Re: Serializing Lua functions (was Re: status and perceptions of luaproc)

[Daurnimator <quae@...>]

On 8 August 2015 at 08:38, Sean Conner <sean@conman.org> wrote:
> It was thus said that the Great Rena once stated:
>>
>> The thread libraries I've used run a separate Lua state in each thread and
>> provide some type of communication channel between them. This is a nice
>> simple model, but maybe not the most efficient. In particular, while it's
>> usually possible to pass most types of Lua objects between threads, tables
>> can only be recursively copied, functions have to be dumped and recompiled
>> (and can't have upvalues), and userdata can't safely be passed around
>> unless it's designed to be referenced by multiple Lua states.
>
>   Actually, you can serialize Lua functions with upvalues.  I've done it
> (just not shown the code).  In fact, I was able to serialize quite a bit,
> including tables with circular references.  The only things I couldn't
> handle were coroutines, user data and Lua functions written in C [1].
>
>   As it stands, the function serialization is only good across the same
> architecture (everything else I could serialize was CPU independent) and I
> started working on fixing that by diving into the "dump format" used by Lua.
>
>   -spc (I kind of lost interest when I realized I didn't have a need for
>         this)
>
> [1]     At least not directly.  I could "serialize" the function io.write(),
>         but I did so by reference, assuming the receiver side could resolve
>         such a reference.  I could even handle known userdata types like
>         io.stdout by again, using references. [2]
>
> [2]     Strings basically.  I just passed the name along.
>
>

The lua 'full' serialisation project was 'Pluto' this has been
succeeded (for 5.2+) by Eris.
https://github.com/fnuecke/eris
They have the concept of "special persistence". see
https://github.com/fnuecke/eris#special-persistence
Which allows you to add a '__persist' field to a metatable.

I think this is a good approach, and have been meaning to add such a
field to my lua libraries.

The other interesting thing they bring up is duplication (and
serialisation) of coroutines.
This unfortunately requires modifications to lua. So if there was a
single change to come out of this discussion
merged into lua, I'd love to see an api to do this without modifications.