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1 " |
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2 COPYRIGHT (c) 1993 by Claus Gittinger |
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3 All Rights Reserved |
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4 |
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5 This software is furnished under a license and may be used |
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6 only in accordance with the terms of that license and with the |
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7 inclusion of the above copyright notice. This software may not |
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8 be provided or otherwise made available to, or used by, any |
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9 other person. No title to or ownership of the software is |
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10 hereby transferred. |
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11 " |
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12 |
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13 Object subclass:#Queue |
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14 instanceVariableNames:'contentsArray readPosition writePosition tally' |
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15 classVariableNames:'' |
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16 poolDictionaries:'' |
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17 category:'Collections-Ordered' |
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18 ! |
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19 |
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20 Queue comment:' |
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21 Queues provides a simple implementation of a queue - it is not |
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22 safe when two processes access Queues simultanously - see SharedQueue |
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23 for this. |
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24 |
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25 $Header: /cvs/stx/stx/libbasic2/Queue.st,v 1.1 1993-11-08 02:31:40 claus Exp $ |
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26 '! |
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27 |
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28 !Queue class methodsFor:'instance creation'! |
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29 |
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30 new:size |
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31 "return a new queue with space for size elements" |
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32 |
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33 ^ super new init:size |
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34 |
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35 " |
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36 |q| |
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37 |
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38 q := Queue new. |
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39 q nextPut:1. |
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40 q nextPut:2. |
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41 q nextPut:3. |
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42 q nextPut:4. |
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43 q nextPut:5. |
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44 Transcript show:(q next) printString; space. |
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45 Transcript show:(q next) printString; space. |
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46 Transcript show:(q next) printString; space. |
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47 Transcript show:(q next) printString; space. |
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48 q nextPut:6. |
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49 q nextPut:7. |
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50 q nextPut:8. |
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51 q nextPut:9. |
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52 q nextPut:10. |
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53 Transcript show:(q next) printString; space. |
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54 Transcript show:(q next) printString; space. |
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55 Transcript show:(q next) printString; space. |
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56 Transcript show:(q next) printString; space. |
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57 Transcript show:(q next) printString; space. |
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58 Transcript show:(q next) printString; space. |
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59 Transcript show:(q next) printString; space. |
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60 Transcript show:(q next) printString; space. |
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61 Transcript show:(q next) printString; space. |
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62 Transcript show:(q next) printString; space. |
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63 " |
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64 ! |
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65 |
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66 new |
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67 "return a new queue with space for 10 elements" |
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68 |
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69 ^ self new:10 |
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70 ! ! |
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71 |
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72 !Queue methodsFor:'initialization'! |
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73 |
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74 init:size |
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75 contentsArray := Array new:size. |
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76 readPosition := writePosition := 1. |
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77 tally := 0. |
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78 ! ! |
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79 |
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80 !Queue methodsFor:'accessing'! |
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81 |
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82 next |
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83 "return the next value in the queue; if it its empty, return nil" |
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84 |
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85 |value| |
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86 |
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87 (tally == 0) ifTrue:[^ nil]. |
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88 value := contentsArray at:readPosition. |
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89 readPosition := readPosition + 1. |
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90 readPosition > contentsArray size ifTrue:[ |
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91 readPosition := 1 |
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92 ]. |
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93 tally := tally - 1. |
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94 ^ value |
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95 ! |
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96 |
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97 nextPut:anObject |
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98 "enter anObject into the queue - if the queue is full, report an error" |
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99 |
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100 (tally == contentsArray size) ifTrue:[ |
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101 self error:'queue is full'. |
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102 ^ self |
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103 ]. |
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104 contentsArray at:writePosition put:anObject. |
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105 writePosition := writePosition + 1. |
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106 writePosition > contentsArray size ifTrue:[ |
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107 writePosition := 1 |
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108 ]. |
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109 tally := tally + 1 |
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110 ! ! |
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111 |
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112 !Queue methodsFor:'queries'! |
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113 |
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114 size |
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115 "return the number of elements in the queue" |
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116 |
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117 ^ tally |
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118 ! ! |