// time_mp4.java  four computational threads for four processors

import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;

public class time_mp4
{
  static final int nthread = 4;
  int cfctr = 4000000; // computation iterations for delay
  static double cpu_start[] = new double[nthread]; // for each thread
  static double cpu_end[] = new double[nthread];
  Thread t[] = new Thread[nthread];

  time_mp4()
  {
    System.out.println("time_mp4 constructor starting");
    for(int i=0; i<nthread; i++) t[i] = new MyThread(i);
    for(int i=0; i<nthread; i++) t[i].start();
    try
    {
      for(int i=0; i<nthread; i++) t[i].join();
    }
    catch(InterruptedException e)
    {
    }
    System.out.println("time_mp4 constructor ending");
  } // end time_mp4 constructor
  
  class MyThread extends Thread
  {
    int id;
    
    MyThread(int who)
    {
      id = who;
    } // end MyThread constructor
    
    public void run()
    {
      double x, y, z, th_end, tb_end;
      long th_start, tb_start;
      ThreadMXBean tb = ManagementFactory.getThreadMXBean();

      cpu_start[id] = tb.getCurrentThreadCpuTime()/1.0E9;

      try
      {
        for(int i=0; i<2; i++)
        {
          z = 0.001;
          System.out.println("id="+id+", iteration="+i);

          sleep(0); // this releases so other threads can run
          for(int j=0; j<cfctr; j++) // do parallel computation
	  {
	      y = Math.exp(Math.sin(z)-Math.cos(z));
              x = Math.sqrt(Math.sqrt(y));
              z = z + x;
	  }
        }
      }
      catch(InterruptedException e)
      {
      }
      cpu_end[id] = tb.getCurrentThreadCpuTime()/1.0E9;
      System.out.println("thread "+id+" ends");
    } // end Run
  } // end class MyThread
  
  static public void main(String[] args)
  {
    double wall_start; // local
    double wall_end;
    double total_cpu, diff;

    System.out.println("time_mp4 main starting");
    wall_start = System.currentTimeMillis()/1000.0;
    new time_mp4();
    wall_end = System.currentTimeMillis()/1000.0;
    System.out.println("start="+wall_start+", end="+wall_end+", ran "+
                       (wall_end-wall_start)+" seconds");

    total_cpu = 0.0;
    for(int i=0; i<nthread; i++)
    {
      diff = cpu_end[i]-cpu_start[i];
      total_cpu += diff;
      System.out.println("id="+i+" cpu_start="+cpu_start[i]+
                         ", cpu_end="+cpu_end[i]+" ran "+
                         diff+" seconds");
    }
    System.out.println("total wall time="+(wall_end-wall_start)+" seconds");
    System.out.println("total, all threads, cpu tine="+total_cpu+" seconds");
    System.out.println("average number of cpu's used "+
                       (total_cpu/(wall_end-wall_start)));
    System.out.println("time_mp4 main ending");
  } // end main
} // end class time_mp4