Thread: lwlocknames.h beautification attempt

Gurjeet Singh <gurjeet@singh.im> writes:
> I propose the following change to the generation script,
> generate-lwlocknames.pl
> ...
> which produces the lock names in this format

> #define ShmemIndexLock                 (&MainLWLockArray[1].lock)
> #define OidGenLock                     (&MainLWLockArray[2].lock)
> #define XidGenLock                     (&MainLWLockArray[3].lock)
> #define ProcArrayLock                  (&MainLWLockArray[4].lock)
> #define SInvalReadLock                 (&MainLWLockArray[5].lock)

This looks reasonably in line with project style ...

> Yet another format, which I prefer, can be achieved by right-aligning the
> lock names.

> #define                 ShmemIndexLock (&MainLWLockArray[1].lock)
> #define                     OidGenLock (&MainLWLockArray[2].lock)
> #define                     XidGenLock (&MainLWLockArray[3].lock)
> #define                  ProcArrayLock (&MainLWLockArray[4].lock)
> #define                 SInvalReadLock (&MainLWLockArray[5].lock)

... but that doesn't.  I challenge you to provide even one example
of that layout in our source tree, or to explain why it's better.

            regards, tom lane

On Sat, Mar 1, 2025 at 10:26 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Gurjeet Singh <gurjeet@singh.im> writes:
> > I propose the following change to the generation script,
> > generate-lwlocknames.pl
> > ...
> > which produces the lock names in this format
>
> > #define ShmemIndexLock                 (&MainLWLockArray[1].lock)
> > #define OidGenLock                     (&MainLWLockArray[2].lock)
> > #define XidGenLock                     (&MainLWLockArray[3].lock)
> > #define ProcArrayLock                  (&MainLWLockArray[4].lock)
> > #define SInvalReadLock                 (&MainLWLockArray[5].lock)
>
> This looks reasonably in line with project style ...

Should I create a commitfest entry for this patch, or is it
uncontroversial enough and small enough to not warrant that?

> > Yet another format, which I prefer, can be achieved by right-aligning the
> > lock names.
>
> > #define                 ShmemIndexLock (&MainLWLockArray[1].lock)
> > #define                     OidGenLock (&MainLWLockArray[2].lock)
> > #define                     XidGenLock (&MainLWLockArray[3].lock)
> > #define                  ProcArrayLock (&MainLWLockArray[4].lock)
> > #define                 SInvalReadLock (&MainLWLockArray[5].lock)
>
> ... but that doesn't.  I challenge you to provide even one example
> of that layout in our source tree, or to explain why it's better.

I haven't seen this style in any other project, let alone in Postgres. I
just mentioned it since I personally liked it slightly better after
trying a couple of different styles, because of the aligned suffix in
the lock names.



Best regards,
Gurjeet
http://Gurje.et

Gurjeet Singh <gurjeet@singh.im> writes:
> On Sat, Mar 1, 2025 at 10:26 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> This looks reasonably in line with project style ...

> Should I create a commitfest entry for this patch, or is it
> uncontroversial enough and small enough to not warrant that?

The controversy would be more about whether it's worth bothering
with.  In the past we've taken some care to ensure that generated
files would pass pgindent's ideas of correct formatting, but
not more than that.  AFAICT from some quick tests, pgindent has
no opinions about layout of #define lines.

            regards, tom lane

On Sun, Mar 2, 2025 at 1:10 AM Gurjeet Singh <gurjeet@singh.im> wrote:
> I propose the following change to the generation script, generate-lwlocknames.pl
>
> -    print $h "#define ${lockname}Lock (&MainLWLockArray[$lockidx].lock)\n";
> +    printf $h "#define %-30s %s\n", "${lockname}Lock", "(&MainLWLockArray[$lockidx].lock)";

-1. That seems worse to me.

--
Robert Haas
EDB: http://www.enterprisedb.com

On 2025-Mar-01, Gurjeet Singh wrote:

> I propose the following change to the generation script,
> generate-lwlocknames.pl
> 
> -    print $h "#define ${lockname}Lock (&MainLWLockArray[$lockidx].lock)\n";
> +    printf $h "#define %-30s %s\n", "${lockname}Lock", "(&MainLWLockArray[$lockidx].lock)";
> 
> which produces the lock names in this format
> 
> #define ShmemIndexLock                 (&MainLWLockArray[1].lock)
> #define OidGenLock                     (&MainLWLockArray[2].lock)

This format seems more than acceptable.  It'd be nice to avoid printf
for such a small thing; but at least we can use the %-specifiers only
where necessary, so I'd do this instead:

diff --git a/src/backend/storage/lmgr/generate-lwlocknames.pl b/src/backend/storage/lmgr/generate-lwlocknames.pl
index 084da2ea6e0..2927f144905 100644
--- a/src/backend/storage/lmgr/generate-lwlocknames.pl
+++ b/src/backend/storage/lmgr/generate-lwlocknames.pl
@@ -108,7 +108,8 @@ while (<$lwlocklist>)
     $continue = ",\n";
 
     # Add a "Lock" suffix to each lock name, as the C code depends on that
-    print $h "#define ${lockname}Lock (&MainLWLockArray[$lockidx].lock)\n";
+    printf $h "#define %-32s (&MainLWLockArray[$lockidx].lock)\n",
+      "${lockname}Lock";
 }
 
 die


-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/

On 2025-Mar-01, Gurjeet Singh wrote:

> I propose the following change to the generation script,
> generate-lwlocknames.pl
> 
> -    print $h "#define ${lockname}Lock (&MainLWLockArray[$lockidx].lock)\n";
> +    printf $h "#define %-30s %s\n", "${lockname}Lock",
> "(&MainLWLockArray[$lockidx].lock)";

I forgot to send a note here that I pushed this patch.  Thank you.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
[…] indem ich in meinem Leben oft an euch gedacht, euch glücklich zu machen. Seyd es!
A menudo he pensado en vosotros, en haceros felices. ¡Sedlo, pues!
        Heiligenstädter Testament, L. v. Beethoven, 1802
        https://de.wikisource.org/wiki/Heiligenstädter_Testament

On Fri, Mar 14, 2025 at 3:38 PM Álvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> I forgot to send a note here that I pushed this patch.  Thank you.

I'm confused. Tom and I both said we didn't like this change, so you
committed the patch without further discussion?

I mean, this is a pretty unimportant detail, so I don't really want to
fight about it too much, but that really doesn't seem like a consensus
to me.

--
Robert Haas
EDB: http://www.enterprisedb.com

On 2025-Mar-16, Robert Haas wrote:

> On Fri, Mar 14, 2025 at 3:38 PM Álvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> > I forgot to send a note here that I pushed this patch.  Thank you.
> 
> I'm confused. Tom and I both said we didn't like this change, so you
> committed the patch without further discussion?

Tom didn't say he didn't like this change.  He said he didn't like a
different change, which is not the one I committed.  And your opinion
was quite thin on arguments, and you didn't reply for 11 days after I
expressed intention to apply a simplified version of Gurjeet's patch.

> I mean, this is a pretty unimportant detail, so I don't really want to
> fight about it too much, but that really doesn't seem like a consensus
> to me.

Would you have objected if I had proposed to use that style to begin with?
You can see that the thread where this was discussed [1] was pretty
light on coding style/output style discussion.  It seems hard to argue
that the original had achieved any kind of consensus.

[1] https://postgr.es/m/202401231025.gbv4nnte5fmm@alvherre.pgsql

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/

(resending the email because it was held for moderation; replaced image
attachment with a link, which might be the reason for being put in the
moderation queue)

On Sun, Mar 16, 2025 at 7:53 PM Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Fri, Mar 14, 2025 at 3:38 PM Álvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> > I forgot to send a note here that I pushed this patch. Thank you.
>
> I'm confused. Tom and I both said we didn't like this change,

To me, Tom's feedback felt as being between ambivalent to the change and perhaps
agree with the change, as long as pgindent did not throw a fit, which
it did not.
It definitely did not feel like a -1.

On Mon, Mar 3, 2025 at 8:40 AM Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Sun, Mar 2, 2025 at 1:10 AM Gurjeet Singh <gurjeet@singh.im> wrote:
> > I propose the following change to the generation script, generate-lwlocknames.pl
> >
> > - print $h "#define ${lockname}Lock (&MainLWLockArray[$lockidx].lock)\n";
> > + printf $h "#define %-30s %s\n", "${lockname}Lock", "(&MainLWLockArray[$lockidx].lock)";
>
> -1. That seems worse to me.

I read your objection to be about the perl code change, whereas the real change
the patch was seeking is in the generated output (lwlocknames.h). I'm guessing
some others may also have taken your feedback to mean the same as I did.

Alvaro committed the following patch, which is better code than mine. If your
objection was about the perl code, perhaps this addresses your concern.

- print $h "#define ${lockname}Lock (&MainLWLockArray[$lockidx].lock)\n";
+ printf $h "#define %-32s (&MainLWLockArray[$lockidx].lock)\n",
+ $lockname . "Lock";

I have ~attached~ linked a comparison of before and after screenshots of the
generated output. It's hard to argue that the generated code in the left/before
image is better than the right/after image.

https://photos.app.goo.gl/hNL3FaUMuEwnaYTt9

Best regards,
Gurjeet
http://Gurje.et

Gurjeet Singh <gurjeet@singh.im> writes:
> On Sun, Mar 16, 2025 at 7:53 PM Robert Haas <robertmhaas@gmail.com> wrote:
>> I'm confused. Tom and I both said we didn't like this change,

> To me, Tom's feedback felt as being between ambivalent to the change and perhaps
> agree with the change, as long as pgindent did not throw a fit, which
> it did not.

Geez, are we really going to argue about whitespace in a generated
file?  But anyway, what I said was that I didn't like the style with
the define'd symbol right-justified, because it didn't look like
anything else in our code.  I'm entirely okay with the committed
version, which has plenty of precedent formatting-wise.

            regards, tom lane

On 2025-Mar-16, Gurjeet Singh wrote:

> (resending the email because it was held for moderation; replaced image
> attachment with a link, which might be the reason for being put in the
> moderation queue)

Kindly don't do this (specifically: cancel the original message and send
a different copy).  Just have patience with the moderation queue.
Messages are typically approved within a day anyway.

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/

On Mon, Mar 17, 2025 at 2:43 AM Álvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> Tom didn't say he didn't like this change.  He said he didn't like a
> different change, which is not the one I committed.

Sorry, I should have read the emails more carefully. I missed the fact
that there were two different proposals. It was the idea of
right-aligning things that I was unhappy about.

So, no objection to what you actually committed... except that I don't
think that using % specifiers in SOME places in a format string is
better than using them in ALL the places. It's not broken because
$lockidx can't contain a % sign, but in general I think when we switch
from print to printf it's better for us to have the format string be a
constant so that it's clear that we can't accidentally get an extra %
escape in there depending on the values of variables being
interpolated.

--
Robert Haas
EDB: http://www.enterprisedb.com

On 2025-Mar-17, Robert Haas wrote:

> On Mon, Mar 17, 2025 at 2:43 AM Álvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> > Tom didn't say he didn't like this change.  He said he didn't like a
> > different change, which is not the one I committed.
> 
> Sorry, I should have read the emails more carefully. I missed the fact
> that there were two different proposals. It was the idea of
> right-aligning things that I was unhappy about.

Ah, okay.

> So, no objection to what you actually committed... except that I don't
> think that using % specifiers in SOME places in a format string is
> better than using them in ALL the places. It's not broken because
> $lockidx can't contain a % sign, but in general I think when we switch
> from print to printf it's better for us to have the format string be a
> constant so that it's clear that we can't accidentally get an extra %
> escape in there depending on the values of variables being
> interpolated.

I suppose this is a reasonable complaint; however, I don't see an actual
problem here.  Even if I hack the regexp in generate-lwlocknames.pl to
accept a %-sign in the lock name (and introduce a matching % in
wait_event_names.txt), then that % is emitted verbatim rather than
attempted to further expand.  Is this because this is Perl rather than
C?  I'm not sure.

Note that a % in the lock number (which also needs a regexp hack) can't
cause a problem either, because of the check that the lock numbers are
an ordered sequence.

I think it's quite difficult to cause actual problems here.

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/