LockSupport

J.U.C框架中有一个叫做LockSupport的类，可以精准地阻塞和唤醒特定的线程，并作为其他同步类的原语。
LockSupport包含一个park(Object blocker)和unpark(Object blocker)方法，分别用于阻塞和唤醒。

举个例子，下面的代码包含一个线程thread1和主线程，在thread1中调用park方法，在主线程中调用unpark，然后打印thread1的状态：

import java.util.concurrent.locks.LockSupport;


public class Main{
    public static void main(String[] args) throws InterruptedException {

    Thread thread1 = new Thread(new Runnable() {

        @Override
        public void run() {
        System.out.println("thread 1 start");
        LockSupport.park(Thread.currentThread());
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("thread 1 end");
        }
    });
    thread1.start();
    System.out.println("main thread start,thread1 "+thread1.getState());
    Thread.sleep(2000);
    System.out.println("main thread running,thread1 "+thread1.getState());
    LockSupport.unpark(thread1);
    Thread.sleep(6000);
    System.out.println("main thread end,thread1 "+thread1.getState());
    }
}

执行结果：

thread 1 start
main thread start,thread1 RUNNABLE
main thread running,thread1 WAITING
thread 1 end
main thread end,thread1 TERMINATED

可以看到，park之后thread1变成WAITTING，unpark之后唤醒继续执行直到结束