/*
 * 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.commons.pool.impl;

import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Timer;
import java.util.TimerTask;

 Provides a shared idle object eviction timer for all pools. This class wraps the standard 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. 

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>
 * 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 /** Timer instance */
    private static Timer _timer; //@GuardedBy("this")
    
    
Static usage count tracker /** Static usage count tracker */
    private static int _usageCount; //@GuardedBy("this")

    
Prevent instantiation /** 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 cancel(TimerTask) to cancel the task to prevent memory and/or thread leaks in application server environments. 
Params:
task –      Task to be scheduled
delay –     Delay in milliseconds before task is executed
period –    Time in milliseconds between executions/**
     * 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 = 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.
Params:
task –      Task to be scheduled/**
     * 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;
        }
    }
    
    
PrivilegedAction used to get the ContextClassLoader /** 
     * {@link PrivilegedAction} used to get the ContextClassLoader
     */
    private static class PrivilegedGetTccl implements PrivilegedAction<ClassLoader> {

        
{@inheritDoc}
/** 
         * {@inheritDoc}
         */
        public ClassLoader run() {
            return Thread.currentThread().getContextClassLoader();
        }
    }

    
PrivilegedAction used to set the ContextClassLoader /** 
     * {@link PrivilegedAction} used to set the ContextClassLoader
     */
    private static class PrivilegedSetTccl implements PrivilegedAction<ClassLoader> {

        
ClassLoader /** ClassLoader */
        private final ClassLoader cl;

        
Create a new PrivilegedSetTccl using the given classloader
Params:
cl – ClassLoader to use/**
         * Create a new PrivilegedSetTccl using the given classloader
         * @param cl ClassLoader to use
         */
        PrivilegedSetTccl(ClassLoader cl) {
            this.cl = cl;
        }

        
{@inheritDoc}
/** 
         * {@inheritDoc}
         */
        public ClassLoader run() {
            Thread.currentThread().setContextClassLoader(cl);
            return null;
        }
    }

}