Java tutorial
/* * 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.util.threads; import java.lang.Thread.UncaughtExceptionHandler; import java.util.concurrent.BlockingQueue; import java.util.concurrent.RejectedExecutionException; import java.util.concurrent.RejectedExecutionHandler; import java.util.concurrent.ThreadFactory; import java.util.concurrent.TimeUnit; import java.util.concurrent.atomic.AtomicInteger; import java.util.concurrent.atomic.AtomicLong; import com.sun.org.apache.commons.logging.Log; import com.sun.org.apache.commons.logging.LogFactory; /** * Same as a java.util.concurrent.ThreadPoolExecutor but implements a much more efficient * {@link #getSubmittedCount()} method, to be used to properly handle the work queue. * If a RejectedExecutionHandler is not specified a default one will be configured * and that one will always throw a RejectedExecutionException * @author fhanik * */ public class ThreadPoolExecutor extends java.util.concurrent.ThreadPoolExecutor { /** * The string manager for this package. */ private static final Log log = LogFactory.getLog(ThreadPoolExecutor.class); /** * The number of tasks submitted but not yet finished. This includes tasks * in the queue and tasks that have been handed to a worker thread but the * latter did not start executing the task yet. * This number is always greater or equal to {@link #getActiveCount()}. */ private final AtomicInteger submittedCount = new AtomicInteger(0); private final AtomicLong lastContextStoppedTime = new AtomicLong(0L); /** * Most recent time in ms when a thread decided to kill itself to avoid * potential memory leaks. Useful to throttle the rate of renewals of * threads. */ private final AtomicLong lastTimeThreadKilledItself = new AtomicLong(0L); /** * Delay in ms between 2 threads being renewed. If negative, do not renew threads. */ private long threadRenewalDelay = Constants.DEFAULT_THREAD_RENEWAL_DELAY; public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, RejectedExecutionHandler handler) { super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, handler); } public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory, RejectedExecutionHandler handler) { super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory, handler); } public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory) { super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory, new RejectHandler()); } public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) { super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, new RejectHandler()); } public long getThreadRenewalDelay() { return threadRenewalDelay; } public void setThreadRenewalDelay(long threadRenewalDelay) { this.threadRenewalDelay = threadRenewalDelay; } @Override protected void afterExecute(Runnable r, Throwable t) { submittedCount.decrementAndGet(); if (t == null) { stopCurrentThreadIfNeeded(); } } /** * If the current thread was started before the last time when a context was * stopped, an exception is thrown so that the current thread is stopped. */ protected void stopCurrentThreadIfNeeded() { if (currentThreadShouldBeStopped()) { long lastTime = lastTimeThreadKilledItself.longValue(); if (lastTime + threadRenewalDelay < System.currentTimeMillis()) { if (lastTimeThreadKilledItself.compareAndSet(lastTime, System.currentTimeMillis() + 1)) { // OK, it's really time to dispose of this thread final String msg = "Parando hilo " + Thread.currentThread().getName() + " para evita fallos potenciales de memoria tras haberse parado un contexto."; Thread.currentThread().setUncaughtExceptionHandler(new UncaughtExceptionHandler() { @Override public void uncaughtException(Thread t, Throwable e) { // yes, swallow the exception log.debug(msg); } }); throw new RuntimeException(msg); } } } } protected boolean currentThreadShouldBeStopped() { if (threadRenewalDelay >= 0 && Thread.currentThread() instanceof TaskThread) { TaskThread currentTaskThread = (TaskThread) Thread.currentThread(); if (currentTaskThread.getCreationTime() < this.lastContextStoppedTime.longValue()) { return true; } } return false; } public int getSubmittedCount() { return submittedCount.get(); } /** * {@inheritDoc} */ @Override public void execute(Runnable command) { execute(command, 0, TimeUnit.MILLISECONDS); } /** * Executes the given command at some time in the future. The command * may execute in a new thread, in a pooled thread, or in the calling * thread, at the discretion of the <tt>Executor</tt> implementation. * If no threads are available, it will be added to the work queue. * If the work queue is full, the system will wait for the specified * time and it throw a RejectedExecutionException if the queue is still * full after that. * * @param command the runnable task * @throws RejectedExecutionException if this task cannot be * accepted for execution - the queue is full * @throws NullPointerException if command or unit is null */ public void execute(Runnable command, long timeout, TimeUnit unit) { submittedCount.incrementAndGet(); try { super.execute(command); } catch (RejectedExecutionException rx) { if (super.getQueue() instanceof TaskQueue) { final TaskQueue queue = (TaskQueue) super.getQueue(); try { if (!queue.force(command, timeout, unit)) { submittedCount.decrementAndGet(); throw new RejectedExecutionException("Queue capacity is full."); } } catch (InterruptedException x) { submittedCount.decrementAndGet(); Thread.interrupted(); throw new RejectedExecutionException(x); } } else { submittedCount.decrementAndGet(); throw rx; } } } public void contextStopping() { this.lastContextStoppedTime.set(System.currentTimeMillis()); // save the current pool parameters to restore them later int savedCorePoolSize = this.getCorePoolSize(); TaskQueue taskQueue = getQueue() instanceof TaskQueue ? (TaskQueue) getQueue() : null; if (taskQueue != null) { // note by slaurent : quite oddly threadPoolExecutor.setCorePoolSize // checks that queue.remainingCapacity()==0. I did not understand // why, but to get the intended effect of waking up idle threads, I // temporarily fake this condition. taskQueue.setForcedRemainingCapacity(Integer.valueOf(0)); } // setCorePoolSize(0) wakes idle threads this.setCorePoolSize(0); // wait a little so that idle threads wake and poll the queue again, // this time always with a timeout (queue.poll() instead of // queue.take()) // even if we did not wait enough, TaskQueue.take() takes care of timing // out, so that we are sure that all threads of the pool are renewed in // a limited time, something like // (threadKeepAlive + longest request time) try { Thread.sleep(200L); } catch (InterruptedException e) { // yes, ignore } if (taskQueue != null) { // ok, restore the state of the queue and pool taskQueue.setForcedRemainingCapacity(null); } this.setCorePoolSize(savedCorePoolSize); } private static class RejectHandler implements RejectedExecutionHandler { @Override public void rejectedExecution(Runnable r, java.util.concurrent.ThreadPoolExecutor executor) { throw new RejectedExecutionException(); } } }