CS 3733 Operating Systems, Spring 2006 Assignment 4 Comments

This assignment was graded on the basis of 30 points.

1. Handle errors on all I/O.
2. Global variables should have static linkage.
3. No more than one declaration per line.
4. Do not return negative values from main.
5. In testing part 3, send at least three signals, one before any compiles one after a compile and one after another compile.
6. In the signal handler, save and restore errno.
7. How to print a number in a signal handler:
   • Use write along with your own conversion function.
   • Use fprintf but don't use it or any I/O or string functions in the main program without blocking the signal.
   • Create a message to be printed in the main program and print it with write.
     This produces critical sections. Block the signal while preparing the message.
8. How to do Part 3
   Problem: main program keeps count but the child (the one that waits for the exec'ed program) gets the return status.
   • When cleaning up zombies, get teh status.
     If you just do a normal wait without the NOHANG the server is now a serial server.
   • Use a signal to send the status back to the main program.
   • Send the info through a pipe which is read by the signal handler.
     You need to be careful, and either use non-blocking I/O or have the signal handler also write to the pipe so you know when to stop reading.