JUC-多线程锁Synchronized锁的八种情况1

客官°小女子只卖身不卖艺 2024-04-06 12:37 71阅读 0赞

**情况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();
        }
    }

![75fac6330a4540b8975e66c228400ca6.png][]

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

--------------------

**情况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();
        }
    }

![ce66498484de433287688980e435729b.png][]

--------------------

**情况2---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();
        }
    }

![3260ff20e4194c13858fdf4bdf650eb3.png][]

[75fac6330a4540b8975e66c228400ca6.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/025daaa908134009996a6e0cea97e926.png
[ce66498484de433287688980e435729b.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/1b07965b67b54536ac48e82966580400.png
[3260ff20e4194c13858fdf4bdf650eb3.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/113a1bfd78134e37a816796f0dbbd052.png