test_threads.lua

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

n_task = 3
local pools = {}

for task=1,n_task do
    pools[task] = threads.Threads(5,
        function()
            -- Needed only for serialized elements
            -- The others can be required in a local
            -- in the job
        end
    )
end

local endcallback
local finish_task
-- Scope the callback
do
    -- Variable to get back the returned value
    local returned_value
    -- The endcallback for the tasks
    endcallback = function(work_result)
        returned_value = work_result
    end
    -- The function to get the returned value
    finish_task = function(task)
        pools[task]:dojob()
        return returned_value
    end
end

function start_task(task)
    local task = task

    print("M" .. task .. ": adding job")
    pools[task]:addjob(
        function()
            local sys = require "sys"
            local threads = require "threads"
            local torch = require "torch"

            print("T" .. task .. ": started")
            -- Work
            local work_time = torch.random(1,2)
            sys.sleep(work_time)
            local work_result = torch.random(1,100)
            print("T" .. task .. ": result of work " .. work_result)

            return work_result
        end,
        endcallback
    )
end

-- Initially start all tasks
start_task(1)
start_task(2)
start_task(3)

-- Start main loop
while true do
    -- Get random task
    local task = torch.random(1, 3)

    print("M" .. task .. ": finishing task")
    local result = finish_task(task)
    print("M" .. task .. ": result is " .. result)
    
    print("M" .. task .. ": restarting task")
    start_task(task)
end