I'm thoroughly confused and increasingly desperate. *All* of the threads in my application periodically are blocked for 30-50 ms pretty regularly, about every 150 ms.
I'm processing a bunch of data via NSOperations running in a couple of "serial" (maxConcurrentOperationCount = 1) NSOperationQueues. Each of the operations is itself synchronous (overriding -main). Everything works as expected. For performance reasons, I want to move one of the operation types to being asynchronous and eventually allow two concurrent operations. So to start with, I took the synchronous code in -main, moved it into -start, and added the appropriate KVO notifications for isExecuting, isFinished, and implemented the right accessors etc. So effectively the operation says it's asynchronous, but all of its work is actually done in -start, followed by notifying it's finished. The work is all done correctly, but I noticed it took significantly longer to complete. Thankfully I have a nifty bit of debugging code which tracks the start and ends of each of these operations and visualizes them, and this is what I noticed: http://www.sethwillits.com/temp/upshot/upshot_yJutoKqY.png At very regular intervals everything takes longer. First I thought it maybe didn't like my semi-async op, so I made it truly async, and it behaved exactly the same. To make a long story short, I looked at this a few different ways in Instruments, and have confirmed that what's actually happening is *every thread is blocked* for those 30-50ms, and then it just wakes up and everything continues. The threads are literally all in "Blocked" states. I can't figure out *why* everything is blocked. I can't figure out why simply making the NSOperation asynchronous would have this crazy effect. It's 100% reproducible. For what it's worth, this one particular operation is doing some Metal rendering, and that operation is blocked during a call to -waitUntilCompleted. Which yes, sound suspicious, but is exactly what's happening in the very-explicitly-synchronous version of the operation, and it takes 10x less time. I am pretty certain this has nothing to do with the Metal rendering itself, and has more to do with something confusing the dispatch manager and every thread is being blocked. Can anyone think of what I should look for to figure out *why* they're blocked? Looking at the system calls in the Instruments trace timeline just isn't telling *me* anything. -- Seth Willits _______________________________________________ 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
