added support for (de)serializing closures/upvalues

[nicholas-leonard]

fixes #28 for Lua 5.2. This won't work with LuaJIT (pretty sure, though untested).

• [x] ipc.workqueue.writeup() to write upvalues
• [x] unit test on LuaJIT
• [x] documentation
  • [x] writeup: how to use and not use upvalues
  • [x] write: multi-write is not documented

[nicholas-leonard]

Just finished discussing this PR with @luketwitter. We think it would be best to have the user accept upvalues/closures by adding arguments to ipc.workqueue, ipc.map, and so on. We also need to add doc explaining some tricky use-cases, i.e.:

local mylib = require "mylib"

local closure = function()
   ...
   mylib.somefunction()
   ...
end

local q = ipc.workqueue()
q:write(closure, true)

In the above, mylib would get serialized. The trick would be to require the package inside the closure:

local closure = function()
   local mylib = require "mylib"
   ...
   mylib.somefunction()
   ...
end

[soumith]

imo closures which have upvalues should not be allowed. this makes the interface much more cleaner and usable without magic bad performance issues!

[nicholas-leonard]

@soumith Yeah this is why we are making it optional: workqueue.writeup allows for upvalues, workqueue.write doesn't. And all other serializations don't allow upvalues either (i.e. ipc.map, etc.).

[soumith]

ah cool!