CSci 4061: Introduction to Operating Systems

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• CSci 4061 Introduction to Operating Systems
• Recitation IX
• 03/31/2008

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Todays agenda!

• Download Lab_Ex9.tgz
• UnTAR it and check if you have a file prodcom.c
• We are going to discuss an implementation of the
  Producer-Consumer problem in conjunction with
  Assignment IV.
• All set?

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Producer-Consumer Problem

• A classic example of multi-process
  synchronization
• Also called the Bounded-Buffer Problem
• Producer pushes an entity into the buffer and the
  Consumer retrieves it
• But the buffer is bounded?
• What are the implications?
• The last slide has references to some good
  discussions on the topic, just in case

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prodcom.c The program

• gcc w lpthread prodcom.c
• ./a.out
• Produces multiple lines of output!
• Let us take a look at the code constructs
• Open the source code in your favourite editor!

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Assignment IV A Multi-Producer Multi-Consumer
Problem

• Five producer threads named Red, White, Blue,
  Green and Orange
• Read from their respective input files named
  red.in, white.in, blue.in, green.in and orange.in
  respectively.
• Write to a shared buffer called CHANNEL of size
  20 records!
• Why is the size important? How will you
  synchronize the working of producer threads?

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Assignment IV A Multi-Producer Multi-Consumer
Problem (Contd.)

• Another thread called Router pops out the entries
  from the buffer CHANNEL and writes them to the
  respective mailboxes of the consumer threads
• How does it identify which buffer to write to?
  Colour coding of input!
• Consumer threads then pick the entries from
  their respective buffers and write to their
  respective output files. Simple!

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A Picture Speaks Better .
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Parallels with the Original Problem

• Similarities
• Buffer is bounded
• Thread synchronization required
• Inter-thread communication
• Differences
• An intermediary called Router
• A producer and its corresponding consumer do not
  use the same buffer
• Synchronization between producers

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Issues!

• Synchronization of the producers
• The working of Router
• Synchronization of the consumer threads
• Most importantly, the size of the input files is
  not bounded!

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Reference

• https//computing.llnl.gov/tutorials/pthreads/
• http//en.wikipedia.org/wiki/Producer-consumer_pro
  blem
• http//www.dcs.ed.ac.uk/home/adamd/essays/ex1.html
  
• Remember, no reference is given for the heck of
  it!

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Questions/ Criticisms?

• Anything is welcome!