What is an Algorithm? (might not be in the chapter text). Give an example.
1 answer:
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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
