(Android) Using coroutines when creating a child crashes the app if the component context is created using defaultComponentContext()

[YektaDev]

Hi. I just found out that in order to create a Decompose component context using the defaultComponentContext function, which uses lifecycle.EssentyLifecycleInterop.subscribe underneath, breaks the app (most likely because of its interaction with androidx.lifecycle), and the workaround is to either not use coroutines when creating a child or create the child in Dispatchers.Main. Otherwise the app crashes immediately with error logs similar to this (Replaced app package with com.company.app):

E/AndroidRuntime: FATAL EXCEPTION: DefaultDispatcher-worker-1
    Process: com.company.app, PID: 25237
    java.lang.IllegalStateException: Method addObserver must be called on the main thread
        at androidx.lifecycle.LifecycleRegistry.enforceMainThreadIfNeeded(LifecycleRegistry.java:323)
        at androidx.lifecycle.LifecycleRegistry.addObserver(LifecycleRegistry.java:178)
        at com.arkivanov.essenty.lifecycle.EssentyLifecycleInterop.subscribe(AndroidExt.kt:32)
        at com.arkivanov.decompose.lifecycle.MergedLifecycle.<init>(MergedLifecycle.kt:27)
        at com.arkivanov.decompose.lifecycle.MergedLifecycle.<init>(MergedLifecycle.kt:15)
        at com.arkivanov.decompose.router.stack.RouterEntryFactoryImpl.invoke(RouterEntryFactoryImpl.kt:26)
        at com.arkivanov.decompose.router.stack.RouterEntryFactory$DefaultImpls.invoke$default(RouterEntryFactory.kt:8)
        at com.arkivanov.decompose.router.stack.StackControllerImpl.navigate(StackControllerImpl.kt:39)
        at com.arkivanov.decompose.router.stack.ChildStackController.navigateActual(ChildStackController.kt:45)
        at com.arkivanov.decompose.router.stack.ChildStackController.access$navigateActual(ChildStackController.kt:14)
        at com.arkivanov.decompose.router.stack.ChildStackController$queue$1.invoke(ChildStackController.kt:26)
        at com.arkivanov.decompose.router.stack.ChildStackController$queue$1.invoke(ChildStackController.kt:26)
        at com.arkivanov.decompose.SerializedQueue.drain(SerializedQueue.kt:23)
        at com.arkivanov.decompose.SerializedQueue.offer(SerializedQueue.kt:17)
        at com.arkivanov.decompose.router.stack.ChildStackController$eventObserver$1.invoke(ChildStackController.kt:38)
        at com.arkivanov.decompose.router.stack.ChildStackController$eventObserver$1.invoke(ChildStackController.kt:38)
        at com.arkivanov.decompose.Relay$queue$1.invoke(Relay.kt:13)
        at com.arkivanov.decompose.Relay$queue$1.invoke(Relay.kt:12)
        at com.arkivanov.decompose.SerializedQueue.drain(SerializedQueue.kt:23)
        at com.arkivanov.decompose.SerializedQueue.offer(SerializedQueue.kt:17)
        at com.arkivanov.decompose.Relay.accept(Relay.kt:25)
        at com.arkivanov.decompose.router.stack.StackNavigationImpl.navigate(StackNavigationFactory.kt:18)
        at com.arkivanov.decompose.router.stack.StackNavigatorExtKt.push(StackNavigatorExt.kt:16)
        at com.arkivanov.decompose.router.stack.StackNavigatorExtKt.push$default(StackNavigatorExt.kt:15)
        at com.company.app.root.RootComponentImpl$createChild$createAuthScreen$1.invoke-bFv73x8(RootComponentImpl.kt:42)
        at com.company.app.root.RootComponentImpl$createChild$createAuthScreen$1.invoke(RootComponentImpl.kt:42)
        at com.company.app.authentication.AuthenticationScreenImpl$1.invokeSuspend(AuthenticationScreenImpl.kt:51)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
        at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
        at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:570)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:750)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:677)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:664)
    	Suppressed: kotlinx.coroutines.DiagnosticCoroutineContextException: [StandaloneCoroutine{Cancelling}@1089d7d, Dispatchers.Default]

MainActivity.kt:

import androidx.activity.compose.setContent
import androidx.appcompat.app.AppCompatActivity
import com.arkivanov.decompose.defaultComponentContext
// ...
import android.os.Bundle

internal val app = MyCustomApplicationStarterLogic()

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        app.init(AppInitData(this, defaultComponentContext()))
        setContent { ApplicationScreen(app.root) }
    }
}

Emulator: Pixel 4 XL API 25 (Android 7.1.1 Google APIs | x86)

Just wanted to report this (edge?) case.

[arkivanov]

The stack trace suggests that the navigation is performed on a background thread. The navigation must be always performed on the main thread. But without a reproducer code it's hard to say where is the mistake exactly.

[YektaDev]

What I did that caused the issue was simply pushing a configuration to my stack navigation inside a coroutine. I know this can be solved simply by adding a withContext(Dispatchers.Main) {...} inside the coroutine right before the navigation, but I just wanted to report this behavior for the sake of it 😃.

[arkivanov]

Thanks for reporting. This is expected, we have to explicitly switch to the main despatcher before navigating.

[bennysway]

I have the same problem but in compose desktop. Logs are as follows

Exception in thread "AWT-EventQueue-0" java.lang.IllegalStateException: Access from different threads is detected, must be on the main thread only.Current thread: AWT-EventQueue-0. First thread: DefaultDispatcher-worker-1.
	at com.arkivanov.decompose.AssertMainThreadKt.assertMainThread(AssertMainThread.kt:8)
	at com.arkivanov.decompose.value.MutableValueImpl$special$$inlined$observable$1.afterChange(Delegates.kt:71)
	at kotlin.properties.ObservableProperty.setValue(ObservableProperty.kt:41)
	at com.arkivanov.decompose.value.MutableValueImpl.setValue(MutableValueBuilder.kt:21)
	at com.arkivanov.decompose.router.children.ChildrenFactoryKt.children$onAfterNavigate(ChildrenFactory.kt:106)
	at com.arkivanov.decompose.router.children.ChildrenFactoryKt.access$children$onAfterNavigate(ChildrenFactory.kt:1)
	at com.arkivanov.decompose.router.children.ChildrenFactoryKt$children$eventObserver$1.invoke(ChildrenFactory.kt:124)
	at com.arkivanov.decompose.router.children.ChildrenFactoryKt$children$eventObserver$1.invoke(ChildrenFactory.kt:119)
	at com.arkivanov.decompose.Relay$queue$1.invoke(Relay.kt:13)
	at com.arkivanov.decompose.Relay$queue$1.invoke(Relay.kt:12)
	at com.arkivanov.decompose.SerializedQueue.drain(SerializedQueue.kt:23)
	at com.arkivanov.decompose.SerializedQueue.offer(SerializedQueue.kt:17)
	at com.arkivanov.decompose.Relay.accept(Relay.kt:25)
	at com.arkivanov.decompose.router.stack.DefaultStackNavigation.navigate(DefaultStackNavigation.kt:11)
	at com.arkivanov.decompose.router.stack.StackNavigatorExtKt.bringToFront(StackNavigatorExt.kt:82)
	at com.arkivanov.decompose.router.stack.StackNavigatorExtKt.bringToFront$default(StackNavigatorExt.kt:81)
	at component.app.AppRootComponentImpl.gotoWindow(AppRootComponentImpl.kt:102)
	at component.app.AppRootComponentImpl$child$1.invoke(AppRootComponentImpl.kt:52)
	at component.app.AppRootComponentImpl$child$1.invoke(AppRootComponentImpl.kt:51)
	at component.login.root.LoginRootComponentImpl.openDashboardWindow(LoginRootComponentImpl.kt:151)

...
CommonButton(
            modifier = Modifier
                .width(418.dp)
                .height(56.dp)
                .align(Alignment.End),
            onClick = {
                component?.openDashboardWindow()
            },
            text = "Go to Dashboard",
...

[YektaDev]

@bennysway This check that you're encountering is actually added in a recent version, here.
Switching to Dispatchers.Main or Dispatchers.Main.immediate is required in this case.

[arkivanov]

Yes, and also make sure that you create the root ComponentContext on the UI thread! See

Decompose/sample/app-desktop/src/jvmMain/kotlin/com/arkivanov/sample/app/Main.kt

Line 53 in fc7f226

runOnUiThread {

Reopening the issue to mention this in the docs.

[arkivanov]

Docs updated in 6b10c44.

[YektaDev]

Isn't the UI thread the thread in which the program executes by default before entering any coroutines, like in Android?

[arkivanov]

@YektaDev unfortunately no, the program starts on the main thread, and then Swing starts it's own UI thread. All event callbacks in Compose are called on the UI thread.