Message 80191 - Python tracker (original) (raw)

Kristjan, please understanding that setting the CRT error handling is not thread-safe, and trying to do it in a fine-grained way can cause all kinds of crazy races. With your patch, the following sequencce of events is possible if two threads T1 and T2 simultaneously try to access the CRT:

1. T1 saves the old mode (O), installs its own mode (N1)
2. T1 releases the GIL, invokes CRT operation
3. T2 starts running, saves the old mode (N1), installs its own mode (N2)
4. T1 completes, restores the old mode (O)
5. T2 completes, restores the old mode (N1)

As a net result, the original error handling is not restored.