/*
 *  Calculation of Pi using quadrature realized with a fork/join approach with JCSP to partition the problem
 *  and hence harness all processors available to the JVM.
 *
 *  Copyright © 2009–2011 Russel Winder
 */

import org.jcsp.lang.Channel ;
import org.jcsp.lang.CSProcess ;
import org.jcsp.lang.One2OneChannel ;
import org.jcsp.lang.Parallel ;

import java.util.ArrayList ;
import java.util.Arrays ;
import java.util.List ;

public class Pi_Java_JCSP_List {
  private static void execute ( final int numberOfTasks ) {
    final int n = 1000000000 ;
    final double delta = 1.0 / n ;
    final long startTimeNanos = System.nanoTime ( ) ;
    final int sliceSize = n / numberOfTasks ;
    //
    //  Cannot just do:
    //
    //    final List<One2OneChannel<Object>> channels = Arrays.asList ( Channel.one2oneArray ( numberOfTasks ) ) ;
    //
    //  as this gets the wrong version of the type-parameterized one2oneArray method.
    //
    final One2OneChannel<Double>[] backing = Channel.one2oneArray ( numberOfTasks ) ;
    final List<One2OneChannel<Double>> channels = Arrays.asList ( backing ) ;
    final List<CSProcess> processes = new ArrayList<CSProcess> ( ) ;
    for ( int i = 0 ; i < numberOfTasks ; ++i ) {
      final int taskId = i ;
      processes.add ( new CSProcess ( ) {
          @Override public void run ( ) {
            final int start = 1 + taskId * sliceSize ;
            final int end = ( taskId + 1 ) * sliceSize ;
            double sum = 0.0 ;
            for ( int i = start ; i <= end ; ++i ) {
              final double x = ( i - 0.5 ) * delta ;
              sum += 1.0 / ( 1.0 + x * x ) ;
            }
            channels.get ( taskId ).out ( ).write ( sum ) ;
          }
        } ) ;
    }
    processes.add ( new CSProcess ( ) {
        @Override public void run ( ) {
          double sum = 0.0 ;
          for ( One2OneChannel<Double> c : channels ) {  sum += c.in ( ).read ( ) ; }
          final double pi = 4.0 * delta * sum ;
          final double elapseTime = ( System.nanoTime ( ) - startTimeNanos ) / 1e9 ;
          System.out.println ( "==== Java JCSP List pi = " + pi ) ;
          System.out.println ( "==== Java JCSP List iteration count = " + n ) ;
          System.out.println ( "==== Java JCSP List elapse = " + elapseTime ) ;
          System.out.println ( "==== Java JCSP List processor count = " + Runtime.getRuntime ( ).availableProcessors ( ) ) ;
          System.out.println ( "==== Java JCSP List task count = " + numberOfTasks ) ;
        }
      } ) ;
    ( new Parallel ( processes.toArray ( new CSProcess [0] ) ) ).run ( ) ;
  }
  public static void main ( final String[] args ) {
    Pi_Java_JCSP_List.execute ( 1 ) ;
    System.out.println ( ) ;
    Pi_Java_JCSP_List.execute ( 2 ) ;
    System.out.println ( ) ;
    Pi_Java_JCSP_List.execute ( 8 ) ;
    System.out.println ( ) ;
    Pi_Java_JCSP_List.execute ( 32 ) ;
  }
}