Class: UnlimitedSharedQueue

• Inheritance
• Description
• Instance protocol
  • private
• Examples

Inheritance:

   Object
   |
   +--Collection
      |
      +--Queue
         |
         +--SharedQueue
            |
            +--UnlimitedSharedQueue

Package:

stx:libbasic2

Category:

Kernel-Processes

Version:

rev: 1.5 date: 2021/01/20 12:20:55

user: cg

file: UnlimitedSharedQueue.st directory: libbasic2

module: stx stc-classLibrary: libbasic2

Description:

Like the superclass, SharedQueue, this provide a safe mechanism for processes to communicate.
They are basically queues, with added secure access to the internals,
allowing use from multiple processes (i.e. the access methods use
critical regions to protect against confusion due to a process
switch within a modification).

In contrast to SharedQueues, which block the writer when the queue is full,
instances of me grow the underlying container, so the writer will never block
(of course, the reader will still block in #next, if the queue is empty).

This kind of queue is eg. needed if the reader process itself wants to
add more (write) to the queue. 
For this, a limited sharedQueue would block the reader process (when writing),
if the queue is full, which would lead to a deadlock situation.

copyright
COPYRIGHT (c) 2016 by eXept Software AG
             All Rights Reserved

This software is furnished under a license and may be used
only in accordance with the terms of that license and with the
inclusion of the above copyright notice.   This software may not
be provided or otherwise made available to, or used by, any
other person.  No title to or ownership of the software is
hereby transferred.

Instance protocol:

 commonWriteWith: aBlock

common code for nextPut / nextPutFirst;
do NOT wait for available space, if the queue is full; instead resize as required.
After the put, signal availablity of a datum to readers.

Examples:

  |reader writer q|
  
  q := SharedQueue new:10.
  
  reader :=
      [
          [
              |element|
              
              element := q next.
              element == true ifTrue:[
                  q nextPut:#xx.
                  q nextPut:#xx.
                  q nextPut:#xx.
              ].
              Transcript showCR:element.
          ] loop.    
      ] fork.

  writer :=
      [
          q nextPut:false.
          q nextPut:false.
          q nextPut:false.
          q nextPut:false.
          q nextPut:false.
          q nextPut:true.
          q nextPut:true.
          q nextPut:true.
          q nextPut:true.
          q nextPut:true.
          q nextPut:false.
          q nextPut:false.
          q nextPut:false.
          Transcript showCR:'writer finished'.
      ] fork.

  |reader writer q|

  q := UnlimitedSharedQueue new:10.

  reader :=
      [
          [
              |element|

              element := q next.
              element == true ifTrue:[
                  q nextPut:#xx.
                  q nextPut:#xx.
                  q nextPut:#xx.
              ].
              Transcript showCR:element.
          ] loop.    
      ] fork.

  writer :=
      [
          q nextPut:false.
          q nextPut:false.
          q nextPut:false.
          q nextPut:false.
          q nextPut:false.
          q nextPut:true.
          q nextPut:true.
          q nextPut:true.
          q nextPut:true.
          q nextPut:true.
          q nextPut:false.
          q nextPut:false.
          q nextPut:false.
          Transcript showCR:'writer finished'.
      ] fork.