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"{ Encoding: utf8 }"
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4069
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"
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COPYRIGHT (c) 2016 by eXept Software AG
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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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"{ Package: 'stx:libbasic2' }"
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"{ NameSpace: Smalltalk }"
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SharedQueue subclass:#UnlimitedSharedQueue
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instanceVariableNames:''
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classVariableNames:''
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poolDictionaries:''
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category:'Kernel-Processes'
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!
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!UnlimitedSharedQueue class methodsFor:'documentation'!
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copyright
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"
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4280
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COPYRIGHT (c) 2016 by eXept Software AG
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4069
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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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Like the superclass, SharedQueue, this provide a safe mechanism for processes to communicate.
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They are basically queues, with added secure access to the internals,
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allowing use from multiple processes (i.e. the access methods use
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critical regions to protect against confusion due to a process
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switch within a modification).
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In contrast to SharedQueues, which block the writer when the queue is full,
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instances of me grow the underlying container, so the writer will never block
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(of course, the reader will still block in #next, if the queue is empty).
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This kind of queue is eg. needed if the reader process itself wants to
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add more (write) to the queue.
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For this, a limited sharedQueue would block the reader process (when writing),
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if the queue is full, which would lead to a deadlock situation.
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[author:]
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Claus Gittinger
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[see also:]
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SharedQueue
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SharedCollection
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OrderedCollection
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Queue
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Semaphore
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Process
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CodingExamples::SharedQueueExamples
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"
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!
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examples
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"
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ATTENTION:
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Using a regular SharedQueue will lead to a deadlock when the reader writes itself.
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(you'll have to terminate the two processes in the process monitor):
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[exBegin]
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|reader writer q|
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q := SharedQueue new:10.
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reader :=
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[
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[
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|element|
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element := q next.
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element == true ifTrue:[
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q nextPut:#xx.
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q nextPut:#xx.
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q nextPut:#xx.
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].
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Transcript showCR:element.
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] loop.
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] fork.
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writer :=
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[
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q nextPut:false.
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q nextPut:false.
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q nextPut:false.
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q nextPut:false.
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q nextPut:false.
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q nextPut:true.
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q nextPut:true.
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q nextPut:true.
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q nextPut:true.
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q nextPut:true.
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q nextPut:false.
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q nextPut:false.
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q nextPut:false.
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Transcript showCR:'writer finished'.
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] fork.
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[exEnd]
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this will not lead to a deadlock
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(you'll have to terminate the two processes in the process monitor):
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[exBegin]
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|reader writer q|
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q := UnlimitedSharedQueue new:10.
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reader :=
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[
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[
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|element|
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element := q next.
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element == true ifTrue:[
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q nextPut:#xx.
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q nextPut:#xx.
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q nextPut:#xx.
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].
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Transcript showCR:element.
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] loop.
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] fork.
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writer :=
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[
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q nextPut:false.
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q nextPut:false.
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q nextPut:false.
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q nextPut:false.
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q nextPut:false.
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q nextPut:true.
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q nextPut:true.
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q nextPut:true.
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q nextPut:true.
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q nextPut:true.
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q nextPut:false.
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q nextPut:false.
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q nextPut:false.
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Transcript showCR:'writer finished'.
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] fork.
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[exEnd]
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"
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! !
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!UnlimitedSharedQueue methodsFor:'private'!
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commonWriteWith:aBlock
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"common code for nextPut / nextPutFirst;
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do NOT wait for available space, if the queue is full; instead resize as required.
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After the put, signal availablity of a datum to readers."
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|myCapacity|
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accessLock critical:[
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myCapacity := self capacity.
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self size == myCapacity ifTrue:[
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self capacity:(myCapacity * 1.5 // 1).
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].
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aBlock value.
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dataAvailable signal.
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].
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^ self.
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! !
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!UnlimitedSharedQueue class methodsFor:'documentation'!
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version
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^ '$Header$'
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!
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version_CVS
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^ '$Header$'
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! !
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