concurrencyexample.java

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/**
 *  Concurrency utilities (JSR-166) example
 **/
package threadpool;

import java.net.*;
import java.io.*;
import java.util.concurrent.*;

public class ConcurrencyExample {
  private final static int MAX_THREADS = 2;

  private final ServerSocket serverSocket;
  private final ThreadPoolExecutor pool;
  private final ArrayBlockingQueue<Runnable> workQueue;

  /**
   *  Constructor
   **/
  public ConcurrencyExample(int port, int poolSize) throws IOException {
    /*  Create a new ServerSocket to listen for incoming connections  */
    serverSocket = new ServerSocket(port);

    /*  In order to create a pool of threads we must first have a queue
     *  that will be used to hold the work tasks before they are executed
     *  For this example we use a ArrayBlockingQueue that can hold the 
     *  same number of tasks as we have maximum threads
     */
    workQueue = new ArrayBlockingQueue<Runnable>(MAX_THREADS);

    /*  Now create the ThreadPool.  The initial and maximum number of 
     *  threads are the same in this example
     */
    pool = new ThreadPoolExecutor(MAX_THREADS, MAX_THREADS,
      60, TimeUnit.SECONDS, workQueue);
  }

  /**
   *  Service requests
   **/
  public void serviceRequests() {
    int count = 1;
    int qLength = 0;

    try {
      for (;;) {
        if ((qLength = workQueue.size()) > 0)
          System.out.println("Queue length is " + qLength);

        pool.execute(new ConnectionHandler(serverSocket.accept(), count++));
      }
    } catch (IOException ioe) {
      System.out.println("IO Error in ConnectionHandler: " + ioe.getMessage());
      pool.shutdown();
    }
  }

  /**
   *  Main entry point
   *
   * @param args Command line arguments
   **/
  public static void main(String[] args) {
    System.out.println("Listening for connections...");
    ConcurrencyExample ce = null;

    try {
      ce = new ConcurrencyExample(8100, 4);
      ce.serviceRequests();
    } catch (IOException ioe) {
      System.out.println("IO Error creating listener: " + ioe.getMessage());
    }
  }
}