对象锁的同步和异步问题

版权声明：本文由哎呀妈呀脑壳疼脑壳疼原创，转载请注明 https://blog.csdn.net/u013983628/article/details/82941179

一、异步访问
method1加了synchronized修饰，method2没有加synchronized修饰。

package com.louis.线程;

public class MyObject {
    public synchronized void method1(){
        try {
            System.out.println(Thread.currentThread().getName());
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    /** synchronized */
    public void method2(){
        System.out.println(Thread.currentThread().getName());
    }

    public static void main(String[] args) {

        final MyObject mo = new MyObject();
        
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                mo.method1();
            }
        },"t1");

        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                mo.method2();
            }
        },"t2");

        t1.start();
        t2.start();

    }
}

t1、t2是同时打印的。
二、同步访问
method1加了synchronized修饰，method2加synchronized修饰。

package com.louis.线程;

public class MyObject {
    public synchronized void method1(){
        try {
            System.out.println(Thread.currentThread().getName());
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    /** synchronized */
    public synchronized void method2(){
        System.out.println(Thread.currentThread().getName());
    }

    public static void main(String[] args) {

        final MyObject mo = new MyObject();
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                mo.method1();
            }
        },"t1");

        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                mo.method2();
            }
        },"t2");

        t1.start();
        t2.start();

    }
}

t1休眠4秒后再打印t2

总结
（1）t1线程先持有object对象的Lock锁，t2线程可以以异步的方式调用对象中的非synchronized修饰的方法
（2） t1线程先持有object对象的Lock锁，t2线程如果在这个时候调用对象中的同步（synchronized）方法则需等待，也就是同步