problem-20

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

sem_t rw_mutex; // Semaphore for reader-writer mutual exclusion
sem_t mutex;    // Semaphore for reader count update
int read_count = 0;

void *reader(void *arg) {
    int reader_id = *((int *)arg);
    while (1) {
        sem_wait(&mutex);
        read_count++;
        if (read_count == 1) {
            sem_wait(&rw_mutex); // First reader locks the writer
        }
        sem_post(&mutex);

        printf("Reader %d is reading\n", reader_id);
        sleep(rand() % 3);

        sem_wait(&mutex);
        read_count--;
        if (read_count == 0) {
            sem_post(&rw_mutex); // Last reader unlocks the writer
        }
        sem_post(&mutex);

        sleep(rand() % 3);
    }
}

void *writer(void *arg) {
    int writer_id = *((int *)arg);
    while (1) {
        sem_wait(&rw_mutex);
        printf("Writer %d is writing\n", writer_id);
        sleep(rand() % 3);
        sem_post(&rw_mutex);
        sleep(rand() % 3);
    }
}

int main() {
    pthread_t readers[5], writers[5];
    int reader_ids[5], writer_ids[5];

    sem_init(&rw_mutex, 0, 1);
    sem_init(&mutex, 0, 1);

    for (int i = 0; i < 5; i++) {
        reader_ids[i] = i + 1;
        writer_ids[i] = i + 1;
        pthread_create(&readers[i], NULL, reader, &reader_ids[i]);
        pthread_create(&writers[i], NULL, writer, &writer_ids[i]);
    }

    for (int i = 0; i < 5; i++) {
        pthread_join(readers[i], NULL);
        pthread_join(writers[i], NULL);
    }

    sem_destroy(&rw_mutex);
    sem_destroy(&mutex);

    return 0;
}