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Title: Py_SetStandardStreamEncoding leads to a memory error in debug mode
Type: crash Stage: resolved
Components: Interpreter Core Versions: Python 3.7
Status: closed Resolution: fixed
Dependencies: Superseder:
Assigned To: Nosy List: ncoghlan, vstinner
Priority: normal Keywords:

Created on 2017-03-15 11:27 by ncoghlan, last changed 2022-04-11 14:58 by admin. This issue is now closed.

Messages (2)
msg289668 - (view) Author: Nick Coghlan (ncoghlan) * (Python committer) Date: 2017-03-15 11:27
For PEP 538, setting PYTHONIOENCODING turned out to have undesirable side effects on Python 2 instances in subprocesses, since Python 2 has no 'surrogateescape' error handler.

So I switched to using the "Py_SetStandardStreamEncoding" API defined in instead, but this turns out to have problematic interactions with the dynamic memory allocator management, so it fails with a fatal exception in debug mode. An example of the error can be seen here:

The problem appears to be that between the allocation of the memory with `_PyMem_RawStrdup` in `Py_SetStandardStreamEncoding` and the release of that memory in `initstdio`, the active memory manager has changed (at least in a debug build), so the deallocation as part of the interpreter startup fails.

That interpretation is based on this comment in Programs/python.c:

    /* Force again malloc() allocator to release memory blocks allocated
       before Py_Main() */

The allocations in Py_SetStandardStreamEncoding happen before the call to Py_Main/Py_Initialize, but the deallocation happens in Py_Initialize.

The "fix" I applied to the PEP branch was to make the default allocator conditional in Programs/python.c as well:

#ifdef Py_DEBUG
#  else
#  endif

While that works (at least in the absence of a PYTHONMALLOC setting) it seems fragile. It would be nicer if there was a way for Py_SetStandardStreamEncoding to indicate which allocator should be used for the deallocation.
msg342540 - (view) Author: STINNER Victor (vstinner) * (Python committer) Date: 2019-05-15 02:53
I fixed this issue in Python 3.7. Py_SetStandardStreamEncoding() now uses:

    PyMemAllocatorEx old_alloc;
    _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);

    ... _PyMem_RawStrdup() ...

    PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
Date User Action Args
2022-04-11 14:58:44adminsetgithub: 74004
2019-05-15 02:53:12vstinnersetstatus: open -> closed
versions: - Python 3.6
messages: + msg342540

components: + Interpreter Core
resolution: fixed
stage: needs patch -> resolved
2017-03-15 11:28:01ncoghlansetversions: + Python 3.6, Python 3.7
2017-03-15 11:27:39ncoghlancreate