Timer programing in C

[Tess]

Hi!

I searched a lot the forums for some clues, but unfortunately nothing cleared it up for me.

I am trying to program a timer and a function which checks the input while the timer didn't expire. Something like:

while (timer not expired)
{
do_action();
}


i already created my timer, but i don't manage to call any function only before this timer expired. If I call any function after I start the timer, I get an segmentation fault error.

Could anybody suggest some solutions to my problem, please?

Thanks!

[GNU-Fan]

If your code segfaults, you should post the relevant part here so it can be examined.

[Rubberman]

This is not enough information to go on. There are several types of timers available for C/C++ programming and their behavior is quite distinct. There can also be many reasons why your program segfaults that are totally irrelevant to your use of a timer. Please provide the source code that is causing (you thing) this problem.

[Tess]

Here is the part of my code which deals the timer(s):


//timer.c___________________________________________ ________
#include "timer.h"

timer_t Counter_t1, Timer_5s, Timer_4s;

int i=0;

timer_t CreateTimer(int signo, int freq, int choice)
{
struct sigevent signal_event;
struct itimerspec its;
timer_t timerid;

signal_event.sigev_notify = SIGEV_SIGNAL;
signal_event.sigev_signo = signo;
signal_event.sigev_value.sival_ptr = &timerid;

if (timer_create(CLOCKID, &signal_event, &timerid) == -1)
errExit("timer_create");

its.it_value.tv_sec = freq / 1000;
its.it_value.tv_nsec = freq % 1000;

if (choice == 1)
{
its.it_interval.tv_sec = its.it_value.tv_sec;
its.it_interval.tv_nsec = its.it_value.tv_nsec;
}
else {
its.it_interval.tv_sec = 0;
its.it_interval.tv_nsec = 0;
}

if (timer_settime(timerid, 0, &its, NULL) == -1)
errExit("timer_settime");


return timerid;
}

static void SignalHandler(int signo, siginfo_t *info, void *context)
{

if (signo == TIMER5S)
{
// Send();
// ... <-- here i initially implemented some other code which was sending some information. Idon't need it anymore, so the "if" condition is actually empty at the moment

}

else if (signo == SIGINT)
{
timer_delete(Timer_5s);
errExit("CTRL + C pressed!");
}
}

void StartTimer()
{
struct sigaction signal_action;

sigemptyset(&signal_action.sa_mask);
signal_action.sa_flags = SA_SIGINFO;
signal_action.sa_sigaction = SignalHandler;

if (sigaction(TIMER1S, &signal_action, NULL) == -1)
errExit("sigaction");

sigaction(SIGINT, &signal_action, NULL);

Timer_5s = CreateTimer (TIMER5S, 5000, 0);

printf("timer_1s ID is 0x%lx\n", (long) Timer_5s);
}


// timer.h___________________________________________ ___

#ifndef _TIMER_H_
#define _TIMER_H_

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <time.h>
#include <fcntl.h>


#define CLOCKID CLOCK_REALTIME
#define TIMER5S SIGRTMAX

#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
} while (0)

timer_t CreateTimer(int signo, int freq, int choice);

void StartTimer();

#endif /* _TIMER_H_ */


xyz.c_________________________________
#include "timer.h"

int abc()
{
// some other code <--everything what belongs to this part is executed properly
StartTimer();

// if I add some other code here, I get the error. Anyway, what I'm trying to do is to check for some action while the timer is still running. If the action was executed, i want my timer to stop and reset. This what i have here at the moment helped me by doing something when the timer expired.

return 0;
}

int main()
{
abc();

for(;
;

return 0;
}



______________________________________________

It's still in development phase, so many things are missing and many are probably not right!

Thanks!

[Rubberman]

I'll look at this code as soon as I have a little time - probably later tonight.

[Rubberman]

The likely cause of your core dump. In your CreateTimer() function you are declaring timer_t and struct sigevent variables as automatics (on the stack), yet you are passing them to a function that has to live outside of the scope of CreateTimer(). So, either you need to declare them static, either in the translation unit - the source file, or in the CreateTimer() function itself, or allocate them on the heap. I suggest that you declare them as static variables at the top of the source file. You should also not be returning the timer by value. Remember, you have registered the timer by address with the timer_create() function. So, after CreateTimer() returns, it is no longer a valid address, so the entire timer sub-system is now fubar (at least in your program)!

[Tess]

Thanks for your reply!

I still have some questions which haven't been answered.
How can I check for a function so long as the timer hasn't expired? Can I use all of this in doing such a function? Something like:

while (timer not expired)
{
do_action();
}

[Rubberman]

Sure. In your timer handler function, just set a variable that your loop can see, such as timer_not_expired perhaps?