# zmq_timers(3) Manual Page

## NAME

zmq_timers - helper functions for cross-platform timers callbacks

## SYNOPSIS

typedef void(zmq_timer_fn) (int timer_id, void *arg);

void *zmq_timers_new (void);

int zmq_timers_destroy (void *timers_p);*

int zmq_timers_add (void *timers, size_t interval, zmq_timer_fn handler, void *arg);

int zmq_timers_cancel (void *timers, int timer_id);

int zmq_timers_set_interval (void *timers, int timer_id, size_t interval);

int zmq_timers_reset (void *timers, int timer_id);

long zmq_timers_timeout (void *timers);

int zmq_timers_execute (void *timers);

## DESCRIPTION

The zmq_timers*_ functions provide cross-platform access to timers callbacks. Once a timer has been registered, it will repeat at the specified interval until it gets manually cancelled. To run the callbacks, zmq_timers_execute must be ran.

zmq_timers_new and zmq_timers_destroy manage the lifetime of a timer instance. zmq_timers_new creates and returns a new timer instance, while zmq_timers_destroy destroys it. A pointer to a valid timer must be passed as the timers_p argument of zmq_timers_destroy. In particular, zmq_timers_destroy may not be called multiple times for the same timer instance. zmq_timers_destroy sets the passed pointer to NULL in case of a successful execution.

zmq_timers_add and zmq_timers_cancel manage the timers registered.

zmq_timers_add registers a new timer with a given instance. timers must point to a valid timers object. The interval parameter specifies the expiration of the timer in milliseconds. handler and arg specify the callback that will be invoked on expiration and the optional parameter that will be passed through. The callback must be a valid function implementing the zmq_timer_fn prototype. An ID will be returned that can be used to modify or cancel the timer.

zmq_timers_cancel will cancel the timer associated with timer_id from the instance timers.

zmq_timers_set_interval will set the expiration of the timer associated with timer_id from the instance timers to interval milliseconds into the future.

zmq_timers_reset will restart the timer associated with timer_id from the instance timers.

zmq_timers_timeout will return the time left in milliseconds until the next timer registered with timers expires.

zmq_timers_execute will run callbacks of all expired timers from the instance timers.

## THREAD SAFETY

Like most other ØMQ objects, timers are not thread-safe. All operations must be called from the same thread. Otherwise, behaviour is undefined.

## RETURN VALUE

zmq_timers_new always returns a valid pointer to a poller.

All functions that return an int, return -1 in case of a failure. In that case, zmq_errno() can be used to query the type of the error as described below.

zmq_timers_timeout returns the time left in milliseconds until the next timer registered with timers expires, or -1 if there are no timers left.

All other functions return 0 in case of a successful execution.

## ERRORS

On zmq_timers_destroy, zmq_poller_cancel, zmq_timers_set_interval, zmq_timers_reset, zmq_timers_timeout_, and zmq_timers_execute: EFAULT:: timers did not point to a valid timer. Note that passing an invalid pointer (e.g. pointer to deallocated memory) may cause undefined behaviour (e.g. an access violation).

On zmq_timers_add: EFAULT:: timers did not point to a valid timer or handler did not point to a valid function.

On zmq_poller_cancel, zmq_timers_set_interval and zmq_timers_timeout_: EINVAL:: timer_id did not exist or was already cancelled.

## EXAMPLE

Add one timer with a simple callback that changes a boolean.

        void handler (int timer_id_, void *arg_)
        {
            (void) timer_id_; //  Stop 'unused' compiler warnings
            *((bool *) arg_) = true;
        }

        ...

        void *timers = zmq_timers_new ();
        assert (timers);

        bool timer_invoked = false;

        const unsigned long full_timeout = 100;

        int timer_id =
          zmq_timers_add (timers, full_timeout, handler, &timer_invoked);
        assert (timer_id);

        //  Timer should not have been invoked yet
        int rc = zmq_timers_execute (timers);
        assert (rc == 0);

        //  Wait half the time and check again
        long timeout = zmq_timers_timeout (timers);
        assert (rc != -1);
        msleep (timeout / 2);
        rc = zmq_timers_execute (timers);
        assert (rc == 0);

        // Wait until the end
        rc = msleep (zmq_timers_timeout (timers));
        assert (rc == 0);
        assert (timer_invoked);

        rc = zmq_timers_destroy (&timers);
        assert (rc == 0);

## SEE ALSO

zmq(7)

## AUTHORS

This page was written by the ØMQ community. To make a change please read the ØMQ Contribution Policy at http://www.zeromq.org/docs:contributing.