Re: embedding G-I into apps

[Johan Dahlin <johan gnome org>]

Colin Walters wrote:
> (Using this list for gobject-introspection development for now,
> probably ignore if you're not jdahlin =))
>
> I was looking a bit today about applying our shiny new introspection
> tool to Totem, with an eye to eliminating the manual binding
> infrastructure, and more generally figure out how existing C
> applications can use g-i (and something like Alex' GScript API) to
> have a nicer way to embed Python or Spidermonkey.

As far as I can see it there are two options:
A) dlopen the executable (not portable)
B) create a temporary shared library
C) execute the scanner inside the application (as you suggested)

Discarding A, as we want to be portable. I've always thought about using
a temporary shared library to solve this particular problem, but the one you 
suggested appears to be better in many ways.

> Now, the scanner requires, at build time, to load the app's code so we
> can call the foo_get_type() functions and introspect
> properties/signals etc.  This is problematic because on some platforms
> you can't just dlopen() an executable.  Owen and I had a discussion
> about this and it sounds like basically what we need to do is actually
> invoke the scanner from inside the application.  So here's how it
> could work:

get_type() functions obviously needs to be available to the whole application.

> o Add a hidden --introspect option to application
> o When given, dlopen("gobject-introspection-sanner.so")
> o dlsym("g_introspection_scan")
> o Pass our current argv to that function
> o This function (in a separate shared library from
> gobject-introspection.so), uses the cPython API to create an
> interpreter and load /usr/bin/g-ir-scanner
> o Locate the main() function inside the Python script g-ir-scanner,
> and invoke it with the argv originally passed
>
> Kind of gross admittedly, but apps should only need a small patch for
> this approach and it seems most likely to work on random platforms.
> If someone knows a better/nicer way, let me know!

I would rather do it the other way around, by creating C bindings
for the scanner, so you could do:

scanner = gi_scanner_new ()
gi_scanner_set_namespace (scanner, "totem");
gi_scanner_add_sources (scanner, "totem-menu.h", "totem-video-widget.h");
etc.

That would make it sufficient to just g_module_open(NULL);

To do that we'd need two tools:
1) one to generate A GIR for a python interface
2) another to create C bindings for a python method.

I have the beginning of a tool which does 2, which shouldn't be too hard to 
fix up to make it possible just to generate this small piece of clue.

Johan