In what way does wait(NULL) work exactly in C?

Question

If I use wait(null), and I know (for sure) that the child will finish (exit) before we reach to wait(null) in the parent process, does the wait(null) block the parent process?

I mean, the wait() won't get any signal, right?

int main() {
    int pipe_descs[2];
    int i, n, p;

    srand(time(NULL(;
    pipe(pipe_descs);

    for (i = 0; i < 2; i++) {
        pid_t status = fork();

        if (status == 0) {
            n = rand() % 100;
            p = (int) getpid();

            write(pipe_descs[1], &n, sizeof(int));
            write(pipe_descs[1], &p, sizeof(int));
            exit(0);
        }
        else {
            read(pipe_descs[0],  &n,  sizeof(int));
            read(pipe_descs[0],  &p,  sizeof(int));
            printf(" %d %d\n", n, p);
            wait(NULL); // (1)
        }
    }
    return 0;
}

Answer 1

wait(NULL) will block the parent process until any of its children has finished. If the child terminates before the parent process reaches wait(NULL) then the child process turns to a zombie process until its parent waits on it and its released from memory.

If the parent process doesn't wait for its child, and the parent finishes first, then the child process becomes an orphan and is assigned to init as its child. And init will wait and release the process entry in the process table.

In other words: the parent process will be blocked until the child process returns an exit status to the operating system which is then returned to the parent process. If the child finishes before the parent reaches wait(NULL) then it will read the exit status, release the process entry in the process table and continue execution until it finishes as well.