SnapshotStateList: ConcurrentModificationException when iterating during snapshot modification [272334463]

Assigned

Feature Request

Status Update

No update yet.

Description

ta...@mercury.com

created issue #1

Mar 8, 2023 09:08PM

SnapshotStateList.iterator() returns an iterator that throws when the snapshot is modified while iterating values. I expected this to behave similarly to MutableState, where reads operate on a snapshot record and concurrent writes update the snapshot state.

To do this with SnapshotStateList, one must remember to call toList() to obtain the PersistentList held in the current snapshot record. Unfortunately, this is difficult to remember to do: a simple read or indexed access can operate concurrently, but many Kotlin stdlib extensions invoke iterator() under the hood to iterate the list, including map, fold, forEach, etc.

Ideally, one should be able to read whlie iterating on a snapshot value, but fail with the CME when modifying through the iterator.

A similar problem exists with the iterator returned by SnapshotStateMap.entries.iterator(), and many Kotlin stdlib extensions call .entries.iterator() internally.

Jetpack Compose version: 1.4.0-beta02 Jetpack Compose component used: Runtime Android Studio Build: 2022.2.1 Beta 4 Kotlin version: 1.8.10

Steps to Reproduce or Code Sample to Reproduce:

val list = mutableStateListOf<Int>()

val sortedList by derivedStateOf {
    list.sorted()
}

// Update the list outside of the composition, e.g. in a LaunchedEffect
list.addAll(6, 5, 4, 3, 2, 1)

Stack trace (if applicable):

java.util.ConcurrentModificationException
        at androidx.compose.runtime.snapshots.StateListIterator.validateModification(SnapshotStateList.kt:295)
        at androidx.compose.runtime.snapshots.StateListIterator.next(SnapshotStateList.kt:274)
        at kotlin.collections.CollectionsKt___CollectionsKt.mapTo(CollectionsKt___CollectionsKt:1620)
        at com.mercury.app.data.UserState$depositoryAccounts$2.invoke(UserState.kt:103)
        at com.mercury.app.data.UserState$depositoryAccounts$2.invoke(UserState.kt:102)
        at androidx.compose.runtime.snapshots.Snapshot.enter(Snapshot:124)
        at androidx.compose.runtime.snapshots.Snapshot$Companion.observe(Snapshot.kt:461)
        at androidx.compose.runtime.DerivedSnapshotState.currentRecord(DerivedState.kt:161)
        at androidx.compose.runtime.DerivedSnapshotState.current(DerivedSnapshotState:131)
        at androidx.compose.runtime.DerivedSnapshotState$ResultRecord.readableHash(DerivedState.kt:109)
        at androidx.compose.runtime.DerivedSnapshotState$ResultRecord.isValid(DerivedSnapshotState:91)
        at androidx.compose.runtime.DerivedSnapshotState.currentRecord(DerivedState.kt:139)
        at androidx.compose.runtime.DerivedSnapshotState.current(DerivedSnapshotState:131)
        at androidx.compose.runtime.DerivedSnapshotState$ResultRecord.readableHash(DerivedState.kt:109)
        at androidx.compose.runtime.DerivedSnapshotState$ResultRecord.isValid(DerivedSnapshotState:91)
        at androidx.compose.runtime.DerivedSnapshotState.currentRecord(DerivedState.kt:139)
        at androidx.compose.runtime.DerivedSnapshotState.getCurrentValue(DerivedState.kt:231)
        at androidx.compose.runtime.snapshots.SnapshotStateObserver$ObservedScopeMap.recordInvalidation(SnapshotStateObserver.kt:523)
        at androidx.compose.runtime.snapshots.SnapshotStateObserver.drainChanges(SnapshotStateObserver.kt:66)
        at androidx.compose.runtime.snapshots.SnapshotStateObserver.access$drainChanges(SnapshotStateObserver.kt:38)
        at androidx.compose.runtime.snapshots.SnapshotStateObserver$applyObserver$1.invoke(SnapshotStateObserver.kt:45)
        at androidx.compose.runtime.snapshots.SnapshotStateObserver$applyObserver$1.invoke(SnapshotStateObserver.kt:43)
        at androidx.compose.runtime.snapshots.SnapshotKt.advanceGlobalSnapshot(Snapshot.kt:1765)
        at androidx.compose.runtime.snapshots.SnapshotKt.advanceGlobalSnapshot(Snapshot.kt:1772)
        at androidx.compose.runtime.snapshots.SnapshotKt.access$advanceGlobalSnapshot(Snapshot.kt:1)
        at androidx.compose.runtime.snapshots.Snapshot$Companion.sendApplyNotifications(Snapshot:568)
        at androidx.compose.ui.platform.GlobalSnapshotManager$ensureStarted$1.invokeSuspend(GlobalSnapshotManager.android.kt:46)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
        at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
        at androidx.compose.ui.platform.AndroidUiDispatcher.performTrampolineDispatch(AndroidUiDispatcher.android.kt:81)
        at androidx.compose.ui.platform.AndroidUiDispatcher.access$performTrampolineDispatch(AndroidUiDispatcher.android.kt:41)
        at androidx.compose.ui.platform.AndroidUiDispatcher$dispatchCallback$1.run(AndroidUiDispatcher.android.kt:57)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:6981)
        at java.lang.reflect.Method.invoke(Method.java:-2)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1445)

Comments

ch...@google.com <ch...@google.com> Apr 7, 2023 05:02PM

Reassigned to ch...@google.com.

ch...@google.com <ch...@google.com> #2Apr 7, 2023 09:01PM

Triage notes: Still P3, still a real issue. Compat issue.

ds...@gmail.com <ds...@gmail.com> #3Sep 28, 2023 11:50PM

Hello the Home Assistant Wear OS app is also facing this same exact issue it seems. The traceback in our issue is very close to the issue posted here.

According to play console we have about 1k impacted users.

https://github.com/home-assistant/android/issues/3325

Exception java.util.ConcurrentModificationException:
  at androidx.compose.runtime.snapshots.StateListIterator.validateModification (SnapshotStateList.kt:295)
  at androidx.compose.runtime.snapshots.StateListIterator.next (SnapshotStateList.kt:274)
  at io.homeassistant.companion.android.home.views.MainViewKt$MainView$1$3$1.invoke (MainView.kt:382)
  at io.homeassistant.companion.android.home.views.MainViewKt$MainView$1$3$1.invoke (MainView.kt:77)
  at androidx.wear.compose.material.ScalingLazyColumnKt$ScalingLazyColumn$1$1$2$1.invoke (ScalingLazyColumn.kt:425)
  at androidx.wear.compose.material.ScalingLazyColumnKt$ScalingLazyColumn$1$1$2$1.invoke (ScalingLazyColumn.kt:410)
  at androidx.compose.foundation.lazy.LazyListItemProviderKt$rememberLazyListItemProvider$1$itemProviderState$1.invoke (LazyListItemProvider.kt:54)
  at androidx.compose.foundation.lazy.LazyListItemProviderKt$rememberLazyListItemProvider$1$itemProviderState$1.invoke (LazyListItemProvider.kt:53)
  at androidx.compose.runtime.snapshots.Snapshot$Companion.observe (Snapshot.kt:2200)
  at androidx.compose.runtime.DerivedSnapshotState.currentRecord (DerivedState.kt:161)
  at androidx.compose.runtime.DerivedSnapshotState.getCurrentValue (DerivedState.kt:231)
  at androidx.compose.runtime.snapshots.SnapshotStateObserver$ObservedScopeMap.recordInvalidation (SnapshotStateObserver.kt:523)
  at androidx.compose.runtime.snapshots.SnapshotStateObserver.drainChanges (SnapshotStateObserver.kt:66)
  at androidx.compose.runtime.snapshots.SnapshotStateObserver.access$drainChanges (SnapshotStateObserver.kt:38)
  at androidx.compose.runtime.snapshots.SnapshotStateObserver$applyObserver$1.invoke (SnapshotStateObserver.kt:45)
  at androidx.compose.runtime.snapshots.SnapshotStateObserver$applyObserver$1.invoke (SnapshotStateObserver.kt:43)
  at androidx.compose.runtime.snapshots.MutableSnapshot.apply (Snapshot.kt:748)
  at androidx.compose.runtime.Recomposer.applyAndCheck (Recomposer.kt:1124)
  at androidx.compose.runtime.Recomposer.performRecompose (Recomposer.kt:1483)
  at androidx.compose.runtime.Recomposer.access$performRecompose (Recomposer.kt:124)
  at androidx.compose.runtime.Recomposer$runRecomposeAndApplyChanges$2$2.invoke (Recomposer.kt:541)
  at androidx.compose.runtime.Recomposer$runRecomposeAndApplyChanges$2$2.invoke (Recomposer.kt:510)
  at androidx.compose.ui.platform.AndroidUiFrameClock$withFrameNanos$2$callback$1.doFrame (AndroidUiFrameClock.android.kt:34)
  at androidx.compose.ui.platform.AndroidUiDispatcher.performFrameDispatch (AndroidUiDispatcher.android.kt:109)
  at androidx.compose.ui.platform.AndroidUiDispatcher.access$performFrameDispatch (AndroidUiDispatcher.android.kt:41)
  at androidx.compose.ui.platform.AndroidUiDispatcher$dispatchCallback$1.doFrame (AndroidUiDispatcher.android.kt:69)
  at android.view.Choreographer$CallbackRecord.run (Choreographer.java:996)
  at android.view.Choreographer.doCallbacks (Choreographer.java:796)
  at android.view.Choreographer.doFrame (Choreographer.java:727)
  at android.view.Choreographer$FrameDisplayEventReceiver.run (Choreographer.java:983)
  at android.os.Handler.handleCallback (Handler.java:938)
  at android.os.Handler.dispatchMessage (Handler.java:99)
  at android.os.Looper.loop (Looper.java:246)
  at android.app.ActivityThread.main (ActivityThread.java:7690)
  at java.lang.reflect.Method.invoke
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:593)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:995)

ch...@google.com <ch...@google.com> #4Oct 2, 2023 03:38PM

Part (2) of this was implemented in aosp/2751617 and should be available in 1.6 which will remove the exception.

However, I still recommend against any derivedStateOf lambda from having side-effects as described above as it is not possible to produce a consistent snapshot if derivedStateOf has a side-effect as the result of the .value call is not guaranteed to be consistent with the snapshot it is produced for.

al...@google.com <al...@google.com> #5Apr 17, 2024 04:16PM

Triage notes, there is still some remaining work here.

he...@lemi.bot <he...@lemi.bot> #6Aug 30, 2024 10:39PM

val sessions by viewModel.sessions.collectAsStateWithLifecycle()
val selectedSessions = remember { mutableStateListOf<Session>() }

LaunchedEffect(sessions) {
    selectedSessions.removeIf { it !in sessions.orEmpty() }
}

I'm having a similar issue

java.util.ConcurrentModificationException
    at androidx.compose.runtime.snapshots.StateListIterator.validateModification(SnapshotStateList.kt:320)
    at androidx.compose.runtime.snapshots.StateListIterator.next(SnapshotStateList.kt:296)

What's the correct way to implement this?

ch...@google.com <ch...@google.com> #7Sep 5, 2024 05:09PM

Part (2) of this change, relaxing under what conditions a concurrent modification exception is generated, landed in 1.6.

For example, the following code does not generate a concurrent modification exception beginning with 1.6.

    Column {
        val list = remember {
            mutableStateListOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
        }
        for (item in list) {
            Text("Item $item")
        }
        LaunchedEffect(list) {
            delay(500)
            list.removeIf { item -> item % 2 != 0}
        }
    }

al...@google.com <al...@google.com> #8Nov 21, 2024 07:22PM

Triage notes: Still some P3 work pending here before we can close this out.