vulkan-wsi-layer/util/custom_allocator.hpp

/*
 * Copyright (c) 2020-2021 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 <cassert>
#include <memory>

#include <vulkan/vulkan.h>

#pragma once

namespace util
{

template <typename T>
class deleter;

/**
 * @brief Wrapper for unique_ptr.
 *
 * This is a wrapper for unique_ptr that can be used to construct/destroy objects using the allocators in
 * VkAllocationCallbacks. This smart pointer contains a full copy of the VkAllocationCallbacks, so its size is
 * considerably larger than sizeof(void*).
 *
 * allocator::make_unique is provided to facilitate creating instances of this object.
 */
template <typename T>
using unique_ptr = std::unique_ptr<T, deleter<T>>;

/**
 * @brief Minimalistic wrapper of VkAllocationCallbacks.
 */
class allocator
{
public:
   /**
    * @brief Get an allocator that can be used if VkAllocationCallbacks are not provided.
    */
   static const allocator& get_generic();

   /**
    * @brief Construct a new wrapper for the given VK callbacks and scope.
    * @param scope The scope to use for this allocator.
    * @param callbacks Pointer to allocation callbacks. If this is @c nullptr, then default
    *   allocation callbacks are used. These can be accessed through #m_callbacks.
    */
   allocator(VkSystemAllocationScope scope, const VkAllocationCallbacks *callbacks);

   /**
    * @brief Construct a new allocator that uses @p callbacks or @p allocator callbacks if the
    *        @p callbacks are @c nullptr with the @c scope.
    *
    * @param other If @p callbacks is @c nullptr, the callbacks from this allocator will be used instead.
    * @param new_scope The scope to use for allocations
    * @param callbacks Pointer to allocation callbacks. If this is @c nullptr, then the callbacks
    * from the @p allocator will be used.
    */
   allocator(const allocator &other, VkSystemAllocationScope new_scope,
             const VkAllocationCallbacks *callbacks = nullptr);

   /**
    * @brief Get a pointer to the allocation callbacks provided while constructing this object.
    * @return a copy of the #VkAllocationCallback argument provided in the allocator constructor
    *   or @c nullptr if this argument was provided as @c nullptr.
    * @note The #m_callbacks member is always populated with callable pointers for pfnAllocation,
    *   pfnReallocation and pfnFree.
    */
   const VkAllocationCallbacks *get_original_callbacks() const;

   /**
    * @brief Helper method to allocate and construct objects with a custom allocator.
    * @param num_objects Number of objects to create.
    * @return Pointer to the newly created objects or @c nullptr if allocation failed.
    */
   template <typename T, typename... arg_types>
   T *create(size_t num_objects, arg_types &&... args) const noexcept;

   /**
    * @brief Helper method to destroy and deallocate objects constructed with allocator::create().
    * @param num_objects Number of objects to destroy.
    */
   template <typename T>
   void destroy(size_t num_objects, T *obj) const noexcept;

   template <typename T, typename... Args>
   util::unique_ptr<T> make_unique(Args &&...args) const noexcept;

   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;
}

template <typename T, typename... arg_types>
T *allocator::create(size_t num_objects, arg_types &&... args) const noexcept
{
   if (num_objects < 1)
   {
      return nullptr;
   }

   custom_allocator<T> allocator(*this);
   T *ptr;
   try
   {
      ptr = allocator.allocate(num_objects);
   }
   catch (...)
   {
      return nullptr;
   }

   size_t objects_constructed = 0;
   try
   {
      while (objects_constructed < num_objects)
      {
         T *next_object = &ptr[objects_constructed];
         new (next_object) T(std::forward<arg_types>(args)...);
         objects_constructed++;
      }
   }
   catch (...)
   {
      /* We catch all exceptions thrown while constructing the object, not just
       * std::bad_alloc.
       */
      while (objects_constructed > 0)
      {
         objects_constructed--;
         ptr[objects_constructed].~T();
      }
      allocator.deallocate(ptr, num_objects);
      return nullptr;
   }
   return ptr;
}

template <typename T>
void allocator::destroy(size_t num_objects, T *objects) const noexcept
{
   assert((objects == nullptr) == (num_objects == 0));
   if (num_objects == 0)
   {
      return;
   }

   custom_allocator<T> allocator(*this);
   for (size_t i = 0; i < num_objects; i++)
   {
      objects[i].~T();
   }
   allocator.deallocate(objects, num_objects);
}

/**
 * @brief Class deleter is used to free the resource managed by the util::unique_ptr. Uses the passed in allocator's
 *        destroy method.
 */
template <typename T>
class deleter
{
public:
   deleter(allocator allocator)
      : m_allocator(std::move(allocator))
   {}

   void operator()(T *object)
   {
      m_allocator.destroy<T>(1, object);
   }

private:
   allocator m_allocator;
};

/**
 * @brief Creates a util::unique_ptr object using the allocator for the deleter.
 */
template <typename T, typename... Args>
util::unique_ptr<T> allocator::make_unique(Args &&...args) const noexcept
{
   T *object = create<T>(1, std::forward<Args>(args)...);
   return util::unique_ptr<T>(object, *this);
}

/**
 * @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 */