bisect: avoid copying ancestor list for non-merge commits
During a bisection, hg needs to compute a list of all ancestors for every
candidate commit. This is accomplished via a bottom-up traversal of the set of
candidates, during which each revision's ancestor list is populated using the
ancestor list of its parent(s). Previously, this involved copying the entire
list, which could be very long in if the bisection range was large.
To help improve this, we can observe that each candidate commit is visited
exactly once, at which point its ancestor list is copied into its children's
lists and then dropped. In the case of non-merge commits, a commit's ancestor
list consists exactly of its parent's list plus itself. This means that we can
trivially reuse the parent's existing list for one of its non-merge children,
which avoids copying entirely if that commit is the parent's only child. This
makes bisections over linear ranges of commits much faster.
During some informal testing in the large publicly-available `mozilla-central`
repository, this noticeably sped up bisections over large ranges of history:
Setup:
$ cd mozilla-central
$ hg bisect --reset
$ hg bisect --good 0
$ hg log -r tip -T '{rev}\n'
628417
Test:
$ time hg bisect --bad tip --noupdate
Before:
real 3m35.927s
user 3m35.553s
sys 0m0.319s
After:
real 1m41.142s
user 1m40.810s
sys 0m0.285s
#!/usr/bin/env python
"""Test the running system for features availability. Exit with zero
if all features are there, non-zero otherwise. If a feature name is
prefixed with "no-", the absence of feature is tested.
"""
import hghave
import optparse
import os
import sys
checks = hghave.checks
def list_features():
for name, feature in sorted(checks.items()):
desc = feature[1]
print(name + ':', desc)
def test_features():
failed = 0
for name, feature in checks.items():
check, _ = feature
try:
check()
except Exception as e:
print("feature %s failed: %s" % (name, e))
failed += 1
return failed
parser = optparse.OptionParser("%prog [options] [features]")
parser.add_option(
"--test-features", action="store_true", help="test available features"
)
parser.add_option(
"--list-features", action="store_true", help="list available features"
)
def _loadaddon():
if 'TESTDIR' in os.environ:
# loading from '.' isn't needed, because `hghave` should be
# running at TESTTMP in this case
path = os.environ['TESTDIR']
else:
path = '.'
if not os.path.exists(os.path.join(path, 'hghaveaddon.py')):
return
sys.path.insert(0, path)
try:
import hghaveaddon
assert hghaveaddon # silence pyflakes
except BaseException as inst:
sys.stderr.write(
'failed to import hghaveaddon.py from %r: %s\n' % (path, inst)
)
sys.exit(2)
sys.path.pop(0)
if __name__ == '__main__':
options, args = parser.parse_args()
_loadaddon()
if options.list_features:
list_features()
sys.exit(0)
if options.test_features:
sys.exit(test_features())
hghave.require(args)