Is there an example of a working timer that executes some function every x amount seconds using C.
I\'d appreciate an example working code.
You could spawn a new thread:
void *threadproc(void *arg)
{
while(!done)
{
sleep(delay_in_seconds);
call_function();
}
return 0;
}
...
pthread_t tid;
pthread_create(&tid, NULL, &threadproc, NULL);
Or, you could set an alarm with alarm(2) or setitimer(2):
void on_alarm(int signum)
{
call_function();
if(!done)
alarm(delay_in_seconds); // Reschedule alarm
}
...
// Setup on_alarm as a signal handler for the SIGALRM signal
struct sigaction act;
act.sa_handler = &on_alarm;
act.sa_mask = 0;
act.sa_flags = SA_RESTART; // Restart interrupted system calls
sigaction(SIGALRM, &act, NULL);
alarm(delay_in_seconds); // Setup initial alarm
Of course, both of these methods have the problem that the function you're calling periodically needs to be thread-safe.
The signal method is particularly dangerous because it must also be async-safe, which is very hard to do -- even something as simple as printf
is unsafe because printf
might allocate memory, and if the SIGALRM
interrupted a call to malloc
, you're in trouble because malloc
is not reentrant. So I wouldn't recommend the signal method, unless all you do is set a flag in the signal handler which later gets checked by some other function, which puts you back in the same place as the threaded version.