src/tint/utils/block_allocator.h - dawn - Git at Google

 // Copyright 2021 The Tint 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
 //
 //     http://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.

 #ifndef SRC_TINT_UTILS_BLOCK_ALLOCATOR_H_
 #define SRC_TINT_UTILS_BLOCK_ALLOCATOR_H_

 #include <array>
 #include <cstring>
 #include <utility>

 #include "src/tint/utils/bitcast.h"
 #include "src/tint/utils/math.h"

 namespace tint::utils {

 /// A container and allocator of objects of (or deriving from) the template type `T`.
 /// Objects are allocated by calling Create(), and are owned by the BlockAllocator.
 /// When the BlockAllocator is destructed, all constructed objects are automatically destructed and
 /// freed.
 ///
 /// Objects held by the BlockAllocator can be iterated over using a View.
 template <typename T, size_t BLOCK_SIZE = 64 * 1024, size_t BLOCK_ALIGNMENT = 16>
 class BlockAllocator {
     /// Pointers is a chunk of T* pointers, forming a linked list.
     /// The list of Pointers are used to maintain the list of allocated objects.
     /// Pointers are allocated out of the block memory.
     struct Pointers {
         static constexpr size_t kMax = 32;
         std::array<T*, kMax> ptrs;
         Pointers* next;
     };

     /// Block is linked list of memory blocks.
     /// Blocks are allocated out of heap memory.
     ///
     /// Note: We're not using std::aligned_storage here as this warns / errors on MSVC.
     struct alignas(BLOCK_ALIGNMENT) Block {
         uint8_t data[BLOCK_SIZE];
         Block* next;
     };

     // Forward declaration
     template <bool IS_CONST>
     class TView;

     /// An iterator for the objects owned by the BlockAllocator.
     template <bool IS_CONST>
     class TIterator {
         using PointerTy = std::conditional_t<IS_CONST, const T*, T*>;

       public:
         /// Equality operator
         /// @param other the iterator to compare this iterator to
         /// @returns true if this iterator is equal to other
         bool operator==(const TIterator& other) const {
             return ptrs == other.ptrs && idx == other.idx;
         }

         /// Inequality operator
         /// @param other the iterator to compare this iterator to
         /// @returns true if this iterator is not equal to other
         bool operator!=(const TIterator& other) const { return !(*this == other); }

         /// Advances the iterator
         /// @returns this iterator
         TIterator& operator++() {
             if (ptrs != nullptr) {
                 ++idx;
                 if (idx == Pointers::kMax) {
                     idx = 0;
                     ptrs = ptrs->next;
                 }
             }
             return *this;
         }

         /// @returns the pointer to the object at the current iterator position
         PointerTy operator*() const { return ptrs ? ptrs->ptrs[idx] : nullptr; }

       private:
         friend TView<IS_CONST>;  // Keep internal iterator impl private.
         explicit TIterator(const Pointers* p, size_t i) : ptrs(p), idx(i) {}

         const Pointers* ptrs;
         size_t idx;
     };

     /// View provides begin() and end() methods for looping over the objects owned by the
     /// BlockAllocator.
     template <bool IS_CONST>
     class TView {
       public:
         /// @returns an iterator to the beginning of the view
         TIterator<IS_CONST> begin() const {
             return TIterator<IS_CONST>{allocator_->data.pointers.root, 0};
         }

         /// @returns an iterator to the end of the view
         TIterator<IS_CONST> end() const {
             return allocator_->data.pointers.current_index >= Pointers::kMax
                        ? TIterator<IS_CONST>(nullptr, 0)
                        : TIterator<IS_CONST>(allocator_->data.pointers.current,
                                              allocator_->data.pointers.current_index);
         }

       private:
         friend BlockAllocator;  // For BlockAllocator::operator View()
         explicit TView(BlockAllocator const* allocator) : allocator_(allocator) {}
         BlockAllocator const* const allocator_;
     };

   public:
     /// An iterator type over the objects of the BlockAllocator
     using Iterator = TIterator<false>;

     /// An immutable iterator type over the objects of the BlockAllocator
     using ConstIterator = TIterator<true>;

     /// View provides begin() and end() methods for looping over the objects owned by the
     /// BlockAllocator.
     using View = TView<false>;

     /// ConstView provides begin() and end() methods for looping over the objects owned by the
     /// BlockAllocator.
     using ConstView = TView<true>;

     /// Constructor
     BlockAllocator() = default;

     /// Move constructor
     /// @param rhs the BlockAllocator to move
     BlockAllocator(BlockAllocator&& rhs) { std::swap(data, rhs.data); }

     /// Move assignment operator
     /// @param rhs the BlockAllocator to move
     /// @return this BlockAllocator
     BlockAllocator& operator=(BlockAllocator&& rhs) {
         if (this != &rhs) {
             Reset();
             std::swap(data, rhs.data);
         }
         return *this;
     }

     /// Destructor
     ~BlockAllocator() { Reset(); }

     /// @return a View of all objects owned by this BlockAllocator
     View Objects() { return View(this); }

     /// @return a ConstView of all objects owned by this BlockAllocator
     ConstView Objects() const { return ConstView(this); }

     /// Creates a new `TYPE` owned by the BlockAllocator.
     /// When the BlockAllocator is destructed the object will be destructed and freed.
     /// @param args the arguments to pass to the type constructor
     /// @returns the pointer to the constructed object
     template <typename TYPE = T, typename... ARGS>
     TYPE* Create(ARGS&&... args) {
         static_assert(std::is_same<T, TYPE>::value || std::is_base_of<T, TYPE>::value,
                       "TYPE does not derive from T");
         static_assert(std::is_same<T, TYPE>::value || std::has_virtual_destructor<T>::value,
                       "TYPE requires a virtual destructor when calling Create() for a type "
                       "that is not T");

         auto* ptr = Allocate<TYPE>();
         new (ptr) TYPE(std::forward<ARGS>(args)...);
         AddObjectPointer(ptr);
         data.count++;

         return ptr;
     }

     /// Frees all allocations from the allocator.
     void Reset() {
         for (auto ptr : Objects()) {
             ptr->~T();
         }
         auto* block = data.block.root;
         while (block != nullptr) {
             auto* next = block->next;
             delete block;
             block = next;
         }
         data = {};
     }

     /// @returns the total number of allocated objects.
     size_t Count() const { return data.count; }

   private:
     BlockAllocator(const BlockAllocator&) = delete;
     BlockAllocator& operator=(const BlockAllocator&) = delete;

     /// Allocates an instance of TYPE from the current block, or from a newly allocated block if the
     /// current block is full.
     template <typename TYPE>
     TYPE* Allocate() {
         static_assert(sizeof(TYPE) <= BLOCK_SIZE,
                       "Cannot construct TYPE with size greater than BLOCK_SIZE");
         static_assert(alignof(TYPE) <= BLOCK_ALIGNMENT, "alignof(TYPE) is greater than ALIGNMENT");

         auto& block = data.block;

         block.current_offset = utils::RoundUp(alignof(TYPE), block.current_offset);
         if (block.current_offset + sizeof(TYPE) > BLOCK_SIZE) {
             // Allocate a new block from the heap
             auto* prev_block = block.current;
             block.current = new Block;
             if (!block.current) {
                 return nullptr;  // out of memory
             }
             block.current->next = nullptr;
             block.current_offset = 0;
             if (prev_block) {
                 prev_block->next = block.current;
             } else {
                 block.root = block.current;
             }
         }

         auto* base = &block.current->data[0];
         auto* ptr = utils::Bitcast<TYPE*>(base + block.current_offset);
         block.current_offset += sizeof(TYPE);
         return ptr;
     }

     /// Adds `ptr` to the linked list of objects owned by this BlockAllocator.
     /// Once added, `ptr` will be tracked for destruction when the BlockAllocator is destructed.
     void AddObjectPointer(T* ptr) {
         auto& pointers = data.pointers;

         if (pointers.current_index >= Pointers::kMax) {
             auto* prev_pointers = pointers.current;
             pointers.current = Allocate<Pointers>();
             if (!pointers.current) {
                 return;  // out of memory
             }
             pointers.current->next = nullptr;
             pointers.current_index = 0;

             if (prev_pointers) {
                 prev_pointers->next = pointers.current;
             } else {
                 pointers.root = pointers.current;
             }
         }

         pointers.current->ptrs[pointers.current_index++] = ptr;
     }

     struct {
         struct {
             /// The root block of the block linked list
             Block* root = nullptr;
             /// The current (end) block of the blocked linked list.
             /// New allocations come from this block
             Block* current = nullptr;
             /// The byte offset in #current for the next allocation.
             /// Initialized with BLOCK_SIZE so that the first allocation triggers a block
             /// allocation.
             size_t current_offset = BLOCK_SIZE;
         } block;

         struct {
             /// The root Pointers structure of the pointers linked list
             Pointers* root = nullptr;
             /// The current (end) Pointers structure of the pointers linked list.
             /// AddObjectPointer() adds to this structure.
             Pointers* current = nullptr;
             /// The array index in #current for the next append.
             /// Initialized with Pointers::kMax so that the first append triggers a allocation of
             /// the Pointers structure.
             size_t current_index = Pointers::kMax;
         } pointers;

         size_t count = 0;
     } data;
 };

 }  // namespace tint::utils

 #endif  // SRC_TINT_UTILS_BLOCK_ALLOCATOR_H_
	// Copyright 2021 The Tint 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
	//
	// http://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.

	#ifndef SRC_TINT_UTILS_BLOCK_ALLOCATOR_H_
	#define SRC_TINT_UTILS_BLOCK_ALLOCATOR_H_

	#include <array>
	#include <cstring>
	#include <utility>

	#include "src/tint/utils/bitcast.h"
	#include "src/tint/utils/math.h"

	namespace tint::utils {

	/// A container and allocator of objects of (or deriving from) the template type `T`.
	/// Objects are allocated by calling Create(), and are owned by the BlockAllocator.
	/// When the BlockAllocator is destructed, all constructed objects are automatically destructed and
	/// freed.
	///
	/// Objects held by the BlockAllocator can be iterated over using a View.
	template <typename T, size_t BLOCK_SIZE = 64 * 1024, size_t BLOCK_ALIGNMENT = 16>
	class BlockAllocator {
	/// Pointers is a chunk of T* pointers, forming a linked list.
	/// The list of Pointers are used to maintain the list of allocated objects.
	/// Pointers are allocated out of the block memory.
	struct Pointers {
	static constexpr size_t kMax = 32;
	std::array<T*, kMax> ptrs;
	Pointers* next;
	};

	/// Block is linked list of memory blocks.
	/// Blocks are allocated out of heap memory.
	///
	/// Note: We're not using std::aligned_storage here as this warns / errors on MSVC.
	struct alignas(BLOCK_ALIGNMENT) Block {
	uint8_t data[BLOCK_SIZE];
	Block* next;
	};

	// Forward declaration
	template <bool IS_CONST>
	class TView;

	/// An iterator for the objects owned by the BlockAllocator.
	template <bool IS_CONST>
	class TIterator {
	using PointerTy = std::conditional_t<IS_CONST, const T, T>;

	public:
	/// Equality operator
	/// @param other the iterator to compare this iterator to
	/// @returns true if this iterator is equal to other
	bool operator==(const TIterator& other) const {
	return ptrs == other.ptrs && idx == other.idx;
	}

	/// Inequality operator
	/// @param other the iterator to compare this iterator to
	/// @returns true if this iterator is not equal to other
	bool operator!=(const TIterator& other) const { return !(*this == other); }

	/// Advances the iterator
	/// @returns this iterator
	TIterator& operator++() {
	if (ptrs != nullptr) {
	++idx;
	if (idx == Pointers::kMax) {
	idx = 0;
	ptrs = ptrs->next;
	}
	}
	return *this;
	}

	/// @returns the pointer to the object at the current iterator position
	PointerTy operator*() const { return ptrs ? ptrs->ptrs[idx] : nullptr; }

	private:
	friend TView<IS_CONST>; // Keep internal iterator impl private.
	explicit TIterator(const Pointers* p, size_t i) : ptrs(p), idx(i) {}

	const Pointers* ptrs;
	size_t idx;
	};

	/// View provides begin() and end() methods for looping over the objects owned by the
	/// BlockAllocator.
	template <bool IS_CONST>
	class TView {
	public:
	/// @returns an iterator to the beginning of the view
	TIterator<IS_CONST> begin() const {
	return TIterator<IS_CONST>{allocator_->data.pointers.root, 0};
	}

	/// @returns an iterator to the end of the view
	TIterator<IS_CONST> end() const {
	return allocator_->data.pointers.current_index >= Pointers::kMax
	? TIterator<IS_CONST>(nullptr, 0)
	: TIterator<IS_CONST>(allocator_->data.pointers.current,
	allocator_->data.pointers.current_index);
	}

	private:
	friend BlockAllocator; // For BlockAllocator::operator View()
	explicit TView(BlockAllocator const* allocator) : allocator_(allocator) {}
	BlockAllocator const* const allocator_;
	};

	public:
	/// An iterator type over the objects of the BlockAllocator
	using Iterator = TIterator<false>;

	/// An immutable iterator type over the objects of the BlockAllocator
	using ConstIterator = TIterator<true>;

	/// View provides begin() and end() methods for looping over the objects owned by the
	/// BlockAllocator.
	using View = TView<false>;

	/// ConstView provides begin() and end() methods for looping over the objects owned by the
	/// BlockAllocator.
	using ConstView = TView<true>;

	/// Constructor
	BlockAllocator() = default;

	/// Move constructor
	/// @param rhs the BlockAllocator to move
	BlockAllocator(BlockAllocator&& rhs) { std::swap(data, rhs.data); }

	/// Move assignment operator
	/// @param rhs the BlockAllocator to move
	/// @return this BlockAllocator
	BlockAllocator& operator=(BlockAllocator&& rhs) {
	if (this != &rhs) {
	Reset();
	std::swap(data, rhs.data);
	}
	return *this;
	}

	/// Destructor
	~BlockAllocator() { Reset(); }

	/// @return a View of all objects owned by this BlockAllocator
	View Objects() { return View(this); }

	/// @return a ConstView of all objects owned by this BlockAllocator
	ConstView Objects() const { return ConstView(this); }

	/// Creates a new `TYPE` owned by the BlockAllocator.
	/// When the BlockAllocator is destructed the object will be destructed and freed.
	/// @param args the arguments to pass to the type constructor
	/// @returns the pointer to the constructed object
	template <typename TYPE = T, typename... ARGS>
	TYPE* Create(ARGS&&... args) {
	static_assert(std::is_same<T, TYPE>::value \|\| std::is_base_of<T, TYPE>::value,
	"TYPE does not derive from T");
	static_assert(std::is_same<T, TYPE>::value \|\| std::has_virtual_destructor<T>::value,
	"TYPE requires a virtual destructor when calling Create() for a type "
	"that is not T");

	auto* ptr = Allocate<TYPE>();
	new (ptr) TYPE(std::forward<ARGS>(args)...);
	AddObjectPointer(ptr);
	data.count++;

	return ptr;
	}

	/// Frees all allocations from the allocator.
	void Reset() {
	for (auto ptr : Objects()) {
	ptr->~T();
	}
	auto* block = data.block.root;
	while (block != nullptr) {
	auto* next = block->next;
	delete block;
	block = next;
	}
	data = {};
	}

	/// @returns the total number of allocated objects.
	size_t Count() const { return data.count; }

	private:
	BlockAllocator(const BlockAllocator&) = delete;
	BlockAllocator& operator=(const BlockAllocator&) = delete;

	/// Allocates an instance of TYPE from the current block, or from a newly allocated block if the
	/// current block is full.
	template <typename TYPE>
	TYPE* Allocate() {
	static_assert(sizeof(TYPE) <= BLOCK_SIZE,
	"Cannot construct TYPE with size greater than BLOCK_SIZE");
	static_assert(alignof(TYPE) <= BLOCK_ALIGNMENT, "alignof(TYPE) is greater than ALIGNMENT");

	auto& block = data.block;

	block.current_offset = utils::RoundUp(alignof(TYPE), block.current_offset);
	if (block.current_offset + sizeof(TYPE) > BLOCK_SIZE) {
	// Allocate a new block from the heap
	auto* prev_block = block.current;
	block.current = new Block;
	if (!block.current) {
	return nullptr; // out of memory
	}
	block.current->next = nullptr;
	block.current_offset = 0;
	if (prev_block) {
	prev_block->next = block.current;
	} else {
	block.root = block.current;
	}
	}

	auto* base = &block.current->data[0];
	auto* ptr = utils::Bitcast<TYPE*>(base + block.current_offset);
	block.current_offset += sizeof(TYPE);
	return ptr;
	}

	/// Adds `ptr` to the linked list of objects owned by this BlockAllocator.
	/// Once added, `ptr` will be tracked for destruction when the BlockAllocator is destructed.
	void AddObjectPointer(T* ptr) {
	auto& pointers = data.pointers;

	if (pointers.current_index >= Pointers::kMax) {
	auto* prev_pointers = pointers.current;
	pointers.current = Allocate<Pointers>();
	if (!pointers.current) {
	return; // out of memory
	}
	pointers.current->next = nullptr;
	pointers.current_index = 0;

	if (prev_pointers) {
	prev_pointers->next = pointers.current;
	} else {
	pointers.root = pointers.current;
	}
	}

	pointers.current->ptrs[pointers.current_index++] = ptr;
	}

	struct {
	struct {
	/// The root block of the block linked list
	Block* root = nullptr;
	/// The current (end) block of the blocked linked list.
	/// New allocations come from this block
	Block* current = nullptr;
	/// The byte offset in #current for the next allocation.
	/// Initialized with BLOCK_SIZE so that the first allocation triggers a block
	/// allocation.
	size_t current_offset = BLOCK_SIZE;
	} block;

	struct {
	/// The root Pointers structure of the pointers linked list
	Pointers* root = nullptr;
	/// The current (end) Pointers structure of the pointers linked list.
	/// AddObjectPointer() adds to this structure.
	Pointers* current = nullptr;
	/// The array index in #current for the next append.
	/// Initialized with Pointers::kMax so that the first append triggers a allocation of
	/// the Pointers structure.
	size_t current_index = Pointers::kMax;
	} pointers;

	size_t count = 0;
	} data;
	};

	} // namespace tint::utils

	#endif // SRC_TINT_UTILS_BLOCK_ALLOCATOR_H_