ScalingThreadPoolExecutor.java

/*
 * Copyright 2004-2009 the original author or authors.
 *
 * 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 org.compass.core.util.concurrent;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Extends a {@link java.util.concurrent.ThreadPoolExecutor} and gives better performance
 * when asking for the {@link #getActiveCount()}.
 *
 * @author kimchy
 */
public class ScalingThreadPoolExecutor extends ThreadPoolExecutor {
    
    /**
     * number of threads that are actively executing tasks
     */
    private final AtomicInteger activeCount = new AtomicInteger();

    public ScalingThreadPoolExecutor(int corePoolSize, int maximumPoolSize,
                                     long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
    }

    @Override
    public int getActiveCount() {
        return activeCount.get();
    }

    @Override
    protected void beforeExecute(Thread t, Runnable r) {
        activeCount.incrementAndGet();
    }

    @Override
    protected void afterExecute(Runnable r, Throwable t) {
        activeCount.decrementAndGet();
    }
}