bignums.java

并行java编程 应用多线程提高查找速度的java例子

// 
// 
// Cong Wang, 58211415 
// 
// CA670, Assessed Exercise 1, Standard Version
// 
// My program performs as required by the problem specification. 
// 
// This is my own work. I have not received assistance beyond what is 
// normal, and I have cited any sources from which I have borrowed. I 
// have not given a copy of my work, or part of my work, to anyone.   
// I am aware that copying or giving a copy may have serious 
//  consequences, including an outright fail for the module.

import java.util.*;

public class BigNums {

	public static void main(String[] args) {
		double[] list = new double[1 << 22];
		for (int i = 0; i < list.length; i++)
			list[i] = Math.random();
		long startTime = System.nanoTime();
		double[] bigs = bigNums(list);
		long endTime = System.nanoTime();
		System.out.println("Running time = " + ((endTime - startTime) / 1000));
		System.out.println(bigs.length);

	}

	private static double[] bigNums(final double[] b) {
		int numProc=Runtime.getRuntime().availableProcessors();
		final int range=b.length/numProc;
		Thread[] tt=new Thread[numProc];
		//Calculation for the average
		double sum=0;
		final double[] sums=new double[numProc];
		for(int i=0;i<numProc;i++)
		{
			final int lo=i*range;
			final int ii=i;
			tt[i]=new Thread(
					new Runnable()
					{
						public void run()
						{
							for(int j=lo;j<Math.min(lo+range, b.length);j++)
							{
								sums[ii]+=b[j];
							}						
						}
					}
					);
			tt[i].start();
		}
		for(int k=0;k<numProc;k++)
		{
					try{tt[k].join();}catch(InterruptedException e){};
					sum+=sums[k];
		}
		final double avr=sum/b.length;
		//Pick up the bigs and place them in bigs[][]
		final double[][] bigs=new double[numProc][range];
		final int[] lens=new int[numProc];
		int len=0;
		for(int i=0;i<numProc;i++)
		{
			final int lo=i*range;
			final int ii=i;
			tt[i]=new Thread(
					new Runnable()
					{
						public void run()
						{
							int len=0;
							for(int j=lo;j<Math.min(lo+range, b.length);j++)
							{
								if(b[j]>avr) {bigs[ii][j-lo]=b[j];len++;}
							}
							lens[ii]=len;
						}
					}
					);
			tt[i].start();
		}
		for(int k=0;k<numProc;k++)
		{
					try{tt[k].join();}catch(InterruptedException e){};
					len+=lens[k];
		}
		//merge the bigs[][] to bignums[]
		double[] bignums=new double[len];
		int pos=0;
		for(int i=0;i<numProc;i++)
		{
			System.arraycopy(bigs[i], 0, bignums, pos, lens[i]);
			pos+=lens[i];
		}
		
		return bignums;

	}
	

}