Garbage collection of App, Auth, Instance ID, Realtime Database, Storage garbage collection can crash.

[mgrogin]

My app occasionally crashing since upgrading to firebase 5.1.1
The only indication of the source of the problem that I have is in this crash information from xcode from users using IOS 11.4.1
based on the stack it looks like the problem is firebase database

any ideas?

Crash information:

This is what the pod file looks like:

source 'https://github.com/CocoaPods/Specs.git'
source 'https://github.com/CocoaPods/Specs'
platform :ios, '8.2'

target 'Unity-iPhone' do
pod 'Firebase/Analytics', '5.3.0'
pod 'Firebase/Auth', '5.3.0'
pod 'Firebase/Core', '5.3.0'
pod 'Firebase/Database', '5.3.0'
pod 'Firebase/DynamicLinks', '5.3.0'
pod 'Firebase/Messaging', '5.3.0'
pod 'Firebase/RemoteConfig', '5.3.0'
pod 'FirebaseInstanceID', '3.1.1'
pod 'GoogleMobileAdsMediationUnity', '2.2.1.0'
pod 'Google-Mobile-Ads-SDK', '~> 7.0'
end

[chkuang-g]

We are trying to pinpoint the potential causes. May I ask some questions regarding to the crashes?

• Which Firebase SDK version were you using before you upgraded to 5.1.1?
• Do you know which Firebase Database API causes this crash?
• In your C# code, did you hold a reference of Firebase.Database.FirebaseDatabase somehere?
  Ex. Firebase.Database.FirebaseDatabase database = Firebase.Database.FirebaseDatabase.DefaultInstance;
  Or do you always use FirebaseDatabase.DefaultInstance directly? It would be great if you can share a snippet of the way you call Database API.
• Do you have multiple database instances?

Thank you,
Shawn

[mgrogin]

Hi Shawn,

• I was using version 4.5.2 (I reverted my code back to that version for now)
• I don't know which Firebase Database API causes this crash - I'm only writing to the database (I use Anonymous authentication [auth.SignInAnonymouslyAsync().ContinueWith(task => .....] )
• I have one function with this line:
  DatabaseReference databaseRef = FirebaseDatabase.DefaultInstance.RootReference;
  so once you exit that function theres no reference to it
  the usage I have in that function is
  databaseRef.Child("users").Child(firebaseAuthUserId).SetRawJsonValueAsync(json);
• I don't have multiple database instances

This is the pod file I reverted to:

source 'https://github.com/CocoaPods/Specs.git'
source 'https://github.com/CocoaPods/Specs'
platform :ios, '8.2'

target 'Unity-iPhone' do
pod 'Firebase/Analytics', '4.11.0'
pod 'Firebase/Auth', '4.11.0'
pod 'Firebase/Core', '4.11.0'
pod 'Firebase/Messaging', '4.11.0'
pod 'Firebase/RemoteConfig', '4.11.0'
pod 'GoogleMobileAdsMediationUnity', '2.2.1.0'
pod 'Google-Mobile-Ads-SDK', '~> 7.0'
end

Thanks for looking in to this @chkuang-g !!

[chkuang-g]

Thank you for the information.

We did have bug that FirebaseDatabase.DefaultInstance gets garbage-collected once nothing is referencing it. However, I think we've fixed that already.

We will investigate if this is still a potential issue. At the meantime, what you can do is to keep a reference of FirebaseDatabase.DefaultInstance somewhere in a script that lives way longer than the scope of a function, AFTER FirebaseApp.CheckAndFixDependenciesAsync() is done. For example, in a GameObject that lives as long as the game is on. Keeping a reference of DatabaseReference will do as well. And please let us know if this fixes the occasion crashes.

Also, I'd like to collect a bit more information, just in case this only happens to certain configuration.

• What is your Unity version?
• What is your .NET version? (See your "Scripting Runtime Version" and "Api Compatibility" settings in your Player Settings)
• What is your Scripting Backend? (You can find this in your Player Settings as well)
• What is your Xcode version?

Thank you,
Shawn

[mgrogin]

This is my Configuration:

• Unity version 5.6.5f1
• API Compatibility Level .NET 2.0
• Scripting Backend IL2CPP
• Xcode Version 9.4.1 (9F2000)

[gldio]

my app crashes as well. i got this errors. but It started to crash less after updating.
xcode 9.3 (9e145)
firebase sdk 5.2.1
unity 2018.2.6f1
.net 2.0
backend IL2CPP

[chkuang-g]

Hi @gldio,

We are gradually pushing out fixes for GC related crashes. However, it is still on-going.
At the meantime, please try to keep a reference of FirebaseDatabase to prevent it from being garbage-collected.

Sorry for the inconvenience.
Shawn

[stewartmiles]

To summarize, @chkuang-g discovered a general issue with garbage collection across the SDK. If you create an object release the reference then create effectively the same object (e.g the same database reference) again it's possible for the SDK to end up with two C# objects, one in the garbage collection queue and the other held by the application, pointing at the same C++ object. When the object in the garbage collection queue is finally deleted, it also deletes the C++ object and we end up with a C# object referencing a stale pointer to a C++ object. @chkuang-g is working on a fix at the moment.

In the meantime, you should keep references around to objects that are reused on a regular basis in your application.

[stewartmiles]

@chkuang-g I'm pretty sure #200 is the same thing.

[asger60]

I think I have this issue aswell.
The Unity editor keeps crashing on me whenever i try to do firebase stuff.
This happens whenever i enter build mode about 50% of the time.
Could you please explain how I should keep an reference to the database object?

[asger60]

I've changed my code to run in a editor window, but the crashes prevail. It seems to happen whenever Unity has recompiled the code and I try to fetch data.

[chkuang-g]

@asger60 This issue was on iOS. Yours seems like a different one.
Could you open a different issue and detailed the environment you had (ex. Unity version, Firebase version)

Also, you can fetch editor log here.
https://docs.unity3d.com/Manual/LogFiles.html
It would be helpful if you can find some log related to your crash in the log and include that in the description.

Thank you,
Shawn