Switching default multiprocessing context to "spawn" on POSIX as well

Core Development
14

There are some potential edge cases where "forkserver" can result in threads being started before fork():

  1. Python has an API, ForkServer.set_forkserver_preload(), to add modules to import in the parent process that gets fork()ed for workers; I’ve seen people recommend this specifically for large scientific computing/numeric libraries. It’s not documented in the Python documentation though, perhaps it could just be deprecated too.
  2. __main__ is always preloaded by default, for some definition of __main__. I am not certain whether or not this is a problem; it’s a bunch of code and I don’t really understand what it’s doing at first glance (there’s even a one-off hack to handle an ipython bug from 2013!).
  3. Code that runs via .pth files; I do this for the Python profiler I’m working on, I believe manhole does this. This is fairly rare I suspect. My profiler does make an effort to handle fork() without execve().