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java如何使用wait和notify防止IllegalMonitorStateException

2021-01-13项目经验
java如何使用wait和notify防止IllegalMonitorStateException

一、概述

我有2个矩阵,我需要将它们相乘,然后打印每个单元格的结果。准备好一个单元格后,我就需要打印它,但是例如,即使[2] [0]的结果先准备好,我也需要在单元格[2] [0]之前打印[0] [0]单元格。所以我需要按顺序打印它。因此,我的想法是让打印机线程等待,直到multiplyThread通知它准备打印正确的单元格,然后printerThread它将打印该单元格并返回等待状态,依此类推。

所以我有这个线程做乘法:

public void run() 
{
    int countNumOfActions = 0; // How many multiplications have we done
    int maxActions = randomize(); // Maximum number of actions allowed

    for (int i = 0; i < size; i++)
    {       
        result[rowNum][colNum] = result[rowNum][colNum] + row[i] * col[i];
        countNumOfActions++;
        // Reached the number of allowed actions
        if (countNumOfActions >= maxActions)
        {
            countNumOfActions = 0;
            maxActions = randomize();
            yield();
        }   
    }
    isFinished[rowNum][colNum] = true;
    notify();
}

打印每个单元格结果的线程:

public void run()
{
    int j = 0; // Columns counter
    int i = 0; // Rows counter
    System.out.println("The result matrix of the multiplication is:");

    while (i < creator.getmThreads().length)
    {
        synchronized (this)
        {
            try 
            {
                this.wait();
            } 
            catch (InterruptedException e1) 
            {
            }
        }
        if (creator.getmThreads()[i][j].getIsFinished()[i][j] == true)
        {
            if (j < creator.getmThreads()[i].length)
            {
                System.out.print(creator.getResult()[i][j] + " ");
                j++;
            }
            else
            {
                System.out.println();
                j = 0;
                i++;
                System.out.print(creator.getResult()[i][j] + " ");
            }
        }
    }

现在,我抛出了这些异常:

Exception in thread "Thread-9" java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at multiplyThread.run(multiplyThread.java:49)
Exception in thread "Thread-6" Exception in thread "Thread-4" java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at multiplyThread.run(multiplyThread.java:49)
java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at multiplyThread.run(multiplyThread.java:49)
Exception in thread "Thread-5" java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at multiplyThread.run(multiplyThread.java:49)
Exception in thread "Thread-8" java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at multiplyThread.run(multiplyThread.java:49)
Exception in thread "Thread-7" java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at multiplyThread.run(multiplyThread.java:49)
Exception in thread "Thread-11" java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at multiplyThread.run(multiplyThread.java:49)
Exception in thread "Thread-10" java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at multiplyThread.run(multiplyThread.java:49)
Exception in thread "Thread-12" java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at multiplyThread.run(multiplyThread.java:49)

第49行multiplyThread是“ notify()”。我想我需要以不同的方式使用同步,但是我不确定如何使用。

如果有人可以帮助该代码正常工作,我将非常感谢。

二、详解

为了能够调用notify(),您需要在同一对象上进行同步。

synchronized (someObject) {
    someObject.wait();
}

/* different thread / object */
synchronized (someObject) {
    someObject.notify();
}