OMP_GET_THREAD_NUM

Purpose:

Returns the thread number of the thread, within the team, making this call. This number will be between 0 and OMP_GET_NUM_THREADS-1. The master thread of the team is thread 0.

Format:

Fortran

INTEGER FUNCTION OMP_GET_THREAD_NUM()

C/C++

#include <omp.h>
int omp_get_thread_num(void)

Notes & Restrictions:

If called from a nested parallel region, or a serial region, this function will return 0.

Examples in Fortran:determining the number of threads in a parallel region

• Example 1 is the correct way to determine the number of threads in a parallel region.
• Example 2 is incorrect - the TID variable must be PRIVATE
• Example 3 is incorrect - the OMP_GET_THREAD_NUM call is outside the parallel region

Example 1: Correct

      PROGRAM HELLO

      INTEGER TID, OMP_GET_THREAD_NUM

!$OMP PARALLEL PRIVATE(TID)

      TID = OMP_GET_THREAD_NUM()
      PRINT *, 'Hello World from thread = ', TID

      ...

!$OMP END PARALLEL

      END

Example 2: Incorrect

      PROGRAM HELLO

      INTEGER TID, OMP_GET_THREAD_NUM

!$OMP PARALLEL 

      TID = OMP_GET_THREAD_NUM()
      PRINT *, 'Hello World from thread = ', TID

      ...

!$OMP END PARALLEL

      END

Example 3: Incorrect

      PROGRAM HELLO

      INTEGER TID, OMP_GET_THREAD_NUM

      TID = OMP_GET_THREAD_NUM()
      PRINT *, 'Hello World from thread = ', TID

!$OMP PARALLEL 

      ...

!$OMP END PARALLEL

      END