使用监视器的作家/读者无法正常工作

Question

我正在做一个作业，正在实现使用监视器进行同步的Writer / Reader问题。

方案：编写者应一次将列表中的一个字符串写入一个缓冲区（该缓冲区一次只能容纳一个字符串）。 然后，读取器应从缓冲区中读取字符串，并在gui中打印字符串，两次打印之间要暂停0.5秒。 该程序使用一个单一的编写器线程和一个单一的读取器线程，当按下gui中的按钮时，它们会同时启动。

我的问题是：我无法使同步正常工作，读取器仅每0.5秒打印一次null（这意味着当读取器尝试从中读取缓冲区时，缓冲区很可能是空的）。 我设法找到一个错误： buffer.put(text.get(i))器没有到达try where buffer.put(text.get(i)) ，尽管我不知道为什么。

任何可以帮助的人吗？ 非常感激！ 我的代码在下面，希望足够了，我不想发送太多代码。 （我还是Writer / Reader问题的新手，但已经阅读了一些编码示例等。）

作家：

public void run() {
    buffer.length(text.size());
    for (int i = 0; i < text.size(); i++) { //loops thorugh the list of strings
        System.out.println("hj"); //reaches this
        try {
            buffer.put(text.get(i)); //put the string into the buffer
            System.out.println("put done"); // never reaches this
            sleep(); //pauses the thread for 0.5 seconds
        } catch (InterruptedException e) {
            System.out.println("error"); //never reaches this either
            e.printStackTrace();
        }
    }
}

缓冲：

/**
 * gets a string from the writer
 * @throws InterruptedException 
 */
public synchronized void put(String string) throws InterruptedException {
    while(hasString == false) { //we only want to put a string into the buffer if it is empty
        wait();
        this.string = string;
        hasString = true;
        notify();
    }
}

/**
 * passes on a string to the reader
 * @throws InterruptedException 
 */
public synchronized String get() throws InterruptedException {
    while(hasString == true) { //we only want to pass on a string if the buffer is NOT empty
        wait();
        hasString = false;
        notify();
    }
    return string;
}

读者：

/**
 * reads a string from the buffer and writes it to the gui in the destination-tab
 */
public void run() {
    for (int i  = 0; i < buffer.getLength(); i++) { //loops through the length of the list with strings
        try {
            string = buffer.get(); //gets string from buffer
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }
        //writes the string in the gui
        sb.append(string);
        GUIMonitor.txtPaneDest.setText(sb.toString());
        try {
            sleep(); //pauses the thread for 0.5 seconds
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

Answer 1

您可以尝试此解决方案，只需在while块外将值分配给“ hasString”。

 /**
 * gets a string from the writer
 * @throws InterruptedException 
 */
public synchronized void put(String string) throws InterruptedException {
    while(hasString == false) { //we only want to put a string into the buffer if it is empty
        wait();
    }
    this.string = string;
    hasString = true;
    notify();

}

/**
 * passes on a string to the reader
 * @throws InterruptedException 
 */
public synchronized String get() throws InterruptedException {
    while(hasString == true) { //we only want to pass on a string if the buffer is NOT empty
        wait();
    }
    hasString = false;
    notify();
    return string;
}

Answer 2

通过仅更改Buffer-class中的代码，而Writer和Reader都保持不变，代码现在可以工作（在@whaat答案的帮助下）。 我将在这里保留缓冲区的担心代码，以防其他人遇到与我相同的问题：）

/**
 * gets a string from the writer
 * @throws InterruptedException 
 */
public synchronized void put(String string) throws InterruptedException {
    while(hasString == true) { //we only want to put a string into the buffer if it is empty
        wait();

    }
    this.string = string;
    hasString = true;
    notify();
}

/**
 * passes on a string to the reader
 * @throws InterruptedException 
 */
public synchronized String get() throws InterruptedException {
    while(hasString == false) { //we only want to pass on a string if the buffer is NOT empty
        wait();
    }
    hasString = false;
    notify();
    return string;
}