文章目录
java中wait和sleep的区别
在本篇文章中,我们将会讨论一下java中wait()和sleep()方法的区别。并讨论一下怎么使用这两个方法。
Wait和sleep的区别
wait() 是Object中定义的native方法:
public final native void wait(long timeout) throws InterruptedException;
所以每一个类的实例都可以调用这个方法。wait()只能在synchronized block中调用。它会释放synchronized时加在object上的锁。
sleep()是定义Thread中的native静态类方法:
public static native void sleep(long millis) throws InterruptedException;
所以Thread.sleep()可以在任何情况下调用。Thread.sleep()将会暂停当前线程,并且不会释放任何锁资源。
我们先看一下一个简单的wait使用:
@Slf4jpublic class WaitUsage {private static Object LOCK = new Object();public static void WaitExample() throws InterruptedException {synchronized (LOCK) {LOCK.wait(1000);log.info("Object '" + LOCK + "' is woken after" +" waiting for 1 second");}}}
再看一下sleep的使用:
@Slf4jpublic class SleepUsage {public static void sleepExample() throws InterruptedException {Thread.sleep(1000);log.info("Thread '" + Thread.currentThread().getName() +"' is woken after sleeping for 1 second");}}
唤醒wait和sleep
sleep()方法自带sleep时间,时间过后,Thread会自动被唤醒。
或者可以通过调用interrupt()方法来中断。
相比而言wait的唤醒会比较复杂,我们需要调用notify() 和 notifyAll()方法来唤醒等待在特定wait object上的线程。
notify()会根据线程调度的机制选择一个线程来唤醒,而notifyAll()会唤醒所有等待的线程,由这些线程重新争夺资源锁。
wait,notity通常用在生产者和消费者情形,我们看下怎么使用:
@Slf4jpublic class WaitNotifyUsage {private int count =0;public void produceMessage() throws InterruptedException {while(true) {synchronized (this) {while (count == 5) {log.info("count == 5 , wait ....");wait();}count++;log.info("produce count {}", count);notify();}}}public void consumeMessage() throws InterruptedException {while (true) {synchronized (this) {while (count == 0) {log.info("count == 0, wait ...");wait();}log.info("consume count {}", count);count--;notify();}}}}
看下怎么调用:
@Testpublic void testWaitNotifyUsage() throws InterruptedException{WaitNotifyUsage waitNotifyUsage=new WaitNotifyUsage();ExecutorService executorService=Executors.newFixedThreadPool(4);executorService.submit(()-> {try {waitNotifyUsage.produceMessage();} catch (InterruptedException e) {e.printStackTrace();}});executorService.submit(()-> {try {waitNotifyUsage.consumeMessage();} catch (InterruptedException e) {e.printStackTrace();}});Thread.sleep(50000);}
本文的例子可以参考https://github.com/ddean2009/learn-java-concurrency/tree/master/wait-sleep
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