[ MPI 文章收集 ] Mixing MPI and OpenMP

來源自 這裡
Preface:
下面範例說明如何在 MPI 上使用 OpenMP. 程式的邏輯是每個 process 都執行 rank+1 次的 for loop, 並將該 for loop 使用 OpenMP 平行化並列印 Hello 訊息.

Example:
- 範例代碼 mpi_with_openmp.c:

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1. #include   
2. #include   
3. #include   
4.   
5. int main(int argc, char *argv[])  
6. {  
7.     int numprocs, rank, namelen;  
8.     char processor_name[MPI_MAX_PROCESSOR_NAME];  
9.     int iam=0, np=1, i;  
10.   
11.     MPI_Init(&argc, &argv);  
12.     MPI_Comm_size(MPI_COMM_WORLD, &numprocs);  
13.     MPI_Comm_rank(MPI_COMM_WORLD, &rank);  
14.     MPI_Get_processor_name(processor_name, &namelen);  
15.   
16.     #pragma omp parallel for private(iam, np)  
17.     for(i=0; i1; i++)  
18.     {  
19.         np = omp_get_num_threads();  
20.         iam = omp_get_thread_num();  
21.         printf("Hello from thread %d out of %d from process %d out of %d on  %s - Round%d\n",   
22.                iam, np, rank, numprocs, processor_name, i);  
23.     }  
24.   
25.     MPI_Finalize();  
26. }  

接著可以如下編譯與執行:

# mpic++ -fopenmp mpi_with_openmp.c -o mpi_with_openmp
# mpiexec -n 3 mpi_with_openmp
Hello from thread 2 out of 24 from process 2 out of 3 on linux1 - Round2
Hello from thread 0 out of 24 from process 2 out of 3 on linux1 - Round0
Hello from thread 0 out of 24 from process 0 out of 3 on linux1 - Round0
Hello from thread 0 out of 24 from process 1 out of 3 on linux1 - Round0
Hello from thread 1 out of 24 from process 1 out of 3 on linux1 - Round1
Hello from thread 1 out of 24 from process 2 out of 3 on linux1 - Round1