589 lines
16 KiB
Java
589 lines
16 KiB
Java
/* Timer.java -- Timer that runs TimerTasks at a later time.
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Copyright (C) 2000, 2001 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA.
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As a special exception, if you link this library with other files to
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produce an executable, this library does not by itself cause the
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resulting executable to be covered by the GNU General Public License.
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This exception does not however invalidate any other reasons why the
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executable file might be covered by the GNU General Public License. */
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package java.util;
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/**
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* Timer that can run TimerTasks at a later time.
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* TimerTasks can be scheduled for one time execution at some time in the
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* future. They can be scheduled to be rescheduled at a time period after the
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* task was last executed. Or they can be scheduled to be executed repeatedly
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* at a fixed rate.
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* <p>
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* The normal scheduling will result in a more or less even delay in time
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* between successive executions, but the executions could drift in time if
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* the task (or other tasks) takes a long time to execute. Fixed delay
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* scheduling guarantees more or less that the task will be executed at a
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* specific time, but if there is ever a delay in execution then the period
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* between successive executions will be shorter. The first method of
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* repeated scheduling is prefered for repeated tasks in response to user
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* interaction, the second method of repeated scheduling is prefered for tasks
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* that act like alarms.
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* <p>
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* The Timer keeps a binary heap as a task priority queue which means that
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* scheduling and serving of a task in a queue of n tasks costs O(log n).
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*
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* @see TimerTask
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* @since 1.3
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* @author Mark Wielaard (mark@klomp.org)
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*/
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public class Timer
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{
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/**
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* Priority Task Queue.
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* TimerTasks are kept in a binary heap.
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* The scheduler calls sleep() on the queue when it has nothing to do or
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* has to wait. A sleeping scheduler can be notified by calling interrupt()
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* which is automatically called by the enqueue(), cancel() and
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* timerFinalized() methods.
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*/
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private static final class TaskQueue
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{
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/** Default size of this queue */
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private final int DEFAULT_SIZE = 32;
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/** Wheter to return null when there is nothing in the queue */
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private boolean nullOnEmpty;
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/**
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* The heap containing all the scheduled TimerTasks
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* sorted by the TimerTask.scheduled field.
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* Null when the stop() method has been called.
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*/
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private TimerTask heap[];
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/**
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* The actual number of elements in the heap
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* Can be less then heap.length.
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* Note that heap[0] is used as a sentinel.
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*/
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private int elements;
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/**
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* Creates a TaskQueue of default size without any elements in it.
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*/
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public TaskQueue()
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{
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heap = new TimerTask[DEFAULT_SIZE];
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elements = 0;
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nullOnEmpty = false;
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}
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/**
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* Adds a TimerTask at the end of the heap.
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* Grows the heap if necessary by doubling the heap in size.
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*/
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private void add(TimerTask task)
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{
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elements++;
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if (elements == heap.length)
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{
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TimerTask new_heap[] = new TimerTask[heap.length * 2];
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System.arraycopy(heap, 0, new_heap, 0, heap.length);
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heap = new_heap;
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}
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heap[elements] = task;
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}
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/**
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* Removes the last element from the heap.
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* Shrinks the heap in half if
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* elements+DEFAULT_SIZE/2 <= heap.length/4.
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*/
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private void remove()
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{
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// clear the entry first
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heap[elements] = null;
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elements--;
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if (elements + DEFAULT_SIZE / 2 <= (heap.length / 4))
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{
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TimerTask new_heap[] = new TimerTask[heap.length / 2];
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System.arraycopy(heap, 0, new_heap, 0, elements + 1);
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heap = new_heap;
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}
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}
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/**
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* Adds a task to the queue and puts it at the correct place
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* in the heap.
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*/
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public synchronized void enqueue(TimerTask task)
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{
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// Check if it is legal to add another element
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if (heap == null)
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{
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throw new IllegalStateException
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("cannot enqueue when stop() has been called on queue");
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}
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heap[0] = task; // sentinel
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add(task); // put the new task at the end
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// Now push the task up in the heap until it has reached its place
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int child = elements;
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int parent = child / 2;
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while (heap[parent].scheduled > task.scheduled)
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{
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heap[child] = heap[parent];
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child = parent;
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parent = child / 2;
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}
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// This is the correct place for the new task
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heap[child] = task;
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heap[0] = null; // clear sentinel
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// Maybe sched() is waiting for a new element
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this.notify();
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}
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/**
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* Returns the top element of the queue.
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* Can return null when no task is in the queue.
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*/
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private TimerTask top()
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{
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if (elements == 0)
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{
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return null;
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}
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else
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{
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return heap[1];
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}
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}
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/**
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* Returns the top task in the Queue.
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* Removes the element from the heap and reorders the heap first.
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* Can return null when there is nothing in the queue.
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*/
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public synchronized TimerTask serve()
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{
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// The task to return
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TimerTask task = null;
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while (task == null)
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{
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// Get the next task
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task = top();
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// return null when asked to stop
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// or if asked to return null when the queue is empty
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if ((heap == null) || (task == null && nullOnEmpty))
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{
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return null;
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}
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// Do we have a task?
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if (task != null)
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{
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// The time to wait until the task should be served
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long time = task.scheduled - System.currentTimeMillis();
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if (time > 0)
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{
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// This task should not yet be served
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// So wait until this task is ready
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// or something else happens to the queue
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task = null; // set to null to make sure we call top()
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try
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{
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this.wait(time);
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}
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catch (InterruptedException _)
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{
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}
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}
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}
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else
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{
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// wait until a task is added
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// or something else happens to the queue
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try
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{
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this.wait();
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}
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catch (InterruptedException _)
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{
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}
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}
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}
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// reconstruct the heap
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TimerTask lastTask = heap[elements];
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remove();
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// drop lastTask at the beginning and move it down the heap
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int parent = 1;
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int child = 2;
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heap[1] = lastTask;
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while (child <= elements)
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{
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if (child < elements)
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{
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if (heap[child].scheduled > heap[child + 1].scheduled)
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{
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child++;
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}
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}
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if (lastTask.scheduled <= heap[child].scheduled)
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break; // found the correct place (the parent) - done
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heap[parent] = heap[child];
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parent = child;
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child = parent * 2;
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}
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// this is the correct new place for the lastTask
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heap[parent] = lastTask;
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// return the task
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return task;
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}
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/**
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* When nullOnEmpty is true the serve() method will return null when
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* there are no tasks in the queue, otherwise it will wait until
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* a new element is added to the queue. It is used to indicate to
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* the scheduler that no new tasks will ever be added to the queue.
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*/
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public synchronized void setNullOnEmpty(boolean nullOnEmpty)
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{
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this.nullOnEmpty = nullOnEmpty;
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this.notify();
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}
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/**
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* When this method is called the current and all future calls to
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* serve() will return null. It is used to indicate to the Scheduler
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* that it should stop executing since no more tasks will come.
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*/
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public synchronized void stop()
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{
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this.heap = null;
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this.notify();
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}
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} // TaskQueue
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/**
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* The scheduler that executes all the tasks on a particular TaskQueue,
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* reschedules any repeating tasks and that waits when no task has to be
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* executed immediatly. Stops running when canceled or when the parent
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* Timer has been finalized and no more tasks have to be executed.
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*/
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private static final class Scheduler implements Runnable
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{
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// The priority queue containing all the TimerTasks.
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private TaskQueue queue;
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/**
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* Creates a new Scheduler that will schedule the tasks on the
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* given TaskQueue.
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*/
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public Scheduler(TaskQueue queue)
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{
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this.queue = queue;
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}
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public void run()
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{
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TimerTask task;
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while ((task = queue.serve()) != null)
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{
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// If this task has not been canceled
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if (task.scheduled >= 0)
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{
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// Mark execution time
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task.lastExecutionTime = task.scheduled;
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// Repeatable task?
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if (task.period < 0)
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{
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// Last time this task is executed
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task.scheduled = -1;
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}
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// Run the task
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try
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{
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task.run();
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}
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catch (Throwable t)
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{
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/* ignore all errors */
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}
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}
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// Calculate next time and possibly re-enqueue
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if (task.scheduled >= 0)
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{
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if (task.fixed)
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{
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task.scheduled += task.period;
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}
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else
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{
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task.scheduled = task.period + System.currentTimeMillis();
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}
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queue.enqueue(task);
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}
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}
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}
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} // Scheduler
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// Number of Timers created.
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// Used for creating nice Thread names.
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private static int nr = 0;
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// The queue that all the tasks are put in.
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// Given to the scheduler
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private TaskQueue queue;
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// The Scheduler that does all the real work
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private Scheduler scheduler;
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// Used to run the scheduler.
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// Also used to checked if the Thread is still running by calling
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// thread.isAlive(). Sometimes a Thread is suddenly killed by the system
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// (if it belonged to an Applet).
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private Thread thread;
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// When cancelled we don't accept any more TimerTasks.
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private boolean canceled;
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/**
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* Creates a new Timer with a non deamon Thread as Scheduler, with normal
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* priority and a default name.
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*/
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public Timer()
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{
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this(false);
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}
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/**
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* Creates a new Timer with a deamon Thread as scheduler if deamon is true,
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* with normal priority and a default name.
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*/
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public Timer(boolean daemon)
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{
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this(daemon, Thread.NORM_PRIORITY);
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}
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/**
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* Creates a new Timer with a deamon Thread as scheduler if deamon is true,
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* with the priority given and a default name.
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*/
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private Timer(boolean daemon, int priority)
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{
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this(daemon, priority, "Timer-" + (++nr));
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}
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/**
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* Creates a new Timer with a deamon Thread as scheduler if deamon is true,
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* with the priority and name given.E
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*/
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private Timer(boolean daemon, int priority, String name)
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{
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canceled = false;
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queue = new TaskQueue();
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scheduler = new Scheduler(queue);
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thread = new Thread(scheduler, name);
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thread.setDaemon(daemon);
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thread.setPriority(priority);
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thread.start();
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}
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/**
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* Cancels the execution of the scheduler. If a task is executing it will
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* normally finish execution, but no other tasks will be executed and no
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* more tasks can be scheduled.
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*/
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public void cancel()
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{
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canceled = true;
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queue.stop();
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}
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/**
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* Schedules the task at Time time, repeating every period
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* milliseconds if period is positive and at a fixed rate if fixed is true.
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*
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* @exception IllegalArgumentException if time is negative
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* @exception IllegalStateException if the task was already scheduled or
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* canceled or this Timer is canceled or the scheduler thread has died
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*/
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private void schedule(TimerTask task, long time, long period, boolean fixed)
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{
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if (time < 0)
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throw new IllegalArgumentException("negative time");
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if (task.scheduled == 0 && task.lastExecutionTime == -1)
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{
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task.scheduled = time;
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task.period = period;
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task.fixed = fixed;
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}
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else
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{
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throw new IllegalStateException
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("task was already scheduled or canceled");
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}
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if (!this.canceled && this.thread != null)
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{
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queue.enqueue(task);
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}
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else
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{
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throw new IllegalStateException
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("timer was canceled or scheduler thread has died");
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}
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}
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private static void positiveDelay(long delay)
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{
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if (delay < 0)
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{
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throw new IllegalArgumentException("delay is negative");
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}
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}
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private static void positivePeriod(long period)
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{
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if (period < 0)
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{
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throw new IllegalArgumentException("period is negative");
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}
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}
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/**
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* Schedules the task at the specified data for one time execution.
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*
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* @exception IllegalArgumentException if date.getTime() is negative
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* @exception IllegalStateException if the task was already scheduled or
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* canceled or this Timer is canceled or the scheduler thread has died
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*/
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public void schedule(TimerTask task, Date date)
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{
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long time = date.getTime();
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schedule(task, time, -1, false);
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}
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/**
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* Schedules the task at the specified date and reschedules the task every
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* period milliseconds after the last execution of the task finishes until
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* this timer or the task is canceled.
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*
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* @exception IllegalArgumentException if period or date.getTime() is
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* negative
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* @exception IllegalStateException if the task was already scheduled or
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* canceled or this Timer is canceled or the scheduler thread has died
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*/
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public void schedule(TimerTask task, Date date, long period)
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{
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positivePeriod(period);
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long time = date.getTime();
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schedule(task, time, period, false);
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}
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/**
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* Schedules the task after the specified delay milliseconds for one time
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* execution.
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*
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* @exception IllegalArgumentException if delay or
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* System.currentTimeMillis + delay is negative
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* @exception IllegalStateException if the task was already scheduled or
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* canceled or this Timer is canceled or the scheduler thread has died
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*/
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public void schedule(TimerTask task, long delay)
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{
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positiveDelay(delay);
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long time = System.currentTimeMillis() + delay;
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schedule(task, time, -1, false);
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}
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/**
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* Schedules the task after the delay milliseconds and reschedules the
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* task every period milliseconds after the last execution of the task
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* finishes until this timer or the task is canceled.
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*
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* @exception IllegalArgumentException if delay or period is negative
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* @exception IllegalStateException if the task was already scheduled or
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* canceled or this Timer is canceled or the scheduler thread has died
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*/
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public void schedule(TimerTask task, long delay, long period)
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{
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positiveDelay(delay);
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positivePeriod(period);
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long time = System.currentTimeMillis() + delay;
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schedule(task, time, period, false);
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}
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/**
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* Schedules the task at the specified date and reschedules the task at a
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* fixed rate every period milliseconds until this timer or the task is
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* canceled.
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*
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* @exception IllegalArgumentException if period or date.getTime() is
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* negative
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* @exception IllegalStateException if the task was already scheduled or
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* canceled or this Timer is canceled or the scheduler thread has died
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*/
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public void scheduleAtFixedRate(TimerTask task, Date date, long period)
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{
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positivePeriod(period);
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long time = date.getTime();
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schedule(task, time, period, true);
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}
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/**
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* Schedules the task after the delay milliseconds and reschedules the task
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* at a fixed rate every period milliseconds until this timer or the task
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* is canceled.
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*
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* @exception IllegalArgumentException if delay or
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* System.currentTimeMillis + delay is negative
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* @exception IllegalStateException if the task was already scheduled or
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* canceled or this Timer is canceled or the scheduler thread has died
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*/
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public void scheduleAtFixedRate(TimerTask task, long delay, long period)
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{
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positiveDelay(delay);
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positivePeriod(period);
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long time = System.currentTimeMillis() + delay;
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schedule(task, time, period, true);
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}
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/**
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* Tells the scheduler that the Timer task died
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* so there will be no more new tasks scheduled.
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*/
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protected void finalize()
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{
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queue.setNullOnEmpty(true);
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}
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}
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