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merge: fix race that could cause wrong size in dirstate...

merge: fix race that could cause wrong size in dirstate The problem is that hg merge/update/etc work the following way: 1. figure out what files to update 2. apply the update to disk 3. apply the update to in-memory dirstate 4. write dirstate where step3 looks at the filesystem and assumes it sees the result of step2. If a file is changed between step2 and step3, step3 will record incorrect information in the dirstate. I avoid this by passing the size step3 needs directly from step2, for the common path (not implemented for change/delete conflicts for instance). I didn't fix the same race for the exec bit for now, because it's less likely to be problematic and I had trouble due to the fact that the dirstate stores the permissions differently from the manifest (st_mode vs '' 'l' 'x'), in combination with tests that pretend that symlinks are not supported. However, I moved the lstat from step3 to step2, which should tighten the race window markedly, both for the exec bit and for the mtime. Differential Revision: https://phab.mercurial-scm.org/D6475

Valentin Gatien-Baron - - Load All Authors

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      Checking the size/permissions/file-type of files stored in the

      dirstate after an update where the files are changed concurrently

      outside of hg's control.

        $ hg init repo

        $ cd repo

        $ echo a > a

        $ hg commit -qAm _

        $ echo aa > a

        $ hg commit -m _

        $ hg debugdirstate --no-dates

        n 644          3 (set  |unset)               a (re)

        $ cat >> $TESTTMP/dirstaterace.py << EOF

        > from mercurial import (

        >     extensions,

        >     merge,

        > )

        > def extsetup(ui):

        >     extensions.wrapfunction(merge, 'applyupdates', wrap)

        > def wrap(orig, *args, **kwargs):

        >     res = orig(*args, **kwargs)

        >     with open("a", "w"):

        >         pass # just truncate the file

        >     return res

        > EOF

      Do an update where file 'a' is changed between hg writing it to disk

      and hg writing the dirstate. The dirstate is correct nonetheless, and

      so hg status correctly shows a as clean.

        $ hg up -r 0 --config extensions.race=$TESTTMP/dirstaterace.py

        1 files updated, 0 files merged, 0 files removed, 0 files unresolved

        $ hg debugdirstate --no-dates

        n 644          2 (set  |unset)               a (re)

        $ echo a > a; hg status; hg diff

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				Checking the size/permissions/file-type of files stored in the
				dirstate after an update where the files are changed concurrently
				outside of hg's control.

				$ hg init repo
				$ cd repo
				$ echo a > a
				$ hg commit -qAm _
				$ echo aa > a
				$ hg commit -m _

				$ hg debugdirstate --no-dates
				n 644 3 (set \|unset) a (re)

				$ cat >> $TESTTMP/dirstaterace.py << EOF
				> from mercurial import (
				> extensions,
				> merge,
				> )
				> def extsetup(ui):
				> extensions.wrapfunction(merge, 'applyupdates', wrap)
				> def wrap(orig, args, *kwargs):
				> res = orig(args, *kwargs)
				> with open("a", "w"):
				> pass # just truncate the file
				> return res
				> EOF

				Do an update where file 'a' is changed between hg writing it to disk
				and hg writing the dirstate. The dirstate is correct nonetheless, and
				so hg status correctly shows a as clean.

				$ hg up -r 0 --config extensions.race=$TESTTMP/dirstaterace.py
				1 files updated, 0 files merged, 0 files removed, 0 files unresolved
				$ hg debugdirstate --no-dates
				n 644 2 (set \|unset) a (re)
				$ echo a > a; hg status; hg diff