如何在UE4中创建线程

FRunnable和FRunnableThread方法对于大多数问题来说无疑是一个可行的解决方案。但是，在创建许多任务时，您可能会达到CPU可以处理的并发上限，此时并发线程实际上会在争用CPU时间时相互阻碍。然后可能值得查看FQueuedThreadPool以限制任务可用的线程数。

虚幻引擎4还提供了全局GThreadPool ，但是此线程池仅设置为单个线程（UE4.14.3）。它似乎只是为了在另一个核心上运行并发任务。

下面的代码是什么

创建一个线程来计算前50,000个素数
将增量完成数据发送回游戏线程
具有静态访问器，用于启动，关闭和查找线程是否已完成。

静态函数

您将在下面的代码中注意到我使用静态函数轻松启动新线程，如果我需要匆忙关闭线程（例如播放器退出），我也可以使用GameThread中的静态Shutdown（）函数游戏）

性能

我首先使用任务图系统计算前50,000个素数，并创建50,000个任务（每个素数找1个）。

在本教程中看到的代码中，我创建了一个专用线程来计算前50,000个素数！

性能优势是非凡的！

我的fps在下面的代码中为这个线程的整个运行保持稳定90（我选择的最大fps）。

而对于任务图系统，当我接近50,000时，fps下降了最多40。

对于较大的任务，请务必尝试实际的多线程！

.H

//~~~~~ Multi Threading ~~~
class FPrimeNumberWorker : public FRunnable
{	/** Singleton instance, can access the thread any time via static accessor, if it is active! */static  FPrimeNumberWorker* Runnable;/** Thread to run the worker FRunnable on */FRunnableThread* Thread;/** The Data Ptr */TArray<uint32>* PrimeNumbers;/** The PC */AVictoryGamePlayerController* ThePC;/** Stop this thread? Uses Thread Safe Counter */FThreadSafeCounter StopTaskCounter;//The actual finding of prime numbersint32 FindNextPrimeNumber();private:int32				PrimesFoundCount;
public:int32				TotalPrimesToFind;//Done?bool IsFinished() const{return PrimesFoundCount >= TotalPrimesToFind;}//~~~ Thread Core Functions ~~~//Constructor / DestructorFPrimeNumberWorker(TArray<uint32>& TheArray, const int32 IN_PrimesToFindPerTick, AVictoryGamePlayerController* IN_PC);virtual ~FPrimeNumberWorker();// Begin FRunnable interface.virtual bool Init();virtual uint32 Run();virtual void Stop();// End FRunnable interface/** Makes sure this thread has stopped properly */void EnsureCompletion();//~~~ Starting and Stopping Thread ~~~/* Start the thread and the worker from static (easy access)! This code ensures only 1 Prime Number thread will be able to run at a time. This function returns a handle to the newly started instance.*/static FPrimeNumberWorker* JoyInit(TArray<uint32>& TheArray, const int32 IN_TotalPrimesToFind, AVictoryGamePlayerController* IN_PC);/** Shuts down the thread. Static so it can easily be called from outside the thread context */static void Shutdown();static bool IsThreadFinished();};

.CPP

//***********************************************************
//Thread Worker Starts as NULL, prior to being instanced
//		This line is essential! Compiler error without it
FPrimeNumberWorker* FPrimeNumberWorker::Runnable = NULL;
//***********************************************************FPrimeNumberWorker::FPrimeNumberWorker(TArray<uint32>& TheArray, const int32 IN_TotalPrimesToFind, AVictoryGamePlayerController* IN_PC): ThePC(IN_PC), TotalPrimesToFind(IN_TotalPrimesToFind), StopTaskCounter(0), PrimesFoundCount(0)
{//Link to where data should be storedPrimeNumbers = &TheArray;Thread = FRunnableThread::Create(this, TEXT("FPrimeNumberWorker"), 0, TPri_BelowNormal); //windows default = 8mb for thread, could specify more
}FPrimeNumberWorker::~FPrimeNumberWorker()
{delete Thread;Thread = NULL;
}//Init
bool FPrimeNumberWorker::Init()
{//Init the Data PrimeNumbers->Empty();PrimeNumbers->Add(2);PrimeNumbers->Add(3);if(ThePC) {ThePC->ClientMessage("**********************************");ThePC->ClientMessage("Prime Number Thread Started!");ThePC->ClientMessage("**********************************");}return true;
}//Run
uint32 FPrimeNumberWorker::Run()
{//Initial wait before startingFPlatformProcess::Sleep(0.03);//While not told to stop this thread //		and not yet finished finding Prime Numberswhile (StopTaskCounter.GetValue() == 0 && ! IsFinished()){PrimeNumbers->Add(FindNextPrimeNumber());PrimesFoundCount++;//***************************************//Show Incremental Results in Main Game Thread!//	Please note you should not create, destroy, or modify UObjects here.//	  Do those sort of things after all thread are completed.//	  All calcs for making stuff can be done in the threads//	     But the actual making/modifying of the UObjects should be done in main game thread.ThePC->ClientMessage(FString::FromInt(PrimeNumbers->Last()));//***************************************//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~//prevent thread from using too many resources//FPlatformProcess::Sleep(0.01);//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~}//Run FPrimeNumberWorker::Shutdown() from the timer in Game Thread that is watching//to see when FPrimeNumberWorker::IsThreadFinished()return 0;
}//stop
void FPrimeNumberWorker::Stop()
{StopTaskCounter.Increment();
}FPrimeNumberWorker* FPrimeNumberWorker::JoyInit(TArray<uint32>& TheArray, const int32 IN_TotalPrimesToFind, AVictoryGamePlayerController* IN_PC)
{//Create new instance of thread if it does not exist//		and the platform supports multi threading!if (!Runnable && FPlatformProcess::SupportsMultithreading()){Runnable = new FPrimeNumberWorker(TheArray,IN_TotalPrimesToFind,IN_PC);			}return Runnable;
}void FPrimeNumberWorker::EnsureCompletion()
{Stop();Thread->WaitForCompletion();
}void FPrimeNumberWorker::Shutdown()
{if (Runnable){Runnable->EnsureCompletion();delete Runnable;Runnable = NULL;}
}bool FPrimeNumberWorker::IsThreadFinished()
{if(Runnable) return Runnable->IsFinished();return true;
}
int32 FPrimeNumberWorker::FindNextPrimeNumber()
{//Last known prime number  + 1int32 TestPrime = PrimeNumbers->Last();bool NumIsPrime = false;while( ! NumIsPrime){NumIsPrime = true;//Try Next NumberTestPrime++;//Modulus from 2 to current number - 1 for(int32 b = 2; b < TestPrime; b++){//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~//prevent thread from using too many resources//FPlatformProcess::Sleep(0.01);//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~if(TestPrime % b == 0) {NumIsPrime = false;break;//~~~}}}//Success!return TestPrime;
}

Starting the thread

//In the .h for the player controller
// this is the actual data
TArray<uint32> PrimeNumbers;

//player controller .cpp
//Multi-threading, returns handle that could be cached.
//		use static function FPrimeNumberWorker::Shutdown() if necessary
FPrimeNumberWorker::JoyInit(PrimeNumbers, 50000, this);

线程管理

您应该查看“FRunnable”的代码库，以查看多线程和锁定/解锁保护的扩展用途。

我用了一个简单的例子来帮助你入门，但是多线程时需要考虑很多:)

使用Sleep进行线程管理

你应该考虑使用

  FPlatformProcess :: Sleep （ 秒 ）;

防止1个线程占用太多系统资源:)

什么不该做

不要尝试从其他线程修改，创建或删除UObject！

您可以准备所有数据/进行所有计算，但只有游戏线程应该实际产生/修改/删除UObjects / AActors。

不要尝试在游戏线程之外使用TimerManager :)

不要试图绘制调试行/点等，因为它可能会崩溃，即DrawDebugLine（等...）
通知（自4.11起）：

如果要使用计时器，删除和修改变量，请使用它：
```
  #include “Async.h” ...AsyncTask （ ENamedThreads :: GameThread ， []（） {//这里在游戏线程上执行的代码}）;
```
GameThread中的计时器功能

您可以在游戏线程中运行计时器功能，以定期检查您创建的其他线程收集的数据。

如何支持单线程平台？

如果您的代码绝对必须在HTML5等单线程环境中运行，那么请查看

AsyncIOSystemBase.h
```
  struct CORE_API FAsyncIOSystemBase：public FIOSystem，FRunnable，FSingleThreadRunnable
```
Runnable可以扩展SingleThreadRunnable，并为单线程情况下的FRunnable钩子返回自己：

/*** Gets single thread interface pointer used for ticking this runnable when multi-threading is disabled.* If the interface is not implemented, this runnable will not be ticked when FPlatformProcess::SupportsMultithreading() is false.** @return Pointer to the single thread interface or nullptr if not implemented.*/
virtual class FSingleThreadRunnable* GetSingleThreadInterface( )
{return nullptr;
}