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JUC-多线程锁Synchronized锁的八种情况1

news 来源：原创 2024/5/5 16:51:32

1、标准情况下：

package com.nanjing.juc;

class Phone {

    public synchronized void sendSMS() throws Exception {
        System.out.println(Thread.currentThread().getName()+"---发短信---sendSMS");
    }

    public synchronized void sendEmail() throws Exception {
        System.out.println(Thread.currentThread().getName()+"---发邮件---sendEmail");
    }

}

public class ThreadDemo_10 {

    public static void main(String[] args) throws Exception {

        Phone phone = new Phone();

        new Thread(() -> {
            try {
                phone.sendSMS();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }, "AA").start();

        Thread.sleep(100);

        new Thread(() -> {
            try {
                phone.sendEmail();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }, "BB").start();
    }
}

synchronized锁的对象是方法的调用者！
两个方法用的是同一个锁，谁先拿到谁执行！

2、sendSms方法延迟4秒

因为synchronized锁的对象是方法的调用者！

两个方法用的是同一个锁，谁先拿到谁执行！

AA线程先执行，拿到锁准备执行sendSms方法，

先等4秒，4秒后才开始打印AA---发短信---sendSMS

最后才执行sendEmail方法，打印BB---发邮件---sendEmail

package com.nanjing.juc;

import java.util.concurrent.TimeUnit;

class Phone1 {

    public synchronized void sendSMS() throws Exception {
        TimeUnit.SECONDS.sleep(4);//或者Thread.sleep(4000);
        System.out.println(Thread.currentThread().getName()+"---发短信---sendSMS");
    }

    public synchronized void sendEmail() throws Exception {
        //TimeUnit.SECONDS.sleep(4);//或者Thread.sleep(4000);
        System.out.println(Thread.currentThread().getName()+"---发邮件---sendEmail");
    }

}

public class ThreadDemo_11 {

    public static void main(String[] args) throws Exception {

        Phone1 phone1 = new Phone1();

        new Thread(() -> {
            try {
                phone1.sendSMS();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }, "AA").start();

        Thread.sleep(100);

        new Thread(() -> {
            try {
                phone1.sendEmail();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }, "BB").start();
    }
}

3、如果sendEmail方法延迟4秒，则结果不同

因为synchronized锁的对象是方法的调用者！

两个方法用的是同一个锁，谁先拿到谁执行！

AA线程先执行，拿到锁准备执行sendSms方法，打印AA---发短信---sendSMS

最后才执行sendEmail方法，先等4秒，4秒后打印BB---发邮件---sendEmail

package com.nanjing.juc;

import java.util.concurrent.TimeUnit;

class Phone1 {

    public synchronized void sendSMS() throws Exception {
        //TimeUnit.SECONDS.sleep(4);//或者Thread.sleep(4000);
        System.out.println(Thread.currentThread().getName()+"---发短信---sendSMS");
    }

    public synchronized void sendEmail() throws Exception {
        TimeUnit.SECONDS.sleep(4);//或者Thread.sleep(4000);
        System.out.println(Thread.currentThread().getName()+"---发邮件---sendEmail");
    }

}

public class ThreadDemo_11 {

    public static void main(String[] args) throws Exception {

        Phone1 phone1 = new Phone1();

        new Thread(() -> {
            try {
                phone1.sendSMS();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }, "AA").start();

        Thread.sleep(100);

        new Thread(() -> {
            try {
                phone1.sendEmail();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }, "BB").start();
    }
}