元表错误

Question

我正在尝试设置一个玩具示例，用于在火炬中进行线程化但是我在运行下面的代码时收到错误。我想这可能只是我设置表格的方式，但我不确定。

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)

错误发生在.new函数的:addjob()中。但是，稍后在:addjob()函数中调用相同的:getBatch()可以正常工作。在设置metatable之前，我是否不允许调用._getFromThreads(), ._getFromThreads()函数？这是错误，我认为这意味着._getFromThreads()没有返回任何内容;

/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

Answer 1

当new函数中的代码运行时，metatable尚未设置，所以当您使用self._getFromThreads和self._pushResult时，那里没有任何内容，而您得到nil，但这无效。

new函数返回后工作因为此时已添加metatable，所以查找使用__index元方法查找条目。

你可以做到

local self = setmetatable({}, DataThreads)

立即设置metatable，然后

return self

最后。