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Run method every x seconds in C

Is there an example of a working timer that performs some function every x seconds using C.

I would appreciate an example of working code.

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2 answers

You can create 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 can 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 a problem that the function you call periodically must be thread safe.

The signal method is especially dangerous, since it must also be asynchronous, which is very difficult to do - even that which is simply printf insecure because printf can allocate memory, and if SIGALRM interrupted the call to malloc , you have problems because malloc not repeated. Therefore, I would not recommend a signal method, unless you select the checkbox in the signal handler, which is later checked by some other function that returns you to the same place as the streaming version.

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There are various inherited ways to do this using interval timers and signals, but I'm going to introduce two modern approaches:

Using POSIX Timers

The POSIX timer_create function creates a timer that can be configured to deliver a one-time or periodic notification when the timer expires. When creating a timer, you can request delivery by signal or in a new stream. Since using the signals correctly is difficult (there are strict rules about what you can and cannot do from the signal handler, and breaking the rules often “seems to work” until you're lucky), I would recommend using stream delivery .

Scrolling your own timer using a thread

It really is as simple as it sounds. Create a new thread that goes into the loop, and do whatever you need each time the required time is up.

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