etl/include/etl/queue_spsc_atomic.h

///\file

/******************************************************************************
The MIT License(MIT)

Embedded Template Library.
https://github.com/ETLCPP/etl
https://www.etlcpp.com

Copyright(c) 2018 jwellbelove

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#ifndef ETL_SPSC_QUEUE_ATOMIC_INCLUDED
#define ETL_SPSC_QUEUE_ATOMIC_INCLUDED

#include <stddef.h>
#include <stdint.h>

#include "platform.h"
#include "alignment.h"
#include "parameter_type.h"
#include "atomic.h"

#undef ETL_FILE
#define ETL_FILE "47"

namespace etl
{
  class queue_spsc_atomic_base
  {
  public:

    //*************************************************************************
    /// Is the queue empty?
    /// Accurate from the 'pop' thread.
    /// 'Not empty' is a guess from the 'push' thread.
    //*************************************************************************
    bool empty() const
    {
      return read.load(etl::memory_order_acquire) == write.load(etl::memory_order_acquire);
    }

    //*************************************************************************
    /// Is the queue full?
    /// Accurate from the 'push' thread.
    /// 'Not full' is a guess from the 'pop' thread.
    //*************************************************************************
    bool full() const
    {
      size_t next_index = get_next_index(write.load(etl::memory_order_acquire), RESERVED);

      return (next_index == read.load(etl::memory_order_acquire));
    }

    //*************************************************************************
    /// How many items in the queue?
    /// Due to concurrency, this is a guess.
    //*************************************************************************
    size_t size() const
    {
      size_t write_index = write.load(etl::memory_order_acquire);
      size_t read_index = read.load(etl::memory_order_acquire);

      size_t n;

      if (write_index >= read_index)
      {
        n = write_index - read_index;
      }
      else
      {
        n = RESERVED - read_index + write_index - 1;
      }

      return n;
    }

    //*************************************************************************
    /// How much free space available in the queue.
    /// Due to concurrency, this is a guess.
    //*************************************************************************
    size_t available() const
    {
      return RESERVED - size() - 1;
    }

    //*************************************************************************
    /// How many items can the queue hold.
    //*************************************************************************
    size_t capacity() const
    {
      return RESERVED - 1;
    }

    //*************************************************************************
    /// How many items can the queue hold.
    //*************************************************************************
    size_t max_size() const
    {
      return RESERVED - 1;
    }

  protected:

    queue_spsc_atomic_base(size_t reserved_)
      : write(0),
        read(0),
        RESERVED(reserved_)
    {
    }

    //*************************************************************************
    /// Calculate the next index.
    //*************************************************************************
    static size_t get_next_index(size_t index, size_t maximum)
    {
      ++index;

      if (index == maximum)
      {
        index = 0;
      }

      return index;
    }

    etl::atomic_size_t write; ///< Where to input new data.
    etl::atomic_size_t read;  ///< Where to get the oldest data.
    const size_t RESERVED;    ///< The maximum number of items in the queue.

  private:

    //*************************************************************************
    /// Destructor.
    //*************************************************************************
#if defined(ETL_POLYMORPHIC_SPSC_QUEUE_ATOMIC) || defined(ETL_POLYMORPHIC_CONTAINERS)
  public:
    virtual ~queue_spsc_atomic_base()
    {
    }
#else
  protected:
    ~queue_spsc_atomic_base()
    {
    }
#endif
  };
  
  //***************************************************************************
  ///\ingroup queue_spsc_atomic
  ///\brief This is the base for all queue_spscs that contain a particular type.
  ///\details Normally a reference to this type will be taken from a derived queue_spsc.
  ///\code
  /// etl::queue_spsc_atomic<int, 10> myQueue;
  /// etl::iqueue_spsc_atomic<int>& iQueue = myQueue;
  ///\endcode
  /// This queue supports concurrent access by one producer and one consumer.
  /// \tparam T The type of value that the queue_spsc_atomic holds.
  //***************************************************************************
  template <typename T>
  class iqueue_spsc_atomic : public queue_spsc_atomic_base
  {
  private:

    typedef typename etl::parameter_type<T>::type parameter_t;

  public:

    typedef T        value_type;      ///< The type stored in the queue.
    typedef T&       reference;       ///< A reference to the type used in the queue.
    typedef const T& const_reference; ///< A const reference to the type used in the queue.
    typedef size_t   size_type;       ///< The type used for determining the size of the queue.

    //*************************************************************************
    /// Push a value to the queue.
    //*************************************************************************
    bool push(parameter_t value)
    {
      size_t write_index = write.load(etl::memory_order_relaxed);
      size_t next_index  = get_next_index(write_index, RESERVED);

      if (next_index != read.load(etl::memory_order_acquire))
      {
        ::new (&p_buffer[write_index]) T(value);

        write.store(next_index, etl::memory_order_release);

        return true;
      }
      
      // Queue is full.
      return false;
    }

    //*************************************************************************
    /// Pop a value from the queue.
    //*************************************************************************
    bool pop(reference value)
    {     
      size_t read_index = read.load(etl::memory_order_relaxed);
      
      if (read_index == write.load(etl::memory_order_acquire)) 
      {
        // Queue is empty
        return false;
      }

      size_t next_index = get_next_index(read_index, RESERVED);

      value = p_buffer[read_index];
      p_buffer[read_index].~T();

      read.store(next_index, etl::memory_order_release);

      return true;
    }

    //*************************************************************************
    /// Pop a value from the queue and discard.
    //*************************************************************************
    bool pop()
    {
      size_t read_index = read.load(etl::memory_order_relaxed);

      if (read_index == write.load(etl::memory_order_acquire))
      {
        // Queue is empty
        return false;
      }

      size_t next_index = get_next_index(read_index, RESERVED);

      p_buffer[read_index].~T();

      read.store(next_index, etl::memory_order_release);

      return true;
    }

    //*************************************************************************
    /// Clear the queue.
    /// Must be called from thread that pops the queue or when there is no
    /// possibility of concurrent access.
    //*************************************************************************
    void clear()
    {
      while (pop())
      {
        // Do nothing.
      }
    }

  protected:

    //*************************************************************************
    /// The constructor that is called from derived classes.
    //*************************************************************************
    iqueue_spsc_atomic(T* p_buffer_, size_type reserved_)
      : queue_spsc_atomic_base(reserved_),
        p_buffer(p_buffer_)
    {
    }

  private:

    // Disable copy construction and assignment.
    iqueue_spsc_atomic(const iqueue_spsc_atomic&);
    iqueue_spsc_atomic& operator =(const iqueue_spsc_atomic&);

    T* p_buffer; ///< The internal buffer.
  };

  //***************************************************************************
  ///\ingroup queue_spsc
  /// A fixed capacity spsc queue.
  /// This queue supports concurrent access by one producer and one consumer.
  /// \tparam T    The type this queue should support.
  /// \tparam SIZE The maximum capacity of the queue.
  //***************************************************************************
  template <typename T, size_t SIZE>
  class queue_spsc_atomic : public iqueue_spsc_atomic<T>
  {
    typedef etl::iqueue_spsc_atomic<T> base_t;

    static const size_t RESERVED_SIZE = SIZE + 1;

  public:

    static const size_t MAX_SIZE = SIZE;

    //*************************************************************************
    /// Default constructor.
    //*************************************************************************
    queue_spsc_atomic()
      : base_t(reinterpret_cast<T*>(&buffer[0]), RESERVED_SIZE)
    {
    }

    //*************************************************************************
    /// Destructor.
    //*************************************************************************
    ~queue_spsc_atomic()
    {
      base_t::clear();
    }

  private:

    /// The uninitialised buffer of T used in the queue_spsc.
    typename etl::aligned_storage<sizeof(T), etl::alignment_of<T>::value>::type buffer[RESERVED_SIZE];
  };
};

#endif