synchronized及wait()/notify()的一些实验

最近在项目中运用多线程比较多，对synchronized，wait()，notify()，做了一些实验。

 

1、针对方法的synchronized实际上是对该对象加锁。

package com.test.wait_notify;

/**
 * 锅巴
 * 描述
 * @version 1.0 2010-8-10
 */
public class Main {

    public static void main(String[] args) throws InterruptedException {
        Main main = new Main();
        (new Thread(new MyThread(main))).start();
        Thread.sleep(1000);
        main.test2();
    }
    
    public synchronized void test3() throws InterruptedException{
        System.out.println(Thread.currentThread().getName() + " test3()");
        notify();
        wait();
    }
    
    public synchronized void test2(){
        for(int i=0; i<10; i++){
            System.out.println(Thread.currentThread().getName() + " test2()");
        }
    }
    
    public synchronized void test1() throws InterruptedException{
        System.out.println(Thread.currentThread().getName() + " test1() start");
        //wait();
        Thread.sleep(5000);
        System.out.println(Thread.currentThread().getName() + " test1() end");
    }
}

 

class MyThread implements Runnable{

    private Main main;
    
    public MyThread(Main main){
        this.main = main;
    }
    
    public void run() {
        // TODO Auto-generated method stub
        try {
            main.test1();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    
    
}

 

运行结果

Thread-0 test1() start
Thread-0 test1() end
main test2()
main test2()
main test2()
main test2()
main test2()
main test2()
main test2()
main test2()
main test2()
main test2()

MyThread.run中调用synchronized void test1() ，这时对main对象加锁

main.test2()要等待main锁释放。

 

结论：当某线程调用某synchronized 修饰的方法时，会对该对象加锁。其他对象在调用其他synchronized 修饰方法时要等该获得该对象锁。

 

2、wait()，notify()，notifyAll() 必须在 synchronized 修饰内才有用。

 

3、wait()是让线程等待，放弃执行权力，并释放锁。

/**
 * 锅巴
 * 描述
 *
 * @version 1.0 2010-8-10
 */
public class Main {

    public static void main(String[] args) throws InterruptedException {
        Main main = new Main();
        (new Thread(new MyThread(main))).start();
        (new Thread(new MyThread(main))).start();
        (new Thread(new MyThread(main))).start();
        Thread.sleep(1000);
        main.test2();
        Thread.sleep(1000);
        main.test3();
        main.test3();
        main.test3();
    }
    
    public synchronized void test3() throws InterruptedException{
        System.out.println(Thread.currentThread().getName() + " test3()");
        notify();
    }
    
    public synchronized void test2(){
        for(int i=0; i<10; i++){
            System.out.println(Thread.currentThread().getName() + " test2()");
        }
    }
    
    public synchronized void test1() throws InterruptedException{
        System.out.println(Thread.currentThread().getName() + " test1() start");
        wait();
        System.out.println(Thread.currentThread().getName() + " test1() end");
    }
}

class MyThread implements Runnable{

    private Main main;
    
    public MyThread(Main main){
        this.main = main;
    }
    
    public void run() {
        // TODO Auto-generated method stub
        try {
            main.test1();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    
    
}

 执行结果

 

Thread-0 test1() start
Thread-2 test1() start
Thread-1 test1() start
main test2()
main test2()
main test2()
main test2()
main test2()
main test2()
main test2()
main test2()
main test2()
main test2()
main test3()
main test3()
main test3()
Thread-0 test1() end
Thread-1 test1() end
Thread-2 test1() end

 

在各线程调用main.test1()时碰到wait()，休眠并释放锁，其他线程可以进入。

main.test2()在各线程都wait()时调用