LockSupport的park與unpark調用順序驗證

1.unpark在thread start之前調用

    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");

    }

執行結果：

main thread
thread1 start
thread1 run before park

（程序沒有退出，線程1一直掛起）

2.unpark在park之前執行

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");

    }

執行結果：

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

3.unpark在park之後執行

    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);
    }

執行結果：

main thread
thread1 run before park
thread1 run after park

總結

1.unpark必須在thread start之後纔有用，之前調用沒有任何效果；

2.thread start之後，unpark在park之前還是之後，作用是一樣的，都會重新喚醒線程；