[issue35686] BufferError with memory.release()

Stefan Krah added the comment: Eryk Sun: Yes, the behavior is technically not guaranteed. I'm not sure about memoryview(x, start, stop, step) but I'll keep it in mind. Thomas Waldmann: > do you think this is as good as it gets for this kind of code? I guess so, there's a lot going on in tha

[issue35686] BufferError with memory.release()

Thomas Waldmann added the comment: https://github.com/borgbackup/borg/pull/4247/files this is the current code i have for this (it is not as simple there as in the minimal code samples i attached here). i meanwhile think i can not use a contextmanager there. do you think this is as good as

[issue35686] BufferError with memory.release()

Eryk Sun added the comment: > Or, obviously: > > with open(fn, 'rb') as fd: > with mmap.mmap(fd.fileno(), 0, access=mmap.ACCESS_READ) as mm: > with memoryview(mm)[:2] as data: > print(data) Doesn't this rely on the immediate finalization of the unreferenced memoryview

[issue35686] BufferError with memory.release()

Stefan Krah added the comment: Or, obviously: with open(fn, 'rb') as fd: with mmap.mmap(fd.fileno(), 0, access=mmap.ACCESS_READ) as mm: with memoryview(mm)[:2] as data: print(data) -- ___ Python tracker

[issue35686] BufferError with memory.release()

Stefan Krah added the comment: s/on export/one export/ -- ___ Python tracker ___ ___ Python-bugs-list mailing list Unsubscribe: ht

[issue35686] BufferError with memory.release()

Stefan Krah added the comment: Well, the problem in b) is that data[:2] creates a new memoryview, so the underlying ManagedBufferObject now has two exports: - One from the context manager. - The second from the slice. So memoryview.__exit__() decrements on export, but the second one is h

[issue35686] BufferError with memory.release()

Thomas Waldmann added the comment: I see 2 issues here: 1. I would expect that the CM approach (b) behaves equivalent to try/finally (c), but it does not and even causes an exception. 2. The traceback given in the BufferError (in (b)) is misleading, it points to the "print", but should rath

[issue35686] BufferError with memory.release()

Thomas Waldmann added the comment: hmm, issue tracker does not make it easy to see which file was uploaded for which comment, so: a: original code, works, potentially problematic exception handling (memoryview not always being released) b: using the memoryview context manager, fails with Bu

[issue35686] BufferError with memory.release()

Thomas Waldmann added the comment: with try/finally: works. -- Added file: https://bugs.python.org/file48033/issue35686c.py ___ Python tracker ___

[issue35686] BufferError with memory.release()

Thomas Waldmann added the comment: with context manager, does not work. -- Added file: https://bugs.python.org/file48032/issue35686b.py ___ Python tracker ___

[issue35686] BufferError with memory.release()

Stefan Krah added the comment: The behavior seems to be correct to me: If there are exports, the memoryview cannot be released. The application needs to ensure that release() is not called when there are exports left. -- ___ Python tracker

[issue35686] BufferError with memory.release()

Thomas Waldmann added the comment: working, but potentially problematic because .release is not always called (e.g. in case of an exception). -- Added file: https://bugs.python.org/file48031/issue35686a.py ___ Python tracker

[issue35686] BufferError with memory.release()

Stefan Krah added the comment: We use "crash" for segmentation fault, but this appears to be a regular traceback that includes BufferError. The BufferError message appears to be from mmapmodule.c. -- title: memoryview contextmanager causing strange crash -> BufferError with memory.r