question about bzrlib.tag

[Alexander Belchenko]

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from bzrlib/tags.py class BasicTags:

    def _set_tag_dict(self, new_dict):
        """Replace all tag definitions

        :param new_dict: Dictionary from tag name to target.
        """
        self.branch.lock_read()
        try:
            self.branch._transport.put_bytes('tags',
                self._serialize_tag_dict(new_dict))
        finally:
            self.branch.unlock()

Why this method acquire read lock? This method actually write not read data.
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[µ]
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