Turn off OpenMP

Question

In my C++ program, I'd like to run its executable sometimes with and sometimes without using OpenMP (i.e. multi-threading or single-threading). I am considering any of the following two cases how my code is using OpenMP:

(1) Assume that my code is only having #include <omp.h> and OpenMP directives.

(2) Same as (1) and my code further calls OpenMP functions like omp_get_thread_num().

In order not to have different code for different running, is it the only way using some self-defined precompiler variable to guard where OpenMP appears in my code ?

Thanks and regards!

Answer 1

You can use the environment variable:

set OMP_NUM_THREADS=1

Actually, it will not turn OpenMP off. It will force OpenMP to create only one thread for an application. It works without recompilation. I use this variable to test scalability on 1, 2, 3, 4 etc threads.