mercurial/revlogutils/concurrency_checker.py
author Arseniy Alekseyev <aalekseyev@janestreet.com>
Tue, 09 Apr 2024 11:12:24 +0100
changeset 51602 68929cf3c0c6
parent 46607 e9901d01d135
child 51864 1c5810ce737e
permissions -rw-r--r--
match: avoid rust fast path if the matcher was tampered with Otherwise the fast path does not respect the modifications made by the extension (concretely largefiles, but other extensions can start using that too)
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from ..i18n import _
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from .. import error
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def get_checker(ui, revlog_name=b'changelog'):
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    """Get a function that checks file handle position is as expected.
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    This is used to ensure that files haven't been modified outside of our
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    knowledge (such as on a networked filesystem, if `hg debuglocks` was used,
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    or writes to .hg that ignored locks happened).
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    Due to revlogs supporting a concept of buffered, delayed, or diverted
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    writes, we're allowing the files to be shorter than expected (the data may
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    not have been written yet), but they can't be longer.
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    Please note that this check is not perfect; it can't detect all cases (there
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    may be false-negatives/false-OKs), but it should never claim there's an
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    issue when there isn't (false-positives/false-failures).
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    """
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    vpos = ui.config(b'debug', b'revlog.verifyposition.' + revlog_name)
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    # Avoid any `fh.tell` cost if this isn't enabled.
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    if not vpos or vpos not in [b'log', b'warn', b'fail']:
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        return None
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    def _checker(fh, fn, expected):
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        if fh.tell() <= expected:
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            return
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        msg = _(b'%s: file cursor at position %d, expected %d')
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        # Always log if we're going to warn or fail.
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        ui.log(b'debug', msg + b'\n', fn, fh.tell(), expected)
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        if vpos == b'warn':
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            ui.warn((msg + b'\n') % (fn, fh.tell(), expected))
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        elif vpos == b'fail':
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            raise error.RevlogError(msg % (fn, fh.tell(), expected))
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    return _checker