Re: validity of foreign functions across saved image s

Kevin Rosenberg wrote:

>AllegroCL dumplisp.htm documentation file:
>17.0 How the dumped image finds loaded library files
>
>Foreign loading is done on Unix by `loading' .so or .sl files with
>dlopen() or an equivalent and on Windows by loading .dll files. Dumped
>images must find these files when it starts up.

Interesting. This is what the CLISP-FFI has been doing for the Amiga for years (Bruno Haible implemented it this way), but I didn't like the "on startup" feature. The reason is that some shared libraries may not be available on startup and require user interaction, e.g. the Amiga bsdsocket.library: the user has first to start the TCP/IP stack. Similarly, I believe one must start winsock on MS-Windows: it need not be there right from the start: opening would fail before that.

What happens if Allegro cannot find that library? CLISP's FFI on Amiga would error out, which is IMHO not acceptable.


>"Unloading all .so files and reloading them upon startup. In this
>example, we unload the (in our case single) .so file with
>ff:unload-foreign-library and show how to modify
>*restart-init-function* so the .so file is reloaded."

And ff:load-foreign-library makes all old function pointers valid again?
Are they scanning the shared object for names?
Or do they remember all functions from this library and revalidate, e.g. maintain a table of functions objects and dlsym() each in turn, after reopening the library?
I can't believe so, since a symbol found via dlsym() need not necessarily be in the library opened via dlopen() - depending on flags.
E.g., I believe Allegro UFFI users don't supply :module most of the time: I suspect Allegro to look for the symbol in any currently opened library.


>Sure. I know that you were working on dynamic loading of shared
>libraries during a single session. Have you finished tha, and now you
>are working on doing this across saved images?
It's not finished nor released. I guess I'm too much of a "better is worse" guy. I want to have some idea about how to do FF across images before I throw in something which could not cope. I've yet to live more with increments.

Regards,
	Jorg Hohle.