books/apue/signal.c

   1 /*
   2  * 10.11: Demonstrates the use of sigpending() and sigismember()
   3  * by installing a handler for SIGQUIT, blocking it and checking
   4  * if it was sent.
   5  */
   6 #include <stdio.h>
   7 #include <unistd.h>
   8 #include <stdlib.h>
   9 #include <signal.h>
  10
  11 static void sig_quit(int signo)
  12 {
  13         fprintf(stderr, "caught SIGQUIT\n");
  14
  15         if (signal(SIGQUIT, SIG_DFL) == SIG_ERR) {
  16                 fprintf(stderr, "can't reset SIGQUIT\n");
  17                 exit(1);
  18         }
  19 }
  20
  21 int main(void)
  22 {
  23         sigset_t newmask, oldmask, pendmask;
  24
  25         /* Installs sig_quit() as our handler for SIGQUIT */
  26         if (signal(SIGQUIT, sig_quit) == SIG_ERR) {
  27                 fprintf(stderr, "can't catch SIGQUIT\n");
  28                 exit(1);
  29         }
  30
  31         /* Blocks SIGQUIT */
  32         sigemptyset(&newmask);
  33         sigaddset(&newmask, SIGQUIT);
  34
  35         if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0) {
  36                 fprintf(stderr, "SIG_BLOCK error\n");
  37                 exit(1);
  38         }
  39
  40         /*
  41          * Sleeps for five seconds. In this period we should
  42          * receive a SIGQUIT, but as it's blocked we continue
  43          * to sleep
  44          */
  45         sleep(5);
  46
  47         if (sigpending(&pendmask) < 0) {
  48                 fprintf(stderr, "sigpending error\n");
  49                 exit(1);
  50         }
  51
  52         if (sigismember(&pendmask, SIGQUIT))
  53                 printf("SIGQUIT pending\n");
  54
  55         if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0) {
  56                 fprintf(stderr, "SIG_SETMASK error\n");
  57                 exit(1);
  58         }
  59         printf("SIGQUIT unblocked\n");
  60
  61         exit(0);
  62 }