CSCI 4061 Lab08: Signal Handlers

> seq 10                        # demonstrate 'seq' output: sequence of numbers
1
2
3
4
5
6
7
8
9
10

> seq 10 | wc                   # pipe 'seq' to the 'wc' wordcount utility
     10      10      21         # 10 lines, 10 words, 21 characters

> yes | wc                      # pipe infinite 'yes' output to wc
  C-c                           # send interrupt via Ctrl-c
                                # no output from wc which was terminated

> make                          # build wc_signal program
gcc -Wall -Werror -g  -c wc_signal.c
gcc -Wall -Werror -g  -o wc_signal wc_signal.o

> seq 10 | ./wc_signal          # pipe 'seq' output to wc_signal

10 lines 10 words 21 chars      # input ends, reports amount read

> yes | ./wc_signal             # pipe inifinite 'yes' output to wc_signal
  C-c                           # send interrupt via Ctrl-c, output still reported
28725026 lines 28725027 words 57450053 chars

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                            LAB 08 QUESTIONS
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Lab Instructions
================

  Follow the instructions below to experiment with topics related to
  this lab.
  - For sections marked QUIZ, fill in an (X) for the appropriate
    response in this file. Use the command `make test-quiz' to see if
    all of your answers are correct.
  - For sections marked CODE, complete the code indicated. Use the
    command `make test-code' to check if your code is complete.
  - DO NOT CHANGE any parts of this file except the QUIZ sections as it
    may interfere with the tests otherwise.
  - If your `QUESTIONS.txt' file seems corrupted, restore it by copying
    over the `QUESTIONS.txt.bk' backup file.
  - When you complete the exercises, check your answers with `make test'
    and if all is well, create a zip file with `make zip' and upload it
    to Gradescope. Ensure that the Autograder there reflects your local
    results.
  - IF YOU WORK IN A GROUP only one member needs to submit and then add
    the names of their group.


QUIZ Questions sigaction() function
===================================

  Which of the following options must be set in the `struct sigaction'
  to indicate that on receiving a signal, system calls should be
  restarted automatically? (You may wish to consult the manual pages for
  `sigaction()').

  - ( ) SA_AGAIN
  - ( ) SA_SYSCALL
  - ( ) SA_RESTART
  - ( ) SA_RESETHAND

  How does one indicate that a custom handler function should be run
  when a signal is received using the `sigaction()' function?
  - ( ) The `.sa_handler' field of a `struct sigaction' is set to the
    function and the struct is passed to `sigaction()'
  - ( ) The a pointer is to the function is passed as an argument
    `sigaction()'
  - ( ) Global functions which start with the name `handler_...()' are
    automatically assigned to be signal handlers
  - ( ) Trick question: the `sigaction()' function cannot be used to set
    up a signal handler.

  An easy way to convey that a signal has been received from the signal
  handling function to the main body of a code is..
  - ( ) To send a second signal the process within the signal handler
  - ( ) To call a recursive function defined by the code
  - ( ) To call `printf()' to print out that the signal has been caught
  - ( ) To change the value of a global variable


CODE Complete wc_signal.c
=========================

  Complete the code in `wc_signal.c' so that the program catches
  `SIGINT' and prints its current counts prior to shutting down as shown
  in the demo below. Sections to do so are marked as TODO.

  ,----
  | > make                          # build wc_signal program
  | gcc -Wall -Werror -g  -c wc_signal.c
  | gcc -Wall -Werror -g  -o wc_signal wc_signal.o
  | 
  | > seq 10 | ./wc_signal          # pipe 'seq' output to wc_signal
  | 
  | 10 lines 10 words 21 chars      # input ends, reports amount read
  | 
  | > yes | ./wc_signal             # pipe inifinite 'yes' output to wc_signal
  |   C-c                           # send interrupt via Ctrl-c, output still reported
  | 28725026 lines 28725027 words 57450053 chars
  `----