An excerpt that shows how to do multiprocessing

tests_lib_filesystem.py

import os
import multiprocessing
import subprocess
import sys
import traceback

def make_unreadable_file(path):
    os.chmod(path, 0o000)
    if sys.platform == "win32":
        # Once we drop PY2 we can use `os.getlogin()` instead.
        username = os.environ["USERNAME"]
        # Remove "Read Data/List Directory" permission for current user, but
        # leave everything else.
        args = ["icacls", path, "/deny", username + ":(RD)"]
        result = subprocess.check_call(args)
        print('icacls result', result)


def external_file_opener(conn):
    """
    This external process is run with multiprocessing.
    It waits for a path from the parent, opens it, and then wait for another message before closing it.

    :param conn: bi-directional pipe
    :return: nothing
    """
    f = None
    try:
        # Wait for parent to send path
        msg = conn.recv()
        if msg is True:
            # Do nothing - we have been told to exit without a path or action
            pass
        else:
            path, action = msg
            # Open the file
            try:
                f = open(path, 'r')
                if action == 'lock':
                    lock_action(f)
                elif action == 'noaccess':
                    make_unreadable_file(path)
            except OSError as e:
                traceback.print_exc(None, sys.stderr)

            # Indicate the file is opened
            conn.send(True)
            # Now path is open and we wait for signal to exit
            conn.recv()
    finally:
        if f:
            f.close()
        conn.close()


class FileOpener(object):

    def __init__(self, path=None, action=None):
        self.path = None
        self.conn, child_conn = multiprocessing.Pipe()
        self.child = multiprocessing.Process(target=external_file_opener, daemon=True, args=(child_conn,))
        self.child.start()
        if path:
            self.send(path, action)

    def send(self, path, action=None):
        if self.path is not None:
            raise AttributeError('path may only be set once')
        self.path = str(path)
        self.conn.send( (str(path), action) )
        return self.conn.recv()

    def cleanup(self):
        # send a message to the child to exit; it will exit whether the path was sent or not
        self.conn.send(True)
        self.child.join()

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.cleanup()