Question

4. (20 points) In the class we mentioned briefly the readers-writers problem with writers priority. The problem can be solved in guarded commands as follows: void writer) void reader --owriters when writers0 readers++i when (readers0)&&(active writers0) active writers++ //read //write [readers--1 [writers-- active writers-- Here writers represents the number of threads that are either writing or waiting to write. The variable active_writers represents the number of threads (0 or1) that are currently writing. Implement the solution using either POSIX threads or SDL threads. Again simulate the tasks by reading from and writing to a file named counter:txt as in problem 4 of Homework 3. Turn in your programs along with your outputs.

Answer 1

code: #include<pthread.h> #include«semaphore.h> sem_t mutex,writeblock int data O,rcount 0; void "readerfvoid "arg) int f f = ((int)arg) sem_wait(&mutex); rcount = rcount 1; iffrcount1) sem_wait(&writeblock); sem_post(&mutex) printf("Data read by the reader%d is %d\n",f,data); sleep(1); sem_wait(&mutex); rcount rcount 1 if rcount-0) sem_post(&writeblock); sem_post(&mutex);

void "writer(void "arg) int f f = ((int) arg) sem_wait(&writeblock); data++ printf("Data writen by the writer%d is %d\n",f,data); sleep(1) sem_post(&writeblock); int main int i,b; pthread_t rtid[5],wtid[5) sem_init(&mutex,0,1); sem_init(&writeblock,0,1); for(i=0;i<=2;i++) pthread_create(&wtid[i],NULL,writer (void *)); pthread_create(&rtid[il,NULL,reader (void )i); for(i=0;i<=2;i++) pthread_join(wtid i],NULL); pthread_join(rtid[i),NULL); return O;
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void "writer(void "arg) int f f = ((int) arg) sem_wait(&writeblock); data++ printf("Data writen by the writer%d is %d\n",f,data); sleep(1) sem_post(&writeblock); int main int i,b; pthread_t rtid[5],wtid[5) sem_init(&mutex,0,1); sem_init(&writeblock,0,1); for(i=0;i<=2;i++) pthread_create(&wtid[i],NULL,writer (void *)); pthread_create(&rtid[il,NULL,reader (void )i); for(i=0;i<=2;i++) pthread_join(wtid i],NULL); pthread_join(rtid[i),NULL); return O;
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out put: Data read by the read Data read by the readerl is o Data read by the reader0 is o Data writen by the writer2 is 1 Data writen by the writerl is 2 er2 is 0 Data writen by the writer0 is 3