[Python-3000] socket GC worries (original) (raw)

roudkerk r.m.oudkerk at gmail.com
Wed Oct 31 19:19:05 CET 2007

Guido van Rossum <guido python.org> writes:

2007/10/29, Greg Ewing <greg.ewing canterbury.ac.nz>: > I don't see what's so difficult about this. Each file > descriptor should be owned by exactly one object. If > two objects need to share a fd, then you dup() it so > that each one has its own fd. When the object is > close()d or GCed, it closes its fd. On Windows you can't dup() a fd.

You can use os.dup() on an fd. But with sockets you must use DuplicateHandle() instead because socket.fileno() returns a handle not an fd.

socket.py has this comment:

These classes are used by the socket() defined on Windows and BeOS

platforms to provide a best-effort implementation of the cleanup

semantics needed when sockets can't be dup()ed.

These are not actually used on other platforms.

I don't know whether BeOS still matters to anyone... I would just implement _socket.socket.dup() on Windows using DuplicateHandle().

Example of DuplicateHandle():

import ctypes, socket from _subprocess import *

send a message to a socket object 'conn'

listener = socket.socket() listener.bind(('localhost', 0)) listener.listen(1) client = socket.socket() client.connect(listener.getsockname()) conn, addr = listener.accept() client.sendall('hello world')

duplicate handle

handle = conn.fileno() duphandle = DuplicateHandle( GetCurrentProcess(), handle, GetCurrentProcess(), 0, False, DUPLICATE_SAME_ACCESS ).Detach()

use duplicate handle to read the message

buffer = ctypes.c_buffer(20) ctypes.windll.ws2_32.recv(duphandle, buffer, 20, 0) print handle, duphandle, buffer.value

BTW. On Windows can we please have a socket.fromfd() function (or maybe that should be socket.fromhandle()).

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