DSO Terms Galore

On Fri, Jul 19, 2024 at 03:27:49PM -0400, David E. Wheeler wrote:

I�m trying to understand the standard terms for extension libraries.
There seem too a bewildering number of terms used to refer to a shared
object library, for example:

[...]

What is the standard term for these things? Or perhaps, what *should* it
be? "Module"? "Library"? "Object"? "Shared ____"? "Dynamic ____"?

Would it be useful to decide on one term (perhaps with "file" appended
where it refers to a file that contains one of these things) and
standardize the docs?

The lack of consistent terminology seems at least potentially confusing for
readers. My first reaction is that "shared library" is probably fine.

--
nathan

On Jul 19, 2024, at 15:46, Nathan Bossart <nathandbossart@gmail.com> wrote:

The lack of consistent terminology seems at least potentially confusing for
readers. My first reaction is that "shared library" is probably fine.

That’s the direction I was leaning, as well, but I thought I heard somewhere that the project used the term “module” for this feature specifically. That would be a bit nicer for the new PGXN Meta Spec revision I’m working on[1]https://github.com/pgxn/rfcs/pull/3, where these three different types of things could be usefully separated:

* extensions: CREATE EXTENSION extensions
* modules: loadable modules for extensions, hooks, and workers (anything else?)
* apps: Programs and scripts like pg_top, pgAdmin, or pg_partman scripts[2]https://github.com/pgpartman/pg_partman/tree/master/bin/common

Here the term “libraries” would be a little over-generic, and “share_libraries” longer than I'd like (these are JSON object keys).

Best,

David

[1]: https://github.com/pgxn/rfcs/pull/3
[2]: https://github.com/pgpartman/pg_partman/tree/master/bin/common

On 19.07.24 21:27, David E. Wheeler wrote:

I’m trying to understand the standard terms for extension libraries. There seem too a bewildering number of terms used to refer to a shared object library, for example:

* LOAD[1]:
* “shared library”
* “shared library file”
* dynamic_library_path[2]:
* “dynamically loadable module”
* xfunc-c[3]:
* “dynamically loadable object”
* “shared library”
* “loadable object”
* “loadable object file”
* “object file”
* “dynamically loaded object file”
* pg_config[5]:
* “object code libraries” (static?)
* “dynamically loadable modules”
* PGXS[4]:
* “MODULES”
* “shared-library objects”
* “shared library”

I think in the POSIX-ish realm, the best term is "dynamically loadable
library". It's a library, because it contains functions you can, uh,
borrow, just like a static library. And it's dynamically loadable, as
opposed to being loaded in a fixed manner at startup time.

Also, the "dl" in dlopen() etc. presumably stands for dynamic-something
load-something.

Libtool uses the term "dlopened module" for this, and the command-line
option is -module.
(https://www.gnu.org/software/libtool/manual/libtool.html#Dlopened-modules)

Meson uses shared_module() for this. (It has shared_library() and
static_library() for things like libpq.)

Things like "object" or "object file" or probably wrong-ish. I
understand an object file to be a .o file, which you can't dlopen directly.

Shared library is semi-ok because on many platforms, link-time shared
libraries (like libpq) and dynamically loadable libraries (like plpgsql)
are the same file format. But on some they're not, so it leads to
confusion.

I think we can unify this around terms like "dynamically loadable
library" and "dynamically loadable module" (or "loaded" in cases where
it's talking about a file that has already been loaded).

On Jul 23, 2024, at 07:26, Peter Eisentraut <peter@eisentraut.org> wrote:

Things like "object" or "object file" or probably wrong-ish. I understand an object file to be a .o file, which you can't dlopen directly.

Agreed.

Another option, however, is “dynamically shared object” (DSO), which corresponds to the usual *nix extension, .so. I think I know the term most from Apache. It’s curious that I didn’t run across it while perusing the Postgres docs.

I think we can unify this around terms like "dynamically loadable library" and "dynamically loadable module" (or "loaded" in cases where it's talking about a file that has already been loaded).

+1 for “dynamically loadable module” and, in common usage, “module”, since I don’t think it would be confused for anything else. “dynamically loadable library” would either have to always be used in full --- because “library” can be static, too --- or to “DLL”, which has strong Windows associations.

Best,

David