manual/examples/sigusr.c

   1 /* Using kill for Communication
   2    Copyright (C) 1991-2015 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, if not, see <http://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.  */
  26 volatile sig_atomic_t usr_interrupt = 0;
  27
  28 void
  29 synch_signal (int sig)
  30 {
  31   usr_interrupt = 1;
  32 }
  33
  34 /* The child process executes this function. */
  35 void
  36 child_function (void)
  37 {
  38   /* Perform initialization. */
  39   printf ("I'm here!!!  My pid is %d.\n", (int) getpid ());
  40
  41   /* Let parent know you're done. */
  42   kill (getppid (), SIGUSR1);
  43
  44   /* Continue with execution. */
  45   puts ("Bye, now....");
  46   exit (0);
  47 }
  48
  49 int
  50 main (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, &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 ("That's all, folks!");
  76
  77   return 0;
  78 }