Some wrong about sigsetjmp - c

Question

I am reading the APUE, Chapter 10. Here is my code.
#include "apue.h"
#include <unistd.h>
#include <setjmp.h>
#include <time.h>
#include <errno.h>
static void sig_usr1(int), sig_alrm(int);
static sigjmp_buf jmpbuf;
static volatile sig_atomic_t canjmp;
int
main(void)
{
if(signal(SIGUSR1, sig_usr1) == SIG_ERR)
err_sys("signal(SIGUSR1) error");
if(signal(SIGALRM, sig_alrm) == SIG_ERR)
err_sys("signal(SIGALRM) error");
//print signal.
pr_mask("Starting main: ");
if(sigsetjmp(jmpbuf, 1)) {
pr_mask("End main: ");
exit(0);
}
canjmp = 1;
for(;;)
pause();
}
static void
sig_usr1(int signo)
{
time_t starttime;
if(canjmp == 0) {
return;
}
pr_mask("starting sig_usr1: ");
alarm(3);
starttime = time(NULL);
for(;;)
if(time(NULL) > starttime + 5)
break;
pr_mask("finishing sig_usr1: ");
canjmp = 0;
siglongjmp(jmpbuf, 1);
}
static void
sig_alrm(int signo)
{
pr_mask("in sig_arlm: ");
}
void
pr_mask(const char *str)
{
sigset_t sigset;
int errno_save;
errno_save = errno; /* we can be called by signal handlers */
if (sigprocmask(0, NULL, &sigset) < 0)
err_sys("sigprocmask error");
printf("%s", str);
if (sigismember(&sigset, SIGUSR1)) printf("SIGUSR1 ");
if (sigismember(&sigset, SIGALRM)) printf("SIGALRM ");
/* remaining signals can go here */
printf("\n");
errno = errno_save;
}
I thought the output would be like this:
Starting main:
starting sig_usr1: SIGUSR1
in sig_alrm: SIGUSR1 SIGALRM
finishing sig_usr1: SIGUSR1
End main:
but it seems something wrong, this is my output in fact:
Starting main:
starting sig_usr1:
in sig_alrm:
finishing sig_usr1:
End main:
that is no signals. Please help me.

Answer 1

I think the trouble is probably that you are using signal() and not sigaction() to set the signal handling. And signal() does not mask any other signals - so there are no signals to show as being blocked. I modified your code as shown below, to use signal() and sigaction() depending on whether there are any arguments or not.
#include <signal.h>
#include <unistd.h>
#include <setjmp.h>
#include <time.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
typedef void (*Handler)(int);
static void sig_usr1(int), sig_alrm(int);
static sigjmp_buf jmpbuf;
static volatile sig_atomic_t canjmp;
static void pr_mask(const char *str);
static void err_sys(const char *str)
{
int errnum = errno;
fprintf(stderr, "%s (%d: %s)\n", str, errnum, strerror(errnum));
exit(1);
}
static void set_sigaction(int signum, Handler handler)
{
struct sigaction nact;
nact.sa_handler = handler;
sigfillset(&nact.sa_mask);
//sigemptyset(&nact.sa_mask);
nact.sa_flags = 0;
if (sigaction(signum, &nact, 0) != 0)
err_sys("Failed to set signal handling");
}
int
main(int argc, char **argv)
{
printf("PID = %u\n", (unsigned)getpid());
if (argc > 1)
{
if (signal(SIGUSR1, sig_usr1) == SIG_ERR)
err_sys("signal(SIGUSR1) error");
if (signal(SIGALRM, sig_alrm) == SIG_ERR)
err_sys("signal(SIGALRM) error");
}
else
{
set_sigaction(SIGUSR1, sig_usr1);
set_sigaction(SIGALRM, sig_alrm);
}
//print signal.
pr_mask("Starting main: ");
if (sigsetjmp(jmpbuf, 1)) {
pr_mask("End main: ");
exit(0);
}
canjmp = 1;
for (;;)
pause();
}
static void
sig_usr1(int signo)
{
time_t starttime;
if (canjmp == 0) {
return;
}
pr_mask("starting sig_usr1: ");
alarm(3);
starttime = time(NULL);
for (;;)
if (time(NULL) > starttime + 5)
break;
pr_mask("finishing sig_usr1: ");
canjmp = 0;
siglongjmp(jmpbuf, 1);
}
static void
sig_alrm(int signo)
{
pr_mask("in sig_arlm: ");
}
void
pr_mask(const char *str)
{
sigset_t sigset;
int errno_save;
errno_save = errno; /* we can be called by signal handlers */
if (sigprocmask(0, NULL, &sigset) < 0)
err_sys("sigprocmask error");
printf("%s", str);
if (sigismember(&sigset, SIGUSR1)) printf("SIGUSR1 ");
if (sigismember(&sigset, SIGALRM)) printf("SIGALRM ");
/* remaining signals can go here */
printf("\n");
errno = errno_save;
}
Running on MacOS X 10.7.2 with current XCode (4.2?), I get (for example):
$ ./sigtest
PID = 11066
Starting main:
starting sig_usr1: SIGUSR1 SIGALRM
finishing sig_usr1: SIGUSR1 SIGALRM
in sig_arlm: SIGUSR1 SIGALRM
End main:
$ ./sigtest 1
PID = 11067
Starting main:
starting sig_usr1: SIGUSR1
in sig_arlm: SIGUSR1 SIGALRM
finishing sig_usr1: SIGUSR1
End main:
$