omp_set_num_threads broken when compiling with iface:cvf

[Mick_Pont]

The omp_set_num_threads() function seems not to have an iface:cvf variant available.
I'm using this compiler:
Intel Visual Fortran Compiler XE for applications running on IA-32, Version 12.1.0.233 Build 20110811
on a 32-bit Windows system.

Take this program proga.f90:

Program main
Integer, External :: omp_get_max_threads
External :: omp_set_num_threads
Integer maxthd
maxthd = 2
Write(*,*) 'maxthd = ', maxthd
Call omp_set_num_threads(maxthd)
Write(*,*) 'omp_get_max_threads() returns ', omp_get_max_threads()
End Program main

and compile it like this:

ifort /Qopenmp proga.f90

Running it you get the expected results:
proga.exe
maxthd = 2
omp_get_max_threads() returns 2

But if you switch on /iface:cvf this happens:

ifort /Qopenmp /iface:cvf proga.f90
proga.exe
maxthd = 2
omp_get_max_threads() returns 32768

In a real OpenMP program that leads to a major resource problem.

I suspect that there is no CVF variant of omp_set_num_threads, and the __cdecl variant always gets linked in instead. If I modify my program to introduce an explicit interface for omp_set_num_threads(), telling the compiler that omp_set_num_threads is in fact __cdecl like this:

Module CPROC
Interface
Subroutine omp_set_num_threads(n)
!DEC$ ATTRIBUTES C :: omp_set_num_threads
End Subroutine omp_set_num_threads
End Interface
End Module CPROC
Program main
Use cproc
Integer, External :: omp_get_max_threads
! external omp_set_num_threads
Integer maxthd
maxthd = 2
Write(*,*) 'maxthd = ', maxthd
call omp_set_num_threads(maxthd)
Write(*,*) 'omp_get_max_threads() returns ', omp_get_max_threads()
End Program main

then everything works fine.

Mick Pont

[Steven_L_Intel1]

Yes, we've had that reported before. The OpenMP library people tell me that the STDCALL routines in the library are not supported and that they will be removed. Include omp_lib.f90 to get the correct declarations.