I have a situation where sometimes (not always) my asynchronous job is not able to process results by the time needed and I have to return some kind of message to the client saying that his request is still being prepared by checking for it in the database.
The request and creating necessary object for it is handled in one database Transaction, the asynchronous process is handled in the different Transaction. I am using ScheduledThreadPoolExecutor by passing the runnable instance to the execute method.
The problems that sometimes the client makes a request and while the his browser is loading my asynchronous job is able to prepare the necessary data for it, but sometimes it isn't.
So my question is: Is there anyway I can tell asynchronous job to wait until the data is ready?
I am afraid that using just a Runnable instance you are not be able to tell the process to wait unless you sleep the Thread for sometime or looping and keep asking for the results which both are bad ideas.
In order to make this happen correctly, you should use a FutureTask for this by passing Callable instance to it's constructor. By overriding your call() method you should tell you transactional handler to do the job.
You also need to have some kind of a task manager which will add the task to the queue and creates a thread pool which takes and processes those tasks. For the queue purpose I would suggest to use for e.g.: LinkedBlockingDeque which accepts the generic type of FutureTask.
Also you should have a map of future tasks mapped by their name or something which takes the FutureTask as a value. In terms of waiting for the results when your Thread is processed the given FutureTask already you have to immediately remove it from the futures map. Then when your client requests you should check: if the futures map contains the task get the FutureTask from it and call futureTask.get() on it. This will wait until the task is finished.
This is just approach with which I would go. Hope this helps.