wait notify notifyAll

wait()、notify()、notifyAll()是三个定义在Object类里的方法，可以用来控制线程的状态。

 

这三个方法最终调用的都是jvm级的native方法。随着jvm运行平台的不同可能有些许差异。

 

 

 

• 如果对象调用了wait方法就会使持有该对象的线程把该对象的控制权交出去，然后处于等待状态。
• 如果对象调用了notify方法就会通知某个正在等待这个对象的控制权的线程可以继续运行。
• 如果对象调用了notifyAll方法就会通知所有等待这个对象控制权的线程继续运行。 

其中wait方法有三个over load方法：

 

wait()

wait(long)

wait(long,int)

wait方法通过参数可以指定等待的时长。如果没有指定参数，默认一直等待直到被通知。

和synchronize结合使用

 

http://longdick.iteye.com/blog/453615 讲解的异常java.lang.IllegalMonitorStateException。

1. 任何一个时刻，对象的控制权（monitor）只能被一个线程拥有。
2. 无论是执行对象的wait、notify还是notifyAll方法，必须保证当前运行的线程取得了该对象的控制权（monitor）
3. 如果在没有控制权的线程里执行对象的以上三种方法，就会报java.lang.IllegalMonitorStateException异常。
4. JVM基于多线程，默认情况下不能保证运行时线程的时序性

修改后的代码

package com.swntek.czm.myzxingdemo;

public class NotifyTest {
    private Boolean flag = true;
    private Object obj = new Object();
    class NotifyThread extends Thread {
        public NotifyThread(String name) {
            super(name);
        }

        public void run() {
            try {
                sleep(3000);//推迟3秒钟通知
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized (obj) {
                flag = false;
                obj.notifyAll();
            }
        }
    }
    class WaitThread extends Thread {
        public WaitThread(String name) {
            super(name);
        }
        public void run() {
            synchronized (obj) {
                while (flag) {
                    System.out.println(getName() + " begin waiting!");
                    long waitTime = System.currentTimeMillis();
                    try {
                        obj.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    waitTime = System.currentTimeMillis() - waitTime;
                    System.out.println("wait time :" + waitTime);
                }
                System.out.println(getName() + " end waiting!");
            }
        }
    }
    public static void main(String[] args) throws InterruptedException {
        System.out.println("Main Thread Run!");
        NotifyTest test = new NotifyTest();
        NotifyThread notifyThread = test.new NotifyThread("notify01");
        WaitThread waitThread01 = test.new WaitThread("waiter01");
        WaitThread waitThread02 = test.new WaitThread("waiter02");
        WaitThread waitThread03 = test.new WaitThread("waiter03");
        notifyThread.start();
        waitThread01.start();
        waitThread02.start();
        waitThread03.start();
    }
}

 

jdk1.5Lock取代了synchronized

Condition替代了wait notify

 

Condition

newCondition()            返回用来与此 Lock 实例一起使用的 Condition 实例。

private Lock lock=new ReentrantLock();

private Lock lock=new ReentrantLock();

Condition con=lock.newCondition();

con.await();con.signal();con.signalAll()

 

http://ifeve.com/understand-condition/

  

package com.swntek.czm.myzxingdemo;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class NotifyTest {
    private static Lock reentrantLock = new ReentrantLock();
    private static Condition condition;
    private Boolean flag = true;

    class NotifyThread extends Thread {
        public NotifyThread(String name) {
            super(name);
        }

        public void run() {
            try {
                sleep(3000);//推迟3秒钟通知
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            reentrantLock.lock();
            flag = false;
            condition.signalAll();
            reentrantLock.unlock();
        }
    }

    class WaitThread extends Thread {
        public WaitThread(String name) {
            super(name);
        }

        public void run() {
            reentrantLock.lock();
            while (flag) {
                System.out.println(getName() + " begin waiting!");
                long waitTime = System.currentTimeMillis();
                try {
                    condition.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                waitTime = System.currentTimeMillis() - waitTime;
                System.out.println("wait time :" + waitTime);
            }
            System.out.println(getName() + " end waiting!");
            reentrantLock.unlock();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        System.out.println("Main Thread Run!");
        condition = reentrantLock.newCondition();
        NotifyTest test = new NotifyTest();
        NotifyThread notifyThread = test.new NotifyThread("notify01");
        WaitThread waitThread01 = test.new WaitThread("waiter01");
        WaitThread waitThread02 = test.new WaitThread("waiter02");
        WaitThread waitThread03 = test.new WaitThread("waiter03");
        notifyThread.start();
        waitThread01.start();
        waitThread02.start();
        waitThread03.start();
    }
}