// Sample code that demonstrates a data race between threads reading and writing // from the same shared global variable in Static Data. // Interleaving of reads and writes will sometimes cause printed sum to be less // than expected. // // Remember to compile with -pthread #include #include using std::cout; using std::cerr; using std::endl; const int NUM_THREADS = 50; const int LOOP_NUM = 1000; static int sum_total = 0; // increment sum_total LOOP_NUM times void* thread_main(void* arg) { for (int i = 0; i < LOOP_NUM; i++) { sum_total++; } return nullptr; // return type is a pointer } int main(int argc, char** argv) { pthread_t thds[NUM_THREADS]; // array of thread ids // create threads to run thread_main() for (int i = 0; i < NUM_THREADS; i++) { if (pthread_create(&thds[i], nullptr, &thread_main, nullptr) != 0) { cerr << "pthread_create failed" << endl; } } // wait for all child threads to finish // (children may terminate out of order, but cleans up in order) for (int i = 0; i < NUM_THREADS; i++) { if (pthread_join(thds[i], nullptr) != 0) { cerr << "pthread_join failed" << endl; } } // print out the final sum (expecting NUM_THREADS * LOOP_NUM) cout << "Total: " << sum_total << endl; return EXIT_SUCCESS; }