Subj : timer thread & signal question
To   : comp.programming.threads
From : VK
Date : Thu Jan 06 2005 08:07 pm

Hi,

Please help me with this newbie problem.  I'm trying to set up a timer
thread with the signal handler.  My problem is that when I have 2
timers that go off at the same time, the signal SIGUSR2 is sent twice
to sigwait(), but since they are 2 identical signals, sigwait() sees it
as 1 signal only.  How do I tell sigwait() that there are 2 of the same
signal?

I tried sigwaitinfo() also as I thought sigwaitinfo() "returns the
queued signal value so that applications can differentiate between
multiple events queued to the same signal number".  But it didn't do it
:(

Can anyone please help me?  Thanks a lot in advance.  My test file is
as below.

#include <iostream>
#include <signal.h>
#include <pthread.h>
#include <time.h>
#include <unistd.h>


pthread_t thread;


void signalHandler (int signum)
{
pthread_kill(thread, SIGUSR2 );
std::cout << "sending signal...\n";
}


void* threadHandler (void*)
{
int signum;
sigset_t set;


struct sigaction sigact;
sigact.sa_handler = signalHandler;
sigaction (SIGUSR2, &sigact, NULL);
sigemptyset(&set);
sigaddset(&set, SIGUSR2);


while (1)
{
sigwait(&set, &signum);
std::cout <<"Signal received!\n";
}
pthread_exit(NULL);
}


timer_t timerStart (int sec, int sec_itv)
{
timer_t pTimer;
struct sigevent sig;
struct itimerspec req, old;
sig.sigev_notify = SIGEV_SIGNAL;
sig.sigev_signo = SIGUSR2;
req.it_value.tv_sec = sec;
req.it_value.tv_nsec = 0;
req.it_interval.tv_sec = sec_itv;
req.it_interval.tv_nsec = 0;


if (timer_create (CLOCK_REALTIME, &sig, &pTimer))
std::cout <<"timer create failed\n";
if (timer_settime(pTimer, 0, &req, &old))
std::cout <<"timer settime failed\n";
std::cout << "timer is created and set\n";
return pTimer;
}


int main()
{
pthread_attr_t attr;


pthread_attr_init(&attr);
pthread_create(&thread, &attr, threadHandler, NULL);
timer_t t0 = timerStart(4,0);
timer_t t1 = timerStart(2,1);
pthread_join(thread, NULL);
return 0;
}

Program output:
[vkincaid@nms2 signal]$ g++ -lrt -lpthread TimerThread.cpp
[vkincaid@nms2 signal]$ ./a.out
timer is created and set
timer is created and set
--> wait for 2 secs
sending signal...   --> t1 fires
Signal received!
sending signal...   --> t1 fires
Signal received!
sending signal...   --> t0 fires
sending signal...   --> t1 fires at the same time
Signal received!    --> signal is only received once
sending signal...
Signal received!
Ctrl-C

.