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annotate mercurial/revlogutils/concurrency_checker.py @ 48575:e91aa800ae5b

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rhg: desambiguate status without decompressing filelog if possible When status is unsure based on `stat()` and the dirstate if a file is clean or modified, we need to compare it against the filelog. This comparison can skip looking at contents if the lengths differ. This changeset optimize this further to deduce what we can about the length if the filelog without decompressing it or resolving deltas. Differential Revision: https://phab.mercurial-scm.org/D11965
author Simon Sapin <simon.sapin@octobus.net>
date Fri, 07 Jan 2022 14:40:21 +0100
parents e9901d01d135
children 1c5810ce737e
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1 from ..i18n import _
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2 from .. import error
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3
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4
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5 def get_checker(ui, revlog_name=b'changelog'):
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6 """Get a function that checks file handle position is as expected.
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7
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8 This is used to ensure that files haven't been modified outside of our
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9 knowledge (such as on a networked filesystem, if `hg debuglocks` was used,
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10 or writes to .hg that ignored locks happened).
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11
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12 Due to revlogs supporting a concept of buffered, delayed, or diverted
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13 writes, we're allowing the files to be shorter than expected (the data may
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14 not have been written yet), but they can't be longer.
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16 Please note that this check is not perfect; it can't detect all cases (there
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17 may be false-negatives/false-OKs), but it should never claim there's an
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18 issue when there isn't (false-positives/false-failures).
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19 """
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20
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21 vpos = ui.config(b'debug', b'revlog.verifyposition.' + revlog_name)
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22 # Avoid any `fh.tell` cost if this isn't enabled.
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23 if not vpos or vpos not in [b'log', b'warn', b'fail']:
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24 return None
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25
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26 def _checker(fh, fn, expected):
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27 if fh.tell() <= expected:
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28 return
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29
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30 msg = _(b'%s: file cursor at position %d, expected %d')
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31 # Always log if we're going to warn or fail.
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32 ui.log(b'debug', msg + b'\n', fn, fh.tell(), expected)
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33 if vpos == b'warn':
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34 ui.warn((msg + b'\n') % (fn, fh.tell(), expected))
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35 elif vpos == b'fail':
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36 raise error.RevlogError(msg % (fn, fh.tell(), expected))
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37
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38 return _checker