Question

Task 1*(100 points) Implement a program that will communicate the value of an integer x, between processes. You can do this using a file to store the value of x, or you can use shared memory with shmget or mmap. Shared memory is out of the scope of this class, so you will have to teach yourself how to use it, however if you put in the effort to learn, it results in simpler more elegant code. x will start with the value 19530, and you must print that value. Then you will loop 5 times where in each loop: the child goes first and subtracts 5 from x, the parent then divides x by 5, and both processes print who they are and their result of x after the operation. If you use a file and not shared memory, then during each iteration of the loop both processes must get the value of x from the file, and store the resulting value of x to the file. wait() is a required function call, so you will need to create a new process, and terminate it each time through the loop. The following system calls are required for this lab: • fork() • wait() The following functions may be useful for this lab: • open(), read(), write() • sleep(): make the process wait for a number of seconds • atoi(): converts string to integer • sprintf(): can be used to convert integer to string • fflush(): forces a file buffer to flush. This is useful to flush stdout before creating a child so you don't have two processes printing the same buffer to the screen. This can sometimes fix strange printing behavior.

_{^{GIVEN CODE- FILL IN THE BLANK!}}

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

// Function ptototypes
int readX();
void writeX(int);

int main() /// chi read x ---> divi ---> write x into file ---> par read x --> sub--> write x into file---> chi read x-->etc
{
   int pid;           // pid: used to keep track of the child process
   int x = 19530;       // x: our value as integer
   int i;               // iterator  

   // output inital value to the screen
   printf("x = %d\n", x); /// x= 19530

   // Write x to file
   ______;

   // loop 5 times
   for( i = 0; i<5; i++)
   {
       // output the current loop iteration
       printf("\nITERATION %d\n", i+1);

       // flush here so that the stdout buffer doesn't
       //        get printed in both processes
       fflush(stdout);

       // fork child process
       if (________) /// fork()
       {
           perror("Error with fork");
           exit(1);
       }

       // PARENT waits a second for the child to go first
       else if (_____)
       {
           _____;
       }

       // Both processes read x from file
       ______;

       // CHILD prints child, and performs subraction
       if (____)
       {
           printf("Child: ");
           ____; /// x= x - 5
       }

       // PARENT prints parent, and performs division
       else if (____)
       {
           printf("Parent: ");
           ____;
       }

       // Both processes output x value and write x to file...
       printf("x = %d\n", x);
       ______;

       // The child terminates
       if (____)
       {
           ____;
       }
   }

   exit(0);
}

/// Returns the value read from .shareX.dat /////// int num=readX(); value in file---> num
int readX()
{
   char xChar[10];       // xChar: our value as a char
   int fd;               // fd: file descriptor

   // open to read and store x
   if ( (fd = open(".shareX.dat", O_RDONLY )) == -1 )
   {
       perror("Error opening file");
       exit(2);
   }

   // read xChar from the file
   if ( read(fd, xChar, 10) == -1 )
   {
       perror("Error reading file");
       exit(3);
   }

   // close file for reading
   close(fd);

   // convert xChar to int and return
   return atoi(xChar);
}

/// Writes the writeX value to the file .shareX.dat /////// writeX(num) ===> write num into file
void writeX(int writeX)
{
   char xChar[10];       // xChar: our value as a char
   int fd;               // fd: file descriptor
   int xBytes;           // how much to write

   // open, clear, and create file if not createdi
   if ( (fd = open(".shareX.dat",
                   O_CREAT | O_TRUNC | O_WRONLY, 0644 )) == -1 )
   {
       perror("Error opening file");
       exit(4);
   }

   // convert x to char
   xBytes = sprintf(xChar, "%d", writeX);

   // put xChar in file
   if ( write(fd, xChar, xBytes) == -1 )
   {
       perror("Error writing to file");
       exit(5);
   }

   // close the file for writing
   close(fd);

   return;
}

Answer 1

program code to copy

main.c


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

// Function ptototypes
int readX();
void writeX(int);

int main()
{
        int pid;                        // pid: used to keep track of the child process
        int x = 19530;          // x: our value as integer
        int i;                          // iterator     

        // Write x to file
        writeX(x);

        // output inital value to the screen
        printf("x = %d\n", x);

        // loop 5 times
        for( i = 0; i<5; i++)
        {
                // output the current loop iteration
                printf("\nITERATION %d\n", i+1);

                // flush here so that the stdout buffer doesn't
                //              get printed in both processes
                fflush(stdout);

                // Check if fork child process creates a process
                if ((pid = fork()) == -1) 
                {
                        perror("Error with fork");
                        exit(1);
                }

                // Parent waits a second for the parent to go first
                else if (pid > 0)
                {
                        wait(0);
                }

                // Both processes read x from file
                x = readX();

                // Parent prints parent, and performs subraction
                if (pid > 0)
                {
            x = x / 5;  
                        printf("Parent: ");     
                
                }

                // Child prints child, and performs division
                else if (pid == 0)
                {
            x = x - 5;
                        printf("Child: ");      
            

                }

                // Both processes output x value and write x to file...
                printf("x = %d\n", x);
                writeX(x);

                // The child terminates
                if (pid == 0)
                {
                        exit(0);
                }

        }

        exit(0);
}

/// Returns the value read from .shareX.dat
int readX()
{
        char xChar[10];         // xChar: our value as a char
        int fd;                         // fd: file descriptor

        // open to read and store x
        if ( (fd = open(".shareX.dat", O_RDONLY )) == -1 )
        {
                perror("Error opening file");
                exit(2);
        }

        // read xChar from the file
        if ( read(fd, xChar, 10) == -1 )
        {
                perror("Error reading file");
                exit(3);
        }

        // close file for reading
        close(fd);

        // convert xChar to int and return
        return  atoi(xChar);
}

/// Writes the writeX value to the file .shareX.dat
void writeX(int writeX)
{
        char xChar[10];         // xChar: our value as a char
        int fd;                         // fd: file descriptor
        int xBytes;                     // how much to write

        // open, clear, and create file if not createdi
        if ( (fd = open(".shareX.dat",
                                        O_CREAT | O_TRUNC | O_WRONLY, 0644 )) == -1 )
        {
                perror("Error opening file");
                exit(4);
        }

        // convert x to char
        xBytes = sprintf(xChar, "%d", writeX);

        // put xChar in file
        if ( write(fd, xChar, xBytes) == -1 )
        {
                perror("Error writing to file");
                exit(5);
        }

        // close the file for writing
        close(fd);

        return;
}

sample output

input x = 19530 ITERATION 1 Child: x = 19525 Parent: x = 3905 ITERATION 2 Child: x = 3900 Parent: x = 780 ITERATION 3 Child: x = 775 Parent: x = 155 ITERATION 4 Child: x = 150 Parent: x = 30 ITERATION 5 Child: x = 25 Parent: x = 5