Answer Posted / masud

#include <pthread.h>
#include <sched.h>
#include <semaphore.h>
#include <stdio.h>
#include <unistd.h>

#define MAXTHREAD 10 /* define # readers */


void access_database(); /* prototypes */
void non_access_database();

void* reader(void*);
void* writer(void*);

sem_t q; /* establish que */
int rc = 0; /* number of processes reading or
wanting to */
int wc = 0;
int write_request = 0;

int main()
{
pthread_t readers[MAXTHREAD],writerTh;
int index;
int ids[MAXTHREAD]; /* readers and initialize mutex, q
and db-set them to 1 */
sem_init (&q,0,1);
for(index = 0; index < MAXTHREAD; index ++)
{
ids[index]=index+1;
/* create readers and error
check */
if(pthread_create(&readers[index],0,reader,&ids
[index])!=0){
perror("Cannot create reader!");
exit(1);

}
}
if(pthread_create(&writerTh,0,writer,0)!=0){
perror("Cannot create writer"); /* create
writers and error check */
exit(1);
}

pthread_join(writerTh,0);
sem_destroy (&q);
return 0;
}

void* reader(void*arg) /* readers function
to read */
{
int index = *(int*)arg;
int can_read;
while(1){
can_read = 1;

sem_wait(&q);
if(wc == 0 && write_request == 0) rc++;
else can_read = 0;
sem_post(&q);

if(can_read) {
access_database();
printf("Thread %d reading\n", index);
sleep(index);

sem_wait(&q);
rc--;
sem_post(&q);
}

sched_yield();
}
return 0;
}

void* writer(void*arg) /* writer's function to
write */
{
int can_write;
while(1){
can_write = 1;
non_access_database();

sem_wait (&q);
if(rc == 0) wc++;
else { can_write = 0; write_request = 1; }
sem_post(&q);

if(can_write) {
access_database();
printf("Writer is now writing...Number of
readers: %d\n",rc);

sleep(3);

sem_wait(&q);
wc--;
write_request = 0;
sem_post(&q);
}

sched_yield();
}
return 0;
}

void access_database()
{

}


void non_access_database()
{

}

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