Allow Dispatchers to be specified in collectAsState

[mr-thierry]

We are sometime seeing tests that fails with:

java.lang.IllegalStateException: The current thread must have a looper!

This seemed to be caused by Composition not happening on the main thread. This is the stacktrace:

java.lang.IllegalStateException: The current thread must have a looper!
	at android.view.Choreographer$1.initialValue(Choreographer.java:111)
	at android.view.Choreographer$1.initialValue(Choreographer.java:106)
	at java.lang.ThreadLocal.setInitialValue(ThreadLocal.java:180)
	at java.lang.ThreadLocal.get(ThreadLocal.java:170)
	at android.view.Choreographer.getInstance(Choreographer.java:296)
	at androidx.compose.foundation.lazy.layout.AndroidPrefetchScheduler.<init>(PrefetchScheduler.android.kt:108)
	at androidx.compose.foundation.lazy.layout.PrefetchScheduler_androidKt.rememberDefaultPrefetchScheduler(PrefetchScheduler.android.kt:38)
	at androidx.compose.foundation.lazy.layout.LazyLayoutKt$LazyLayout$3.invoke(LazyLayout.kt:90)
	at androidx.compose.foundation.lazy.layout.LazyLayoutKt$LazyLayout$3.invoke(LazyLayout.kt:82)
	at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:118)
	at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:35)
	at androidx.compose.foundation.lazy.layout.LazySaveableStateHolderKt$LazySaveableStateHolderProvider$1.invoke(LazySaveableStateHolder.kt:51)
	at androidx.compose.foundation.lazy.layout.LazySaveableStateHolderKt$LazySaveableStateHolderProvider$1.invoke(LazySaveableStateHolder.kt:49)
	at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:109)
	at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:35)
	at androidx.compose.runtime.CompositionLocalKt.CompositionLocalProvider(CompositionLocal.kt:401)
	at androidx.compose.foundation.lazy.layout.LazySaveableStateHolderKt.LazySaveableStateHolderProvider(LazySaveableStateHolder.kt:49)
	at androidx.compose.foundation.lazy.layout.LazyLayoutKt.LazyLayout(LazyLayout.kt:82)
	at androidx.compose.foundation.lazy.LazyListKt.LazyList(LazyList.kt:106)
	at androidx.compose.foundation.lazy.LazyDslKt.LazyColumn(LazyDsl.kt:368)
	at com.example.LazyColumn(LazyColumn.kt:205)
	at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:118)
	at androidx.compose.runtime.internal.ComposableLambdaImpl$invoke$1.invoke(ComposableLambda.jvm.kt:130)
	at androidx.compose.runtime.internal.ComposableLambdaImpl$invoke$1.invoke(ComposableLambda.jvm.kt:129)
	at androidx.compose.runtime.RecomposeScopeImpl.compose(RecomposeScopeImpl.kt:192)
	at androidx.compose.runtime.ComposerImpl.recomposeToGroupEnd(Composer.kt:2825)
	at androidx.compose.runtime.ComposerImpl.skipCurrentGroup(Composer.kt:3116)
	at androidx.compose.runtime.ComposerImpl.doCompose(Composer.kt:3607)
	at androidx.compose.runtime.ComposerImpl.recompose$runtime_release(Composer.kt:3552)
	at androidx.compose.runtime.CompositionImpl.recompose(Composition.kt:948)
	at androidx.compose.runtime.Recomposer.performRecompose(Recomposer.kt:1206)
	at androidx.compose.runtime.Recomposer.access$performRecompose(Recomposer.kt:132)
	at androidx.compose.runtime.Recomposer$runRecomposeAndApplyChanges$2$1.invoke(Recomposer.kt:616)
	at androidx.compose.runtime.Recomposer$runRecomposeAndApplyChanges$2$1.invoke(Recomposer.kt:585)
	at androidx.compose.ui.test.TestMonotonicFrameClock$withFrameNanos$2$1$1.invoke(TestMonotonicFrameClock.jvm.kt:104)
	at androidx.compose.ui.test.TestMonotonicFrameClock$withFrameNanos$2$1$1.invoke(TestMonotonicFrameClock.jvm.kt:103)
	at androidx.compose.ui.test.TestMonotonicFrameClock$performFrame$1.invoke(TestMonotonicFrameClock.jvm.kt:149)
	at androidx.compose.ui.test.TestMonotonicFrameClock$performFrame$1.invoke(TestMonotonicFrameClock.jvm.kt:132)
	at androidx.compose.ui.test.FrameDeferringContinuationInterceptor.runWithoutResumingCoroutines(FrameDeferringContinuationInterceptor.jvm.kt:60)
	at androidx.compose.ui.test.TestMonotonicFrameClock.performFrame(TestMonotonicFrameClock.jvm.kt:132)
	at androidx.compose.ui.test.TestMonotonicFrameClock.access$performFrame(TestMonotonicFrameClock.jvm.kt:53)
	at androidx.compose.ui.test.TestMonotonicFrameClock$withFrameNanos$2$1$2.invokeSuspend(TestMonotonicFrameClock.jvm.kt:110)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.internal.DispatchedContinuationKt.resumeCancellableWith(DispatchedContinuation.kt:359)
	at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable(Cancellable.kt:26)
	at kotlinx.coroutines.CoroutineStart.invoke(CoroutineStart.kt:358)
	at kotlinx.coroutines.AbstractCoroutine.start(AbstractCoroutine.kt:124)
	at kotlinx.coroutines.BuildersKt__Builders_commonKt.launch(Builders.common.kt:52)
	at kotlinx.coroutines.BuildersKt.launch(Unknown Source:1)
	at kotlinx.coroutines.BuildersKt__Builders_commonKt.launch$default(Builders.common.kt:43)
	at kotlinx.coroutines.BuildersKt.launch$default(Unknown Source:1)
	at androidx.compose.ui.test.TestMonotonicFrameClock.withFrameNanos(TestMonotonicFrameClock.jvm.kt:108)
	at androidx.compose.runtime.Recomposer$runRecomposeAndApplyChanges$2.invokeSuspend(Recomposer.kt:585)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at androidx.compose.ui.test.ApplyingContinuationInterceptor$SendApplyContinuation.resumeWith(ApplyingContinuationInterceptor.kt:65)
	at androidx.compose.ui.test.FrameDeferringContinuationInterceptor$FrameDeferredContinuation.resumeWith(FrameDeferringContinuationInterceptor.jvm.kt:194)
	at kotlinx.coroutines.DispatchedTaskKt.resume(DispatchedTask.kt:165)
	at kotlinx.coroutines.DispatchedTaskKt.dispatch(DispatchedTask.kt:154)
	at kotlinx.coroutines.CancellableContinuationImpl.dispatchResume(CancellableContinuationImpl.kt:470)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl$kotlinx_coroutines_core(CancellableContinuationImpl.kt:504)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl$kotlinx_coroutines_core$default(CancellableContinuationImpl.kt:493)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeWith(CancellableContinuationImpl.kt:359)
	at androidx.compose.runtime.Recomposer$recompositionRunner$2$unregisterApplyObserver$1.invoke(Recomposer.kt:1042)
	at androidx.compose.runtime.Recomposer$recompositionRunner$2$unregisterApplyObserver$1.invoke(Recomposer.kt:1026)
	at androidx.compose.runtime.snapshots.SnapshotKt.advanceGlobalSnapshot(Snapshot.kt:1945)
	at androidx.compose.runtime.snapshots.SnapshotKt.advanceGlobalSnapshot(Snapshot.kt:1960)
	at androidx.compose.runtime.snapshots.SnapshotKt.access$advanceGlobalSnapshot(Snapshot.kt:1)
	at androidx.compose.runtime.snapshots.Snapshot$Companion.sendApplyNotifications(Snapshot.kt:692)
	at androidx.compose.ui.test.ApplyingContinuationInterceptor$SendApplyContinuation.resumeWith(ApplyingContinuationInterceptor.kt:66)
	at androidx.compose.ui.test.FrameDeferringContinuationInterceptor$FrameDeferredContinuation.resumeWith(FrameDeferringContinuationInterceptor.jvm.kt:194)
	at kotlinx.coroutines.DispatchedTaskKt.resume(DispatchedTask.kt:165)
	at kotlinx.coroutines.DispatchedTaskKt.dispatch(DispatchedTask.kt:154)
	at kotlinx.coroutines.CancellableContinuationImpl.dispatchResume(CancellableContinuationImpl.kt:470)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl$kotlinx_coroutines_core(CancellableContinuationImpl.kt:504)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl$kotlinx_coroutines_core$default(CancellableContinuationImpl.kt:493)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeWith(CancellableContinuationImpl.kt:359)
	at kotlinx.coroutines.flow.SharedFlowImpl.tryEmit(SharedFlow.kt:414)
	at kotlinx.coroutines.flow.SharedFlowImpl.emit$suspendImpl(SharedFlow.kt:419)
	at kotlinx.coroutines.flow.SharedFlowImpl.emit(Unknown Source:0)
	at com.airbnb.mvrx.CoroutinesStateStore$flushQueuesOnce$2$1.invokeSuspend(CoroutinesStateStore.kt:87)
	at com.airbnb.mvrx.CoroutinesStateStore$flushQueuesOnce$2$1.invoke(Unknown Source:8)
	at com.airbnb.mvrx.CoroutinesStateStore$flushQueuesOnce$2$1.invoke(Unknown Source:4)
	at kotlinx.coroutines.selects.SelectImplementation$ClauseData.invokeBlock(Select.kt:846)
	at kotlinx.coroutines.selects.SelectImplementation.complete(Select.kt:715)
	at kotlinx.coroutines.selects.SelectImplementation.doSelectSuspend(Select.kt:456)
	at kotlinx.coroutines.selects.SelectImplementation.access$doSelectSuspend(Select.kt:251)
	at kotlinx.coroutines.selects.SelectImplementation$doSelectSuspend$1.invokeSuspend(Unknown Source:14)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:101)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
	at java.lang.Thread.run(Thread.java:920)

I could not determine why sometime the CoroutinesStateStore emits in a background coroutine. Could this be caused by the Channel hitting a buffer limit, and then resuming?

A search in the Android Issue Tracker didn't result in any bug that could be present in Compose

In any case, I was able to avoid this exception by specifying the context in collectAsState:

@Composable
fun <VM : MavericksViewModel<S>, S : MavericksState> VM.collectAsState(): State<S> {
    return stateFlow.collectAsState(initial = withState(this) { it }, context = Dispatchers.Main)
}

As such I suggest that we modify collectAsState() to allow the caller to be able to specify a coroutine context. I think this context should be Dispatchers.Main by default.

[elihart]

I believe the state is collected by default in the coroutine context specified by currentComposer.applyCoroutineContext, which is set by the recomposer. It's possible that in the test environment this context is limited somehow.

Since the issue is just in tests, you can likely also solve this by configuring your tests to use a "synchronous" data store instead of the coroutine based data store that is used in production.

MockBehavior(
            stateStoreBehavior = MockBehavior.StateStoreBehavior.Synchronous,
        ),

Used with MockableMavericks.initialize when initializing mavericks in your tests (such as in your base test class).

This is the pattern we always use in tests to avoid having to deal with coroutines in tests.

If you want to update the collectAsState() function to take an optional coroutine context, that is fine too - I'm happy to review a PR if you put one up

[elihart]

Support was added with #722