/* | |
* 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.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.commons.pool2.impl.BaseGenericObjectPool.Evictor, long, TimeUnit)} | |
* 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<>(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 && 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((PrivilegedAction<Void>) () -> { | |
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); | |
} | |
} | |
} | |
} |