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| author | Patrick Steinhardt <ps@pks.im> | 2019-06-27 09:23:59 +0200 |
|---|---|---|
| committer | Patrick Steinhardt <ps@pks.im> | 2019-07-11 08:37:46 +0200 |
| commit | 2ba7020f62127dfbff7c94923a52fb8346e6c6b0 (patch) | |
| tree | 99cd243c6a2e52eaee559b27919716f1cbce1ef7 /src/diff.c | |
| parent | a0dc3027f118119d3336db08251c646291f2c098 (diff) | |
| download | libgit2-2ba7020f62127dfbff7c94923a52fb8346e6c6b0.tar.gz | |
config_file: avoid re-reading files on write
When we rewrite the configuration file due to any of its values
being modified, we call `config_refresh` to update the in-memory
representation of our config file backend. This is needlessly
wasteful though, as `config_refresh` will always open the on-disk
representation to reads the file contents while we already know
the complete file contents at this point in time as we have just
written it to disk.
Implement a new function `config_refresh_from_buffer` that will
refresh the backend's config entries from a buffer instead of
from the config file itself. Note that this will thus _not_
update the backend's timestamp, which will cause us to re-read
the buffer when performing a read operation on it. But this is
still an improvement as we now lazily re-read the contents, and
most importantly we will avoid constantly re-reading the contents
if we perform multiple write operations.
The following strace demonstrates this if we're re-writing a key
multiple times. It uses our config example with `config_set`
changed to update the file 10 times with different keys:
$ strace lg2 config x.x z |& grep '^open.*config'
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/home/pks/.config/git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
And now with the optimization of `config_refresh_from_buffer`:
$ strace lg2 config x.x z |& grep '^open.*config'
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 3
open("/home/pks/.config/git/config", O_RDONLY|O_CLOEXEC) = 3
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
open("/tmp/repo/.git/config.lock", O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 3
open("/tmp/repo/.git/config", O_RDONLY|O_CLOEXEC) = 4
As can be seen, this is quite a lot of `open` calls less.
Diffstat (limited to 'src/diff.c')
0 files changed, 0 insertions, 0 deletions