Meta table error

I am trying to set up a toy example for threading in torch but I am getting an error from running the code below. I think it might just be the way I set up the table but I am not sure.

Threads = require 'threads'
Threads.serialization('threads.sharedserialize')

DataThreads = {}
DataThreads.__index = DataThreads
local result = {}
local unpack = unpack and unpack or table.unpack

function DataThreads.new(nThreads,opt_)
        local self = {}
        opt_ = opt_ or {}
        self.threads = Threads(nThreads,
                           function()
                                   print("background stuff")
                           end 
                        )   
        self.threads:synchronize()

        -- The below for loop is causing the error but the same :addjob() works later on
        for i=1, nThreads do
                self.threads:addjob(self._getFromThreads, self._pushResult)
        end 
        return setmetatable(self,DataThreads)
end


function DataThreads._getFromThreads()
              x,y = torch.uniform(),torch.uniform()
              return x,y 
end

function DataThreads._pushResult(...)
        local res = {...}
        if res == nil then 
                self.threads:synchronize()
        end 
        result[1] = res 
end

function DataThreads:getBatch()
        self.threads:addjob(self._getFromThreads, self._pushResult)
        self.threads:dojob()
        local res = result[1]
                result[1] = nil
        if torch.type(res) == 'table' then
                return unpack(res)
        end
                print(type(res))
        return res
end

d = DataThreads.new(4)

The error occurs in :addjob() in the .new function. However calling the same :addjob() later on in the :getBatch() function works. Am I not allowed to call the ._getFromThreads(), ._getFromThreads() functions before the metatable is set? Here is the error, which I think means ._getFromThreads() is not returning anything;

/home/msmith/torch/install/bin/luajit: ...e/msmith/torch/install/share/lua/5.1/threads/threads.lua:215: function callback expected
stack traceback:
    [C]: in function 'assert'
    ...e/msmith/torch/install/share/lua/5.1/threads/threads.lua:215: in function 'addjob'
    threads.lua:21: in function 'new'
    threads.lua:54: in main chunk