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Deadlock in UE4 cancelling callbacks during GC

+1 vote

Hi there,

  We are experiencing occasional but serious deadlocks using Wwise (2018.1.5.6835.1218) in UE4 (4.21.2).  

 

Basic Repro (low probability due to threading issues):

1. Have a streaming level with an AkEvent that has a Blueprint callback

2. Unload the streaming level

3. Deadlock during GC

 

Some Notes:

- The game objects on each thread seem to be unrelated

- This seems to be a deadlock on the hash table lock between the AKManualEvent wait during GC that I'm guessing is waiting on the event thread and the Event Thread attempting to dispatch a new callback.

- While we have only seen this during level streaming, it seems like any garbage collection pass is at risk for this deadlock.

 

Callstack for our Game Thread:

[External Code]
[Inline Frame] IllGame.exe!AkManualEvent::Wait() Line 47 C++
IllGame.exe!CAkPlayingMgr::CancelCallbackGameObject(unsigned __int64 in_gameObjectID) Line 120 C++
IllGame.exe!FAkComponentCallbackManager::UnregisterGameObject(unsigned __int64 in_gameObjID) Line 224 C++
[Inline Frame] IllGame.exe!FAkAudioDevice::UnregisterComponent(UAkComponent *) Line 2380 C++
IllGame.exe!UAkComponent::UnregisterGameObject() Line 733 C++
IllGame.exe!UActorComponent::BeginDestroy() Line 469 C++
IllGame.exe!UObject::ConditionalBeginDestroy() Line 954 C++
IllGame.exe!UnhashUnreachableObjects(bool bUseTimeLimit, float TimeLimit) Line 1645 C++
IllGame.exe!CollectGarbageInternal(EObjectFlags KeepFlags, bool bPerformFullPurge) Line 1591 C++
IllGame.exe!TryCollectGarbage(EObjectFlags KeepFlags, bool bPerformFullPurge) Line 1700 C++
IllGame.exe!UEngine::ConditionalCollectGarbage() Line 1230 C++
IllGame.exe!UWorld::Tick(ELevelTick TickType, float DeltaSeconds) Line 1647 C++
IllGame.exe!UGameEngine::Tick(float DeltaSeconds, bool bIdleMode) Line 1365 C++
IllGame.exe!UILLGameEngine::Tick(float DeltaSeconds, bool bIdleMode) Line 194 C++
IllGame.exe!FEngineLoop::Tick() Line 3699 C++
[Inline Frame] IllGame.exe!EngineTick() Line 62 C++
IllGame.exe!GuardedMain(const wchar_t * CmdLine, HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, int nCmdShow) Line 174 C++
IllGame.exe!GuardedMainWrapper(const wchar_t * CmdLine, HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, int nCmdShow) Line 145 C++
IllGame.exe!WinMain(HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, char * __formal, int nCmdShow) Line 276 C++

Callstack for our AK Event Manager Thread:
[Inline Frame] IllGame.exe!Windows::EnterCriticalSection(Windows::CRITICAL_SECTION *) Line 173 C++
[Inline Frame] IllGame.exe!FWindowsCriticalSection::Lock() Line 50 C++
[Inline Frame] IllGame.exe!FUObjectHashTables::Lock() Line 316 C++
[Inline Frame] IllGame.exe!FHashTableLock::{ctor}(FUObjectHashTables &) Line 343 C++
IllGame.exe!StaticFindObjectFastInternalThreadSafe(FUObjectHashTables & ThreadHash, UClass * ObjectClass, UObject * ObjectPackage, FName ObjectName, bool bExactClass, bool bAnyPackage, EObjectFlags ExcludeFlags, EInternalObjectFlags ExclusiveInternalFlags) 
IllGame.exe!StaticFindObjectFastInternal(UClass * ObjectClass, UObject * ObjectPackage, FName ObjectName, bool bExactClass, bool bAnyPackage, EObjectFlags ExcludeFlags, EInternalObjectFlags ExclusiveInternalFlags) Line 563 C++
IllGame.exe!MakeUniqueObjectName(UObject * Parent, UClass * Class, FName InBaseName) Line 1861 C++
IllGame.exe!StaticAllocateObject(UClass * InClass, UObject * InOuter, FName InName, EObjectFlags InFlags, EInternalObjectFlags InternalSetFlags, bool bCanRecycleSubobjects, bool * bOutRecycledSubobject) Line 2371 C++
IllGame.exe!StaticConstructObject_Internal(UClass * InClass, UObject * InOuter, FName InName, EObjectFlags InFlags, EInternalObjectFlags InternalSetFlags, UObject * InTemplate, bool bCopyTransientsFromClassDefaults, FObjectInstancingGraph * InInstanceGraph, bool bAssumeTemplateIsArchetype) Line 3155 C++
[Inline Frame] IllGame.exe!NewObject(UObject * Outer) Line 1175 C++
IllGame.exe!UAkEventCallbackInfo::Create(AkEventCallbackInfo * AkEventCbInfo) Line 83 C++
IllGame.exe!AkCallbackTypeHelpers::GetBlueprintableCallbackInfo(AkCallbackType CallbackType, AkCallbackInfo * CallbackInfo) Line 42 C++
IllGame.exe!FAkBlueprintDelegateEventCallbackPackage::HandleAction(AkCallbackType in_eType, AkCallbackInfo * in_pCallbackInfo) Line 52 C++
IllGame.exe!FAkComponentCallbackManager::AkComponentCallback(AkCallbackType in_eType, AkCallbackInfo * in_pCallbackInfo) Line 100 C++
IllGame.exe!CAkPlayingMgr::CheckRemovePlayingID(unsigned long in_PlayingID, CAkPlayingMgr::PlayingMgrItem * in_pItem) Line 196 C++
IllGame.exe!CAkPlayingMgr::Remove(unsigned long in_PlayingID, CAkTransportAware * in_pPBI) Line 595 C++
IllGame.exe!CAkPBI::Term(bool __formal) Line 211 C++
[Inline Frame] IllGame.exe!CAkURenderer::DestroyPBI(CAkPBI * in_pPBI) Line 931 C++
IllGame.exe!CAkURenderer::PerformContextNotif() Line 915 C++
IllGame.exe!CAkAudioMgr::Perform() Line 555 C++
IllGame.exe!CAkAudioThread::EventMgrThreadFunc(void * lpParameter) Line 74 C++
 

I'll be investigating potential solutions here, but I'm wondering if this is a known issue and/or if there is a workaround or fix?

 
Thanks,
 - Chance

 

 

in General Discussion by Chance L. (130 points)
Deferring UAkCallbackInfo creation until the AsyncTask is run seems like the easiest and most correct solution.  Something like below:

// ILLFONIC CHANGE BEGIN - chance.lyon - Making this thread-safe by deferring UObject creation until the game thread
        /* OLD CODE
        UAkCallbackInfo* CachedAkCallbackInfo = AkCallbackTypeHelpers::GetBlueprintableCallbackInfo(in_eType, in_pCallbackInfo);
        EAkCallbackType BlueprintCallbackType = AkCallbackTypeHelpers::GetBlueprintCallbackTypeFromAkCallbackType(in_eType);
        auto CachedBlueprintCallback = BlueprintCallback;
        AsyncTask(ENamedThreads::GameThread, [CachedAkCallbackInfo, BlueprintCallbackType, CachedBlueprintCallback]()
        {
            CachedBlueprintCallback.ExecuteIfBound(BlueprintCallbackType, CachedAkCallbackInfo);
        });
        */

        AkCallbackInfo* ClonedInfo = AkCallbackTypeHelpers::CloneCallbackinfo(in_eType, in_pCallbackInfo);
        auto CachedBlueprintCallback = BlueprintCallback;

        AsyncTask(ENamedThreads::GameThread, [ClonedInfo, in_eType, CachedBlueprintCallback]()
        {
            EAkCallbackType BlueprintCallbackType = AkCallbackTypeHelpers::GetBlueprintCallbackTypeFromAkCallbackType(in_eType);
            UAkCallbackInfo* CachedAkCallbackInfo = AkCallbackTypeHelpers::GetBlueprintableCallbackInfo(in_eType, ClonedInfo);
            CachedBlueprintCallback.ExecuteIfBound(BlueprintCallbackType, CachedAkCallbackInfo);

            delete ClonedInfo;
// ILLFONIC CHANGE END
by Chance L. (130 points)
I am also seeing this issue. Is there an official fix for this?
by Erik I. (170 points)

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