Improve performance of mesecon.turnon and mesecon.turnoff (#556)

1 files changed, 62 insertions, 0 deletions

diff --git a/mesecons/fifo_queue.lua b/mesecons/fifo_queue.lua
new file mode 100644
index 0000000..a71c71b
--- /dev/null
+++ b/mesecons/fifo_queue.lua
@@ -0,0 +1,62 @@
+
+-- a simple first-in-first-out queue
+-- very similar to the one in https://github.com/minetest/minetest/pull/7683
+
+local fifo_queue = {}
+
+local metatable = {__index = fifo_queue}
+
+-- creates a new empty queue
+function fifo_queue.new()
+	local q = {n_in = 0, n_out = 0, i_out = 1, buf_in = {}, buf_out = {}}
+	setmetatable(q, metatable)
+	return q
+end
+
+-- adds an element to the queue
+function fifo_queue.add(self, v)
+	local n = self.n_in + 1
+	self.n_in = n
+	self.buf_in[n] = v
+end
+
+-- removes and returns the next element, or nil of empty
+function fifo_queue.take(self)
+	local i_out = self.i_out
+	if i_out <= self.n_out then
+		local v = self.buf_out[i_out]
+		self.i_out = i_out + 1
+		self.buf_out[i_out] = true
+		return v
+	end
+
+	-- buf_out is empty, try to swap
+	self.i_out = 1
+	self.n_out = 0
+	if self.n_in == 0 then
+		return nil -- empty
+	end
+
+	-- swap
+	self.n_out = self.n_in
+	self.n_in = 0
+	self.buf_out, self.buf_in = self.buf_in, self.buf_out
+
+	local v = self.buf_out[1]
+	self.i_out = 2
+	self.buf_out[1] = true
+	return v
+end
+
+-- returns whether the queue is empty
+function fifo_queue.is_empty(self)
+	return self.n_out == self.i_out + 1 and self.n_in == 0
+end
+
+-- returns stuff for iteration in a for loop, like pairs
+-- adding new elements while iterating is no problem
+function fifo_queue.iter(self)
+	return fifo_queue.take, self, nil
+end
+
+return fifo_queue