On Apr 30, 2015, at 23:46:53, Graham Cox <graham....@bigpond.com> wrote: > > Well, here’s a huge clue. > > I use NSOperationQueue with the default -maxConcurrentOperationCount which is > NSOperationQueueDefaultMaxConcurrentOperationCount, i.e. let the system > figure it out. That appears to create 4 threads for my particular machine, > which has a Core i3 (2 cores) CPU. My peak CPU usage is reported as 418%. I’m > not sure how it achieves that from a dual core CPU, but one would assume that > Apple know what they’re doing [/irony]. > > So, I tried setting that NSOperationQueue property directly to something > less, and lo-and-behold, the problem goes away with a limit of 3 or less. A > limit of 4 produces the same problem. > > This appears to suggest that if you let NSOperationQueue take all of the CPU > resources, the main thread is left high and dry if it needs to create another > thread, e.g. for an XPC call. Maybe this is intentional, but it’s a bloody > nuisance - surely a better outcome for the “let the system figure it out” > would be to say “whatever the max is -1”, so it leaves some capacity in hand > for the main thread. The way it works now might give slightly better > performance overall, but it causes an app to hang unresponsively for some > indeterminate period in some cases. Of course I can set the limit to 3 > myself, but if I found myself on a 16 core machine, that's very suboptimal. > > I’m tempted to report this as a bug, but I’d like to hear what others think > about this first.
I’ve run into this too, where letting the OS figure out how many operations to queue at once doesn’t always work like a human wants it to work. I ended up doing what you did - leave one for the main thread. NSOperationQueueDefaultMaxConcurrentOperationCount really isn’t smart enough, or they need to add another constant NSOperationQueueDefaultMaxConcurrentButDontBeAJerkOperationCount. -- Steve Mills Drummer, Mac geek _______________________________________________ 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
