status: prefer relative paths in Rust code … when the repository root is under the current directory, so the kernel needs to traverse fewer directory in every call to `read_dir` or `symlink_metadata`. Better yet would be to use libc functions like `openat` and `fstatat` to remove such repeated traversals entirely, but the standard library does not provide APIs based on those. Maybe with a crate like https://crates.io/crates/openat instead? Benchmarks of `rhg status` show that this patch is neutral in some configurations, and makes the command up to ~20% faster in others. Below is semi-arbitrary subset of results. The four numeric columns are: time (in seconds) with this changeset’s parent, time with this changeset, time difference (negative is better), time ratio (less than 1 is better). ``` mercurial-dirstate-v1 | default-plain-clean.no-iu.pbr | 0.0061 -> 0.0059: -0.0002 (0.97) mercurial-dirstate-v2 | default-plain-clean.no-iu.pbr | 0.0029 -> 0.0028: -0.0001 (0.97) mozilla-dirstate-v1 | default-plain-clean.no-iu.pbr | 0.2110 -> 0.2102: -0.0007 (1.00) mozilla-dirstate-v2 | default-copies-clean.ignored.pbr | 0.0489 -> 0.0401: -0.0088 (0.82) mozilla-dirstate-v2 | default-copies-clean.no-iu.pbr | 0.0479 -> 0.0393: -0.0085 (0.82) mozilla-dirstate-v2 | default-copies-large.all.pbr | 0.1262 -> 0.1210: -0.0051 (0.96) mozilla-dirstate-v2 | default-copies-small.ignored-unknown.pbr | 0.1262 -> 0.1200: -0.0062 (0.95) mozilla-dirstate-v2 | default-copies-small.ignored.pbr | 0.0536 -> 0.0417: -0.0119 (0.78) mozilla-dirstate-v2 | default-copies-small.no-iu.pbr | 0.0482 -> 0.0393: -0.0089 (0.81) mozilla-dirstate-v2 | default-plain-clean.ignored.pbr | 0.0518 -> 0.0402: -0.0116 (0.78) mozilla-dirstate-v2 | default-plain-clean.no-iu.pbr | 0.0481 -> 0.0392: -0.0088 (0.82) mozilla-dirstate-v2 | default-plain-large.all.pbr | 0.1271 -> 0.1218: -0.0052 (0.96) mozilla-dirstate-v2 | default-plain-small.ignored-unknown.pbr | 0.1225 -> 0.1202: -0.0022 (0.98) mozilla-dirstate-v2 | default-plain-small.ignored.pbr | 0.0510 -> 0.0418: -0.0092 (0.82) mozilla-dirstate-v2 | default-plain-small.no-iu.pbr | 0.0480 -> 0.0394: -0.0086 (0.82) netbeans-dirstate-v1 | default-plain-clean.no-iu.pbr | 0.1442 -> 0.1422: -0.0020 (0.99) netbeans-dirstate-v2 | default-plain-clean.no-iu.pbr | 0.0325 -> 0.0282: -0.0043 (0.87) ``` Differential Revision: https://phab.mercurial-scm.org/D12175

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# Support code for event tracing in Mercurial. Lives in demandimport

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# so it can also be used in demandimport.

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#

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# Copyright 2018 Google LLC.

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#

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# This software may be used and distributed according to the terms of the

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# GNU General Public License version 2 or any later version.

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from __future__ import absolute_import

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import contextlib

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import os

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_pipe = None

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_checked = False

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_session = 'none'

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def _isactive():

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    global _pipe, _session, _checked

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    if _pipe is None:

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        if _checked:

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            return False

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        _checked = True

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        if 'HGCATAPULTSERVERPIPE' not in os.environ:

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            return False

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

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

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    return True

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    30

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@contextlib.contextmanager

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def log(whencefmt, *whenceargs):

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    if not _isactive():

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        yield

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        return

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    whence = whencefmt % whenceargs

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    try:

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        # Both writes to the pipe are wrapped in try/except to ignore

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        # errors, as we can see mysterious errors in here if the pager

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        # is active. Presumably other conditions could trigger

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        # problems too.

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        try:

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            _pipe.write('START %s %s\n' % (_session, whence))

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        except IOError:

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            pass

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        yield

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    finally:

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        try:

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            _pipe.write('END %s %s\n' % (_session, whence))

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        except IOError:

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            pass

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def counter(label, amount, *labelargs):

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    if not _isactive():

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        return

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    l = label % labelargs

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    # See above in log() for why this is in a try/except.

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    try:

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        _pipe.write('COUNTER %s %d %s\n' % (_session, amount, l))

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    except IOError:

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        pass