24d82185d2
The tempfile API keeps to-be-cleaned tempfiles in a singly-linked list and never removes items from the list. A future patch would like to start removing items, but removal from a singly linked list is O(n), as we have to walk the list to find the predecessor element. This means that a process which takes "n" simultaneous lockfiles (for example, an atomic transaction on "n" refs) may end up quadratic in "n". Before we start allowing items to be removed, it would be nice to have a way to cover this case in linear time. The simplest solution is to make an assumption about the order in which tempfiles are added and removed from the list. If both operations iterate over the tempfiles in the same order, then by putting new items at the end of the list our removal search will always find its items at the beginning of the list. And indeed, that would work for the case of refs. But it creates a hidden dependency between unrelated parts of the code. If anybody changes the ref code (or if we add a new caller that opens multiple simultaneous tempfiles) they may unknowingly introduce a performance regression. Another solution is to use a better data structure. A doubly-linked list works fine, and we already have an implementation in list.h. But there's one snag: the elements of "struct tempfile" are all marked as "volatile", since a signal handler may interrupt us and iterate over the list at any moment (even if we were in the middle of adding a new entry). We can declare a "volatile struct list_head", but we can't actually use it with the normal list functions. The compiler complains about passing a pointer-to-volatile via a regular pointer argument. And rightfully so, as the sub-function would potentially need different code to deal with the volatile case. That leaves us with a few options: 1. Drop the "volatile" modifier for the list items. This is probably a bad idea. I checked the assembly output from "gcc -O2", and the "volatile" really does impact the order in which it updates memory. 2. Use macros instead of inline functions. The irony here is that list.h is entirely implemented as trivial inline functions. So we basically are already generating custom code for each call. But sadly there's no way in C to declare the inline function to take a more generic type. We could do so by switching the inline functions to macros, but it does make the end result harder to read. And it doesn't fully solve the problem (for instance, the declaration of list_head needs to change so that its "prev" and "next" pointers point to other volatile structs). 3. Don't use list.h, and just make our own ad-hoc doubly-linked list. It's not that much code to implement the basics that we need here. But if we're going to do so, why not add the few extra lines required to model it after the actual list.h interface? We can even reuse a few of the macro helpers. So this patch takes option 3, but actually implements a parallel "volatile list" interface in list.h, where it could potentially be reused by other code. This implements just enough for tempfile.c's use, though we could easily port other functions later if need be. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com> |
||
---|---|---|
.github | ||
block-sha1 | ||
builtin | ||
ci | ||
compat | ||
contrib | ||
Documentation | ||
ewah | ||
git-gui | ||
gitk-git | ||
gitweb | ||
mergetools | ||
outgoing | ||
perl | ||
po | ||
ppc | ||
refs | ||
sha1collisiondetection@19d97bf5af | ||
sha1dc | ||
t | ||
templates | ||
vcs-svn | ||
xdiff | ||
.gitattributes | ||
.gitignore | ||
.gitmodules | ||
.mailmap | ||
.travis.yml | ||
abspath.c | ||
aclocal.m4 | ||
advice.c | ||
advice.h | ||
alias.c | ||
alloc.c | ||
apply.c | ||
apply.h | ||
archive-tar.c | ||
archive-zip.c | ||
archive.c | ||
archive.h | ||
argv-array.c | ||
argv-array.h | ||
attr.c | ||
attr.h | ||
base85.c | ||
bisect.c | ||
bisect.h | ||
blame.c | ||
blame.h | ||
blob.c | ||
blob.h | ||
branch.c | ||
branch.h | ||
builtin.h | ||
bulk-checkin.c | ||
bulk-checkin.h | ||
bundle.c | ||
bundle.h | ||
cache-tree.c | ||
cache-tree.h | ||
cache.h | ||
check_bindir | ||
check-builtins.sh | ||
check-racy.c | ||
color.c | ||
color.h | ||
column.c | ||
column.h | ||
combine-diff.c | ||
command-list.txt | ||
commit-slab.h | ||
commit.c | ||
commit.h | ||
common-main.c | ||
config.c | ||
config.h | ||
config.mak.in | ||
config.mak.uname | ||
configure.ac | ||
connect.c | ||
connect.h | ||
connected.c | ||
connected.h | ||
convert.c | ||
convert.h | ||
copy.c | ||
COPYING | ||
credential-cache--daemon.c | ||
credential-cache.c | ||
credential-store.c | ||
credential.c | ||
credential.h | ||
csum-file.c | ||
csum-file.h | ||
ctype.c | ||
daemon.c | ||
date.c | ||
decorate.c | ||
decorate.h | ||
delta.h | ||
diff-delta.c | ||
diff-lib.c | ||
diff-no-index.c | ||
diff.c | ||
diff.h | ||
diffcore-break.c | ||
diffcore-delta.c | ||
diffcore-order.c | ||
diffcore-pickaxe.c | ||
diffcore-rename.c | ||
diffcore.h | ||
dir-iterator.c | ||
dir-iterator.h | ||
dir.c | ||
dir.h | ||
editor.c | ||
entry.c | ||
environment.c | ||
exec_cmd.c | ||
exec_cmd.h | ||
fast-import.c | ||
fetch-pack.c | ||
fetch-pack.h | ||
fmt-merge-msg.h | ||
fsck.c | ||
fsck.h | ||
generate-cmdlist.sh | ||
gettext.c | ||
gettext.h | ||
git-add--interactive.perl | ||
git-archimport.perl | ||
git-bisect.sh | ||
git-compat-util.h | ||
git-cvsexportcommit.perl | ||
git-cvsimport.perl | ||
git-cvsserver.perl | ||
git-difftool--helper.sh | ||
git-filter-branch.sh | ||
git-instaweb.sh | ||
git-merge-octopus.sh | ||
git-merge-one-file.sh | ||
git-merge-resolve.sh | ||
git-mergetool--lib.sh | ||
git-mergetool.sh | ||
git-p4.py | ||
git-parse-remote.sh | ||
git-quiltimport.sh | ||
git-rebase--am.sh | ||
git-rebase--interactive.sh | ||
git-rebase--merge.sh | ||
git-rebase.sh | ||
git-remote-testgit.sh | ||
git-request-pull.sh | ||
git-send-email.perl | ||
git-sh-i18n.sh | ||
git-sh-setup.sh | ||
git-stash.sh | ||
git-submodule.sh | ||
git-svn.perl | ||
GIT-VERSION-GEN | ||
git-web--browse.sh | ||
git.c | ||
git.rc | ||
gpg-interface.c | ||
gpg-interface.h | ||
graph.c | ||
graph.h | ||
grep.c | ||
grep.h | ||
hash.h | ||
hashmap.c | ||
hashmap.h | ||
help.c | ||
help.h | ||
hex.c | ||
http-backend.c | ||
http-fetch.c | ||
http-push.c | ||
http-walker.c | ||
http.c | ||
http.h | ||
ident.c | ||
imap-send.c | ||
INSTALL | ||
iterator.h | ||
khash.h | ||
kwset.c | ||
kwset.h | ||
levenshtein.c | ||
levenshtein.h | ||
LGPL-2.1 | ||
line-log.c | ||
line-log.h | ||
line-range.c | ||
line-range.h | ||
list-objects.c | ||
list-objects.h | ||
list.h | ||
ll-merge.c | ||
ll-merge.h | ||
lockfile.c | ||
lockfile.h | ||
log-tree.c | ||
log-tree.h | ||
mailinfo.c | ||
mailinfo.h | ||
mailmap.c | ||
mailmap.h | ||
Makefile | ||
match-trees.c | ||
merge-blobs.c | ||
merge-blobs.h | ||
merge-recursive.c | ||
merge-recursive.h | ||
merge.c | ||
mergesort.c | ||
mergesort.h | ||
mru.c | ||
mru.h | ||
name-hash.c | ||
notes-cache.c | ||
notes-cache.h | ||
notes-merge.c | ||
notes-merge.h | ||
notes-utils.c | ||
notes-utils.h | ||
notes.c | ||
notes.h | ||
object.c | ||
object.h | ||
oidset.c | ||
oidset.h | ||
pack-bitmap-write.c | ||
pack-bitmap.c | ||
pack-bitmap.h | ||
pack-check.c | ||
pack-objects.c | ||
pack-objects.h | ||
pack-revindex.c | ||
pack-revindex.h | ||
pack-write.c | ||
pack.h | ||
packfile.c | ||
packfile.h | ||
pager.c | ||
parse-options-cb.c | ||
parse-options.c | ||
parse-options.h | ||
patch-delta.c | ||
patch-ids.c | ||
patch-ids.h | ||
path.c | ||
path.h | ||
pathspec.c | ||
pathspec.h | ||
pkt-line.c | ||
pkt-line.h | ||
preload-index.c | ||
pretty.c | ||
prio-queue.c | ||
prio-queue.h | ||
progress.c | ||
progress.h | ||
prompt.c | ||
prompt.h | ||
quote.c | ||
quote.h | ||
reachable.c | ||
reachable.h | ||
read-cache.c | ||
README.md | ||
ref-filter.c | ||
ref-filter.h | ||
reflog-walk.c | ||
reflog-walk.h | ||
refs.c | ||
refs.h | ||
RelNotes | ||
remote-curl.c | ||
remote-testsvn.c | ||
remote.c | ||
remote.h | ||
replace_object.c | ||
repository.c | ||
repository.h | ||
rerere.c | ||
rerere.h | ||
resolve-undo.c | ||
resolve-undo.h | ||
revision.c | ||
revision.h | ||
run-command.c | ||
run-command.h | ||
send-pack.c | ||
send-pack.h | ||
sequencer.c | ||
sequencer.h | ||
server-info.c | ||
setup.c | ||
sh-i18n--envsubst.c | ||
sha1_file.c | ||
sha1_name.c | ||
sha1-array.c | ||
sha1-array.h | ||
sha1-lookup.c | ||
sha1-lookup.h | ||
sha1dc_git.c | ||
sha1dc_git.h | ||
shallow.c | ||
shell.c | ||
shortlog.h | ||
show-index.c | ||
sideband.c | ||
sideband.h | ||
sigchain.c | ||
sigchain.h | ||
split-index.c | ||
split-index.h | ||
strbuf.c | ||
strbuf.h | ||
streaming.c | ||
streaming.h | ||
string-list.c | ||
string-list.h | ||
sub-process.c | ||
sub-process.h | ||
submodule-config.c | ||
submodule-config.h | ||
submodule.c | ||
submodule.h | ||
symlinks.c | ||
tag.c | ||
tag.h | ||
tar.h | ||
tempfile.c | ||
tempfile.h | ||
thread-utils.c | ||
thread-utils.h | ||
tmp-objdir.c | ||
tmp-objdir.h | ||
trace.c | ||
trace.h | ||
trailer.c | ||
trailer.h | ||
transport-helper.c | ||
transport.c | ||
transport.h | ||
tree-diff.c | ||
tree-walk.c | ||
tree-walk.h | ||
tree.c | ||
tree.h | ||
unicode_width.h | ||
unimplemented.sh | ||
unix-socket.c | ||
unix-socket.h | ||
unpack-trees.c | ||
unpack-trees.h | ||
upload-pack.c | ||
url.c | ||
url.h | ||
urlmatch.c | ||
urlmatch.h | ||
usage.c | ||
userdiff.c | ||
userdiff.h | ||
utf8.c | ||
utf8.h | ||
varint.c | ||
varint.h | ||
version.c | ||
version.h | ||
versioncmp.c | ||
walker.c | ||
walker.h | ||
wildmatch.c | ||
wildmatch.h | ||
worktree.c | ||
worktree.h | ||
wrap-for-bin.sh | ||
wrapper.c | ||
write_or_die.c | ||
ws.c | ||
wt-status.c | ||
wt-status.h | ||
xdiff-interface.c | ||
xdiff-interface.h | ||
zlib.c |
Git - fast, scalable, distributed revision control system
Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.
Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.
Please read the file INSTALL for installation instructions.
Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.
See Documentation/gittutorial.txt to get started, then see
Documentation/giteveryday.txt for a useful minimum set of commands, and
Documentation/git-.txt for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with man gittutorial
or git help tutorial
, and the
documentation of each command with man git-<commandname>
or git help <commandname>
.
CVS users may also want to read Documentation/gitcvs-migration.txt
(man gitcvs-migration
or git help cvs-migration
if git is
installed).
The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission). To subscribe to the list, send an email with just "subscribe git" in the body to majordomo@vger.kernel.org. The mailing list archives are available at https://public-inbox.org/git/, http://marc.info/?l=git and other archival sites.
The maintainer frequently sends the "What's cooking" reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.
The name "git" was given by Linus Torvalds when he wrote the very first version. He described the tool as "the stupid content tracker" and the name as (depending on your mood):
- random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of "get" may or may not be relevant.
- stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
- "global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
- "goddamn idiotic truckload of sh*t": when it breaks