FirebaseAuth Java SDK - Hanging in GlobalScope.launch(Dispatchers.Main)

[meavydev]

I am using the firebase-kotlin-sdk (2.1.0) in my JVM API code and it uses the firebase-java-sdk for FirebaseAuth.
On signing in to Firebase their Java SDK is using a section of code inside a GlobalScope.launch(Dispatchers.Main) section which hangs under Kobweb.

If relevant, specify:

• OS: MacOS Sequoia 15.3.1
• Kobweb libs version: 0.20.3
• Kobweb CLI version: 0.9.18

---

The section failing in their FirebaseAuth class:

        private set(value) {
            if (field != value) {
                val prev = field
                field = value

                if (value == null) {
                    FirebasePlatform.firebasePlatform.clear(app.key)
                } else {
                    FirebasePlatform.firebasePlatform.store(app.key, jsonParser.encodeToString(FirebaseUserImpl.serializer(), value))
                }

                GlobalScope.launch(Dispatchers.Main) {
                    if (prev?.uid != value?.uid) {
                        authStateListeners.forEach { l -> l.onAuthStateChanged(this@FirebaseAuth) }
                    }

                    if (prev?.idToken != value?.idToken) {
                        val result = InternalTokenResult(value?.idToken)
                        for (listener in internalIdTokenListeners) {
                            Log.i("FirebaseAuth", "Calling onIdTokenChanged for ${value?.uid} on listener $listener")
                            listener.onIdTokenChanged(result)
                        }
                        for (listener in idTokenListeners) {
                            listener.onIdTokenChanged(this@FirebaseAuth)
                        }
                    }
                }
            }
        }

I am not sure if it's down to a Kobweb configuration issue on my side or just that their SDK shouldn't be using GlobalScope with Dispatchers.Main.

I have tried updating to kotlinx-coroutines-core-jvm 1.10.1.

I have raised issues in firebase-kotlin-sdk and firebase-java-sdk (the main issue).

Any ideas welcome.

[bitspittle]

I have no idea why they're using GlobalScope.launch(Main). That indeed seems like a very very bad idea. At the very least and they should have commented the heck out of it, because that is screaming anti-pattern to me. It's runBlocking essentially. I really don't like they created a coroutine whose lifecycle isn't managed -- they should have probably created something that would get cancelled if the auth instance was changed. And why use main...? 🤔

How did you confirm their code was hanging? Printing console output before and after you set it?

Meanwhile you should also test that GlobalScope.launch(Dispatchers.Main) works fine if you call it in your own code and basically do nothing. Just GlobalScope.launch(Dispatchers.Main) { println("hello") }. Please try this and let me know if it blocks for you

Otherwise, looks like they're just setting and triggering listeners. The only things I can imagine might block are the firebase platform calls or some bad blocking listener.

[meavydev]

I have been debugging using Kobweb JVM debugging in IntelliJ, so I could set breakpoints and step through their code... well and not when it hangs ;)
As a local hack, I am currently building the firebase-java-sdk locally and I have left all the GlobalScope.launch sections in their FirebaseAuth.kt code, but I have stripped out all the Dispatchers.Main references.
This has actually got me to the point where the FirebaseAuth is working and I can try and access FireStore, although that is failing with a permissions error, probably due to me locking down the DB too much (I think, although it could be FirebaseAuth still).

[bitspittle]

Oh, using a debugger, nice 😎

So what exactly was hanging? Just spinning up the global scope? Or one of the statements inside it?

[meavydev]

I think the lack of an implementation of Dispatchers.Main in a standard JVM, means the GlobalScope.launch fails, as setting a breakpoint in the launch code is never reached.
I'm guessing an internal exception in the Coroutine implementation.

[bitspittle]

Yes I've confirmed the issue is a missing Main coroutine dispatcher. I'm checking right now if I can add one to the Kobweb server.

[bitspittle]

The fix might be simple. Add a dependency on org.jetbrains.kotlinx:kotlinx-coroutines-swing and tell me if that solves it for you.

Even if you're not using Swing yourself -- it is a UI framework after all -- JVMs all include it as part of the package, and they provide useful scheduling functionality that coroutines take advantage of here.

For me, this looks like:

gradle/libs.versions.toml

kotlinx-coroutines = "1.10.1"

[libraries]
kotlinx-coroutines-core = { module = "org.jetbrains.kotlinx:kotlinx-coroutines-core", version.ref = "kotlinx-coroutines" }
kotlinx-coroutines-swing = { module = "org.jetbrains.kotlinx:kotlinx-coroutines-swing", version.ref = "kotlinx-coroutines" }

[bundles]
kotlinx-coroutines = ["kotlinx-coroutines-core", "kotlinx-coroutines-swing"]

site/build.gradle.kts

jvmMain.dependencies {
   implementation(libs.bundles.kotlinx.coroutines)
}

[meavydev]

I never thought to try Swing. I did try Android, but that didn't work of course ;)
Thanks, as that has fixed it :)

[bitspittle]

Thanks for the discussion! I learned some new things today about how the coroutine main dispatcher works.