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
"""
Small and dumb HTTP server for use in tests.
"""
import optparse
import os
import signal
import socket
import sys
from mercurial import (
encoding,
pycompat,
server,
util,
)
httpserver = util.httpserver
OptionParser = optparse.OptionParser
if os.environ.get('HGIPV6', '0') == '1':
class simplehttpserver(httpserver.httpserver):
address_family = socket.AF_INET6
else:
simplehttpserver = httpserver.httpserver
class _httprequesthandler(httpserver.simplehttprequesthandler):
def log_message(self, format, *args):
httpserver.simplehttprequesthandler.log_message(self, format, *args)
sys.stderr.flush()
class simplehttpservice:
def __init__(self, host, port):
self.address = (host, port)
def init(self):
self.httpd = simplehttpserver(self.address, _httprequesthandler)
def run(self):
self.httpd.serve_forever()
if __name__ == '__main__':
parser = OptionParser()
parser.add_option(
'-p',
'--port',
dest='port',
type='int',
default=8000,
help='TCP port to listen on',
metavar='PORT',
)
parser.add_option(
'-H',
'--host',
dest='host',
default='localhost',
help='hostname or IP to listen on',
metavar='HOST',
)
parser.add_option('--logfile', help='file name of access/error log')
parser.add_option(
'--pid',
dest='pid',
help='file name where the PID of the server is stored',
)
parser.add_option(
'-f',
'--foreground',
dest='foreground',
action='store_true',
help='do not start the HTTP server in the background',
)
parser.add_option('--daemon-postexec', action='append')
(options, args) = parser.parse_args()
signal.signal(signal.SIGTERM, lambda x, y: sys.exit(0))
if options.foreground and options.logfile:
parser.error(
"options --logfile and --foreground are mutually " "exclusive"
)
if options.foreground and options.pid:
parser.error("options --pid and --foreground are mutually exclusive")
opts = {
b'pid_file': options.pid,
b'daemon': not options.foreground,
b'daemon_postexec': pycompat.rapply(
encoding.strtolocal, options.daemon_postexec
),
}
service = simplehttpservice(options.host, options.port)
runargs = [sys.executable, __file__] + sys.argv[1:]
runargs = [pycompat.fsencode(a) for a in runargs]
server.runservice(
opts,
initfn=service.init,
runfn=service.run,
logfile=options.logfile,
runargs=runargs,
)