hgdemandimport/tracing.py

bundle2: make server.bundle2.stream default to True

Support for bundle2 streaming clones has been shipped in Mercurial 4.5
(7eedbd5d4880), but was never activated by default. It's time to have more
people use it. The new format allows streaming clones to transport cache
(hooray for speed) and phaseroots (fixes phase-related issues).

Changes in tests:

bundle2 capabilities now have "stream=v2" (plus a '\n' as a separator) and
therefore take 14 bytes more: "%0Astream%3Dv2". Tip for tests that have data
encoded with CBOR: 0xd3 - 0xc5 = 14.

$USUAL_BUNDLE2_CAPS$ replaces $USUAL_BUNDLE2_CAPS_SERVER$, which is the same
thing, but without "stream=v2".

Since streaming clones now also transfer caches, the reported byte and file
counts are higher (e.g. 816 bytes in 9 files instead of 613 bytes in 4 files,
a bit of --debug and manual math confirms that the caches take these extra 203
bytes in 5 files).

Differential Revision: https://phab.mercurial-scm.org/D4680

# 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