src/dawn_native/CommandAllocator.h - dawn - Git at Google

 // Copyright 2017 The Dawn 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 DAWNNATIVE_COMMAND_ALLOCATOR_H_
 #define DAWNNATIVE_COMMAND_ALLOCATOR_H_

 #include "common/Assert.h"
 #include "common/Math.h"

 #include <cstddef>
 #include <cstdint>
 #include <vector>

 namespace dawn_native {

     // Allocation for command buffers should be fast. To avoid doing an allocation per command
     // or to avoid copying commands when reallocing, we use a linear allocator in a growing set
     // of large memory blocks. We also use this to have the format to be (u32 commandId, command),
     // so that iteration over the commands is easy.

     // Usage of the allocator and iterator:
     //     CommandAllocator allocator;
     //     DrawCommand* cmd = allocator.Allocate<DrawCommand>(CommandType::Draw);
     //     // Fill command
     //     // Repeat allocation and filling commands
     //
     //     CommandIterator commands(allocator);
     //     CommandType type;
     //     while(commands.NextCommandId(&type)) {
     //         switch(type) {
     //              case CommandType::Draw:
     //                  DrawCommand* draw = commands.NextCommand<DrawCommand>();
     //                  // Do the draw
     //                  break;
     //              // other cases
     //         }
     //     }

     // Note that you need to extract the commands from the CommandAllocator before destroying it
     // and must tell the CommandIterator when the allocated commands have been processed for
     // deletion.

     // These are the lists of blocks, should not be used directly, only through CommandAllocator
     // and CommandIterator
     struct BlockDef {
         size_t size;
         uint8_t* block;
     };
     using CommandBlocks = std::vector<BlockDef>;

     namespace detail {
         constexpr uint32_t kEndOfBlock = std::numeric_limits<uint32_t>::max();
         constexpr uint32_t kAdditionalData = std::numeric_limits<uint32_t>::max() - 1;
     }  // namespace detail

     class CommandAllocator;

     // TODO(cwallez@chromium.org): prevent copy for both iterator and allocator
     class CommandIterator {
       public:
         CommandIterator();
         ~CommandIterator();

         CommandIterator(CommandIterator&& other);
         CommandIterator& operator=(CommandIterator&& other);

         CommandIterator(CommandAllocator&& allocator);
         CommandIterator& operator=(CommandAllocator&& allocator);

         template <typename E>
         bool NextCommandId(E* commandId) {
             return NextCommandId(reinterpret_cast<uint32_t*>(commandId));
         }
         template <typename T>
         T* NextCommand() {
             return static_cast<T*>(NextCommand(sizeof(T), alignof(T)));
         }
         template <typename T>
         T* NextData(size_t count) {
             return static_cast<T*>(NextData(sizeof(T) * count, alignof(T)));
         }

         // Sets iterator to the beginning of the commands without emptying the list. This method can
         // be used if iteration was stopped early and the iterator needs to be restarted.
         void Reset();

         // This method must to be called after commands have been deleted. This indicates that the
         // commands have been submitted and they are no longer valid.
         void MakeEmptyAsDataWasDestroyed();

       private:
         bool IsEmpty() const;

         DAWN_FORCE_INLINE bool NextCommandId(uint32_t* commandId) {
             uint8_t* idPtr = AlignPtr(mCurrentPtr, alignof(uint32_t));
             ASSERT(idPtr + sizeof(uint32_t) <=
                    mBlocks[mCurrentBlock].block + mBlocks[mCurrentBlock].size);

             uint32_t id = *reinterpret_cast<uint32_t*>(idPtr);

             if (id != detail::kEndOfBlock) {
                 mCurrentPtr = idPtr + sizeof(uint32_t);
                 *commandId = id;
                 return true;
             }
             return NextCommandIdInNewBlock(commandId);
         }

         bool NextCommandIdInNewBlock(uint32_t* commandId);

         DAWN_FORCE_INLINE void* NextCommand(size_t commandSize, size_t commandAlignment) {
             uint8_t* commandPtr = AlignPtr(mCurrentPtr, commandAlignment);
             ASSERT(commandPtr + sizeof(commandSize) <=
                    mBlocks[mCurrentBlock].block + mBlocks[mCurrentBlock].size);

             mCurrentPtr = commandPtr + commandSize;
             return commandPtr;
         }

         DAWN_FORCE_INLINE void* NextData(size_t dataSize, size_t dataAlignment) {
             uint32_t id;
             bool hasId = NextCommandId(&id);
             ASSERT(hasId);
             ASSERT(id == detail::kAdditionalData);

             return NextCommand(dataSize, dataAlignment);
         }

         CommandBlocks mBlocks;
         uint8_t* mCurrentPtr = nullptr;
         size_t mCurrentBlock = 0;
         // Used to avoid a special case for empty iterators.
         uint32_t mEndOfBlock = detail::kEndOfBlock;
     };

     class CommandAllocator {
       public:
         CommandAllocator();
         ~CommandAllocator();

         template <typename T, typename E>
         T* Allocate(E commandId) {
             static_assert(sizeof(E) == sizeof(uint32_t), "");
             static_assert(alignof(E) == alignof(uint32_t), "");
             static_assert(alignof(T) <= kMaxSupportedAlignment, "");
             T* result = reinterpret_cast<T*>(
                 Allocate(static_cast<uint32_t>(commandId), sizeof(T), alignof(T)));
             if (!result) {
                 return nullptr;
             }
             new (result) T;
             return result;
         }

         template <typename T>
         T* AllocateData(size_t count) {
             static_assert(alignof(T) <= kMaxSupportedAlignment, "");
             T* result = reinterpret_cast<T*>(AllocateData(sizeof(T) * count, alignof(T)));
             if (!result) {
                 return nullptr;
             }
             for (size_t i = 0; i < count; i++) {
                 new (result + i) T;
             }
             return result;
         }

       private:
         // This is used for some internal computations and can be any power of two as long as code
         // using the CommandAllocator passes the static_asserts.
         static constexpr size_t kMaxSupportedAlignment = 8;

         // To avoid checking for overflows at every step of the computations we compute an upper
         // bound of the space that will be needed in addition to the command data.
         static constexpr size_t kWorstCaseAdditionalSize =
             sizeof(uint32_t) + kMaxSupportedAlignment + alignof(uint32_t) + sizeof(uint32_t);

         friend CommandIterator;
         CommandBlocks&& AcquireBlocks();

         DAWN_FORCE_INLINE uint8_t* Allocate(uint32_t commandId,
                                             size_t commandSize,
                                             size_t commandAlignment) {
             ASSERT(mCurrentPtr != nullptr);
             ASSERT(mEndPtr != nullptr);
             ASSERT(commandId != detail::kEndOfBlock);

             // It should always be possible to allocate one id, for kEndOfBlock tagging,
             ASSERT(IsPtrAligned(mCurrentPtr, alignof(uint32_t)));
             ASSERT(mEndPtr >= mCurrentPtr);
             ASSERT(static_cast<size_t>(mEndPtr - mCurrentPtr) >= sizeof(uint32_t));

             // The memory after the ID will contain the following:
             //   - the current ID
             //   - padding to align the command, maximum kMaxSupportedAlignment
             //   - the command of size commandSize
             //   - padding to align the next ID, maximum alignof(uint32_t)
             //   - the next ID of size sizeof(uint32_t)

             // This can't overflow because by construction mCurrentPtr always has space for the next
             // ID.
             size_t remainingSize = static_cast<size_t>(mEndPtr - mCurrentPtr);

             // The good case were we have enough space for the command data and upper bound of the
             // extra required space.
             if ((remainingSize >= kWorstCaseAdditionalSize) &&
                 (remainingSize - kWorstCaseAdditionalSize >= commandSize)) {
                 uint32_t* idAlloc = reinterpret_cast<uint32_t*>(mCurrentPtr);
                 *idAlloc = commandId;

                 uint8_t* commandAlloc = AlignPtr(mCurrentPtr + sizeof(uint32_t), commandAlignment);
                 mCurrentPtr = AlignPtr(commandAlloc + commandSize, alignof(uint32_t));

                 return commandAlloc;
             }
             return AllocateInNewBlock(commandId, commandSize, commandAlignment);
         }

         uint8_t* AllocateInNewBlock(uint32_t commandId,
                                     size_t commandSize,
                                     size_t commandAlignment);

         DAWN_FORCE_INLINE uint8_t* AllocateData(size_t commandSize, size_t commandAlignment) {
             return Allocate(detail::kAdditionalData, commandSize, commandAlignment);
         }

         bool GetNewBlock(size_t minimumSize);

         CommandBlocks mBlocks;
         size_t mLastAllocationSize = 2048;

         // Pointers to the current range of allocation in the block. Guaranteed to allow for at
         // least one uint32_t if not nullptr, so that the special kEndOfBlock command id can always
         // be written. Nullptr iff the blocks were moved out.
         uint8_t* mCurrentPtr = nullptr;
         uint8_t* mEndPtr = nullptr;

         // Data used for the block range at initialization so that the first call to Allocate sees
         // there is not enough space and calls GetNewBlock. This avoids having to special case the
         // initialization in Allocate.
         uint32_t mDummyEnum[1] = {0};
     };

 }  // namespace dawn_native

 #endif  // DAWNNATIVE_COMMAND_ALLOCATOR_H_
	// Copyright 2017 The Dawn 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 DAWNNATIVE_COMMAND_ALLOCATOR_H_
	#define DAWNNATIVE_COMMAND_ALLOCATOR_H_

	#include "common/Assert.h"
	#include "common/Math.h"

	#include <cstddef>
	#include <cstdint>
	#include <vector>

	namespace dawn_native {

	// Allocation for command buffers should be fast. To avoid doing an allocation per command
	// or to avoid copying commands when reallocing, we use a linear allocator in a growing set
	// of large memory blocks. We also use this to have the format to be (u32 commandId, command),
	// so that iteration over the commands is easy.

	// Usage of the allocator and iterator:
	// CommandAllocator allocator;
	// DrawCommand* cmd = allocator.Allocate<DrawCommand>(CommandType::Draw);
	// // Fill command
	// // Repeat allocation and filling commands
	//
	// CommandIterator commands(allocator);
	// CommandType type;
	// while(commands.NextCommandId(&type)) {
	// switch(type) {
	// case CommandType::Draw:
	// DrawCommand* draw = commands.NextCommand<DrawCommand>();
	// // Do the draw
	// break;
	// // other cases
	// }
	// }

	// Note that you need to extract the commands from the CommandAllocator before destroying it
	// and must tell the CommandIterator when the allocated commands have been processed for
	// deletion.

	// These are the lists of blocks, should not be used directly, only through CommandAllocator
	// and CommandIterator
	struct BlockDef {
	size_t size;
	uint8_t* block;
	};
	using CommandBlocks = std::vector<BlockDef>;

	namespace detail {
	constexpr uint32_t kEndOfBlock = std::numeric_limits<uint32_t>::max();
	constexpr uint32_t kAdditionalData = std::numeric_limits<uint32_t>::max() - 1;
	} // namespace detail

	class CommandAllocator;

	// TODO(cwallez@chromium.org): prevent copy for both iterator and allocator
	class CommandIterator {
	public:
	CommandIterator();
	~CommandIterator();

	CommandIterator(CommandIterator&& other);
	CommandIterator& operator=(CommandIterator&& other);

	CommandIterator(CommandAllocator&& allocator);
	CommandIterator& operator=(CommandAllocator&& allocator);

	template <typename E>
	bool NextCommandId(E* commandId) {
	return NextCommandId(reinterpret_cast<uint32_t*>(commandId));
	}
	template <typename T>
	T* NextCommand() {
	return static_cast<T*>(NextCommand(sizeof(T), alignof(T)));
	}
	template <typename T>
	T* NextData(size_t count) {
	return static_cast<T>(NextData(sizeof(T) count, alignof(T)));
	}

	// Sets iterator to the beginning of the commands without emptying the list. This method can
	// be used if iteration was stopped early and the iterator needs to be restarted.
	void Reset();

	// This method must to be called after commands have been deleted. This indicates that the
	// commands have been submitted and they are no longer valid.
	void MakeEmptyAsDataWasDestroyed();

	private:
	bool IsEmpty() const;

	DAWN_FORCE_INLINE bool NextCommandId(uint32_t* commandId) {
	uint8_t* idPtr = AlignPtr(mCurrentPtr, alignof(uint32_t));
	ASSERT(idPtr + sizeof(uint32_t) <=
	mBlocks[mCurrentBlock].block + mBlocks[mCurrentBlock].size);

	uint32_t id = reinterpret_cast<uint32_t>(idPtr);

	if (id != detail::kEndOfBlock) {
	mCurrentPtr = idPtr + sizeof(uint32_t);
	*commandId = id;
	return true;
	}
	return NextCommandIdInNewBlock(commandId);
	}

	bool NextCommandIdInNewBlock(uint32_t* commandId);

	DAWN_FORCE_INLINE void* NextCommand(size_t commandSize, size_t commandAlignment) {
	uint8_t* commandPtr = AlignPtr(mCurrentPtr, commandAlignment);
	ASSERT(commandPtr + sizeof(commandSize) <=
	mBlocks[mCurrentBlock].block + mBlocks[mCurrentBlock].size);

	mCurrentPtr = commandPtr + commandSize;
	return commandPtr;
	}

	DAWN_FORCE_INLINE void* NextData(size_t dataSize, size_t dataAlignment) {
	uint32_t id;
	bool hasId = NextCommandId(&id);
	ASSERT(hasId);
	ASSERT(id == detail::kAdditionalData);

	return NextCommand(dataSize, dataAlignment);
	}

	CommandBlocks mBlocks;
	uint8_t* mCurrentPtr = nullptr;
	size_t mCurrentBlock = 0;
	// Used to avoid a special case for empty iterators.
	uint32_t mEndOfBlock = detail::kEndOfBlock;
	};

	class CommandAllocator {
	public:
	CommandAllocator();
	~CommandAllocator();

	template <typename T, typename E>
	T* Allocate(E commandId) {
	static_assert(sizeof(E) == sizeof(uint32_t), "");
	static_assert(alignof(E) == alignof(uint32_t), "");
	static_assert(alignof(T) <= kMaxSupportedAlignment, "");
	T* result = reinterpret_cast<T*>(
	Allocate(static_cast<uint32_t>(commandId), sizeof(T), alignof(T)));
	if (!result) {
	return nullptr;
	}
	new (result) T;
	return result;
	}

	template <typename T>
	T* AllocateData(size_t count) {
	static_assert(alignof(T) <= kMaxSupportedAlignment, "");
	T* result = reinterpret_cast<T>(AllocateData(sizeof(T) count, alignof(T)));
	if (!result) {
	return nullptr;
	}
	for (size_t i = 0; i < count; i++) {
	new (result + i) T;
	}
	return result;
	}

	private:
	// This is used for some internal computations and can be any power of two as long as code
	// using the CommandAllocator passes the static_asserts.
	static constexpr size_t kMaxSupportedAlignment = 8;

	// To avoid checking for overflows at every step of the computations we compute an upper
	// bound of the space that will be needed in addition to the command data.
	static constexpr size_t kWorstCaseAdditionalSize =
	sizeof(uint32_t) + kMaxSupportedAlignment + alignof(uint32_t) + sizeof(uint32_t);

	friend CommandIterator;
	CommandBlocks&& AcquireBlocks();

	DAWN_FORCE_INLINE uint8_t* Allocate(uint32_t commandId,
	size_t commandSize,
	size_t commandAlignment) {
	ASSERT(mCurrentPtr != nullptr);
	ASSERT(mEndPtr != nullptr);
	ASSERT(commandId != detail::kEndOfBlock);

	// It should always be possible to allocate one id, for kEndOfBlock tagging,
	ASSERT(IsPtrAligned(mCurrentPtr, alignof(uint32_t)));
	ASSERT(mEndPtr >= mCurrentPtr);
	ASSERT(static_cast<size_t>(mEndPtr - mCurrentPtr) >= sizeof(uint32_t));

	// The memory after the ID will contain the following:
	// - the current ID
	// - padding to align the command, maximum kMaxSupportedAlignment
	// - the command of size commandSize
	// - padding to align the next ID, maximum alignof(uint32_t)
	// - the next ID of size sizeof(uint32_t)

	// This can't overflow because by construction mCurrentPtr always has space for the next
	// ID.
	size_t remainingSize = static_cast<size_t>(mEndPtr - mCurrentPtr);

	// The good case were we have enough space for the command data and upper bound of the
	// extra required space.
	if ((remainingSize >= kWorstCaseAdditionalSize) &&
	(remainingSize - kWorstCaseAdditionalSize >= commandSize)) {
	uint32_t* idAlloc = reinterpret_cast<uint32_t*>(mCurrentPtr);
	*idAlloc = commandId;

	uint8_t* commandAlloc = AlignPtr(mCurrentPtr + sizeof(uint32_t), commandAlignment);
	mCurrentPtr = AlignPtr(commandAlloc + commandSize, alignof(uint32_t));

	return commandAlloc;
	}
	return AllocateInNewBlock(commandId, commandSize, commandAlignment);
	}

	uint8_t* AllocateInNewBlock(uint32_t commandId,
	size_t commandSize,
	size_t commandAlignment);

	DAWN_FORCE_INLINE uint8_t* AllocateData(size_t commandSize, size_t commandAlignment) {
	return Allocate(detail::kAdditionalData, commandSize, commandAlignment);
	}

	bool GetNewBlock(size_t minimumSize);

	CommandBlocks mBlocks;
	size_t mLastAllocationSize = 2048;

	// Pointers to the current range of allocation in the block. Guaranteed to allow for at
	// least one uint32_t if not nullptr, so that the special kEndOfBlock command id can always
	// be written. Nullptr iff the blocks were moved out.
	uint8_t* mCurrentPtr = nullptr;
	uint8_t* mEndPtr = nullptr;

	// Data used for the block range at initialization so that the first call to Allocate sees
	// there is not enough space and calls GetNewBlock. This avoids having to special case the
	// initialization in Allocate.
	uint32_t mDummyEnum[1] = {0};
	};

	} // namespace dawn_native

	#endif // DAWNNATIVE_COMMAND_ALLOCATOR_H_