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Bug 2764

Summary: Timer is not rescheduled with the returned interval
Product: SDL Reporter: afwlehmann
Component: timerAssignee: Sam Lantinga <slouken>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 CC: afwlehmann, philipp.wiesemann
Version: 2.0.3   
Hardware: x86_64   
OS: Linux   

Description afwlehmann 2014-10-23 13:51:44 UTC 
According to the API documentation, a timer callback is always called with the current interval which should correspond to the return value from the previous call. Instead, the implementation is always using the same interval:

            /* We're going to do something with this timer */
            data->timers = current->next;

            if (current->canceled) {
                interval = 0;
            } else {
                interval = current->callback(current->interval, current->param);
            }

            if (interval > 0) {
                /* Reschedule this timer */
                current->scheduled = tick + interval;
                SDL_AddTimerInternal(data, current);
                ...
Comment 1 afwlehmann 2014-10-23 13:55:11 UTC 
Err, seems I made a mistake. It actually gets updated. Please close this bug.
Comment 2 Philipp Wiesemann 2014-12-12 19:31:04 UTC 
Resolved as invalid because it is no bug. See previous comments.
Comment 3 afwlehmann 2015-03-19 16:36:46 UTC 
Sorry for re-opening, but it turns out that the current interval is indeed not updated. I've just checked the source code of the 2.0.3 release again:

   163	    if (current->canceled) {
   164	        interval = 0;
   165	    } else {
   166	        interval = current->callback(current->interval, current->param);
   167	    }
   168	
   169	    if (interval > 0) {
   170	        /* Reschedule this timer */
   171	        current->interval = interval; // <-- this line is missing
   172	        current->scheduled = tick + interval;
   173	        SDL_AddTimerInternal(data, current);
   174	    } else {

According to the documentation: "The callback function is passed the current timer interval and the user supplied parameter from the SDL_AddTimer() call and returns the next timer interval. If the returned value from the callback is 0, the timer is canceled." 

If I understand the text correctly, then the current interval should in fact be updated according to the returned value. Otherwise there would be a discrepancy between the next time for which the timer is actually re-scheduled and the value that's passed to the callback once the timer fires again.

This could be fixed by adding line #171.
Comment 4 Sam Lantinga 2017-08-14 04:49:02 UTC 
Good point. This is fixed, thanks!
https://hg.libsdl.org/SDL/rev/37f4d29e155d