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annotate mercurial/revlogutils/concurrency_checker.py @ 48497:2c6084f67a86

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changelog-v2: use helper constant in the code to pack/unpack entries This makes the code simpler to read and modify. This is probably less efficient, but we are talking about the Python implementation here, so performance is concerne secondary to readability. Differential Revision: https://phab.mercurial-scm.org/D11934
author Pierre-Yves David <pierre-yves.david@octobus.net>
date Tue, 14 Dec 2021 19:24:24 +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