Question

Create a program which will input data into a pipe one character at a time. Count the number of characters as they are written into the pipe. Print out a message after every 1K (1024) characters are written to the pipe. If the process does not read from the pipe, eventually the pipe will fill and the next attempted write to the pipe will block the process. Use the alarm function to prevent the process from hanging indefinitely after the pipe gets full, but be sure to set the time limit large enough so that you can be sure the pipe is completely filled. In the interrupt handler function, print out a message showing the final count of characters that can be input to the pipe (i.e., the maximum size of pipes on your system). [15 pts]

Answer 1

Answer:

a)

#include<stdio.h>

#include<stdlib.h>

#include<fcntl.h>

#include<unistd.h>

 

#define BUFSIZE 16

int main(){

   //pipe descriptors

   char msg[BUFSIZE];

   char buf[BUFSIZE];

   int pipefd[2];

   if(pipe(pipefd) == -1){

       //pipe creation error

       perror("pipe");

       exit(EXIT_FAILURE);

   }

   //pipe creation successfull

   //write four messages

   sprintf(msg , "apple");

   write(pipefd[1], msg, BUFSIZE);

   printf("Written %s\n", msg);

   sprintf(msg , "boy");

   write(pipefd[1], msg, BUFSIZE);

   printf("Written %s\n", msg);

   sprintf(msg , "cat");

   write(pipefd[1], msg, BUFSIZE);

   printf("Written %s\n", msg);

   sprintf(msg , "dog");

   write(pipefd[1], msg, BUFSIZE);

   printf("Written %s\n", msg);

   //read

   read(pipefd[0], buf, BUFSIZE);

   printf("Read: %s\n", buf);

   read(pipefd[0], buf, BUFSIZE);

   printf("Read: %s\n", buf);

   read(pipefd[0], buf, BUFSIZE);

   printf("Read: %s\n", buf);

   read(pipefd[0], buf, BUFSIZE);

   printf("Read: %s\n", buf);

   close(pipefd[0]);

   close(pipefd[1]);

   return 0;

}

(b)

#include<stdio.h>

#include<stdlib.h>

#include<fcntl.h>

#include<unistd.h>

#include<wait.h>

#define BUFSIZE 16

int main(){

   //pipe descriptors

   char msg[BUFSIZE];

   char buf[BUFSIZE];

   int pipefd[2];

   if(pipe(pipefd) == -1){

       //pipe creation error

       perror("pipe");

       exit(EXIT_FAILURE);

   }

   //pipe creation successfull

   //write four messages

   if(fork() == 0){

       //this is child

       //close unused write end

       close(pipefd[1]);

       read(pipefd[0], buf, BUFSIZE);

       printf("This is child process reading first message. Content is %s\n", buf);

       read(pipefd[0], buf, BUFSIZE);

       printf("This is child process reading second message. Content is %s\n", buf);

       read(pipefd[0], buf, BUFSIZE);

       printf("This is child process reading third message. Content is %s\n", buf);

       read(pipefd[0], buf, BUFSIZE);

       printf("This is child process reading fourth message. Content is %s\n", buf);

       close(pipefd[0]);

       //exit from child

       exit(EXIT_SUCCESS);

   }

   //this is parent process

   //close unused read end

   close(pipefd[0]);

   sprintf(msg , "apple");

   printf("This is parent process. Writing first message into pipe\n");

   write(pipefd[1], msg, BUFSIZE);

   sprintf(msg , "boy");

   printf("This is parent process. Writing second message into pipe\n");

   write(pipefd[1], msg, BUFSIZE);

   sprintf(msg , "cat");

   printf("This is parent process. Writing third message into pipe\n");

   write(pipefd[1], msg, BUFSIZE);

   sprintf(msg , "dog");

   printf("This is parent process. Writing fourth message into pipe\n");

   write(pipefd[1], msg, BUFSIZE);

   close(pipefd[1]);

   //wait for child

   wait(NULL);

   return 0;

}

(c)

#include<stdio.h>

#include<stdlib.h>

#include<fcntl.h>

#include<unistd.h>

#include<sys/wait.h>

#include<sys/types.h>

#include<signal.h>

typedef struct sigaction Sigaction;

unsigned long long size = 0;

void alarmhandler(int sig){

   //alarm fired writing blocked

   printf("Write blocked after %llu characters\n", size);

   exit(EXIT_SUCCESS);

}

int main(){

   //pipe descriptors

   int pipefd[2];

   if(pipe(pipefd) == -1){

       //pipe creation error

       perror("pipe");

       exit(EXIT_FAILURE);

   }

   //install handler

   sigset_t mask , prev;

   sigemptyset(&mask);

   sigaddset(&mask , SIGALRM);

   sigprocmask(SIG_BLOCK , &mask , &prev);

   Sigaction new_action;

   sigemptyset(&new_action.sa_mask);

   new_action.sa_flags = SA_RESTART;

   new_action.sa_handler = alarmhandler;

   sigaction(SIGALRM , &new_action , NULL);

   sigprocmask(SIG_SETMASK , &prev, NULL);

   while(1){

     

       //print size on multiple of 4

       if(size != 0 && size % 1024 == 0){

           printf("%llu characters in pipe\n", size);

       }

       //reset previous alarm

       alarm(0);

       //set new alarm for 5 seconds

       alarm(5);

       //write to pipe one character

       write(pipefd[1], "A", sizeof(char));

       size++;

   }

   return 0;

}

Explanation:

Output for a, b, c are pasted accordingly