From 3baf1a2f17b3415329e0127648b014db1ad50c8d Mon Sep 17 00:00:00 2001
From: teknomunk <teknomunk@protonmail.com>
Date: Mon, 8 Apr 2024 08:45:53 +0000
Subject: [PATCH] Add FIFO, implement scheduler timestep

---
 mods/CORE/mcl_scheduler/fifo.lua | 44 +++++++++++++++++++++++++
 mods/CORE/mcl_scheduler/init.lua | 55 +++++++++++++++++++++++++++++++-
 2 files changed, 98 insertions(+), 1 deletion(-)
 create mode 100644 mods/CORE/mcl_scheduler/fifo.lua

diff --git a/mods/CORE/mcl_scheduler/fifo.lua b/mods/CORE/mcl_scheduler/fifo.lua
new file mode 100644
index 000000000..5b2b47d35
--- /dev/null
+++ b/mods/CORE/mcl_scheduler/fifo.lua
@@ -0,0 +1,44 @@
+local mod = mcl_scheduler
+
+function Class()
+	local cls = {}
+	cls.mt = { __index = cls }
+	function cls:new(...)
+		local inst = setmetatable({}, cls.mt)
+		local construct = inst.construct
+		if construct then inst:construct(...) end
+		return inst
+	end
+	return cls
+end
+
+-- Amoritized O(1) insert/delete functional First In, First Out (FIFO) queue
+local fifo = Class()
+mod.fifo = fifo
+function fifo.insert(node)
+	node.next = fifo.inbox
+	fifo.inbox = node.next
+end
+function fifo.get()
+	if not fifo.outbox then
+		-- reverse inbox
+		local iter = fifo.inbox
+		fifo.inbox = nil
+
+		while iter do
+			local i = iter
+			iter = iter.next
+
+			i.next = fifo.outbox
+			fifo.outbox = i
+		end
+	end
+
+	local res = fifo.outbox
+	if res then
+		fifo.outbox = res.next
+		res.next = nil
+	end
+	return res
+end
+
diff --git a/mods/CORE/mcl_scheduler/init.lua b/mods/CORE/mcl_scheduler/init.lua
index 1e3adc831..71377c84a 100644
--- a/mods/CORE/mcl_scheduler/init.lua
+++ b/mods/CORE/mcl_scheduler/init.lua
@@ -5,6 +5,7 @@ mcl_scheduler = {}
 local mod = mcl_scheduler
 
 dofile(modpath.."/queue.lua")
+dofile(modpath.."/fifo.lua")
 
 function mod.test()
 	local t = mod.queue.new()
@@ -35,5 +36,57 @@ function mod.test()
 	end
 end
 
-mod.test()
+local run_queues = {}
+for i = 1,4 do
+	run_queues[i] = mod.fifo:new()
+end
+local time = 0
+local priority_queue = mod.queue:new()
+local functions = {}
+
+print(dump(run_queues))
+
+minetest.register_globalstep(function(dtime)
+	local start_time = minetest.get_us_time()
+	time = time + dtime
+	local limit = 4
+	while time > 0.05 and limit > 0 do
+		-- Add tasks to the run queues
+		local iter = priority_queue:tick()
+		while iter do
+			local task = iter
+			iter = iter.next
+
+			local priority = task.priority or 3
+			run_queues[priority]:insert(task)
+		end
+
+		-- Run tasks until we run out of timeslice
+		local i = 1
+		while i < 4 and (minetest.get_us_time() - start_time) < 50000 do
+			local task = run_queues[i]:get()
+			if task then
+				print("Running task "..dump(task))
+				local func = functions[task.fid]
+				local cancel = false
+				if func then
+					local err
+					cancel,err = pcall(func, task.dtime, table.unpack(task.args))
+					if err then
+						minetest.log("error","Error while running task: err")
+					end
+				end
+
+				-- Add 
+				if task.period and not cancel then
+					task.time = task.period
+					priority_queue:add_task(task)
+				end
+			end
+		end
+
+		time = time - 0.05
+		limit = limit - 1
+	end
+end)