LockSupport

LockSupport是高级线程同步类的基础，用来block和释放线程。这里要区别notify和wait的点在于这里可以先unpark，再park。（有点类似于unpark等于-1，park等于+1。+1-1=0 或者-1+1=0 ，只有1的状态是阻塞的。）

Blocker参数是用来辅助排查阻塞而已。

package com.github;

import java.util.concurrent.locks.LockSupport;

class MyThread extends Thread {

private Object object;

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

public void run() {
System.out.println("before unpark");
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
// 获取blocker
System.out.println("Blocker info " + LockSupport.getBlocker((Thread) object));
// 释放许可
LockSupport.unpark((Thread) object);
// 再次获取blocker
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Blocker info " + LockSupport.getBlocker((Thread) object));
System.out.println("after unpark");
}
}

public class App {
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");
}
}