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

diff --git a/util/queue.lua b/util/queue.lua
new file mode 100644 (file)
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--- /dev/null
+++ b/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;
+};
+