Parallel Programming in Fortran 95 using OpenMP - People

56 4. The OpenMP run-time library
The number of threads imposed by a call to this subroutine has always precedence
over the value specified in the OMP NUM THREADS environment variable.
4.1.2 OMP get num threads
This function allows to know the number of threads currently in the team executing
the parallel region from which it is called. Therefore, this function is meant to be used
from inside a parallel region; although when called from a serial region or from inside
a serialized nested parallel region, it returns the correct result, namely 1 thread. Its
interface declaration is:
function OMP_get_num_threads()
integer(kind = OMP_integer_kind) :: OMP_get_num_threads
end function OMP_get_num_threads
where the returned value will be the number of threads in use.
4.1.3 OMP get max threads
This function returns the maximum number of threads that can be used in the program.
Its result may differ from the one returned by the function OMP get num threads, ifthe
dynamic adjustment of threads is enabled; otherwise, the results will be equal. Its interface
declaration is equivalent to the one of the function OMP get num threads:
function OMP_get_max_threads()
integer(kind = OMP_integer_kind) :: OMP_get_max_threads
end function OMP_get_max_threads
where the returned value is the maximum allowed number of threads. Since the
returned value has nothing to do with the actual number of threads used in a given
parallel region, this function can be called from serial regions as well as from parallel
regions.
4.1.4 OMP get thread num
This function returns the identification number of the current thread within the team.
The identification numbers are between 0, the master thread, and OMP get num threads()
- 1, inclusive. The interface of this function is:
function OMP_get_thread_num()
integer(kind = OMP_integer_kind) :: OMP_get_thread_num
end function OMP_get_thread_num
This function returns 0, when called from inside a serial region or a serialized nested
parallel region, which is the identification number of the lonely master thread.