linux - Interpreting time command output on a multi threaded program -

i have multi threaded program , profiling time taken starting before pthread_create's , after pthread_join's.

now find time, lets call x, shown below in "done in xms" user + sys time of time output. in app number argument a.out controls how many threads spawn. ./a.out 1 spawn 1 pthread , ./a.out 2 spawns 2 threads each thread same amount of work.

i expecting x real time instead of user + sys time. can please tell me why not so? means app indeed running parallel without locking between threads.

[jithin@whatsoeverclever tests]$ time ./a.out 1 done in 320ms  real    0m0.347s user    0m0.300s sys     0m0.046s [jithin@whatsoeverclever tests]$ time ./a.out 2 done in 450ms  real    0m0.266s user    0m0.383s sys     0m0.087s [jithin@whatsoeverclever tests]$ time ./a.out 3 done in 630ms  real    0m0.310s user    0m0.532s sys     0m0.105s 

code

int main(int argc, char **argv) {    //read words   getwords();    //set number of words use   int maxwords = words.size();   if(argc > 1) {      int numwords = atoi(argv[1]);      if(numwords > 0 && numwords < maxwords) maxwords = numwords;   }    //init model   model = new model(model_path);   pthread_t *threads = new pthread_t[maxwords];   pthread_attr_t attr;   void *status;    // initialize , set thread joinable   pthread_attr_init(&attr);   pthread_attr_setdetachstate(&attr, pthread_create_joinable);    int rc; clock_t starttime = clock();    for(unsigned i=0; i<maxwords; i++) {      //create thread      rc = pthread_create(&threads[i], null, processword, (void *)&words[i] );      if (rc){          cout << "error:unable create thread: " << << "," << rc << endl;          exit(-1);       }   }    // free attribute , wait other threads   pthread_attr_destroy(&attr);   for(unsigned i=0; i<maxwords; i++) {      rc = pthread_join(threads[i], &status);      if (rc){          cout << "error:unable join thread: " << << "," << rc << endl;          exit(-1);       }   }    clock_t endtime = clock();    float diff = (((float)endtime - (float)starttime) / 1000000.0f ) * 1000;   cout<<"done in "<< diff << "ms\n";   delete[] threads;   delete model; } 

the clock function documented return processor time used process. if want measure wall time elapsed, it's not right function.