Question

Directions: use only the signal mechanism system calls don’t use ( wait() or pipe() )in this problem. You can still read/write from/to a file. You must use ( kill() and pause() ) system calls.  

rewrite code below to do kill and pause system calls

#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);

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

                // Child waits a second for the parent to go first
                else if (pid ==0)
                {
                        sleep(1);
                        // NOTE: may need to sleep more seconds for busy or slower OSes
                }

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

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

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

                // 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);
                }

                // Parent waits for child to terminate before continuing loop
                wait(NULL);
        }

        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;
}

Answer 1

Solution:

#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <signal.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);

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

                // Child waits a second for the parent to go first
                else if (pid ==0)
                {
                        sleep(1);
                        // NOTE: may need to sleep more seconds for busy or slower OSes
                }

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

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

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

                // 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);
                }

                // Parent waits for child to terminate before continuing loop
                pause();
        }
        kill(pid,0);
     
}

/// Returns the value read from .shareX.dat
int readX()
{
          int pid = fork();
        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");
                kill(pid,2);
        }

        // read xChar from the file
        if ( read(fd, xChar, 10) == -1 )
        {
                perror("Error reading file");
               kill(pid,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)
{
     int pid = fork();
        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");
                kill(pid,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");
                kill(pid,5);
        }

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

        return;
}