iOS 9 performance issues

[karmeye]

I got major performance degradation on iOS 9 compared to iOS 8. I suspect it's related to these radars and this method:

[NSObject addObserver:forKeyPath:options:context:]

• https://openradar.appspot.com/22718949
• https://openradar.appspot.com/22718754

Anyone else who can relate?
I notice it mostly when loading / reloading collection views, which means signals are created and observers added for views, view models and models related to the cells.

[joshaber]

Yup, this is a problem for us too. Unclear at this point how we can mitigate it.

[neilpa]

facebookarchive/KVOController#72 has a disturbing graph of the problem

[karmeye]

@neilpa Ouch, that's looks really bad.

addObserver is pretty much the heart of RAC isn't it?
Guess we're dependent on a fix from Apple. Even if we can somehow mitigate it, its not good enough if its not around O(1).

I'll go dupe these radars.

[neilpa]

My guess is they "fixed" the dealloc races that existed in KVO prior to iOS9. Working around those races is the main reason for KVOController. There's numerous past issues in this repo that touch on the problem as well.

[mdiep]

This was part of the motivation for #2334.

[neilpa]

Sadly, RACCommand is likely only a small portion of the general RACObserve usage across an app.

[karmeye]

Apparently many KVO issues was fixed.

But this issue has now been "observed" :) No need to dupe more radars:

https://twitter.com/Catfish_Man/status/644928403402018820
https://twitter.com/steipete/status/644903661626331141