主要是使用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(); } }
时间: 2024-11-05 18:44:29