Readers Writers Problem using Semaphores

Reader Priority problem

Readers Writers problem in operating system for solving synchronization problem can be solved. This program is for unix machine as their only you can run this code. This program demonstrate reader priority code for reader writer problem.
Problem statement for implement Readers Writers problem using semaphores with reader  priority using C language. Use mutex and semaphores to implement above problem in c language environment.

In the context of concurrent programming, the “reader priority case” refers to a scenario where readers are given precedence over writers when accessing a shared resource, such as a database or a file. This means that if there are both read and write requests pending, the system will prioritize servicing the read requests first before attending to any write requests.

In this scenario, whenever a writer wants to access the shared resource, it has to wait if there are any ongoing read operations. This ensures that readers are not kept waiting indefinitely and that their access to the resource is not unnecessarily delayed by write operations.

Simulating the readers-writers problem allows us to observe how different strategies for managing access to shared resources perform in real-world scenarios. By implementing and analyzing various algorithms and techniques for handling concurrent read and write operations, we can gain insights into the trade-offs involved and determine the most efficient and fair approach for different applications.

In essence, through this simulation, we can understand and evaluate the mechanisms for managing reader and writer access to shared resources in a real-time environment, helping us design more robust and efficient concurrent systems.

 #include   
 #include   
 #include   
 void * reader(void *) ;  
 void *writer (void *) ;  
 sem_t wsem,mutex ;  
 int readcount=0 ;  
 main()  
 {  
  int a=1,b=1;  
     system("clear");  
  sem_init(&wsem,0,1) ;  
  sem_init(&mutex,0,1) ;  
  pthread_t r,w,r1,w1 ;  
  pthread_create(&r,NULL,reader,(void *)a);  
     a++;  
  pthread_create(&w1,NULL,writer,(void *)b);  
     b++;  
  pthread_create(&r1,NULL,reader,(void *)a);  
  pthread_create(&w,NULL,writer,(void *)b);  
  pthread_join(r,NULL);  
  pthread_join(w1,NULL);  
  pthread_join(r1,NULL);  
  pthread_join(w,NULL) ;  
  printf("main terminated\n");  
 }  
 void * reader(void * arg)  
 {  
  int c=(int)arg ;  
  printf("\nreader %d is created",c);  
     sleep(1);  
  sem_wait(&mutex) ;  
     readcount++;  
     if(readcount==1)  
         sem_wait(&wsem) ;  
  sem_post(&mutex) ;  
 /*Critcal Section */  
  printf("\n\nreader %d is reading\n ",c);  
  sleep(1) ;  
  printf("\nreader%d finished reading\n",c);  
 /* critical section completd */  
  sem_wait(&mutex) ;  
     readcount-- ;  
     if(readcount==0)  
         sem_post(&wsem) ;  
  sem_post(&mutex) ;  
 }  
 void * writer(void * arg)  
 {  
  int c=(int)arg ;  
  printf("\nwriter %d is created",c);  
     sleep(1);  
  sem_wait(&wsem) ;  
  printf("\nwriter %d is writing\n",c) ;  
  sleep(1);  
  printf("\nwriter%d finished writing\n",c);  
  sem_post(&wsem) ;  
 }