Right now when an image node enters preload state, we kick off an image request with the default priority. Then when it enters display state, we change the priority to "imminent" which is mapped to the default priority as well. This means that requests from preload and display nodes have the same priority and are put to the same pool. The right behavior would be that preload requests should have a lower priority from the beginning.
Another problem is that, due to the execution order of -didEnter(Preload|Display|Visible)State calls, a node may kick off a low priority request when it enters preload state even though it knows that it's also visible. By the time -didEnterVisibleState is called, the low priority request may have already been consumed and the download/data task won't pick up the new higher priority, or some work needs to be done to move it to another queue. A better behavior would be to always use the current interface state to determine the priority. This means that visible nodes will kick off high priority requests as soon as -didEnterPreloadState is called.
The last (and smaller) issue is that a node marks its request as preload/low priority as soon as it exits visible state. I'd argue that this is too agressive. It may be reasonble for nodes in the trailing direction. Even so, we already handle this case by (almost always) have smaller trailing buffers. So this diff makes sure that nodes that exited visible state will have imminent/default priority if they remain in the display range.
All of these new behaviors are wrapped in an experiment and will be tested carefully before being rolled out.
* Add imports
* Fix build failure
* Encapsulate common logics into methods
* Address comments
* Add an experimental flag to use native dispatch_apply instead of our core count * 2 approach. This has shown performance wins in some profiling.
* Add in other places
* Add experiment to skip waiting until all updates of collection/table view are committed in -accessibilityElements
The wait was introduced in #1217 which blocks the main thread until updates are proccessed. We suspect this causes perf regressions accross the app and need to confirm this via an experiment.
* Add option to skip default behavior of ASCellLayoutMode
* Fix unit test
* Fix unit test in another way
* Remove import
* Minor change
* Add ASCellLayoutModeSyncForSmallContent
* Update unit tests
* Remove unnecessary change
* Remove unnecessary changes
This is a follow up on #1136. Our experiment results show that clearing data frequently is the cause of our #1 crash. @maicki and I believe that this is because if the collection view is being used, silently clearing its data without notifying the backing UICollectionView can put it out-of-sync and causes mayhem next time the collection view processes a batch update. If you look at the stack trace closely, you'll notice that the crash doesn't occur on the same run loop that clearData is called. This made it extremely tricky to investigate and identify the root cause.
Another interesting question would be whether or not we want to clear the data during deallocation at all, since the data will be cleared out soon anyway.
* Add an experimental framesetter cache in ASTextNode2, and stop keeping framesetters around
* Update configuration schema
* Fix imports
* Fix import again and remove set statement
* Fork dealloc queue in an experiment
* Fix and put back
* Use the right selector
* Go simpler
* Clarify name
* Type inference
* Use CFTypeRefs like a boss
* Improve comments
* License header
* Introduce ASRecursiveUnfairLock and tests
* Document it and put underscores to scare people away
* Increment changelog
* Integrate it with ASDN::Mutex behind experiment
* Rename the experiment
* Love these license headers oh so much
* Move internal header because we have to
* Address Jon's feedback
* Update the dangerfile
* Make a trivial change to test new dangerfile
* Try out the new value with another trivial change
* Add a configuration API to make a unified place for pulling config from clients safely
* Specify properties for delegate
* Finish removing text experiment global enable
* Generate the config file
* Clean up configuration to fix tests
* Work on making it serializable
* Finish it up
* Fix example code
* Update sample project
* Clean up a few things
* Align with new project order
* Make it faster and update license header
* Add an option to specify your config at compile time
* Update another license header
* Add a version field, and bring interface state coalescing into configuration
* Update CA queue code
* Update CATransactionQueue tests
* Turn transaction queue on by default (for now, see comment)
* Update the tests
* Update the tests AGAIN
* Remove unused ordered set
