Spreading expensive operations out over multiple server steps using coroutines

approx_pi.lua

local jobs = {}

minetest.register_globalstep(function(dtime)
	local remaining_jobs = {}
	local time_per_job = dtime / #jobs
	for _, job in ipairs(jobs) do
		local time_s = minetest.get_us_time() / 1e6
		repeat
			assert(coroutine.resume(job))
			local dtime_s = minetest.get_us_time() / 1e6 - time_s
		until dtime_s > time_per_job or coroutine.status(job) == "dead"
		if coroutine.status(job) == "suspended" then
			table.insert(remaining_jobs, job)
		else
			assert(coroutine.status(job) == "dead")
		end
	end
	jobs = remaining_jobs
end)

minetest.register_chatcommand("approximate_pi", {
	func = function()
		local function job()
			-- Approximate pi (very inefficiently)
			local hits = 0
			local m = 1e5
			local k = 1000
			local n = m * k
			for _ = 1, m do
				-- Do many iterations in a row to reduce overhead from yielding
				for _ = 1, k do
					local x, y = math.random(), math.random()
					if x^2 + y^2 < 1 then
						hits = hits + 1
					end
				end
				coroutine.yield() -- give control back to scheduler
			end
			local pi = 4 * hits / n
			minetest.chat_send_all("pi = " .. pi)
		end
		table.insert(jobs, coroutine.create(job))
	end,
})