对相同数据执行 Java 线程

Question

首先是代码，大家可以复制粘贴

import java.util.ArrayList;

public class RepetionCounter implements Runnable{
private int x;
private int y;
private int[][] matrix;
private int xCounter;
private int yCounter;
private ArrayList<Thread> threadArray;
private int rowIndex;
private boolean[] countCompleted; 

public RepetionCounter(int x, int y, int [][]matrix)
{
    this.x = x;
    this.y = y;
    this.matrix = matrix;
    this.threadArray = new ArrayList<Thread>(matrix.length);
    this.rowIndex = 0;
    for(int i = 0; i < matrix.length; i++){
        threadArray.add(new Thread(this));
    }
    countCompleted = new boolean[matrix.length];
}

public void start(){
    for (int i = 0; i < threadArray.size(); i++){
        threadArray.get(i).start();
        this.rowIndex++;
    }
}

public void count(int rowIndex)
{
    for(int i = 0; i < matrix[rowIndex].length; i++){
        if (matrix[rowIndex][i] == x){
            this.xCounter++;
        } else if (matrix[rowIndex][i] == y){
            this.yCounter++;
        }
    }
}

@Override
public void run() {
    count(this.rowIndex);
    countCompleted[this.rowIndex] = true;
}

public int getxCounter() {
    return xCounter;
}

public void setxCounter(int xCounter) {
    this.xCounter = xCounter;
}

public int getyCounter() {
    return yCounter;
}

public void setyCounter(int yCounter) {
    this.yCounter = yCounter;
}

public boolean[] getCountCompleted() {
    return countCompleted;
}

public void setCountCompleted(boolean[] countCompleted) {
    this.countCompleted = countCompleted;
}

public static void main(String args[]){
    int[][] matrix = {{0,2,1}, {2,3,4}, {3,2,0}};
    RepetionCounter rc = new RepetionCounter(0, 2, matrix);
    rc.start();
    boolean ready = false;
    while(!ready){
        for(int i = 0; i < matrix.length; i++){
            if (rc.getCountCompleted()[i]){
                ready = true;
            } else {
                ready = false;
            }
        }
    }
    if (rc.getxCounter() > rc.getyCounter()){
        System.out.println("Thre are more x than y");
    } else {System.out.println("There are:"+rc.getxCounter()+" x and:"+rc.getyCounter()+" y");

    }
}

}

我想让这段代码做什么:我给对象一个矩阵和两个数字，我想知道这两个数字在矩阵中出现了多少次。我创建了与矩阵的行数一样多的线程(这就是为什么有那个 ArrayList)，所以在这个对象中我有 k 个线程(假设 k 是行数)，每个线程都计算两个线程的出现次数数字。问题是:如果我第一次运行它，一切正常，但如果我再次尝试执行它，我会得到 IndexOutOfBoundException，或者发生次数不正确，奇怪的是，如果我得到错误，并修改代码，之后它将再次运行一次。你能给我解释一下为什么会这样吗？

Answer 1

您正在为每个线程使用相同的 RepetitionCounter 实例:

for(int i = 0; i < matrix.length; i++){
    threadArray.add(new Thread(this));
}

因此它们将共享相同的 rowIndex。代码非常困惑，所以我建议您将线程的逻辑封装在一个单独的 Runnable 类中，并带有单独的行 ID:

class ThreadTask implements Runnable {
    private int rowId;
    private int[][] matrix;

    public ThreadTask(int[][] matrix, int rowId) {
        this.matrix = matrix; // only a reference is passed here so no worries
        this.rowId = rowId;
    }

    public void run() {
       // search on my row
    }
}

然后:

for(int i = 0; i < matrix.length; i++) {
     threadArray.add(new Thread(new ThreadTask(matrix, i)));
}