[Python-Dev] Inherance of file descriptor and handles on Windows (PEP 446) (original) (raw)

Guido van Rossum guido at python.org
Wed Jul 24 20:17:13 CEST 2013

On Wed, Jul 24, 2013 at 11:13 AM, Richard Oudkerk <shibturn at gmail.com> wrote:

Wow. Indeed you can -- I just tested this myself. How is this accomplished? I guess the CRT has a backchannel to talk to itself when it creates a process using spawn*? CreateProcess() takes a STARTUPINFO argument with undocumented fields cbReserved2, lpReserved2. They are used to pass an array of fds.

Does it also inherit sockets (which take up a different namespace than regular FDs in CRT, unlike UNIX)?

But I'm also ready to propose that all this is such a mess that we

should change the default fd/handle inheritance to False, *across platforms*, and damn the torpedoes -- i.e. accept breaking all existing 3rd party UNIX code for subprocess creation that bypasses the subprocess module, as well as breaking uses of os.spawn*() on both platforms that depend on FD inheritance beyond stdin/stdout/stderr). +1

Thanks! This was a difficult conclusion to come to. "Damn the torpedoes" is occasionally a nice meme. :-(

We can fix multiprocessing any anything else in the stdlib that this breaks, I presume. In the experimental branch of multiprocessing, child processes no longer inherit unnecessary handles.

And if we default individual handles to uninheritable, we can presumably fix the ones that multiprocessing creates with the express purpose of being inherited easily. (If it even uses that -- I haven't read the source code, maybe it uses named pipes? :-)

-- --Guido van Rossum (python.org/~guido)

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