Fix gRPC client retry deadlock #2209
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Fixes #2206
I believe the problem is caused by a call's TCS being created without
RunContinuationsAsynchronously. When the call is disposed under a lock, the TCS is completed, and continuations are run on the same thread, still holding the lock. That includes logic after the await here in RetryCall.The simple fix would be to add that setting. Unfortunately,
RunContinuationsAsynchronouslycan't be used here because it breaksActivity.Instead, I moved disposing the active call outside of the lock. I think this fixes the deadlock, but I don't have repro to confirm.
Another idea I had, which isn't in this PR, is to place a
Task.Yield()after the await in RetryCall. It forces the call's TCS to stop executing synchronously,_callTcs.TrySetResult(...)returns, the call's dispose finishes, and exits the lock.cc @andrewhickman