Subj : Re: timer thread & signal question
To   : comp.programming.threads
From : VK
Date : Sat Jan 08 2005 10:05 pm


Loic Domaigne wrote:
> You must used queued signal. If your implementation supports it, use
> realtime signal: signal whose number is between SIGRTMIN and
SIGRTMAX.

Thanks Loic, I tried with SIGRTMIN and pthread_sigmask (SIG_BLOCK,
&set, NULL); and it works.

My next problem now is that when a timer goes off, I want to be able to
know which timer id associated with the expired timer.  In order to do
this, I passed in timer event's sigev_value.sival_ptr the address of
timer id.  However, when the timer expires, the data stored in
siginfo.si_ptr is not the same as the generated timer id eventhough the
address is the same.  I've been banging my head in the wall for a few
hours now.  Could you give me some hints of what's gone wrong?  Thanks
so much again.

Here's the new code for my test file.

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


pthread_t thread;


void signalHandler (int signum, siginfo_t* info, void* notused)
{
pthread_kill(thread, SIGRTMIN );
std::cout << "sending signal...\n";
}


void* threadHandler (void*)
{
siginfo_t info;
sigset_t set;


struct sigaction sigact;
sigemptyset (&sigact.sa_mask);
sigact.sa_flags = SA_SIGINFO;
sigact.sa_sigaction = signalHandler;
sigaction (SIGRTMIN, &sigact, NULL);
sigemptyset(&set);
sigaddset(&set, SIGRTMIN);


while (1)
{
pthread_sigmask (SIG_BLOCK, &set, NULL);
sigwaitinfo(&set, &info);
std::cout <<"timerId = " << *(timer_t*)info.si_ptr << "\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 = SIGRTMIN;
sig.sigev_value.sival_ptr = (void*)&pTimer;
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 << "created timer id = " << pTimer << "\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's output:
[vkincaid@nms2 signal]$ ./a.out
created timer id = -1218664448
created timer id = -1218664284
sending signal...
timerId = -1219691112
sending signal...
timerId = -1219691112
sending signal...
sending signal...
timerId = -1219691112
timerId = -1219691112
sending signal...
timerId = -1219691112

.