csci4061/lab03-code/QUESTIONS.txt

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                            LAB 03 QUESTIONS
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- Name: Michael Zhang
- NetID: zhan4854

Answer the questions below according to the lab specification. Write
your answers directly in this text file and submit it to complete Lab01.


PROBLEM 1 `wait-fork.c'
=======================

A
~

  Compile and run the program in `wait-loop.c'. Does the loop in the
  program ever end? How must one "exit" the program?

The program doesn't end, since there's a while loop that continuously asks the
user for input, without any option that makes it exit. The only way to "exit"
the program is to terminate it either through sending the signal using ^C, or
else opening another terminal window and killing the process by id.


B
~

  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.


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>

int main(void) {
    // Make sure to compile sleep_print first:
    // gcc -o sleep_print sleep_print.c
    char *child_argv[] = {"./sleep_print", "5", "CHILD: Awake and Done", NULL};
    pid_t child_pid = fork();
    if (child_pid == 0) {
        execvp(child_argv[0], child_argv);
        perror("errno indicates");
        printf("Couldn't run '%s': is it compiled??\n", child_argv[0]);
        exit(1);
    }

    while (1) {
        printf("Type text then press enter to check on child:\n");
        char buffer[1024];
        char *input = fgets(buffer, 1024, stdin);
        input[strlen(input) - 1] = '\0';  // Eliminate newline in buffer
        printf("Entered text: '%s'\n", input);

        printf("Waiting\n");
        int status;
        pid_t pid = waitpid(child_pid, &status, 0);
        if (pid == child_pid) {
            printf("CHILD FINISHED: ");
            printf("\n");
            break;
        } else {
            printf("Child not finished: wait returned %d\n", pid);
        }
        printf("\n");
    }
    printf("Exiting wait-loop\n");
    return 0;
}


C
~

  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.


    if (WIFEXITED(status)) {
        printf("CHILD FINISHED: %d", WEXITSTATUS(status));
        printf("\n");
        break;
    }

D
~

  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 the `strncmp()'
  function. Do some research on this function as it will prove generally
  useful.

  Paste the code you used below.


E
~

  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.