Answer Posted / avinash

#include<pthread.h>
#include<semaphore.h>
#include<stdlib.h>
#include<stdio.h>
#include<malloc.h>
sem_t mutex, cnt;

int readcount = 0;
int rcnt, wcnt;

void *wfun (void *args)
{
sem_wait (&cnt);
printf("\nIn writer : value of read cnt is %d", readcount );
sem_post(&cnt);
}

void *rfun (void *args)
{
sem_wait(&mutex);
readcount ++;
if(readcount == 1)
sem_wait(&cnt);
sem_post(&mutex);
printf("\nIn reader : reader has incremented read cnt, its value is %d",readcount );
sem_wait(&mutex);
readcount --;
if(readcount == 0)
sem_post(&cnt);
sem_post(&mutex);

}

int main()
{

int i, *t;
t = (int*)malloc(sizeof(int));

printf("\nenter number of readers: ");
scanf("%d",&rcnt);
printf("\nenter number of writers: ");
scanf("%d",&wcnt);

//initialize semaphores
sem_init(&mutex,0,1);
sem_init(&cnt,0,1);
pthread_t rdrs[10];
pthread_t wrs[10];

//create reader threads
for(i=0;i<rcnt;i++)
{
*t = i;
pthread_create(&rdrs[i],NULL,rfun, (void *)t);
}

//create writer threads
for(i=0;i<wcnt;i++)
{
*t=i;
pthread_create(&wrs[i],NULL,wfun,(void *)t);
}

for(i=0;i<rcnt;i++)
pthread_join(rdrs[i],NULL);

for(i=0;i<wcnt;i++)
pthread_join(wrs[i],NULL);
return(0);
}

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