LockSupport的park与unpark调用顺序验证_locksupport 先unpark 然后park-优快云博客

本文链接：https://blog.youkuaiyun.com/enjoyinwind/article/details/106411306

本文通过三个实验深入探讨了Java中LockSupport类的unpark和park方法的使用时机与效果，揭示了线程唤醒的机制。实验表明，unpark必须在线程启动后才能生效，无论是在park前还是后调用，都能成功唤醒线程。

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1.unpark在thread start之前调用

    public static void main(String[] args) throws InterruptedException{
        Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("thread1 start");

                try{
                    Thread.sleep(2000);
                } catch (Exception e){
                    e.printStackTrace();
                }

                System.out.println("thread1 run before park");

                LockSupport.park();

                System.out.println("thread1 run after park");
            }
        });
        LockSupport.unpark(thread1);
        thread1.start();

        System.out.println("main thread");

    }

执行结果：

main thread
thread1 start
thread1 run before park

（程序没有退出，线程1一直挂起）

2.unpark在park之前执行

public static void main(String[] args) throws InterruptedException{
        Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("thread1 start");

                try{
                    Thread.sleep(2000);
                } catch (Exception e){
                    e.printStackTrace();
                }

                System.out.println("thread1 run before park");

                LockSupport.park();

                System.out.println("thread1 run after park");
            }
        });
        thread1.start();
        LockSupport.unpark(thread1);

        System.out.println("main thread");

    }

执行结果：

thread1 start
main thread
thread1 run before park
thread1 run after park

3.unpark在park之后执行

    public static void main(String[] args) throws InterruptedException{
        Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("thread1 run before park");

                LockSupport.park();

                System.out.println("thread1 run after park");
            }
        });

        thread1.start();

        System.out.println("main thread");
        Thread.sleep(3000);
        LockSupport.unpark(thread1);
    }

执行结果：

main thread
thread1 run before park
thread1 run after park