On Jun 4, 2014, at 2:24 PM, Alex Zavatone wrote: > As it turned out, my coworker had created a dispatch_async thread to start > processing the video and within it, started at a framecount of 0, incremented > it within a while(true) loop and grabbed the frame every time there was a new > framePixelbuffer. All within the while(true) loop. > > Well, OF COURSE memory's not going to be released and of course it's not a > leak, but here's where I need some help understanding how to explain this and > why this approach is a bad idea within Cocoa.
> But within the convert to grayscale routine in the external lib where we > create a CGContextRef and later issue a CFRelease on it, memory is allocated > within CGContextDrawImage. However it builds up for every frame grabbed and > is not released until the while loop is exited. This is where we lose 3.52 > MB each pass, but it's not really lost since it's allocated but can't be > released by ARC since it's within a while loop. > My first inclination is, "DUDE. You silly rabbit! You created an async > process, then wrapped the whole video processing section in a while loop and > you expected memory to get released by ARC? ARGH! WHY? Bad codemonkey, bad!" > This is where I'm seeking a better explanation than I can give. Does anyone > have a better explanation for "this is why we never do things this way - even > though you can wrap time consuming operations in repeats and whiles, it > doesn't mean that you should and expect ARC to work"? You have a misconception as illustrated in the above quotes. I think you think of ARC as a garbage collector that needs idle time or for execution to return to the frameworks in order to work. It is not and does not. For the most part, ARC just inserts retains and releases just as you would in manual retain-release mode if you were extremely careful. (The exception is weak pointers which get nil-ed out when the pointed-to object is deallocated. There's also the returned-autoreleased object optimization that you couldn't achieve on your own, but that's not relevant here.) It sounds to me like this is just the classic sort of peak memory usage you would get with autoreleased objects with manual retain-release code if you don't drain the autorelease pool in your loops. Regards, Ken _______________________________________________ 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: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
