java高级---->Thread之CompletionService的使用
CompletionService的功能是以异步的方式一边生产新的任务,一边处理已完成任务的结果,这样可以将执行任务与处理任务分离开来进行处理。今天我们通过实例来学习一下CompletionService的用法。
CompletionService的简单使用
使用submit()方法执行任务,使用take取得已完成的任务,并按照完成这些任务的时间顺序处理它们的结果。
一、CompletionService的submit方法
public class CompletionServiceTest {
public static void main(String[] args) throws Exception {
ExecutorService service = Executors.newFixedThreadPool(5);
CompletionService<String> completionService = new ExecutorCompletionService<String>(service);
for (int i = 0; i < 5; i++) {
completionService.submit(new ReturnAfterSleepCallable(i));
}
System.out.println("after submit");
for (int i = 0; i < 5; i++) {
System.out.println("result: " + completionService.take().get()); // 这个方法是阻塞的
}
System.out.println("after get");
service.shutdown();
}
private static class ReturnAfterSleepCallable implements Callable<String> {
int sleep;
public ReturnAfterSleepCallable(int sleep) {
this.sleep = sleep;
}
@Override
public String call() throws Exception {
TimeUnit.SECONDS.sleep(sleep);
return System.currentTimeMillis() + ",sleep=" + String.valueOf(sleep);
}
}
}
运行的结果如下:
after submit
result: 1501052486631,sleep=0
result: 1501052487632,sleep=1
result: 1501052488632,sleep=2
result: 1501052489632,sleep=3
result: 1501052490633,sleep=4
after get
官方文档上的说明:
Submits a value-returning task for execution and returns a Future representing the pending results of the task. Upon completion, this task may be taken or polled.
二、使用CompletionService的take方法
take()方法取得最先完成任务的Future对象,谁执行时间最短谁最先返回。
package com.linux.thread;
import java.util.Random;
import java.util.concurrent.*;
public class RunMain1 {
public static void main(String[] args) {
try {
ExecutorService executorService = Executors.newCachedThreadPool();
ExecutorCompletionService<String> completionService = new ExecutorCompletionService<>(executorService);
for (int i = 0; i < 10; i++) {
completionService.submit(new Callable<String>() {
@Override
public String call() throws Exception {
int sleepValue = new Random().nextInt(5);
System.out.println("sleep = " + sleepValue + ", name: " + Thread.currentThread().getName());
TimeUnit.SECONDS.sleep(sleepValue);
return "huhx: " + sleepValue + ", " + Thread.currentThread().getName();
}
});
}
for (int i = 0; i < 10; i++) {
System.out.println(completionService.take().get());
}
executorService.shutdown();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
}
一次的运行结果如下:
sleep = 4, name: pool-1-thread-1
sleep = 0, name: pool-1-thread-2
sleep = 0, name: pool-1-thread-3
huhx: 0, pool-1-thread-3
huhx: 0, pool-1-thread-2
sleep = 1, name: pool-1-thread-4
sleep = 4, name: pool-1-thread-5
sleep = 3, name: pool-1-thread-6
sleep = 4, name: pool-1-thread-7
sleep = 0, name: pool-1-thread-8
huhx: 0, pool-1-thread-8
sleep = 4, name: pool-1-thread-9
sleep = 3, name: pool-1-thread-10
huhx: 1, pool-1-thread-4
huhx: 3, pool-1-thread-6
huhx: 3, pool-1-thread-10
huhx: 4, pool-1-thread-1
huhx: 4, pool-1-thread-5
huhx: 4, pool-1-thread-7
huhx: 4, pool-1-thread-9
官方文档上的说明:
Retrieves and removes the Future representing the next completed task, waiting if none are yet present.
三、使用CompletionService的poll方法
方法poll的作用是获取并移除表示下一个已完成任务的Future,如果不存在这样的任务,则返回null,方法poll是无阻塞的。
package com.linux.thread;
import java.util.concurrent.*;
public class RunMain2 {
public static void main(String[] args) {
ExecutorService executorService = Executors.newCachedThreadPool();
CompletionService<String> service = new ExecutorCompletionService<String>(executorService);
service.submit(new Callable<String>() {
@Override
public String call() throws Exception {
TimeUnit.SECONDS.sleep(3);
System.out.println("3 seconds pass.");
return "3秒";
}
});
System.out.println(service.poll());
executorService.shutdown();
}
}
运行的结果如下:
null
3 seconds pass.
官方文档上的说明:
Retrieves and removes the Future representing the next completed task or null if none are present.
作者:
huhx
出处: www.cnblogs.com/huhx
格言:你尽力了,才有资格说自己的运气不好。
版权:本文版权归作者huhx和博客园共有,欢迎转载。未经作者同意必须保留此段声明,且在文章页面明显位置给出原文链接,否则保留追究法律责任的权利。
出处: www.cnblogs.com/huhx
格言:你尽力了,才有资格说自己的运气不好。
版权:本文版权归作者huhx和博客园共有,欢迎转载。未经作者同意必须保留此段声明,且在文章页面明显位置给出原文链接,否则保留追究法律责任的权利。