92aaa24628
From-SVN: r49104
146 lines
5.1 KiB
Java
146 lines
5.1 KiB
Java
/* TimerTask.java -- Task that can be run at a later time if given to a Timer.
|
|
Copyright (C) 2000 Free Software Foundation, Inc.
|
|
|
|
This file is part of GNU Classpath.
|
|
|
|
GNU Classpath is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation; either version 2, or (at your option)
|
|
any later version.
|
|
|
|
GNU Classpath is distributed in the hope that it will be useful, but
|
|
WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with GNU Classpath; see the file COPYING. If not, write to the
|
|
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
|
|
02111-1307 USA.
|
|
|
|
Linking this library statically or dynamically with other modules is
|
|
making a combined work based on this library. Thus, the terms and
|
|
conditions of the GNU General Public License cover the whole
|
|
combination.
|
|
|
|
As a special exception, the copyright holders of this library give you
|
|
permission to link this library with independent modules to produce an
|
|
executable, regardless of the license terms of these independent
|
|
modules, and to copy and distribute the resulting executable under
|
|
terms of your choice, provided that you also meet, for each linked
|
|
independent module, the terms and conditions of the license of that
|
|
module. An independent module is a module which is not derived from
|
|
or based on this library. If you modify this library, you may extend
|
|
this exception to your version of the library, but you are not
|
|
obligated to do so. If you do not wish to do so, delete this
|
|
exception statement from your version. */
|
|
|
|
package java.util;
|
|
|
|
/**
|
|
* Task that can be run at a later time if given to a Timer.
|
|
* The TimerTask must implement a run method that will be called by the
|
|
* Timer when the task is scheduled for execution. The task can check when
|
|
* it should have been scheduled and cancel itself when no longer needed.
|
|
* <p>
|
|
* Example:
|
|
* <code>
|
|
* Timer timer = new Timer();
|
|
* TimerTask task = new TimerTask() {
|
|
* public void run() {
|
|
* if (this.scheduledExecutionTime() < System.currentTimeMillis() + 500)
|
|
* // Do something
|
|
* else
|
|
* // Complain: We are more then half a second late!
|
|
* if (someStopCondition)
|
|
* this.cancel(); // This was our last execution
|
|
* };
|
|
* timer.scheduleAtFixedRate(task, 1000, 1000); // schedule every second
|
|
* </code>
|
|
* <p>
|
|
* Note that a TimerTask object is a one shot object and can only given once
|
|
* to a Timer. (The Timer will use the TimerTask object for bookkeeping,
|
|
* in this implementation).
|
|
* <p>
|
|
* This class also implements <code>Runnable</code> to make it possible to
|
|
* give a TimerTask directly as a target to a <code>Thread</code>.
|
|
*
|
|
* @see Timer
|
|
* @since 1.3
|
|
* @author Mark Wielaard (mark@klomp.org)
|
|
*/
|
|
public abstract class TimerTask implements Runnable
|
|
{
|
|
/**
|
|
* If positive the next time this task should be run.
|
|
* If negative this TimerTask is canceled or executed for the last time.
|
|
*/
|
|
long scheduled;
|
|
|
|
/**
|
|
* If positive the last time this task was run.
|
|
* If negative this TimerTask has not yet been scheduled.
|
|
*/
|
|
long lastExecutionTime;
|
|
|
|
/**
|
|
* If positive the number of milliseconds between runs of this task.
|
|
* If -1 this task doesn't have to be run more then once.
|
|
*/
|
|
long period;
|
|
|
|
/**
|
|
* If true the next time this task should be run is relative to
|
|
* the last scheduled time, otherwise it can drift in time.
|
|
*/
|
|
boolean fixed;
|
|
|
|
/**
|
|
* Creates a TimerTask and marks it as not yet scheduled.
|
|
*/
|
|
protected TimerTask()
|
|
{
|
|
this.scheduled = 0;
|
|
this.lastExecutionTime = -1;
|
|
}
|
|
|
|
/**
|
|
* Marks the task as canceled and prevents any further execution.
|
|
* Returns true if the task was scheduled for any execution in the future
|
|
* and this cancel operation prevents that execution from happening.
|
|
* <p>
|
|
* A task that has been canceled can never be scheduled again.
|
|
* <p>
|
|
* In this implementation the TimerTask it is possible that the Timer does
|
|
* keep a reference to the TimerTask until the first time the TimerTask
|
|
* is actually scheduled. But the reference will disappear immediatly when
|
|
* cancel is called from within the TimerTask run method.
|
|
*/
|
|
public boolean cancel()
|
|
{
|
|
boolean prevented_execution = (this.scheduled >= 0);
|
|
this.scheduled = -1;
|
|
return prevented_execution;
|
|
}
|
|
|
|
/**
|
|
* Method that is called when this task is scheduled for execution.
|
|
*/
|
|
public abstract void run();
|
|
|
|
/**
|
|
* Returns the last time this task was scheduled or (when called by the
|
|
* task from the run method) the time the current execution of the task
|
|
* was scheduled. When the task has not yet run the return value is
|
|
* undefined.
|
|
* <p>
|
|
* Can be used (when the task is scheduled at fixed rate) to see the
|
|
* difference between the requested schedule time and the actual time
|
|
* that can be found with <code>System.currentTimeMillis()</code>.
|
|
*/
|
|
public long scheduledExecutionTime()
|
|
{
|
|
return lastExecutionTime;
|
|
}
|
|
}
|