
373 * time with the specified period, in milliseconds. If period is
374 * positive, the task is scheduled for repeated execution; if period is
375 * zero, the task is scheduled for one-time execution. Time is specified
376 * in Date.getTime() format. This method checks timer state, task state,
377 * and initial execution time, but not period.
378 *
379 * @throws IllegalArgumentException if <tt>time</tt> is negative.
380 * @throws IllegalStateException if task was already scheduled or
381 * cancelled, timer was cancelled, or timer thread terminated.
382 */
383 private void sched(TimerTask task, long time, long period) {
384 if (time < 0)
385 throw new IllegalArgumentException(
386 "Illegal execution time.");
387
388 synchronized (queue) {
389 if (!thread.newTasksMayBeScheduled)
390 throw new IllegalStateException(
391 "Timer already cancelled.");
392
393 synchronized (task.lock) {
394 if (task.state != TimerTask.VIRGIN)
395 throw new IllegalStateException(
396 "Task already scheduled or cancelled");
397 task.nextExecutionTime = time;
398 task.period = period;
399 task.state = TimerTask.SCHEDULED;
400 }
401
402 queue.add(task);
403 if (queue.getMin() == task)
404 queue.notify();
405 }
406 }
407
408 /**
409 * Terminates this timer, discarding any currently scheduled tasks.
410 * Does not interfere with a currently executing task (if it exists).
411 * Once a timer has been terminated, its execution thread terminates
412 * gracefully, and no more tasks may be scheduled on it.
413 *
414 * <p>Note that calling this method from within the run method of a
415 * timer task that was invoked by this timer absolutely guarantees that
416 * the ongoing task execution is the last task execution that will ever
417 * be performed by this timer.
418 *
419 * <p>This method may be called repeatedly; the second and subsequent
420 * calls have no effect.
421 */
422 public void cancel() {
423 synchronized (queue) {
424 thread.newTasksMayBeScheduled = false;
425 queue.clear();
426 queue.notify(); // In case queue was already empty.
427 }
428 }
429
430 /**
431 * Removes all cancelled tasks from this timer's task queue. <i>Calling
432 * this method has no effect on the behavior of the timer</i>, but
433 * eliminates the references to the cancelled tasks from the queue.
434 * If there are no external references to these tasks, they become
435 * eligible for garbage collection.
436 *
437 * <p>Most programs will have no need to call this method.
438 * It is designed for use by the rare application that cancels a large
439 * number of tasks. Calling this method trades time for space: the
440 * runtime of the method may be proportional to n + c log n, where n
441 * is the number of tasks in the queue and c is the number of cancelled
442 * tasks.
443 *
444 * <p>Note that it is permissible to call this method from within a
445 * a task scheduled on this timer.
446 *
447 * @return the number of tasks removed from the queue.
448 * @since 1.5
449 */
450 public int purge() {
451 int result = 0;
452
453 synchronized (queue) {
454 for (int i = queue.size(); i > 0; i--) {
455 if (queue.get(i).state == TimerTask.CANCELLED) {
456 queue.quickRemove(i);
457 result++;
458 }
459 }
460
461 if (result != 0)
462 queue.heapify();
463 }
464
465 return result;
466 }
467 }
468
469 /**
470 * This "helper class" implements the timer's task execution thread, which
471 * waits for tasks on the timer queue, executions them when they fire,
472 * reschedules repeating tasks, and removes cancelled tasks and spent
473 * non-repeating tasks from the queue.
474 */
475 class TimerThread extends Thread {
476 /**
477 * This flag is set to false by the reaper to inform us that there
478 * are no more live references to our Timer object. Once this flag
479 * is true and there are no more tasks in our queue, there is no
480 * work left for us to do, so we terminate gracefully. Note that
481 * this field is protected by queue's monitor!
482 */
483 boolean newTasksMayBeScheduled = true;
484
485 /**
486 * Our Timer's queue. We store this reference in preference to
487 * a reference to the Timer so the reference graph remains acyclic.
488 * Otherwise, the Timer would never be garbage-collected and this
489 * thread would never go away.
490 */
491 private TaskQueue queue;
492
493 TimerThread(TaskQueue queue) {
494 this .queue = queue;
495 }
496
497 public void run() {
498 try {
499 mainLoop();
500 } finally {
501 // Someone killed this Thread, behave as if Timer cancelled
502 synchronized (queue) {
503 newTasksMayBeScheduled = false;
504 queue.clear(); // Eliminate obsolete references
505 }
506 }
507 }
508
509 /**
510 * The main timer loop. (See class comment.)
511 */
512 private void mainLoop() {
513 while (true) {
514 try {
515 TimerTask task;
516 boolean taskFired;
517 synchronized (queue) {
518 // Wait for queue to become non-empty
519 while (queue.isEmpty() && newTasksMayBeScheduled)
520 queue.wait();
521 if (queue.isEmpty())
522 break; // Queue is empty and will forever remain; die
523
524 // Queue nonempty; look at first evt and do the right thing
525 long currentTime, executionTime;
526 task = queue.getMin();
527 synchronized (task.lock) {
528 if (task.state == TimerTask.CANCELLED) {
529 queue.removeMin();
530 continue; // No action required, poll queue again
531 }
532 currentTime = System.currentTimeMillis();
533 executionTime = task.nextExecutionTime;
534 if (taskFired = (executionTime <= currentTime)) {
535 if (task.period == 0) { // Non-repeating, remove
536 queue.removeMin();
537 task.state = TimerTask.EXECUTED;
538 } else { // Repeating task, reschedule
539 queue
540 .rescheduleMin(task.period < 0 ? currentTime
541 - task.period
542 : executionTime
543 + task.period);
544 }
545 }
546 }
547 if (!taskFired) // Task hasn't yet fired; wait
548 queue.wait(executionTime - currentTime);
549 }
550 if (taskFired) // Task fired; run it, holding no locks
551 task.run();
552 } catch (InterruptedException e) {
553 }
554 }
555 }
556 }
557
558 /**
559 * This class represents a timer task queue: a priority queue of TimerTasks,
560 * ordered on nextExecutionTime. Each Timer object has one of these, which it
561 * shares with its TimerThread. Internally this class uses a heap, which
562 * offers log(n) performance for the add, removeMin and rescheduleMin
563 * operations, and constant time performance for the getMin operation.
564 */
565 class TaskQueue {
566 /**
567 * Priority queue represented as a balanced binary heap: the two children
568 * of queue[n] are queue[2*n] and queue[2*n+1]. The priority queue is
569 * ordered on the nextExecutionTime field: The TimerTask with the lowest
570 * nextExecutionTime is in queue[1] (assuming the queue is nonempty). For
571 * each node n in the heap, and each descendant of n, d,
572 * n.nextExecutionTime <= d.nextExecutionTime.
573 */
574 private TimerTask[] queue = new TimerTask[128];
575
576 /**
577 * The number of tasks in the priority queue. (The tasks are stored in
578 * queue[1] up to queue[size]).
579 */
580 private int size = 0;
581
582 /**
583 * Returns the number of tasks currently on the queue.
584 */
585 int size() {
586 return size;
587 }
588
589 /**
590 * Adds a new task to the priority queue.
591 */
592 void add(TimerTask task) {
593 // Grow backing store if necessary
594 if (size + 1 == queue.length)
595 queue = Arrays.copyOf(queue, 2 * queue.length);
596
597 queue[++size] = task;
598 fixUp(size);
599 }
600
601 /**
602 * Return the "head task" of the priority queue. (The head task is an
603 * task with the lowest nextExecutionTime.)
604 */
605 TimerTask getMin() {
606 return queue[1];
607 }
608
609 /**
610 * Return the ith task in the priority queue, where i ranges from 1 (the
611 * head task, which is returned by getMin) to the number of tasks on the
612 * queue, inclusive.
613 */
614 TimerTask get(int i) {
615 return queue[i];
616 }
617
618 /**
619 * Remove the head task from the priority queue.
620 */
621 void removeMin() {
622 queue[1] = queue[size];
623 queue[size--] = null; // Drop extra reference to prevent memory leak
624 fixDown(1);
625 }
626
627 /**
628 * Removes the ith element from queue without regard for maintaining
629 * the heap invariant. Recall that queue is one-based, so
630 * 1 <= i <= size.
631 */
632 void quickRemove(int i) {
633 assert i <= size;
634
635 queue[i] = queue[size];
636 queue[size--] = null; // Drop extra ref to prevent memory leak
637 }
638
639 /**
640 * Sets the nextExecutionTime associated with the head task to the
641 * specified value, and adjusts priority queue accordingly.
642 */
643 void rescheduleMin(long newTime) {
644 queue[1].nextExecutionTime = newTime;
645 fixDown(1);
646 }
647
648 /**
649 * Returns true if the priority queue contains no elements.
650 */
651 boolean isEmpty() {
652 return size == 0;
653 }
654
655 /**
656 * Removes all elements from the priority queue.
657 */
658 void clear() {
659 // Null out task references to prevent memory leak
660 for (int i = 1; i <= size; i++)
661 queue[i] = null;
662
663 size = 0;
664 }
665
666 /**
667 * Establishes the heap invariant (described above) assuming the heap
668 * satisfies the invariant except possibly for the leaf-node indexed by k
669 * (which may have a nextExecutionTime less than its parent's).
670 *
671 * This method functions by "promoting" queue[k] up the hierarchy
672 * (by swapping it with its parent) repeatedly until queue[k]'s
673 * nextExecutionTime is greater than or equal to that of its parent.
674 */
675 private void fixUp(int k) {
676 while (k > 1) {
677 int j = k >> 1;
678 if (queue[j].nextExecutionTime <= queue[k].nextExecutionTime)
679 break;
680 TimerTask tmp = queue[j];
681 queue[j] = queue[k];
682 queue[k] = tmp;
683 k = j;
684 }
685 }
686
687 /**
688 * Establishes the heap invariant (described above) in the subtree
689 * rooted at k, which is assumed to satisfy the heap invariant except
690 * possibly for node k itself (which may have a nextExecutionTime greater
691 * than its children's).
692 *
693 * This method functions by "demoting" queue[k] down the hierarchy
694 * (by swapping it with its smaller child) repeatedly until queue[k]'s
695 * nextExecutionTime is less than or equal to those of its children.
696 */
697 private void fixDown(int k) {
698 int j;
699 while ((j = k << 1) <= size && j > 0) {
700 if (j < size
701 && queue[j].nextExecutionTime > queue[j + 1].nextExecutionTime)
702 j++; // j indexes smallest kid
703 if (queue[k].nextExecutionTime <= queue[j].nextExecutionTime)
704 break;
705 TimerTask tmp = queue[j];
706 queue[j] = queue[k];
707 queue[k] = tmp;
708 k = j;
709 }
710 }
711
712 /**
713 * Establishes the heap invariant (described above) in the entire tree,
714 * assuming nothing about the order of the elements prior to the call.
715 */
716 void heapify() {
717 for (int i = size / 2; i >= 1; i--)
718 fixDown(i);
719 }
720 }
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