Re: [boost] Is there any interest in a library for actor programming? serialization + uniform names

Subject: Re: [boost] Is there any interest in a library for actor programming? serialization + uniform names
From: Charousset, Dominik (Dominik.Charousset_at_[hidden])
Date: 2014-05-14 03:24:35

The serialization and uniform name really boils down to the uniform_type_info class:

Uniform names are simply a necessity if you need to identify a type based on its name. The goal is to send any kind of value to a remote machine and being able to deserialize it. If you have platofrm-independent names, you can simply prefix the binary serialized value with its type name and then get the RTTI (uniform_type_info) from the type name and deserialize the rest of the data. Boost.Actor is a bit more cleverer than that and maintains a list of type ids for each node it's connected to. Whenever you send a message with a type you didn't use beforehand, you send the type name along with its newly generated, unique ID and only use that ID going forward. But that's just an optimization. When talking about stateless communication (e.g. UDP), you can't do this and have to generate self-consistent messages.

The fact that we even have to do this, is because std::type_info::name() is utterly useless. It returns a mangled name on GCC/Clang and a more sophisticated version of the type name on MSVC. The uniform name is the type name as it appears in code. So the first part of generating the uniform name is to demangle the platform-dependent name (https://github.com/Neverlord/boost.actor/blob/master/src/demangle.cpp). After that, we need to decompose the whole thing and make sure that qualifiers are always in the same order etc (https://github.com/Neverlord/boost.actor/blob/master/src/to_uniform_name.cpp).

All this really is only aiming at having at type_info that is actually useful, i.e., name() returns *the exact same string* on each platform and it provides you with an interface for (1) generating values, (2) serializing and deserializing values, and (3) compare values. When generating a value through an uniform_type_info, you'll get a uniform_value, which is bascially a wrapper keeping {uniform_type_info*, void*}.

Since we need a way to pass a serializer to a uniform_type_info instance, we can't use a templated approach as the archives in boost.serialization. The serialization classes in use (https://github.com/Neverlord/boost.actor/blob/master/boost/actor/serializer.hpp) operate on sequences and primitive types. With the begin_object member function you also have a way of define serialization recursively, but I don't know if it's really needed to be honest. The write_tuple member function is probably not needed either, since you can simply just write the values one by one. However, it does give you a way of grouping values representing a single member together, which can be quite helpful when serializing to strings for instance. By the way, each announced type in Boost.Actor implicitly has a to_string(), which simply passes the value to a string serializer. There's also a from_string() that passes the input to a string deserializer, which gives you a simple way of injecting messages to the system. But the whole string serialization is not really fleshed out and the format not well defined.



________________________________________
From: Boost [boost-bounces_at_[hidden]] on behalf of Hartmut Kaiser [hartmut.kaiser_at_[hidden]]
Sent: Tuesday, May 13, 2014 20:46
To: boost_at_[hidden]
Subject: Re: [boost] Is there any interest in a library for actor       programming? serialization + uniform names

I'd be interested in hearing more details about this.

Regards Hartmut
---------------
http://boost-spirit.com
http://stellar.cct.lsu.edu

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