CircularQueue.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
#include "Containers/CircularBuffer.h"
#include "Templates/Atomic.h"
 
// WARNING: This queue is planned for deprecation in favor of TSpscQueue
 
template<typename T> class TCircularQueue
{
public:
    using FElementType = T;
 
    explicit TCircularQueue(uint32 CapacityPlusOne)
        : Buffer(CapacityPlusOne)
        , Head(0)
        , Tail(0)
    { }
 
public:
 
    uint32 Count() const
    {
        int32 Count = Tail.Load() - Head.Load();
 
        if (Count < 0)
        {
            Count += Buffer.Capacity();
        }
 
        return (uint32)Count;
    }
 
    bool Dequeue(FElementType& OutElement)
    {
        const uint32 CurrentHead = Head.Load();
 
        if (CurrentHead != Tail.Load())
        {
            OutElement = MoveTemp(Buffer[CurrentHead]);
            Head.Store(Buffer.GetNextIndex(CurrentHead));
 
            return true;
        }
 
        return false;
    }
 
    bool Dequeue()
    {
        const uint32 CurrentHead = Head.Load();
 
        if (CurrentHead != Tail.Load())
        {
            Head.Store(Buffer.GetNextIndex(CurrentHead));
 
            return true;
        }
 
        return false;
    }
 
    void Empty()
    {
        Head.Store(Tail.Load());
    }
 
    bool Enqueue(const FElementType& Element)
    {
        const uint32 CurrentTail = Tail.Load();
        uint32 NewTail = Buffer.GetNextIndex(CurrentTail);
 
        if (NewTail != Head.Load())
        {
            Buffer[CurrentTail] = Element;
            Tail.Store(NewTail);
 
            return true;
        }
 
        return false;
    }
 
    bool Enqueue(FElementType&& Element)
    {
        const uint32 CurrentTail = Tail.Load();
        uint32 NewTail = Buffer.GetNextIndex(CurrentTail);
 
        if (NewTail != Head.Load())
        {
            Buffer[CurrentTail] = MoveTemp(Element);
            Tail.Store(NewTail);
 
            return true;
        }
 
        return false;
    }
 
    UE_FORCEINLINE_HINT bool IsEmpty() const
    {
        return (Head.Load() == Tail.Load());
    }
 
    bool IsFull() const
    {
        return (Buffer.GetNextIndex(Tail.Load()) == Head.Load());
    }
 
    bool Peek(FElementType& OutItem) const
    {
        const uint32 CurrentHead = Head.Load();
 
        if (CurrentHead != Tail.Load())
        {
            OutItem = Buffer[CurrentHead];
 
            return true;
        }
 
        return false;
    }
 
    const FElementType* Peek() const
    {
        const uint32 CurrentHead = Head.Load();
 
        if (CurrentHead != Tail.Load())
        {
            return &Buffer[CurrentHead];
        }
 
        return nullptr;
    }
 
private:
 
    TCircularBuffer<FElementType> Buffer;
 
    TAtomic<uint32> Head;
 
    TAtomic<uint32> Tail;
};