util.queue: Small fast FIFO/ringbuffer/queue library

util/queue.lua

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+-- 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)
+	-- 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
+
+	return {
+		size = size;
+		count = function (self) return items; end;
+		push = function (self, item)
+			if items >= size then
+				return nil, "queue full";
+			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;
+	};
+end
+
+return {
+	new = new;
+};
+