parsers: a C implementation of the new ancestors algorithm
The performance of both the old and new Python ancestor algorithms
depends on the number of revs they need to traverse. Although the
new algorithm performs far better than the old when revs are
numerically and topologically close, both algorithms become slow
under other circumstances, taking up to 1.8 seconds to give answers
in a Linux kernel repo.
This C implementation of the new algorithm is a fairly straightforward
transliteration. The only corner case of interest is that it raises
an OverflowError if the number of GCA candidates found during the
first pass is greater than 24, to avoid the dual perils of fixnum
overflow and trying to allocate too much memory. (If this exception
is raised, the Python implementation is used instead.)
Performance numbers are good: in a Linux kernel repo, time for "hg
debugancestors" on two distant revs (24bf01de7537 and c2a8808f5943)
is as follows:
Old Python: 0.36 sec
New Python: 0.42 sec
New C: 0.02 sec
For a case where the new algorithm should perform well:
Old Python: 1.84 sec
New Python: 0.07 sec
New C: measures as zero when using --time
(This commit includes a paranoid cross-check to ensure that the
Python and C implementations give identical answers. The above
performance numbers were measured with that check disabled.)
"""Extension to verify locks are obtained in the required places.
This works by wrapping functions that should be surrounded by a lock
and asserting the lock is held. Missing locks are called out with a
traceback printed to stderr.
This currently only checks store locks, not working copy locks.
"""
import os
import traceback
def _warnstack(ui, msg, skip=1):
'''issue warning with the message and the current stack, skipping the
skip last entries'''
ui.warn('%s at:\n' % msg)
entries = traceback.extract_stack()[:-skip]
fnmax = max(len(entry[0]) for entry in entries)
for fn, ln, func, _text in entries:
ui.warn(' %*s:%-4s in %s\n' % (fnmax, fn, ln, func))
def _checklock(repo):
l = repo._lockref and repo._lockref()
if l is None or not l.held:
_warnstack(repo.ui, 'missing lock', skip=2)
def reposetup(ui, repo):
orig = repo.__class__
class lockcheckrepo(repo.__class__):
def _writejournal(self, *args, **kwargs):
_checklock(self)
return orig._writejournal(self, *args, **kwargs)
def transaction(self, *args, **kwargs):
_checklock(self)
return orig.transaction(self, *args, **kwargs)
# TODO(durin42): kiilerix had a commented-out lock check in
# _writebranchcache and _writerequirements
def _tag(self, *args, **kwargs):
_checklock(self)
return orig._tag(self, *args, **kwargs)
def write(self, *args, **kwargs):
assert os.path.lexists(self._join('.hg/wlock'))
return orig.write(self, *args, **kwargs)
repo.__class__ = lockcheckrepo