File

util/queue.lua @ 12518:73ee3855f970

mod_smacks: Factor out some convenience functions Those lines are long and the risk of mistakes if another one needs to be added seems high, but lower when factored out like this.
author Kim Alvefur <zash@zash.se>
date Fri, 11 Feb 2022 16:09:42 +0100
parent 11114:6a608ecb3471
child 12975:d10957394a3c
line wrap: on
line source

-- Prosody IM
-- Copyright (C) 2008-2015 Matthew Wild
-- Copyright (C) 2008-2015 Waqas Hussain
--
-- This project is MIT/X11 licensed. Please see the
-- COPYING file in the source package for more information.
--

-- Small ringbuffer library (i.e. an efficient FIFO queue with a size limit)
-- (because unbounded dynamically-growing queues are a bad thing...)

local have_utable, utable = pcall(require, "util.table"); -- For pre-allocation of table

local function new(size, allow_wrapping)
	-- Head is next insert, tail is next read
	local head, tail = 1, 1;
	local items = 0; -- Number of stored items
	local t = have_utable and utable.create(size, 0) or {}; -- Table to hold items
	--luacheck: ignore 212/self
	return {
		_items = t;
		size = size;
		count = function (self) return items; end;
		push = function (self, item)
			if items >= size then
				if allow_wrapping then
					tail = (tail%size)+1; -- Advance to next oldest item
					items = items - 1;
				else
					return nil, "queue full";
				end
			end
			t[head] = item;
			items = items + 1;
			head = (head%size)+1;
			return true;
		end;
		pop = function (self)
			if items == 0 then
				return nil;
			end
			local item;
			item, t[tail] = t[tail], 0;
			tail = (tail%size)+1;
			items = items - 1;
			return item;
		end;
		peek = function (self)
			if items == 0 then
				return nil;
			end
			return t[tail];
		end;
		replace = function (self, data)
			if items == 0 then
				return self:push(data);
			end
			t[tail] = data;
			return true;
		end;
		items = function (self)
			return function (_, pos)
				if pos >= items then
					return nil;
				end
				local read_pos = tail + pos;
				if read_pos > self.size then
					read_pos = (read_pos%size);
				end
				return pos+1, t[read_pos];
			end, self, 0;
		end;
		consume = function (self)
			return self.pop, self;
		end;
	};
end

return {
	new = new;
};