Question

In C programming language.

Problem 1 (Building a given Process Tree) 10 points) In this exercise you are asked to write a program which generates the following process tree (Scheme 1) Scheme 1: A given process tree The processes that you generate must remain active for some considerable window of time in order for the user to be able to observe the tree. The leaf process executes a call to: sleep() The internal process awaits of the termination of all its children processes. Every process printsa corresponding message every time it transitions to another phase (for example: start, loop to wait for children termination, allowing its own termination), so that the validation of the correct program operation is feasible. In order to separate the processes, please make sure that every process terminates with a different return code. In this example, one scenario can be At this point, you may find helpful a number of auxiliary functions for process handling, such as those that 1) have to do with identifying the circumstances under which a child process terminated (included in your ppt slides) 2) display the process tree starting from the root process (included in the appendix) 3) are related with different ways of recursively traversing a tree once the whole process tree is generated, etc

Answer 1

The output snapshot is followed by the code. Explanatory comments are added.

umairaz@umairaz:~/CHEGGS gcc processtree.c umairaz@umairaz:-/CHEGG$ umairaz@umairaz:-/CHEGG$ umairaz@umairaz:~/CHEGGS ./a.out Started process A, pid=28208 Process A, pid-28208: Forked B, pid-28209 Started process B, pid=28209 Process A, pid-28208: Forked C, pid-28210 Process A, pid 28208: Waiting for children to end Process B, pid-28209: Forked D, pid-28211 Process B, pid 28209: Waiting for children to end Started process D, pid-28211 Process D, pid 28211: Waiting for children to end Started process c, pid=28210 Process C, pid 28210: Waiting for children to end Process D, pid 28211: ending process Process C, pid 28210: ending process Process B, pid-28209: Child exited with status 12 Process B, pid 28209: ending process Process A, pid-28208: Child exited with status 9 Process A, pid-28208: Child exited with status 8 Process A, pid 28208: ending process umairaz@umairaz:-/CHEGG$ umairaz@umairaz:-/CHEGGS echo $? umairaz@unairaz:~/CHEGGS

#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

/* Structures to define the process tree */
struct processInfo
{
    char processName; /* A, B, C, D */
    int numChild;
    char children[5];
    int retValue;
};

/* Define the process tree */
struct processInfo process[] = {
    { 'A', 2, {'B', 'C'}, 5},
    { 'B', 1, {'D'}, 9 },
    { 'C', 0, { }, 8 },
    { 'D', 0, { }, 12 },
};

char myId = 'A'; /* my process id */
int retVal;

void processfunction()
{
    int i, j;
    int n = sizeof(process) / sizeof(struct processInfo);

    printf("Started process %c, pid=%d\n", myId, getpid());

    /* Get the children details */
    for(i = 0; i < n; i++)
    {
        if(myId == process[i].processName) /* process details found */
            break;
    }
    if(i < n) /* entry found */
    {
        /* update return value */
        retVal = process[i].retValue;
        /* create forked children */
        pid_t pids[5];
        for(j = 0; j < process[i].numChild; j++)
        {
            pids[j] = fork();
            if(pids[j] < 0)
            {
                printf("Process %c, pid=%d: fork failed\n", myId, getpid());
            }
            if(pids[j] == 0)
            {
                /* child process */
                /* 1. update id */
                myId = process[i].children[j];
                /* 2. call the processfunction, and return */
                processfunction();
                return;
            }
            else
            {
                printf("Process %c, pid=%d: Forked %c, pid=%d\n", myId, getpid(), process[i].children[j], pids[j]);
            }
        }
        /* Children forked, wait for children to end */
        printf("Process %c, pid=%d: Waiting for children to end\n", myId, getpid());
        for(j = 0; j < process[i].numChild; j++)
        {
            int status;
            if(pids[j] > 0) /* child was successfully forked */
            {
                waitpid(pids[j], &status, 0);
                printf("Process %c, pid=%d: Child exited with status %d\n", myId, getpid(), WEXITSTATUS(status));
            }
        }
    }

    /* Sleep for sometime */
    sleep(10);
    printf("Process %c, pid=%d: ending process\n", myId, getpid());
}

int main()
{
    processfunction();
    return retVal;
}