JAVA多线程编程核心技术--synchronized关键词

JAVA多线程编程核心技术--synchronized关键词

这个是书当中的例子

synchronized关键词

特性

• 可重入

锁this对象

• Service.java

package com.service;

public class Service {
    public void sayA() throws InterruptedException {
\t//注意，new String()和 = “”是不同的概念
        String anyString = new String();
        synchronized (anyString){
            System.out.println("线程名称为"+ Thread.currentThread().getName()+"在"+ System.currentTimeMillis()+ " 进入同步快");

            Thread.sleep(2000);

            System.out.println("线程名称为"+ Thread.currentThread().getName()+"在"+ System.currentTimeMillis()+ " 离开同步快");
        }
    }

    public void sayB() throws InterruptedException {
        synchronized(this){
            System.out.println("线程名称为"+ Thread.currentThread().getName()+"在"+ System.currentTimeMillis()+ " 进入同步块");
            Thread.sleep(2000);
            System.out.println("线程名称为"+ Thread.currentThread().getName()+"在"+ System.currentTimeMillis()+ " 离开同步块");
        }
    }
}

• ThreadA.java

package com.service;

public class ThreadA extends Thread {

    private Service service;

    public ThreadA(Service service){
        this.service = service;
    }

    @Override
    public void run() {
        try {
            service.sayA();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

• ThreadB.java

ppackage com.service;

public class ThreadB extends Thread {

    private Service service;

    public ThreadB(Service service){
        this.service = service;
    }

    @Override
    public void run() {
        try {
            service.sayB();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

• Run.java

package com.service;

public class Run {
    public static void main(String[] args) {
        Service service = new Service();
        ThreadA a = new ThreadA(service);
        a.setName("A");
        a.start();

        ThreadB b = new ThreadB(service);
        b.setName("B");
        b.start();
    }
}

运行结果

线程名称为A在1572859726886 进入同步快
线程名称为B在1572859726887 进入同步块
线程名称为A在1572859728887 离开同步快
线程名称为B在1572859728888 离开同步块

Process finished with exit code 0

结果

this对象锁与string锁是异步的

锁class和static方法

• synchronized(this) 锁的该类的实例对象--局部锁
• synchronized(Service.class) 锁的是class类--全局锁
• 如果synchronized修饰的是静态方法，代表了用的class锁

public class Service {
    public synchronized static int getValue(){
        return 1;
    }
}