prosody
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util/queue.lua

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util/queue.lua @ 6911:56c9bc4ba247

util.queue: Add :items() iterator
author Matthew Wild <mwild1@gmail.com>
date Sun, 18 Oct 2015 21:42:33 +0100
parent 6731:d4a6c9ee4bc5
child 6912:cb5b14c95b7b
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343ca80ceb36 util.queue: Small fast FIFO/ringbuffer/queue library
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1 -- Prosody IM
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2 -- Copyright (C) 2008-2015 Matthew Wild
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3 -- Copyright (C) 2008-2015 Waqas Hussain
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4 --
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5 -- This project is MIT/X11 licensed. Please see the
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6 -- COPYING file in the source package for more information.
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7 --
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8
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9 -- Small ringbuffer library (i.e. an efficient FIFO queue with a size limit)
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10 -- (because unbounded dynamically-growing queues are a bad thing...)
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11
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12 local have_utable, utable = pcall(require, "util.table"); -- For pre-allocation of table
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13
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14 local function new(size, allow_wrapping)
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15 -- Head is next insert, tail is next read
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16 local head, tail = 1, 1;
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17 local items = 0; -- Number of stored items
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18 local t = have_utable and utable.create(size, 0) or {}; -- Table to hold items
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19
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20 return {
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21 _items = t;
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22 size = size;
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23 count = function (self) return items; end;
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24 push = function (self, item)
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25 if items >= size then
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26 if allow_wrapping then
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27 tail = (tail%size)+1; -- Advance to next oldest item
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28 items = items - 1;
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29 else
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30 return nil, "queue full";
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31 end
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32 end
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33 t[head] = item;
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34 items = items + 1;
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35 head = (head%size)+1;
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36 return true;
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37 end;
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38 pop = function (self)
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39 if items == 0 then
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40 return nil;
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41 end
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42 local item;
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43 item, t[tail] = t[tail], 0;
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44 tail = (tail%size)+1;
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45 items = items - 1;
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46 return item;
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47 end;
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48 peek = function (self)
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49 if items == 0 then
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50 return nil;
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51 end
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52 return t[tail];
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53 end;
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54 items = function (self)
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55 return function (t, pos)
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56 if pos >= t:count() then
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57 return nil;
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58 end
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59 local read_pos = tail + pos;
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60 if read_pos > t.size then
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61 read_pos = (read_pos%size);
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62 end
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63 return pos+1, t._items[read_pos];
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64 end, self, 0;
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65 end;
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66 };
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67 end
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68
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69 return {
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70 new = new;
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71 };
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72