FacebookSDK generates excessive permanent GC memory

[Razenpok]

Checklist

• [x] I've updated to the latest released version of the SDK
• [x] I've searched for existing GitHub issues
• [x] I've looked for existing answers on Stack Overflow, the Facebook Developer Community Forum and the Facebook Developers Group
• [x] I've read the Code of Conduct
• [x] This issue is not security related and can safely be disclosed publicly on GitHub

Environment

Describe your dev environment here, giving as many details as possible. If you have them, make sure to include:

• Unity Editor Version: 2021.3.25f1
• Unity SDK Version: 15.1.0
• Installation Platform & Verison: Any platform

Code Samples & Details

As per Unity docs

Mono and IL2CPP internally cache all C# reflection (System.Reflection) objects and by design, Unity doesn’t garbage collect them. The result of this behavior is that the garbage collector continuously scans the cached C# reflection objects during the lifetime of your application, which causes unnecessary and potentially significant garbage collector overhead.

To minimize the garbage collector overhead, avoid methods such as Assembly.GetTypes and Type.GetMethods() in your application, which create a lot of C# reflection objects at runtime. Instead, you should scan assemblies in the Editor for the required data and serialize and/or codegen it for use at runtime.

FacebookSDK goes through assemblies one by one during the search for IAPButton class from UnityEngine.Purchasing:

https://github.com/facebook/facebook-sdk-for-unity/blob/b8db43b2b6006e2cf698cf42cba8205d94c71472/Facebook.Unity/Utils/CodelessIAPAutoLog.cs#L103

Again, the generated GC memory from Assembly.GetTypes() is permanent, as it won't ever be collected.

This issue could be fixed with the following steps:

1. Add a method for a developer to disable the automatic invocation of addListenerToIAPButtons completely, as not all projects use codeless IAP buttons
2. Optimize reflection code:

private static System.Type FindTypeInAssemblies(string assemblyName, string typeName, string nameSpace)
{
    var assemblies = System.AppDomain.CurrentDomain.GetAssemblies();
    for (int i = 0; i < assemblies.Length; i++)
    {
        var assembly = assemblies[i];
        if (assembly.GetName().Name != assemblyName)
        {
            continue;
        }

        var type = assembly.GetType(nameSpace + "." + typeName);
        if (type != null && typeName == type.Name && nameSpace == type.Namespace)
        {
            return type;
        }
    }

    return null;
}

[MarkZaytsev]

I can confirm this. It became a problem in our project. It causes 1 MB allocation by doing 16500 method calls on every scene load. And we don't even use CodelessIAP.

[kocburak]

If you are not using CodelessIAP, Just remove it. Why bother optimize? If something goes wrong just return null. What could possible go worng :D