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Pi Estimator

The value of PI can be calculated in a number of ways. Consider the following method of estimating PI

  • Inscribe a circle in a square
  • Randomly generate points in the square
  • Determine the number of points in the square that are also in the circle
  • Let r be the number of points in the circle divided by the number of points in the square
  • PI ~ 4 r

Serial pseudo code for this procedure as below:

iterations = 10000
circle_count = 0

do j = 1,iterations
  generate 2 random numbers between 0 and 1
  xcoordinate = random1
  ycoordinate = random2
  if (xcoordinate, ycoordinate) inside circle
  then circle_count = circle_count + 1
end do

PI = 4.0*circle_count/iterations

The BSP implementation for Pi

A distributed strategy in HAMA with BSP programming model, is break the loop into portions that can be executed by the tasks.

  • Each task executes locally its portion of the loop a number of times.
  • One task acts as master and collects the results through the BSP communication interface. 
public class SerializePrinting {
  private static String TMP_OUTPUT = "/tmp/test-example/";

  public static class HelloBSP extends BSP {
    public static final Log LOG = LogFactory.getLog(HelloBSP.class);
    private Configuration conf;
    private final static int PRINT_INTERVAL = 5000;

    public void bsp(BSPPeerProtocol bspPeer) throws IOException,
        KeeperException, InterruptedException {
      int num = Integer.parseInt(conf.get("bsp.peers.num"));
      FileSystem fileSys = FileSystem.get(conf);

      int i = 0;
      for (String otherPeer : bspPeer.getAllPeerNames()) {
        if (bspPeer.getPeerName().equals(otherPeer)) {
          LOG.info("Hello BSP from " + (i + 1) + " of " + num + ": "
              + bspPeer.getPeerName());

          SequenceFile.Writer writer = SequenceFile.createWriter(fileSys, conf,
              new Path(TMP_OUTPUT + i), LongWritable.class, Text.class,
              CompressionType.NONE);
          writer.append(new LongWritable(System.currentTimeMillis()), new Text(
              "Hello BSP from " + (i + 1) + " of " + num + ": "
                  + bspPeer.getPeerName()));
          writer.close();

        }

        Thread.sleep(PRINT_INTERVAL);
        bspPeer.sync();
        i++;
      }
    }

    public Configuration getConf() {
      return conf;
    }

    public void setConf(Configuration conf) {
      this.conf = conf;
    }

  }

  public static void main(String[] args) throws InterruptedException,
      IOException {
    // BSP job configuration
    HamaConfiguration conf = new HamaConfiguration();

    BSPJob bsp = new BSPJob(conf, SerializePrinting.class);
    // Set the job name
    bsp.setJobName("serialize printing");
    bsp.setBspClass(HelloBSP.class);

    // Set the task size as a number of GroomServer
    BSPJobClient jobClient = new BSPJobClient(conf);
    ClusterStatus cluster = jobClient.getClusterStatus(false);
    bsp.setNumBspTask(cluster.getGroomServers());

    FileSystem fileSys = FileSystem.get(conf);
    if (fileSys.exists(new Path(TMP_OUTPUT))) {
      fileSys.delete(new Path(TMP_OUTPUT), true);
    }
    BSPJobClient.runJob(bsp);

    System.out.println("Each task printed the \"Hello World\" as below:");
    for (int i = 0; i < cluster.getGroomServers(); i++) {
      SequenceFile.Reader reader = new SequenceFile.Reader(fileSys, new Path(
          TMP_OUTPUT + i), conf);
      LongWritable timestamp = new LongWritable();
      Text message = new Text();
      reader.next(timestamp, message);
      System.out.println(new Date(timestamp.get()) + ": " + message);
      reader.close();
    }
  }
}
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