CS 3733 Operating Systems, Spring 2005 Assignment 5 Comments

General Comments:

• This assignment was graded on the basis of 30 points.
• Basic operation of the program (without the extra credit) was similar to assignment 3.
• Transfer file extra credit: worth 3 points.
  5 students got credit for this.
• Using signals extra credit was harder, although any more students attempted it.
  • If I wrote OK in reference to this on your paper, it means that you demonstrated it, and it seemed to work.
  • This does not mean that you got credit for it.
  • Only 2 students (out of about 15 who tried it) had it close to being correct and got credit (up to 5 points) for this.
  • Most attempted solutions had a server that looked like this:
    • create a pipe
    • fork a child to handle the communication
    • child sends back information as a line through the pipe
    • parent: after forking a child, read a line from the pipe before going back to wait for additional connections.
  • The above is a serial server since the parent cannot wait for additional connections until the child is complete.
  • If you are going to use a serial server, there is no need to create a child or use a pipe to send information back to the parent.
• The two closest solutions used threads.
  Each of these had some minor synchronization problems.
• To do this using forked processes and a pipe, one way is as follows:
  • Create a pipe, and fork a child (pipe-reading child).
  • The pipe-reading child only reads from the pipe.
  • The parent does not access the pipe directly.
  • Create a child for each connection.
  • The parent immediately goes back and waits for the next connection.
  • The connection-handling child writes information to the pipe.
  • The pipe-reading child catches a signal.
    You could use the same SIGUSR1 signal or use SIGUSR2.
  • When the original parent receives a signal, it just sends a signal to the pipe-reading child.
  • When the pipe-reading child receives a signal, it displays the required information.
  • The pipe-reading child must block its signals while it is updating the byte and file counts (after a successful readline).