Question

I’m having a tough time producing a scenario that will display a time difference between invocation of a simple local function vs. the same function but within a child process. The particular function I’m testing shows no difference (time = 0) for the difftime(x,y) function for both the local function and the child process. Can someone generalize potential time differences in these two methods of doing the same thing?

As a side note, I tried doing each task 1000 times and then dividing time by 1000, but even then the time returned is 0. For example, I have:

time(&start);    
for(int i = 0; i<1000; i++){
  reply[i] = my_channel.send_request("hello");
}
time(&end);
time_req_1 = difftime(end,start);

And time returned for “time_req_1” = 0.
I only put this code segment in just in case I’ve done something incorrect.

Answer 1

You have to remember that the resolution for time is in seconds. A common way to time e.g. a function call is to use clock:

clock_t start_time = clock();

some_lengthy_function_call();

clock_t end_time = clock();

printf("Elapsed time: %.02f seconds\n",
       (double) (end_time - start_time) / CLOCKS_PER_SEC);

Edit: If you want even better accuracy and resolution than clock can provide, see the comment by Jonathan Leffler to your question.