Re: [RFC/PATCH 4/5] completion: get rid of compgen

From: Felipe Contreras <felipe.contreras@gmail.com>
Date: Nov 17, 2012, 19:33 UTC
Message-ID: <CAMP44s0YnoGwJEgUbXZ831_OrgO=dDf5_QHxT5JYnGUHYPuiTw@mail.gmail.com>
In-Reply-To: <20121117141215.GG12052@goldbirke>

On Sat, Nov 17, 2012 at 3:12 PM, SZEDER Gábor <szeder@ira.uka.de> wrote:

Show 59 quoted lines

> On Sat, Nov 17, 2012 at 12:42:38PM +0100, Felipe Contreras wrote:
>> On Sat, Nov 17, 2012 at 12:00 PM, SZEDER Gábor <szeder@ira.uka.de> wrote:
>> > On Sat, Nov 17, 2012 at 02:38:17AM +0100, Felipe Contreras wrote:
>> >> The functionality we use is very simple, plus, this fixes a known
>> >> breakage 'complete tree filename with metacharacters'.
>> >>
>> >> Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
>> >> ---
>> >>  contrib/completion/git-completion.bash | 6 +++++-
>> >>  1 file changed, 5 insertions(+), 1 deletion(-)
>> >>
>> >> diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
>> >> index 975ae13..ad3e1fe 100644
>> >> --- a/contrib/completion/git-completion.bash
>> >> +++ b/contrib/completion/git-completion.bash
>> >> @@ -227,7 +227,11 @@ fi
>> >>
>> >>  __gitcompadd ()
>> >>  {
>> >> -     COMPREPLY=($(compgen -W "$1" -P "$2" -S "$4" -- "$3"))
>> >> +     for x in $1; do
>> >> +             if [[ "$x" = "$3"* ]]; then
>> >> +                     COMPREPLY+=("$2$x$4")
>> >> +             fi
>> >> +     done
>> >
>> > The whole point of creating __gitcomp_nl() back then was to fill
>> > COMPREPLY without iterating through all words in the wordlist, making
>> > completion faster for large number of words, e.g. a lot of refs, or
>> > later a lot of symbols for 'git grep' in a larger project.
>> >
>> > The loop here kills that optimization.
>>
>> So your solution is to move the loop to awk? I fail to see how that
>> could bring more optimization, specially since it includes an extra
>> fork now.
>
> This patch didn't aim for more optimization, but it was definitely a
> goal not to waste what we gained by creating __gitcomp_nl() in
> a31e6262 (completion: optimize refs completion, 2011-10-15).  However,
> as it turns out the new version with awk is actually faster than
> current master with compgen:
>
>   Before:
>
>     $ refs="$(for i in {0..9999} ; do echo branch$i ; done)"
>     $ time __gitcomp_nl "$refs"
>
>     real    0m0.242s
>     user    0m0.220s
>     sys     0m0.028s
>
>   After:
>
>     $ time __gitcomp_nl "$refs"
>
>     real    0m0.109s
>     user    0m0.096s
>     sys     0m0.012s

This one is even faster:

while read -r x; do
	if [[ "$x" == "$3"* ]]; then
		COMPREPLY+=("$2$x$4")
	fi
done <<< $1

== 10000 == one: real 0m0.148s user 0m0.134s sys 0m0.025s two: real 0m0.055s user 0m0.054s sys 0m0.000s

-- 
Felipe Contreras