The Linux Programming Interface

470 Chapter 22

In the output for the accepted SIGUSR1 signal, we see that the si_value field has the

value 100. This is the value to which the field was initialized by the preceding signal

that was sent using sigqueue(). We noted earlier that the si_value field contains valid

information only for signals sent using sigqueue().

Listing 22-6: Synchronously waiting for a signal with sigwaitinfo()

––––––––––––––––––––––––––––––––––––––––––––––––––– signals/t_sigwaitinfo.c

#define _GNU_SOURCE

#include <string.h>

#include <signal.h>

#include <time.h>

#include "tlpi_hdr.h"

int

main(int argc, char *argv[])

{

int sig;

siginfo_t si;

sigset_t allSigs;

if (argc > 1 && strcmp(argv[1], "--help") == 0)

usageErr("%s [delay-secs]\n", argv[0]);

printf("%s: PID is %ld\n", argv[0], (long) getpid());

/* Block all signals (except SIGKILL and SIGSTOP) */

sigfillset(&allSigs);

if (sigprocmask(SIG_SETMASK, &allSigs, NULL) == -1)

errExit("sigprocmask");

printf("%s: signals blocked\n", argv[0]);

if (argc > 1) { /* Delay so that signals can be sent to us */

printf("%s: about to delay %s seconds\n", argv[0], argv[1]);

sleep(getInt(argv[1], GN_GT_0, "delay-secs"));

printf("%s: finished delay\n", argv[0]);

}

for (;;) { /* Fetch signals until SIGINT (^C) or SIGTERM */

sig = sigwaitinfo(&allSigs, &si);

if (sig == -1)

errExit("sigwaitinfo");

if (sig == SIGINT || sig == SIGTERM)

exit(EXIT_SUCCESS);

printf("got signal: %d (%s)\n", sig, strsignal(sig));

printf(" si_signo=%d, si_code=%d (%s), si_value=%d\n",

si.si_signo, si.si_code,

(si.si_code == SI_USER)? "SI_USER" :

(si.si_code == SI_QUEUE)? "SI_QUEUE" : "other",

si.si_value.sival_int);