branchcache: skip entries that are topological heads in the on disk file
In the majority of cases, topological heads are also branch heads. We have
efficient way to get the topological heads and efficient way to retrieve
their branch information. So there is little value in putting them in the branch
cache file explicitly. On the contrary, writing them explicitly tend to create
very large cache file that are inefficient to read and update.
So the branch cache v3 format is no longer including them. This changeset focus
on the format aspect and have no focus on the performance aspect. We will cover
that later.
# Support code for event tracing in Mercurial. Lives in demandimport
# so it can also be used in demandimport.
#
# Copyright 2018 Google LLC.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
import contextlib
import os
_pipe = None
_checked = False
_session = 'none'
def _isactive():
global _pipe, _session, _checked
if _pipe is None:
if _checked:
return False
_checked = True
if 'HGCATAPULTSERVERPIPE' not in os.environ:
return False
_pipe = open(os.environ['HGCATAPULTSERVERPIPE'], 'w', 1)
_session = os.environ.get('HGCATAPULTSESSION', 'none')
return True
@contextlib.contextmanager
def log(whencefmt, *whenceargs):
if not _isactive():
yield
return
whence = whencefmt % whenceargs
try:
# Both writes to the pipe are wrapped in try/except to ignore
# errors, as we can see mysterious errors in here if the pager
# is active. Presumably other conditions could trigger
# problems too.
try:
_pipe.write('START %s %s\n' % (_session, whence))
except IOError:
pass
yield
finally:
try:
_pipe.write('END %s %s\n' % (_session, whence))
except IOError:
pass
def counter(label, amount, *labelargs):
if not _isactive():
return
l = label % labelargs
# See above in log() for why this is in a try/except.
try:
_pipe.write('COUNTER %s %d %s\n' % (_session, amount, l))
except IOError:
pass