转载:http://tomyz0223.iteye.com/blog/1018969 作者:tomyz0223
感谢~
CountDownLatch
CountDownlatch,是一种Sychronizer,它可以延迟线程的进度直到线程的进度到线程到达终止状态。
它本身而言是Java并发包中非常有用的一个类,它可以让某些任务完成以后再继续运行下面的内容,每个任务本身执行完毕后让计数器减一,直到计数器清零后,以下的内容才可以继续运行,否则将阻塞等待。
想了一下,这个场景非常适合用于项目中这样的场景: 我们有个项目,它需要三个第三方的API,并把结果拿到,在一个线程中顺序去拿结果没有问题,但是这里这三个任务是非常耗时的操作,如果顺序获取性能非常差,因此可以考虑用三个线程,当三个线程拿到结果后才继续主线程的工作,等三个线程运行结束后,由主线程去取子线程运行的结果。 这里有个很重要的前提:我们的系统运行在4个cpu的server上,这样多线程才能体现性能,JVM会分配这些线程尽量运行在不同的cpu上。
CountDownLatch有以下基本方法:
1)await(),阻塞等待,直到计数器清零
2)await(int timeout, TimeUnit unit),使线程阻塞,除非被中断或者超过等待的最大时间
如果达到计数器清零,则await返回true,如果等待超过了最大的等待时间,则返回false
3)countDown(),计数器减一,当计数器清零时,await的线程被唤醒,线程继续执行
4)getCount (),获取当前计数器的大小
package countdownlatch;
import java.util.concurrent.CountDownLatch;
/**
*
*<p>Test</p>
*<p>Description:</P>
*<p>Company:</p>
*<p>Department:CAS</p>
*@Author: Tommy Zhou
*@Since: 1.0
*@Version:Date:2011-4-26
*
**/
public class CountDownLatchSample {
public static void main(String[] args) {
String[] strs = getResult();
for (int i = 0; i < strs.length; i++) {
System.out.println(strs[i]);
}
}
public static String[] getResult(){
String[] strs = new String[3];
CountDownLatch countDownLatch = new CountDownLatch(3);
Work1 work1 = new Work1(countDownLatch,strs[0]);
Work2 work2 = new Work2(countDownLatch,strs[1]);
Work3 work3 = new Work3(countDownLatch,strs[2]);
work1.start();
work2.start();
work3.start();
try {
countDownLatch.await();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
strs[0] = work1.str1;
strs[1] = work2.str2;
strs[2] = work3.str3;
return strs;
}
}
class Work1 extends Thread{
public String str1;
public CountDownLatch latch1;
public Work1(CountDownLatch latch1,String str1){
this.latch1 = latch1;
this.str1 = str1;
}
public void run(){
str1="work1";
latch1.countDown();
}
}
class Work2 extends Thread{
public String str2;
public CountDownLatch latch2;
public Work2(CountDownLatch latch2,String str2){
this.latch2 = latch2;
this.str2 = str2;
}
public void run(){
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
str2="work2";
latch2.countDown();
}
}
class Work3 extends Thread{
public String str3;
public CountDownLatch latch3;
public Work3(CountDownLatch latch3,String str3){
this.latch3 = latch3;
this.str3 = str3;
}
public void run(){
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
str3="work3";
latch3.countDown();
}
}