OpenMP Application Programming Interface Examples

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C / C++
The if clauses work the same way for the following Fortran code. When the if clause conditional
expression on the target construct evaluates to false, the target region will execute on the host
device. However, the target data construct created an enclosing device data environment that
mapped the p array (and v1 and v2) to a device data environment on the default target device. At the
end of the target data region the p array will be assigned from the device data environment to
the corresponding variable in the data environment of the task that encountered the target data
construct, resulting in undefined values in p.
Example target_data.7.f90
Fortran
S-1 module params
S-2 integer, parameter :: THRESHOLD=1000000
S-3 end module
S-4 subroutine vec_mult(p, v1, v2, N)
S-5 use params
S-6 real :: p(N), v1(N), v2(N)
S-7 integer :: i
S-8 call init(v1, v2, N)
S-9 !$omp target data map(from: p)
S-10 !$omp target if(N>THRESHOLD) map(to: v1, v2)
S-11 !$omp parallel do
S-12 do i=1,N
S-13 p(i) = v1(i) * v2(i)
S-14 end do
S-15 !$omp end target
S-16 !$omp end target data
S-17 call output(p, N) !*** UNDEFINED behavior if N