001 /* Timer.java -- Timer that runs TimerTasks at a later time.
002 Copyright (C) 2000, 2001, 2005 Free Software Foundation, Inc.
003
004 This file is part of GNU Classpath.
005
006 GNU Classpath is free software; you can redistribute it and/or modify
007 it under the terms of the GNU General Public License as published by
008 the Free Software Foundation; either version 2, or (at your option)
009 any later version.
010
011 GNU Classpath is distributed in the hope that it will be useful, but
012 WITHOUT ANY WARRANTY; without even the implied warranty of
013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014 General Public License for more details.
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019 02110-1301 USA.
020
021 Linking this library statically or dynamically with other modules is
022 making a combined work based on this library. Thus, the terms and
023 conditions of the GNU General Public License cover the whole
024 combination.
025
026 As a special exception, the copyright holders of this library give you
027 permission to link this library with independent modules to produce an
028 executable, regardless of the license terms of these independent
029 modules, and to copy and distribute the resulting executable under
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031 independent module, the terms and conditions of the license of that
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034 this exception to your version of the library, but you are not
035 obligated to do so. If you do not wish to do so, delete this
036 exception statement from your version. */
037
038 package java.util;
039
040 /**
041 * Timer that can run TimerTasks at a later time.
042 * TimerTasks can be scheduled for one time execution at some time in the
043 * future. They can be scheduled to be rescheduled at a time period after the
044 * task was last executed. Or they can be scheduled to be executed repeatedly
045 * at a fixed rate.
046 * <p>
047 * The normal scheduling will result in a more or less even delay in time
048 * between successive executions, but the executions could drift in time if
049 * the task (or other tasks) takes a long time to execute. Fixed delay
050 * scheduling guarantees more or less that the task will be executed at a
051 * specific time, but if there is ever a delay in execution then the period
052 * between successive executions will be shorter. The first method of
053 * repeated scheduling is preferred for repeated tasks in response to user
054 * interaction, the second method of repeated scheduling is preferred for tasks
055 * that act like alarms.
056 * <p>
057 * The Timer keeps a binary heap as a task priority queue which means that
058 * scheduling and serving of a task in a queue of n tasks costs O(log n).
059 *
060 * @see TimerTask
061 * @since 1.3
062 * @author Mark Wielaard (mark@klomp.org)
063 */
064 public class Timer
065 {
066 /**
067 * Priority Task Queue.
068 * TimerTasks are kept in a binary heap.
069 * The scheduler calls sleep() on the queue when it has nothing to do or
070 * has to wait. A sleeping scheduler can be notified by calling interrupt()
071 * which is automatically called by the enqueue(), cancel() and
072 * timerFinalized() methods.
073 */
074 private static final class TaskQueue
075 {
076 /** Default size of this queue */
077 private static final int DEFAULT_SIZE = 32;
078
079 /** Whether to return null when there is nothing in the queue */
080 private boolean nullOnEmpty;
081
082 /**
083 * The heap containing all the scheduled TimerTasks
084 * sorted by the TimerTask.scheduled field.
085 * Null when the stop() method has been called.
086 */
087 private TimerTask heap[];
088
089 /**
090 * The actual number of elements in the heap
091 * Can be less then heap.length.
092 * Note that heap[0] is used as a sentinel.
093 */
094 private int elements;
095
096 /**
097 * Creates a TaskQueue of default size without any elements in it.
098 */
099 public TaskQueue()
100 {
101 heap = new TimerTask[DEFAULT_SIZE];
102 elements = 0;
103 nullOnEmpty = false;
104 }
105
106 /**
107 * Adds a TimerTask at the end of the heap.
108 * Grows the heap if necessary by doubling the heap in size.
109 */
110 private void add(TimerTask task)
111 {
112 elements++;
113 if (elements == heap.length)
114 {
115 TimerTask new_heap[] = new TimerTask[heap.length * 2];
116 System.arraycopy(heap, 0, new_heap, 0, heap.length);
117 heap = new_heap;
118 }
119 heap[elements] = task;
120 }
121
122 /**
123 * Removes the last element from the heap.
124 * Shrinks the heap in half if
125 * elements+DEFAULT_SIZE/2 <= heap.length/4.
126 */
127 private void remove()
128 {
129 // clear the entry first
130 heap[elements] = null;
131 elements--;
132 if (elements + DEFAULT_SIZE / 2 <= (heap.length / 4))
133 {
134 TimerTask new_heap[] = new TimerTask[heap.length / 2];
135 System.arraycopy(heap, 0, new_heap, 0, elements + 1);
136 heap = new_heap;
137 }
138 }
139
140 /**
141 * Adds a task to the queue and puts it at the correct place
142 * in the heap.
143 */
144 public synchronized void enqueue(TimerTask task)
145 {
146 // Check if it is legal to add another element
147 if (heap == null)
148 {
149 throw new IllegalStateException
150 ("cannot enqueue when stop() has been called on queue");
151 }
152
153 heap[0] = task; // sentinel
154 add(task); // put the new task at the end
155 // Now push the task up in the heap until it has reached its place
156 int child = elements;
157 int parent = child / 2;
158 while (heap[parent].scheduled > task.scheduled)
159 {
160 heap[child] = heap[parent];
161 child = parent;
162 parent = child / 2;
163 }
164 // This is the correct place for the new task
165 heap[child] = task;
166 heap[0] = null; // clear sentinel
167 // Maybe sched() is waiting for a new element
168 this.notify();
169 }
170
171 /**
172 * Returns the top element of the queue.
173 * Can return null when no task is in the queue.
174 */
175 private TimerTask top()
176 {
177 if (elements == 0)
178 {
179 return null;
180 }
181 else
182 {
183 return heap[1];
184 }
185 }
186
187 /**
188 * Returns the top task in the Queue.
189 * Removes the element from the heap and reorders the heap first.
190 * Can return null when there is nothing in the queue.
191 */
192 public synchronized TimerTask serve()
193 {
194 // The task to return
195 TimerTask task = null;
196
197 while (task == null)
198 {
199 // Get the next task
200 task = top();
201
202 // return null when asked to stop
203 // or if asked to return null when the queue is empty
204 if ((heap == null) || (task == null && nullOnEmpty))
205 {
206 return null;
207 }
208
209 // Do we have a task?
210 if (task != null)
211 {
212 // The time to wait until the task should be served
213 long time = task.scheduled - System.currentTimeMillis();
214 if (time > 0)
215 {
216 // This task should not yet be served
217 // So wait until this task is ready
218 // or something else happens to the queue
219 task = null; // set to null to make sure we call top()
220 try
221 {
222 this.wait(time);
223 }
224 catch (InterruptedException _)
225 {
226 }
227 }
228 }
229 else
230 {
231 // wait until a task is added
232 // or something else happens to the queue
233 try
234 {
235 this.wait();
236 }
237 catch (InterruptedException _)
238 {
239 }
240 }
241 }
242
243 // reconstruct the heap
244 TimerTask lastTask = heap[elements];
245 remove();
246
247 // drop lastTask at the beginning and move it down the heap
248 int parent = 1;
249 int child = 2;
250 heap[1] = lastTask;
251 while (child <= elements)
252 {
253 if (child < elements)
254 {
255 if (heap[child].scheduled > heap[child + 1].scheduled)
256 {
257 child++;
258 }
259 }
260
261 if (lastTask.scheduled <= heap[child].scheduled)
262 break; // found the correct place (the parent) - done
263
264 heap[parent] = heap[child];
265 parent = child;
266 child = parent * 2;
267 }
268
269 // this is the correct new place for the lastTask
270 heap[parent] = lastTask;
271
272 // return the task
273 return task;
274 }
275
276 /**
277 * When nullOnEmpty is true the serve() method will return null when
278 * there are no tasks in the queue, otherwise it will wait until
279 * a new element is added to the queue. It is used to indicate to
280 * the scheduler that no new tasks will ever be added to the queue.
281 */
282 public synchronized void setNullOnEmpty(boolean nullOnEmpty)
283 {
284 this.nullOnEmpty = nullOnEmpty;
285 this.notify();
286 }
287
288 /**
289 * When this method is called the current and all future calls to
290 * serve() will return null. It is used to indicate to the Scheduler
291 * that it should stop executing since no more tasks will come.
292 */
293 public synchronized void stop()
294 {
295 this.heap = null;
296 this.elements = 0;
297 this.notify();
298 }
299
300 /**
301 * Remove all canceled tasks from the queue.
302 */
303 public synchronized int purge()
304 {
305 int removed = 0;
306 // Null out any elements that are canceled. Skip element 0 as
307 // it is the sentinel.
308 for (int i = elements; i > 0; --i)
309 {
310 if (heap[i].scheduled < 0)
311 {
312 ++removed;
313
314 // Remove an element by pushing the appropriate child
315 // into place, and then iterating to the bottom of the
316 // tree.
317 int index = i;
318 while (heap[index] != null)
319 {
320 int child = 2 * index;
321 if (child >= heap.length)
322 {
323 // Off end; we're done.
324 heap[index] = null;
325 break;
326 }
327
328 if (child + 1 >= heap.length || heap[child + 1] == null)
329 {
330 // Nothing -- we're done.
331 }
332 else if (heap[child] == null
333 || (heap[child].scheduled
334 > heap[child + 1].scheduled))
335 ++child;
336 heap[index] = heap[child];
337 index = child;
338 }
339 }
340 }
341
342 // Make a new heap if we shrank enough.
343 int newLen = heap.length;
344 while (elements - removed + DEFAULT_SIZE / 2 <= newLen / 4)
345 newLen /= 2;
346 if (newLen != heap.length)
347 {
348 TimerTask[] newHeap = new TimerTask[newLen];
349 System.arraycopy(heap, 0, newHeap, 0, elements + 1);
350 heap = newHeap;
351 }
352
353 return removed;
354 }
355 } // TaskQueue
356
357 /**
358 * The scheduler that executes all the tasks on a particular TaskQueue,
359 * reschedules any repeating tasks and that waits when no task has to be
360 * executed immediately. Stops running when canceled or when the parent
361 * Timer has been finalized and no more tasks have to be executed.
362 */
363 private static final class Scheduler implements Runnable
364 {
365 // The priority queue containing all the TimerTasks.
366 private TaskQueue queue;
367
368 /**
369 * Creates a new Scheduler that will schedule the tasks on the
370 * given TaskQueue.
371 */
372 public Scheduler(TaskQueue queue)
373 {
374 this.queue = queue;
375 }
376
377 public void run()
378 {
379 TimerTask task;
380 while ((task = queue.serve()) != null)
381 {
382 // If this task has not been canceled
383 if (task.scheduled >= 0)
384 {
385
386 // Mark execution time
387 task.lastExecutionTime = task.scheduled;
388
389 // Repeatable task?
390 if (task.period < 0)
391 {
392 // Last time this task is executed
393 task.scheduled = -1;
394 }
395
396 // Run the task
397 try
398 {
399 task.run();
400 }
401 catch (ThreadDeath death)
402 {
403 // If an exception escapes, the Timer becomes invalid.
404 queue.stop();
405 throw death;
406 }
407 catch (Throwable t)
408 {
409 // If an exception escapes, the Timer becomes invalid.
410 queue.stop();
411 }
412 }
413
414 // Calculate next time and possibly re-enqueue.
415 if (task.scheduled >= 0)
416 {
417 if (task.fixed)
418 {
419 task.scheduled += task.period;
420 }
421 else
422 {
423 task.scheduled = task.period + System.currentTimeMillis();
424 }
425
426 try
427 {
428 queue.enqueue(task);
429 }
430 catch (IllegalStateException ise)
431 {
432 // Ignore. Apparently the Timer queue has been stopped.
433 }
434 }
435 }
436 }
437 } // Scheduler
438
439 // Number of Timers created.
440 // Used for creating nice Thread names.
441 private static int nr;
442
443 // The queue that all the tasks are put in.
444 // Given to the scheduler
445 private TaskQueue queue;
446
447 // The Scheduler that does all the real work
448 private Scheduler scheduler;
449
450 // Used to run the scheduler.
451 // Also used to checked if the Thread is still running by calling
452 // thread.isAlive(). Sometimes a Thread is suddenly killed by the system
453 // (if it belonged to an Applet).
454 private Thread thread;
455
456 // When cancelled we don't accept any more TimerTasks.
457 private boolean canceled;
458
459 /**
460 * Creates a new Timer with a non daemon Thread as Scheduler, with normal
461 * priority and a default name.
462 */
463 public Timer()
464 {
465 this(false);
466 }
467
468 /**
469 * Creates a new Timer with a daemon Thread as scheduler if daemon is true,
470 * with normal priority and a default name.
471 */
472 public Timer(boolean daemon)
473 {
474 this(daemon, Thread.NORM_PRIORITY);
475 }
476
477 /**
478 * Create a new Timer whose Thread has the indicated name. It will have
479 * normal priority and will not be a daemon thread.
480 * @param name the name of the Thread
481 * @since 1.5
482 */
483 public Timer(String name)
484 {
485 this(false, Thread.NORM_PRIORITY, name);
486 }
487
488 /**
489 * Create a new Timer whose Thread has the indicated name. It will have
490 * normal priority. The boolean argument controls whether or not it
491 * will be a daemon thread.
492 * @param name the name of the Thread
493 * @param daemon true if the Thread should be a daemon thread
494 * @since 1.5
495 */
496 public Timer(String name, boolean daemon)
497 {
498 this(daemon, Thread.NORM_PRIORITY, name);
499 }
500
501 /**
502 * Creates a new Timer with a daemon Thread as scheduler if daemon is true,
503 * with the priority given and a default name.
504 */
505 private Timer(boolean daemon, int priority)
506 {
507 this(daemon, priority, "Timer-" + (++nr));
508 }
509
510 /**
511 * Creates a new Timer with a daemon Thread as scheduler if daemon is true,
512 * with the priority and name given.E
513 */
514 private Timer(boolean daemon, int priority, String name)
515 {
516 canceled = false;
517 queue = new TaskQueue();
518 scheduler = new Scheduler(queue);
519 thread = new Thread(scheduler, name);
520 thread.setDaemon(daemon);
521 thread.setPriority(priority);
522 thread.start();
523 }
524
525 /**
526 * Cancels the execution of the scheduler. If a task is executing it will
527 * normally finish execution, but no other tasks will be executed and no
528 * more tasks can be scheduled.
529 */
530 public void cancel()
531 {
532 canceled = true;
533 queue.stop();
534 }
535
536 /**
537 * Schedules the task at Time time, repeating every period
538 * milliseconds if period is positive and at a fixed rate if fixed is true.
539 *
540 * @exception IllegalArgumentException if time is negative
541 * @exception IllegalStateException if the task was already scheduled or
542 * canceled or this Timer is canceled or the scheduler thread has died
543 */
544 private void schedule(TimerTask task, long time, long period, boolean fixed)
545 {
546 if (time < 0)
547 throw new IllegalArgumentException("negative time");
548
549 if (task.scheduled == 0 && task.lastExecutionTime == -1)
550 {
551 task.scheduled = time;
552 task.period = period;
553 task.fixed = fixed;
554 }
555 else
556 {
557 throw new IllegalStateException
558 ("task was already scheduled or canceled");
559 }
560
561 if (!this.canceled && this.thread != null)
562 {
563 queue.enqueue(task);
564 }
565 else
566 {
567 throw new IllegalStateException
568 ("timer was canceled or scheduler thread has died");
569 }
570 }
571
572 private static void positiveDelay(long delay)
573 {
574 if (delay < 0)
575 {
576 throw new IllegalArgumentException("delay is negative");
577 }
578 }
579
580 private static void positivePeriod(long period)
581 {
582 if (period < 0)
583 {
584 throw new IllegalArgumentException("period is negative");
585 }
586 }
587
588 /**
589 * Schedules the task at the specified data for one time execution.
590 *
591 * @exception IllegalArgumentException if date.getTime() is negative
592 * @exception IllegalStateException if the task was already scheduled or
593 * canceled or this Timer is canceled or the scheduler thread has died
594 */
595 public void schedule(TimerTask task, Date date)
596 {
597 long time = date.getTime();
598 schedule(task, time, -1, false);
599 }
600
601 /**
602 * Schedules the task at the specified date and reschedules the task every
603 * period milliseconds after the last execution of the task finishes until
604 * this timer or the task is canceled.
605 *
606 * @exception IllegalArgumentException if period or date.getTime() is
607 * negative
608 * @exception IllegalStateException if the task was already scheduled or
609 * canceled or this Timer is canceled or the scheduler thread has died
610 */
611 public void schedule(TimerTask task, Date date, long period)
612 {
613 positivePeriod(period);
614 long time = date.getTime();
615 schedule(task, time, period, false);
616 }
617
618 /**
619 * Schedules the task after the specified delay milliseconds for one time
620 * execution.
621 *
622 * @exception IllegalArgumentException if delay or
623 * System.currentTimeMillis + delay is negative
624 * @exception IllegalStateException if the task was already scheduled or
625 * canceled or this Timer is canceled or the scheduler thread has died
626 */
627 public void schedule(TimerTask task, long delay)
628 {
629 positiveDelay(delay);
630 long time = System.currentTimeMillis() + delay;
631 schedule(task, time, -1, false);
632 }
633
634 /**
635 * Schedules the task after the delay milliseconds and reschedules the
636 * task every period milliseconds after the last execution of the task
637 * finishes until this timer or the task is canceled.
638 *
639 * @exception IllegalArgumentException if delay or period is negative
640 * @exception IllegalStateException if the task was already scheduled or
641 * canceled or this Timer is canceled or the scheduler thread has died
642 */
643 public void schedule(TimerTask task, long delay, long period)
644 {
645 positiveDelay(delay);
646 positivePeriod(period);
647 long time = System.currentTimeMillis() + delay;
648 schedule(task, time, period, false);
649 }
650
651 /**
652 * Schedules the task at the specified date and reschedules the task at a
653 * fixed rate every period milliseconds until this timer or the task is
654 * canceled.
655 *
656 * @exception IllegalArgumentException if period or date.getTime() is
657 * negative
658 * @exception IllegalStateException if the task was already scheduled or
659 * canceled or this Timer is canceled or the scheduler thread has died
660 */
661 public void scheduleAtFixedRate(TimerTask task, Date date, long period)
662 {
663 positivePeriod(period);
664 long time = date.getTime();
665 schedule(task, time, period, true);
666 }
667
668 /**
669 * Schedules the task after the delay milliseconds and reschedules the task
670 * at a fixed rate every period milliseconds until this timer or the task
671 * is canceled.
672 *
673 * @exception IllegalArgumentException if delay or
674 * System.currentTimeMillis + delay is negative
675 * @exception IllegalStateException if the task was already scheduled or
676 * canceled or this Timer is canceled or the scheduler thread has died
677 */
678 public void scheduleAtFixedRate(TimerTask task, long delay, long period)
679 {
680 positiveDelay(delay);
681 positivePeriod(period);
682 long time = System.currentTimeMillis() + delay;
683 schedule(task, time, period, true);
684 }
685
686 /**
687 * Tells the scheduler that the Timer task died
688 * so there will be no more new tasks scheduled.
689 */
690 protected void finalize() throws Throwable
691 {
692 queue.setNullOnEmpty(true);
693 }
694
695 /**
696 * Removes all cancelled tasks from the queue.
697 * @return the number of tasks removed
698 * @since 1.5
699 */
700 public int purge()
701 {
702 return queue.purge();
703 }
704 }