Question

I am trying to implement a code where I want to call a function from JNI which should have a timeout. If it exceeds the timeout, I want to terminate the native task. I am posting a piece of code to show as an example.

void myFunction(timeOutInSeconds)
{
    if(timeOutInSeconds > 0)
    {
        ExecutorService executor = Executors.newCachedThreadPool();
        Callable<Integer> task = new Callable<Integer>() {
            public Integer call() {
                System.out.println("Calling JNI Task");
                JNI_Task();
                System.out.println("Finished JNI Task");
                return 0;                              
            }
        };

        Future<Integer> future = executor.submit(task);
        try 
        {
            @SuppressWarnings("unused")
            Integer result = future.get(timeOutInSeconds, TimeUnit.SECONDS); 
        } 
        catch (TimeoutException ex)
        {
            // handle the timeout               
            kill_task_in_JNI();     

            // future.cancel(true);
            return TIMEOUT;

        } catch (InterruptedException e) {
            // handle the interrupts
        } catch (ExecutionException e) {
            // handle other exceptions
        } 
        finally 
        {
            // future.cancel(true);
            executor.shutdown();
        }
    }
    else
        JNI_Task();
}

There are several questions –

• Where should I exactly put future.cancel(). There are 2 locations which are commented.
• If I run this function with timeOutInSeconds = 0, it runs perfectly.
  However Irrespective of the value of timeOutInSeconds, the task gets stuck up and
  the JNI task does not get called. I check this by putting printf’s in the JNI
  code. The task takes 1 second to execute and I gave 30 seconds, 5 minutes etc. still it
  is stuck up.

Is there any problem with such approach?

Answer 1

You can (and in this case should) call future.cancel() only in the finally block. http://docs.oracle.com/javase/tutorial/essential/exceptions/finally.html.

About the 2nd question, its not clear for me if the problem also occur when timeOutInSeconds=0. Is this the case? Can you provide the content of the JNI_TASK() method?