Java中如何暂停Runnable或线程？wait()抛异常解析与解决

问题重现 #

你定义的Runnable类：

package com.example.testtest;

public class FootballRunner implements Runnable {
    @Override
    public void run() {
        while (true) {
            System.out.println("Running " + Thread.currentThread().getId() + " " + Math.random());
            try {
                Thread.sleep(1_000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    }
}

主类代码：

package com.example.testtest;

public class TestScheduling {
    public static void main(String[] args) throws InterruptedException {
        FootballRunner footballRunner = new FootballRunner();
        Thread t1 = new Thread(footballRunner, "one");
        t1.start();
        t1.wait();
    }
}

运行后抛出异常：

Exception in thread "main" java.lang.IllegalMonitorStateException: current thread is not owner
    at java.base/java.lang.Object.wait(Native Method)
    at java.base/java.lang.Object.wait(Object.java:338)
    at com.example.testtest.TestScheduling.main(TestScheduling.java:8)

1. "current thread is not owner" 是什么意思？ #

wait()是Object类的核心方法，它的调用有严格前提：当前线程必须持有该对象的监视器锁（即通过synchronized关键字获取的锁）。

你在main线程中直接调用t1.wait()，但main线程从未通过synchronized(t1)代码块获取t1对象的锁，所以JVM会抛出IllegalMonitorStateException，提示的"current thread is not owner"直白来说就是：你当前的线程（main）不是t1这个对象监视器锁的持有者，没有资格调用它的wait()方法。

另外要明确：wait()的作用是让持有锁的线程自己进入等待状态，并释放锁，它不是用来暂停其他线程的工具，你的用法完全误解了这个方法的用途。

2. 如何正确实现线程t1的暂停？ #

Thread类的suspend()方法已被废弃（容易导致死锁，锁无法释放），推荐用以下两种标准方式：

方法一：利用线程中断机制 #

通过中断标志位控制线程循环，同时正确响应中断异常：

package com.example.testtest;

public class FootballRunner implements Runnable {
    @Override
    public void run() {
        // 循环前检查线程中断状态
        while (!Thread.currentThread().isInterrupted()) {
            System.out.println("Running " + Thread.currentThread().getId() + " " + Math.random());
            try {
                Thread.sleep(1_000);
            } catch (InterruptedException e) {
                // 捕获中断后，重置中断状态（因为sleep会清除中断标志）
                Thread.currentThread().interrupt();
                break; // 退出循环，终止线程
            }
        }
        System.out.println("线程t1已停止");
    }
}

主类中调用interrupt()触发中断：

package com.example.testtest;

public class TestScheduling {
    public static void main(String[] args) throws InterruptedException {
        FootballRunner footballRunner = new FootballRunner();
        Thread t1 = new Thread(footballRunner, "one");
        t1.start();
        
        // 让main线程等待3秒后，中断t1
        Thread.sleep(3000);
        t1.interrupt();
    }
}

方法二：使用volatile标志位控制 #

定义一个volatile修饰的布尔变量（保证多线程下的可见性），通过修改该变量来终止线程循环：

package com.example.testtest;

public class FootballRunner implements Runnable {
    // volatile保证变量修改对其他线程立即可见
    private volatile boolean isRunning = true;

    // 提供外部调用的停止方法
    public void stopThread() {
        isRunning = false;
    }

    @Override
    public void run() {
        while (isRunning) {
            System.out.println("Running " + Thread.currentThread().getId() + " " + Math.random());
            try {
                Thread.sleep(1_000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
        System.out.println("线程t1已停止");
    }
}

主类中调用stopThread()方法：

package com.example.testtest;

public class TestScheduling {
    public static void main(String[] args) throws InterruptedException {
        FootballRunner footballRunner = new FootballRunner();
        Thread t1 = new Thread(footballRunner, "one");
        t1.start();
        
        Thread.sleep(3000);
        footballRunner.stopThread(); // 触发线程停止
    }
}

内容的提问来源于stack exchange，提问作者ilhan