[Lazarus] RE : RE : RE : Dynamic loading of a custom sqlite library

[Ludo Brands]

You're right. My scenario doesn't cause a problem. All symbols are resolved
before lib2 is loaded and loading lib2 won't change the symbols alread
resolved. It would only affect new symbol lookups after lib2 is loaded and
when using dlopen(nil,...). 
 
Ludo 

-----Message d'origine-----
De : Max Vlasov [mailto:max.vlasov at gmail.com] 
Envoyé : dimanche 12 juin 2011 11:41
À : Lazarus mailing list
Objet : Re: [Lazarus] RE : RE : Dynamic loading of a custom sqlite library




2011/6/12 Ludo Brands <ludo.brands at free.fr>



 >  So what did you mean by saying 'dangerous'?   
 
You should have read a little further in the message: "Possibly everything
is fine for sqlite3 but documenting it as a general solution is IMHO not
correct.". The scenario I was talking about assumed an initialization
(before lib2 is loaded) and a finalization routine which would/could run in
different librarie. This is not the case in your example. 
I proposed to test if  the library was loaded before loading again as a more
general solution to the problem. 
Don't get me wrong. I'm happy this is working for you. I'm only saying it is
not a good idea to document/promote this as a general solution for avoiding
problems with double loaded libraries.





Ludo, ok, I just tried to see the level of the problem you described. I just
recently found this flag so I want to be sure it is working as I expect. 

You wrote in your previous post "At the end the unit that used
lib1 could execute some finalization routines. But this time they run in
lib2". I don't see why a function (let's call it somelibrary_somefinalize())
linked with external directive and used somewhere in the sources should be
called from the lib2 this time (if RTLD_DEEPBIND flag is used). For dynamic
loading there's always a variable and this new address was obtained with
dlsym call and this is the only place that aware of
lib2.somelibrary_somefinalize. I may be wrong, but this is how I understood
the logic behind it. 

I recently saw that I was wrong assuming that read-only code and data is
safe, because there are usually different versions of libraries so to ensure
imho any symbol should be bind separately. 

Max


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