pool.h

// Copyright 2024 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#pragma once
 
#include <cstddef>
#include <cstdint>
 
#include "pw_allocator/capability.h"
#include "pw_allocator/deallocator.h"
#include "pw_allocator/layout.h"
#include "pw_allocator/unique_ptr.h"
#include "pw_assert/assert.h"
#include "pw_bytes/span.h"
#include "pw_result/result.h"
 
namespace pw::allocator {
 
 
class Pool : public Deallocator {
 public:
  constexpr const Layout& layout() const { return layout_; }
 
  void* Allocate() { return DoAllocate(); }
 
  template <typename T, int&... kExplicitGuard, typename... Args>
  [[nodiscard]] std::enable_if_t<!std::is_array_v<T>, T*> New(Args&&... args);
 
  template <typename T,
            int&... kExplicitGuard,
            typename ElementType = std::remove_extent_t<T>>
  [[nodiscard]] std::enable_if_t<pw::is_bounded_array_v<T>, ElementType*> New();
 
  template <typename T,
            int&... kExplicitGuard,
            typename ElementType = std::remove_extent_t<T>>
  [[nodiscard]] std::enable_if_t<pw::is_unbounded_array_v<T>, ElementType*>
  New();
 
  template <typename T, int&... kExplicitGuard, typename... Args>
  std::enable_if_t<!std::is_array_v<T>, UniquePtr<T>> MakeUnique(
      Args&&... args);
 
  template <typename T>
  std::enable_if_t<pw::is_bounded_array_v<T>, UniquePtr<T>> MakeUnique();
 
  template <typename T>
  std::enable_if_t<pw::is_unbounded_array_v<T>, UniquePtr<T>> MakeUnique();
 
 protected:
  constexpr Pool(const Capabilities& capabilities, const Layout& layout)
      : Deallocator(capabilities), layout_(layout) {}
 
  virtual void* DoAllocate() = 0;
 
 private:
  // Helper to create arrays.
  template <typename ElementType>
  [[nodiscard]] ElementType* NewArray(size_t count);
 
  const Layout layout_;
};
 
 
// Template method implementations.
 
template <typename T, int&... kExplicitGuard, typename... Args>
std::enable_if_t<!std::is_array_v<T>, T*> Pool::New(Args&&... args) {
  PW_ASSERT(Layout::Of<T>() == layout_);
  void* ptr = Allocate();
  return ptr != nullptr ? new (ptr) T(std::forward<Args>(args)...) : nullptr;
}
 
template <typename T, int&... kExplicitGuard, typename ElementType>
std::enable_if_t<pw::is_bounded_array_v<T>, ElementType*> Pool::New() {
  return NewArray<ElementType>(std::extent_v<T>);
}
 
template <typename T, int&... kExplicitGuard, typename ElementType>
std::enable_if_t<pw::is_unbounded_array_v<T>, ElementType*> Pool::New() {
  return NewArray<ElementType>(layout_.size() / sizeof(ElementType));
}
 
template <typename T, int&... kExplicitGuard, typename... Args>
std::enable_if_t<!std::is_array_v<T>, UniquePtr<T>> Pool::MakeUnique(
    Args&&... args) {
  return UniquePtr<T>(New<T>(std::forward<Args>(args)...), *this);
}
 
template <typename T>
std::enable_if_t<pw::is_bounded_array_v<T>, UniquePtr<T>> Pool::MakeUnique() {
  using ElementType = std::remove_extent_t<T>;
  return UniquePtr<T>(NewArray<ElementType>(std::extent_v<T>), *this);
}
 
template <typename T>
std::enable_if_t<pw::is_unbounded_array_v<T>, UniquePtr<T>> Pool::MakeUnique() {
  using ElementType = std::remove_extent_t<T>;
  size_t size = layout_.size() / sizeof(ElementType);
  return UniquePtr<T>(NewArray<ElementType>(size), size, *this);
}
 
// Helper to create arrays.
template <typename ElementType>
ElementType* Pool::NewArray(size_t count) {
  Layout layout = Layout::Of<ElementType[]>(count);
  PW_ASSERT(layout.size() == layout_.size());
  PW_ASSERT(layout.alignment() <= layout_.alignment());
  void* ptr = DoAllocate();
  return ptr != nullptr ? new (ptr) ElementType[count] : nullptr;
}
 
}  // namespace pw::allocator