How to remove java.util.concurrent.RejectedExecutionException while using Future Interface

Question

I have a controller in which I am using future interface and creating 5 threads in threadpool. This controller is called by an ajax call. When I call this controller the first time it runs fine but if I make the request again it shows the exception below.

  java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.FutureTask@1cbbac9 rejected from java.util.concurrent.ThreadPoolExecutor@53ee53[Terminated, pool size = 0, active threads = 0, queued tasks = 0, completed tasks = 5]

I am posting code how I am calling the tasks.

  private static final ExecutorService threadpool = Executors.newFixedThreadPool(20);
    FactorialCalculator task1 = new FactorialCalculator("A"); 
    FactorialCalculator task2 = new FactorialCalculator("B"); 
    FactorialCalculator task3= new FactorialCalculator("C"); 
    FactorialCalculator task4 = new FactorialCalculator("D"); 
    FactorialCalculator task5= new FactorialCalculator("E"); 
    System.out.println("Submitting Task ..."); 
    Future future1 = threadpool.submit(task1); 
    Future future2 = threadpool.submit(task2); 
    Future future3 = threadpool.submit(task3); 
    Future future4 = threadpool.submit(task4); 
    Future future5 = threadpool.submit(task5);  
    System.out.println("Task is submitted");

In first request it is running all tasks- A,B,C,D and E but when I make request again it prints submitting tasks but doesn't print Task is submitted. Can someone help out what am I doing wrong.

Do happen to shut the executor down? – Fildor May 03 '16 at 11:13 — Fildor, May 03 '16 at 11:13

Andrzej Doyle · Accepted Answer · 2016-05-03T11:31:38.237

You haven't mentioned specifically which version of Java you're using, but I suspect the relevant classes haven't changed much. The ThreadPoolExecutor will throw that exception from it's execute method in two cases, both of which rely on the executor's state being SHUTDOWN.

So I am fairly confident that the executor is rejecting your task submissions because it is being shut down at some point. I notice your code is not telling the whole story, as it looks like the executor is a class field that might be referenced by other methods. Check whether you're calling shutdown anywhere else. (Note that the executor will be shut down by its finalizer; though in the block of code you've posted there's no way it will be eligible for garbage collection as it's a final field.)

As a footnote, whenever you're having trouble with code it's useful to provide a SSCCE. The code you've posted doesn't compile, but after fixing this, it runs successfully. Are you able to fork my Ideone script and reproduce your problem?

Note that when you scroll the exception’s message of the question horizontally, you can see from the executor’s `toString()` output that its state is indeed `Terminated`… — Holger, May 03 '16 at 12:27

How to remove java.util.concurrent.RejectedExecutionException while using Future Interface

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