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. -- Greg Parker gpar...@apple.com Runtime Wrangler _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
