How to async task in Unreal Engine

Unreal Engine has a nice feature called AsyncTask, which is used to execute a code asynchronously. It works by running certain code on a specified thread, and this functionality is mostly used when the task is heavy enough to be executed instantly without blocking the game thread.

It also provides a solution to all issues arising from multithreading, in particular, accessing parameters from one thread that are supposed to be used and/or edited in another thread. ¹

AsyncTask(ENamedThreads::AnyThread, []()
{
	// This code will run asynchronously, without freezing the game thread
});

You can also create nested calls to asynchronous tasks, for example:

AsyncTask(ENamedThreads::AnyThread, []()
{
	// This code will run asynchronously, without freezing the game thread
		
	AsyncTask(ENamedThreads::GameThread, []()
	{
		// This code will be executed on the game thread
	});
});

You can also combine this with delegates and execute your code asynchronously with Blueprints

DECLARE_DYNAMIC_DELEGATE_OneParam(FAsyncDelegateExample, const TArray<float>&, OutData);

// Class, meta, etc

UFUNCTION(BlueprintCallable)
static void AddNumbersAsync(TArray<float> InData, const FAsyncDelegateExample& Result)
{
	AsyncTask(ENamedThreads::AnyThread, [InData = MoveTemp(InData), Result]() mutable
	{
		// Just for example
		for (float& InDataElement : InData)
		{
			InDataElement += 10;
		}

		AsyncTask(ENamedThreads::GameThread, [OutData = MoveTemp(InData), Result]() mutable
		{
			Result.ExecuteIfBound(OutData);
		});
	});
}

Async BP example

It is known that it is not possible to safely access an object from one thread that is being edited on another thread without using synchronization techniques such as mutexes . But some engine-specific code does not have these thread synchronization features, so the only way to safely access these objects is to simply access them from the desired thread ↩︎