IPlugQueue.h

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/*
 ==============================================================================
 
 This file is part of the iPlug 2 library. Copyright (C) the iPlug 2 developers. 
 
 See LICENSE.txt for  more info.
 
 ==============================================================================
*/

#pragma once

#include <atomic>
#include <cstddef>

#include "heapbuf.h"

BEGIN_IPLUG_NAMESPACE

template<typename T>
class IPlugQueue final
{
public:
  IPlugQueue(int size)
  {
    Resize(size);
  }

  ~IPlugQueue(){}

  IPlugQueue(const IPlugQueue&) = delete;
  IPlugQueue& operator=(const IPlugQueue&) = delete;
    
  void Resize(int size)
  {
    mData.Resize(size + 1);
  }

  bool Push(const T& item)
  {
    const auto currentWriteIndex = mWriteIndex.load(std::memory_order_relaxed);
    const auto nextWriteIndex = Increment(currentWriteIndex);
    if(nextWriteIndex != mReadIndex.load(std::memory_order_acquire))
    {
      mData.Get()[currentWriteIndex] = item;
      mWriteIndex.store(nextWriteIndex, std::memory_order_release);
      return true;
    }
    return false;
  }

  bool Pop(T& item)
  {
    const auto currentReadIndex = mReadIndex.load(std::memory_order_relaxed);
    if(currentReadIndex == mWriteIndex.load(std::memory_order_acquire))
    {
      return false; // empty the queue
    }
    item = mData.Get()[currentReadIndex];
    mReadIndex.store(Increment(currentReadIndex), std::memory_order_release);
    return true;
  }

  size_t ElementsAvailable() const
  {
    return (mWriteIndex.load(std::memory_order_acquire) - mReadIndex.load(std::memory_order_relaxed))%mData.GetSize();
  }

  const T& Peek()
  {
    const auto currentReadIndex = mReadIndex.load(std::memory_order_relaxed);
    return mData[currentReadIndex];
  }

  bool WasEmpty() const
  {
    return (mWriteIndex.load() == mReadIndex.load());
  }

  bool WasFull() const
  {
    const auto nextWriteIndex = Increment(mWriteIndex.load());
    return (nextWriteIndex == mReadIndex.load());
  }

private:
  size_t Increment(size_t idx) const
  {
    return (idx + 1) % (mData.GetSize());
  }

  WDL_TypedBuf<T> mData;
  std::atomic<size_t> mWriteIndex{0};
  std::atomic<size_t> mReadIndex{0};
};

END_IPLUG_NAMESPACE