'Start monitoring, or restart after a fork.
No effect if called multiple times.
.. warning:: Topology is shared among multiple threads and is protected
by mutual exclusion. Using Topology from a process other than the one
that initialized it will emit a warning and may result in deadlock. To
prevent this from happening, MongoClient must be created after any
forking OR MongoClient must be started with connect=False.'

def open(self):

    if (self._pid is None):
        self._pid = os.getpid()
    elif (os.getpid() != self._pid):
        warnings.warn("MongoClient    opened    before    fork.    Create    MongoClient    with    connect=False,    or    create    client    after    forking.    See    PyMongo's    documentation    for    details:    http://api.mongodb.org/python/current/faq.html#pymongo-fork-safe>")
    with self._lock:
        self._ensure_opened()
