Re: Observing Time
Re: Observing Time
- Subject: Re: Observing Time
- From: email@hidden
- Date: Fri, 26 Jul 2013 13:37:42 +0900
On Jul 26, 2013, at 12:09 PM, Ken Thomases <email@hidden> wrote:
> On Jul 25, 2013, at 9:26 PM, email@hidden wrote:
>
>> Yep, I know of these, but this is tied to the run loop and timers on the runloop can be delayed.
>> The reason I went with dispatch_timer is because it can be done with its own thread and if I understand correctly, frees it from the runloop...
>>
>> _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,
>> dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0UL));
>> dispatch_source_set_timer(_timer, dispatch_walltime(NULL, 0),
>> (unsigned)(delayInSeconds * NSEC_PER_SEC), 0);
>> dispatch_source_set_event_handler(_timer, ^{
>> // Get updated time here.
>> dispatch_async(dispatch_get_main_queue(), ^{
>> // Talk back to main thread here.
>> });
>> });
>
> Since you're updating the GUI, you're tied to the responsiveness of the main thread's run loop, anyway. The dispatch to the main queue in the code above is conceptually similar to having a timer fire on the main thread's run loop.
>
> Also, the above code doesn't adjust the timer to fire on the second as Rick suggested. You're asking it to fire every so many seconds (delayInSeconds) but you aren't specifying when during the second to fire. Rather than passing 0 as the second parameter of dispatch_walltime(), you should compute an adjustment to try to get close to a whole second. Since dispatch_walltime() uses gettimeofday() when you pass NULL for the first parameter, I'd use that same call to fill in a timeval structure and then pass NSEC_PER_SEC - (tp.tv_usec * NSEC_PER_USEC) as the second parameter.
>
> Regards,
> Ken
>
Thanks Ken, no I hadn't yet bothered to do this, as dispatch_walltime() was initially close enough to work on the other bits of the app.
It would make a difference to reduce some lag.
What is the part in the second parameter your are doing there…
> NSEC_PER_SEC - (tp.tv_usec * NSEC_PER_USEC)
Looks like something to adust it but what is tp.tv_usec ?
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