"""A utility module which has FD-related functions.

This module mostly exists for L{clean_fds}, so it can be imported without
accidentally getting a reactor or something else that might create a critical
file descriptor.
"""

import os
import resource


def clean_fds():
"""Close all non-stdio file descriptors.

This should be called at the beginning of a program to avoid inheriting any
unwanted file descriptors from the invoking process. Unfortunately, this
is really common in unix!
"""
rlimit_nofile = resource.getrlimit(resource.RLIMIT_NOFILE)[1]
total_descriptors = min(4096, rlimit_nofile)
for fd in range(3, total_descriptors):
try:
os.close(fd)
except OSError:
pass