[Python-Dev] PEP 446: Open issues/questions (original) (raw)

Richard Oudkerk shibturn at gmail.com
Fri Aug 2 10:02:00 CEST 2013

On 02/08/2013 7:44am, Charles-François Natali wrote:

Then how about changing the default to creating file descriptors unheritable on Windows (which is apparently the default)? Then you can implement keepfds by setting them inheritable right before creation, and resetting them right after: sure there's a race in a multi-threaded program, but AFAICT that's already the case right now, and Windows API doesn't leave us any other choice. Amusingly, they address this case by recommending putting process creation in a critical section: http://support.microsoft.com/kb/315939/en-us

This way, we keep default platform behavior on Unix and on Windows (so user using low-level syscalls/APIs won't be surprised), and we have a clean way to selectively inherit FD in child processes through subprocess.

http://bugs.python.org/issue16500 is a proposal/patch for adding atfork. But it also has a public recursive lock which is held when starting processes using fork()/subprocess/multiprocessing. This is so that users can safely manipulate fds while holding the lock, without these sorts of race conditions. For example

 with atfork.getlock():
     fd = os.open("somefile", os.O_CREAT | os.O_WRONLY, 0600)
     flags = fcntl.fcntl(fd, fcntl.F_GETFL)
     fcntl.fcntl(fd, fcntl.F_SETFL, flags | fcntl.FD_CLOEXEC)

-- Richard

More information about the Python-Dev mailing list