On Unity, compiling the Android version to il2cpp causes an ExecutionEngineException at runtime

[Giacom]

My code is working fine on Android, with Mono, and on iOS with il2cpp but I wanted to try compiling my Unity game on Android with il2cpp, as it is now supported, but I have encountered an error which causes the UnityMainThreadDispatcher to be null.

In my GameController object I have a script which attaches the UnityInitialiser to itself, as instructed:

UnityInitializer.AttachToGameObject(gameObject);

Compiling this and running it will cause this exception to occur:

I/Unity   ( 7756): (Filename: ./artifacts/generated/Android/runtime/UnityEngineDebugBindings.gen.cpp Line: 45)
I/Unity   ( 7756): 
I/Unity   ( 7756): ExecutionEngineException: Attempting to call method 'UnityEngine.AndroidJavaObject::Get' for which no ahead of time (AOT) code was generated.
I/Unity   ( 7756): 
I/Unity   ( 7756): Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.

Which disrupts the initialisation and UnityMainThreadDispatcher is not correctly added as a component to my GameController. (It will be null if I attempt to retrieve it).
Searching about this error lead me to this (CTRL+F "ExecutionEngineException") if that helps.

It is hard for me to debug this more as I am just using the provided DLLs on a non-Windows machine. I am guessing this is just a case of Android il2cpp not being supported, if that is the case then I hope it will be supported in the future.

[sstevenkang]

Hi. I am confused to ask what the request is. Could you explain a bit more how the SDK is involved in your project and detail specific feature requests if any? From the code snippets it seems like a general C# and and Unity issue.

[Giacom]

Yeah sure. I use the SDK for Cognito Sync for online save data storage in Unity.

The Unity Engine had recently released il2cpp for android, allowing developers to natively compile their game from C# to C++. The SDK doesn't seem to work with it, even though it works for il2cpp on iOS.

[sstevenkang]

This seems like an issue with il2cpp than the SDK itself. Unity forum/support would be a more appropriate place to ask this question. Feel free to reopen, if you find issues with the SDK.

[EulBart]

Hi,

I'm not quite sure this is an IL2CPP issue.
We have a similar problem in our project:

Android log extract:

 ExecutionEngineException: Attempting to call method 'UnityEngine.AndroidJavaObject::Get' for which no ahead of time (AOT) code was generated.
   at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0 
   at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in <filename unknown>:0 
   at Amazon.Util.Internal.AndroidInterop.GetJavaField[T] (System.Object androidJavaObject, System.String methodName) [0x00000] in <filename unknown>:0 
   at Amazon.Util.Internal.AmazonHookedPlatformInfo.Init () [0x00000] in <filename unknown>:0 
   at Amazon.Util.Internal.AmazonHookedPlatformInfo.get_Instance () [0x00000] in <filename unknown>:0 
   at Amazon.UnityInitializer.Awake () [0x00000] in <filename unknown>:0 
   at UnityEngine.GameObject.AddComponent[T] () [0x00000] in <filename unknown>:0 

Let’s have a look at AmazonHookedPlatformInfo.Init:

public void Init()
{
  if (InternalSDKUtils.IsAndroid)
  {
    ...
    object androidJavaObject2 = AndroidInterop.CallMethod(androidJavaObject1, "getPackageInfo", (object) this.PackageName, (object) 0);
    ...
    this.VersionCode = Convert.ToString(AndroidInterop.GetJavaField<int>(androidJavaObject2, "versionCode"));

And AndroidInterop’s GetJavaField:

public static T GetJavaField<T>(object androidJavaObject, string methodName)
{
  return (T) ((IEnumerable<MethodInfo>) androidJavaObject.GetType().GetMethods()).Where<MethodInfo>((Func<MethodInfo, bool>) (x => x.Name == "Get")).First<MethodInfo>((Func<MethodInfo, bool>) (x => x.ContainsGenericParameters)).MakeGenericMethod(typeof (T)).Invoke(androidJavaObject, new object[1]
  {
    (object) methodName
  });
}

It seems we are in the case described in https://docs.unity3d.com/Manual/ScriptingRestrictions.html#AOT with class AOTProblemExample.

The suggested fix is to force the compiler to generate the code by calling the wanted function with explicit type. Unfortunately, It's not particularly obvious in our case for what Type a Get should be generated AOT, and I’m not sure (not tried it yet) if it can be done outside of AWSSDK.Core.dll

It’s worth noting that the iOS version doesn’t do that kind of trickery and works in IL2CPP, and that AWS should make sure the sdk works on android/IL2CPP

Cheers!

[nzmkey]

Here is a workaround that I use works for my project.

Put below method in one of your GameObject, preferably with one that loads quite early on and in every scene.

	#if UNITY_ANDROID
	public void UsedOnlyForAOTCodeGeneration() {
		//Bug reported on github https://github.com/aws/aws-sdk-net/issues/477
		//IL2CPP restrictions: https://docs.unity3d.com/Manual/ScriptingRestrictions.html
		//Inspired workaround: https://docs.unity3d.com/ScriptReference/AndroidJavaObject.Get.html

		AndroidJavaObject jo = new AndroidJavaObject("android.os.Message");
		int valueString = jo.Get<int>("what");
	}
	#endif

[karthiksaligrama]

Reopening as we want to fix this in the sdk

[EulBart]

Thanks, it worked!

[Giacom]

Thanks, the workaround is working for me.

[Jotamaza]

Working for me too. Thanks!

[felipeengelyump]

The workaround also work for me too. (It still happening in the latest SDK 3.3.158.0)
Thanks.

[Nomy1]

Workaround valid still in Unity 2017.1.1f1 in SDK v3.3.1730

[pjc0247]

2yrs passed since reporting, never fixed.