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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Passing Ada Proc as a C Function Pointer
Newsgroups: comp.lang.ada
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Date: Wed, 4 Aug 2010 19:14:25 +0200
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Date: 2010-08-04T19:14:21+02:00
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On Wed, 4 Aug 2010 09:40:29 -0700 (PDT), Warren wrote:

> I some types defined as:
> 
>   type Thread_Context is private;

pragma Convention (C, Thread_Context);

>   type Stack_Area is new String;

pragma Convention (C, Stack_Area);  -- Won't work with String

>   type Thread_Proc is access procedure;

pragma Convention (C, Thread_Proc);  -- Called from C
 
> and an Ada API function:
> 
>     procedure Thread_Start(Context : out Thread_Context;

Context : access Thread_Context;
    -- Prevent temp object, if the type is not limited

> Proc : Thread_Proc;
> Stack : out Stack_Area) is

Stack : access Stack_Area

>         procedure avr_thread_start(Context : System.Address;
>                     Proc : C_Func_Ptr;

Proc : Thread_Proc;

>                     Stack : System.Address;
>                     Size : Unsigned_16);
>         pragma import(C,avr_thread_start,"avr_thread_start");
> 
>         Func : C_Func_Ptr := Proc.all'Access;
>     begin
> 
> avr_thread_start(Context'Address,Func,Stack(Stack'First)'Address,Stack'Length);
> 
>     end Thread_Start;
> 
> Because this part of the Ada code is not working, I'm suspicious that
> the passed function pointer is incorrect (I have an all-C thread
> example working).

You have to pass a pointer to a procedure of C convention. You also must
ensure that other parameters aren't passed by copy.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de