I am working on a project in C#.NET using the .NET framework version 3.5.
My project has a class called Focuser.cs which represents a physical device, a telescope focuser, that can communicate with a PC via a serial (RS-232) port. My class (Focuser) has properties such as CurrentPosition, CurrentTemperature, ect which represents the current conditions of the focuser which can change at any time. So, my Focuser class needs to continually poll the device for these values and update its internal fields. My question is, what is the best way to perform this continual polling sequence? Occasionally, the user will need to switch the device into a different mode which will require the ability to stop the polling, perform some action, and then resume polling.
My first attempt was to use a time that ticks every 500ms and then calls up a background worker which polls for one position and one temperature then returns. When the timer ticks if the background worker isBusy then it just returns and tries again 500ms later. Someone suggested that I get rid of the background worker all together and just do the poll in the timer tick event. So I set the AutoReset property of the timer to false and then just restart the timer every time a poll finishes. These two techniques seemed to behave the exact same way in my application so I am not sure if one is better than the other. I also tried creating a new thread every time I want to do a poll operation using a new ThreadStart and all that. This also seemed to work fine.
I should mention one other thing. This class is part of a COM object server which basically means that the class library that is produced will be called upon via COM. I am not sure if this has any influence on the answer but I just thought I should throw it out there.
The reason I am asking all of this is that all of my test harness runs and debug builds work just fine but when I do a release build and try to make calls to my class from another application, that application freezes up and I am having a hard time determining the cause.
Any advice, suggestions, comments would be appreciated.
Thanks, Jordan
Remember that the timer hides its own background worker thread, which basically sleeps for the interval, then fires its Elapsed event. Knowing that, it makes sense just to put the polling in Elapsed. This would be the best practice IMO, rather than starting a thread from a thread. You can start and stop Timers as well, so the code that switches modes can Stop() the Timer, perform the task, then Start() it again, and the Timer doesn’t even have to know the telescope IsBusy.
However, what I WOULD keep track of is whether another instance of the Elapsed event handler is still running. You could lock the Elapsed handler’s code, or you could set a flag, visible from any thread, that indicates another Elapsed() event handler is still working; Elapsed event handlers that see this flag set can exit immediately, avoiding concurrency problems working with the serial port.