1、sleep介绍
sleep() 定义在Thread.java中,sleep() 的作用是让当前线程休眠,即当前线程会从“运行状态”进入到“休眠(阻塞)状态”。sleep()会指定休眠时间,线程休眠的时间会大于/等于该指定休眠时间;在线程重新被唤醒时,它会由“阻塞状态”变成“就绪状态”,从而等待cpu的调度执行
2、示例:
public class YieldThread extends Thread {
public YieldThread(String name) {
super(name);
}
@Override
public synchronized void run() {
try {
for (int i = 0; i < 10; i++) {
System.out.printf("%s [%d]:%d\n", this.getName(), this.getPriority(), i);
if (i % 4 == 0)
Thread.sleep(3000);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
//测试
public class MainTest {
public static void main(String args[]) {
YieldThread t1 = new YieldThread("t1");
YieldThread t2 = new YieldThread("t2");
t1.start();
t2.start();
}
}
//结果
t1 [5]:0
t2 [5]:0
t1 [5]:1//3秒钟后
t1 [5]:2
t1 [5]:3
t1 [5]:4
t2 [5]:1
t2 [5]:2
t2 [5]:3
t2 [5]:4
t1 [5]:5//再3秒后
t1 [5]:6
t1 [5]:7
t1 [5]:8
t2 [5]:5
t2 [5]:6
t2 [5]:7
t2 [5]:8
t1 [5]:9//再3秒后
t2 [5]:9
3、sleep()和wait()比较
wait()的作用是让当前线程由“运行状态”进入“等待(阻塞)状态”,同时会释放对象的同步锁;而sleep()的作用是让当前线程由“运行状态”进入到“休眠(阻塞)状态”,但不会释放锁。示例:
public class MainTest {
private static Object obj = new Object();
public static void main(String args[]) {
ThreadInner t1 = new ThreadInner("t1");
ThreadInner t2 = new ThreadInner("t2");
t1.start();
t2.start();
}
// 静态内部类
static class ThreadInner extends Thread {
public ThreadInner(String name) {
super(name);
}
public void run() {
synchronized (obj) {
for (int i = 0; i < 10; i++) {
System.out.printf("%s: %d\n", this.getName(), i);
if (i % 4 == 0)
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
}
//结果
t1: 0
t1: 1//两秒后
t1: 2
t1: 3
t1: 4
t1: 5//两秒后
t1: 6
t1: 7
t1: 8
t1: 9//两秒后
t2: 0
t2: 1//两秒后
t2: 2
t2: 3
t2: 4
t2: 5//两秒后
t2: 6
t2: 7
t2: 8
t2: 9//两秒后
可以看到先执行的线程在休眠后并没有释放锁,后执行的现在只能在先执行的线程执行完同步代码块释放锁之后再获取锁得以执行