etl/queue_base.h

///\file

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

Embedded Template Library.

Copyright(c) 2014 jwellbelove

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******************************************************************************/

#ifndef __etl_queue_base__
#define __etl_queue_base__

#include <cstddef>

#include "exception.h"

///\defgroup Queue Queue
///\ingroup Containers

namespace etl
{
#ifdef ETL_USE_EXCEPTIONS
  //***************************************************************************
  ///\ingroup Queue
  ///\brief This is the base for all queues.
  ///\detail This is the base for all queues. Instances or references to this type should never need to be created.
  /// The base class for queue exceptions.
  //***************************************************************************
  class queue_exception : public exception
  {
  public:

    queue_exception(const char* what)
      : exception(what)
    {
    }
  };

  //***************************************************************************
  ///\ingroup Queue
  /// The exception thrown when the queue is full.
  //***************************************************************************
  class queue_full_exception : public queue_exception
  {
  public:

    queue_full_exception()
      : queue_exception("queue full exception")
    {
    }
  };

  //***************************************************************************
  ///\ingroup Queue
  /// The exception thrown when the queue is empty.
  //***************************************************************************
  class queue_empty_exception : public queue_exception
  {
  public:

    queue_empty_exception()
      : queue_exception("queue empty exception")
    {
    }
  };
#endif

  //***************************************************************************
  ///\ingroup Queue
  /// A fixed capacity queue written in the STL style.
  /// \warning This queue cannot be used for concurrent access from multiple threads.
  //***************************************************************************
  class queue_base
  {
  public:

    typedef size_t size_type; ///< The type used for determining the size of queue.

    //*************************************************************************
    /// Returns the current number of items in the queue.
    //*************************************************************************
    size_type size() const
    {
      return size;
    }

    //*************************************************************************
    /// Returns the maximum number of items that can be queued.
    //*************************************************************************
    size_type capacity() const
    {
      return MAX_SIZE;
    }

    //*************************************************************************
    /// Returns the maximum number of items that can be queued.
    //*************************************************************************
    size_type max_size() const
    {
      return MAX_SIZE;
    }

    //*************************************************************************
    /// Clears the queue to the empty state.
    //*************************************************************************
    void clear()
    {
      in   = 0;
      out  = 0;
      size = 0;
    }

    //*************************************************************************
    /// Checks to see if the queue is empty.
    /// \return <b>true</b> if the queue is empty, otherwise <b>false</b>
    //*************************************************************************
    bool empty() const
    {
      return size == 0;
    }

    //*************************************************************************
    /// Checks to see if the queue is full.
    /// \return <b>true</b> if the queue is full, otherwise <b>false</b>
    //*************************************************************************
    bool full() const
    {
      return size == MAX_SIZE;
    }

    //*************************************************************************
    /// Removes the oldest item from the back of the queue.
    /// Does nothing if the queue is already empty.
    //*************************************************************************
    void pop()
    {
      if (!empty())
      {
        out = (out == (MAX_SIZE - 1)) ? 0 : ++out;
        --size;
      }
    }

  protected:

    //*************************************************************************
    /// The constructor that is called from derived classes.
    //*************************************************************************
    queue_base(size_type max_size)
      : MAX_SIZE(max_size)
    {
      clear();
    }

    size_type in;             ///< Where to input new data.
    size_type out;            ///< Where to get the oldest data.
    size_type size;           ///< The number of items in the queue.
    const size_type MAX_SIZE; ///< The maximum number of items in the queue.
  };
}