Queued WCF Service which processes every X seconds

Question

I need to create a service which can process queued requests on a configured time interval. For example go to the web and get financial data from a site the requires we limit requests to once per second. I am new to WCF and I am not sure if (1) WCF with MSMQ a proper choice for implementing this? and (2) if so what is the best mechanism for enforcing the interval? a thread wait? a timer (not sure how that would work).

Answer 1

There's nothing built into WCF that would allow you to handle this explicitly, so you'd still need to do all the work yourself.

While your service could certainly process requests from MSMQ, the MSMQ listeners in WCF will pick and process messages as soon as possible; you can't configure them to process messages every X seconds only (you could fake it given the right tools, but seems to me it wouldn't be all that great).

One option if your delay between processing requests isn't very short, would be to use an intermediate queue to hold pending requests. That is, whatever sends the real requests writes them to a queue nobody is directly listening to (queue A), while your WCF service listens on a differet queue (queue B). Then, have something else (could be as simple as a script run from task scheduler) that runs once every X seconds/minutes/whatever and moves just 1 message from queue A to queue B, thus triggering the actual WCF service to run.

Answer 2

Or you could just use a window service to consume the messages instead. If you are not using the WCF functionality of consuming a message as soon as it is posted, then you probably have no reason to use wcf in the first place

Answer 3

WCF and MSMQ are a great team! Definitely worth checking out.

The part that WCF doesn't provide out of the box is the "check every x seconds". The best approach here would be to host your WCF service inside a Windows NT Service, and have a timer inside the NT Service that goes to check the MSMQ queue only once every x seconds. Shouldn't be too hard to implement, really. The beauty is: you can very easily self-host a WCF Service inside a NT Service - just a few lines of code, and you get complete control over what's happening, and when. See the MSDN docs on How to Host a WCF service in a managed application for details.

Resources:

• Tom Hollander's blog post series on MSMQ, WCF, IIS: Getting them to play nice
• Motley Queue: MSMQ and WCF Getting Started
• SOAizing MSMQ with WCF (and why it's worth it)