Explain the use of locksupport in detail

One 、 brief introduction

1. The picture below is Java api Description in ：

2. Its methods are as follows , The circled method is the core method ：

3. Common methods of waking up and blocking threads include LockSupport：

Two 、LockSupport Advantages of wake-up blocking method

1.Object Class provides the wait and notify Need to be in synchronized Used in code blocks , Otherwise it will be reported IllegalMonitorStateException abnormal ！ also notify Must be in wait Method can take effect only after it is executed .( Here is the correct usage ！)

    public static void main(String[] args) {
    
        Object objectlock = new Object();
        new Thread(()->{
    
            synchronized (objectlock){
    
                System.out.println(Thread.currentThread().getName()+"：\tcome in~");
                try {
    objectlock.wait();} catch (InterruptedException e) {
    e.printStackTrace();}
                System.out.println(Thread.currentThread().getName()+": \t Awakened ");
            }
        },"A").start();
		// Sleep 1 second 
        try {
    TimeUnit.SECONDS.sleep(1);} catch (InterruptedException e) {
    e.printStackTrace();}

        new Thread(()->{
    
            synchronized (objectlock) {
    
                objectlock.notify();
                System.out.println(Thread.currentThread().getName()+": \t A notice ！");
            }
        },"B").start();
    }

2.ReentrantLock Class provides the await and signal There is still the problem of execution sequence , The following case makes signal Method first , After the results are found await It didn't wake up ！

public static void main(String[] args) {
    
        Lock lock = new ReentrantLock();
        Condition condition = lock.newCondition();
        new Thread(()->{
    
        	// Pause 1 second , Give Way B The line program is executed first ！
            try {
    TimeUnit.SECONDS.sleep(1);} catch (InterruptedException e) {
    e.printStackTrace();}
            lock.lock();
            try {
    
                System.out.println(Thread.currentThread().getName()+"：\tcome in~");
                condition.await();
                System.out.println(Thread.currentThread().getName()+": \t Awakened ");
            } catch (InterruptedException e) {
    
                e.printStackTrace();
            }finally {
    
                lock.unlock();
            }
        },"A").start();

        new Thread(()->{
    
            lock.lock();
            try {
    
                condition.signal();
                System.out.println(Thread.currentThread().getName()+": \t A notice ！");
            }finally {
    
                lock.unlock();
            }
        },"B").start();
    }

3.LockSupport There is no such problem , Similar to highway ETC, Bought the pass in advance unpark, Directly lift the railing at the gate and let it go park Intercepted . but unpark Repeated execution can only accumulate one pass , So if the commented parts of the following code are removed , that A The thread will be blocked ！

    public static void main(String[] args) {
    
        Thread a = new Thread(() -> {
    
            System.out.println(Thread.currentThread().getName()+" Sleep 1s");
            try {
    TimeUnit.SECONDS.sleep(1);} catch (InterruptedException e) {
    e.printStackTrace();}
            LockSupport.park();
            //LockSupport.park();
            System.out.println(Thread.currentThread().getName()+" Unblock successful ！！！");
        }, "A");
        a.start();

        new Thread(()->{
    
            System.out.println(Thread.currentThread().getName()+" Issue passes ！！");
            LockSupport.unpark(a);
            //LockSupport.unpark(a);
        },"B").start();
    }