# UE4.8 Freezes when I kill a thread **URL:** \ **Category:** Programming & Scripting\ **Tags:** unreal-engine\ **Created:** [October 5, 2015, 8:43am UTC](https://forums.unrealengine.com/t/ue4-8-freezes-when-i-kill-a-thread/334294 "2015-10-05T08:43:18Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![plangton](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@plangton](https://forums.unrealengine.com/u/plangton)\ **Post date:** [October 5, 2015, 8:43am UTC](https://forums.unrealengine.com/t/ue4-8-freezes-when-i-kill-a-thread/334294/1 "2015-10-05T08:43:18Z")
Hi, Consider the following scenario : 1 - I have a class (class X ) derived from Frunnable. 2 - class X has a member variable of FrunnableThread 3 - I have a class ( class Y ) which is of type UActorComponent 4 - Class Y has member pointer to an instance of class X Now, there are two function that are public and I use in class Y and they are accessible in blueprints 1 - starting a new instance of frunnable thread in class X 2 - killing the running Thread When I try to kill the running thread with Kill(true) UE4 gets not responding. funnily enough when I compile the code in debug mode there is no issue. **I want to know if you can help me solve this problem ? is it because I am trying to kill it in blueprints ? if so then how can I solve this problem ?** PS : it is a very basic code, so I mainly do nothing. it is just a test on running and killing threads via blueprints ---
**Author:** ![MrGrr](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@MrGrr](https://forums.unrealengine.com/u/MrGrr)\ **Post date:** [October 5, 2015, 9:32am UTC](https://forums.unrealengine.com/t/ue4-8-freezes-when-i-kill-a-thread/334294/2 "2015-10-05T09:32:51Z")
This question is confusing… Can you clarify, or send a screen shot of the error or code that causes the error? killing a class(which would remove all instances from the game, so is not really a good idea) You could also remove the class/component from the actor killing threads?(not sure why you would want to mess with this if trying to “kill” a class or actor) killing actors? you could always destroy them ---
**Author:** ![plangton](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@plangton](https://forums.unrealengine.com/u/plangton)\ **Post date:** [October 5, 2015, 9:50am UTC](https://forums.unrealengine.com/t/ue4-8-freezes-when-i-kill-a-thread/334294/3 "2015-10-05T09:50:50Z")
oh it was a mistype. I do not kill any class, I kill the running thread using a blueprint node which calls a function in the Frunnable class that calls Kill over FrunnableThread onject. I will modify the description now. As for the code I can provide it by the evening ---
**Author:** ![plangton](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@plangton](https://forums.unrealengine.com/u/plangton)\ **Post date:** [October 5, 2015, 6:42pm UTC](https://forums.unrealengine.com/t/ue4-8-freezes-when-i-kill-a-thread/334294/4 "2015-10-05T18:42:07Z")
#pragma region FRunnable functionalities ``` bool myKinect::Init() { stopRunnable = false; return true; } uint32 myKinect::Run() { FPlatformProcess::Sleep(0.03); while (!stopRunnable) { ;// calculate; } return 0; } void myKinect::Stop() { stopRunnable = true; } void myKinect::Exit() { } void myKinect::StartSensor() { if (!kinectThread) { kinectThread = FRunnableThread::Create(this, TEXT("FKinectThread"), 0, EThreadPriority::TPri_AboveNormal); } } void myKinect::StopSensor() { if (kinectThread) { kinectThread->Kill(true); delete kinectThread; kinectThread = nullptr; } } #pragma endregion // now here is the UactorComponent that runs the thread in myKinect class void UMyKinectHandlerComponent::BeginPlay() { Super::BeginPlay(); kinectHandler = myKinect::getHandler(); // this is a singleton } // Called every frame void UMyKinectHandlerComponent::TickComponent( float DeltaTime, ELevelTick TickType, FActorComponentTickFunction* ThisTickFunction ) { Super::TickComponent( DeltaTime, TickType, ThisTickFunction ); // ... } #pragma region Kinect Handling Functions void UMyKinectHandlerComponent::StartSensor() { kinectHandler->StartSensor(); } void UMyKinectHandlerComponent::StopSensor() { kinectHandler->StopSensor(); // crash happens whe this is getting called } #pragma endregion ``` ---
**Author:** ![plangton](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@plangton](https://forums.unrealengine.com/u/plangton)\ **Post date:** [October 5, 2015, 6:44pm UTC](https://forums.unrealengine.com/t/ue4-8-freezes-when-i-kill-a-thread/334294/5 "2015-10-05T18:44:22Z")
I have posted the code under the main question for you to have a look 🙂 ---
**Author:** ![plangton](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@plangton](https://forums.unrealengine.com/u/plangton)\ **Post date:** [October 6, 2015, 10:55am UTC](https://forums.unrealengine.com/t/ue4-8-freezes-when-i-kill-a-thread/334294/6 "2015-10-06T10:55:35Z")
I have found out that the problem is with Kill(true). meaning that if I call it Kill(false) then it wouldn’t be a problem. UE4 freezes due to stuck in WaitForSingleObject(Thread,INFINITE); in the following function Interestingly there is no problem with debug mode ☹ ``` virtual bool Kill( bool bShouldWait = false ) override { check(Thread && "Did you forget to call Create()?"); bool bDidExitOK = true; // Let the runnable have a chance to stop without brute force killing if (Runnable) { Runnable->Stop(); } // If waiting was specified, wait the amount of time. If that fails, // brute force kill that thread. Very bad as that might leak. if (bShouldWait == true) { // Wait indefinitely for the thread to finish. IMPORTANT: It's not safe to just go and // kill the thread with TerminateThread() as it could have a mutex lock that's shared // with a thread that's continuing to run, which would cause that other thread to // dead-lock. (This can manifest itself in code as simple as the synchronization // object that is used by our logging output classes. Trust us, we've seen it!) WaitForSingleObject(Thread,INFINITE); } // Now clean up the thread handle so we don't leak CloseHandle(Thread); Thread = NULL; return bDidExitOK; } ``` ---
**Author:** ![Rama](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/rama/32/882413_2.png) [@Rama](https://forums.unrealengine.com/u/Rama)\ **Post date:** [November 1, 2015, 9:11am UTC](https://forums.unrealengine.com/t/ue4-8-freezes-when-i-kill-a-thread/334294/7 "2015-11-01T09:11:15Z")
#Let the Thread complete You should be allowing the thread to complete! See the code in my PrimeNumber multi thread example! > **[A new, community-hosted Unreal Engine Wiki](https://forums.unrealengine.com/t/a-new-community-hosted-unreal-engine-wiki/141494)** > > After over a year in maintenance mode, the official Unreal Engine Wiki is now permanently offline. These resources now live on a new community-run Unreal Engine Community Wiki — ue4community.wiki! You will be able to find content from the official... ``` void FPrimeNumberWorker::EnsureCompletion() { Stop(); Thread->WaitForCompletion(); } void FPrimeNumberWorker::Shutdown() { if (Runnable) { Runnable->EnsureCompletion(); delete Runnable; Runnable = NULL; } } ``` 🙂 Rama ---
**Author:** ![plangton](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@plangton](https://forums.unrealengine.com/u/plangton)\ **Post date:** [November 2, 2015, 1:30pm UTC](https://forums.unrealengine.com/t/ue4-8-freezes-when-i-kill-a-thread/334294/8 "2015-11-02T13:30:58Z")
Hi, I have found the issue, and the solution. there is no need of the thread to be completed at all. the problem is that since the stop function of the thread is using windows standard functionalities the cpp or at least the part in charge of stopping should be wrapped in #include “AllowWindowsPlatformTypes.h” and #include “HideWindowsPlatformTypes.h”. it will solve the problem. ``` #include "DepthKinect2Plugin.h" #include "myKinect.h" #include "AllowWindowsPlatformTypes.h" myKinect::myKinect() { ... } myKinect::~myKinect() { ... } bool myKinect::Init() { ... } uint32 myKinect::Run() { ... } void myKinect::Stop() { ... } void myKinect::Exit() { ... } bool myKinect::IsRunning() { ... } void myKinect::StartSensor() { if (!kinectThread) { kinectThread = FRunnableThread::Create(this, TEXT("FKinectThread"), 0, EThreadPriority::TPri_Normal); UE_LOG(LogClass, Log, _T("Kinect Thread is Created Successfully")); } } void myKinect::StopSensor() { UE_LOG(LogClass, Log, _T("Stop Sensor Function for Kinect Thread is Called")); if (kinectThread) { kinectThread->Kill(true); delete kinectThread; kinectThread = nullptr; } } #include "HideWindowsPlatformTypes.h" ``` ---
**Author:** ![plangton](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@plangton](https://forums.unrealengine.com/u/plangton)\ **Post date:** [November 2, 2015, 1:32pm UTC](https://forums.unrealengine.com/t/ue4-8-freezes-when-i-kill-a-thread/334294/9 "2015-11-02T13:32:14Z")
although your code does not make issue and it is ok the problem is that for your code the thread will and should finish by finishing its work. I might want to have a code which stops the thread on demand. I have posted the solution I have had found for the problem