java并发(二）：初探syncronized

参考博客

Java多线程系列--“基础篇”04之 synchronized关键字

synchronized基本规则

第一条	当线程访问A对象的synchronized方法和同步块的时候，其他线程无法访问A对象的synchronized方法和同步块
第二条	当线程访问A对象的synchronized方法和同步块的时候，其他线程可以访问A对象的非synchronized方法和同步块
第三条	当线程访问A对象的synchronized方法和同步块的时候，其他线程不可以访问A对象其他synchronizedd方法和同步块

第三条基本原则测试

import lombok.extern.slf4j.Slf4j;

@Slf4j
public class SysDemo3 {
    public static void main(String[] args) {
        final  Count count =new Count();
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                count.synMethodA();
            }
        },"t1");
        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                count.synMethodB();
            }
        },"t2");
        t1.start();
        t2.start();
    }


}
@Slf4j
class Count {
    int countsize =5;

    public synchronized void synMethodA(){
        int count =0;
        while(count<countsize){
            log.info("synMethodA, Current thread is : {}, count = {}",Thread.currentThread().getName(),count++);
        }

    }
    public synchronized void synMethodB(){
        int count =0;
        while(count<countsize){
            log.info("synMethodB, Current thread is : {}, count = {}",Thread.currentThread().getName(),count++);
        }

    }
}

测试结果

2019-07-25 13:40:44,482   [t1] INFO  Count  - synMethodA, Current thread is : t1, count = 0
2019-07-25 13:40:44,482   [t1] INFO  Count  - synMethodA, Current thread is : t1, count = 1
2019-07-25 13:40:44,482   [t1] INFO  Count  - synMethodA, Current thread is : t1, count = 2
2019-07-25 13:40:44,482   [t1] INFO  Count  - synMethodA, Current thread is : t1, count = 3
2019-07-25 13:40:44,482   [t1] INFO  Count  - synMethodA, Current thread is : t1, count = 4
2019-07-25 13:40:44,482   [t2] INFO  Count  - synMethodB, Current thread is : t2, count = 0
2019-07-25 13:40:44,482   [t2] INFO  Count  - synMethodB, Current thread is : t2, count = 1
2019-07-25 13:40:44,482   [t2] INFO  Count  - synMethodB, Current thread is : t2, count = 2
2019-07-25 13:40:44,482   [t2] INFO  Count  - synMethodB, Current thread is : t2, count = 3
2019-07-25 13:40:44,482   [t2] INFO  Count  - synMethodB, Current thread is : t2, count = 4

说明

每个对象都有一把同步锁，同步锁是依赖对象存在的。上面的结果说明当A对象的同步方法或者同步块被调用的时候，这把锁
就在使用者中，其他的使用者调用A对象的同步方法或者同步块的时候，是不会获取到锁的。

实例锁与全局锁

实例锁是锁在对象上
全局锁是锁在类上，static syncronized方法或者同步块

不同的线程调用一个类的不同的static syncronized方法。

不同的线程调用一个类的不同的static syncronized方法：x.classSyn1()与y.classSyn2()，x不释放，y是无法运行静态同步方法的。

测试

import lombok.extern.slf4j.Slf4j;

import static java.lang.Thread.sleep;
/*
    全局锁的使用，类的static syncronized方法或代码块被线程调用，
    其他线程没有拥有全局锁，无法调用其他的同步方法和同步块
 */
@Slf4j
public class SysDemo5 {
    static  class Count {
        static int countsize =5;

        public synchronized void synMethodA(){
            int count =0;
            while(count<countsize){
                log.info("synMethodA, Current thread is : {}, count = {}",Thread.currentThread().getName(),count++);
                try {
                    sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        }
        public synchronized void synMethodB(){
            int count =0;

            while(count<countsize){
                log.info("synMethodB, Current thread is : {}, count = {}",Thread.currentThread().getName(),count++);
                try {
                    sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        }
        public static synchronized  void cSynMethodA(){
            int count =0;
            while(count<countsize){
                log.info("class synMethodA, Current thread is : {}, count = {}",Thread.currentThread().getName(),count++);
                try {
                    sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
        public static synchronized  void cSynMethodB(){
            int count =0;
            while(count<countsize){
                log.info("class synMethodB, Current thread is : {}, count = {}",Thread.currentThread().getName(),count++);
                try {
                    sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    public static void main(String[] args) {
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                Count.cSynMethodA();
            }
        },"t1");
        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
               Count.cSynMethodB();
            }
        },"t2");
        t1.start();
        t2.start();
    }
}

测试结果

2019-07-25 17:31:24,358   [t1] INFO  SysDemo5  - class synMethodA, Current thread is : t1, count = 0
2019-07-25 17:31:24,857   [t1] INFO  SysDemo5  - class synMethodA, Current thread is : t1, count = 1
2019-07-25 17:31:25,356   [t1] INFO  SysDemo5  - class synMethodA, Current thread is : t1, count = 2
2019-07-25 17:31:25,855   [t1] INFO  SysDemo5  - class synMethodA, Current thread is : t1, count = 3
2019-07-25 17:31:26,354   [t1] INFO  SysDemo5  - class synMethodA, Current thread is : t1, count = 4
2019-07-25 17:31:26,853   [t2] INFO  SysDemo5  - class synMethodB, Current thread is : t2, count = 0
2019-07-25 17:31:27,351   [t2] INFO  SysDemo5  - class synMethodB, Current thread is : t2, count = 1
2019-07-25 17:31:27,850   [t2] INFO  SysDemo5  - class synMethodB, Current thread is : t2, count = 2
2019-07-25 17:31:28,349   [t2] INFO  SysDemo5  - class synMethodB, Current thread is : t2, count = 3
2019-07-25 17:31:28,847   [t2] INFO  SysDemo5  - class synMethodB, Current thread is : t2, count = 4

x.classSyn1与x.sysn1

对象的同步方法和类的同步方法互不影响

测试

import lombok.extern.slf4j.Slf4j;

import static java.lang.Thread.sleep;

@Slf4j
public class SysDemo4 {
    static  class Count {
        static int countsize =5;

        public synchronized void synMethodA(){
            int count =0;
            while(count<countsize){
                log.info("synMethodA, Current thread is : {}, count = {}",Thread.currentThread().getName(),count++);
                try {
                    sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        }
        public synchronized void synMethodB(){
            int count =0;

            while(count<countsize){
                log.info("synMethodB, Current thread is : {}, count = {}",Thread.currentThread().getName(),count++);
                try {
                    sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        }
        public static synchronized  void cSynMethodA(){
            int count =0;
            while(count<countsize){
                log.info("class synMethodA, Current thread is : {}, count = {}",Thread.currentThread().getName(),count++);
                try {
                    sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    public static void main(String[] args) {
        final  Count count =new Count();
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                count.synMethodA();
            }
        },"t1");
        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                Count.cSynMethodA();
            }
        },"t2");
        t1.start();
        t2.start();
    }


}

测试结果

2019-07-25 19:04:53,184   [t2] INFO  SysDemo4  - class synMethodA, Current thread is : t2, count = 0
2019-07-25 19:04:53,199   [t1] INFO  SysDemo4  - synMethodA, Current thread is : t1, count = 0
2019-07-25 19:04:53,683   [t2] INFO  SysDemo4  - class synMethodA, Current thread is : t2, count = 1
2019-07-25 19:04:53,699   [t1] INFO  SysDemo4  - synMethodA, Current thread is : t1, count = 1
2019-07-25 19:04:54,182   [t2] INFO  SysDemo4  - class synMethodA, Current thread is : t2, count = 2
2019-07-25 19:04:54,198   [t1] INFO  SysDemo4  - synMethodA, Current thread is : t1, count = 2
2019-07-25 19:04:54,682   [t2] INFO  SysDemo4  - class synMethodA, Current thread is : t2, count = 3
2019-07-25 19:04:54,697   [t1] INFO  SysDemo4  - synMethodA, Current thread is : t1, count = 3
2019-07-25 19:04:55,181   [t2] INFO  SysDemo4  - class synMethodA, Current thread is : t2, count = 4
2019-07-25 19:04:55,197   [t1] INFO  SysDemo4  - synMethodA, Current thread is : t1, count = 4

Process finished with exit code 0