Hot Reload crashes Editor

Development Getting Started & Setup
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1

Since 4.25 HotReload doesn’t work properly. Everytime when I compile a project in Visual Studio or inside UE4 Editor I’ve got a crash with the following CallStack and Exception

Unhandled exception at 0x00007FF9AC0F0DA8 (UE4Editor-CoreUObject.dll) in UE4Minidump.dmp: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF. occurred

[Inline Frame] UE4Editor-CoreUObject.dll!FField::HasAnyCastFlags(const unsigned __int64) Line 499 C++
[Inline Frame] UE4Editor-CoreUObject.dll!CastField(FField *) Line 796 C++
[Inline Frame] UE4Editor-CoreUObject.dll!TFieldPath::{ctor}(FField * InProperty, TFieldPath::EDummy1) Line 325 C++
UE4Editor-CoreUObject.dll!FPropertyProxyArchive::operator<<(FField * & Value) Line 45 C++
[Inline Frame] UE4Editor-CoreUObject.dll!operator<<(FArchive &) Line 93 C++
UE4Editor-CoreUObject.dll!UStruct::SerializeExpr(int & iCode, FArchive & Ar) Line 222 C++
UE4Editor-CoreUObject.dll!UStruct::SerializeExpr(int & iCode, FArchive & Ar) Line 314 C++
UE4Editor-CoreUObject.dll!UStruct::Serialize(FArchive & Ar) Line 1925 C++
UE4Editor-CoreUObject.dll!UFunction::Serialize(FArchive & Ar) Line 5555 C++
[Inline Frame] UE4Editor-HotReload.dll!FHotReloadModule::ReplaceReferencesToReconstructedCDOs::__l2::FFindRefTask::DoWork() Line 983 C++
UE4Editor-HotReload.dll!FAsyncTask<FHotReloadModule::ReplaceReferencesToReconstructedCDOs'::2’::FFindRefTask>::DoWork() Line 271 C++
UE4Editor-HotReload.dll!FAsyncTask<FHotReloadModule::ReplaceReferencesToReconstructedCDOs'::2’::FFindRefTask>::DoThreadedWork() Line 296 C++
UE4Editor-Core.dll!FQueuedThread::Run() Line 855 C++
UE4Editor-Core.dll!FRunnableThreadWin::Run() Line 86 C++
UE4Editor-Core.dll!FRunnableThreadWin::GuardedRun() Line 35 C++

2

I am getting the same error since upgrading to 4.25.1 with the same call stack. If you want to try to troubleshoot this with me here’s my company Discord: PARIAH

3

Did you get anywhere with this? I’m getting the same crash, 4.25, when compiling blueprints in editor…

4

Same here, I am looking for an answer to this.

5

Same s*** here

6

Different callstack but same issue for me. About a third of all hot-reloads from Visual Studio crash the editor. 4.25 has been absolute hell for me, the editor crashes far more often than it did in 4.24.

7

Exact same error for me, all the time. Don’t know what’s going on…

8

This started happening on our team when we switched to 4.25 as well.

9

For our project, this was caused by doing the following in an Actor’s constructor:

FSoftClassPath ClassReference = ...
UClass* MyClass = ClassReference.ResolveClass();
if (!MyClass)
{
    MyClass = ClassReference.TryLoadClass<AMyClass>();
}

Protecting this code with

if (!HasAnyFlags(RF_ClassDefaultObject))

solved the hot reloading issue.

1 Like
10

Same issue in 4.26

11

The bengoog’s answer really points to the right side. I’d add a more general assumption: any complicated stuff in U- and A- classes’ constructors should be relocated to other functions or protected like in the unswer above. In my case a similar crash was caused by a TArray::SetNum() + elements initializing in a constructor. So the main problem is to keep in mind all your subclasses and go through them all.

1 Like