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65961d5a75
strbuf_setlen(., 0) writes '\0' to sb.buf[0], where buf is either
allocated and unique to sb, or the global slopbuf. The slopbuf is meant
to provide a guarantee that buf is not NULL and that a freshly
initialized buffer contains the empty string, but it is not supposed to
be written to. That strbuf_setlen writes to slopbuf has at least two
implications:
First, it's wrong in principle. Second, it might be hiding misuses which
are just waiting to wreak havoc. Third, ThreadSanitizer detects a race
when multiple threads write to slopbuf at roughly the same time, thus
potentially making any more critical races harder to spot.
Avoid writing to strbuf_slopbuf in strbuf_setlen. Let's instead assert
on the first byte of slopbuf being '\0', since it helps ensure the
promised invariant of buf[len] == '\0'. (We know that "len" was already
0, or someone has messed with "alloc". If someone has fiddled with the
fields that much beyond the correct interface, they're on their own.)
This is a function which is used in many places, possibly also in hot
code paths. There are two branches in strbuf_setlen already, and we are
adding a third and possibly a fourth (in the assert). In hot code paths,
we hopefully reuse the buffer in order to avoid continous reallocations.
Thus, after a start-up phase, we should always take the same path,
which might help branch prediction, and we would never make the assert.
If a hot code path continuously reallocates, we probably have bigger
performance problems than this new safety-check.
Simple measurements do not contradict this reasoning. 100000000 times
resetting a buffer and adding the empty string takes 5.29/5.26 seconds
with/without this patch (best of three). Releasing at every iteration
yields 18.01/17.87. Adding a 30-character string instead of the empty
string yields 5.61/5.58 and 17.28/17.28(!).
This patch causes the git binary emitted by gcc 5.4.0 -O2 on my machine
to grow from 11389848 bytes to 11497184 bytes, an increase of 0.9%.
I also tried to piggy-back on the fact that we already check alloc,
which should already tell us whether we are using the slopbuf:
if (sb->alloc) {
if (len > sb->alloc - 1)
die("BUG: strbuf_setlen() beyond buffer");
sb->buf[len] = '\0';
} else {
if (len)
die("BUG: strbuf_setlen() beyond buffer");
assert(!strbuf_slopbuf[0]);
}
sb->len = len;
That didn't seem to be much slower (5.38, 18.02, 5.70, 17.32 seconds),
but it does introduce some minor code duplication. The resulting git
binary was 11510528 bytes large (another 0.1% increase).
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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