Unreal Engine Issues and Bug Tracker (UE-74191)

Description

TriggerMontageEndedEvent is calling RemoveAtSwap after the NotifyEnd callback which is not safe if the ActiveAninNotifyState array is modified by the callback.

WorkAround: Add a Delay node before calling DestroyActor. Licensee suggests "It might be safer to cache the array before iterating or somehow lock the array or block certain functions."

Steps to Reproduce

*Project has been attached for easier replication

Create a new Blueprint Third Person Template Project

Open the ThirdPersonCharacter Blueprint

Add a new Custom Event "KillActor" and have it call DestroyActor on self

Create a new AnimNotifyState Blueprint (Notify_Death)

Open the AnimNotifyState Blueprint.

Within the AnimNotifyState Blueprint Override Received Notify End function of the state Blueprint.

Create a new Montage from any sequence (ex. jump)

Add Notify State (Notify_Death) to the Notifies track of your new montage

Implement function on Notify End with GetOwner/Cast-to-ThirdPersonCharacter and call KillActor function.

Open the ThirdPersonCharacter Blueprint again

Implement a keyboard "X" trigger and PlayAnimMontage for the new animation

PIE and press the X key...

Result: Editor crash.

Expected: Montage to play successfully, calling destroy actor at the notify end function.

Callstack

LoginId:677a448d48352201d90930b796056d79
EpicAccountId:74cb1785c0a148f0a87ef74601ae977a

Unhandled exception

VCRUNTIME140
UE4Editor_Engine!UAnimInstance::TriggerMontageEndedEvent() [d:\ue4 monteue4main\engine\source\runtime\engine\private\animation\animinstance.cpp:1576]
UE4Editor_Engine!UAnimInstance::TriggerQueuedMontageEvents() [d:\ue4 monteue4main\engine\source\runtime\engine\private\animation\animinstance.cpp:1602]
UE4Editor_Engine!UAnimInstance::DispatchQueuedAnimEvents() [d:\ue4 monteue4main\engine\source\runtime\engine\private\animation\animinstance.cpp:553]
UE4Editor_Engine!USkeletalMeshComponent::ConditionallyDispatchQueuedAnimEvents() [d:\ue4 monteue4main\engine\source\runtime\engine\private\components\skeletalmeshcomponent.cpp:1306]
UE4Editor_Engine!USkeletalMeshComponent::FinalizeBoneTransform() [d:\ue4 monteue4main\engine\source\runtime\engine\private\components\skeletalmeshcomponent.cpp:3631]
UE4Editor_Engine!USkeletalMeshComponent::FinalizeAnimationUpdate() [d:\ue4 monteue4main\engine\source\runtime\engine\private\physicsengine\physanim.cpp:394]
UE4Editor_Engine!USkeletalMeshComponent::PostAnimEvaluation() [d:\ue4 monteue4main\engine\source\runtime\engine\private\components\skeletalmeshcomponent.cpp:2433]
UE4Editor_Engine!USkeletalMeshComponent::CompleteParallelAnimationEvaluation() [d:\ue4 monteue4main\engine\source\runtime\engine\private\components\skeletalmeshcomponent.cpp:3522]
UE4Editor_Engine!FParallelAnimationCompletionTask::DoTask() [d:\ue4 monteue4main\engine\source\runtime\engine\private\components\skeletalmeshcomponent.cpp:151]
UE4Editor_Engine!TGraphTask<FParallelAnimationCompletionTask>::ExecuteTask() [d:\ue4 monteue4main\engine\source\runtime\core\public\async\taskgraphinterfaces.h:847]
UE4Editor_Core!FNamedTaskThread::ProcessTasksNamedThread() [d:\ue4 monteue4main\engine\source\runtime\core\private\async\taskgraph.cpp:685]
UE4Editor_Core!FNamedTaskThread::ProcessTasksUntilQuit() [d:\ue4 monteue4main\engine\source\runtime\core\private\async\taskgraph.cpp:582]
UE4Editor_Core!FTaskGraphImplementation::WaitUntilTasksComplete() [d:\ue4 monteue4main\engine\source\runtime\core\private\async\taskgraph.cpp:1457]
UE4Editor_Engine!FTickTaskSequencer::ReleaseTickGroup() [d:\ue4 monteue4main\engine\source\runtime\engine\private\ticktaskmanager.cpp:557]
UE4Editor_Engine!FTickTaskManager::RunTickGroup() [d:\ue4 monteue4main\engine\source\runtime\engine\private\ticktaskmanager.cpp:1518]
UE4Editor_Engine!UWorld::RunTickGroup() [d:\ue4 monteue4main\engine\source\runtime\engine\private\leveltick.cpp:789]
UE4Editor_Engine!UWorld::Tick() [d:\ue4 monteue4main\engine\source\runtime\engine\private\leveltick.cpp:1595]
UE4Editor_UnrealEd!UEditorEngine::Tick() [d:\ue4 monteue4main\engine\source\editor\unrealed\private\editorengine.cpp:1618]
UE4Editor_UnrealEd!UUnrealEdEngine::Tick() [d:\ue4 monteue4main\engine\source\editor\unrealed\private\unrealedengine.cpp:403]
UE4Editor_Win64_DebugGame!FEngineLoop::Tick() [d:\ue4 monteue4main\engine\source\runtime\launch\private\launchengineloop.cpp:4207]
UE4Editor_Win64_DebugGame!GuardedMain() [d:\ue4 monteue4main\engine\source\runtime\launch\private\launch.cpp:173]
UE4Editor_Win64_DebugGame!GuardedMainWrapper() [d:\ue4 monteue4main\engine\source\runtime\launch\private\windows\launchwindows.cpp:147]
UE4Editor_Win64_DebugGame!WinMain() [d:\ue4 monteue4main\engine\source\runtime\launch\private\windows\launchwindows.cpp:277]
UE4Editor_Win64_DebugGame!__scrt_common_main_seh() [d:\agent\_work\2\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
kernel32
ntdll

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Fixed

Component	OLD - Anim
Affects Versions	4.20, 4.21, 4.22, 4.23
Target Fix	4.23

Fix Commit	6840981
Main Commit	6863572

Created	May 6, 2019
Resolved	Jun 4, 2019
Updated	May 18, 2020

View Jira Issue

UE-74191

Trigger Montage Ended Event results in Unhanded Exception

Trigger Montage Ended Event results in Unhanded Exception

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