Computer Science 322 Operating Systems Mount Holyoke College Spring 2008

Agenda

• Announcements
  • CPU scheduling simulator - demonstrate them!
  • Shell lab - don't let yourself be stuck for long - ask!
  • Scheduling issues over the next couple weeks (see schedule page)
• Unix Systems Programming
  • Pipes
    • Another interprocess communication mechanism
    • Powerful command-line tool: |
    • Unnamed pipe created with pipe(2)
      • fd[0] is the "read end", fd[1] is the "write end"
      • these are file descriptors
    • Named pipe created with mkfifo(1) or mkfifo(2)
      • part of the file system
  • Duplicating file descriptors
    • dup2(2): reroute things intended for one file descriptor to another
    • redirect existing file descriptors (0=stdin, 1=stdout, 2=stderr)
    • hook the output of one pipe to the input of another
  • Other useful C tips and tricks
    • gcc -Wall
    • debuggers: gdb, ddd
    • initialization of memory (or not)
    • string manipulation: see string(3)
    • memory management: malloc(3), free(3) - no garbage collector here!
    • "object oriented" C programming
• Deadlock
  • Idea
  • Necessary conditions: mutex, hold and wait, no preemption, circular wait
  • Resource allocation graphs
  • Prevention

Lecture Assignment

• SG&G 7.1
• A system has two processes and three identical resources. Each process needs a maximum of two resources. Is deadlock possible? Why or why not?

Examples