执行器服务 - 线程超时

问题描述

当我探索 longMethod（）

但是按照下面的代码， c $ c>似乎运行超时超时（2秒），我真的很困惑理解这一点。任何人都可以指向我正确的路径？

  import java.util.concurrent.Callable; 
 import java.util.concurrent.ExecutorService; 
 import java.util.concurrent.Executors; 
 import java.util.concurrent.TimeUnit; 
 
 public class Timeout implements Callable< String> {
 
 public void longMethod（）{
 for（int i = 0; i  System.out.println（a）; 
} 
} 
 
 @Override 
 public String call（）throws Exception {
 longMethod（）; 
 returndone; 
} 
 
 
 / ** 
 * @param args 
 * / 
 public static void main（String [] args）{
 ExecutorService service = Executors.newSingleThreadExecutor（）; 
 
 try {
 service.submit（new Timeout（））。get（2，TimeUnit.SECONDS）; 
} catch（Exception e）{
 e.printStackTrace（）; 
} 
} 
 
 
} 
  

不正确。

如果您要取消该任务：

  timeout.cancel（true）// Timeout timeout = new Timeout（）; 
  

因为你有它现在这个中断将没有什么影响。

例如，此代码会考虑中断：

  private static final class MyCallable implements Callable< String> {
 
 @Override 
 public String call（）throws Exception {
 StringBuilder builder = new StringBuilder ）; 
 try {
 for（int i = 0; i< Integer.MAX_VALUE; ++ i）{
 builder.append（a）; 
 Thread.sleep（100）; 
} 
} catch（InterruptedException e）{
 System.out.println（Thread was interrupted）; 
} 
 return builder.toString（）; 
} 
} 
  

然后：

  ExecutorService service = Executors.newFixedThreadPool（1）; 
 MyCallable myCallable = new MyCallable（）; 
 Future< String> futureResult = service.submit（myCallable）; 
 String result = null; 
 try {
 result = futureResult.get（1000，TimeUnit.MILLISECONDS）; 
} catch（TimeoutException e）{
 System.out.println（一秒钟后没有响应）; 
 futureResult.cancel（true）; 
} 
 service.shutdown（）; 
  

While I was exploring ExecutorService, I encountered a method Future.get() which accepts the timeout.

The Java doc of this method says

---

Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.

Parameters:

timeout the maximum time to wait

unit the time unit of the timeout argument

---

As per my understanding, we are imposing a timeout on the callable, we submit to the ExecutorService so that, my callable will interrupt after the specified time(timeout) has passed

But as per below code, the longMethod() seems to be running beyond the timeout(2 seconds), and I am really confused understanding this. Can anyone please point me to the right path?

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class Timeout implements Callable<String> {

    public void longMethod() {
        for(int i=0; i< Integer.MAX_VALUE; i++) {
            System.out.println("a");
        }
    }

    @Override
    public String call() throws Exception {
        longMethod();
        return "done";
    }


    /**
     * @param args
     */
    public static void main(String[] args) {
        ExecutorService service = Executors.newSingleThreadExecutor();

        try {
            service.submit(new Timeout()).get(2, TimeUnit.SECONDS);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }


}

解决方案

my callable will interrupt after the specified time(timeout) has passed

Not true. The task will continue to execute, instead you will have a null string after the timeout.

If you want to cancel it:

  timeout.cancel(true) //Timeout timeout = new Timeout();

P.S. As you have it right now this interrupt will have no effect what so ever. You are not checking it in any way.

For example this code takes into account interrupts:

    private static final class MyCallable implements Callable<String>{

    @Override
    public String call() throws Exception {
        StringBuilder builder = new StringBuilder();
        try{
            for(int i=0;i<Integer.MAX_VALUE;++i){
                builder.append("a");
                Thread.sleep(100);
            }
        }catch(InterruptedException e){
            System.out.println("Thread was interrupted");
        }
        return builder.toString();
    }
}

And then:

        ExecutorService service = Executors.newFixedThreadPool(1);
    MyCallable myCallable = new MyCallable();
    Future<String> futureResult = service.submit(myCallable);
    String result = null;
    try{
        result = futureResult.get(1000, TimeUnit.MILLISECONDS);
    }catch(TimeoutException e){
        System.out.println("No response after one second");
        futureResult.cancel(true);
    }
    service.shutdown();

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