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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.jackrabbit.util;
import java.util.TimerTask;
/**
* Timer wraps the standard Java {@link java.util.Timer} class
* and implements a guaranteed shutdown of the background thread running
* in the Timer instance after a certain {@link #IDLE_TIME}.
*/
public class Timer {
/**
* Idle time in milliseconds. When a timer instance is idle for this amount
* of time the underlying timer is canceled.
*/
static final int IDLE_TIME = 3 * 1000;
/**
* The interval at which the idle checker task runs.
*/
static final int CHECKER_INTERVAL = 1000;
/**
* The timer implementation we us internally.
*/
private java.util.Timer delegatee;
/**
* Indicates whether the timer thread should run as deamon.
*/
private final boolean runAsDeamon;
/**
* The number of currently scheduled tasks. If this value drops to zero
* the internal {@link java.util.Timer} instance is canceled. Whenever
* this value increases from zero to one a new {@link java.util.Timer}
* instance is created and started.
*/
private int numScheduledTasks = 0;
/**
* The time when the last task was scheduled.
*/
private long lastTaskScheduled;
/**
* Creates a new Timer instance.
*
* @param isDeamon if true the background thread wil run as
* deamon.
*/
public Timer(boolean isDeamon) {
runAsDeamon = isDeamon;
}
/**
* Schedules the specified task for repeated fixed-delay execution,
* beginning after the specified delay. Subsequent executions take place
* at approximately regular intervals separated by the specified period.
*
* @param task task to be scheduled.
* @param delay delay in milliseconds before task is to be executed.
* @param period time in milliseconds between successive task executions.
* @throws IllegalArgumentException if delay is negative, or
* delay + System.currentTimeMillis() is negative.
* @throws IllegalStateException if task was already scheduled or
* cancelled, timer was cancelled, or timer thread terminated.
* @see java.util.Timer#schedule(java.util.TimerTask, long, long)
*/
public void schedule(Task task, long delay, long period) {
if (delay < 0)
throw new IllegalArgumentException("Negative delay.");
if (period <= 0)
throw new IllegalArgumentException("Non-positive period.");
synchronized (this) {
if (delegatee == null) {
delegatee = new java.util.Timer(runAsDeamon);
// run idle checker every second
Task idleChecker = new IdleCheckerTask();
idleChecker.setTimer(this);
delegatee.schedule(idleChecker, IDLE_TIME, CHECKER_INTERVAL);
}
delegatee.schedule(task, delay, period);
task.setTimer(this);
numScheduledTasks++;
lastTaskScheduled = System.currentTimeMillis();
}
}
/**
* Terminates this timer, discarding any currently scheduled tasks.
* Does not interfere with a currently executing task (if it exists).
* Once a timer has been terminated, its execution thread terminates
* gracefully, and no more tasks may be scheduled on it.
*
* Note that calling this method from within the run method of a
* timer task that was invoked by this timer absolutely guarantees that
* the ongoing task execution is the last task execution that will ever
* be performed by this timer.
*
*
This method may be called repeatedly; the second and subsequent
* calls have no effect.
*/
public void cancel() {
synchronized (this) {
if (delegatee != null) {
delegatee.cancel();
numScheduledTasks = 0;
delegatee = null;
}
}
}
/**
* @return true if this timer has a running backround thread
* for scheduled tasks. This method is only for test purposes.
*/
boolean isRunning() {
synchronized (this) {
return delegatee != null;
}
}
/**
* Notifies this Timer that a task has been canceled.
*/
private void taskCanceled() {
synchronized (this) {
--numScheduledTasks;
}
}
/**
* Extends the TimerTask with callback hooks to this
* Timer implementation.
*/
public static abstract class Task extends TimerTask {
/**
* The Timer instance where this Task is
* scheduled on.
*/
private Timer timer;
/**
* Sets the timer instance where this task is scheduled on.
* @param timer the timer instance.
*/
private void setTimer(Timer timer) {
this.timer = timer;
}
/**
* {@inheritDoc}
*/
public final boolean cancel() {
if (timer != null) {
timer.taskCanceled();
timer = null;
}
return super.cancel();
}
}
/**
* Checks if the enclosing timer had been idle for at least
* {@link Timer#IDLE_TIME} and cancels it in that case.
*/
private class IdleCheckerTask extends Task {
public void run() {
synchronized (Timer.this) {
if (numScheduledTasks == 0 &&
System.currentTimeMillis() > lastTaskScheduled + IDLE_TIME) {
if (delegatee != null) {
delegatee.cancel();
delegatee = null;
}
}
}
}
}
}