笔记-LockSupport和Thread.suspend对比

作用

挂起和释放线程

与suspend和resume的对比

– 线程挂起时的状态不同

package com.wenbin.locksipport;

import org.omg.PortableServer.THREAD_POLICY_ID;

import java.util.concurrent.locks.LockSupport;

public class Demo {
    public static void main(String[] args) {
        Thread supportThread = new Thread(() -> {
            System.out.println("park线程执行");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            // 挂起线程
            LockSupport.park();
            System.out.println("park线程继续执行");
        }, "locksupport-park");
        Thread suspendThread = new Thread(() -> {
            System.out.println("suspend线程执行");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            // 挂起线程
            Thread.currentThread().suspend();
            System.out.println("suspend线程继续执行");
        }, "Thread-suspend");
        supportThread.start();
        suspendThread.start();

        /*LockSupport.unpark(supportThread);
        suspendThread.resume();*/
    }
}

运行上面代码后，两个线程被挂起，通过jstack查看线程状态如下

两个线程都是被挂起，但是用suspend方法挂起的线程是RUNNABLE状态

– 释放线程

package com.wenbin.locksipport;

import org.omg.PortableServer.THREAD_POLICY_ID;

import java.util.concurrent.locks.LockSupport;

public class Demo {
    public static void main(String[] args) {
        Thread supportThread = new Thread(() -> {
            System.out.println("park线程执行");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            LockSupport.park();
            System.out.println("park线程继续执行");
        }, "locksupport-park");
        Thread suspendThread = new Thread(() -> {
            System.out.println("suspend线程执行");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            Thread.currentThread().suspend();
            System.out.println("suspend线程继续执行");
        }, "Thread-suspend");
        supportThread.start();
        suspendThread.start();

        LockSupport.unpark(supportThread);
        suspendThread.resume();
    }
}

控制台的信息如下，因为使用suspend挂起的线程，释放方法先执行了，所以线程一直处于挂起状态，而LockSupport解决了这个问题。

结论

结合两个比较的结果，就能知道为什么JDK把suspend和resume标记为不推荐使用，如果不小心没有释放线程，jstack查看的时候是运行态，想解决就只能通过读代码完成。

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