Re: Carbon is C++?
Re: Carbon is C++?
- Subject: Re: Carbon is C++?
- From: Ken Ferry <email@hidden>
- Date: Mon, 19 Apr 2010 00:23:14 -0700
On Mon, Mar 1, 2010 at 4:03 AM, Greg Parker <email@hidden> wrote:
> On Feb 28, 2010, at 7:24 PM, Erik Buck wrote:
> > I disagree. I have written very low latency device drivers in
> Objective-C. Why do you think Objective-C has too much "latency" for audio?
> When properly used, Objective-C programs are no more likely to be preempted
> than any other kind of program. Message dispatch generally has constant
> time and is only 2.5 times the cost of a C function call. There aren't many
> function calls or messages sent in audio processing anyway. Signal
> processing routines tend to be long loops. Objective-C _IS_ C which means
> it is likely usable in any situation where C is usable.
>
> Message dispatch is generally fast. For many real-time-ish purposes that's
> good enough. But occasionally message dispatch (1) takes much longer, and
> (2) acquires locks. For some real-time-ish purposes, this sort of surprise
> is fatal when it occurs. Since there's no way for the program to control
> when dispatch is fast and when it is slow, clients with sufficiently tight
> "no surprises" requirements should avoid it altogether. If your requirements
> are demanding enough that you can't call malloc(), then you probably can't
> call objc_msgSend() either.
>
> It's the locks that kill. With care, a real-time-ish thread can pretty much
> solve problems of page faults and scheduling and the like. But the moment
> you take a lock, you're at the mercy of some other thread that may not be so
> careful.
>
> Audio clients tend to be the most paranoid about this on Mac OS X. They're
> the closest to truly-real-time requirements that I see, with good reason: if
> your audio playback skips, ever, you probably just lost a customer.
>
Just for those who haven't already noticed this interesting detail, audio is
more constrained than video. If your movie skips a frame? You probably
cannot tell. If your audio drops? Urgh!
-Ken
>
>
> --
> Greg Parker email@hidden Runtime Wrangler
>
>
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