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"
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COPYRIGHT (c) 1993 by Claus Gittinger
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All Rights Reserved
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This software is furnished under a license and may be used
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only in accordance with the terms of that license and with the
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inclusion of the above copyright notice. This software may not
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be provided or otherwise made available to, or used by, any
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other person. No title to or ownership of the software is
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hereby transferred.
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"
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Object subclass:#Queue
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instanceVariableNames:'contentsArray readPosition writePosition tally'
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classVariableNames:''
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poolDictionaries:''
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category:'Collections-Ordered'
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!
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Queue comment:'
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Queues provides a simple implementation of a queue - it is not
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safe when two processes access Queues simultanously - see SharedQueue
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for this.
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$Header: /cvs/stx/stx/libbasic2/Queue.st,v 1.1 1993-11-08 02:31:40 claus Exp $
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'!
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!Queue class methodsFor:'instance creation'!
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new:size
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"return a new queue with space for size elements"
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^ super new init:size
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"
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|q|
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q := Queue new.
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q nextPut:1.
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q nextPut:2.
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q nextPut:3.
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q nextPut:4.
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q nextPut:5.
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Transcript show:(q next) printString; space.
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Transcript show:(q next) printString; space.
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Transcript show:(q next) printString; space.
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Transcript show:(q next) printString; space.
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q nextPut:6.
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q nextPut:7.
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q nextPut:8.
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q nextPut:9.
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q nextPut:10.
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Transcript show:(q next) printString; space.
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Transcript show:(q next) printString; space.
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Transcript show:(q next) printString; space.
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Transcript show:(q next) printString; space.
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Transcript show:(q next) printString; space.
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Transcript show:(q next) printString; space.
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Transcript show:(q next) printString; space.
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Transcript show:(q next) printString; space.
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Transcript show:(q next) printString; space.
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Transcript show:(q next) printString; space.
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"
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!
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new
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"return a new queue with space for 10 elements"
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^ self new:10
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! !
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!Queue methodsFor:'initialization'!
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init:size
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contentsArray := Array new:size.
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readPosition := writePosition := 1.
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tally := 0.
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! !
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!Queue methodsFor:'accessing'!
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next
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"return the next value in the queue; if it its empty, return nil"
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|value|
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(tally == 0) ifTrue:[^ nil].
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value := contentsArray at:readPosition.
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readPosition := readPosition + 1.
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readPosition > contentsArray size ifTrue:[
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readPosition := 1
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].
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tally := tally - 1.
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^ value
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!
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nextPut:anObject
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"enter anObject into the queue - if the queue is full, report an error"
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(tally == contentsArray size) ifTrue:[
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self error:'queue is full'.
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^ self
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].
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contentsArray at:writePosition put:anObject.
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writePosition := writePosition + 1.
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writePosition > contentsArray size ifTrue:[
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writePosition := 1
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].
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tally := tally + 1
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! !
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!Queue methodsFor:'queries'!
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size
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"return the number of elements in the queue"
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^ tally
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! !
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