Mercurial > hg
view hgdemandimport/tracing.py @ 44781:ed684a82e29b stable
procutil: always waiting on child processes to prevent zombies with 'hg serve'
When runbgcommand is invoked by an extension with ensurestart=False, we never
called waitpid - which is fine in most cases, except if that's happening on a
command server (e.g. chg), in which case the child defunct process will just
sit there for as long as the server is running.
The actual semantics of SIGCHLD signal handling is a lot more complex than
it seems, and the POSIX standard *seems* to read that it's ignored by default
and everything would just work without the waitpid if we're not listening for
it, but the truth is that it's only ignored if we *explicitly* set it to
SIG_IGN. We further cannot set it to SIG_IGN or to a catch-all handler across
all of 'hg serve', because Python's suprocess.Popen relies on that signal,
and a few specific parts of hg also set custom handlers, so instead we wait
for specific PIDs in dedicated threads.
I did a poor-man's benchmark of the thread creation and it seems to take
about 1ms, which is way better than the 20+ms from ensurestart=True.
Differential Revision: https://phab.mercurial-scm.org/D8497
author | Rodrigo Damazio Bovendorp <rdamazio@google.com> |
---|---|
date | Thu, 07 May 2020 03:14:52 -0700 |
parents | 2372284d9457 |
children | 6000f5b25c9b |
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# 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. from __future__ import absolute_import 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