view hgdemandimport/tracing.py @ 45464:4a0ccbecbaa6

repo: avoid copying/updating a dict on every `repo.__getitem__`

This has some mild performance benefits. I'm looking into a pathological case
where one of our `hg log` invocations takes several seconds, and according to
hyperfine this reduces the wall time of the entire operation (running in chg)
from:

```
  Time (mean ± σ):      7.390 s ±  0.106 s    [User: 7.058 s, System: 0.271 s]

  Range (min … max):    7.300 s …  7.625 s
```

to:

```
  Time (mean ± σ):      7.046 s ±  0.091 s    [User: 6.714 s, System: 0.279 s]

  Range (min … max):    6.916 s …  7.169 s
```

Note: the log command is slow due to an issue in our custom stuff executing
`repo[<arg>]` 298,800 times. This performance improvement is likely not
noticeable during normal operation, but I don't feel like it's making the code
more difficult to understand, and every small bit helps.

Differential Revision: https://phab.mercurial-scm.org/D9022

# 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