ConcurrentModificationException on trying to reverse a mutableStateListOf [219554654]

Fixed

Bug

Status Update

No update yet.

Description

ph...@gmail.com

created issue #1

Feb 15, 2022 06:38AM

Jetpack Compose release version: 1.1.0 & 1.2.0-alpha03

Here's a sample code to reproduce the issue:

val list = remember { List(100) { it }.toMutableStateList() }
LaunchedEffect(Unit) {
    delay(1.seconds)
    list.reverse()
}
Text(list.toList().toString())

A crash occurs with the next stack trace:

java.util.ConcurrentModificationException
    at androidx.compose.runtime.snapshots.StateListIterator.validateModification(SnapshotStateList.kt:278)
    at androidx.compose.runtime.snapshots.StateListIterator.set(SnapshotStateList.kt:271)
    at java.util.Collections.reverse(Collections.java:435)
    at kotlin.collections.CollectionsKt___CollectionsJvmKt.reverse(_CollectionsJvm.kt:43)
    at com.example.composeplayground.MainActivityKt$TestScreen$1$1.invokeSuspend(MainActivity.kt:748)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
    at androidx.compose.ui.platform.AndroidUiDispatcher.performTrampolineDispatch(AndroidUiDispatcher.android.kt:81)
    at androidx.compose.ui.platform.AndroidUiDispatcher.access$performTrampolineDispatch(AndroidUiDispatcher.android.kt:41)
    at androidx.compose.ui.platform.AndroidUiDispatcher$dispatchCallback$1.run(AndroidUiDispatcher.android.kt:57)
    at android.os.Handler.handleCallback(Handler.java:938)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loopOnce(Looper.java:201)
    at android.os.Looper.loop(Looper.java:288)
    at android.app.ActivityThread.main(ActivityThread.java:7842)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)

Comments

ry...@google.com <ry...@google.com> Feb 22, 2022 10:14AM

Assigned to je...@google.com.

ch...@google.com <ch...@google.com> Sep 9, 2022 10:24PM

Reassigned to ch...@google.com.

ah...@gmail.com <ah...@gmail.com> #2Sep 13, 2023 01:50PM

Project: platform/frameworks/support
Branch: androidx-main

commit 700259f0afe267dfe78b93db932a3cfd827a119d
Author: Sherry Hu <shuanghu@google.com>
Date: Mon May 10 14:23:09 2021

Add transition motion between fold and unfold.

Bug: 186211031
Test: manual
Change-Id: Id60f07311eca2d94ef91dc28ae45823a475160b4

M slidingpanelayout/slidingpanelayout/build.gradle
M slidingpanelayout/slidingpanelayout/src/androidTest/java/androidx/slidingpanelayout/widget/FoldTest.kt
M slidingpanelayout/slidingpanelayout/src/main/java/androidx/slidingpanelayout/widget/SlidingPaneLayout.java

https://android-review.googlesource.com/1702066

ch...@google.com <ch...@google.com> #3Sep 14, 2023 11:02PM

reverse() constructs two iterators (if the list is > 18 in size), one forward walking and one backwards walking and will modify the array using both iterators. This is currently treated as a concurrent modification as the array was modified after the iterator was created. This is too strict for the Java algorithms. They expect a concurrent modification exception to only be thrown if a structural chagne to the list is made, e.g. an insert or delete, not a value change.

First, mutableStateListOf() lists will be changed to not interpret setting the value of the slot of an element as a concurrent. Second, they will be changed to support RandomAccess which avoids the algorithms using the iterators for operations that would be faster if they used get and set directly.

ap...@google.com <ap...@google.com> #4Sep 15, 2023 07:49PM

Marked as fixed.

Project: platform/frameworks/support
Branch: androidx-main

commit 75f720e1695c3574930d0385211341fac876a834
Author: Chuck Jazdzewski <chuckj@google.com>
Date: Thu Sep 14 15:22:33 2023

Relax concurrent modification exception for snapshot state list

The snapshot state list iterator considered any change made outside the
iterator as a concurrent change. This change relaxes the checking to
only consider structural changes (adding and removing) to be treated as
a concurrent change. This allows SnapshotStateList to be used with
`reverse()` which assumes that setting the value of an element is not a
concurrent change.

Adds RandomeAccess interface to MutableStateList to signal collection
extensions functions they can use direct indexing versions of their
algorithm.

Corrects the set() after a call previous() to update the correct
element.

Fixes: 219554654
Test: ./gradlew :compose:r:r:tDUT
Relnote: """SnapshotStateList is not marked as RandomAccess to enable
the direct indexing version of list helpers to be used"

Change-Id: I5210ca5c0f490619381ecf93ac0b1ccb03071e36

M compose/runtime/runtime/api/current.txt
M compose/runtime/runtime/api/restricted_current.txt
M compose/runtime/runtime/src/commonMain/kotlin/androidx/compose/runtime/snapshots/SnapshotStateList.kt
M compose/runtime/runtime/src/nonEmulatorCommonTest/kotlin/androidx/compose/runtime/snapshots/SnapshotStateListTests.kt

https://android-review.googlesource.com/2751617

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