Thanks to Eryk Sun who pointed out that you can now just directly pass the socket object to the child process in multiprocessing (instead of the fileno int). I confirmed that worked for my use case.
http://bugs.python.org/issue28906 thanks, Preston On Tue, Dec 6, 2016 at 5:11 PM Preston Landers <pland...@gmail.com> wrote: Hello, Please excuse me if this is not the appropriate forum. I'm porting a Python 2.6 based application to Python 3.6. This app uses a customized version of the "flup" package to do FastCGI services on Windows using the multiprocessing package. This requires a few sockets to be inherited across processes - the main FastCGI protocol socket plus a control socket. In Python 2.6, the `socket.from_fd` function was not available on Windows. However I patched Python's socketmodule.c to provide that function using DuplicateHandle. In Python 2.6's version of multiprocessing it spawned a process with CreateProcess and bInheritHandles=True. This worked beautifully for me. Now I'm trying to get this working after moving from Python 2.6 to 3.6. Fortunately, the socket module now has a working `socket.from_fd` on Windows so I no longer have to patch that. Unfortunately for me, though, the multiprocessing module now calls CreateProcess with bInheritHandles=False. This causes my scenario to fail. Here's a short test script which illustrates this problem: https://gist.github.com/Preston-Landers/712fee10fb557cf0b5592b57561a7c08 If you run with an unpatched multiprocessing, it will fail with an error like: OSError: [WinError 10038] An operation was attempted on something that is not a socket If you patch multiprocessing to set bInheritHandles=True this now works. (Change is in popen_spawn_win32.py where it does _winapi.CreateProcess.) I'm sure there's a good reason for that change in multiprocessing, whether for security or for unrelated/undesired file handles being passed. https://www.python.org/dev/peps/pep-0446/#inheritance-of-file-descriptors-on-windows However it does break my scenario and I don't see a way to tell multiprocessing to allow certain handles to be inherited. The docs for multiprocessing say "In particular, unnecessary file descriptors and handles from the parent process will not be inherited." It would be nice to have a way to tell it that my sockets are "necessary." You would think that calling socket.set_inheritable(True) would do it. In fact you must do that, but you must also pass bInheritHandles=True to CreateProcess for it to actually work. I do realize I could be going about this completely wrong, though. But right now it looks like my immediate options are: a) Go ahead and patch my copy of popen_spawn_win32.py to allow inherited handles. b) Try to rewrite things to not use multiprocessing at all and directly spawn my processes instead. That's not attractive because multiprocessing otherwise does what I need to do. Are there any other options I'm missing? thanks, Preston
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