if (OpenMP)
Specifies whether a loop should be executed in parallel or in serial.
if(expression)
Заметки
where,
- expression
An integral expression that, if it evaluates to true (nonzero), causes the code in the parallel region to execute in parallel. If the expression evaluates to false (zero), the parallel region is executed in serial (by a single thread).
Заметки
if applies to the following directives:
For more information, see 2.3 parallel Construct.
Пример
// omp_if.cpp
// compile with: /openmp
#include <stdio.h>
#include <omp.h>
void test(int val)
{
#pragma omp parallel if (val)
if (omp_in_parallel())
{
#pragma omp single
printf_s("val = %d, parallelized with %d threads\n",
val, omp_get_num_threads());
}
else
{
printf_s("val = %d, serialized\n", val);
}
}
int main( )
{
omp_set_num_threads(2);
test(0);
test(2);
}
val = 0, serialized
val = 2, parallelized with 2 threads