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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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Collection 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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COPYRIGHT (c) 1993 by Claus Gittinger
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All Rights Reserved
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$Header: /cvs/stx/stx/libbasic2/Queue.st,v 1.8 1995-05-12 12:35:19 claus Exp $
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'!
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!Queue class methodsFor:'documentation'!
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copyright
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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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!
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version
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"
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$Header: /cvs/stx/stx/libbasic2/Queue.st,v 1.8 1995-05-12 12:35:19 claus Exp $
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"
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!
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documentation
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"
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Queues provides a simple implementation of a queue, where
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elements are enterred at one end and removed at the other.
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Access protocol is somewhat like a streams protocol, i.e. access
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is by #nextPut: and #next.
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The queue is created with a size argument, defining how many elements
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are to be stored. It will report an error if the queue ever becomes full
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and another element is to be added. Likewise, it will report an error
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if its empty and an element is to be removed.
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It is not safe when two processes access Queues simultanously,
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since accesses to the internals are not protected against process-switches.
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See SharedQueue for a class which is safe with processes and blocks
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on write when full or on read when empty.
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"
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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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(1 to:5) do:[:i | q nextPut:i].
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Transcript show:(q next); space.
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Transcript show:(q next); space.
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Transcript show:(q next); space.
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Transcript show:(q next); space.
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q nextPutAll:(6 to:10).
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Transcript show:(q next); space.
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Transcript show:(q next); space.
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Transcript show:(q next); space.
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Transcript show:(q next); space.
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Transcript show:(q next); space.
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Transcript show:(q next); space.
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Transcript show:(q next); space.
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Transcript show:(q next); space.
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Transcript show:(q next); space.
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Transcript showCr:(q next).
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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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"initialize the receiver for size entries"
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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;
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Return nil, if the queue is empty"
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|value pos "{ Class: SmallInteger }"|
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(tally == 0) ifTrue:[^ nil].
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pos := readPosition.
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value := contentsArray at:pos.
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pos := pos + 1.
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pos > contentsArray size ifTrue:[pos := 1].
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readPosition := pos.
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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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|sz pos "{ Class: SmallInteger }" |
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sz := contentsArray size.
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pos := writePosition.
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(tally == sz) 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:pos put:anObject.
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pos := pos + 1.
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pos > sz ifTrue:[pos := 1].
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writePosition := pos.
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tally := tally + 1
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!
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nextPutAll:aCollection
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"enter all elements from aCollection into the queue."
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aCollection do:[:element | self nextPut:element]
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! !
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!Queue methodsFor:'enumerating'!
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do:aBlock
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"evaluate the argument, aBlock for each element in the queue"
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|pos endPos|
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pos := readPosition.
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endPos := writePosition.
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1 to:tally do:[:i |
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aBlock value:(contentsArray at:pos).
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pos := pos + 1.
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pos > contentsArray size ifTrue:[
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pos := 1
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]
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]
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! !
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!Queue methodsFor:'queries'!
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isEmpty
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"return true, if there are no elements in the queue"
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^ tally == 0
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!
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isFull
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"return true, if the queue is full i.e. if writing is not
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possible"
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^ tally == contentsArray size
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!
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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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