EvictionTimer.java
/*
* 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.tomcat.dbcp.pool2.impl;
import java.lang.ref.WeakReference;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.HashMap;
import java.util.Map.Entry;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
/**
* Provides a shared idle object eviction timer for all pools.
* <p>
* This class is currently implemented using {@link ScheduledThreadPoolExecutor}. This implementation may change in any
* future release. This class keeps track of how many pools are using it. If no pools are using the timer, it is
* cancelled. 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>
* <p>
* This class is intended to be thread-safe.
* </p>
*
* @since 2.0
*/
class EvictionTimer {
/** Executor instance */
private static ScheduledThreadPoolExecutor executor; //@GuardedBy("EvictionTimer.class")
/** Keys are weak references to tasks, values are runners managed by executor. */
private static final HashMap<WeakReference<Runnable>, WeakRunner> taskMap = new HashMap<>(); // @GuardedBy("EvictionTimer.class")
/** Prevents instantiation */
private EvictionTimer() {
// Hide the default constructor
}
/**
* @since 2.4.3
*/
@Override
public String toString() {
final StringBuilder builder = new StringBuilder();
builder.append("EvictionTimer []");
return builder.toString();
}
/**
* Adds the specified eviction task to the timer. Tasks that are added with
* a call to this method *must* call {@link
* #cancel(org.apache.tomcat.dbcp.pool2.impl.BaseGenericObjectPool.Evictor, long, TimeUnit, boolean)}
* 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(
final BaseGenericObjectPool<?>.Evictor task, final long delay, final long period) {
if (null == executor) {
executor = new ScheduledThreadPoolExecutor(1, new EvictorThreadFactory());
executor.setRemoveOnCancelPolicy(true);
executor.scheduleAtFixedRate(new Reaper(), delay, period, TimeUnit.MILLISECONDS);
}
final WeakReference<Runnable> ref = new WeakReference<Runnable>(task);
final WeakRunner runner = new WeakRunner(ref);
final ScheduledFuture<?> scheduledFuture =
executor.scheduleWithFixedDelay(runner, delay, period, TimeUnit.MILLISECONDS);
task.setScheduledFuture(scheduledFuture);
taskMap.put(ref, runner);
}
/**
* Removes the specified eviction task from the timer.
*
* @param evictor Task to be cancelled.
* @param timeout If the associated executor is no longer required, how
* long should this thread wait for the executor to
* terminate?
* @param unit The units for the specified timeout.
* @param restarting The state of the evictor.
*/
static synchronized void cancel(
final BaseGenericObjectPool<?>.Evictor evictor, final long timeout, final TimeUnit unit, final boolean restarting) {
if (evictor != null) {
evictor.cancel();
remove(evictor);
}
if (!restarting && executor != null) {
if (taskMap.isEmpty()) {
executor.shutdown();
try {
executor.awaitTermination(timeout, unit);
} catch (final InterruptedException e) {
// Swallow
// Significant API changes would be required to propagate this
}
executor.setCorePoolSize(0);
executor = null;
}
}
}
/**
* Removes evictor from the task set and executor.
* Only called when holding the class lock.
*
* @param evictor Eviction task to remove
*/
private static void remove(final BaseGenericObjectPool<?>.Evictor evictor) {
for (Entry<WeakReference<Runnable>, WeakRunner> entry : taskMap.entrySet()) {
if (entry.getKey().get() == evictor) {
executor.remove(entry.getValue());
taskMap.remove(entry.getKey());
break;
}
}
}
/**
* @return the number of eviction tasks under management.
*/
static synchronized int getNumTasks() {
return taskMap.size();
}
/**
* Thread factory that creates a daemon thread, with the context class loader from this class.
*/
private static class EvictorThreadFactory implements ThreadFactory {
@Override
public Thread newThread(final Runnable runnable) {
final Thread thread = new Thread(null, runnable, "commons-pool-evictor-thread");
thread.setDaemon(true); // POOL-363 - Required for applications using Runtime.addShutdownHook().
AccessController.doPrivileged(new PrivilegedAction<Void>() {
@Override
public Void run() {
thread.setContextClassLoader(EvictorThreadFactory.class.getClassLoader());
return null;
}
});
return thread;
}
}
/**
* Task that removes references to abandoned tasks and shuts
* down the executor if there are no live tasks left.
*/
private static class Reaper implements Runnable {
@Override
public void run() {
synchronized (EvictionTimer.class) {
for (Entry<WeakReference<Runnable>, WeakRunner> entry : taskMap.entrySet()) {
if (entry.getKey().get() == null) {
executor.remove(entry.getValue());
taskMap.remove(entry.getKey());
}
}
if (taskMap.isEmpty() && executor != null) {
executor.shutdown();
executor.setCorePoolSize(0);
executor = null;
}
}
}
}
/**
* Runnable that runs the referent of a weak reference. When the referent is no
* no longer reachable, run is no-op.
*/
private static class WeakRunner implements Runnable {
private final WeakReference<Runnable> ref;
/**
* Constructs a new instance to track the given reference.
*
* @param ref the reference to track.
*/
private WeakRunner(final WeakReference<Runnable> ref) {
this.ref = ref;
}
@Override
public void run() {
final Runnable task = ref.get();
if (task != null) {
task.run();
} else {
executor.remove(this);
taskMap.remove(ref);
}
}
}
}