vulkan-wsi-layer/util/custom_allocator.hpp

/*
 * Copyright (c) 2020 Arm Limited.
 *
 * SPDX-License-Identifier: MIT
 *
 * 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.
 */

#include <new>
#include <vector>
#include <string>

#include <vulkan/vulkan.h>

#pragma once

namespace util
{

/**
 * @brief Minimalistic wrapper of VkAllocationCallbacks.
 */
class allocator
{
public:
   allocator(const VkAllocationCallbacks *callbacks, VkSystemAllocationScope scope);

   template <typename T, typename... arg_types>
   T *create(arg_types &&... args) const;

   template <typename T>
   void destroy(T *obj) const;

   VkAllocationCallbacks m_callbacks;
   VkSystemAllocationScope m_scope;
};

/**
 * @brief Implementation of an allocator that can be used with STL containers.
 */
template <typename T>
class custom_allocator
{
public:
   using value_type = T;
   using pointer = T *;

   custom_allocator(const allocator &alloc)
      : m_alloc(alloc)
   {
   }

   template <typename U>
   custom_allocator(const custom_allocator<U> &other)
      : m_alloc(other.get_data())
   {
   }

   const allocator &get_data() const
   {
      return m_alloc;
   }

   pointer allocate(size_t n) const
   {
      size_t size = n * sizeof(T);
      auto &cb = m_alloc.m_callbacks;
      void *ret = cb.pfnAllocation(cb.pUserData, size, alignof(T), m_alloc.m_scope);
      if (ret == nullptr)
         throw std::bad_alloc();
      return reinterpret_cast<pointer>(ret);
   }

   pointer allocate(size_t n, void *ptr) const
   {
      size_t size = n * sizeof(T);
      auto &cb = m_alloc.m_callbacks;
      void *ret = cb.pfnReallocation(cb.pUserData, ptr, size, alignof(T), m_alloc.m_scope);
      if (ret == nullptr)
         throw std::bad_alloc();
      return reinterpret_cast<pointer>(ret);
   }

   void deallocate(void *ptr, size_t) const noexcept
   {
      m_alloc.m_callbacks.pfnFree(m_alloc.m_callbacks.pUserData, ptr);
   }

private:
   const allocator m_alloc;
};

template <typename T, typename U>
bool operator==(const custom_allocator<T> &, const custom_allocator<U> &)
{
   return true;
}

template <typename T, typename U>
bool operator!=(const custom_allocator<T> &, const custom_allocator<U> &)
{
   return false;
}

/**
 * @brief Helper method to allocate and construct objects with a custom allocator.
 * @return The new object or @c nullptr if allocation failed.
 */
template <typename T, typename... arg_types>
T *allocator::create(arg_types &&... args) const
{
   custom_allocator<T> allocator(*this);
   T *ptr;
   try
   {
      ptr = allocator.allocate(1);
   }
   catch (...)
   {
      return nullptr;
   }

   try
   {
      new (ptr) T(std::forward<arg_types>(args)...);
   }
   catch (...)
   {
      /* We catch all exceptions thrown while constructing the object, not just
       * std::bad_alloc.
       */
      allocator.deallocate(ptr, 1);
      return nullptr;
   }
   return ptr;
}

/**
 * @brief Helper method to destroy and deallocate objects constructed with create_custom().
 */
template <typename T>
void allocator::destroy(T *obj) const
{
   obj->~T();
   custom_allocator<T> allocator(*this);
   allocator.deallocate(obj, 1);
}

template <typename T>
void destroy_custom(T *obj)
{
   T::destroy(obj);
}

/**
 * @brief Vector using a Vulkan custom allocator to allocate its elements.
 * @note The vector must be passed a custom_allocator during construction and it takes a copy
 *   of it, meaning that the user is free to destroy the custom_allocator after constructing the
 *   vector.
 */
template <typename T>
class vector : public std::vector<T, custom_allocator<T>>
{
public:
   using base = std::vector<T, custom_allocator<T>>;
   using base::base;

   /* Delete all methods that can cause allocation failure, i.e. can throw std::bad_alloc.
    *
    * Rationale: we want to force users to use our corresponding try_... method instead:
    * this makes the API slightly more annoying to use, but hopefully safer as it encourages
    * users to check for allocation failures, which is important for Vulkan.
    *
    * Note: deleting each of these methods (below) deletes all its overloads from the base class,
    *   to be precise: the deleted method covers the methods (all overloads) in the base class.
    * Note: clear() is already noexcept since C++11.
    */
   void insert() = delete;
   void emplace() = delete;
   void emplace_back() = delete;
   void push_back() = delete;
   void resize() = delete;
   void reserve() = delete;

   /* Note pop_back(), erase(), clear() do not throw std::bad_alloc exceptions. */

   /* @brief Like std::vector::push_back, but non throwing.
    * @return @c false iff the operation could not be performed due to an allocation failure.
    */
   template <typename... arg_types>
   bool try_push_back(arg_types &&... args) noexcept
   {
      try
      {
         base::push_back(std::forward<arg_types>(args)...);
         return true;
      }
      catch (const std::bad_alloc &e)
      {
         return false;
      }
   }

   /* @brief push back multiple elements at once
    * @return @c false iff the operation could not be performed due to an allocation failure.
    */
   bool try_push_back_many(const T *begin, const T *end) noexcept
   {
      for (const T *it = begin; it != end; ++it)
      {
         if (!try_push_back(*it))
         {
            return false;
         }
      }
      return true;
   }

   /* @brief Like std::vector::resize, but non throwing.
    * @return @c false iff the operation could not be performed due to an allocation failure.
    */
   template <typename... arg_types>
   bool try_resize(arg_types &&... args) noexcept
   {
      try
      {
         base::resize(std::forward<arg_types>(args)...);
         return true;
      }
      catch (const std::bad_alloc &e)
      {
         return false;
      }
   }
};

} /* namespace util */