java中wait和sleep的區別
在本篇文章中，我們將會討論一下java中wait()和sleep()方法的區別。並討論一下怎么使用這兩個方法。
Wait和sleep的區別
wait() 是Object中定義的native方法：
public final native void wait(long timeout) throws InterruptedException;
所以每一個類的實例都可以調用這個方法。wait()只能在synchronized block中調用。它會釋放synchronized時加在object上的鎖。
sleep()是定義Thread中的native靜態類方法：
public static native void sleep(long millis) throws InterruptedException;
所以Thread.sleep()可以在任何情況下調用。Thread.sleep()將會暫停當前線程，並且不會釋放任何鎖資源。
我們先看一下一個簡單的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");
}
}
喚醒wait和sleep
sleep()方法自帶sleep時間，時間過后，Thread會自動被喚醒。
或者可以通過調用interrupt()方法來中斷。
相比而言wait的喚醒會比較復雜，我們需要調用notify() 和 notifyAll()方法來喚醒等待在特定wait object上的線程。
notify()會根據線程調度的機制選擇一個線程來喚醒，而notifyAll()會喚醒所有等待的線程，由這些線程重新爭奪資源鎖。
wait,notity通常用在生產者和消費者情形，我們看下怎么使用：
@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();
}
}
}
}
看下怎么調用：
@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);
}
本文的例子可以參考https://github.com/ddean2009/learn-java-concurrency/tree/master/wait-sleep
更多教程請參考 flydean的博客