There are a bunch of ways to do threads in Unreal. Today we're going to cover
possibly the simplest one, FRunnable.
I updated this example based on how FRunnable is used in the Unreal source code.
If you need more examples of FRunnable, I strongly recommend taking a look.
BUIExampleRunnable.h
#pragma once
#include "CoreMinimal.h"
#include "HAL/Runnable.h"
DECLARE_DYNAMIC( FBUIOnCompleteSignature );
// Note that we do not have to mark our class as UCLASS() if we don't want to
class FBUIExampleRunnable : public FRunnable
{
public:
// Custom constructor for setting up our thread with its target
FBUIExampleRunnable(int32 InTargetCount);
virtual ~FBUIExampleRunnable();
// FRunnable functions
virtual uint32 Run() override;
virtual void Stop() override;
virtual void Exit() override;
// FRunnable
FBUIOnCompleteSignature OnCompleteDelegate;
protected:
FRunnableThread* Thread = nullptr;
TArray<int32> ProcessedNumbers;
int32 TargetCount = -1;
int32 FoundCount = -1;
bool bStopThread = false;
};
BUIExampleRunnable.cpp
#include "ThreadExample.h"
FBUIExampleRunnable::FBUIExampleRunnable( int32 InTargetCount )
{
TargetCount = InTargetCount;
FoundCount = 0;
Thread = FRunnableThread::Create( this, TEXT( "This is my thread example" ) );
}
FBUIExampleRunnable::~FBUIExampleRunnable()
{
if ( Thread != nullptr )
{
Thread->Kill( true );
delete Thread;
}
}
uint32 FBUIExampleRunnable::Run()
{
bStopThread = false;
// Keep processing until we're cancelled through Stop() or we're done,
// although this thread will suspended for other stuff to happen at the same time
while ( !bStopThread && FoundCount < TargetCount )
{
// This is where we would do our expensive threaded processing
// Instead we're going to make a really busy while loop to slow down processing
// You can change INT_MAX to something smaller if you want it to run faster
int32 x = 0;
while ( x < INT_MAX )
{
x++;
}
ProcessedNumbers.Add( FMath::RandRange( 0, 999 ) );
FoundCount += 1;
}
OnCompleteDelegate.ExecuteIfBound();
// Return success
return 0;
}
void FBUIExampleRunnable::Exit()
{
// Here's where we can do any cleanup we want to
}
void FBUIExampleRunnable::Stop()
{
// Force our thread to stop early
bStopThread = true;
}
Running our code
TSharedPtr<FBUIExampleRunnable> SomeRunnable = MakeShared<FBUIExampleRunnable>( 10 );
