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#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;
}
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