(new MatrixThread(...)).start()
而不使用ExecutorService
。此外,当我对多线程方法和传统方法进行基准测试时,传统方法要快得多...
我做错了什么?
矩阵类:
import java.util.*;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
class Matrix
{
private int dimension;
private int[][] template;
public Matrix(int dimension)
{
this.template = new int[dimension][dimension];
this.dimension = template.length;
}
public Matrix(int[][] array)
{
this.dimension = array.length;
this.template = array;
}
public int getMatrixDimension() { return this.dimension; }
public int[][] getArray() { return this.template; }
public void fillMatrix()
{
Random randomNumber = new Random();
for(int i = 0; i < dimension; i++)
{
for(int j = 0; j < dimension; j++)
{
template[i][j] = randomNumber.nextInt(10) + 1;
}
}
}
@Override
public String toString()
{
String retString = "";
for(int i = 0; i < this.getMatrixDimension(); i++)
{
for(int j = 0; j < this.getMatrixDimension(); j++)
{
retString += " " + this.getArray()[i][j];
}
retString += "\n";
}
return retString;
}
public static Matrix classicalMultiplication(Matrix a, Matrix b)
{
int[][] result = new int[a.dimension][b.dimension];
for(int i = 0; i < a.dimension; i++)
{
for(int j = 0; j < b.dimension; j++)
{
for(int k = 0; k < b.dimension; k++)
{
result[i][j] += a.template[i][k] * b.template[k][j];
}
}
}
return new Matrix(result);
}
public Matrix multiply(Matrix multiplier) throws InterruptedException
{
Matrix result = new Matrix(dimension);
ExecutorService es = Executors.newFixedThreadPool(dimension*dimension);
for(int currRow = 0; currRow < multiplier.dimension; currRow++)
{
for(int currCol = 0; currCol < multiplier.dimension; currCol++)
{
//(new MatrixThread(this, multiplier, currRow, currCol, result)).start();
es.execute(new MatrixThread(this, multiplier, currRow, currCol, result));
}
}
es.shutdown();
es.awaitTermination(2, TimeUnit.DAYS);
return result;
}
private class MatrixThread extends Thread
{
private Matrix a, b, result;
private int row, col;
private MatrixThread(Matrix a, Matrix b, int row, int col, Matrix result)
{
this.a = a;
this.b = b;
this.row = row;
this.col = col;
this.result = result;
}
@Override
public void run()
{
int cellResult = 0;
for (int i = 0; i < a.getMatrixDimension(); i++)
cellResult += a.template[row][i] * b.template[i][col];
result.template[row][col] = cellResult;
}
}
}
主类:
import java.util.Scanner;
public class MatrixDriver
{
private static final Scanner kb = new Scanner(System.in);
public static void main(String[] args) throws InterruptedException
{
Matrix first, second;
long timeLastChanged,timeNow;
double elapsedTime;
System.out.print("Enter value of n (must be a power of 2):");
int n = kb.nextInt();
first = new Matrix(n);
first.fillMatrix();
second = new Matrix(n);
second.fillMatrix();
timeLastChanged = System.currentTimeMillis();
//System.out.println("Product of the two using threads:\n" +
first.multiply(second);
timeNow = System.currentTimeMillis();
elapsedTime = (timeNow - timeLastChanged)/1000.0;
System.out.println("Threaded took "+elapsedTime+" seconds");
timeLastChanged = System.currentTimeMillis();
//System.out.println("Product of the two using classical:\n" +
Matrix.classicalMultiplication(first,second);
timeNow = System.currentTimeMillis();
elapsedTime = (timeNow - timeLastChanged)/1000.0;
System.out.println("Classical took "+elapsedTime+" seconds");
}
}
附言:如果需要进一步的澄清,请告知。
Thread
方面,几乎总是一个坏主意。在这种情况下,代码甚至没有启动线程。Thread
实现Runnable
的事实是不幸的。 - Tom Hawtin - tackline