Prevent Python subprocess from passing fds on Windows?

Question

Python's subprocess module by default passes all open file descriptors to any child processes it spawns. This means that if the parent process is listening on a port, and is killed, it cannot restart and begin listening again (even using SO_REUSEADDR) because the child is still in possession of that descriptor. I have no control over the child process.

The subprocess POpen constructor does accept a close_fds argument, which would close descriptors on the child, just as I want. However, there is a restriction, only on Windows, that prevents it from being used if stdin/stdout are also overridden, which I need to do.

Does anyone know of a work-around for this on Windows?

Answer 1

What seems to be the most relevant information that I can find: SetHandleInformation, referenced in this article, should give you pointers.

You'll probably need to use pywin32 and/or ctypes to accomplish what you want.

Answer 2

I don't have a windows box around, so this is untested, but I'd be tempted to try the os.dup and os.dup2 methods; duplicate the file descriptors and use those instead of the parent ones.