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package com.techempower.thread;

import java.util.concurrent.*;
import java.util.concurrent.locks.*;

/**
 * A simple specialization of ScheduledThreadPoolExecutor that allows pausing.
 * This is basically lifted from the Javadocs for ThreadPoolExecutor.
 */
public class PausableScheduledThreadPoolExecutor
  extends    ScheduledThreadPoolExecutor 
{

  //
  // Member variables.
  //
  
  private       boolean paused;
  private final ReentrantLock pauseLock = new ReentrantLock();
  private final Condition unpaused = this.pauseLock.newCondition();
  
  //
  // Member methods.
  //
  
  /**
   * Constructor.
   */
  public PausableScheduledThreadPoolExecutor(int coreThreads)
  {
    super(coreThreads);
  }

  /**
   * Overload the Executor's beforeExecute method to allow execution to be
   * paused.
   */
  @Override
  protected void beforeExecute(Thread t, Runnable r) 
  {
    super.beforeExecute(t, r);
    this.pauseLock.lock();
    try
    {
      while (this.paused)
      {
        this.unpaused.await();
      }
    }
    catch (InterruptedException ie)
    {
      t.interrupt();
    }
    finally
    {
      this.pauseLock.unlock();
    }
  }

  /**
   * Pause the execution of tasks.
   */
  public void pause()
  {
    this.pauseLock.lock();
    try
    {
      this.paused = true;
    }
    finally
    {
      this.pauseLock.unlock();
    }
  }

  /**
   * Resume the execution of tasks.
   */
  public void resume()
  {
    this.pauseLock.lock();
    try
    {
      this.paused = false;
      this.unpaused.signalAll();
    }
    finally
    {
      this.pauseLock.unlock();
    }
  }

  /**
   * Is execution paused?
   */
  public boolean isPaused()
  {
    return this.paused;
  }

}