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//******************************************************************************
//
// File: PiSmp3.java
// Package: edu.rit.smp.monte
// Unit: Class edu.rit.smp.monte.PiSmp3
//
// This Java source file is copyright (C) 2008 by Alan Kaminsky. All rights
// reserved. For further information, contact the author, Alan Kaminsky, at
// ark@cs.rit.edu.
//
// This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
// software; you can redistribute it and/or modify it under the terms of the GNU
// General Public License as published by the Free Software Foundation; either
// version 3 of the License, or (at your option) any later version.
//
// PJ is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
// A PARTICULAR PURPOSE. See the GNU General Public License for more details.
//
// Linking this library statically or dynamically with other modules is making a
// combined work based on this library. Thus, the terms and conditions of the
// GNU General Public License cover the whole combination.
//
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent modules, and
// to copy and distribute the resulting executable under terms of your choice,
// provided that you also meet, for each linked independent module, the terms
// and conditions of the license of that module. An independent module is a
// module which is not derived from or based on this library. If you modify this
// library, you may extend this exception to your version of the library, but
// you are not obligated to do so. If you do not wish to do so, delete this
// exception statement from your version.
//
// A copy of the GNU General Public License is provided in the file gpl.txt. You
// may also obtain a copy of the GNU General Public License on the World Wide
// Web at http://www.gnu.org/licenses/gpl.html.
//
//******************************************************************************
package edu.rit.smp.monte;
//import edu.rit.pj.Comm;
import edu.rit.pj.LongForLoop;
import edu.rit.pj.ParallelTeam;
import edu.rit.pj.ParallelRegion;
import edu.rit.pj.reduction.SharedLong;
import edu.rit.util.Random;
/**
* Class PiSmp3 is an SMP parallel program that calculates an approximate value
* for π using a Monte Carlo technique. The program generates a number of
* random points in the unit square (0,0) to (1,1) and counts how many of them
* lie within a circle of radius 1 centered at the origin. The fraction of the
* points within the circle is approximately π/4.
* <P>
* Usage: java -Dpj.nt=<I>K</I> edu.rit.smp.monte.PiSmp3 <I>seed</I> <I>N</I>
* <BR><I>K</I> = Number of parallel threads
* <BR><I>seed</I> = Random seed
* <BR><I>N</I> = Number of random points
* <P>
* The computation is performed in parallel in multiple threads. The program
* uses class edu.rit.util.Random for its pseudorandom number generator. To
* improve performance, each thread has its own pseudorandom number generator,
* and the program uses the reduction pattern to determine the count. The
* program uses the "sequence splitting" technique with the pseudorandom number
* generators to yield results identical to the sequential version. The program
* measures the computation's running time.
*
* @author Alan Kaminsky
* @version 29-Feb-2008
*/
public class PiSmp3
{
// Prevent construction.
private PiSmp3()
{
}
// Program shared variables.
// Command line arguments.
static long seed;
static long N;
// Number of points within the unit circle.
static SharedLong count;
// Main program.
/**
* Main program.
*/
public static void main
(String[] args)
throws Exception
{
//Comm.init (args);
// Start timing.
long time = -System.currentTimeMillis();
// Validate command line arguments.
if (args.length != 2) usage();
seed = Long.parseLong (args[0]);
N = Long.parseLong (args[1]);
// Generate n random points in the unit square, count how many are in
// the unit circle.
count = new SharedLong (0);
new ParallelTeam().execute (new ParallelRegion()
{
public void run() throws Exception
{
execute (0, N-1, new LongForLoop()
{
// Set up per-thread PRNG and counter.
Random prng_thread = Random.getInstance (seed);
long count_thread = 0;
// Extra padding to avert cache interference.
long p0, p1, p2, p3, p4, p5, p6, p7;
long p8, p9, pa, pb, pc, pd, pe, pf;
// Parallel loop body.
public void run (long first, long last)
{
// Skip PRNG ahead to index <first>.
prng_thread.setSeed (seed);
prng_thread.skip (2 * first);
// Generate random points.
for (long i = first; i <= last; ++ i)
{
double x = prng_thread.nextDouble();
double y = prng_thread.nextDouble();
if (x*x + y*y <= 1.0) ++ count_thread;
}
}
public void finish()
{
// Reduce per-thread counts into shared count.
count.addAndGet (count_thread);
}
});
}
});
// Stop timing.
time += System.currentTimeMillis();
// Print results.
System.out.println
("pi = 4 * " + count + " / " + N + " = " +
(4.0 * count.doubleValue() / N));
System.out.println (time + " msec");
}
// Hidden operations.
/**
* Print a usage message and exit.
*/
private static void usage()
{
System.err.println ("Usage: java -Dpj.nt=<K> edu.rit.smp.monte.PiSmp3 <seed> <N>");
System.err.println ("<K> = Number of parallel threads");
System.err.println ("<seed> = Random seed");
System.err.println ("<N> = Number of random points");
System.exit (1);
}
}
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