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// 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 <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>;
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)));
}
// Needs to be called if iteration was stopped early.
void Reset();
void DataWasDestroyed();
private:
bool IsEmpty() const;
bool NextCommandId(uint32_t* commandId);
void* NextCommand(size_t commandSize, size_t commandAlignment);
void* NextData(size_t dataSize, size_t dataAlignment);
CommandBlocks mBlocks;
uint8_t* mCurrentPtr = nullptr;
size_t mCurrentBlock = 0;
// Used to avoid a special case for empty iterators.
uint32_t mEndOfBlock;
bool mDataWasDestroyed = false;
};
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;
friend CommandIterator;
CommandBlocks&& AcquireBlocks();
uint8_t* Allocate(uint32_t commandId, size_t commandSize, size_t commandAlignment);
uint8_t* AllocateData(size_t dataSize, size_t dataAlignment);
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 EndOfBlock 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_