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2017-11-13Switch empty tree and blob lookups to use hash abstractionLibravatar brian m. carlson1-4/+4
Switch the uses of empty_tree_oid and empty_blob_oid to use the current_hash abstraction that represents the current hash algorithm in use. Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-11-13Integrate hash algorithm support with repo setupLibravatar brian m. carlson1-0/+4
In future versions of Git, we plan to support an additional hash algorithm. Integrate the enumeration of hash algorithms with repository setup, and store a pointer to the enumerated data in struct repository. Of course, we currently only support SHA-1, so hard-code this value in read_repository_format. In the future, we'll enumerate this value from the configuration. Add a constant, the_hash_algo, which points to the hash_algo structure pointer in the repository global. Note that this is the hash which is used to serialize data to disk, not the hash which is used to display items to the user. The transition plan anticipates that these may be different. We can add an additional element in the future (say, ui_hash_algo) to provide for this case. Include repository.h in cache.h since we now need to have access to these struct and variable definitions. Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-11-09Merge branch 'rs/hex-to-bytes-cleanup'Libravatar Junio C Hamano1-0/+7
Code cleanup. * rs/hex-to-bytes-cleanup: sha1_file: use hex_to_bytes() http-push: use hex_to_bytes() notes: move hex_to_bytes() to hex.c and export it
2017-11-06Merge branch 'ma/lockfile-fixes'Libravatar Junio C Hamano1-1/+24
An earlier update made it possible to use an on-stack in-core lockfile structure (as opposed to having to deliberately leak an on-heap one). Many codepaths have been updated to take advantage of this new facility. * ma/lockfile-fixes: read_cache: roll back lock in `update_index_if_able()` read-cache: leave lock in right state in `write_locked_index()` read-cache: drop explicit `CLOSE_LOCK`-flag cache.h: document `write_locked_index()` apply: remove `newfd` from `struct apply_state` apply: move lockfile into `apply_state` cache-tree: simplify locking logic checkout-index: simplify locking logic tempfile: fix documentation on `delete_tempfile()` lockfile: fix documentation on `close_lock_file_gently()` treewide: prefer lockfiles on the stack sha1_file: do not leak `lock_file`
2017-11-01notes: move hex_to_bytes() to hex.c and export itLibravatar René Scharfe1-0/+7
Make the function for converting pairs of hexadecimal digits to binary available to other call sites. Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-10-07read_cache: roll back lock in `update_index_if_able()`Libravatar Martin Ågren1-0/+4
`update_index_if_able()` used to always commit the lock or roll it back. Commit 03b866477 (read-cache: new API write_locked_index instead of write_index/write_cache, 2014-06-13) stopped rolling it back in case a write was not even attempted. This change in behavior is not motivated in the commit message and appears to be accidental: the `else`-path was removed, although that changed the behavior in case the `if` shortcuts. Reintroduce the rollback and document this behavior. While at it, move the documentation on this function from the function definition to the function declaration in cache.h. If `write_locked_index(..., COMMIT_LOCK)` fails, it will roll back the lock for us (see the previous commit). Noticed-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Martin Ågren <martin.agren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-10-07read-cache: leave lock in right state in `write_locked_index()`Libravatar Martin Ågren1-0/+4
If the original version of `write_locked_index()` returned with an error, it didn't roll back the lockfile unless the error occured at the very end, during closing/committing. See commit 03b866477 (read-cache: new API write_locked_index instead of write_index/write_cache, 2014-06-13). In commit 9f41c7a6b (read-cache: close index.lock in do_write_index, 2017-04-26), we learned to close the lock slightly earlier in the callstack. That was mostly a side-effect of lockfiles being implemented using temporary files, but didn't cause any real harm. Recently, commit 076aa2cbd (tempfile: auto-allocate tempfiles on heap, 2017-09-05) introduced a subtle bug. If the temporary file is deleted (i.e., the lockfile is rolled back), the tempfile-pointer in the `struct lock_file` will be left dangling. Thus, an attempt to reuse the lockfile, or even just to roll it back, will induce undefined behavior -- most likely a crash. Besides not crashing, we clearly want to make things consistent. The guarantees which the lockfile-machinery itself provides is A) if we ask to commit and it fails, roll back, and B) if we ask to close and it fails, do _not_ roll back. Let's do the same for consistency. Do not delete the temporary file in `do_write_index()`. One of its callers, `write_locked_index()` will thereby avoid rolling back the lock. The other caller, `write_shared_index()`, will delete its temporary file anyway. Both of these callers will avoid undefined behavior (crashing). Teach `write_locked_index(..., COMMIT_LOCK)` to roll back the lock before returning. If we have already succeeded and committed, it will be a noop. Simplify the existing callers where we now have a superfluous call to `rollback_lockfile()`. That should keep future readers from wondering why the callers are inconsistent. Signed-off-by: Martin Ågren <martin.agren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-10-07read-cache: drop explicit `CLOSE_LOCK`-flagLibravatar Martin Ågren1-3/+2
`write_locked_index()` takes two flags: `COMMIT_LOCK` and `CLOSE_LOCK`. At most one is allowed. But it is also possible to use no flag, i.e., `0`. But when `write_locked_index()` calls `do_write_index()`, the temporary file, a.k.a. the lockfile, will be closed. So passing `0` is effectively the same as `CLOSE_LOCK`, which seems like a bug. We might feel tempted to restructure the code in order to close the file later, or conditionally. It also feels a bit unfortunate that we simply "happen" to close the lock by way of an implementation detail of lockfiles. But note that we need to close the temporary file before `stat`-ing it, at least on Windows. See 9f41c7a6b (read-cache: close index.lock in do_write_index, 2017-04-26). Drop `CLOSE_LOCK` and make it explicit that `write_locked_index()` always closes the lock. Whether it is also committed is governed by the remaining flag, `COMMIT_LOCK`. This means we neither have nor suggest that we have a mode to write the index and leave the file open. Whatever extra contents we might eventually want to write, we should probably write it from within `write_locked_index()` itself anyway. Signed-off-by: Martin Ågren <martin.agren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-10-06cache.h: document `write_locked_index()`Libravatar Martin Ågren1-0/+16
The next patches will tweak the behavior of this function. Document it in order to establish a basis for those patches. Signed-off-by: Martin Ågren <martin.agren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-10-03Merge branch 'jk/no-optional-locks'Libravatar Junio C Hamano1-0/+6
Some commands (most notably "git status") makes an opportunistic update when performing a read-only operation to help optimize later operations in the same repository. The new "--no-optional-locks" option can be passed to Git to disable them. * jk/no-optional-locks: git: add --no-optional-locks option
2017-09-29Merge branch 'rj/no-sign-compare'Libravatar Junio C Hamano1-2/+2
Many codepaths have been updated to squelch -Wsign-compare warnings. * rj/no-sign-compare: ALLOC_GROW: avoid -Wsign-compare warnings cache.h: hex2chr() - avoid -Wsign-compare warnings commit-slab.h: avoid -Wsign-compare warnings git-compat-util.h: xsize_t() - avoid -Wsign-compare warnings
2017-09-27git: add --no-optional-locks optionLibravatar Jeff King1-0/+6
Some tools like IDEs or fancy editors may periodically run commands like "git status" in the background to keep track of the state of the repository. Some of these commands may refresh the index and write out the result in an opportunistic way: if they can get the index lock, then they update the on-disk index with any updates they find. And if not, then their in-core refresh is lost and just has to be recomputed by the next caller. But taking the index lock may conflict with other operations in the repository. Especially ones that the user is doing themselves, which _aren't_ opportunistic. In other words, "git status" knows how to back off when somebody else is holding the lock, but other commands don't know that status would be happy to drop the lock if somebody else wanted it. There are a couple possible solutions: 1. Have some kind of "pseudo-lock" that allows other commands to tell status that they want the lock. This is likely to be complicated and error-prone to implement (and maybe even impossible with just dotlocks to work from, as it requires some inter-process communication). 2. Avoid background runs of commands like "git status" that want to do opportunistic updates, preferring instead plumbing like diff-files, etc. This is awkward for a couple of reasons. One is that "status --porcelain" reports a lot more about the repository state than is available from individual plumbing commands. And two is that we actually _do_ want to see the refreshed index. We just don't want to take a lock or write out the result. Whereas commands like diff-files expect us to refresh the index separately and write it to disk so that they can depend on the result. But that write is exactly what we're trying to avoid. 3. Ask "status" not to lock or write the index. This is easy to implement. The big downside is that any work done in refreshing the index for such a call is lost when the process exits. So a background process may end up re-hashing a changed file multiple times until the user runs a command that does an index refresh themselves. This patch implements the option 3. The idea (and the test) is largely stolen from a Git for Windows patch by Johannes Schindelin, 67e5ce7f63 (status: offer *not* to lock the index and update it, 2016-08-12). The twist here is that instead of making this an option to "git status", it becomes a "git" option and matching environment variable. The reason there is two-fold: 1. An environment variable is carried through to sub-processes. And whether an invocation is a background process or not should apply to the whole process tree. So you could do "git --no-optional-locks foo", and if "foo" is a script or alias that calls "status", you'll still get the effect. 2. There may be other programs that want the same treatment. I've punted here on finding more callers to convert, since "status" is the obvious one to call as a repeated background job. But "git diff"'s opportunistic refresh of the index may be a good candidate. The test is taken from 67e5ce7f63, and it's worth repeating Johannes's explanation: Note that the regression test added in this commit does not *really* verify that no index.lock file was written; that test is not possible in a portable way. Instead, we verify that .git/index is rewritten *only* when `git status` is run without `--no-optional-locks`. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-09-22cache.h: hex2chr() - avoid -Wsign-compare warningsLibravatar Ramsay Jones1-2/+2
Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-09-14pack: make packed_git_mru global a value instead of a pointerLibravatar Jonathan Nieder1-2/+2
The MRU cache that keeps track of recently used packs is represented using two global variables: struct mru packed_git_mru_storage; struct mru *packed_git_mru = &packed_git_mru_storage; Callers never assign to the packed_git_mru pointer, though, so we can simplify by eliminating it and using &packed_git_mru_storage (renamed to &packed_git_mru) directly. This variable is only used by the packfile subsystem, making this a relatively uninvasive change (and any new unadapted callers would trigger a compile error). Noticed while moving these globals to the object_store struct. Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Acked-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-09-10Merge branch 'sb/sha1-file-cleanup' into maintLibravatar Junio C Hamano1-1/+0
Code clean-up. * sb/sha1-file-cleanup: sha1_file: make read_info_alternates static
2017-09-10Merge branch 'jk/hashcmp-memcmp' into maintLibravatar Junio C Hamano1-8/+1
Code clean-up. * jk/hashcmp-memcmp: hashcmp: use memcmp instead of open-coded loop
2017-08-26Merge branch 'jt/packmigrate'Libravatar Junio C Hamano1-121/+1
Code movement to make it easier to hack later. * jt/packmigrate: (23 commits) pack: move for_each_packed_object() pack: move has_pack_index() pack: move has_sha1_pack() pack: move find_pack_entry() and make it global pack: move find_sha1_pack() pack: move find_pack_entry_one(), is_pack_valid() pack: move check_pack_index_ptr(), nth_packed_object_offset() pack: move nth_packed_object_{sha1,oid} pack: move clear_delta_base_cache(), packed_object_info(), unpack_entry() pack: move unpack_object_header() pack: move get_size_from_delta() pack: move unpack_object_header_buffer() pack: move {,re}prepare_packed_git and approximate_object_count pack: move install_packed_git() pack: move add_packed_git() pack: move unuse_pack() pack: move use_pack() pack: move pack-closing functions pack: move release_pack_memory() pack: move open_pack_index(), parse_pack_index() ...
2017-08-26Merge branch 'po/object-id'Libravatar Junio C Hamano1-3/+3
* po/object-id: sha1_file: convert index_stream to struct object_id sha1_file: convert hash_sha1_file_literally to struct object_id sha1_file: convert index_fd to struct object_id sha1_file: convert index_path to struct object_id read-cache: convert to struct object_id builtin/hash-object: convert to struct object_id
2017-08-26Merge branch 'sb/diff-color-move'Libravatar Junio C Hamano1-0/+2
"git diff" has been taught to optionally paint new lines that are the same as deleted lines elsewhere differently from genuinely new lines. * sb/diff-color-move: (25 commits) diff: document the new --color-moved setting diff.c: add dimming to moved line detection diff.c: color moved lines differently, plain mode diff.c: color moved lines differently diff.c: buffer all output if asked to diff.c: emit_diff_symbol learns about DIFF_SYMBOL_SUMMARY diff.c: emit_diff_symbol learns about DIFF_SYMBOL_STAT_SEP diff.c: convert word diffing to use emit_diff_symbol diff.c: convert show_stats to use emit_diff_symbol diff.c: convert emit_binary_diff_body to use emit_diff_symbol submodule.c: migrate diff output to use emit_diff_symbol diff.c: emit_diff_symbol learns DIFF_SYMBOL_REWRITE_DIFF diff.c: emit_diff_symbol learns about DIFF_SYMBOL_BINARY_FILES diff.c: emit_diff_symbol learns DIFF_SYMBOL_HEADER diff.c: emit_diff_symbol learns DIFF_SYMBOL_FILEPAIR_{PLUS, MINUS} diff.c: emit_diff_symbol learns DIFF_SYMBOL_CONTEXT_INCOMPLETE diff.c: emit_diff_symbol learns DIFF_SYMBOL_WORDS[_PORCELAIN] diff.c: migrate emit_line_checked to use emit_diff_symbol diff.c: emit_diff_symbol learns DIFF_SYMBOL_NO_LF_EOF diff.c: emit_diff_symbol learns DIFF_SYMBOL_CONTEXT_FRAGINFO ...
2017-08-23pack: move for_each_packed_object()Libravatar Jonathan Tan1-6/+1
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move has_pack_index()Libravatar Jonathan Tan1-2/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move has_sha1_pack()Libravatar Jonathan Tan1-2/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move find_sha1_pack()Libravatar Jonathan Tan1-3/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move find_pack_entry_one(), is_pack_valid()Libravatar Jonathan Tan1-8/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move check_pack_index_ptr(), nth_packed_object_offset()Libravatar Jonathan Tan1-16/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move nth_packed_object_{sha1,oid}Libravatar Jonathan Tan1-14/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move clear_delta_base_cache(), packed_object_info(), unpack_entry()Libravatar Jonathan Tan1-7/+0
Both sha1_file.c and packfile.c now need read_object(), so a copy of read_object() was created in packfile.c. This patch makes both mark_bad_packed_object() and has_packed_and_bad() global. Unlike most of the other patches in this series, these 2 functions need to remain global. Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move unpack_object_header()Libravatar Jonathan Tan1-1/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move get_size_from_delta()Libravatar Jonathan Tan1-1/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move unpack_object_header_buffer()Libravatar Jonathan Tan1-1/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move {,re}prepare_packed_git and approximate_object_countLibravatar Jonathan Tan1-15/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move install_packed_git()Libravatar Jonathan Tan1-1/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move add_packed_git()Libravatar Jonathan Tan1-1/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move unuse_pack()Libravatar Jonathan Tan1-1/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move use_pack()Libravatar Jonathan Tan1-1/+0
The function open_packed_git() needs to be temporarily made global. Its scope will be restored to static in a subsequent commit. Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move pack-closing functionsLibravatar Jonathan Tan1-8/+0
The function close_pack_fd() needs to be temporarily made global. Its scope will be restored to static in a subsequent commit. Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move open_pack_index(), parse_pack_index()Libravatar Jonathan Tan1-8/+0
alloc_packed_git() in packfile.c is duplicated from sha1_file.c. In a subsequent commit, alloc_packed_git() will be removed from sha1_file.c. Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move pack_report()Libravatar Jonathan Tan1-2/+0
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23pack: move pack name-related functionsLibravatar Jonathan Tan1-23/+0
Currently, sha1_file.c and cache.h contain many functions, both related to and unrelated to packfiles. This makes both files very large and causes an unclear separation of concerns. Create a new file, packfile.c, to hold all packfile-related functions currently in sha1_file.c. It has a corresponding header packfile.h. In this commit, the pack name-related functions are moved. Subsequent commits will move the other functions. Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-23Merge branch 'jt/subprocess-handshake' into maintLibravatar Junio C Hamano1-0/+3
Code cleanup. * jt/subprocess-handshake: sub-process: refactor handshake to common function Documentation: migrate sub-process docs to header convert: add "status=delayed" to filter process protocol convert: refactor capabilities negotiation convert: move multiple file filter error handling to separate function convert: put the flags field before the flag itself for consistent style t0021: write "OUT <size>" only on success t0021: make debug log file name configurable t0021: keep filter log files on comparison
2017-08-23Merge branch 'sb/sha1-file-cleanup'Libravatar Junio C Hamano1-1/+0
Code clean-up. * sb/sha1-file-cleanup: sha1_file: make read_info_alternates static
2017-08-22Merge branch 'jk/hashcmp-memcmp'Libravatar Junio C Hamano1-8/+1
Code clean-up. * jk/hashcmp-memcmp: hashcmp: use memcmp instead of open-coded loop
2017-08-22Merge branch 'bw/grep-recurse-submodules'Libravatar Junio C Hamano1-1/+1
"git grep --recurse-submodules" has been reworked to give a more consistent output across submodule boundary (and do its thing without having to fork a separate process). * bw/grep-recurse-submodules: grep: recurse in-process using 'struct repository' submodule: merge repo_read_gitmodules and gitmodules_config submodule: check for unmerged .gitmodules outside of config parsing submodule: check for unstaged .gitmodules outside of config parsing submodule: remove fetch.recursesubmodules from submodule-config parsing submodule: remove submodule.fetchjobs from submodule-config parsing config: add config_from_gitmodules cache.h: add GITMODULES_FILE macro repository: have the_repository use the_index repo_read_index: don't discard the index
2017-08-20sha1_file: convert hash_sha1_file_literally to struct object_idLibravatar Patryk Obara1-1/+1
Convert all remaining callers as well. Signed-off-by: Patryk Obara <patryk.obara@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-20sha1_file: convert index_fd to struct object_idLibravatar Patryk Obara1-1/+1
Convert all remaining callers as well. Signed-off-by: Patryk Obara <patryk.obara@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-20sha1_file: convert index_path to struct object_idLibravatar Patryk Obara1-1/+1
Convert all remaining callers as well. Signed-off-by: Patryk Obara <patryk.obara@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-15sha1_file: make read_info_alternates staticLibravatar Stefan Beller1-1/+0
read_info_alternates is not used from outside, so let's make it static. We have to declare the function before link_alt_odb_entry instead of moving the code around, link_alt_odb_entry calls read_info_alternates, which in turn calls link_alt_odb_entry. Signed-off-by: Stefan Beller <sbeller@google.com> Reviewed-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-08-11Merge branch 'ls/filter-process-delayed'Libravatar Junio C Hamano1-0/+3
The filter-process interface learned to allow a process with long latency give a "delayed" response. * ls/filter-process-delayed: convert: add "status=delayed" to filter process protocol convert: refactor capabilities negotiation convert: move multiple file filter error handling to separate function convert: put the flags field before the flag itself for consistent style t0021: write "OUT <size>" only on success t0021: make debug log file name configurable t0021: keep filter log files on comparison
2017-08-11Merge branch 'bc/object-id'Libravatar Junio C Hamano1-24/+23
Conversion from uchar[20] to struct object_id continues. * bc/object-id: sha1_name: convert uses of 40 to GIT_SHA1_HEXSZ sha1_name: convert GET_SHA1* flags to GET_OID* sha1_name: convert get_sha1* to get_oid* Convert remaining callers of get_sha1 to get_oid. builtin/unpack-file: convert to struct object_id bisect: convert bisect_checkout to struct object_id builtin/update_ref: convert to struct object_id sequencer: convert to struct object_id remote: convert struct push_cas to struct object_id submodule: convert submodule config lookup to use object_id builtin/merge-tree: convert remaining caller of get_sha1 to object_id builtin/fsck: convert remaining caller of get_sha1 to object_id
2017-08-09hashcmp: use memcmp instead of open-coded loopLibravatar Jeff King1-8/+1
In 1a812f3a70 (hashcmp(): inline memcmp() by hand to optimize, 2011-04-28), it was reported that an open-coded loop outperformed memcmp() for comparing sha1s. Discussion[1] a few years later in 2013 showed that this depends on your libc's version of memcmp(). In particular, glibc 2.13 optimized their memcmp around 2011. Here are current timings with glibc 2.24 (best-of-five, on linux.git): [before this patch, open-coded] $ time git rev-list --objects --all real 0m35.357s user 0m35.016s sys 0m0.340s [after this patch, memcmp] real 0m32.930s user 0m32.630s sys 0m0.300s Now that we've had 6 years for that version of glibc to make its way onto people's machines, it's worth revisiting our benchmarks and switching to memcmp(). It may be that there are other non-glibc systems where memcmp() isn't as well optimized. But since our single data point in favor of open-coding was on a now-ancient glibc, we should probably assume the system memcmp is good unless proven otherwise. We may end up with a SLOW_MEMCMP Makefile knob, but we can hold off on that until we actually find such a system in practice. [1] https://public-inbox.org/git/20130318073229.GA5551@sigill.intra.peff.net/ Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>