Re: glist: _Generic wrapper for selective dlist/dclist usage

On Wed Sep 2, 2026 at 11:36 AM UTC, Matthias van de Meent wrote:
> Hi,
>
> I'd like to track the size of a dlist for data structure validation
> purposes[^0]. Normally, one would use a dclist, as this tracks a
> count of list elements contained therein, but because this code would
> not be called in most normal production builds using a dclist would
> waste precious memory.
> Manually tracking the length is possible, but tedious, and a local
> wrapper around the used dclist/dlist APIs (with different
> implementations conditioned with #ifdefs to use the right types) would
> also be a significant amount of effort, that'd be duplicated every
> time .
>
> Attached is a patch that adds glist_* macros, which wrap several
> dlist/dclist_* APIs, so that developers can use dlist/dclist
> selectively in different environments, without significant visual
> overhead in the code. I'm planning to use this in the Proxy memory
> contexts over at [1].
>
> I've considered also adding slist_* to the macros, but I've never
> needed selective slist vs dlist/dclist before, so I ignored that list
> type for now.
>
>
> Kind regards,
>
> Matthias van de Meent
> Databricks (https://www.databricks.com)
>
>
> [^0]: This case for builds with MEMORY_CONTEXT_CHECKING, but builds
> with USE_ASSERT_CHECKING or WRITE_READ_PARSE_PLAN_TREES -like options
> may also want this.
>
> [1]: https://www.postgresql.org/message-id/flat/CAEze2WiPyruOtUOSyRUV8mQssjmYwno0M6hkxC_iUpH-=W8WcA(at)mail(dot)gmail(dot)com

I can't speak much to the purpose, but the patch itself looks correct
given my understanding of _Generic. I also checked that the dlist/dclist
function names match up with the glist function names. Do you think it
makes sense to add a comment of how one might use glist? There is
a large comment at the top of ilist.h where it could make sense to add
one if you think it would be useful. Maybe dglist would be a better name
to keep it more scoped to doubly linked lists?

--
Tristan Partin
PostgreSQL Contributors Team
AWS (https://aws.amazon.com)