Linux C ignore event for x seconds - c

Question

I have the following arduino code:
uint32_t hold_time=600000;
uint32_t curr_time;
uint32_t last_event;
bool on_hold=false;
beginning of main loop
curr_time = millis();
if (on_hold && curr_time - last_event >= hold_time) {
on_hold = false;
}
...
if (!on_hold)
{
run the function();
on_hold = true; // Ignore this function for 1 minute
}
This basically will execute the main loop many times but the run_the_function(); only when it is unlocked so in this example once in every minute. I would like to accomplish the same in standard POSIX C which works on BSDs as well.

Answer 1

Since you asked for POSIX, I will give you POSIX. This is a sample code that is able to run a timer without using pthreads, but only through OS provided timers. It runs a specific function every 2 seconds. You can configure it to make it run every 60 seconds, if you prefer. I have comment thoroughly the code, and I hope it is easy enough to understand:
#include <stdlib.h> // For declaration of exit
#include <stdio.h> // For printf function
#include <signal.h> // Will be used for the signal callbacks
#include <time.h> // Timer and current time stuff
#define TIMER_SECONDS 2 // To test more rapidly I will wait
// only for 2 seconds instead of a minute...
int counter = 0; // Whe want to call the timer a limited number
// of time for this example
// BEFORE READING THIS, READ THE MAIN:
// This function is your "run_the_function" callback. As for now,
// it has no arguments and returns nothing. It asks to the system the current
// time and prints it, just to check if the timer works. It uses **printf**
// and this should be avoided in signal handlers!
static void run_the_function() {
time_t rawtime; // This is the current time variable
struct tm * timeinfo; // This is a strut that contains the time
// broken down to its components
time( &rawtime ); // To get from the system the current time
timeinfo = localtime ( &rawtime ); // For splitting the time in its components
printf("Timer CALLED %d times :: %s", ++counter, asctime(timeinfo));
}
// BEFORE READING THIS, READ THE MAIN
// This is the signal handler, a function that is called when the timer
// signals that has finished to count
static void timer_callback(int sig, siginfo_t *si, void *uc) {
run_the_function();
}
int main() {
timer_t timer_id; // An unique identifier for the timer that you are creating
struct itimerspec intervals; // Specify the intervals for the timer that we are creating
struct sigevent timer_event; // The structure that handles the event generated by the timer
struct sigaction timer_action; // The action for the timer event
// First you need to implement the action to do when the timer reaches zero,
// then you need to say that you want an event for a timer that reaches zero,
// and only at the end you set the timer.
// The function "sigaction" connects your timer event to the timer signal SIGRTMIN.
// The timer_event.sigev_signo instructs to create an EVENT for the signal SIGRTMIN, and
// for that event you prepared a custom action.
// The timer sends the SIGRTMIN signal every time it reaches zero, and when you
// create it, you connect it to the timer_event.
// Now we define what is the action to perform
timer_action.sa_flags = SA_SIGINFO; // The action to perform is to run a callback
timer_action.sa_sigaction = timer_callback; // The callback is "timer_callback"
sigemptyset(&timer_action.sa_mask); // And we are initializing the event structure
if (sigaction(SIGRTMIN, &timer_action, NULL) < 0) // We are binding this action
exit(1); // to a timer event (SIGRTMIN)
timer_event.sigev_notify = SIGEV_SIGNAL; // Instruct the event that it is related to
// a signal.
timer_event.sigev_signo = SIGRTMIN; // Instruct the event that the signal to track is SIGRTMIN
// At this point we are ready to create the timer, that uses the REAL TIME CLOCK of your
// system. When it reaches zero it raise a timer_event, and it also sets the id of the
// created timer.
if (timer_create(CLOCK_REALTIME, &timer_event, &timer_id) < 0)
exit(1);
// We now need to define the times for the timer. Intervals is composed by
// two structure: it_value, that contains the current time (or the starting time
// for the first run of your timer) and it_intervals, the time at which it will be
// reset after completing one lap. If you set it_interval to zero, the timer runs only
// one time. If you set it_value to zero, the timer does not run.
intervals.it_value.tv_sec = TIMER_SECONDS;
intervals.it_value.tv_nsec = 0;
intervals.it_interval.tv_sec = TIMER_SECONDS;
intervals.it_interval.tv_nsec = 0;
// Let's setup the time and the interval of the timer, so that it starts...
if (timer_settime(timer_id, 0, &intervals, NULL) < 0)
exit(1);
// And now we have only to wait for the timer... Easy, isn't it?
printf("Let's go!\n");
while(counter < 5) { /* Do your stuff here*/ };
return 0;
}
You need to compile it with:
gcc test.c -lrt -o test
and run it with:
./test
Let's go!
Timer CALLED 1 times :: Thu May 3 15:48:29 2018
Timer CALLED 2 times :: Thu May 3 15:48:31 2018
Timer CALLED 3 times :: Thu May 3 15:48:33 2018
Timer CALLED 4 times :: Thu May 3 15:48:35 2018
Timer CALLED 5 times :: Thu May 3 15:48:37 2018