view hgdemandimport/tracing.py @ 44388:5ac1eecc9c64

rust-nodemap: core implementation for shortest

In this implementation, we just make `lookup()` return also the number
of steps that have been needed to come to a conclusion from the
nodetree data, and `validate_candidate()` takes care of the special
cases related to `NULL_NODE`.

This way of doing minimizes code duplication, but it means that
the comparatively slower finding of first non zero nybble will run
for all calls to `find()` where it is not needed.

Still running on the file generated for the mozilla-central repository,
it seems indeed that we now get more ofter 320 ns than 310. The odds that
this could have a significant impact on real life Mercurial performance
are still looking low. Let's wait for actual benchmark runs to see if
an optimization is needed here.

Differential Revision: https://phab.mercurial-scm.org/D7819

# 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