#include <stdio.h> #include <stdlib.h> #include <string.h> #include <time.h> #include <unistd.h> #include <omp.h> #define ARRAY_LEN 1000000 int main(int argc, char* argv[]) { unsigned int seed = 12345; srand(seed); int arr[ARRAY_LEN]; for(int i=0;i<ARRAY_LEN;++i){ arr[i] = rand(); } int realTotalSum = 0; for(int i=0;i<ARRAY_LEN;++i){ realTotalSum += arr[i]; } clock_t start = clock(); const int n = 128; omp_set_num_threads(n); printf("OpenMP running with %d threads\n", omp_get_max_threads()); int localSums[128] = {0}; int localSum = 0; long i = 0; #pragma omp parallel private(localSum) { int id = omp_get_thread_num(); printf("Hello world from thread %d\n", id); #pragma omp for for(long i = 0; i < ARRAY_LEN; ++i){ localSum += arr[i]; } localSums[id] = localSum; printf("local sum in thread: %d\n", localSum); } int totalSum = 0; for(int i = 0;i<n;++i){ totalSum += localSums[i]; } printf("realTotalSum:%d\n", realTotalSum); printf("totalSum:%d\n", totalSum); clock_t end = clock(); double timeSpent = (double)(end - start) / CLOCKS_PER_SEC; printf("time spent = %10.6f\n", timeSpent); return 0; } //This is my code, I just change the const int n = 128 to others for test.