fallback_allocator.hpp

/*****************************************************************************
 * \file
 * \brief This header defines an allocator that falls-back on failure to other
 *        allocators
 *****************************************************************************/

/*
  The MIT License (MIT)

  Copyright (c) 2018 Matthew Rodusek

  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 BIT_MEMORY_ALLOCATORS_FALLBACK_ALLOCATOR_HPP
#define BIT_MEMORY_ALLOCATORS_FALLBACK_ALLOCATOR_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include "detail/named_allocator.hpp" // detail::named_allocator

#include "../utilities/ebo_storage.hpp" // detail::ebo_storage
#include "../utilities/macros.hpp"             // BIT_MEMORY_UNUSED
#include "../utilities/owner.hpp"              // owner

#include "../concepts/Allocator.hpp" // allocator_pointer_t, etc

#include "../traits/allocator_traits.hpp" // allocator_traits

#include <tuple>     // std::forward_as_tuple
#include <utility>   // std::forward
#include <cstddef>   // std::size_t
#include <algorithm> // std::max, std::min

namespace bit {
  namespace memory {

    template<typename...AllocatorStorages>
    class fallback_allocator
      : private ebo_storage<AllocatorStorages...>
    {

      using base_type = ebo_storage<AllocatorStorages...>;

      // TODO(bitwizeshift): Support pretty-pointers by determining the common
      //                     'pointer', 'const_pointer', and 'size_type' of
      //                     each allocator

      //-----------------------------------------------------------------------
      // Constructors
      //-----------------------------------------------------------------------
    public:

      explicit fallback_allocator( AllocatorStorages...storages ) noexcept;

      fallback_allocator( fallback_allocator&& other ) = default;

      fallback_allocator( const fallback_allocator& other ) = default;

      //-----------------------------------------------------------------------

      fallback_allocator& operator=( fallback_allocator&& other ) = default;

      fallback_allocator& operator=( const fallback_allocator& other ) = default;

      //-----------------------------------------------------------------------
      // Allocations
      //-----------------------------------------------------------------------
    public:

      owner<void*> try_allocate( std::size_t size,
                                 std::size_t align ) noexcept;

      void deallocate( owner<void*> p, std::size_t size );

      //-----------------------------------------------------------------------
      // Observers
      //-----------------------------------------------------------------------
    public:

      bool owns( const void* p ) const noexcept;

      //-----------------------------------------------------------------------
      // Capacity
      //-----------------------------------------------------------------------
    public:

      std::size_t max_size() const noexcept;

      std::size_t min_size() const noexcept;

      //-----------------------------------------------------------------------
      // Private Allocation / Deallocation
      //-----------------------------------------------------------------------
    private:

      template<std::size_t Idx>
      void* do_try_allocate( std::integral_constant<std::size_t,Idx>,
                             std::size_t size,
                             std::size_t align ) noexcept;

      void* do_try_allocate( std::integral_constant<std::size_t,sizeof...(AllocatorStorages)-1>,
                             std::size_t size,
                             std::size_t align ) noexcept;

      //-----------------------------------------------------------------------

      template<std::size_t Idx>
      void do_deallocate( std::integral_constant<std::size_t,Idx>,
                          void* p,
                          std::size_t size );

      void do_deallocate( std::integral_constant<std::size_t,sizeof...(AllocatorStorages)-1>,
                          void* p,
                          std::size_t size );

      //-----------------------------------------------------------------------
      // Private Observers
      //-----------------------------------------------------------------------
    private:

      template<std::size_t...Idxs>
      bool do_owns( std::index_sequence<Idxs...>,
                    const void* p ) const noexcept;

      //-----------------------------------------------------------------------
      // Private Capacity
      //-----------------------------------------------------------------------
    private:

      template<std::size_t...Idxs>
      std::size_t do_max_size( std::index_sequence<Idxs...> ) const noexcept;

      template<std::size_t...Idxs>
      std::size_t do_min_size( std::index_sequence<Idxs...> ) const noexcept;

    };

    //-------------------------------------------------------------------------
    // Utilities
    //-------------------------------------------------------------------------

    template<typename...Allocators>
    using named_fallback_allocator = detail::named_allocator<fallback_allocator<Allocators...>>;

    //-------------------------------------------------------------------------

    template<typename...AllocatorStorages>
    fallback_allocator<AllocatorStorages...>
      make_fallback_allocator( AllocatorStorages...storages );

    template<typename...AllocatorStorages>
    named_fallback_allocator<AllocatorStorages...>
      make_named_fallback_allocator( const char* name,
                                     AllocatorStorages...storages );

  } // namespace memory
} // namespace bit

#include "detail/fallback_allocator.inl"

#endif /* BIT_MEMORY_ALLOCATORS_FALLBACK_ALLOCATOR_HPP */