wait notify notifyAll

原創

冰雪巅峰

2020-02-21 05:15

wait()、notify()、notifyAll()是三個定義在Object類裏的方法，可以用來控制線程的狀態。

這三個方法最終調用的都是jvm級的native方法。隨着jvm運行平臺的不同可能有些許差異。

如果對象調用了wait方法就會使持有該對象的線程把該對象的控制權交出去，然後處於等待狀態。
如果對象調用了notify方法就會通知某個正在等待這個對象的控制權的線程可以繼續運行。
如果對象調用了notifyAll方法就會通知所有等待這個對象控制權的線程繼續運行。

其中wait方法有三個over load方法：

wait()

wait(long)

wait(long,int)

wait方法通過參數可以指定等待的時長。如果沒有指定參數，默認一直等待直到被通知。

和synchronize結合使用

http://longdick.iteye.com/blog/453615 講解的異常java.lang.IllegalMonitorStateException。

任何一個時刻，對象的控制權（monitor）只能被一個線程擁有。
無論是執行對象的wait、notify還是notifyAll方法，必須保證當前運行的線程取得了該對象的控制權（monitor）
如果在沒有控制權的線程裏執行對象的以上三種方法，就會報java.lang.IllegalMonitorStateException異常。
JVM基於多線程，默認情況下不能保證運行時線程的時序性

修改後的代碼

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);//推遲3秒鐘通知
            } 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()
返回用來與此 Lock 實例一起使用的 Condition 實例。

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);//推遲3秒鐘通知
            } 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();
    }
}