Re: [ECOS] cyg_thread_create()

[Bart Veer <bartv at redhat dot com>]

>>>>> "Fernando" == Fernando Herrera <fherrera@teisa.unican.es> writes:

    Fernando> Hi!
    Fernando>    I'd wanted to call cyg_thread_create() funcion passing to it
    Fernando> a function member (that is, a method) of a determined class
    Fernando> object, as the 2nd argument. For instance, something like this:

    Fernando> (class declaration)

    Fernando> class myclass {
    Fernando> public:
    Fernando>    int i;
    Fernando>    int func();
    Fernando> }

    Fernando> (object declaration)
    Fernando> myclass myobject;

    Fernando> (... and this is what I want to do:)
    Fernando> cyg_thread_create(..., myobject.func,...)

    Fernando> BUT I FOUND A COMPILING TIME ERROR, because it seems
    Fernando> that cyg_thread_create() necessarily asks a function
    Fernando> pointer, instead of a function member pointer.

    Fernando> I have tried also making and explicit conversion but it
    Fernando> doesn't functions, I'm not very sure, but it seems it's
    Fernando> not posible to convert a method pointer to a function
    Fernando> pointer, at least with the compiler I'm using (g++
    Fernando> 2.95.2).

    Fernando>   So it seems that all the process functionalities must
    Fernando> be defined as functions in eCos. Is this true or there
    Fernando> is another alternative? Can't be this solved somehow?

    Fernando> (I'm new in the forum, so I don't now if this is a
    Fernando> trivial question or is simply a C++ question, (sorry in
    Fernando> advance in that case)), anyway you can tell me about.

What you see is the expected behaviour.

An C++ normal member function is different from an ordinary function
or a static member function: there is an implicit "this" argument.
Hence for any part of the system such as the thread code to invoke a
member function it needs to know two values, the function pointer and
the "this" pointer. The function argument to cyg_thread_create()
can only hold the first of these. The compiler is warning you that
what you are attempting is impossible.

One way around this is to have a utility static member function and
pass the "this" pointer as the entry_data argument to
cyg_thread_create, something along the following lines (untested):

    class myclass {
        ...
        int member_func(void);
        static void call_member(cyg_addrword_t);
    }

   myclass myobject;

   void
   myclass::call_member(cyg_addrword_t objptr)
   {
       myclass* obj = static_cast<myclass*>(objptr);
       obj->member_func();
   }


   int
   main(int argc, char** argv)
   {
       cyg_thread_create( ..., &myclass::call_member, (cyg_addrword_t) &myobject, ...)
   }


The kernel cannot do anything like this for you automatically because
when it is compiled it has no knowledge of myclass or how to invoke
its member functions.

Bart