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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def open(self):
 """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. """

        if self._pid is None:
            self._pid = os.getpid()
        else:
            if os.getpid() != self._pid:
                warnings.warn(
                    "MongoClient opened before fork. Create MongoClient only "
                    "after forking. See PyMongo's documentation for details: "
                    "http://api.mongodb.org/python/current/faq.html#"
                    "is-pymongo-fork-safe")

        with self._lock:
            self._ensure_opened()