'Adds a descriptor to the collection.
:param descriptor:
An instance of :class:`KeventDescriptor` to be added.'

def _add_descriptor(self, descriptor):

    self._descriptors.add(descriptor)
    self._kevents.append(descriptor.kevent)
    self._descriptor_for_path[descriptor.path] = descriptor
    self._descriptor_for_fd[descriptor.fd] = descriptor
