JAVA面试-并发篇 09-LockSupport 和 waitnotify 的区别

LockSupport 与 wait/notify 核心区别详解

一、文章概述

wait/notify是Object类的原生线程通信方法，依赖synchronized同步锁；LockSupport是JUC提供的线程阻塞唤醒工具，是AQS的核心底层组件。本文通过对比表、流程图和完整可运行代码，清晰讲解两者的使用差异与核心特性。

二、核心区别对比

对比维度	wait/notify	LockSupport
使用限制	必须在同步块中，否则抛异常	无锁限制，任意位置调用
执行顺序	必须先等待后唤醒	支持先唤醒后等待
唤醒精度	随机唤醒，无法指定线程	精准唤醒目标线程
锁资源	调用wait会自动释放锁	无锁，无需释放资源

三、执行流程

wait/notify 执行流程

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wait阻塞并释放锁
notify唤醒线程
重新竞争锁执行

LockSupport 执行流程

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unpark精准唤醒
线程恢复执行

四、完整代码示例

1. wait/notify 实现线程通信

java 复制代码

public class WaitNotifyDemo {
    private static final Object lock = new Object();
    public static void main(String[] args) {
        new Thread(() -> {
            synchronized (lock) {
                try { lock.wait(); } // 阻塞并释放锁
                catch (InterruptedException e) {}
                System.out.println("线程被唤醒");
            }
        }).start();
        new Thread(() -> {
            synchronized (lock) { lock.notify(); } // 必须加锁唤醒
        }).start();
    }
}

2. LockSupport 实现线程通信

java 复制代码

import java.util.concurrent.locks.LockSupport;
public class LockSupportDemo {
    public static void main(String[] args) {
        Thread t = new Thread(() -> {
            LockSupport.park(); // 无锁阻塞
            System.out.println("线程被精准唤醒");
        });
        t.start();
        LockSupport.unpark(t); // 精准唤醒指定线程，无需加锁
    }
}

总结

wait/notify强依赖同步锁，使用繁琐且唤醒不精准，仅适用于基础同步场景；LockSupport无使用限制、支持预唤醒、精准操作线程，规避了传统API的缺陷，是Java高并发框架的首选线程协作工具。