Question

我研究了Java多线程编程。我的任务是实现一个多线程程序来计算矩阵产品。每个线程负责生成矩阵的不同行。任务说：＆＃34;在主程序中使用join()等待所有线程完成，然后打印出结果矩阵＆＃34;。

所以这是我的代码：

MatrixProduct.java

package multythreading;

import java.util.Arrays;

public class MatrixProduct {

    public static Matrix a;
    public static Matrix b;

    static {
        a = new Matrix(new int[][]{{1, 2, 3, 4, 5, 6, 7, 8, 9, 10},
                                   {4, 5, 64, 5, 6, 7, 8, 9, 10, 11},
                                   {7, 8, 94, 5, 6, 7, 8, 9, 10, 12},
                                   {7, 8, 94, 5, 6, 7, 8, 9, 10, 13},
                                   {4, 5, 64, 5, 6, 7, 8, 9, 10, 14},
        });
        b = new Matrix(new int[][]{{2, 1, 3},
                                   {4, 2, 1},
                                   {6, 4, 5},
                                   {6, 4, 5},
                                   {4, 2, 1},
                                   {2, 1, 3},
                                   {4, 2, 1},
                                   {6, 4, 5},
                                   {6, 4, 5},
                                   {4, 2, 1}});
    }

    public static void main(String [] args) {
        Thread[] threads = new Thread[a.getRowNum()];
        for (int i = 0; i < threads.length; i++) {
            threads[i] = new Thread(new ResultMatrixLine(i), "Line number " + i + " computation thread");
            threads[i].start();
        }

        for (Thread t: threads) {
            if (t.isAlive()) {
                try {
                    System.out.println(t.getName() + " : " + t.getState()  + " still alive");
                    t.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
        System.out.println("All computation threads terminated and the resulting matrix is ready");
    }
}

class ResultMatrixLine implements Runnable {

    private int lineNumber;

    public ResultMatrixLine(int lineNumber) {
        this.lineNumber  = lineNumber;
    }

    @Override
    public void run() {
        System.out.println("Line number = " + lineNumber + ": " + Arrays.toString(getResultLine()));
    }

    private int[] getResultLine() {
        int[] result = new int[MatrixProduct.b.getColumnNum()];
        for (int i = 0; i < MatrixProduct.b.getColumnNum(); i++)
            for (int j = 0; j < MatrixProduct.a.getColumnNum(); j++)
                result[i] += MatrixProduct.a.getMatrixElement(lineNumber, j)*MatrixProduct.b.getMatrixElement(j, i);
        return result;
    }
}

class Matrix {
    private final int columnNum;
    private final int rowNum;
    private final int[][] matrix;

    public Matrix(int[][] matrix) {
        this.columnNum = matrix[0].length;
        this.rowNum = matrix.length;
        this.matrix = matrix;
    }

    public int getColumnNum() {
        return columnNum;
    }

    public int getRowNum() {
        return rowNum;
    }

    public int getMatrixElement(int columnIndx, int rowIndx) {
        return matrix[columnIndx][rowIndx];
    }
}

生成的矩阵行是独立计算的，所以我唯一关心的是在join()方法中正确使用main()。我的意思是在主线程结束时，必须终止所有其他线程，以便生成的矩阵准备就绪。我的决定乍一看没有问题，但我希望看到任何意见。

Answer 1

以下是我通过修改代码创建的解决方案：

在 Matrix产品中添加了一个ArrayList，以及一个在公共范围内从中删除线程的函数：

private static ArrayList<ResultMatrixLine> threads = new ArrayList<>();


public static void main(String [] args) {
    for (int i = 0; i < a.getRowNum(); i++) {
        // Create a new ResultMatrixLine thread
        ResultMatrixLine thread = new ResultMatrixLine( i );
        // Keep the thread handy for manipulation later
        threads.add( thread );
        // Create a new thread
        thread.start();
    }

    threads.stream().forEach( (thread) -> {
        if( thread.isAlive() ) {
            try {
                thread.join( 1000 );
            } catch( InterruptedException ex ) {
                ex.printStackTrace( System.out );
            }
        }
    });

    System.out.println("All computation threads terminated and the resulting matrix is ready");

}

<强>输出

Line number = 1: [670, 423, 503]
Line number = 3: [876, 556, 667]
Line number = 0: [254, 151, 165]
Line number = 4: [682, 429, 506]
Line number = 2: [872, 554, 666]
All computation threads terminated and the resulting matrix is ready

对线程使用join（）方法，在创建所有线程之后，它将循环遍历ArrayList并检查是否有任何线程处于活动状态。如果是这样，请加入（）他们。

如何确保主线程完成

1 个答案: