在Java中做多线程编程时遇到IllegalMonitorStateException

Question

我写了一个简单的程序来学习同步块。程序如下：

public class SychronizedBlock {

    static int balance = 0;
    static Integer lock = 0;


    public static void deposit(int amt) {
        Thread t1 = new Thread(new Runnable() {
            public void run() {
                acquire_lock();
                int holdings = balance;
                balance = holdings + amt;
                System.out.println("deposit " + amt + ", balance: " + balance);
                release_lock();
            }
        });
        t1.start();

    }

    public static void acquire_lock() {
        synchronized(lock) {
            while (lock == 1) {
                try {
                    lock.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            lock = 1;
        }
    }

    public static void release_lock() {
        synchronized(lock) {
            lock = 0;
            lock.notifyAll();
        }
    }

    public static void test1() {
        balance = 0;
        deposit(500);
        deposit(500);
    }

    public static void main(String[] args) {
        test1();
    }
}

但是，在运行程序时，我遇到了 IllegalMonitorStateException。我想我已经将 wait() 和 notifyAll() 函数放在了同步块中，并且我已经将锁设置为同步的参数。为什么我仍然有异常？

Answer 1

问题在于您的 release_lock 方法。您在调用lock.notifyAll(). 之前将lock 重新分配给0，这意味着将在未锁定的新整数对象上调用notifyAll。将代码更改为以下以解决问题。

public static void release_lock() {
    synchronized(lock) {            
        lock.notifyAll();
        lock = 0;
    }
}