hgdemandimport/tracing.py

chg: make is possible to call by default an hg binary located next to chg

When a single version of hg is in use and it's in the PATH, using chg
is just a matter of calling chg.

But when there are multiple installations of hg+chg around, and hg is
referred to with an absolute path, using chg is more annoying because
it requires both changing the invocation to hg to use chg, but also
setting CHGHG.

Currently, we set HGPATH when we build chg to remove the need to set
CHGHG in the previous paragraph. But that means chg now hardcodes its
installation path, which makes the installation not relocatable. Hence
this proposal to make chg find ./hg relative to itself (as opposed to
CHGHG=./hg which find hg relative to cwd).

This only works on linux as written, but since it's opt-in, it sounds
fine.

Tested by hand, as I'm not sure how else to test this.

Differential Revision: https://phab.mercurial-scm.org/D9006

# 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