Callable、FutureTask中阻塞超时返回的坑点

来源：互联网发布：呱呱漫画软件编辑：程序博客网时间：2024/06/05 16:13

本文转载自：http://www.cnblogs.com/starcrm/p/5010863.html

案例1：

package com.net.thread.future;import java.util.concurrent.Callable;import java.util.concurrent.ExecutionException;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.FutureTask;import java.util.concurrent.TimeUnit; /** * @author  * @Time：2017年8月18日 上午10:49:07 * @version 1.0 * @description */   import java.util.concurrent.ExecutionException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.FutureTask; import java.util.concurrent.TimeUnit; import java.util.concurrent.TimeoutException;   public class FutureTaskExample {       public static void main(String[] args) {         MyCallable callable1 = new MyCallable(1000);         MyCallable callable2 = new MyCallable(5000);           FutureTask<String> futureTask1 = new FutureTask<String>(callable1);         FutureTask<String> futureTask2 = new FutureTask<String>(callable2);           ExecutorService executor = Executors.newFixedThreadPool(2);         executor.execute(futureTask1);         executor.execute(futureTask2);                   while (true)          {             try {                 if(futureTask1.isDone() && futureTask2.isDone()){                     System.out.println("Done");                     //shut down executor service                     executor.shutdown();                     return;                 }                                   if(!futureTask1.isDone()){                 //阻塞futureTask1                 System.out.println("FutureTask1 output="+futureTask1.get());                 }                                  if(!futureTask2.isDone()){                 //阻塞futureTask2                 System.out.println("FutureTask2 output="+futureTask2.get(1000,TimeUnit.MILLISECONDS));                 }             } catch (InterruptedException | ExecutionException e) {                 e.printStackTrace();             }catch(Exception e){                 //do nothing             }         }               }          static class MyCallable implements Callable<String> {               private long waitTime;                   public MyCallable(int timeInMillis){             this.waitTime=timeInMillis;         }         @Override         public String call() throws Exception {             Thread.sleep(waitTime);             return Thread.currentThread().getName();         }           } }

运行结果很简单，必须是：

FutureTask1 output=pool-1-thread-1
FutureTask2 output=pool-1-thread-2
Done

案例2：

package com.net.thread.future;import java.util.concurrent.Callable;import java.util.concurrent.ExecutionException;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.FutureTask;import java.util.concurrent.TimeUnit; /** * @author  * @Time：2017年8月18日 上午10:49:07 * @version 1.0 * @description */public class FutureTaskExample2 {     public static void main(String[] args) {        MyCallable callable1 = new MyCallable(1000);        MyCallable callable2 = new MyCallable(5000);         FutureTask<String> futureTask1 = new FutureTask<String>(callable1);        FutureTask<String> futureTask2 = new FutureTask<String>(callable2);         ExecutorService executor = Executors.newFixedThreadPool(2);        executor.execute(futureTask1);        executor.execute(futureTask2);                 while (true)         {             try {                 if(futureTask1.isDone() && futureTask2.isDone()){                     System.out.println("Done");                     //shut down executor service                     executor.shutdown();                     return;                 }                                   if(!futureTask1.isDone()){                 //阻塞futureTask1                 System.out.println("FutureTask1 output="+futureTask1.get());                 }                                   System.out.println("Waiting for FutureTask2 to complete");                 String s = futureTask2.get(1000, TimeUnit.MILLISECONDS); //阻塞500毫秒                 if(s !=null){                     System.out.println("FutureTask2 output="+s);                 }                 else{                     System.out.println("FutureTask2 output is null");                 }             } catch (InterruptedException | ExecutionException e) {                 e.printStackTrace();             }catch(Exception e){                 //do nothing             }          }    }            static class MyCallable implements Callable<String> {             private long waitTime;                 public MyCallable(int timeInMillis){            this.waitTime=timeInMillis;        }        @Override        public String call() throws Exception {            Thread.sleep(waitTime);            return Thread.currentThread().getName();        }         } }

运行结果：

FutureTask1 output=pool-1-thread-1
Waiting for FutureTask2 to complete
Waiting for FutureTask2 to complete
Waiting for FutureTask2 to complete
Waiting for FutureTask2 to complete
FutureTask2 output=pool-1-thread-2
Done

说明：

1、get()方法用来获取执行结果，这个方法会产生阻塞，会一直等到任务执行完毕才返回；

2、get(long timeout, TimeUnit unit)用来获取执行结果，如果超过指定时间，直接结束执行下面的代码；如果是在循环中，则跳出本次循环进行下一次轮训(continue功能类似)。

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