Notes

#include<pthread.h>
#include<semaphore.h>

sem_t mutex1,mutex2;
int info = 0,counter = 0;

void *reader(void *arg)
{
int num;
num = ((long)arg);

//reader entering critical section for incrementing count

sem_wait(&mutex1);
counter = counter + 1;
printf("Reader %d arrived.Current number of readers are %dn",num,counter);
//the first reader that increments counter to 1 will enter this if
if(counter==1)
//writer waits

sem_wait(&mutex2);

//reader leaving critical section

sem_post(&mutex1);
printf("Data read by the reader%d is %dn",num,info);
sleep(1);
sem_wait(&mutex1);
printf("Current value of counter after reader %d left: %dn",num,counter);
counter = counter - 1;

//last reader will enter this if block
if(counter==0)
sem_post(&mutex2);

sem_post(&mutex1);
}

void *writer(void *arg)
{
int num;
num = ((long) arg);
//writer entering critical section
sem_wait(&mutex2);
info++;
printf("Data writen by the writer%d is %dn",num,info);
sleep(1);
//writer leaving after updating data i.e info
sem_post(&mutex2);
}

//main method
int main()
{ //initializing loop counter
int t1;
pthread_t reader_tid[5],writer_tid[5];

//initializing semaphores (2 semaphores)
sem_init(&mutex1,0,1); //for reader
sem_init(&mutex2,0,1); //for writer

for(t1=0;t1<=3;t1++)
{

//creation of threads
pthread_create(&writer_tid[t1],NULL,writer,(void *)t1);
pthread_create(&reader_tid[t1],NULL,reader,( void *)t1);
printf("n");
}

for(t1=0;t1<=3;t1++)
{
pthread_join(writer_tid[t1],NULL);
pthread_join(reader_tid[t1],NULL);
}
return 0;
}