1  /* Signal Handlers that Return
       2     Copyright (C) 1991-2023 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  #include <signal.h>
      19  #include <stdio.h>
      20  #include <stdlib.h>
      21  
      22  /* This flag controls termination of the main loop. */
      23  volatile sig_atomic_t keep_going = 1;
      24  
      25  /* The signal handler just clears the flag and re-enables itself. */
      26  void
      27  catch_alarm (int sig)
      28  {
      29    keep_going = 0;
      30    signal (sig, catch_alarm);
      31  }
      32  
      33  void
      34  do_stuff (void)
      35  {
      36    puts ("Doing stuff while waiting for alarm....");
      37  }
      38  
      39  int
      40  main (void)
      41  {
      42    /* Establish a handler for SIGALRM signals. */
      43    signal (SIGALRM, catch_alarm);
      44  
      45    /* Set an alarm to go off in a little while. */
      46    alarm (2);
      47  
      48    /* Check the flag once in a while to see when to quit. */
      49    while (keep_going)
      50      do_stuff ();
      51  
      52    return EXIT_SUCCESS;
      53  }