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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:#SharedQueue
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instanceVariableNames:'contentsArray readPosition writePosition
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tally
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accessProtect dataAvailable spaceAvailable'
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classVariableNames:''
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poolDictionaries:''
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category:'Collections-Ordered'!
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SharedQueue comment:'
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SharedQueues provide a safe mechanism for processes to communicate.
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See samples in doc/coding.
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3
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$Header: /cvs/stx/stx/libbasic2/SharedQueue.st,v 1.3 1993-10-13 00:18:13 claus Exp $
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'!
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!SharedQueue class methodsFor:'instance creation'!
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new
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^ self new:10
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!
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new:size
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^ super new init:size
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! !
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!SharedQueue 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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accessProtect := Semaphore forMutualExclusion.
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dataAvailable := Semaphore new.
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spaceAvailable := Semaphore new
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! !
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!SharedQueue methodsFor:'accessing'!
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next
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"return the next value in the queue; if it its empty, wait 'til
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something is put into the receiver.
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When the datum has been removed, signal space-availability to
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writers"
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|value ok|
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ok := false.
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[ok] whileFalse:[
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[tally == 0] whileTrue:[
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dataAvailable wait
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].
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accessProtect critical:[
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"
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this check is needed, since another process may
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have read the value in the meantime ...
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"
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tally == 0 ifFalse:[
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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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tally == (contentsArray size - 1) ifTrue:[
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spaceAvailable signal
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].
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ok := true
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]
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]
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].
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^ value
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!
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nextPut:anObject
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"enter anObject into the queue; wait for available space, if
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the queue is full. After the put, signal availablity of a datum
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to readers."
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1
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|ok|
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0
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ok := false.
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[ok] whileFalse:[
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[tally == contentsArray size] whileTrue:[
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spaceAvailable wait
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].
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accessProtect critical:[
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tally == contentsArray size ifFalse:[
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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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tally == 1 ifTrue:[
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dataAvailable signal
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].
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ok := true
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]
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]
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].
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^ anObject
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! !
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!SharedQueue methodsFor:'queries'!
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1
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size
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"return the number of elements in the shared queue"
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0
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^ tally
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! !
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