Dynamic module building and reloading

Dynamic module building and reloading

[Nicolas Martyanoff]

Hi,

I was playing a bit with dynamic modules and found two issues.

1. There does not seem to be any builtin utilities to deal with
the process of building and loading shared library. I ended up writing a
couple elisp functions to find the location of the C file, spawn cc,
load the shared library… Is this the expected method? In this state, it
would seem that every Emacs packages using dynamic modules has to write
its own build/load code.

2. It seems that once a dynamic module has been loaded, it cannot be
reloaded after the shared library has been rebuilt. A Google search
seems to confirm it. Is there a workaround? If I pursue my little
project, I'll have to write quite a lot of C code in the dynamic module;
I *really* do not want to restart Emacs to test every single
modification.

Hopefully I'm not the only one with these issues!

Regards,

-- 
Nicolas Martyanoff
https://n16f.net
nicolas@n16f.net

Re: Dynamic module building and reloading

[Eli Zaretskii]

> From: Nicolas Martyanoff <nicolas@n16f.net>
> Date: Tue, 13 Jun 2023 18:11:47 +0200
> 
> 1. There does not seem to be any builtin utilities to deal with
> the process of building and loading shared library. I ended up writing a
> couple elisp functions to find the location of the C file, spawn cc,
> load the shared library… Is this the expected method? In this state, it
> would seem that every Emacs packages using dynamic modules has to write
> its own build/load code.

The expected method of building a shared library is the same as you'd
use for building any other shared library out there.  The Emacs
modules aren't special in any way, and the details of their build
procedures depend on what code you are compiling in, which other
libraries you need to link against, etc.  There's no way an Emacs
command could cover all that.  However, if you write a Makefile to
compile and link the module, you can use "M-x compile" to run the Make
utility to build your module.

> 2. It seems that once a dynamic module has been loaded, it cannot be
> reloaded after the shared library has been rebuilt. A Google search
> seems to confirm it. Is there a workaround? If I pursue my little
> project, I'll have to write quite a lot of C code in the dynamic module;
> I *really* do not want to restart Emacs to test every single
> modification.

We don't have a facility to unload a module, no.  The usual way of
testing your development code is to start a new scratch session (in
addition to your production Emacs session) each time you recompile a
module.

Re: Dynamic module building and reloading

[Nicolas Martyanoff]

Got it, thank you for responding this quickly. 

Are there technical limitations against reloading or is this just a case of “if you need it send a patch”? I know that some platforms may have issues with it; but I use foreign library reloading in Common Lisp on Linux all the time, and it also works en BSD.

Nicolas Martyanoff
https://www.n16f.net
nicolas@n16f.net

> On 13 Jun 2023, at 18:55, Eli Zaretskii <eliz@gnu.org> wrote:
> 
> 
>> 
>> From: Nicolas Martyanoff <nicolas@n16f.net>
>> Date: Tue, 13 Jun 2023 18:11:47 +0200
>> 
>> 1. There does not seem to be any builtin utilities to deal with
>> the process of building and loading shared library. I ended up writing a
>> couple elisp functions to find the location of the C file, spawn cc,
>> load the shared library… Is this the expected method? In this state, it
>> would seem that every Emacs packages using dynamic modules has to write
>> its own build/load code.
> 
> The expected method of building a shared library is the same as you'd
> use for building any other shared library out there.  The Emacs
> modules aren't special in any way, and the details of their build
> procedures depend on what code you are compiling in, which other
> libraries you need to link against, etc.  There's no way an Emacs
> command could cover all that.  However, if you write a Makefile to
> compile and link the module, you can use "M-x compile" to run the Make
> utility to build your module.
> 
>> 2. It seems that once a dynamic module has been loaded, it cannot be
>> reloaded after the shared library has been rebuilt. A Google search
>> seems to confirm it. Is there a workaround? If I pursue my little
>> project, I'll have to write quite a lot of C code in the dynamic module;
>> I *really* do not want to restart Emacs to test every single
>> modification.
> 
> We don't have a facility to unload a module, no.  The usual way of
> testing your development code is to start a new scratch session (in
> addition to your production Emacs session) each time you recompile a
> module.

Re: Dynamic module building and reloading

[chad]

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This sounded familiar, so I poked around and found this:


https://emacs.stackexchange.com/questions/33976/how-do-you-reload-a-dynamic-module

which suggests a workaround similar to what I vaguely remembered (fake it
with numbered "module names" during development), with a little bit of
automation glue. It's not something that would work as a supported
user-level feature, but could be helpful for rapid iteration cycles.

Hope that helps,
~Chad

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Re: Dynamic module building and reloading

[Eli Zaretskii]

> From: Nicolas Martyanoff <nicolas@n16f.net>
> Date: Tue, 13 Jun 2023 19:10:25 +0200
> Cc: emacs-devel@gnu.org
> 
> Are there technical limitations against reloading or is this just a case of “if you need it send a patch”? I know that some platforms may have issues with it; but I use foreign library reloading in Common Lisp on Linux all the time, and it also works en BSD.

There are technical issues, AFAIK, yes.  Even unloading a Lisp feature
doesn't work 100% in Emacs, and a module is more complicated than
that.