[PATCH] refs: exit early from the loop if it is not a main worktree

[PATCH] refs: exit early from the loop if it is not a main worktree

[AreaZR via GitGitGadget]

From: Seija Kijin <doremylover123@gmail.com>

The is_main_worktree function just checks for !wt->id,
but the compiler doesn't know this as it is in a different
file, so just exit out early.

Signed-off-by: Seija Kijin <doremylover123@gmail.com>
---
    refs: exit early from the loop if it is not a main worktree
    
    The is_main_worktree function just checks for !wt->id, but the compiler
    doesn't know this as it is in a different file, so just exit out early.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1848%2FAreaZR%2Fexit-early-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1848/AreaZR/exit-early-v1
Pull-Request: https://github.com/git/git/pull/1848

 refs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/refs.c b/refs.c
index 8b713692359..cce63a618d7 100644
--- a/refs.c
+++ b/refs.c
@@ -2791,6 +2791,7 @@ static int has_worktrees(void)
 		if (is_main_worktree(worktrees[i]))
 			continue;
 		ret = 1;
+		break;
 	}
 
 	free_worktrees(worktrees);

base-commit: 063bcebf0c917140ca0e705cbe0fdea127e90086
-- 
gitgitgadget

Re: [PATCH] refs: exit early from the loop if it is not a main worktree

[shejialuo]

On Wed, Dec 18, 2024 at 02:20:45AM +0000, AreaZR via GitGitGadget wrote:
> From: Seija Kijin <doremylover123@gmail.com>
> 
> The is_main_worktree function just checks for !wt->id,
> but the compiler doesn't know this as it is in a different
> file, so just exit out early.
> 

I think maybe we should exit out the loop early. However, the above
statement is confusing. As you have said, `is_main_worktree` checks
whether the `wt->id` is NULL. Why compiler doesn't know this? And why we
need to exit out the loop due to above reason?

> Signed-off-by: Seija Kijin <doremylover123@gmail.com>
> ---
>     refs: exit early from the loop if it is not a main worktree
>     
>     The is_main_worktree function just checks for !wt->id, but the compiler
>     doesn't know this as it is in a different file, so just exit out early.
> 
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1848%2FAreaZR%2Fexit-early-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1848/AreaZR/exit-early-v1
> Pull-Request: https://github.com/git/git/pull/1848
> 
>  refs.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/refs.c b/refs.c
> index 8b713692359..cce63a618d7 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -2791,6 +2791,7 @@ static int has_worktrees(void)
>  		if (is_main_worktree(worktrees[i]))
>  			continue;
>  		ret = 1;
> +		break;

So, when we find a linked worktree, we just return the value. From my
perspective, if we decide to optimize like this way, we could drop the
loop because the first element of the result of `get_worktrees` is the
main worktree. And we could just check whether the "worktrees[1]" is
NULL to do above.

However, I don't know whether it's a good idea to exit the loop early
in the first place. CC Patrick to help.

Thanks,
Jialuo

Re: [PATCH] refs: exit early from the loop if it is not a main worktree

[Eric Sunshine]

On Wed, Dec 18, 2024 at 8:30 AM shejialuo <shejialuo@gmail.com> wrote:
> On Wed, Dec 18, 2024 at 02:20:45AM +0000, AreaZR via GitGitGadget wrote:
> >               if (is_main_worktree(worktrees[i]))
> >                       continue;
> >               ret = 1;
> > +             break;
>
> So, when we find a linked worktree, we just return the value. From my
> perspective, if we decide to optimize like this way, we could drop the
> loop because the first element of the result of `get_worktrees` is the
> main worktree. And we could just check whether the "worktrees[1]" is
> NULL to do above.

You're correct. get_worktrees() guarantees that the main worktree (or
bare repository) is the first item in the list, so merely checking
whether `worktrees[1]` is non-NULL would be sufficient to answer
whether linked worktrees are present; no looping is required.

> However, I don't know whether it's a good idea to exit the loop early
> in the first place. CC Patrick to help.

If the loop is retained for some reason (though it really isn't
needed), then exiting early is indeed desirable. I suspect that the
missing `break` was just a silly oversight on Patrick's part.

Re: [PATCH] refs: exit early from the loop if it is not a main worktree

[Junio C Hamano]

Eric Sunshine <sunshine@sunshineco.com> writes:

> On Wed, Dec 18, 2024 at 8:30 AM shejialuo <shejialuo@gmail.com> wrote:
>> On Wed, Dec 18, 2024 at 02:20:45AM +0000, AreaZR via GitGitGadget wrote:
>> >               if (is_main_worktree(worktrees[i]))
>> >                       continue;
>> >               ret = 1;
>> > +             break;
>>
>> So, when we find a linked worktree, we just return the value. From my
>> perspective, if we decide to optimize like this way, we could drop the
>> loop because the first element of the result of `get_worktrees` is the
>> main worktree. And we could just check whether the "worktrees[1]" is
>> NULL to do above.
>
> You're correct. get_worktrees() guarantees that the main worktree (or
> bare repository) is the first item in the list, so merely checking
> whether `worktrees[1]` is non-NULL would be sufficient to answer
> whether linked worktrees are present; no looping is required.

Thanks for a well-reasoned write-up.

Would many other callers potentially want to know if the repository
has more than one worktree?  It looks to me that the has_worktrees()
helper function in refs.c is a sign that the worktree API is missing
a function.  Calling get_worktrees() to prepare a list of worktrees
and then counting the result, only to see if there are more than
one, sounds a bit wasteful if we need to do so too often.

Re: [PATCH] refs: exit early from the loop if it is not a main worktree

[Eric Sunshine]

On Wed, Dec 18, 2024 at 8:10 PM Junio C Hamano <gitster@pobox.com> wrote:
> Eric Sunshine <sunshine@sunshineco.com> writes:
> > On Wed, Dec 18, 2024 at 8:30 AM shejialuo <shejialuo@gmail.com> wrote:
> >> On Wed, Dec 18, 2024 at 02:20:45AM +0000, AreaZR via GitGitGadget wrote:
> >> >               if (is_main_worktree(worktrees[i]))
> >> >                       continue;
> >> >               ret = 1;
> >> > +             break;
> >>
> >> So, when we find a linked worktree, we just return the value. From my
> >> perspective, if we decide to optimize like this way, we could drop the
> >> loop because the first element of the result of `get_worktrees` is the
> >> main worktree. And we could just check whether the "worktrees[1]" is
> >> NULL to do above.
> >
> > You're correct. get_worktrees() guarantees that the main worktree (or
> > bare repository) is the first item in the list, so merely checking
> > whether `worktrees[1]` is non-NULL would be sufficient to answer
> > whether linked worktrees are present; no looping is required.
>
> Would many other callers potentially want to know if the repository
> has more than one worktree?  It looks to me that the has_worktrees()
> helper function in refs.c is a sign that the worktree API is missing
> a function.  Calling get_worktrees() to prepare a list of worktrees
> and then counting the result, only to see if there are more than
> one, sounds a bit wasteful if we need to do so too often.

If the need to answer this question does become common, then I can
imagine a function being added to the worktree API which tries to be
smart about it by only calling readdir() -- and validating a
.git/worktrees/<id>/ metainformation -- enough times to be able to
answer the question.

However, although I haven't audited the code, I suspect the question
"are there any linked worktrees" is rare, possibly only asked by
`refs.c`. And in that case, it is asked only at the start of a
refs-migration operation. Moreover, it appears that even that case of
asking the question is probably temporary, existing only until someone
extends the migration logic to work correctly in the presence of
worktrees. (I'm sure Patrick can shed more light on this, though.)

Re: [PATCH] refs: exit early from the loop if it is not a main worktree

[Junio C Hamano]

Eric Sunshine <sunshine@sunshineco.com> writes:

> However, although I haven't audited the code, I suspect the question
> "are there any linked worktrees" is rare, possibly only asked by
> `refs.c`. And in that case, it is asked only at the start of a
> refs-migration operation.

That matches my gut feeling.  Thanks.

Re: [PATCH] refs: exit early from the loop if it is not a main worktree

[Patrick Steinhardt]

On Thu, Dec 19, 2024 at 12:54:55AM -0500, Eric Sunshine wrote:
> On Wed, Dec 18, 2024 at 8:10 PM Junio C Hamano <gitster@pobox.com> wrote:
> > Eric Sunshine <sunshine@sunshineco.com> writes:
> > > On Wed, Dec 18, 2024 at 8:30 AM shejialuo <shejialuo@gmail.com> wrote:
> > >> On Wed, Dec 18, 2024 at 02:20:45AM +0000, AreaZR via GitGitGadget wrote:
> > >> >               if (is_main_worktree(worktrees[i]))
> > >> >                       continue;
> > >> >               ret = 1;
> > >> > +             break;
> > >>
> > >> So, when we find a linked worktree, we just return the value. From my
> > >> perspective, if we decide to optimize like this way, we could drop the
> > >> loop because the first element of the result of `get_worktrees` is the
> > >> main worktree. And we could just check whether the "worktrees[1]" is
> > >> NULL to do above.
> > >
> > > You're correct. get_worktrees() guarantees that the main worktree (or
> > > bare repository) is the first item in the list, so merely checking
> > > whether `worktrees[1]` is non-NULL would be sufficient to answer
> > > whether linked worktrees are present; no looping is required.
> >
> > Would many other callers potentially want to know if the repository
> > has more than one worktree?  It looks to me that the has_worktrees()
> > helper function in refs.c is a sign that the worktree API is missing
> > a function.  Calling get_worktrees() to prepare a list of worktrees
> > and then counting the result, only to see if there are more than
> > one, sounds a bit wasteful if we need to do so too often.
> 
> If the need to answer this question does become common, then I can
> imagine a function being added to the worktree API which tries to be
> smart about it by only calling readdir() -- and validating a
> .git/worktrees/<id>/ metainformation -- enough times to be able to
> answer the question.
> 
> However, although I haven't audited the code, I suspect the question
> "are there any linked worktrees" is rare, possibly only asked by
> `refs.c`. And in that case, it is asked only at the start of a
> refs-migration operation. Moreover, it appears that even that case of
> asking the question is probably temporary, existing only until someone
> extends the migration logic to work correctly in the presence of
> worktrees. (I'm sure Patrick can shed more light on this, though.)

Overall I have to say that I found the worktree APIs to be quite
lacking. It's surprising that you don't even have a way to load a single
worktree, for example.

In any case, for this specific case I'm not aware of any other users of
the functionality, so there is no immediate need to lift it up into the
worktree subsystem.

Patrick

Re: [PATCH] refs: exit early from the loop if it is not a main worktree

[Patrick Steinhardt]

On Wed, Dec 18, 2024 at 06:52:02PM -0500, Eric Sunshine wrote:
> On Wed, Dec 18, 2024 at 8:30 AM shejialuo <shejialuo@gmail.com> wrote:
> > On Wed, Dec 18, 2024 at 02:20:45AM +0000, AreaZR via GitGitGadget wrote:
> > >               if (is_main_worktree(worktrees[i]))
> > >                       continue;
> > >               ret = 1;
> > > +             break;
> >
> > So, when we find a linked worktree, we just return the value. From my
> > perspective, if we decide to optimize like this way, we could drop the
> > loop because the first element of the result of `get_worktrees` is the
> > main worktree. And we could just check whether the "worktrees[1]" is
> > NULL to do above.
> 
> You're correct. get_worktrees() guarantees that the main worktree (or
> bare repository) is the first item in the list, so merely checking
> whether `worktrees[1]` is non-NULL would be sufficient to answer
> whether linked worktrees are present; no looping is required.
> 
> > However, I don't know whether it's a good idea to exit the loop early
> > in the first place. CC Patrick to help.
> 
> If the loop is retained for some reason (though it really isn't
> needed), then exiting early is indeed desirable. I suspect that the
> missing `break` was just a silly oversight on Patrick's part.

Yes, indeed, breaking out of the loop feels sensible to me. Checking
whether `worktrees[1]` is non-NULL would be fine, as well.

Patrick