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My knowledge about OpenMP is nothing but superficial. Yet I decided to recap old concepts I've learned in the past and to do so I downloaded some material with theory and examples. One of the 1st of those (Fortran-95) examples is:
Program TestOMP1

Use OMP_LIB

!$OMP PARALLEL
Write(*,*) "Hi from thread: ", OMP_GET_THREAD_NUM()
!$OMP END PARALLEL

End Program TestOMP1


Program TestOMP1

Use OMP_LIB

!$OMP PARALLEL
Write(*,*) "Hi from thread: ", OMP_GET_THREAD_NUM()
!$OMP END PARALLEL

End Program TestOMP1


I think this is the simplest program possible. It works as expected, producing the following output corresponding to my machine's eight threads:
Hi from thread: 2
Hi from thread: 4
Hi from thread: 0
Hi from thread: 6
Hi from thread: 3
Hi from thread: 1
Hi from thread: 7
Hi from thread: 5

Hi from thread: 2
Hi from thread: 4
Hi from thread: 0
Hi from thread: 6
Hi from thread: 3
Hi from thread: 1
Hi from thread: 7
Hi from thread: 5

But when I try to set a smaller number of threads, say four (4), with !$Call OMP_SET_NUM_THREADS() as I've done in the past.:
!$Call OMP_SET_NUM_THREADS()
...
Use OMP_LIB

!$Call OMP_SET_NUM_THREADS(4)

!$OMP PARALLEL
...

...
Use OMP_LIB

!$Call OMP_SET_NUM_THREADS(4)

!$OMP PARALLEL
...

I still get the same eight original threads. What's going on?
I've seen solutions and suggestions to this problem here in SO and elsewhere, stuff like export or set the number of threads as a terminal command, but none worked. If the command exists but is ineffective or useless, why does it exist in first place? Yet, I remember that it used to work in the past. What can I do? Would this be a Cygwin64 -specific problem?
I've seen solutions and suggestions to this problem here in SO and elsewhere
export
set
Cygwin64
Cygwin64 running on Windows 11, GNU Fortran (GCC) 12.4.0.
Cygwin64
Windows 11
GNU Fortran (GCC) 12.4.0


Tags: fortran,openmp,gfortran,cygwin-64Source of the question:
https://stackoverflow.com/questions/7...

Question and source license information:
https://meta.stackexchange.com/help/l...
https://stackoverflow.com/