Coroutines in Lua

Lua coroutines are cooperative execution contexts, not operating-system threads. They run until they return, raise an error, or explicitly yield.

local producer = coroutine.create(function()
    for i = 1, 3 do
        coroutine.yield(i * i)
    end
    return "finished"
end)

while true do
    local ok, value = coroutine.resume(producer)

    if not ok then
        error(value)
    end

    print(value)

    if coroutine.status(producer) == "dead" then
        break
    end
end

Coroutines alone do not make blocking I/O asynchronous. An event loop or nonblocking I/O library is required.

If an abandoned coroutine owns to-be-closed variables, call coroutine.close so their cleanup handlers run.