Deadlock creation in C Linux (Operating System)

Deadlock creation in C Linux (Operating System):-

A deadlock is a situation in which two or more competing actions are each waiting for the other to finish, and thus neither ever does.

Conditions for Deadlock:-

·         Mutual Exclusion: At least one resource must be held in a non-sharable mode. Only one process can use the resource at any given instant of time.

·         Hold and Wait or Resource Holding: A process is currently holding at least one resource and requesting additional resources which are being held by other processes.

·         No Preemption: The operating system must not de-allocate resources once they have been allocated; they must be released by the holding process voluntarily.

·         Circular Wait: A process must be waiting for a resource which is being held by another process, which in turn is waiting for the first process to release the resource. In general, there is a set of waiting processes, P = {P₁, P₂, ..., P_N}, such that P₁ is waiting for a resource held by P₂, P₂ is waiting for a resource held by P₃ and so on until P_N is waiting for a resource held by P₁. 

P1 is with resource 10-20                p2 is with resource 40-60
now p1 is waiting for the resources of p2
and  p2 is waiting for resources of p1 


program1:-
#include<unistd.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<stdlib.h>
#include<stdio.h>
int main()
{
int fd,pt;
        struct flock r1,r2;
        fd=open("myfile22",O_CREAT|O_RDWR,0666);
        r1.l_type=F_WRLCK;
r1.l_whence=SEEK_SET;
        r1.l_start=10;
        r1.l_len=20;

        pt=fcntl(fd,F_SETLKW,&r1);
        if(pt==-1)
          {
             printf("Error in locking region1 in p1\n");
           }
 else
            {
                  printf("Resource allocated in  p1 10-30\n");
    }
sleep(5);
        r2.l_type=F_WRLCK;
        r2.l_whence=SEEK_SET;
r2.l_start=40;
r2.l_len=20;
  pt=-1;    
        while(pt==-1)
   {
                   pt=fcntl(fd,F_SETLK,&r2);
                   if(pt==-1)
             {
                            printf(" waiting for resource(40 -60) in P1\n");
                            sleep(3);
                      }
                   else
                      {
                           printf("Region2 Locked in p1 40-60\n");
                     }
            }
        sleep(10);
}

program2:-

#include<unistd.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<stdlib.h>
#include<stdio.h>
int main()
{
int fd,pt;
struct flock r1,r2;
fd=open("myfile22",O_CREAT|O_RDWR,0666);
r1.l_type=F_WRLCK;
r1.l_whence=SEEK_SET;
r1.l_start=40;
r1.l_len=20;
pt=fcntl(fd,F_SETLK,&r1);
if(pt==-1)
{
printf("Error in locking region1 in p2\n");

}
else
{
printf("Rescource allocated1 in p2 40 - 60\n");

}sleep(5);
r2.l_type=F_WRLCK;
r2.l_whence=SEEK_SET;
r2.l_start=10;
r2.l_len=20;
pt=-1;
while(pt==-1)
{
  pt=fcntl(fd,F_SETLK,&r2);
if(pt==-1)
{
printf("  waiting for resource(10-30) in P2\n"); sleep(3);

}
else
{
printf("Region2Locked in p2 10 - 30\n");

}
}

sleep(20);
}

output:-