Subj : Re: Function pointers in shm shared memory ?
To   : comp.programming.threads
From : Kamal R. Prasad
Date : Sat May 07 2005 01:51 am

>So it is not possible to call my brigde functions
>from the clients ? Can you explain why ?

The function pointer which is in the shared memory segment has to point
to an address in your process address space. You cannot jump to the
text segment of another process -which is what you intend to do. The
process virtual address space is unqiue to every process and (*fn)()
would contain the virtual address of the other process. If you don't
have the mapping, you cannot possibly access the function text.

>  because my server process cannot exist in multiple
>instances, as in fact it is a process using OpenGl to
>draw things..

The shared library text segment will exist as one instance only. Every
process that is linked to it will have its own per-process data segment
containing the shared library data.
 If you want just one copy of the text segment, it is possible to do so
even for the server. by setting bits on the executable. Im not sure why
more than 1 data segment will have a bearing on OpenGL. Even if it did,
just hoist the data into a shared memory region -and you have what you
wanted. Locking is something you would have to live with -if there are
multiple threads of execution.

regards
-kamal

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