Threading, Loops, and Direct3D

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I have an application with a form that direct3d draws to. The direct3d
rendering loop made the application unresponsive, so I created a new
thread to do the rendering and I call Application.Run on the original
thread. This works fine for a while, but then the whole workstation
becomes instantly unresponsive. Any ideas on how to fix this? And,
for the record, I am passing the CreateFlags.MultiThreaded flag to the
device.

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