What's the best way to build a queue for long-running jobs in a Grails app?

Question

I have a Grails app that has some computationally intensive optimizations with a running time of ~5 minutes (perhaps more). Currently, I'm doing these in the main request thread, i.e. it takes 5 minutes for the request to return. It works, but is of course horrible from a usability perspective.

So what's the best way to implement this in an asynchronous way? I assume a ThreadPoolExecutor would have to be involved, but how do I start and access it? Can I model it as a Grails Service? Or a Job (seems that those are only meant for recurring jobs though)?

Also, what's the best way to handle job status? Via a a flag or perhaps an entire new class in the DB? Have the browser show a spinner and keep polling until the status changes?

Answer 1

There is a grails plugin background-thread which might be just what you are looking for.

Of course it would be possible to roll your own thread pooling or use existing Java stuff.

Answer 2

I'd use the grails JMS Plugin for this.

Then you can create a service with an "onMessage" method that interacts automatically with an underlying jms provider (like OpenMQ or ActiveMQ.

It makes this kind of thing pretty easy.

Answer 3

In the spirit of the "simplest thing that could possibly work" I have done something like this as a simple service. (Of course it might be too simple, criticism is welcomed).

I used Groovy's feature that Thread has a static start method that takes a closure. See http://groovy.codehaus.org/groovy-jdk/java/lang/Thread.html

I implemented a method on a service that looked like:

synchronized def runThreadedTask() {
  if(taskRunning) { 
    // taskRunning is defined as a service level flag to monitor job status
    // if we are already running the task just return
    return;
  }

  Thread.start {
    taskRunning = true
    // do job processing here
    taskRunning = false
  }
}

Answer 4

grails install-plugin background-thread

def backgroundService

backgroundService.execute("doing my thing", {

// do work here

});