Lock Condition.notify 抛出 java.lang.IllegalMonitorStateException

Question

我写了一个程序来演示java的Lock.Condition用于多线程目的。我收到 IllegalMonitorStateException。

它抛出异常，以下是输出。

我在根据条件调用通知之前获取锁定。但仍然出现以下错误。有人可以帮忙吗。我用谷歌搜索了很多但找不到解决方案。

Count : 0
lock java.util.concurrent.locks.ReentrantLock@4ce4d37e[Locked by thread Thread-0]
Exception in thread "Thread-0" java.lang.IllegalMonitorStateException: current thread is not owner
at java.base/java.lang.Object.notify(Native Method)
at test.OddEvenPrinter.printEven(Test.java:51)
    at test.Test.lambda$main$1(Test.java:22)
at java.base/java.lang.Thread.run(Thread.java:1589)
Count : 1
lock java.util.concurrent.locks.ReentrantLock@4ce4d37e[Locked by thread Thread-1]
Exception in thread "Thread-1" java.lang.IllegalMonitorStateException: current thread is not owner
    at java.base/java.lang.Object.notify(Native Method)
    at test.OddEvenPrinter.printOdd(Test.java:67)
    at test.Test.lambda$main$0(Test.java:14)
    at java.base/java.lang.Thread.run(Thread.java:1589)

其代码如下：

package test;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class Test {
    public static void main(String[] args) {
        final OddEvenPrinter oddEvenPrinter = new OddEvenPrinter();
        Runnable oddRunnable = () -> {
            try {
                while (true)
                    oddEvenPrinter.printOdd();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };
        Runnable evenRunnable = () -> {
            try {
                while (true)
                    oddEvenPrinter.printEven();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };
        new Thread(evenRunnable).start();
        new Thread(oddRunnable).start();
    }
}

class OddEvenPrinter {
    private final Lock lock = new ReentrantLock();
    private final Condition oddPrint = lock.newCondition();
    private final Condition evenPrint = lock.newCondition();
    private int count;
    public void printEven() throws InterruptedException {
        lock.lock();
        try {
            Thread.sleep(3000);
            while (count % 2 == 1) {
                evenPrint.await();
            }
            System.out.println("Count : " + count++);
            System.out.println("lock " + lock);
            oddPrint.notify();
        } finally {
            lock.unlock();
        }
    }
    public void printOdd() throws InterruptedException {
        lock.lock();
        try {
            Thread.sleep(2000);
            while (count % 2 == 0) {
                oddPrint.await();
            }
            System.out.println("Count : " + count++);
            System.out.println("lock " + lock);
            evenPrint.notify();
        } finally {
            lock.unlock();
        }
    }
}

Answer 1

使用

java.util.concurrent.locks.Condition

时，我们应该使用

signal

或

signalAll

方法。

示例：

public void foo() {
    reentrantLock.lock();
    try {
        condition.signal();
    } finally {
        reentrantLock.unlock();
    }
}

notify

和

notifyAll

是与内在锁相关的方法（带有

synchronized

关键字），例如：

public synchronized void foo() throws InterruptedException {
    this.notify();
}