Question

I’m doing some parallel operations in lua. one thread for receiving, one for processing and one for sending again. To pass the data between threads i have been using tables.

Sadly, now i need to pass more than one variable. How do i create a “Multivalue table” ( a table where i can have multiple values per key) without it impacting performance too much, and is there a more efficient way than using tables?

Simplified code so far:

sendQueue = {}
processQueue = {}

function recieveLoop()
    while true do
        Wait For recieve
        table.insert(processQueue, recievedText)
    end
end

function processLoop(sender, text, raw)
    while true do
        for key,value in pairs(processQueue) do
            processData
            table.insert(recieveQueue, raw)
        end
    end
end

And then the same for receiveLoop

all of these 3 functions are threaded and run independently of each other.

Answer 1

Tables can hold other tables, so you can store as many variables as you need in each message.

Instead of:

table.insert(queue, datum1)

You can have:

local message = {datum1, datum2}
table.insert(queue, message)

Or simply:

table.insert(queue, {datum1, datum2})

Including as many “parts” to the message as you want. On the receiving end, you can refer to the message parts by index:

print('foo:', message[1], 'bar:', message[2])

Or unpack the elements:

local foo, bar = unpack(message) -- this is `table.unpack` in Lua 5.2
print('foo:', foo, 'bar:', bar)

Or you could use named fields in the message:

local message = {
      foo = datam1,
      bar = datum2,
}
table.insert(queue, message)

So on and so forth.