Implement the solutions for Readers-Writers problem using inter process communication technique -Semaphore

 #include<stdio.h>

#include<pthread.h>

#include<semaphore.h>

sem_t mutex;

sem_t db;

int readercount=0;

pthread_t reader1,reader2,writer1,writer2;

void *reader(void *);

void *writer(void *);

main()

{

sem_init(&mutex,0,1);

sem_init(&db,0,1);

while(1)

{

pthread_create(&reader1,NULL,reader,"1");

pthread_create(&reader2,NULL,reader,"2");

pthread_create(&writer1,NULL,writer,"1");

pthread_create(&writer2,NULL,writer,"2");

}

}

void *reader(void *p)

{

printf("prevoius value %dn",mutex);

sem_wait(&mutex);

printf("Mutex acquired by reader %dn",mutex);

readercount++;

if(readercount==1) sem_wait(&db);

sem_post(&mutex);

printf("Mutex returned by reader %dn",mutex);

printf("Reader %s is Readingn",p);

//sleep(3);

sem_wait(&mutex);

printf("Reader %s Completed Readingn",p);

readercount--;

if(readercount==0) sem_post(&db);

sem_post(&mutex);

}

void *writer(void *p)

{

printf("Writer is Waiting n");

sem_wait(&db);

printf("Writer %s is writingn ",p);

sem_post(&db);

//sleep(2);

}