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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 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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documentation
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"
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Queues provides a simple implementation of a queue, where
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elements are added 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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[Implementation note:]
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All of queues functionality is also provided by the OrderedCollection (OC)
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class; OC could easily simulate a queue (using #addLast: / #removeFirst).
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The reason for providing Queue is not any speed advantage (actually,
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OC seems to be a tiny bit faster).
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The point is that an implementation of SharedQueue as a subclass of OC
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would require that many OC methods had to be blocked and/or redefined in
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such a subclass, to care for simultaneous access.
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Since queue implements a much more lightweight protocol,
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the sharedQueue implementation is much cleaner when based on a more
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lightweight Queue class.
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[author:]
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Claus Gittinger
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"
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587
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!
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examples
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"
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adding at one end, removing at the other ...
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[exBegin]
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|q element |
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q := Queue new:10.
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1 to:5 do:[:i |
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Transcript showCR:('adding ' , i printString).
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q nextPut:i
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].
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[q notEmpty] whileTrue:[
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element := q next.
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Transcript showCR:('removed ' , element printString).
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].
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[exEnd]
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timing; Queue vs. OrderedCollection
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[exBegin]
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|q oc tQueue tOC |
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q := Queue new:100.
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tQueue := Time millisecondsToRun:[
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1000 timesRepeat:[
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1 to:100 do:[:i |
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q nextPut:i
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].
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[q isEmpty] whileFalse:[
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q next
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].
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]
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].
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oc := OrderedCollection new:100.
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tOC := Time millisecondsToRun:[
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1000 timesRepeat:[
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1 to:100 do:[:i |
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oc addLast:i
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].
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[oc isEmpty] whileFalse:[
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oc removeFirst
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].
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]
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].
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Transcript showCR:('queue time: ' , tQueue printString , ' ms').
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Transcript showCR:('oc time : ' , tOC printString , ' ms').
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[exEnd]
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"
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! !
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!Queue class methodsFor:'instance creation'!
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new
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"return a new queue with space for some elements"
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^ self new:50
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!
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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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!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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peek
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"return the next value in the queue without removing it.
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If the queue is empty, return nil."
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(tally == 0) ifTrue:[^ nil].
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^ contentsArray at:readPosition.
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!
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removeLast
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"return the last 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 := writePosition.
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pos == 1 ifTrue:[
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pos := contentsArray size
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] ifFalse:[
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pos := pos - 1.
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].
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value := contentsArray at:pos.
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writePosition := pos.
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tally := tally - 1.
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^ value
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"Created: 22.6.1996 / 18:49:41 / cg"
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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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|n "{ Class: SmallInteger }"
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pos "{ Class: SmallInteger }"|
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pos := readPosition.
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n := tally.
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1 to:n 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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"Modified: 18.10.1997 / 16:24:01 / cg"
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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:'queries'!
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capacity
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"return the number of elements the queue can hold"
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^ contentsArray size
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!
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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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!Queue class methodsFor:'documentation'!
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version
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^ '$Header: /cvs/stx/stx/libbasic2/Queue.st,v 1.20 1997-11-02 17:51:14 cg Exp $'
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! !
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