fileset, revset: do not use global parser object for thread safety parse() cannot be called at the same time because a parser object keeps its states. This is no problem for command-line hg client, but it would cause strange errors in multi-threaded hgweb. Creating parser object is not too expensive. original: % python -m timeit -s 'from mercurial import revset' 'revset.parse("0::tip")' 100000 loops, best of 3: 11.3 usec per loop thread-safe: % python -m timeit -s 'from mercurial import revset' 'revset.parse("0::tip")' 100000 loops, best of 3: 13.1 usec per loop