How can I use dlmopen in Fortran? - fortran

Question

I want to load the same .so file twice as separate instances. Based on the example, I have created the app with two dlopen commands.
However, I was facing some issues and I understood that dlmopen should be used if I am using multiple instances of a same .so. However, I don't know how to pass the arguments. Can someone help me how to do this in GFortran?
My code is as below,
program example
use :: iso_c_binding
implicit none
integer(c_int), parameter :: rtld_lazy=1 ! value extracte from the C header file
integer(c_int), parameter :: rtld_now=2 ! value extracte from the C header file
!
! interface to linux API
interface
function dlopen(filename,mode) bind(c,name="dlopen")
! void *dlopen(const char *filename, int mode);
use iso_c_binding
implicit none
type(c_ptr) :: dlopen
character(c_char), intent(in) :: filename(*)
integer(c_int), value :: mode
end function
function dlsym(handle,name) bind(c,name="dlsym")
! void *dlsym(void *handle, const char *name);
use iso_c_binding
implicit none
type(c_funptr) :: dlsym
type(c_ptr), value :: handle
character(c_char), intent(in) :: name(*)
end function
function dlclose(handle) bind(c,name="dlclose")
! int dlclose(void *handle);
use iso_c_binding
implicit none
integer(c_int) :: dlclose
type(c_ptr), value :: handle
end function
end interface
! Define interface of call-back routine.
abstract interface
subroutine called_proc (i, i2) bind(c)
use, intrinsic :: iso_c_binding
integer(c_int), intent(in) :: i
integer(c_int), intent(out) :: i2
end subroutine called_proc
end interface
! testing the dynamic loading
integer i, i2
type(c_funptr) :: proc_addr
type(c_ptr) :: handle1, handle2
character(256) :: pName, lName
procedure(called_proc), bind(c), pointer :: proc
!
i = 15
handle1=dlopen("./test.so"//c_null_char, RTLD_LAZY)
if (.not. c_associated(handle1))then
print*, 'Unable to load DLL ./test.so - First time'
stop
end if
handle2=dlopen("./test.so"//c_null_char, RTLD_LAZY)
if (.not. c_associated(handle2))then
print*, 'Unable to load DLL ./test.so - Second time'
stop
end if
! If I can use dlmopen() I dont know how to pass the arguments
proc_addr=dlsym(handle, "t_times2"//c_null_char)
if (.not. c_associated(proc_addr))then
write(*,*) 'Unable to load the procedure t_times2'
stop
end if
call c_f_procpointer( proc_addr, proc )
call proc(i,i2)
write(*,*) "t_times2, i2=", i2
!
proc_addr=dlsym( handle, "t_square"//c_null_char )
if ( .not. c_associated(proc_addr) )then
write(*,*)'Unable to load the procedure t_square'
stop
end if
call c_f_procpointer(proc_addr, proc)
call proc(i,i2)
write(*,*) "t_square, i2=", i2
contains
end program example
Update:
Based on the suggestion from Vladmir, I tried below but I get Unable to load DLL ./test.so - Third time,
function dlmopen(lmid_t,filename,mode) bind(c,name="dlmopen")
! void *dlopen(const char *filename, int mode);
use iso_c_binding
implicit none
type(c_ptr) :: dlopen
integer(c_long), value :: lmid_t
character(c_char), intent(in) :: filename(*)
integer(c_int), value :: mode
end function
handle3=dlmopen(1,"./test.so"//c_null_char, RTLD_LAZY)
if (.not. c_associated(handle3))then
print*, 'Unable to load DLL ./test.so - Third time'
stop
end if

Answer 1

This is the base that you can start from, it is a modification of your code and because of the #define macros it requires the cpp flags. You can change the defines to a normal parameter declaration if you want, but just copying the macros from the header is easier.
use iso_c_binding
implicit none
! from dlfcn.h
# define LM_ID_BASE 0 /* Initial namespace. */
# define LM_ID_NEWLM -1 /* For dlmopen: request new namespace. */
integer(c_long) :: dlist = LM_ID_NEWLM
integer(c_int), parameter :: rtld_lazy=1 ! value extracte from the C header file
integer(c_int), parameter :: rtld_now=2 ! value extracte from the C header file
type(c_ptr) :: handle3
interface
function dlmopen(lmid_t,filename,mode) bind(c,name="dlmopen")
! void *dlmopen (Lmid_t lmid, const char *filename, int flags);
use iso_c_binding
implicit none
type(c_ptr) :: dlmopen
integer(c_long), value :: lmid_t
character(c_char), intent(in) :: filename(*)
integer(c_int), value :: mode
end function
end interface
handle3=dlmopen(dlist,"test.so"//c_null_char, RTLD_LAZY)
if (.not. c_associated(handle3))then
print*, 'Unable to load DLL ./test.so - Third time'
stop
end if
end
According to the manual, there are two principal values that you can pass as dlist, either LM_ID_BASE or LM_ID_NEWLM. Their values are defined in the header dlfcn.h that is located ammong other standard C and POSIX headers (/usr/include/ or similar). You should not just pass 1, but one of these two values which happen to be 0 and -1 on my computer.