esx_core/async.lua

if Citizen and Citizen.CreateThread then
	CreateThread = Citizen.CreateThread
end

Async = {}

function Async.parallel(tasks, cb)

	local remaining = #tasks
	local results   = {}

	for i=1, #tasks, 1 do
		
		CreateThread(function()
			
			tasks[i](function(result)
				
				table.insert(results, result)
				
				remaining = remaining - 1;

				if remaining == 0 then
					cb(results)
				end

			end)

		end)

	end

end

function Async.parallelLimit(tasks, limit, cb)

	local remaining = #tasks
	local running   = 0
	local queue     = {}
	local results   = {}

	for i=1, #tasks, 1 do
		table.insert(queue, tasks[i])
	end

	local function processQueue()

		if #queue == 0 then
			return
		end

		while running < limit and #queue > 0 do
			
			local task = table.remove(queue, 1)
			
			running = running + 1

			task(function(result)
				
				table.insert(results, result)
				
				remaining = remaining - 1;
				running   = running - 1

				if remaining == 0 then
					cb(results)
				end

			end)

		end

		CreateThread(processQueue)

	end

	processQueue()

end

function Async.series(tasks, cb)
	Async.parallelLimit(tasks, 1, cb)
end