park & unpark

调用LockSupport.park()会阻塞当前的线程，LockSupport.unPark()会唤醒当前线程

public class ParkAndUnPark {
    public static void main(String[] args) {
        MyThread1 thread1 = new MyThread1(Thread.currentThread());
        
            thread1.start();
            System.out.println("before park");
            //阻塞当前线程,当前线程 setBlocker(Blocker:拦截者,阻塞者,相当于是一个标志)
            LockSupport.park("parkAndUnParkDemo");
            System.out.println("after park");
        

    }
}

class MyThread1 extends Thread{
    private Object object;

    public MyThread1(Object o){
        this.object = o;
    }
    @Override
    public  void run(){
        System.out.println("before unpark");
        try {
            Thread.sleep(1000);
        }catch (InterruptedException e){
            e.printStackTrace();
        }
        System.out.println("Blocker info " + LockSupport.getBlocker((Thread) object));
        LockSupport.unpark((Thread) object);
        try {
            Thread.sleep(500);
        }catch (InterruptedException e){
            e.printStackTrace();
        }
        System.out.println("Blocker info " + LockSupport.getBlocker((Thread) object));
        System.out.println("after unpark");
    }
}

LockSupport.park("parkAndUnParkDemo")源码
先设置当前线程的Blocker，再调用UNSAFE.park()阻塞当前线程，直到调用unpark()函数，当前线程会继续执行，并设置Blocker = null

public static void park(Object blocker) {
        Thread t = Thread.currentThread();
        setBlocker(t, blocker);
        UNSAFE.park(false, 0L);
        setBlocker(t, null);
    }

此外LockSupport.park()不会释放锁，这里不会释放thread1这把锁，thread1这个线程一直无法拿到锁，无法调用unpark()函数，主线程会一直处于阻塞状态

public class ParkAndUnPark {
    public static void main(String[] args) {
        MyThread1 thread1 = new MyThread1(Thread.currentThread());
        synchronized (thread1){
            thread1.start();
            System.out.println("before park");
            //阻塞当前线程,当前线程 setBlocker(Blocker:拦截者,阻塞者,相当于是一个标志)
            LockSupport.park("parkAndUnParkDemo");
            System.out.println("after park");
        }

    }
}

class MyThread1 extends Thread{
    private Object object;

    public MyThread1(Object o){
        this.object = o;
    }
    @Override
    public synchronized void run(){
        System.out.println("before unpark");
        try {
            Thread.sleep(1000);
        }catch (InterruptedException e){
            e.printStackTrace();
        }
        System.out.println("Blocker info " + LockSupport.getBlocker((Thread) object));
        LockSupport.unpark((Thread) object);
        try {
            Thread.sleep(500);
        }catch (InterruptedException e){
            e.printStackTrace();
        }
        System.out.println("Blocker info " + LockSupport.getBlocker((Thread) object));
        System.out.println("after unpark");
    }
}

 这里interrupt()(中断)和unpark()的效果一样

class MyThread extends Thread {
    private Object object;

    public MyThread(Object object) {
        this.object = object;
    }

    public void run() {
        System.out.println("before interrupt");        
        try {
            // 休眠3s
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }    
        Thread thread = (Thread) object;
        // 中断线程
        thread.interrupt();
        System.out.println("after interrupt");
    }
}

public class InterruptDemo {
    public static void main(String[] args) {
        MyThread myThread = new MyThread(Thread.currentThread());
        myThread.start();
        System.out.println("before park");
        // 获取许可
        LockSupport.park("ParkAndUnparkDemo");
        System.out.println("after park");
    }
}