多线程程序在单核CPU下运行，耗时为0毫秒是什么原因？
package test;
/**
* @Title: MultiThreadMatrix.java
* @Package matrix
* @Description: 多线程计算矩阵乘法
* @author Aloong
* @date 2010-10-28 下午09:45:56
* @version V1.0
*/
import java.util.Date;
public class MultiThreadMatrix
{
static int[][] matrix1;
static int[][] matrix2;
static int[][] matrix3;
static int m,n,k;
static int index;
static int threadCount;
static long startTime;
public static void main(String[] args) throws InterruptedException
{
//矩阵a高度m=100宽度k=80,矩阵b高度k=80宽度n=50 ==> 矩阵c高度m=100宽度n=50
m = 1024;
n = 1024;
k = 1024;
matrix1 = new int[m][k];
matrix2 = new int[k][n];
matrix3 = new int[m][n];
//随机初始化矩阵a,b
fillRandom(matrix1);
fillRandom(matrix2);
startTime = new Date().getTime();
//输出a,b
// printMatrix(matrix1);
// printMatrix(matrix2);
//创建线程,数量 <= 4
for(int i=0; i<4; i++)
{
if(index < m)
{
Thread t = new Thread(new MyThread());
t.start();
}else
{
break;
}
}
//等待结束后输出
while(threadCount!=0)
{
Thread.sleep(20);
}
// printMatrix(matrix3);
long finishTime = new Date().getTime();
System.out.println("计算完成,用时"+(finishTime-startTime)+"毫秒");
}
static void printMatrix(int[][] x)
{
for (int i=0; i<x.length; i++)
{
for(int j=0; j<x[i].length; j++)
{
System.out.print(x[i][j]+" ");
}
System.out.println("");
}
System.out.println("");
}
static void fillRandom(int[][] x)
{
for (int i=0; i<x.length; i++)
{
for(int j=0; j<x[i].length; j++)
{
//每个元素设置为0到99的随机自然数
x[i][j] = (int) (Math.random() * 100);
}
}
}
synchronized static int getTask()
{
if(index < m)
{
return index++;
}
return -1;
}
}
class MyThread implements Runnable
{
int task;
@Override
public void run()
{
MultiThreadMatrix.threadCount++;
while( (task = MultiThreadMatrix.getTask()) != -1 )
{
//System.out.println("进程: "+Thread.currentThread().getName()+"\t开始计算第 "+(task+1)+"行");
for(int i=0; i<MultiThreadMatrix.n; i++)
{
for(int j=0; j<MultiThreadMatrix.k; j++)
{
MultiThreadMatrix.matrix3[task][i] += MultiThreadMatrix.matrix1[task][j] * MultiThreadMatrix.matrix2[j][i];
}
}
}
MultiThreadMatrix.threadCount--;
}
}
