Can the order of execution of fork() be determined?

Question

I\'m working on an exercise on the textbook \"Operating System Concepts 7th Edition\", and I\'m a bit confused about how does fork() work. From my understanding

Answer 1

But then, how do we know exactly which process runs first? I meant the order of execution.

There is no guarantee to which one ran first. fork returns 0 if it is the child and the pid of the child if it is the parent. Theoretically they could run at exactly the same time on a multiprocessor system. If you actually wanted to determine which ran first you could have a shared lock between the two processes. The one that acquires the lock first could be said to have run first.

In terms of what to do in your else statement. You'll want to wait for the child process to exit using wait or waitpid.

To be honest, I don't see any difference between using fork and not using fork.

The difference is that you create a child process. Another process on the system doing computation. For this simple problem the end user experience is the same. But fork is very different when you are writing systems like servers that need to deal with things concurrently.

Besides, if I want the parent process to handle the input from user, and let the child process handle the display, how could I do that?

You appear to have that setup already. The parent process just needs to wait for the child process to finish. The child process will printf the results to the terminal. And the parent process currently gets user input from the command line.