1 /* Timer.java -- Timer that runs TimerTasks at a later time.
2 Copyright (C) 2000, 2001 Free Software Foundation, Inc.
4 This file is part of GNU Classpath.
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7 it under the terms of the GNU General Public License as published by
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14 General Public License for more details.
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18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
21 Linking this library statically or dynamically with other modules is
22 making a combined work based on this library. Thus, the terms and
23 conditions of the GNU General Public License cover the whole
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27 permission to link this library with independent modules to produce an
28 executable, regardless of the license terms of these independent
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30 terms of your choice, provided that you also meet, for each linked
31 independent module, the terms and conditions of the license of that
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36 exception statement from your version. */
41 * Timer that can run TimerTasks at a later time.
42 * TimerTasks can be scheduled for one time execution at some time in the
43 * future. They can be scheduled to be rescheduled at a time period after the
44 * task was last executed. Or they can be scheduled to be executed repeatedly
47 * The normal scheduling will result in a more or less even delay in time
48 * between successive executions, but the executions could drift in time if
49 * the task (or other tasks) takes a long time to execute. Fixed delay
50 * scheduling guarantees more or less that the task will be executed at a
51 * specific time, but if there is ever a delay in execution then the period
52 * between successive executions will be shorter. The first method of
53 * repeated scheduling is preferred for repeated tasks in response to user
54 * interaction, the second method of repeated scheduling is preferred for tasks
55 * that act like alarms.
57 * The Timer keeps a binary heap as a task priority queue which means that
58 * scheduling and serving of a task in a queue of n tasks costs O(log n).
62 * @author Mark Wielaard (mark@klomp.org)
67 * Priority Task Queue.
68 * TimerTasks are kept in a binary heap.
69 * The scheduler calls sleep() on the queue when it has nothing to do or
70 * has to wait. A sleeping scheduler can be notified by calling interrupt()
71 * which is automatically called by the enqueue(), cancel() and
72 * timerFinalized() methods.
74 private static final class TaskQueue
76 /** Default size of this queue */
77 private final int DEFAULT_SIZE = 32;
79 /** Whether to return null when there is nothing in the queue */
80 private boolean nullOnEmpty;
83 * The heap containing all the scheduled TimerTasks
84 * sorted by the TimerTask.scheduled field.
85 * Null when the stop() method has been called.
87 private TimerTask heap[];
90 * The actual number of elements in the heap
91 * Can be less then heap.length.
92 * Note that heap[0] is used as a sentinel.
97 * Creates a TaskQueue of default size without any elements in it.
101 heap = new TimerTask[DEFAULT_SIZE];
107 * Adds a TimerTask at the end of the heap.
108 * Grows the heap if necessary by doubling the heap in size.
110 private void add(TimerTask task)
113 if (elements == heap.length)
115 TimerTask new_heap[] = new TimerTask[heap.length * 2];
116 System.arraycopy(heap, 0, new_heap, 0, heap.length);
119 heap[elements] = task;
123 * Removes the last element from the heap.
124 * Shrinks the heap in half if
125 * elements+DEFAULT_SIZE/2 <= heap.length/4.
127 private void remove()
129 // clear the entry first
130 heap[elements] = null;
132 if (elements + DEFAULT_SIZE / 2 <= (heap.length / 4))
134 TimerTask new_heap[] = new TimerTask[heap.length / 2];
135 System.arraycopy(heap, 0, new_heap, 0, elements + 1);
141 * Adds a task to the queue and puts it at the correct place
144 public synchronized void enqueue(TimerTask task)
146 // Check if it is legal to add another element
149 throw new IllegalStateException
150 ("cannot enqueue when stop() has been called on queue");
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)
160 heap[child] = heap[parent];
164 // This is the correct place for the new task
166 heap[0] = null; // clear sentinel
167 // Maybe sched() is waiting for a new element
172 * Returns the top element of the queue.
173 * Can return null when no task is in the queue.
175 private TimerTask top()
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.
192 public synchronized TimerTask serve()
194 // The task to return
195 TimerTask task = null;
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))
209 // Do we have a task?
212 // The time to wait until the task should be served
213 long time = task.scheduled - System.currentTimeMillis();
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()
224 catch (InterruptedException _)
231 // wait until a task is added
232 // or something else happens to the queue
237 catch (InterruptedException _)
243 // reconstruct the heap
244 TimerTask lastTask = heap[elements];
247 // drop lastTask at the beginning and move it down the heap
251 while (child <= elements)
253 if (child < elements)
255 if (heap[child].scheduled > heap[child + 1].scheduled)
261 if (lastTask.scheduled <= heap[child].scheduled)
262 break; // found the correct place (the parent) - done
264 heap[parent] = heap[child];
269 // this is the correct new place for the lastTask
270 heap[parent] = lastTask;
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.
282 public synchronized void setNullOnEmpty(boolean nullOnEmpty)
284 this.nullOnEmpty = nullOnEmpty;
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.
293 public synchronized void stop()
303 * The scheduler that executes all the tasks on a particular TaskQueue,
304 * reschedules any repeating tasks and that waits when no task has to be
305 * executed immediatly. Stops running when canceled or when the parent
306 * Timer has been finalized and no more tasks have to be executed.
308 private static final class Scheduler implements Runnable
310 // The priority queue containing all the TimerTasks.
311 private TaskQueue queue;
314 * Creates a new Scheduler that will schedule the tasks on the
317 public Scheduler(TaskQueue queue)
325 while ((task = queue.serve()) != null)
327 // If this task has not been canceled
328 if (task.scheduled >= 0)
331 // Mark execution time
332 task.lastExecutionTime = task.scheduled;
337 // Last time this task is executed
348 /* ignore all errors */
352 // Calculate next time and possibly re-enqueue.
353 if (task.scheduled >= 0)
357 task.scheduled += task.period;
361 task.scheduled = task.period + System.currentTimeMillis();
368 catch (IllegalStateException ise)
370 // Ignore. Apparently the Timer queue has been stopped.
377 // Number of Timers created.
378 // Used for creating nice Thread names.
379 private static int nr = 0;
381 // The queue that all the tasks are put in.
382 // Given to the scheduler
383 private TaskQueue queue;
385 // The Scheduler that does all the real work
386 private Scheduler scheduler;
388 // Used to run the scheduler.
389 // Also used to checked if the Thread is still running by calling
390 // thread.isAlive(). Sometimes a Thread is suddenly killed by the system
391 // (if it belonged to an Applet).
392 private Thread thread;
394 // When cancelled we don't accept any more TimerTasks.
395 private boolean canceled;
398 * Creates a new Timer with a non daemon Thread as Scheduler, with normal
399 * priority and a default name.
407 * Creates a new Timer with a daemon Thread as scheduler if daemon is true,
408 * with normal priority and a default name.
410 public Timer(boolean daemon)
412 this(daemon, Thread.NORM_PRIORITY);
416 * Creates a new Timer with a daemon Thread as scheduler if daemon is true,
417 * with the priority given and a default name.
419 private Timer(boolean daemon, int priority)
421 this(daemon, priority, "Timer-" + (++nr));
425 * Creates a new Timer with a daemon Thread as scheduler if daemon is true,
426 * with the priority and name given.E
428 private Timer(boolean daemon, int priority, String name)
431 queue = new TaskQueue();
432 scheduler = new Scheduler(queue);
433 thread = new Thread(scheduler, name);
434 thread.setDaemon(daemon);
435 thread.setPriority(priority);
440 * Cancels the execution of the scheduler. If a task is executing it will
441 * normally finish execution, but no other tasks will be executed and no
442 * more tasks can be scheduled.
451 * Schedules the task at Time time, repeating every period
452 * milliseconds if period is positive and at a fixed rate if fixed is true.
454 * @exception IllegalArgumentException if time is negative
455 * @exception IllegalStateException if the task was already scheduled or
456 * canceled or this Timer is canceled or the scheduler thread has died
458 private void schedule(TimerTask task, long time, long period, boolean fixed)
461 throw new IllegalArgumentException("negative time");
463 if (task.scheduled == 0 && task.lastExecutionTime == -1)
465 task.scheduled = time;
466 task.period = period;
471 throw new IllegalStateException
472 ("task was already scheduled or canceled");
475 if (!this.canceled && this.thread != null)
481 throw new IllegalStateException
482 ("timer was canceled or scheduler thread has died");
486 private static void positiveDelay(long delay)
490 throw new IllegalArgumentException("delay is negative");
494 private static void positivePeriod(long period)
498 throw new IllegalArgumentException("period is negative");
503 * Schedules the task at the specified data for one time execution.
505 * @exception IllegalArgumentException if date.getTime() is negative
506 * @exception IllegalStateException if the task was already scheduled or
507 * canceled or this Timer is canceled or the scheduler thread has died
509 public void schedule(TimerTask task, Date date)
511 long time = date.getTime();
512 schedule(task, time, -1, false);
516 * Schedules the task at the specified date and reschedules the task every
517 * period milliseconds after the last execution of the task finishes until
518 * this timer or the task is canceled.
520 * @exception IllegalArgumentException if period or date.getTime() is
522 * @exception IllegalStateException if the task was already scheduled or
523 * canceled or this Timer is canceled or the scheduler thread has died
525 public void schedule(TimerTask task, Date date, long period)
527 positivePeriod(period);
528 long time = date.getTime();
529 schedule(task, time, period, false);
533 * Schedules the task after the specified delay milliseconds for one time
536 * @exception IllegalArgumentException if delay or
537 * System.currentTimeMillis + delay is negative
538 * @exception IllegalStateException if the task was already scheduled or
539 * canceled or this Timer is canceled or the scheduler thread has died
541 public void schedule(TimerTask task, long delay)
543 positiveDelay(delay);
544 long time = System.currentTimeMillis() + delay;
545 schedule(task, time, -1, false);
549 * Schedules the task after the delay milliseconds and reschedules the
550 * task every period milliseconds after the last execution of the task
551 * finishes until this timer or the task is canceled.
553 * @exception IllegalArgumentException if delay or period is negative
554 * @exception IllegalStateException if the task was already scheduled or
555 * canceled or this Timer is canceled or the scheduler thread has died
557 public void schedule(TimerTask task, long delay, long period)
559 positiveDelay(delay);
560 positivePeriod(period);
561 long time = System.currentTimeMillis() + delay;
562 schedule(task, time, period, false);
566 * Schedules the task at the specified date and reschedules the task at a
567 * fixed rate every period milliseconds until this timer or the task is
570 * @exception IllegalArgumentException if period or date.getTime() is
572 * @exception IllegalStateException if the task was already scheduled or
573 * canceled or this Timer is canceled or the scheduler thread has died
575 public void scheduleAtFixedRate(TimerTask task, Date date, long period)
577 positivePeriod(period);
578 long time = date.getTime();
579 schedule(task, time, period, true);
583 * Schedules the task after the delay milliseconds and reschedules the task
584 * at a fixed rate every period milliseconds until this timer or the task
587 * @exception IllegalArgumentException if delay or
588 * System.currentTimeMillis + delay is negative
589 * @exception IllegalStateException if the task was already scheduled or
590 * canceled or this Timer is canceled or the scheduler thread has died
592 public void scheduleAtFixedRate(TimerTask task, long delay, long period)
594 positiveDelay(delay);
595 positivePeriod(period);
596 long time = System.currentTimeMillis() + delay;
597 schedule(task, time, period, true);
601 * Tells the scheduler that the Timer task died
602 * so there will be no more new tasks scheduled.
604 protected void finalize() throws Throwable
606 queue.setNullOnEmpty(true);