after fork(), parent or child could be scheduled next
$ make
gcc -o p1 p1.c -Wall
gcc -o p2 p2.c -Wall
gcc -o p3 p3.c -Wall
gcc -o p4 p4.c -Wall
$ cat -n ostep/code/cpu-api/p1.c
1 #include <stdio.h>
2 #include <stdlib.h>
3 #include <unistd.h>
4
5 int
6 main(int argc, char *argv[])
7 {
8 printf("hello world (pid:%d)\n", (int) getpid());
9 int rc = fork();
10 if (rc < 0) {
11 // fork failed; exit
12 fprintf(stderr, "fork failed\n");
13 exit(1);
14 } else if (rc == 0) {
15 // child (new process)
16 printf("hello, I am child (pid:%d)\n", (int) getpid());
17 } else {
18 // parent goes down this path (original process)
19 printf("hello, I am parent of %d (pid:%d)\n",
20 rc, (int) getpid());
21 }
22 return 0;
23 }
$ ./p1
hello world (pid:21918)
hello, I am parent of 21919 (pid:21918)
hello, I am child (pid:21919)
$ ./p1
hello world (pid:21920)
hello, I am child (pid:21921)
hello, I am parent of 21921 (pid:21920)
$
