使用 OpenMP 任務並行處理 ac 列表容器

#include <omp.h>
#include <unistd.h>
#include <iostream>
#include <list>

static void processElement (unsigned n)
{
    // Tell who am I. The #pragma omp critical ensures that
    // only one thread sends data to std::cout
    #pragma omp critical
    std::cout <<
      "Thread " << omp_get_thread_num() << " processing element " << n
      << std::endl;

    // Simulate some work
    usleep (n*1000);
}

int main (void)
{
    std::list<unsigned> lst;

    // Fill the list
    for (unsigned u = 0; u < 16; ++u)
            lst.push_back (1+u);

    // Now process each element of the list in parallel

    #pragma omp parallel  // Create a parallel region
    #pragma omp single    // Only one thread will instantiate tasks
    {
            for (auto element : lst)
            {
                    #pragma omp task firstprivate (element)
                    processElement (element);
            }

            // Wait for all tasks to be finished
            #pragma omp taskwait
    }

    return 0;
}

此示例通過 OpenMP 任務構造（使用 #pragma omp task 指令）模擬並行處理 STL 列表（在程式碼中名為 lst）。該示例為 lst 中的每個元素建立/例項化一個 OpenMP 任務，OpenMP 執行緒在它們準備好執行後立即執行任務。

$ OMP_NUM_THREADS=4 ./a.out
Thread 0 processing element 16
Thread 3 processing element 3
Thread 2 processing element 1
Thread 1 processing element 2
Thread 2 processing element 4
Thread 1 processing element 5
Thread 3 processing element 6
Thread 2 processing element 7
Thread 1 processing element 8
Thread 3 processing element 9
Thread 2 processing element 10
Thread 1 processing element 11
Thread 0 processing element 15
Thread 3 processing element 12
Thread 2 processing element 13
Thread 1 processing element 14