Check just before running update-index if the worktree file's content is
still the same, don't update it when it's been modified. This narrows
the race window a lot, from possibly minutes or hours, to seconds or
less.
(Use replaceFile so that the worktree update happens atomically,
allowing the InodeCache of the new worktree file to itself be gathered
w/o any other race.)
This doesn't eliminate the race; it can still occur in the window before
update-index runs. When annex.queue is large, a lot of files will be
statted by the checks, and so the window may still be large enough to be a
problem.
When only a few files are being processed, the window is as small as it
is in the race where a modification gets overwritten by git-annex when
it updates the worktree. Or maybe as small as whatever race git
checkout/pull/merge may have when the worktree gets modified during it.
Still, I've kept a todo about this race.
This commit was supported by the NSF-funded DataLad project.
Use git update-index --refresh, since it's a little bit more
efficient and the user can be told to run it if a locked index prevents
git-annex from running it.
This also fixes the problem where an annexed file was deleted in the index
and a get of another file that uses the same key caused the index update to
add back the deleted file. update-index will not add back the deleted file.
Documented in tips/unlocked_files.mdwn the gotcha that the index update
may conflict with other operations. I can't see any way to possibly avoid
that conflict.
One new todo about a race that causes a modification to be accidentially
staged.
Note that the assistant only flushes the git command queue when it
commits a modification. I have not tested the assistant with v6 unlocked
files, but assume most users of the assistant won't care if the index
shows a file as modified for a while.
This commit was supported by the NSF-funded DataLad project.
After updating the worktree for an add/drop, update git's index, so git
status will not show the files as modified.
What actually happens is that the index update removes the inode
information from the index. The next git status (or similar) run
then has to do some work. It runs the clean filter.
So, this depends on the clean filter being reasonably fast and on git
not leaking memory when running it. Both problems were fixed in
a96972015d, but only for git 2.5. Anyone
using an older git will see very expensive git status after an add/drop.
This uses the same git update-index queue as other parts of git-annex, so
the actual index update is fairly efficient. Of course, updating the index
does still have some overhead. The annex.queuesize config will control how
often the index gets updated when working on a lot of files.
This is an imperfect workaround... Added several todos about new
problems this workaround causes. Still, this seems a lot better than the
old behavior.
This commit was supported by the NSF-funded DataLad project.
v6 add: Take advantage of improved SIGPIPE handler in git 2.5 to speed up
the clean filter by not reading the file content from the pipe. This also
avoids git buffering the whole file content in memory.
When built with an older git, still consumes stdin. If built with a newer
git and used with an older one, it breaks, but that's acceptable --
checking the git version every time would make repeated smudge runs slow.
This commit was supported by the NSF-funded DataLad project.
