etl/pool.h

///\file

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

Embedded Template Library.

Copyright(c) 2014 jwellbelove

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#ifndef __ETL_POOL__
#define __ETL_POOL__

#include "bitset.h"
#include "nullptr.h"

#include <iterator>

//*****************************************************************************
///\defgroup pool pool
/// A fixed capacity pool.
///\ingroup containers
//*****************************************************************************

namespace etl
{
#ifdef ETL_THROW_EXCEPTIONS
  //***************************************************************************
  /// The base class for pool exceptions.
  ///\ingroup pool
  //***************************************************************************
  class pool_exception : public exception
  {
  public:

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

  //***************************************************************************
  /// The exception thrown when the pool has no more free items.
  ///\ingroup pool
  //***************************************************************************
  class pool_no_allocation : public pool_exception
  {
  public:

    pool_no_allocation()
      : pool_exception("pool: no allocation")
    {}
  };

  //***************************************************************************
  /// The exception thrown when an object is released which does not belong to the pool.
  ///\ingroup pool
  //***************************************************************************
  class pool_object_not_in_pool : public pool_exception
  {
  public:

    pool_object_not_in_pool()
      : pool_exception("pool: not in pool")
    {}
  };
#endif

  //*************************************************************************
  /// A templated pool implementation that uses a fixed size pool.
  /// SIZE_ elements will be always be constructed.
  //*************************************************************************
  template <typename T, const size_t SIZE_>
  class pool
  {
  public:

    static const size_t SIZE = SIZE_;

    //*************************************************************************
    /// Constructor
    //*************************************************************************
    pool()
      : next_free(0),
        count(0)
    {
    }

    //*************************************************************************
    /// Allocate an object from the pool.
    /// If ETL_THROW_EXCEPTIONS is defined and there are no more free items an
    /// etl::pool_no_allocation if thrown, otherwise a nullptr is returned.
    /// \note The state of the object returned is undefined.
    //*************************************************************************
    T* allocate()
    {
      if (next_free != SIZE)
      {
        T* result = &buffer[next_free];
        in_use.set(next_free);
        next_free = in_use.find_first(false);
        ++count;
        return result;
      }
      else
      {
#ifdef ETL_THROW_EXCEPTIONS
        throw pool_no_allocation();
#else
        return nullptr;
#endif
      }
    }

    //*************************************************************************
    /// Free an object in the pool.
    /// If ETL_THROW_EXCEPTIONS is defined and the object does not belong to this
    /// pool then an etl::pool_object_not_in_pool is thrown.
    /// \param object A reference to the object to be released.
    //*************************************************************************
    void release(const T& object)
    {
      release(&object);
    }

    //*************************************************************************
    /// Free an object in the pool.
    /// If ETL_THROW_EXCEPTIONS is defined and the object does not belong to this
    /// pool then an etl::pool_object_not_in_pool is thrown.
    /// \param p_object A pointer to the object to be released.
    //*************************************************************************
    void release(const T* const p_object)
    {
      // Does this object belong to this pool?
      typename std::iterator_traits<T*>::difference_type distance = p_object - buffer;

      // Not within the range of the buffer?
      if ((distance < 0) || (distance >= SIZE))
      {
#ifdef ETL_THROW_EXCEPTIONS
        throw pool_object_not_in_pool();
#endif
      }
      else
      {
        // Mark the object as available.
        next_free = static_cast<size_t>(distance);
        in_use.reset(next_free);
        --count;
      }
    }

    //*************************************************************************
    /// Returns the number of free items in the pool.
    //*************************************************************************
    size_t available() const
    {
      return SIZE - in_use.count();
    }

    //*************************************************************************
    /// Checks to see if there are no free items in the pool.
    /// \return <b>true</b> if there are none free (or 'empty')
    //*************************************************************************
    bool empty() const
    {
      return count == SIZE;
    }

  private:

    size_t       next_free;    ///< The position of the next free item in the pool.
    size_t       count;        ///< The number of objects allocated.
    T            buffer[SIZE]; ///< The pool of objects.
    bitset<SIZE> in_use;       ///< The set of flags that indicate which items are free in the pool.
  };
}
#endif