| /* |
| * Copyright (C) 2020 The Android Open Source Project |
| * |
| * 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 INCLUDE_PERFETTO_PROTOZERO_MESSAGE_ARENA_H_ |
| #define INCLUDE_PERFETTO_PROTOZERO_MESSAGE_ARENA_H_ |
| |
| #include <stdint.h> |
| |
| #include <list> |
| #include <type_traits> |
| |
| #include "perfetto/base/export.h" |
| #include "perfetto/base/logging.h" |
| #include "perfetto/protozero/message.h" |
| |
| namespace protozero { |
| |
| class Message; |
| |
| // Object allocator for fixed-sized protozero::Message objects. |
| // It's a simple bump-pointer allocator which leverages the stack-alike |
| // usage pattern of protozero nested messages. It avoids hitting the system |
| // allocator in most cases, by reusing the same block, and falls back on |
| // allocating new blocks only when using deeply nested messages (which are |
| // extremely rare). |
| // This is used by RootMessage<T> to handle the storage for root-level messages. |
| class PERFETTO_EXPORT MessageArena { |
| public: |
| MessageArena(); |
| ~MessageArena(); |
| |
| // Strictly no copies or moves as this is used to hand out pointers. |
| MessageArena(const MessageArena&) = delete; |
| MessageArena& operator=(const MessageArena&) = delete; |
| MessageArena(MessageArena&&) = delete; |
| MessageArena& operator=(MessageArena&&) = delete; |
| |
| // Allocates a new Message object. |
| Message* NewMessage(); |
| |
| // Deletes the last message allocated. The |msg| argument is used only for |
| // DCHECKs, it MUST be the pointer obtained by the last NewMessage() call. |
| void DeleteLastMessage(Message* msg) { |
| PERFETTO_DCHECK(!blocks_.empty() && blocks_.back().entries > 0); |
| PERFETTO_DCHECK(&blocks_.back().storage[blocks_.back().entries - 1] == |
| static_cast<void*>(msg)); |
| DeleteLastMessageInternal(); |
| } |
| |
| // Resets the state of the arena, clearing up all but one block. This is used |
| // to avoid leaking outstanding unfinished sub-messages while recycling the |
| // RootMessage object (this is extremely rare due to the RAII scoped handles |
| // but could happen if some client does some overly clever std::move() trick). |
| void Reset() { |
| PERFETTO_DCHECK(!blocks_.empty()); |
| blocks_.resize(1); |
| auto& block = blocks_.back(); |
| block.entries = 0; |
| PERFETTO_ASAN_POISON(block.storage, sizeof(block.storage)); |
| } |
| |
| private: |
| void DeleteLastMessageInternal(); |
| |
| struct Block { |
| static constexpr size_t kCapacity = 16; |
| |
| Block() { PERFETTO_ASAN_POISON(storage, sizeof(storage)); } |
| |
| std::aligned_storage<sizeof(Message), alignof(Message)>::type |
| storage[kCapacity]; |
| uint32_t entries = 0; // # Message entries used (<= kCapacity). |
| }; |
| |
| // blocks are used to hand out pointers and must not be moved. Hence why |
| // std::list rather than std::vector. |
| std::list<Block> blocks_; |
| }; |
| |
| } // namespace protozero |
| |
| #endif // INCLUDE_PERFETTO_PROTOZERO_MESSAGE_ARENA_H_ |