问分叉系统调用是如何工作的？

EN

int main (void) 
{
    for (int i = 0; i < 10; i++) {
        pid_t pid = fork ();

        if ( !pid ) {
            printf("CHILD | PID: %d, PPID: %d\n", getpid(), getppid());
            _exit(i + 1);
        }

    }

    for (int i = 0; i < 10; i++) {
        int status;
        waitpid(-1, &status, 0);

        if (WIFEXITED(status)) {
            printf("IM %d AND CHILD WITH EXIT CODE %d TERMINATED\n",
                    getpid(), WEXITSTATUS(status));

        } 
        else {
            printf("ERROR: CHILD NOT EXITED\n");
        }
    }

    return 0;
}

CHILD | PID: 3565, PPID: 3564
CHILD | PID: 3566, PPID: 3564
IM 3564 AND CHILD WITH EXIT CODE 1 TERMINATED
IM 3564 AND CHILD WITH EXIT CODE 2 TERMINATED
CHILD | PID: 3573, PPID: 3564
CHILD | PID: 3567, PPID: 3564
IM 3564 AND CHILD WITH EXIT CODE 9 TERMINATED
IM 3564 AND CHILD WITH EXIT CODE 3 TERMINATED
CHILD | PID: 3568, PPID: 3564
IM 3564 AND CHILD WITH EXIT CODE 4 TERMINATED
CHILD | PID: 3569, PPID: 3564
IM 3564 AND CHILD WITH EXIT CODE 5 TERMINATED
CHILD | PID: 3570, PPID: 3564
IM 3564 AND CHILD WITH EXIT CODE 6 TERMINATED
CHILD | PID: 3571, PPID: 3564
IM 3564 AND CHILD WITH EXIT CODE 7 TERMINATED
CHILD | PID: 3572, PPID: 3564
IM 3564 AND CHILD WITH EXIT CODE 8 TERMINATED
CHILD | PID: 3574, PPID: 3564
IM 3564 AND CHILD WITH EXIT CODE 10 TERMINATED