ExecutorService submit() - Execute in parallel (non-blocking)

Question

I'm trying to run a task in parallel. I have tried the following:

In my constructor:

this.executor = Executors.newFixedThreadPool(5);
executor.awaitTermination(10, TimeUnit.SECONDS);
          

then I add all the items I want to run in parallel to a list:

   Future<Map.Entry<Location, SomeData>> result = this.executor.submit(new Sender(entry));
   resultList.add(result);

Then I loop on that list and use the get() function of Future in order to execute each task - which appears to be blocking:

 for (int i = 0; i < resultList.size(); i++) {

        Future<Map.Entry<Location, SomeData>> result = resultList.get(i);

        try {
            logger.info("[Start] Task" + sendQueue.get(i).getKey() + "-" + i);
            entry = result.get();
        } catch (InterruptedException e) {
            logger.error("Interrupted error", e);
        } catch (ExecutionException e) {
            logger.error("Thread Execution error", e);
        } catch (Exception e) {
            logger.error("Send Error", e);
        }

        if (entry == null) {
            logger.error("Telemetry Send Error");
            return;
        }

        logger.info("[Success] Task" + entry.getKey() + "-" + i);
    }

Sender call():

@Override
    public Map.Entry<Location, Data> call() throws InterruptedException {
        Thread.sleep(5000);
        return this.entry;
    }

I see that each task is executed after the other. I want to execute all tasks in parallel and make it non-blocking.

Any idea what I'm missing? Isn't it what the executor service used to do?

Answer 1

After the invokation to submit you need to invoke awaitTermination . In that way, you will give some time for the task to get executed until a time out defined by you is reached or the execution ends. Then, you should be able to check the future results by invoking get .

Another option provided by the ExecutorService API is to call invokeAll which is a blocking operation that triggers all the tasks. I personally prefer the first option described above.

Update: Also, you didn´t show the ExecutorService configuration but I assume that you are assigning more than one thread to it. Otherwise, the executions will be sequential no matter what you do after the submit .