# 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

@contextlib.contextmanager

def log(whencefmt, *whenceargs):

    global _pipe, _session, _checked

    if _pipe is None:

        if _checked:

            yield

            return

        _checked = True

        if 'HGCATAPULTSERVERPIPE' not in os.environ:

            yield

            return

        _pipe = open(os.environ['HGCATAPULTSERVERPIPE'], 'w', 1)

        _session = os.environ.get('HGCATAPULTSESSION', 'none')

    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