Scripts

local threads = {}

local startExec = function(func)
	local threads = threads
	errorHook(function()
		%threads[%func] = nil
	end)
	threads[func] = 1
	func()
	threads[func] = nil
end

function startThreadOnce(func)
	if not %threads[func] then
		startThread(%startExec, func)
	end
end

function isFunctionRunning(func)
	return %threads[func]
end

In this example, startThreadOnce starts the function only if it is not already running. isFunctionRunning checks if the function is currently running.