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：

@Slf4j

public 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：

@Slf4j

public 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：

@Slf4j

public 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：

@Test

public 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

更多教程请参考 flydean的博客