CMSC216 HW09: Fork, Spoon, and Wait

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                             HW09 QUESTIONS
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Write your answers to the questions below directly in this text file to
prepare for the associated quiz. Credit for the HW is earned by
completing the associated online quiz on Gradescope.


PROBLEM 1 `fork_report.c'
=========================

A
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  Compile and run the program in `fork_report.c'. Run the program
  several times. Show the output of a typical run below.


B
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  Is the output ordered or disordered with respect to the "I am
  number..." statements? Why?


C
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  Add calls to the wait() or waitpid() function to ensure that the
  output is ordered. Compile and rerun the code to ensure that your code
  will enforce ordered output. Paste your completed code below.


D
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  How many parents and children are there in this program? What is their
  arrangement? How are the parent process(es) numbered?


PROBLEM 2 `run_child.c'
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A
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  Compile and run the program in `run_child.c'. Show it's output below.


B
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  Adjust the contents of the `child_argv[]' array. Try removing the "-l"
  element, try adding on ".." prior to the final NULL, or make other
  modifications INCLUDING for the 0th "ls" string.  Recompile and
  describe whether the output has changed.


C
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  Change the child_cmd string from "ls" to be something else like "gcc"
  or "cat". A good combination is "gcc" with the "--version" as the only
  option in the child_argv array. Recompile and explain what happens
  now.


D
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  Currently `run_child.c' does not reach the bottom statements.
  ,----
  |   printf("------------------\n");
  |   printf("Child Finished\n");
  `----
  Correct this by doing the following:
  - Fork a child process
  - Have ONLY the child process call execvp()
  - Have the parent process wait() for the child
  Paste your completed code below.


PROBLEM 3 `wait_loop.c'
=======================

  Examine the C file `wait_loop.c'. It implements a primitive
  interactive loop asking a user to type things while a child process
  runs in the background. By default, the provided `sleep_print.c'
  program is used which creates a delay before the program
  finishes. Make sure to compile `sleep_print' then compile
  `wait_loop.c' and experiment with its behavior.

  Here is a brief demo.
  ,----
  | >> gcc -o sleep_print sleep_print.c 
  | >> gcc wait_loop.c
  | >> ./a.out
  | Type text then press enter to check on child:
  | input: hello there
  | Entered text: 'hello there'
  | Waiting
  | CHILD: Awake and Done 
  | CHILD FINISHED: 
  | 
  | Type text then press enter to check on child:
  | input: what?
  | Entered text: 'what?'
  | Waiting
  | Child not finished: wait returned -1
  | 
  | Type text then press enter to check on child:
  | input: stop
  | Entered text: 'stop'
  | Waiting
  | Child not finished: wait returned -1
  | 
  | Type text then press enter to check on child:
  | input:  Ctrl-c
  | > 
  `----


A
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  Alter the code so that when the child has completed execution, the
  program breaks out of the loop and the program ends normally. Paste in
  the code you used for this.


B
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  Adjust the code so that the exit status of the child process is
  printed when it finishes. Make sure to use the macros
  `WIFEXITED(status)' and `WEXITSTATUS(status)' to deal with the
  `status' set by `waitpid()'.  Paste the code you added for your
  answer.


C
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  Make changes so that if the user types in the string `quit', the
  program exits immediately without waiting further for the
  child. Example:
  ,----
  | > a.out
  | Type text then press enter to check on child:
  | >> quit
  | Entered text: 'quit'
  | Quitting
  | Exiting wait_loop
  | > CHILD: Awake and Done 
  `----
  Note that the child eventually prints output to the screen which is
  fine.

  You will need to check the user input using either the `strcmp()'
  (unsafe) or `strncmp()' (safer) function. Do some research on this
  function if it is unfamiliar as it will prove generally useful.

  Paste the code you used below.


D
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  The current call to `waitpid()' blocks, pausing execution of the
  parent process until the child finishes. Look up the option to pass to
  `waitpid()' that will allow it to do a non-blocking wait which returns
  immediately if the child is not finished. A sample behavior is below.
  ,----
  | > a.out
  | Type text then press enter to check on child:
  | >> stuff
  | Entered text: 'stuff'
  | Waiting
  | Child not finished: wait returned 0
  | 
  | Type text then press enter to check on child:
  | >> more stuff
  | Entered text: 'more stuff'
  | Waiting
  | Child not finished: wait returned 0
  | 
  | Type text then press enter to check on child:
  | >> CHILD: Awake and Done 
  | Looks like you're finally up
  | Entered text: 'Looks like you're finally up'
  | Waiting
  | CHILD FINISHED: Exit status 5
  | Exiting wait_loop
  | > 
  `----

  Paste your entire code for `wait_loop.c' below.