Using native plugin with callbacks in editor (OS X)

Question

I have a native plugin that has callbacks back to the C# code. This is how the callbacks are setup:

C# Side (Unity):

 public delegate void Callback(int value);
 
 [DllImport("NativePlugin")]
 public static extern void setup_callback(Callback callback);
 
 [MonoPInvokeCallback(typeof(Callback))]
 private static void OnCallback(int value)
 {
     Debug.Log("Callback called with value: " + value);
 }
 
 void Start()
 {
     setup_callback(OnCallback);
 }

The Objective-C side (with C wrapper so you'd be able to call it from C#):

 typedef void(*Callback)(int);
 
 Callback _callback = NULL;
 
 void setup_callback(Callback callback)
 {
     _callback = callback;
 }
 
 void on_something_happened(int value)
 {
     if(_callback)
         _callback(value);
 }

Now, most of the time the above code works ok, and I receive the correct values in Unity. But sometimes when I make changes to any one of my C# scripts, Unity crashes with this:

 Exception Type: EXC_BAD_ACCESS (SIGABRT)
 Exception Codes: KERN_INVALID_ADDRESS at 0x00000000ffffffa9
 Exception Note: EXC_CORPSE_NOTIFY

Looking at Unity's Editor logs I found out that when I make changes to a C# script it recompiles Assembly-CSharp.dll and reloads it togheter with some other C# assemblies. So that made me think that this might cause the pointer saved in the native plugin to now point to an invalid address (because Assembly-CSharp.dll is now probably in a different address space). Note that it does not happen every time the dll gets reloaded, is it possible that it gets reloaded to the exact same address space sometimes?

Can I get an event from Unity when the editor reloads the DLL and then re-register the callbacks (assuming that this is the real problem)? Is this even the correct way to setup a callback from native code?

Answer 1

Best Answer

Answer by Untrade · Mar 04, 2017 at 03:12 AM

I ended up using LockReloadAssemblies https://docs.unity3d.com/ScriptReference/EditorApplication.LockReloadAssemblies.html

It let's you prevent Unity from reloading until you call UnlockReloadAssemblies. I just created a new script:

     void Awake()
     {
         //Prevent editor from reloading dlls files during the gameplay
         #if UNITY_EDITOR
         UnityEditor.EditorApplication.LockReloadAssemblies();
         #endif
     }

     void OnApplicationQuit()
     {
         //Prevent editor from reloading dlls files during the gameplay
          #if UNITY_EDITOR
         UnityEditor.EditorApplication.UnlockReloadAssemblies();
         #endif
     }

And put it on some object in the scene.

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Answer 2

Answer by ETLang · Mar 05, 2017 at 03:39 PM

For anyone else with a similar issue, another solution that might work for you is documented here:

http://answers.unity3d.com/questions/704066/callback-before-unity-reloads-editor-assemblies.html

In the code below, Unity will call OnDisable immediately before unloading the assembly and performing a recompile.

  [InitializeOnLoad]
  internal sealed class MyScriptableFriend : ScriptableObject {
      static MyScriptableFriend() { s_Instance = CreateInstance<MyScriptableFriend>(); }
      private static MyScriptableFriend s_Instance;

      private void OnDisable() {
          // Incoming recompile... save yourself!
      }
  }

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Using native plugin with callbacks in editor (OS X)

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