I have a long running series of operations in a .NET 2.0 BackgroundWorker thread. When I make a call to unmanaged code located in a referenced assembly the UI is frozen until the call completes.
Why is this? Should I not be making these calls from the BackgroundWorker thread?
Yes and also, does this happen with all unmanaged code or just a specific component or API? If a specific one, what is that unmanaged code doing?
You've got the COM tag in the question - are you calling into a COM component? Is it an STA component? If so, it may well be marshalling back to do its work on the UI thread somehow. I'll readily admit I'm a long way from being an expert on COM stuff, but I wouldn't be surprised if that were the problem.
What happens if you make the calls from a new thread which you've explicitly created?
Also, you could simply comment out your current code in the BackgroundWorker (you are running RunWorkerAsync right...) and put a sleep in there. If your GUI becomes unresponsive something's not right, otherwise it's the code you are calling as Jon points out could be the case with COM.
OP here... Yes, it is a COM component but I'm not sure how to tell if it's STA or not and what the implications/resolution are/is. I make several calls to that component but it is only the long-running ones where I notice the UI becoming unresponsive.
These calls retrieve data from a server.