Task Execution With Special Requirements In Java

Question

Having to sink in my teeth into Java Executor Service I noticed that it falls flat for some of my requirements:

I need to implement a small reactive system. So a Task can result in a new Task.
The tasks schedule dynamically either as a reaction of an event (waiting for a token pool for instance) or by time.
If a task dies I need to react accordingly so a task may be composed by different event methods or at least provide a listener service (like the Google guava lib)

I do not like the idea to implement it myself. But it is a event listener collection waiting for events to happen and immediately schedule tasks for this. Scheduling a job for a certain point in time is just also generating a timer event that is triggered by a waiting queue waiting for the nearest timer event to happen notify the framework and done.

So is there something around that provides this or a default way to use a Java Executor for this?

Your question is nothing else but "Please recommend a tool" to me. What kind of answers do you expect? — V G, Aug 21 '15 at 10:43
A solution to use the standard tools or a simplification that I do not see? — Martin Kersten, Aug 21 '15 at 12:48

score 0 · Answer 1 · edited May 23 '17 at 12:14

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Use the java concurrency package which borrows concepts from a very up and coming framework called akka. That should be enough to do what you want, if not then use akka. I have an example here: Executing Dependent tasks in parallel in Java

EDIT: Yes correct in my example there was blocking on the get methods, simply use the

future.onComplete(new OnComplete<Object>() )

To remove any blocking.

edited May 23 '17 at 12:14

Community

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answered Aug 21 '15 at 09:43

Derrops

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Your example over there is the exact reason why I can not use the demonstrated approach. First of all your example works only for this example due you restrict the executor pool and using FutureTask.get() blocks the current thread ["void java.util.concurrent.locks.LockSupport.park(Object blocker) -Disables the current thread for thread scheduling purposes unless the permit is available.]. This is undesirable. Also it is not really testable (the big nogo) and the reaction to internal task failures and a task rescheduling itself is not possible. – Martin Kersten Aug 21 '15 at 10:09
Hi, just use the onComplete instead, then there is no blocking. – Derrops Aug 21 '15 at 10:54

score 0 · Answer 2 · answered Aug 21 '15 at 13:59

I found a final working solution for my self. Turned out that I just have to implement a special task and a simple executor of that task. The task can itself use any means to react and delay upon events. Waiting for a event is just a sequence of tasks or a event producer that creates tasks on behalf of an event. Simple as that.

But why building a scheduled executor using delays? That does makes no sense at all. No one ever wants to schedule tasks or events using a delay... .

Task Execution With Special Requirements In Java

2 Answers2