Implementation:Alibaba MNN Protobuf Arena CC
| Knowledge Sources | |
|---|---|
| Domains | Serialization, Memory_Management |
| Last Updated | 2026-02-10 12:00 GMT |
Overview
Core implementation of the Protocol Buffers Arena memory allocator for efficient bulk allocation and deallocation of protobuf messages.
Description
This file implements the google::protobuf::Arena class, which provides region-based memory allocation optimized for protobuf message lifetimes. Instead of allocating each message individually on the heap, the arena allocates large memory blocks and sub-allocates messages within them, enabling O(1) bulk deallocation when the arena is destroyed. MNN vendors this implementation because arena allocation is critical for efficient parsing of large TensorFlow and Caffe model files, where thousands of protobuf message objects may be created during deserialization.
Usage
Vendored dependency used internally by MNN for parsing protobuf-based model formats (TensorFlow, Caffe). Not directly imported by end users.
Code Reference
Source Location
- Repository: Alibaba_MNN
- File:
3rd_party/protobuf/src/google/protobuf/arena.cc - Lines: 1-511
Signature
namespace google {
namespace protobuf {
Arena::Arena(const ArenaOptions& options);
Arena::~Arena();
void* Arena::AllocateAligned(size_t n);
uint64 Arena::SpaceUsed() const;
} // namespace protobuf
} // namespace google
Import
#include "3rd_party/protobuf/src/google/protobuf/arena.h"
I/O Contract
Inputs
| Name | Type | Required | Description |
|---|---|---|---|
| options | ArenaOptions |
No | Configuration for initial block size, max block size, and allocation hooks |
| n | size_t |
Yes | Number of bytes to allocate from the arena |
Outputs
| Name | Type | Description |
|---|---|---|
| pointer | void* |
Aligned memory pointer allocated from the arena's internal block pool |
| space_used | uint64 |
Total bytes consumed by the arena including overhead |
Usage Examples
// MNN internal usage
google::protobuf::Arena arena;
auto* msg = google::protobuf::Arena::CreateMessage<MyProto>(&arena);
msg->ParseFromString(serialized_data);
// All messages freed when arena goes out of scope