etl/src/ipool.h

///\file

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

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

Copyright(c) 2014 jwellbelove

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files(the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions :

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
******************************************************************************/

#ifndef __ETL_IPOOL__
#define __ETL_IPOOL__
#define __ETL_IN_IPOOL_H__

#include <iterator>

#include "platform.h"
#include "nullptr.h"
#include "alignment.h"
#include "error_handler.h"

#include <algorithm>

#undef ETL_FILE
#define ETL_FILE "11"

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

    pool_exception(string_type what, string_type file_name, numeric_type line_number)
      : exception(what, file_name, line_number)
    {}
  };

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

    explicit pool_no_allocation(string_type file_name, numeric_type line_number)
      : pool_exception(ETL_ERROR_TEXT("pool:allocation", ETL_FILE"A"), file_name, line_number)
    {}
  };

  //***************************************************************************
  /// 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(string_type file_name, numeric_type line_number)
      : pool_exception(ETL_ERROR_TEXT("pool:notinpool", ETL_FILE"B"), file_name, line_number)
    {}
  };

  //***************************************************************************
  ///\ingroup pool
  //***************************************************************************
  class ipool
  {
  public:

    typedef size_t size_type;

    //*************************************************************************
    /// Allocate an object from the pool.
    /// Uses the default constructor.
    /// If asserts or exceptions are enabled and there are no more free items an
    /// etl::pool_no_allocation if thrown, otherwise a nullptr is returned.
    //*************************************************************************
    template <typename T>
    T* allocate()
    {
      return reinterpret_cast<T*>(allocate_item());
    }

    //*************************************************************************
    /// Release an object in the pool.
    /// If asserts or exceptions are enabled 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 void* p_object)
    {
      release_item((char*)p_object);
    }

    //*************************************************************************
    /// Release all objects in the pool.
    //*************************************************************************
    void release_all()
    {
      items_allocated   = 0;
      items_initialised = 0;
      p_next = p_buffer;
    }

    //*************************************************************************
    /// Check to see if the object belongs to the pool.
    /// \param p_object A pointer to the object to be checked.
    /// \return <b>true<\b> if it does, otherwise <b>false</b>
    //*************************************************************************
    //template <typename T>
    bool is_in_pool(const void* p_object) const
    {
      return is_item_in_pool((const char*)p_object);
    }

    //*************************************************************************
    /// Returns the maximum number of items in the pool.
    //*************************************************************************
    size_t max_items() const
    {
      return MAX_ITEMS;
    }

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

    //*************************************************************************
    /// Returns the number of allocated items in the pool.
    //*************************************************************************
    size_t size() const
    {
      return items_allocated;
    }

    //*************************************************************************
    /// Checks to see if there are no allocated items in the pool.
    /// \return <b>true</b> if there are none allocated.
    //*************************************************************************
    bool empty() const
    {
      return items_allocated == 0;
    }

    //*************************************************************************
    /// Checks to see if there are no free items in the pool.
    /// \return <b>true</b> if there are none free.
    //*************************************************************************
    bool full() const
    {
      return items_allocated == MAX_ITEMS;
    }

  protected:
    
    //*************************************************************************
    /// Constructor
    //*************************************************************************
    ipool(char* p_buffer_, uint32_t item_size, uint32_t max_items)
      : p_buffer(p_buffer_),
        p_next(p_buffer_),
        items_allocated(0),
        items_initialised(0),
        ITEM_SIZE(item_size),
        MAX_ITEMS(max_items)
    {
    }

  private:

    //*************************************************************************
    /// Allocate an item from the pool.
    //*************************************************************************
    char* allocate_item()
    {
      char* p_value = nullptr;

      // Any free space left?
      if (items_allocated < MAX_ITEMS)
      {
        // Initialise another one if necessary.
        if (items_initialised < MAX_ITEMS)
        {
          uintptr_t p = reinterpret_cast<uintptr_t>(p_buffer + (items_initialised * ITEM_SIZE));
          *reinterpret_cast<uintptr_t*>(p) = p + ITEM_SIZE;
          ++items_initialised;
        }

        // Get the address of new allocated item.
        p_value = p_next;

        ++items_allocated;
        if (items_allocated != MAX_ITEMS)
        {
          // Set up the pointer to the next free item
          p_next = *reinterpret_cast<char**>(p_next);
        }
        else
        {
          // No more left!
          p_next = nullptr;
        }
      }
      else
      {
        ETL_ASSERT(false, ETL_ERROR(etl::pool_no_allocation));
      }

      return p_value;
    }

    //*************************************************************************
    /// Release an item back to the pool.
    //*************************************************************************
    void release_item(char* p_value)
    {
      // Does it belong to us?
      ETL_ASSERT(is_item_in_pool(p_value), ETL_ERROR(pool_object_not_in_pool));

      if (p_next != nullptr)
      {
        // Point it to the current free item.
        *(uintptr_t*)p_value = reinterpret_cast<uintptr_t>(p_next);
      }
      else
      {
        // This is the only free item.
        *((uintptr_t*)p_value) = 0;        
      }

      p_next = p_value;

      --items_allocated;
    }

    //*************************************************************************
    /// Check if the item belongs to this pool.
    //*************************************************************************
    bool is_item_in_pool(const char* p) const
    {
      // Within the range of the buffer?
      intptr_t distance = p - p_buffer;
      bool is_within_range = (distance >= 0) && (distance <= intptr_t((ITEM_SIZE * MAX_ITEMS) - ITEM_SIZE));

      // Modulus and division can be slow on some architectures, so only do this in debug.
#if defined(ETL_DEBUG)
      // Is the address on a valid object boundary?
      bool is_valid_address = ((distance % ITEM_SIZE) == 0);
#else
      bool is_valid_address = true;
#endif

      return is_within_range && is_valid_address;
    }

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

    char* p_buffer;
    char* p_next;
    
    uint32_t  items_allocated;   ///< The number of items allocated.
    uint32_t  items_initialised; ///< The number of items initialised.

    const uint32_t ITEM_SIZE;    ///< The size of allocated items.
    const uint32_t MAX_ITEMS;    ///< The maximum number of objects that can be allocated.
  };
}

#undef ETL_FILE

#undef __ETL_IN_IPOOL_H__

#endif