Write a C program that illustrates file locking using semaphores.

Write a C program that illustrates file locking using semaphores.


#include <stdio.h>
 #include <sys/file.h>
 #include <error.h>
 #include <sys/sem.h>
 #define MAXBUF 100
 #define KEY 1216
 #define SEQFILE “suhritfile”
 int semid,fd;
 void my_lock(int);
 void my_unlock(int);
 union semnum
 {
      int val;
      struct semid_ds *buf;
      short *array;
 }arg;
 int main(])
 {
        int child, i,n, pid, seqno;
        char buff[MAXBUF+1];
        pid=getpid();
        if((semid=semget(KEY, 1, IPC_CREAT | 0666))= = -1)
        {
                 perror(“semget”);
                 exit(1);
        }
        arg.val=1;
        if(semctl(semid,0,SETVAL,arg)<0)
                 perror(“semctl”);
        if((fd=open(SEQFILE,2))<0)
        {
                 perror(“open”);
                 exit(1);
        }
        pid=getpid();
        for(i=0;i<2;i++)
        {
                 my_lock(fd);
                 lseek(fd,01,0);
                 if((n=read(fd,buff,MAXBUF))<0)
                 {
                        perror(“read”);
                        exit(1);
                 }
                 printf(“pid:%d, Seq no:%d\n”, pid, seqno);
                 seqno++;
                 sprintf(buff,”%d\n”, seqno);
                 n=strlen(buff);
                 lseek(fd,01,0);
                 if(write(fd,buff,n)!=n)
                 {
                        perror(“write”);
                        exit(1);
                 }
                 sleep(1);
                 my_unlock(fd);      
        }
 }
    void my_lock(int fd)
    {
              struct sembuff sbuf=(0, -1, 0);
              if(semop(semid, &sbuf, 1)= =0)
                   printf(“Locking: Resource…\n”);
              else
                   printf(“Error in Lock\n”);
    }
    void my_unlock(int fd)
    {
              struct sembuff sbuf=(0, 1, 0);
              if(semop(semid, &sbuf, 1)= =0)
                   printf(“UnLocking: Resource…\n”);
              else
                   printf(“Error in Unlock\n”);
    }