// Class ThreadPool implements a thread pool.
import java.util.*;
import gov.nasa.jpf.jvm.Verify;

public class ThreadPool {
  private LinkedList jobQueue = new LinkedList();
  private Object cond = new Object();
  Thread[] t;
  int numThreads;
  private int activeThreads = numThreads;
  private boolean done = false;

  // Constructor pre-spawn threads for the pool
  public ThreadPool(int numThreads) {
  	this.numThreads = numThreads;
    t = new Thread[numThreads];
    for(int i = 0; i < numThreads; i++) {
      t[i] = new PoolThread();
      t[i].start();
    }
  }
  
  // Method empty checks to see if the job queue is empty
  public synchronized boolean QueueEmpty(){
    return(jobQueue.isEmpty());
    }
  // Method addJob is obtained by applying the translation given in [8]
  // directly to coarse-grained solution <jobQueue.enqueue(job)>
  public synchronized void addJob(GenericJob job) {
    jobQueue.add(job);
    notify();
  }

  private synchronized GenericJob getJob() {
    while(jobQueue.isEmpty()) {
        activeThreads--;
	  if(activeThreads==0)
	    {done=true; notifyAll();}
        else{
	try {wait();} catch (InterruptedException e){}
	}
	if(done) return null;
	activeThreads++;
    }
    return (GenericJob) jobQueue.removeFirst();
  }

   // Implementation of a job thread  (refer to c1 in Section 2.4)
   private class PoolThread extends Thread {
     public void run() {
      GenericJob job;
      while(true) {
      	job = getJob();
	if (job==null) 
	break;
      	while(job.execute());
      }
     }
  }
}