I need to process files which get uploaded and it can take as little as 1 second or as much as 10 minutes. Currently my solution is to make a quartz job with a timer of 30 seconds and then process and arbitrary job whenever it hits. There are several problems with this.
One: if the job will take less than a few seconds it is wasteful to make things wait 30 seconds for the job queue.
Two: if there is only one long job in the queue it could feasibly try to do it twice.
What I want is a timeless queue. When things are added the are started immediately if there is a free worker. Is there a solution for this? I was looking at jesque, but I couldn’t tell if it can do this.
What you are looking for is a basic message queue. There are lots of options out there, but my favorite for Grails is RabbitMQ. The Grails plugin for it is quite good and it performs well in my experience.
In general, message queues allow you to have N producers (things creating jobs”) adding work messages to a queue and then M consumers pulling jobs off of the queue and processing them. When a worker completes it’s job, it simply asks the queue for the next job to process and if there is none, it just waits for the queue to give it something to do. The queue also keeps track of success / failure of message processing (you can control this) so that you don’t give the same message to more than one worker.
This has the advantage of not relying on polling (so you can start processing as soon as things come in) and it’s also much more scaleable. You can scale both your producers and consumers up or down as needed, decoupling the inputs from the outputs so that you can take a traffic spike and then work your way through it as you have the resources (workers) available.