February 20, 2006

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Comments on Homeworks

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• use exit in main as opposed to return, why?
• error checking, error checking, error checking
  • make use of perror
• objective of a Makefile is not to help compile the source files of your program in batch

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Redirecting Standard Error

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$ time alongcommand >/dev/null 2>timelog.txt
$
$ time alongcommand >output.txt 2>&1
$
$ Iwritetostderr 2>&1 | wc -l

• shell time vs. UNIX time
  • former writes to terminal
  • latter writes to standard error
    • use fully qualified path: /bin/time

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More Job Control

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• ;
• nice
• nohup (assumes nice)
• at
• cron

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Canonical vs. Noncanonical Modes of Processing Terminal Input

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• canonical
  • line-at-a-time processing
    • read requests do not return until user enters a line delimiter (usually a newline)
  • ERASE and KILL characters work only on undelimited portion
• noncanonical
  • uses MIN and TIME parameters

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In-class Exercise: Writing a Program to Change our ERASE key to `#'

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Experimenting with the Audio Device on Our System

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• /dev/audio
• yet another example of the uniformity (consistency) in UNIX i/o
• must use at console
• ioctl function
  • gets device status info or sets device control parameters
  • has variable argument list
• pass O_NONBLOCK to open to open device for nonblocking i/o

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Introduction to the Token Ring (of Processes)

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• nodes = processes
• links = pipes
• each process is a filter
  • reads from standard input
  • writes to standard output
• simple
• inexpensive
• unidirectional communication: clockwise
  • each entity has a connection for input and output
• latency increases as #nodes increase
• bandwidth is independent of ring size (#nodes)

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References

[UPE] B. W. Kernighan and R. Pike. The UNIX Programming Environment. Prentice Hall, Second edition, 1984.
[USP] K. A. Robbins and S. Robbins. UNIX Systems Programming: Concurrency, Communication, and Threads. Prentice Hall, 2003