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A set of utilities and tools to speed up and ease programming in Java.
There is a newer version: 0.5
/*
 * (c) 2005 David B. Bracewell
 *
 * 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 com.davidbracewell.concurrent;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Semaphore;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * A ThreadPoolExecutor which blocks when the queue of items to be executed becomes full.
 *
 * @author David B. Bracewell
 */
public class BlockingThreadPoolExecutor extends ThreadPoolExecutor {

  private final AtomicInteger tasksInProgress = new AtomicInteger();
  private final Semaphore semaphore;
  private final Lock lock = new ReentrantLock();
  private final Condition done = lock.newCondition();
  private boolean isDone = false;

  /**
   * Creates an executor with a given core and max pool size and maximum number of items to have waiting in the queue.
   * All threads will execute until completion or failure.
   *
   * @param corePoolSize    core pool size
   * @param maximumPoolSize max pools size
   * @param maxQueueSize    max number of items to have waiting (good for memory)
   */
  public BlockingThreadPoolExecutor(int corePoolSize, int maximumPoolSize, int maxQueueSize) {
    this(corePoolSize, maximumPoolSize, maxQueueSize, 0, TimeUnit.DAYS);
  }

  /**
   * Creates an executor with a given core and max pool size and maximum number of items to have waiting in the queue.
   * All threads will execute until completion or the keep alive time runs out.
   *
   * @param corePoolSize    core pool size
   * @param maximumPoolSize max pools size
   * @param maxQueueSize    max number of items to have waiting (good for memory)
   * @param keepAliveTime   the amount of time to let the thread run
   * @param unit            the time unit associated with keepAliveTime
   */
  public BlockingThreadPoolExecutor(int corePoolSize, int maximumPoolSize, int maxQueueSize, long keepAliveTime, TimeUnit unit) {
    super(corePoolSize, maximumPoolSize, keepAliveTime, unit, new ArrayBlockingQueue(maxQueueSize));
    this.semaphore = new Semaphore(maxQueueSize);
  }

  /**
   * @return The number of tasks in progress
   */
  public int tasksInProgress() {
    return tasksInProgress.get();
  }

  @Override
  public void execute(Runnable command) {
    tasksInProgress.incrementAndGet();
    try {
      semaphore.acquireUninterruptibly();
      super.execute(command);
    } catch (Error e) {
      tasksInProgress.decrementAndGet();
    }
  }


  @Override
  protected void afterExecute(Runnable r, Throwable t) {
    semaphore.release();
    super.afterExecute(r, t);

    synchronized (this) {
      tasksInProgress.decrementAndGet();
      if (tasksInProgress.intValue() == 0) {
        lock.lock();
        try {
          isDone = true;
          done.signalAll();
        } finally {
          lock.unlock();
        }
      }
    }

  }

  /**
   * Awaits termination of the threads
   *
   * @throws InterruptedException The executor was interrupted
   */
  public void awaitTermination() throws InterruptedException {
    lock.lock();
    try {
      while (!isDone) {
        done.await();
      }
    } finally {
      isDone = false;
      lock.unlock();
    }
  }

}//END OF BlockingThreadPoolExecutor