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When we delete a ref that is packed, we rewrite the whole
packed-refs file and simply omit the ref that no longer
exists. However, we base the rewrite on whatever happens to
be in our refs cache, not what is necessarily on disk. That
opens us up to a race condition if another process is
simultaneously packing the refs, as we will overwrite their
newly-made pack-refs file with our potentially stale data,
losing commits.
You can demonstrate the race like this:
# setup some repositories
git init --bare parent &&
(cd parent && git config core.logallrefupdates true) &&
git clone parent child &&
(cd child && git commit --allow-empty -m base)
# in one terminal, repack the refs repeatedly
cd parent &&
while true; do
git pack-refs --all
done
# in another terminal, simultaneously push updates to
# master, and create and delete an unrelated ref
cd child &&
while true; do
git push origin HEAD:newbranch &&
git commit --allow-empty -m foo
us=`git rev-parse master` &&
git push origin master &&
git push origin :newbranch &&
them=`git --git-dir=../parent rev-parse master` &&
if test "$them" != "$us"; then
echo >&2 "$them" != "$us"
exit 1
fi
done
In many cases the two processes will conflict over locking
the packed-refs file, and the deletion of newbranch will
simply fail. But eventually you will hit the race, which
happens like this:
1. We push a new commit to master. It is already packed
(from the looping pack-refs call). We write the new
value (let us call it B) to $GIT_DIR/refs/heads/master,
but the old value (call it A) remains in the
packed-refs file.
2. We push the deletion of newbranch, spawning a
receive-pack process. Receive-pack advertises all refs
to the client, causing it to iterate over each ref; it
caches the packed refs in memory, which points at the
stale value A.
3. Meanwhile, a separate pack-refs process is running. It
runs to completion, updating the packed-refs file to
point master at B, and deleting $GIT_DIR/refs/heads/master
which also pointed at B.
4. Back in the receive-pack process, we get the
instruction to delete :newbranch. We take a lock on
packed-refs (which works, as the other pack-refs
process has already finished). We then rewrite the
contents using the cached refs, which contain the stale
value A.
The resulting packed-refs file points master once again at
A. The loose ref which would override it to point at B was
deleted (rightfully) in step 3. As a result, master now
points at A. The only trace that B ever existed in the
parent is in the reflog: the final entry will show master
moving from A to B, even though the ref still points at A
(so you can detect this race after the fact, because the
next reflog entry will move from A to C).
We can fix this by invalidating the packed-refs cache after
we have taken the lock. This means that we will re-read the
packed-refs file, and since we have the lock, we will be
sure that what we read will be atomically up-to-date when we
write (it may be out of date with respect to loose refs, but
that is OK, as loose refs take precedence).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Avoid unnecessary temporary allocations while looking for matching refs
inside refs API.
By René Scharfe (3) and Junio C Hamano (1)
* rs/refs-string-slice:
refs: do not create ref_entry when searching
refs: use strings directly in find_containing_dir()
refs: convert parameter of create_dir_entry() to length-limited string
refs: convert parameter of search_ref_dir() to length-limited string
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The code to lazily read loose refs unnecessarily read the refs in a
subhierarchy by mistake when we free the data for the subhierarchy.
By Michael Haggerty
* mh/ref-api-lazy-loose:
free_ref_entry(): do not trigger reading of loose refs
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Fixes a performance regression in the earlier series.
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The old code allowed many references to be efficiently added to a
single directory, because it just appended the references to the
containing directory unsorted without doing any searching (and
therefore without requiring any intermediate sorting). But the old
code was inefficient when a large number of subdirectories were added
to a directory, because the directory always had to be searched to see
if the new subdirectory already existed, and this search required the
directory to be sorted first. The same was repeated for every new
subdirectory, so the time scaled like O(N^2), where N is the number of
subdirectories within a single directory.
In practice, references are often added to the ref_cache in
lexicographic order, for example when reading the packed-refs file.
So build some intelligence into add_entry_to_dir() to optimize for the
case of references and/or subdirectories being added in lexicographic
order: if the existing entries were already sorted, and the new entry
comes after the last existing entry, then adjust ref_dir::sorted to
reflect the fact that the ref_dir is still sorted.
Thanks to Peff for pointing out the performance regression that
inspired this change.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The search_ref_dir() function is about looking up an existing ref_entry in
a sorted array of ref_entry stored in dir->entries, but it still allocates
a new ref_entry and frees it before returning. This is only because the
call to bsearch(3) was coded in a suboptimal way. Unlike the comparison
function given to qsort(3), the first parameter to its comparison function
does not need to point at an object that is shaped like an element in the
array.
Introduce a new comparison function that takes a counted string as the key
and an element in an array of ref_entry and give it to bsearch(), so that
we do not have to allocate a new ref_entry that we will never return to
the caller anyway.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Convert the parameter subdirname of search_for_subdir() to a
length-limted string and then simply pass the interesting slice of the
refname from find_containing_dir(), thereby avoiding to duplicate the
string.
Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Do not call get_ref_dir() from within free_ref_entry(), because that
triggers the reading of loose refs, only for them to be freed
immediately.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Refs API is updated to lazily read sub-hierarchies of refs/ namespace,
so that we do not have to grab everything from the filesystem when we
are only interested in listing branches, for example.
By Michael Haggerty (17) and Junio C Hamano (1)
* mh/ref-api-lazy-loose:
refs: fix find_containing_dir() regression
refs: read loose references lazily
read_loose_refs(): eliminate ref_cache argument
struct ref_dir: store a reference to the enclosing ref_cache
search_for_subdir(): return (ref_dir *) instead of (ref_entry *)
get_ref_dir(): add function for getting a ref_dir from a ref_entry
read_loose_refs(): rename function from get_ref_dir()
refs: wrap top-level ref_dirs in ref_entries
find_containing_dir(): use strbuf in implementation of this function
bisect: copy filename string obtained from git_path()
do_for_each_reflog(): use a strbuf to hold logfile name
do_for_each_reflog(): return early on error
get_ref_dir(): take the containing directory as argument
refs.c: extract function search_for_subdir()
get_ref_dir(): require that the dirname argument ends in '/'
get_ref_dir(): rename "base" parameter to "dirname"
get_ref_dir(): use a strbuf to hold refname
get_ref_dir(): return early if directory cannot be read
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The function used to return NULL when asked to find the containing
directory for a ref that does not exist, allowing the caller to
omit iteration altogether. But a misconversion in an earlier change
"refs.c: extract function search_for_subdir()" started returning the
top-level directory entry, forcing callers to walk everything.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Instead of reading the whole directory of loose references the first
time any are needed, only read them on demand, one directory at a
time.
Use a new ref_entry flag bit REF_INCOMPLETE to indicate that the entry
represents a REF_DIR that hasn't been read yet. Whenever any entries
from such a directory are needed, read all of the loose references
from that directory.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The ref_cache can now be read from the ref_dir.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This means that a directory ref_entry contains all of the information
needed by read_loose_refs().
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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That is what all the callers want, so give it to them.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Convert all accesses of a ref_dir within a ref_entry to use this
function. This function will later be responsible for reading loose
references from disk on demand.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The new name better describes the function's purpose, and also makes
the old name available for a more suitable purpose.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Make it turtles all the way down. This affects the loose and packed
fields of ref_cache instances.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This simplifies the bookkeeping and allows an (artificial) restriction
on refname component length to be removed.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Previously, the "dir" argument to get_ref_dir() was a pointer to the
top-level ref_dir. Change the function to expect a pointer to the
ref_dir corresponding to dirname. This allows entries to be added
directly to dir, without having to recurse through the reference trie
each time (i.e., we can use add_entry_to_dir() instead of add_ref()).
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This removes some conditional code and makes it consistent with the
way that direntry names are stored. Please note that this function is
never used on the top-level .git directory; it is always called for
directories at level .git/refs or deeper.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This simplifies the bookkeeping and allows an (artificial) restriction
on refname component length to be removed.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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More message strings marked for i18n.
By Nguyễn Thái Ngọc Duy (10) and Jonathan Nieder (1)
* nd/i18n:
help: replace underlining "help -a" headers using hyphens with a blank line
i18n: bundle: mark strings for translation
i18n: index-pack: mark strings for translation
i18n: apply: update say_patch_name to give translators complete sentence
i18n: apply: mark strings for translation
i18n: remote: mark strings for translation
i18n: make warn_dangling_symref() automatically append \n
i18n: help: mark strings for translation
i18n: mark relative dates for translation
strbuf: convenience format functions with \n automatically appended
Makefile: feed all header files to xgettext
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Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This helps remove \n from translatable strings
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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If the base argument has a "/" chararacter, then only iterate over the
reference subdir whose name is the part up to the last "/".
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Store references hierarchically in a tree that matches the
pseudo-directory structure of the reference names. Add a new kind of
ref_entry (with flag REF_DIR) to represent a whole subdirectory of
references. Sort ref_dirs one subdirectory at a time.
NOTE: the dirs can now be sorted as a side-effect of other function
calls. Therefore, it would be problematic to do something from a
each_ref_fn callback that could provoke the sorting of a directory
that is currently being iterated over (i.e., the directory containing
the entry that is being processed or any of its parents).
This is a bit far-fetched, because a directory is always sorted just
before being iterated over. Therefore, read-only accesses cannot
trigger the sorting of a directory whose iteration has already
started. But if a callback function would add a reference to a parent
directory of the reference in the iteration, then try to resolve a
reference under that directory, a re-sort could be triggered and cause
the iteration to work incorrectly.
Nevertheless...add a comment in refs.h warning against modifications
during iteration.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Use the more usual indexing idiom for clarity.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This purely textual change is in preparation for storing references
hierarchically, when the old ref_array structure will represent one
"directory" of references. Rename functions that deal with this
structure analogously, and also rename the structure's "refs" member
to "entries".
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This change is obviously silly by itself, but it is a step towards
adding a second member to the union.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Return 0 (instead of -1) for zero-length components. Move the
interpretation of zero-length components as illegal to
check_refname_format().
This will make it easier to extend check_refname_format() to also
check whether directory names are valid.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Add a function free_ref_entry(). This function will become nontrivial
when ref_entry (soon) becomes polymorphic.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Save a bunch of lines of code and a couple of strlen() calls.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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It costs a bit of boilerplate, but it means that the function can be
ignorant of how cached refs are stored.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Extract function do_for_each_ref_in_arrays() from do_for_each_ref().
The new function will be a useful building block for storing refs
hierarchically.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Extract function do_for_each_ref_in_array() from do_for_each_ref().
The new function will be a useful building block for storing refs
hierarchically.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Set and clear current_ref within do_one_ref() instead of setting it
here and leaving it to somebody else to clear it.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Reorder definitions in file: first check_refname_format() and helper
functions, then the functions for managing the ref_entry and ref_array
data structures, then ref_cache, then the more "business-logicky"
stuff. No code is changed.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The extra_refs provided a kludgy way to create fake references at a
global level in the hope that they would only affect some particular
code path. The last user of this API been rewritten, so strip this
stuff out before somebody else gets the bad idea of using it.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Add a new function add_packed_ref() that adds a reference directly to
the in-memory packed reference cache. This will be useful for
creating local references while cloning.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Keep track of how many entries at the beginning of a ref_array are already
sorted. In sort_ref_array(), return early if the the array is already
sorted (i.e., if no new references has been appended to the end of the
list since the last call to sort_ref_array()).
Sort ref_arrays only when needed, namely in search_ref_array() and in
do_for_each_ref(). However, never call sort_ref_array() on the
extra_refs, because extra_refs can contain multiple entries with the same
name and because sort_ref_array() not only sorts, but de-dups its
contents.
This change is currently not useful, because entries are not added to
ref_arrays after they are created. But in a moment they will be...
Implementation note: we could store a binary "sorted" value instead of
an integer, but storing the number of sorted entries leaves the way
open for a couple of possible future optimizations:
* In sort_ref_array(), sort *only* the unsorted entries, then merge
them with the sorted entries. This should be faster if most of the
entries are already sorted.
* Teach search_ref_array() to do a binary search of any sorted
entries, and if unsuccessful do a linear search of any unsorted
entries. This would avoid the need to sort the list every time that
search_ref_array() is called, and (given some intelligence about how
often to sort) could significantly improve the speed in certain
hypothetical usage patterns.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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* mh/ref-api:
add_ref(): take a (struct ref_entry *) parameter
create_ref_entry(): extract function from add_ref()
repack_without_ref(): remove temporary
resolve_gitlink_ref_recursive(): change to work with struct ref_cache
Pass a (ref_cache *) to the resolve_gitlink_*() helper functions
resolve_gitlink_ref(): improve docstring
get_ref_dir(): change signature
refs: change signatures of get_packed_refs() and get_loose_refs()
is_dup_ref(): extract function from sort_ref_array()
add_ref(): add docstring
parse_ref_line(): add docstring
is_refname_available(): remove the "quiet" argument
clear_ref_array(): rename from free_ref_array()
refs: rename parameters result -> sha1
refs: rename "refname" variables
struct ref_entry: document name member
Conflicts:
cache.h
refs.c
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resolve_ref() may return a pointer to a shared buffer and can be
overwritten by the next resolve_ref() calls. Callers need to
pay attention, not to keep the pointer when the next call happens.
Rename with "_unsafe" suffix to warn developers (or reviewers) before
introducing new call sites.
This patch is generated using the following command
git grep -l 'resolve_ref(' -- '*.[ch]'|xargs sed -i 's/resolve_ref(/resolve_ref_unsafe(/g'
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Take a pointer to the ref_entry to add to the array, rather than
creating the ref_entry within the function. This opens the way to
having multiple kinds of ref_entries.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Jeff King
Junio C Hamano
Michael Haggerty
René Scharfe
Nguyễn Thái Ngọc Duy