[Bug] iOS 17 + iPhone 15 Pro - Random Crashes

[dganzella]

Describe the bug

iPhone 15 Pro and 15 Pro Max on ios 17 will randomly crash when using ARKIT

To Reproduce
Steps to reproduce the behavior:
Use any arkit sample for little while, with iphone 15 pro on ios 17, then lock the phone and open it again multiple times

the iphone will crash eventually/randomly

Expected behavior
No random crashes

Actual behavior
Crashes

Smartphone (please complete the following information):

• Device: Iphone 15 PRO, Iphone 15 PRO max
• OS: ios 17+
• 2023.1.10f
• ARFoundation version: 5.1.0

[dganzella]

PS. happens even with MT rendering off

[dganzella]

It seems it happens when coming back from the device being locked. It crashes right after opening the application again.

[dganzella]

seems I was able to elimate it. here is the thing:

I found this line of code inside ARKIT:

static readonly bool k_MultithreadedRenderingEnabled =
                k_RenderingThreadingMode is RenderingThreadingMode.MultiThreaded or RenderingThreadingMode.NativeGraphicsJobs;

so you have to disable both MultiThreaded and NativeGraphicsJobs in order to really disable multithreaded rendering.

previously, our app was with k_MultithreadedRenderingEnabled disabled but NativeGraphicsJobs enabled

disabling BOTH seem to have fixed the crashes

[andyb-unity]

Thanks @dganzella for this detailed report.

[dganzella]

hmmm @andyb-unity still crashing

even with MT rendering and graphics jobs OFF, but random this time

[dganzella]

I noticed that after updatign to 17.1 all the crashes went away

we have not had a single crash instance of 17.1. No crashes from the past 10 days

[NJMnm]

@dganzella
Did it work for you with k_MultithreadedRenderingEnabled/NativeGraphicsJobs on or both off?
Thanks ins advance!

[andyb-unity]

@dganzella interesting. I suspect that the iOS 17.1 "fix" may just change something about the thread scheduling that hides the underlying race condition. Our investigation so far has shown that the issue is in Unity's Metal texture implementation, and XR is working with the Graphics team to get them everything they need to implement a fix.

Edit: oh I misread your earlier post and thought that you had claimed that iOS 17.1 fixed the multithreaded rendering issues. As I noted here, we believe the multithreaded crash on lock/unlock is a Unity Graphics issue.

[dganzella]

@NJMnm I tested only with both k_MultithreadedRenderingEnabled/NativeGraphicsJobs off. Im kinda afraid to turn them on :(

[andyb-unity]

We have fixed one possible cause of this crash. This fix is in the following versions:

4.2.10
5.1.2 (release pending)
6.0.0 (release pending)

Review the ARKit changelog in these versions, should you choose to upgrade. The fix also requires specific minimum patch versions of Unity.

We are also investigating a similar report of this crash for scenes that use Occlusion, specifically. Our fix thus far has only touched the Camera subsystem.