February 22, 2006

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Base Case: Token Ring of One Process

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• process communicates to itself through a pipe
• notice data written using printf is buffered

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Now n=2

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• extending a ring of one process to one of two processes is fairly straightforward
• now we need two pipes
• parent's standard input read from standard output of child
• child's standard input read from standard output of parent

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Extending Ring to Arbitrary Number of Processes

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• easily extended
• #pipes necessary = #processes
• still only 1 array of size 2 necessary for pipe file descriptors
• resembles process chain
  • i.e., each process only forks once
• in-class exercise: coding infrastructure necessary for token ring with an arbitrary number of processes
  • take #processes n as a command-line argument
  • done in <65 loc, including all of the error checking code

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References

[USP] K. A. Robbins and S. Robbins. UNIX Systems Programming: Concurrency, Communication, and Threads. Prentice Hall, 2003