Information on use of Netsys.shm_open

Hi
I'm trying this little piece of code to open a shared memory and modify it.
The code looks like this :

open Unix
open Bigarray.Array1

let _ =

    Printf.printf("Test shared memory\n");

    if (Netsys.have_posix_shm () = false) then

        Printf.printf "No POSIX SHM\n"
    else
        (

            Printf.printf "POSIX SHM OK\n";

            let shm_name = "/shm_test" in

            let right_list = ref [] in

            right_list := Netsys.SHM_O_CREAT :: !right_list;
            right_list := Netsys.SHM_O_RDWR :: !right_list;

            ignore(
                    try
                        (
                            Printf.printf "Netsys.shm_open call\n";

                            let sd = Netsys.shm_open shm_name !right_list 1
in

                            Printf.printf "Netsys.shm_open ok\n";

                            let my_big_array = Bigarray.Array1.map_file sd
Bigarray.char Bigarray.c_layout true 100 in

                            let big_array_size = Bigarray.Array1.dim
my_big_array in

                            Printf.printf "Size of BigArray: %d\n"
big_array_size;

                            Bigarray.Array1.set my_big_array 0 'a';
                        )
                    with
                    | Unix_error (_ , invoked_function , shm_name_failure)
->
                            (
                                Printf.printf
                                    "Opening failed through using function
%s on SHM %s\n"
                                    invoked_function
                                    shm_name_failure
                                ;
                            )
                );

            Printf.printf "Shared memory tested\n";
        )

I can create the shared memory file descriptor, but only once.
When I try to access it again (y rzlaunching my program, there is an error
on shm_open.

I have to guess about a cause to this problem: first, I did not set the
right in the right manner and second, I do not use unlink.
The doc about the permissions is very light in this page (
http://projects.camlcity.org/projects/dl/ocamlnet-2.2.9/doc/html-main/Netsys.html).
I tried with with 0, 1, 777 and none of these are working.
For the unlink function, my understanding is that it destroys the file. But
maybe, it has the same behviour as "close" in C for a file descriptor.

Thanks in advance for your time.

Johan Mazel

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