Unreal Engine Issues and Bug Tracker (UE-35830)

Description

If a Curve Float local variable is created for a function, it will be garbage collected when garbage collection occurs. This causes the process to crash due to an null pointer error whenever it is referenced.

Regression?: No
This issue also occurred in 4.12.5 Binary (3039270)

Steps to Reproduce

Download the attached project
Start PIE in a Standalone Window
Open the console and type the following to force garbage collection:
obj gc
Result: The process crashes due to the Float Curve in the function that is being called on tick being garbage collected
Expected: The float curve should not be garbage collected and the process should not crash.

From Scratch:

Create a new project
Create a Curve Float asset (Context Menu > Misc > Curve)
Create an actor blueprint
Create a new function inside of the actor blueprint
Add a local variable of the Curve Float type and then set the value of said variable to your previously created Curve Float
Set up the function in the picture below
Call this new function on Tick in the actor's event graph
Add an instance of the actor blueprint to the level, save the level.
Run the game in Standalone Game
Type the following command into the console to force garbage collection:
obj gc

Callstack

 Assertion failed: Index >= 0 [File:d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\coreuobject\public\uobject\UObjectArray.h] [Line: 402] 



UE4Editor_Core!FDebug::AssertFailed() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\private\misc\outputdevice.cpp:421]
UE4Editor_CoreUObject!UObject::ProcessContextOpcode() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\coreuobject\private\uobject\scriptcore.cpp:2117]
UE4Editor_CoreUObject!UObject::execLet() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\coreuobject\private\uobject\scriptcore.cpp:1925]
UE4Editor_CoreUObject!UObject::ProcessInternal() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\coreuobject\private\uobject\scriptcore.cpp:922]
UE4Editor_CoreUObject!UObject::CallFunction() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\coreuobject\private\uobject\scriptcore.cpp:821]
UE4Editor_CoreUObject!UObject::ProcessInternal() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\coreuobject\private\uobject\scriptcore.cpp:922]
UE4Editor_CoreUObject!UObject::CallFunction() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\coreuobject\private\uobject\scriptcore.cpp:821]
UE4Editor_CoreUObject!UObject::ProcessInternal() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\coreuobject\private\uobject\scriptcore.cpp:922]
UE4Editor_CoreUObject!UFunction::Invoke() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\coreuobject\private\uobject\class.cpp:4280]
UE4Editor_CoreUObject!UObject::ProcessEvent() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\coreuobject\private\uobject\scriptcore.cpp:1305]
UE4Editor_Engine!AActor::ProcessEvent() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\engine\private\actor.cpp:646]
UE4Editor_Engine!AActor::ReceiveTick() [d:\build\++ue4+release-4.13+compile\sync\engine\intermediate\build\win64\ue4editor\inc\engine\engine.generated.1.cpp:2816]
UE4Editor_Engine!AActor::Tick() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\engine\private\actor.cpp:844]
UE4Editor_Engine!AActor::TickActor() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\engine\private\actor.cpp:831]
UE4Editor_Engine!FActorTickFunction::ExecuteTick() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\engine\private\actor.cpp:112]
UE4Editor_Engine!FTickFunctionTask::DoTask() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\engine\private\ticktaskmanager.cpp:251]
UE4Editor_Engine!TGraphTask<FTickFunctionTask>::ExecuteTask() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\public\async\taskgraphinterfaces.h:868]
UE4Editor_Core!FNamedTaskThread::ProcessTasksNamedThread() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\private\async\taskgraph.cpp:932]
UE4Editor_Core!FNamedTaskThread::ProcessTasksUntilQuit() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\private\async\taskgraph.cpp:679]
UE4Editor_Core!FTaskGraphImplementation::WaitUntilTasksComplete() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\private\async\taskgraph.cpp:1776]
UE4Editor_Engine!FTickTaskSequencer::ReleaseTickGroup() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\engine\private\ticktaskmanager.cpp:520]
UE4Editor_Engine!FTickTaskManager::RunTickGroup() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\engine\private\ticktaskmanager.cpp:1426]
UE4Editor_Engine!UWorld::RunTickGroup() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\engine\private\leveltick.cpp:706]
UE4Editor_Engine!UWorld::Tick() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\engine\private\leveltick.cpp:1275]
UE4Editor_Engine!UGameEngine::Tick() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\engine\private\gameengine.cpp:1057]
UE4Editor!FEngineLoop::Tick() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\launch\private\launchengineloop.cpp:2834]
UE4Editor!GuardedMain() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\launch\private\launch.cpp:156]
UE4Editor!GuardedMainWrapper() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:126]
UE4Editor!WinMain() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:202]
UE4Editor!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:264]
kernel32
ntdll

Have Comments or More Details?

There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-35830 in the post.

0	Login to Vote

Fixed

Component	UE - Gameplay - Blueprint
Affects Versions	4.12.5, 4.13, 4.14
Target Fix	4.14

Fix Commit	3132383
Main Commit	3152997

Created	Sep 9, 2016
Resolved	Sep 20, 2016
Updated	Apr 27, 2018

UE-35830

Float Curve that is set as a local variable in an actor's function is garbage collected when in Standalone, causing a crash

Float Curve that is set as a local variable in an actor's function is garbage collected when in Standalone, causing a crash

Have Comments or More Details?