Is there a C++ placement new() operator for messages?

[Michael Wagner]

I would like to use Google Protocol Buffers in a memory constrained environment - not so much that the environment is low on memory as much as memory usage is tracked on a per subsystem basis.

 

Generally, in this environment for other non-Google Protocol Buffers, I use the C++ placement new operator, which allows me to allocate a buffer from a specializes allocator and pass the address of that buffer to the new() operator.

 

char* fooAllocation = memoryBroker->Allocate(MY_SUBSYSTEM_ID, MAX_FOO_SIZE);

 

class Foo foo* = new (fooAllocation);

 

When I am done with foo, I can call

 

memoryBroker->Free(MY_SUBYSTEM_ID, MAX_FOO_SIZE, foo);

 

That allows memoryBroker to keep accurate stats on memory usage by subsystem.

 

I'd like to do the same with a GPB message.

 

Is there some way to do that?

 

Mike

[Feng Xiao]

Not possible with the current implementation but the next version of protobuf will include arena support and with that you will be able to allocate a message and all its sub-fields on an arena. For example:

void ProcessData(const string& data) {

  google::protobuf::ArenaOptions options;

  options.initial_block = memoryBroker->Allocate(MY_SUBSYSTEM_ID, MAX_FOO_SIZE);

  options.initial_block_size = MAX_FOO_SIZE;

  options.max_block_size = 0;  // prevent arena to allocate heap memory by itself.

  {

    google::protobuf::Arena arena(options);

    MyMessage* message = google::protobuf::Arena::CreateMessage<MyMessage>(&arena);

    if (message->ParseFromString(data)) {

      // use message...

    }

    cout << "Memory used for protobuf message: " << arena.SpaceUsed() << endl;

  }

  memoryBroker->Free(MY_SUBSYSTEM_ID, MAX_FOO_SIZE, options.initial_block);

}

 

 

Mike

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