Lab Assignment--Signals

Lab Code

   curl -O -s https://www.labs.cs.uregina.ca/330/Signals/Posix/Lab10.zip
   unzip Lab10.zip

(Please do this lab on os1 or os2)

Part 1: Questions

Write the answers to the following questions as comments at the beginning of your code.

1. The notes for this lab state that each signal has one of four default actions (not including continue):
   • terminate (or exit)
   • core
   • stop
   • ignore

   Use the signal man page to find one signal that corresponds to each of these four actions. Find signals other than SIGILL, SIGHUP, SIGWINCH, and SIGSTOP.

2. For which two signals can you not change the default action?

Part 2: Code

Write a program that forks a child process. The parent will send SIGWINCH to the child. The child will override the default action of SIGWINCH so that a message is displayed and the child exits. Without using wait(), the parent will exit after the child has exited. (Note: automatically, when a child exits, a SIGCHLD signal is sent to the parent)

More Details:

• Child will:
• Overwrite the default action of SIGWINCH
• Loop infinitely and print a message "child waiting". Please note that you will want to introduce a little delay in your loop. Otherwise, you will get too many messages. Hint: Try nanosleep with a value of 5000L instead of 500000L
   
• Parent will:
• Overwrite the default action of SIGCHLD
• nanosleep for 500000ns as in:
  nanosleep((const struct timespec[]){{0, 500000L}}, NULL);
• Optionally: Print a message that the parent is sending a signal - this seems to prevent core dumps
• Send a SIGWINCH to the child
• Loop infinitely and print a message "parent waiting". Please note that you will want to introduce a little delay in your loop. Otherwise, you will get too many messages. Hint: Try nanosleep with a value of 5000L instead of 500000L
   
• You only require one handler for SIGWINCH and SIGCHLD. It will:
• Print the numeric value of the signal received
• Print a message that the child or parent received the signal
• exit

Sample run for the code:

Please note: you might see a different number/order of "Child waiting" and "Parent waiting" messages

% a.out
Child waiting!!
Child waiting!!
Child waiting!!
Child waiting!!
Child waiting!!
Child waiting!!
Child waiting!!
Parent is sending a signal
Parent waiting!!

Signal 28 received.
Child received signal
Parent waiting!!

Signal 17 received.
Parent received signal

Deliverables:

• Answers to the two questions (as comments at the beginning of your code)
• The code for Part 2
• A sample run