omp_get_thread_num– Current thread ID
Returns a unique thread identification number within the current team.
In a sequential parts of the program,
always returns 0. In parallel regions the return value varies
from 0 to
omp_get_num_threads-1 inclusive. The return
value of the primary thread of a team is always 0.
OpenMP specification v4.5, Section 3.2.4.