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/*
* 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.util.Collection;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.TimeUnit;
/**
* As task queue specifically designed to run with a thread pool executor.
* The task queue is optimised to properly utilize threads within
* a thread pool executor. If you use a normal queue, the executor will spawn threads
* when there are idle threads and you wont be able to force items unto the queue itself
* @author fhanik
*
*/
public class TaskQueue extends LinkedBlockingQueue<Runnable> {
private static final long serialVersionUID = 1L;
private ThreadPoolExecutor parent = null;
// no need to be volatile, the one times when we change and read it occur in
// a single thread (the one that did stop a context and fired listeners)
private Integer forcedRemainingCapacity = null;
public TaskQueue() {
super();
}
public TaskQueue(int capacity) {
super(capacity);
}
public TaskQueue(Collection<? extends Runnable> c) {
super(c);
}
public void setParent(ThreadPoolExecutor tp) {
parent = tp;
}
public boolean force(Runnable o) {
if ( parent.isShutdown() ) throw new RejectedExecutionException("Executor not running, can't force a command into the queue");
return super.offer(o); //forces the item onto the queue, to be used if the task is rejected
}
public boolean force(Runnable o, long timeout, TimeUnit unit) throws InterruptedException {
if ( parent.isShutdown() ) throw new RejectedExecutionException("Executor not running, can't force a command into the queue");
return super.offer(o,timeout,unit); //forces the item onto the queue, to be used if the task is rejected
}
@Override
public boolean offer(Runnable o) {
//we can't do any checks
if (parent==null) return super.offer(o);
//we are maxed out on threads, simply queue the object
if (parent.getPoolSize() == parent.getMaximumPoolSize()) return super.offer(o);
//we have idle threads, just add it to the queue
if (parent.getSubmittedCount()<(parent.getPoolSize())) return super.offer(o);
//if we have less threads than maximum force creation of a new thread
if (parent.getPoolSize()<parent.getMaximumPoolSize()) return false;
//if we reached here, we need to add it to the queue
return super.offer(o);
}
@Override
public Runnable poll(long timeout, TimeUnit unit)
throws InterruptedException {
Runnable runnable = super.poll(timeout, unit);
if (runnable == null && parent != null) {
// the poll timed out, it gives an opportunity to stop the current
// thread if needed to avoid memory leaks.
parent.stopCurrentThreadIfNeeded();
}
return runnable;
}
@Override
public Runnable take() throws InterruptedException {
if (parent != null && parent.currentThreadShouldBeStopped()) {
return poll(parent.getKeepAliveTime(TimeUnit.MILLISECONDS),
TimeUnit.MILLISECONDS);
// yes, this may return null (in case of timeout) which normally
// does not occur with take()
// but the ThreadPoolExecutor implementation allows this
}
return super.take();
}
@Override
public int remainingCapacity() {
if (forcedRemainingCapacity != null) {
// ThreadPoolExecutor.setCorePoolSize checks that
// remainingCapacity==0 to allow to interrupt idle threads
// I don't see why, but this hack allows to conform to this
// "requirement"
return forcedRemainingCapacity.intValue();
}
return super.remainingCapacity();
}
public void setForcedRemainingCapacity(Integer forcedRemainingCapacity) {
this.forcedRemainingCapacity = forcedRemainingCapacity;
}
}
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