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authorupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
committerupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
commit554fd8c5195424bdbcabf5de30fdc183aba391bd (patch)
tree976dc5ab7fddf506dadce60ae936f43f58787092 /libjava/classpath/java/util/TimerTask.java
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+/* 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., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 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:
+ * <pre>
+ * Timer timer = new Timer();
+ * TimerTask task = new TimerTask() {
+ * public void run() {
+ * if (this.scheduledExecutionTime() &lt; 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
+ * </pre>
+ * <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;
+ }
+}