1 /* Timer.java -- Timer that runs TimerTasks at a later time.
2 Copyright (C) 2000, 2001, 2005 Free Software Foundation, Inc.
4 This file is part of GNU Classpath.
6 GNU Classpath is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
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12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GNU Classpath; see the file COPYING. If not, write to the
18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, 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
26 As a special exception, the copyright holders of this library give you
27 permission to link this library with independent modules to produce an
28 executable, regardless of the license terms of these independent
29 modules, and to copy and distribute the resulting executable under
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
32 module. An independent module is a module which is not derived from
33 or based on this library. If you modify this library, you may extend
34 this exception to your version of the library, but you are not
35 obligated to do so. If you do not wish to do so, delete this
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 static 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()
301 * Remove all canceled tasks from the queue.
303 public synchronized int purge()
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
)
310 if (heap
[i
].scheduled
< 0)
314 // Remove an element by pushing the appropriate child
315 // into place, and then iterating to the bottom of the
318 while (heap
[index
] != null)
320 int child
= 2 * index
;
321 if (child
>= heap
.length
)
323 // Off end; we're done.
328 if (child
+ 1 >= heap
.length
|| heap
[child
+ 1] == null)
330 // Nothing -- we're done.
332 else if (heap
[child
] == null
333 || (heap
[child
].scheduled
334 > heap
[child
+ 1].scheduled
))
336 heap
[index
] = heap
[child
];
342 // Make a new heap if we shrank enough.
343 int newLen
= heap
.length
;
344 while (elements
- removed
+ DEFAULT_SIZE
/ 2 <= newLen
/ 4)
346 if (newLen
!= heap
.length
)
348 TimerTask
[] newHeap
= new TimerTask
[newLen
];
349 System
.arraycopy(heap
, 0, newHeap
, 0, elements
+ 1);
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.
363 private static final class Scheduler
implements Runnable
365 // The priority queue containing all the TimerTasks.
366 private TaskQueue queue
;
369 * Creates a new Scheduler that will schedule the tasks on the
372 public Scheduler(TaskQueue queue
)
380 while ((task
= queue
.serve()) != null)
382 // If this task has not been canceled
383 if (task
.scheduled
>= 0)
386 // Mark execution time
387 task
.lastExecutionTime
= task
.scheduled
;
392 // Last time this task is executed
401 catch (ThreadDeath death
)
403 // If an exception escapes, the Timer becomes invalid.
409 // If an exception escapes, the Timer becomes invalid.
414 // Calculate next time and possibly re-enqueue.
415 if (task
.scheduled
>= 0)
419 task
.scheduled
+= task
.period
;
423 task
.scheduled
= task
.period
+ System
.currentTimeMillis();
430 catch (IllegalStateException ise
)
432 // Ignore. Apparently the Timer queue has been stopped.
439 // Number of Timers created.
440 // Used for creating nice Thread names.
441 private static int nr
;
443 // The queue that all the tasks are put in.
444 // Given to the scheduler
445 private TaskQueue queue
;
447 // The Scheduler that does all the real work
448 private Scheduler scheduler
;
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
;
456 // When cancelled we don't accept any more TimerTasks.
457 private boolean canceled
;
460 * Creates a new Timer with a non daemon Thread as Scheduler, with normal
461 * priority and a default name.
469 * Creates a new Timer with a daemon Thread as scheduler if daemon is true,
470 * with normal priority and a default name.
472 public Timer(boolean daemon
)
474 this(daemon
, Thread
.NORM_PRIORITY
);
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
483 public Timer(String name
)
485 this(false, Thread
.NORM_PRIORITY
, name
);
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
496 public Timer(String name
, boolean daemon
)
498 this(daemon
, Thread
.NORM_PRIORITY
, name
);
502 * Creates a new Timer with a daemon Thread as scheduler if daemon is true,
503 * with the priority given and a default name.
505 private Timer(boolean daemon
, int priority
)
507 this(daemon
, priority
, "Timer-" + (++nr
));
511 * Creates a new Timer with a daemon Thread as scheduler if daemon is true,
512 * with the priority and name given.E
514 private Timer(boolean daemon
, int priority
, String name
)
517 queue
= new TaskQueue();
518 scheduler
= new Scheduler(queue
);
519 thread
= new Thread(scheduler
, name
);
520 thread
.setDaemon(daemon
);
521 thread
.setPriority(priority
);
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.
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.
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
544 private void schedule(TimerTask task
, long time
, long period
, boolean fixed
)
547 throw new IllegalArgumentException("negative time");
549 if (task
.scheduled
== 0 && task
.lastExecutionTime
== -1)
551 task
.scheduled
= time
;
552 task
.period
= period
;
557 throw new IllegalStateException
558 ("task was already scheduled or canceled");
561 if (!this.canceled
&& this.thread
!= null)
567 throw new IllegalStateException
568 ("timer was canceled or scheduler thread has died");
572 private static void positiveDelay(long delay
)
576 throw new IllegalArgumentException("delay is negative");
580 private static void positivePeriod(long period
)
584 throw new IllegalArgumentException("period is negative");
589 * Schedules the task at the specified data for one time execution.
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
595 public void schedule(TimerTask task
, Date date
)
597 long time
= date
.getTime();
598 schedule(task
, time
, -1, false);
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.
606 * @exception IllegalArgumentException if period or date.getTime() is
608 * @exception IllegalStateException if the task was already scheduled or
609 * canceled or this Timer is canceled or the scheduler thread has died
611 public void schedule(TimerTask task
, Date date
, long period
)
613 positivePeriod(period
);
614 long time
= date
.getTime();
615 schedule(task
, time
, period
, false);
619 * Schedules the task after the specified delay milliseconds for one time
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
627 public void schedule(TimerTask task
, long delay
)
629 positiveDelay(delay
);
630 long time
= System
.currentTimeMillis() + delay
;
631 schedule(task
, time
, -1, false);
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.
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
643 public void schedule(TimerTask task
, long delay
, long period
)
645 positiveDelay(delay
);
646 positivePeriod(period
);
647 long time
= System
.currentTimeMillis() + delay
;
648 schedule(task
, time
, period
, false);
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
656 * @exception IllegalArgumentException if period or date.getTime() is
658 * @exception IllegalStateException if the task was already scheduled or
659 * canceled or this Timer is canceled or the scheduler thread has died
661 public void scheduleAtFixedRate(TimerTask task
, Date date
, long period
)
663 positivePeriod(period
);
664 long time
= date
.getTime();
665 schedule(task
, time
, period
, true);
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
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
678 public void scheduleAtFixedRate(TimerTask task
, long delay
, long period
)
680 positiveDelay(delay
);
681 positivePeriod(period
);
682 long time
= System
.currentTimeMillis() + delay
;
683 schedule(task
, time
, period
, true);
687 * Tells the scheduler that the Timer task died
688 * so there will be no more new tasks scheduled.
690 protected void finalize() throws Throwable
692 queue
.setNullOnEmpty(true);
696 * Removes all cancelled tasks from the queue.
697 * @return the number of tasks removed
702 return queue
.purge();