1/* Using kill for Communication
2 Copyright (C) 1991-2022 Free Software Foundation, Inc.
3
4 This program is free software; you can redistribute it and/or
5 modify it under the terms of the GNU General Public License
6 as published by the Free Software Foundation; either version 2
7 of the License, or (at your option) any later version.
8
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
13
14 You should have received a copy of the GNU General Public License
15 along with this program; if not, see <https://www.gnu.org/licenses/>.
16*/
17
18/*@group*/
19#include <signal.h>
20#include <stdio.h>
21#include <sys/types.h>
22#include <unistd.h>
23/*@end group*/
24
25/* When a @code{SIGUSR1} signal arrives, set this variable. */
26volatile sig_atomic_t usr_interrupt = 0;
27
28void
29synch_signal (int sig)
30{
31 usr_interrupt = 1;
32}
33
34/* The child process executes this function. */
35void
36child_function (void)
37{
38 /* Perform initialization. */
39 printf (format: "I'm here!!! My pid is %d.\n", (int) getpid ());
40
41 /* Let parent know you're done. */
42 kill (pid: getppid (), SIGUSR1);
43
44 /* Continue with execution. */
45 puts (s: "Bye, now....");
46 exit (0);
47}
48
49int
50main (void)
51{
52 struct sigaction usr_action;
53 sigset_t block_mask;
54 pid_t child_id;
55
56 /* Establish the signal handler. */
57 sigfillset (&block_mask);
58 usr_action.sa_handler = synch_signal;
59 usr_action.sa_mask = block_mask;
60 usr_action.sa_flags = 0;
61 sigaction (SIGUSR1, act: &usr_action, NULL);
62
63 /* Create the child process. */
64 child_id = fork ();
65 if (child_id == 0)
66 child_function (); /* Does not return. */
67
68/*@group*/
69 /* Busy wait for the child to send a signal. */
70 while (!usr_interrupt)
71 ;
72/*@end group*/
73
74 /* Now continue execution. */
75 puts (s: "That's all, folks!");
76
77 return 0;
78}
79

source code of glibc/manual/examples/sigusr.c