什么是等待/通知机制
举个栗子:餐厅里,厨师做好菜之后,通知等待中的服务员就是一个简单的等待通知机制
wait:
wait方法代码的作用是使当前执行代码的线程进入等待,wait方法是Object类的方法,该方法用来将当前线程置入“预执行队列当中”,并且在wait所在的代码行处停止执行,直到接到通知或被终端为止。在wait之前,线程必须获得该对象的对象级别锁,即只有在同步方法或同步块中才能调用wait方法。wait方法执行后,当前线程会立马释放锁。
notify:
notify方法在调用前,也要获得当前线程的对象级别的锁,即方法notify也要在同步方法或同步块中调用。该方法用来通知那些可能等待该对象的对象锁的其他线程,需要说明的是,在执行notify方法后,当前线程不会立马释放该对象锁,呈wait状态的线程不能立马获得该对象锁,需要等到notify所在的同步块执行完才会释放该对象锁。
总结:
wait使线程停止运行,notify使通知停止的线程继续执行。
notify一次只会随机唤醒一个线程
看下面的代码:
public class Service {
public void testMothod(Object lock){
try{
synchronized (lock){
System.out.println(Thread.currentThread().getName()+ " begin wait at " + System.currentTimeMillis());
lock.wait();
System.out.println(Thread.currentThread().getName() + " end wait at " + System.currentTimeMillis());
}
} catch (InterruptedException e){
e.printStackTrace();
}
}
}
public class ThreadA extends Thread {
private Object lock;
public ThreadA(Object object){
this.lock = object;
}
@Override
public void run() {
super.run();
Service serivce = new Service();
serivce.testMothod(lock);
}
}
public class ThreadB extends Thread {
private Object lock;
public ThreadB(Object object){
this.lock = object;
}
@Override
public void run() {
super.run();
Service serivce = new Service();
serivce.testMothod(lock);
}
}
public class ThreadC extends Thread {
private Object lock;
public ThreadC(Object object){
this.lock = object;
}
@Override
public void run() {
super.run();
Service serivce = new Service();
serivce.testMothod(lock);
}
}
public class NotifyOne extends Thread {
private Object lock;
public NotifyOne(Object object){
this.lock = object;
}
@Override
public void run() {
super.run();
synchronized (lock){
lock.notify();
}
}
}
public class Test {
public static void main(String[] args) {
try{
Object object = new Object();
ThreadA threadA = new ThreadA(object);
ThreadB threadB = new ThreadB(object);
ThreadC threadC = new ThreadC(object);
threadA.setName("A");
threadB.setName("B");
threadC.setName("C");
threadA.start();
threadB.start();
threadC.start();
Thread.sleep(1000);
NotifyOne notifyOne = new NotifyOne(object);
notifyOne.start();
} catch (InterruptedException e){
e.printStackTrace();
}
}
}
运行结果:
A begin wait at 1563079593045
B begin wait at 1563079593045
C begin wait at 1563079593045
A end wait at 1563079594044
可以看到 notify方法只唤醒了A线程,那么唤醒所有线程的方法就是notifyAll喽
修改NotifyOne类中的notify方法为notifyAll
public class NotifyOne extends Thread {
private Object lock;
public NotifyOne(Object object){
this.lock = object;
}
@Override
public void run() {
super.run();
synchronized (lock){
lock.notifyAll();
}
}
}
运行结果:
A begin wait at 1563079801021
C begin wait at 1563079801022
B begin wait at 1563079801022
B end wait at 1563079802012
C end wait at 1563079802012
A end wait at 1563079802012
Process finished with exit code 0
可以看到,A B C三个线程都被唤醒了
wait(long)方法介绍
该方法是等待参数值的时间内如果没有线程对锁进行唤醒,如果超过这个时间,则自动唤醒。
That's ALL !!!!!!
本文内容由网友自发贡献,版权归原作者所有,本站不承担相应法律责任。如您发现有涉嫌抄袭侵权的内容,请联系:hwhale#tublm.com(使用前将#替换为@)