libevent: make timer persistent - c

Question

I have the following code:
#include <stdio.h>
#include <sys/time.h>
#include <event.h>
void say_hello(int fd, short event, void *arg){
printf("Hello\n");
}
int main(int argc, const char* argv[])
{
struct event ev;
struct timeval tv;
tv.tv_sec = 3;
tv.tv_usec = 0;
event_init();
evtimer_set(&ev,say_hello,NULL);
evtimer_add(&ev, &tv);
event_dispatch();
return 0;
}
Problem is "hello" gets printed once and then the program exits...
I want it to output "hello" indefinitely.
How to do this? Many thanks in advance,

Answer 1

Just to clarify Basile's solution:
I was confused as well until I realized that "timer" in this context refers to a single shot timer. What we need is an interval timer; which requires the EV_PERSIST flag in libevent.
struct timeval time;
time.tv_sec = 1;
time.tv_usec = 0;
event_set(&my_event, 0, EV_PERSIST, my_function, NULL);
evtimer_add(&my_event, &time);

Answer 2

change the code in main to read
evtimer_set(&ev,say_hello,&ev);
and make your say_hello function
void say_hello(int fd, short event, void *arg){
struct event *ev = arg;
struct timeval tv;
printf("Hello\n");
tv.tv_sec = 3;
tv.tv_usec = 0;
evtimer_add(ev, &tv);
}

Answer 3

Here is the example for libevent2:
#include <event2/event.h>
static int n_calls = 0;
void cb_func(evutil_socket_t fd, short what, void *arg)
{
struct event *me = arg;
printf("cb_func called %d times so far.\n", ++n_calls);
if (n_calls > 100)
event_del(me);
}
void run(struct event_base *base)
{
struct timeval one_sec = { 1, 0 };
struct event *ev;
/* We're going to set up a repeating timer to get called called 100
times. */
ev = event_new(base, -1, EV_PERSIST, cb_func, event_self_cbarg());
event_add(ev, &one_sec);
event_base_dispatch(base);
}

Answer 4

Did you read evtimer_set(3) man page? Please read it again.
You probably want to use the flag EV_PERSIST or call evtimer_add from your say_hello callback.

Answer 5

#include <stdio.h>
#include "ev.h"
static void timer_cback_caller(EV_P_ ev_timer* w, int revents)
{
const int new_timeout_in_ms = 1200; // new delay between timer ticks
printf("timer tick\n");
w->repeat = new_timeout_in_ms / 1000.;
ev_timer_again(EV_A_ w);
}
int main()
{
struct ev_loop *loop = ev_default_loop(0);
ev_timer timer;
const int start_delay_in_ms = 1000; // delay before first timer tick
const int timeout_in_ms = 1500; // delay between every timer tick
ev_timer_init(&timer, timer_cback_caller, start_delay_in_ms/1000., timeout_in_ms/1000.);
ev_timer_start(loop, &timer);
ev_run(loop, 0); // will never return
return 0;
}
More examples in libev documentation