Add util function for closing all open fds.

import os

import sys

import errno

import resource

import subprocess

from collections import deque

            cls._instance = super(Singleton, cls).__call__(*args, **kwargs)

        return cls._instance

def close_fds(exclude_fds=None, debug=False):

    """Close all fds uneeded fds in child when using fork.

    :param exclude_fds: list of file descriptors that should not be closed (0,

        1, 2 must not be set here, see debug)

    :param bool debug: indicates if std in/out should be left open (usually for

        debuging purpose)

    """

    # get max fd

    limit = resource.getrlimit(resource.RLIMIT_NOFILE)[1]

    if limit == resource.RLIM_INFINITY:

        max_fd = 2048

    else:

        max_fd = limit

    if exclude_fds is None:

        exclude_fds = []

    if debug:

        exclude_fds += [0, 1, 2]  # debug

    for fd in xrange(max_fd, -1, -1):

        if fd in exclude_fds:

            continue

        try:

            os.close(fd)

        except OSError as exc:

            if exc.errno != errno.EBADF:

                raise

            # wasn't open

    if not debug:

        sys.stdin = open(os.devnull)

        sys.stdout = open(os.devnull)

        sys.stderr = open(os.devnull)

        assert sys.stdin.fileno() == 0

        assert sys.stdout.fileno() == 1

        assert sys.stderr.fileno() == 2