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This is the ehcache core module. Pair it with other modules for added functionality.
/**
* Copyright 2003-2010 Terracotta, Inc.
*
* Licensed 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 net.sf.ehcache.constructs.nonstop;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.WeakHashMap;
import java.util.Map.Entry;
import java.util.concurrent.Callable;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicReference;
/**
* A thread pool that creates another thread pool per requesting thread.
*
* @author Abhishek Sanoujam
*
*/
public class NonstopThreadPool {
private static final long POLL_TIME_MILLIS = 1000;
private static final long NUM_OF_POLLS_BEFORE_CHECK_THREADS_ALIVE = 100;
private final ThreadFactory threadFactory;
private final Map workers = new WeakHashMap();
private final Object workersLock = new Object();
private final AtomicReference state = new AtomicReference(State.RUNNING);
private final ReferenceQueue gcedThreadsReferenceQueue = new ReferenceQueue();
private final ThreadLocal workerThreadLocal = new ThreadLocal() {
@Override
protected WorkerThreadLocal initialValue() {
WorkerThreadLocal local = new WorkerThreadLocal(threadFactory, gcedThreadsReferenceQueue);
synchronized (workersLock) {
if (state.get() == State.SHUTDOWN) {
rejectExecutionAfterShutdown();
}
workers.put(Thread.currentThread(), local);
}
return local;
}
};
/**
* Constructor accepting the threadFactory
*
* @param threadFactory
*/
public NonstopThreadPool(ThreadFactory threadFactory) {
this.threadFactory = threadFactory;
startReaperThread();
}
private void startReaperThread() {
Thread reaperThread = new Thread(new ReaperThread(), "non stop reaper thread");
reaperThread.start();
}
/**
* class which manages the alive non stop threads
*
* @author Raghvendra Singh
*
*/
private class ReaperThread implements Runnable {
public void run() {
int pollCount = 0;
while (state.get() != State.SHUTDOWN) {
WeakWorkerReference gcedThreadReference = null;
try {
gcedThreadReference = (WeakWorkerReference) gcedThreadsReferenceQueue.remove(POLL_TIME_MILLIS);
// check if threads are alive every 10 loop and shut them down
if (++pollCount == NUM_OF_POLLS_BEFORE_CHECK_THREADS_ALIVE) {
Set deadThreads = new HashSet();
pollCount = 0;
synchronized (workersLock) {
for (Entry entry : workers.entrySet()) {
if (!entry.getKey().isAlive()) {
entry.getValue().shutdownNow();
deadThreads.add(entry.getKey());
}
}
for (Thread th : deadThreads) {
workers.remove(th);
}
}
}
} catch (InterruptedException e) {
// ignored
}
if (gcedThreadReference != null) {
gcedThreadReference.getWorker().shutdownNow();
}
}
}
}
private void rejectExecutionAfterShutdown() {
throw new RejectedExecutionException("The thread pool has already shut down.");
}
/**
* Submit a callable task to be executed by the thread pool
*
* @param
* @param task
* @return Future of the task
*/
public Future submit(Callable task) {
if (task == null) {
throw new NullPointerException("Task cannot be null");
}
return workerThreadLocal.get().submit(task);
}
/**
* Shuts down the thread pool
*/
public void shutdownNow() {
state.set(State.SHUTDOWN);
synchronized (workersLock) {
for (WorkerThreadLocal worker : workers.values()) {
worker.shutdownNow();
}
}
}
/**
* Private class
*
* @author Abhishek Sanoujam
*
*/
private static class WorkerThreadLocal {
private final Worker worker;
private final WeakWorkerReference appThreadReference;
public WorkerThreadLocal(ThreadFactory threadFactory, ReferenceQueue gcedThreadsReferenceQueue) {
this.worker = new Worker();
threadFactory.newThread(worker).start();
this.appThreadReference = new WeakWorkerReference(this.worker, Thread.currentThread(), gcedThreadsReferenceQueue);
}
public void shutdownNow() {
worker.shutdownNow();
}
public Future submit(Callable task) {
FutureTask ftask = new FutureTask(task);
worker.addTask(ftask);
return ftask;
}
}
/**
* Worker class
*
* @author Abhishek Sanoujam
*
*/
private static class Worker implements Runnable {
private final WorkerTaskHolder workerTaskHolder;
private volatile boolean shutdown;
private volatile Thread workerThread;
private volatile boolean runningTask;
public Worker() {
this.workerTaskHolder = new WorkerTaskHolder();
}
public void run() {
workerThread = Thread.currentThread();
while (!shutdown) {
waitUntilTaskAvailable();
if (shutdown) {
break;
}
Runnable task = workerTaskHolder.consumeTask();
if (task != null) {
synchronized (this) {
runningTask = true;
if (shutdown) {
break;
}
}
task.run();
synchronized (this) {
runningTask = false;
}
}
}
}
public void shutdownNow() {
shutdown = true;
synchronized (this) {
this.notifyAll();
if (runningTask) {
// interrupt if running task already
workerThread.interrupt();
}
}
}
public void addTask(Runnable runnable) {
synchronized (this) {
workerTaskHolder.addTask(runnable);
this.notifyAll();
}
}
private void waitUntilTaskAvailable() {
synchronized (this) {
while (!workerTaskHolder.isTaskAvailable()) {
if (shutdown) {
return;
}
try {
this.wait();
} catch (InterruptedException e) {
// ignore
}
}
}
}
}
/**
* Private class maintaining single pending task
*
* @author Abhishek Sanoujam
*
*/
private static class WorkerTaskHolder {
private Runnable task;
public synchronized void addTask(Runnable runnable) {
// keep only 1 pending task
this.task = runnable;
}
public synchronized Runnable consumeTask() {
if (task == null) {
return null;
}
Runnable rv = task;
task = null;
return rv;
}
public synchronized boolean isTaskAvailable() {
return task != null;
}
}
/**
* private class maintaining the app thread and its corresponding worker thread
*
* @author Raghvendra Singh
*/
private static class WeakWorkerReference extends WeakReference {
private final Worker worker;
public WeakWorkerReference(Worker worker, Thread referent, ReferenceQueue q) {
super(referent, q);
this.worker = worker;
}
public Worker getWorker() {
return this.worker;
}
}
/**
* Private enum maintaining state of the pool
*
* @author Abhishek Sanoujam
*
*/
private static enum State {
RUNNING, SHUTDOWN;
}
}