Process Forking
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In C, fork() is a system call that, when called by a parent process, will immediately create a new and nearly identical child process. It has a copy of its parent's address space, registers, program counter, etc. The child process will immediately continue execution in parallel to the parent, as though it had itself called fork(). Without special logic in place, due to CPU Virtualisation and scheduling, the program effectively becomes non-deterministic after calling fork(). We don't know for sure whether the parent or child will finish executing first.
To write deterministic code, the return value of fork() must be taken into account. The parent receives the child's process ID (PID) as a return value. The child receives 0 as a return value.
Together with the waitpid() system call (waits for a certain PID to finish before continuing), we can ensure the two processes finish in a certain order.
exec
After calling exec(), the current process is essentially replaced with a new program. Memory is reinitialised and the code loaded into memory is replaced by the new program.
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