Commits on Oct 4, 2022

1. python3Packages.pytest-xdist: Disable fork safety on darwin …

   We run pytest with `--forked` in nixpkgs, to reduce side effects that
   can occur when multiple tests mutate their environment in incompatible
   ways.
   
   Forking on macOS 10.13 and later is unsafe when an application does work
   between calls to fork() and its followup exec(). This may lead to
   crashes when calls into the Objective-C runtime are issued, which will
   in turn coredump the Python interpreter.
   
   One good reproducer for this scenario is when the urllib module tries
   to lookup proxy configurations in `urllib.request.getproxies()` through
   `get_proxies_macos_sysconf` into the native `_scproxy` module.
   
   This is a class of issues that is of course not limited to the urllib
   module. The general recommendation is to use `spawn` instead of `fork`,
   but we don't have any influence on upstream developers to do one or the
   other.
   
   One often cited workaround would be to disable fork safety entirely on
   calls to `initialize()`, which is probably a better solution than
   running without multithreading (slow) or without the `--forked` (prone
   to side effects) mode.
   
   This currently happens on aarch64-linux only, where we use more recent
   11.0 SDK version, while x86_64-darwin has been stuck on 10.12 for a
   while now.
   
   python/cpython#77906 (comment)
   http://www.sealiesoftware.com/blog/archive/2017/6/5/Objective-C_and_fork_in_macOS_1013.html
   
   Closes: NixOS#194290

   

   mweinelt committed Oct 4, 2022
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