/*
* 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.datanucleus.store.rdbms.datasource.dbcp.pool.impl;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Timer;
import java.util.TimerTask;
/**
* <p>
* Provides a shared idle object eviction timer for all pools. This class wraps
* the standard {@link Timer} and keeps track of how many pools are using it.
* If no pools are using the timer, it is canceled. This prevents a thread
* being left running which, in application server environments, can lead to
* memory leads and/or prevent applications from shutting down or reloading
* cleanly.
* </p>
* <p>
* This class has package scope to prevent its inclusion in the pool public API.
* The class declaration below should *not* be changed to public.
* </p>
*/
class EvictionTimer {
/** Timer instance */
private static Timer _timer; //@GuardedBy("this")
/** Static usage count tracker */
private static int _usageCount; //@GuardedBy("this")
/** Prevent instantiation */
private EvictionTimer() {
// Hide the default constuctor
}
/**
* Add the specified eviction task to the timer. Tasks that are added with a
* call to this method *must* call {@link #cancel(TimerTask)} to cancel the
* task to prevent memory and/or thread leaks in application server
* environments.
* @param task Task to be scheduled
* @param delay Delay in milliseconds before task is executed
* @param period Time in milliseconds between executions
*/
static synchronized void schedule(TimerTask task, long delay, long period) {
if (null == _timer) {
// Force the new Timer thread to be created with a context class
// loader set to the class loader that loaded this library
ClassLoader ccl = (ClassLoader) AccessController.doPrivileged(
new PrivilegedGetTccl());
try {
AccessController.doPrivileged(new PrivilegedSetTccl(
EvictionTimer.class.getClassLoader()));
_timer = new Timer(true);
} finally {
AccessController.doPrivileged(new PrivilegedSetTccl(ccl));
}
}
_usageCount++;
_timer.schedule(task, delay, period);
}
/**
* Remove the specified eviction task from the timer.
* @param task Task to be scheduled
*/
static synchronized void cancel(TimerTask task) {
task.cancel();
_usageCount--;
if (_usageCount == 0) {
_timer.cancel();
_timer = null;
}
}
/**
* {@link PrivilegedAction} used to get the ContextClassLoader
*/
private static class PrivilegedGetTccl implements PrivilegedAction {
/**
* {@inheritDoc}
*/
public Object run() {
return Thread.currentThread().getContextClassLoader();
}
}
/**
* {@link PrivilegedAction} used to set the ContextClassLoader
*/
private static class PrivilegedSetTccl implements PrivilegedAction {
/** ClassLoader */
private final ClassLoader cl;
/**
* Create a new PrivilegedSetTccl using the given classloader
* @param cl ClassLoader to use
*/
PrivilegedSetTccl(ClassLoader cl) {
this.cl = cl;
}
/**
* {@inheritDoc}
*/
public Object run() {
Thread.currentThread().setContextClassLoader(cl);
return null;
}
}
}