[issue33030] GetLastError() may be overwritten by Py_END_ALLOW_THREADS

Change by Eryk Sun : -- versions: +Python 3.10, Python 3.9 -Python 3.6, Python 3.7 ___ Python tracker ___ ___ Python-bugs-list maili

[issue33030] GetLastError() may be overwritten by Py_END_ALLOW_THREADS

Alexey Izbyshev added the comment: @eryksun Very interesting! BTW, I looked at CreateFile docs, and the fact that it may set the last error to zero is even documented there. @steve.dower > maybe we don't have to preserve errno on Windows? There are still places where errno is relied upon. PR

[issue33030] GetLastError() may be overwritten by Py_END_ALLOW_THREADS

Eryk Sun added the comment: FYI, here's a sampling of successful calls that modify the last error value. Most Create- functions intentionally set the last error to 0 on success, such as CreateFile, CreateFileMapping, CreateSymbolicLink, CreateJobObject, CreateEvent, CreateMutex, CreateSemapho

[issue33030] GetLastError() may be overwritten by Py_END_ALLOW_THREADS

Steve Dower added the comment: > Before take_gil() knows whether it has to do any work I thought we had a check for when the GIL was not even initialized, but that doesn't seem to exist in master any more. Preserving GetLastError() at the same place we do errno is probably sufficient. There

[issue33030] GetLastError() may be overwritten by Py_END_ALLOW_THREADS

Alexey Izbyshev added the comment: > Ideally, if we don't have to do any work to reacquire the GIL, we shouldn't > do any work to preserve the error code either. Before take_gil() knows whether it has to do any work, it calls MUTEX_LOCK(_PyRuntime.ceval.gil.mutex), which is either EnterCritic

[issue33030] GetLastError() may be overwritten by Py_END_ALLOW_THREADS

Steve Dower added the comment: > GetLastError() docs officially scare us I believe this is a case where the docs were updated from intended/correct behavior to actual behavior, which happens from time to time and is never clearly marked. As I say, they are _supposed_ to leave the error uncha

[issue33030] GetLastError() may be overwritten by Py_END_ALLOW_THREADS

Alexey Izbyshev added the comment: FWIW, GetLastError() docs[1] officially scare us: Most functions that set the thread's last-error code set it when they fail. However, some functions also set the last-error code when they succeed. If the function is not documented to set the last-error code

[issue33030] GetLastError() may be overwritten by Py_END_ALLOW_THREADS

New submission from Steve Dower : Most Win32 API calls are made within Py_BEGIN_ALLOW_THREADS blocks, as they do not access Python objects and so we can release the GIL. However, in general, error handling occurs after the Py_END_ALLOW_THREADS line. Due to the design of the Win32 API, the patt