Windows Service with multiple timers

Question

I have been given a windows service written by a previous intern at my current internship that monitors an archive and alerts specific people through emails and pop-ups should one of the recorded values go outside a certain range. It currently uses a timer to check the archive every 30 seconds, and I have been asked if I would be able to update it to allow a choice of time depending on what "tag" is being monitored. It uses an XML file to keep track of which tags are being monitored. Would creating multiple timers in the service be the most efficient way of going about this? I'm not really sure what approach to take.

The service is written in C# using .NET 3.5.

Answer 1

Depending on the granularity, you could use a single timer that is a common factor of the timing intervals they want. Say they want to put in the XML file that each archive is to be checked every so many minutes. You set up a timer that goes off once a minute, and you check how long it's been since you did each one and whether to do it or not.

If you're getting a chance to re-architect, I would move away from a service to a set of scheduled tasks. Write it so one task does one archive. Then write a controller program that sets up the scheduled tasks (and can stop them, change them etc.) The API for scheduled tasks on Windows 7 is nice and understandable, and unlike a service you can impose restrictions like "don't do it if the computer is on battery" or "only do it if the machine is idle" along with your preferences for what to do if a chance to run the task was missed. 7 or 8 scheduled tasks, each on their own schedule, using the same API of yours, passing in the archive path and the email address, is a lot neater than one service trying to juggle everything at once. Plus the machine will start up faster when you don't have yet another autostart service on it.

Answer 2

Efficient? Possibly not - especially if you have lots of tags, as each timer takes a tiny but finite amount of resources.

An alternative approach might be to have one timer that fires every second, and when that happens you check a list of outstanding requests.

This has the benefit of being easier to debug if things go wrong as there's only one active thread.

As in most code maintenance situations, however, it depends on your existing code, your ability, and how you feel more comfortable.

Answer 3

I woould suggest to just use one timer scheduled at the least common divisor.

For example configure your timer to signal every second and you can handle every interval (1 second, 2 seconds, ...) by counting the according number of timer ticks.