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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 _remove(self, rtracker):
 """ Remove a resource from the pool. :param rtracker: A resource. :type rtracker: :class:`_ResourceTracker` """

        with self._lock:
            i = self._reference_queue.index(rtracker)
            self._reference_queue[i] = None
            self._size -= 1