Updated Week7

OS/C/Week7/q2.c

@@ -0,0 +1,111 @@
+// Write a C program to solve the readers and writers Problem.
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <semaphore.h>
+#include <unistd.h>
+
+#define NUM_READERS 3
+#define NUM_WRITERS 2
+
+// shared data structure - simple integer
+int shared_data = 0;
+
+// sync variables
+pthread_mutex_t mutex;  // mutex for read_count protection
+sem_t wrt;             // semaphore for writer access control
+int read_count = 0;    // tracks active readers
+
+void* reader(void* arg) {
+    int id = *((int*)arg);
+    while (1) {
+        // read delay sim
+        sleep(1);
+
+        // critical section entry
+        pthread_mutex_lock(&mutex);
+        read_count++;
+        if (read_count == 1) {
+            // first reader blocks writers
+            sem_wait(&wrt);
+        }
+        pthread_mutex_unlock(&mutex);
+
+        // critical section
+        printf("Reader %d is reading shared_data = %d\n", id, shared_data);
+        sleep(2);  // read time sim
+
+        // critical section exit
+        pthread_mutex_lock(&mutex);
+        read_count--;
+        if (read_count == 0) {
+            // last reader unblocks writers
+            sem_post(&wrt);
+        }
+        pthread_mutex_unlock(&mutex);
+    }
+    pthread_exit(NULL);
+}
+
+void* writer(void* arg) {
+    int id = *((int*)arg);
+    while (1) {
+        // write delay sim
+        sleep(3);
+
+        // critical section entry
+        sem_wait(&wrt);  // exclusive access control
+
+        // critical section
+        shared_data += 1;
+        printf("Writer %d is writing: shared_data becomes %d\n", id, shared_data);
+        sleep(2);  // write time sim
+
+        // critical section exit
+        sem_post(&wrt);
+    }
+    pthread_exit(NULL);
+}
+
+int main(void) {
+    pthread_t readers[NUM_READERS], writers[NUM_WRITERS];
+    int reader_ids[NUM_READERS], writer_ids[NUM_WRITERS];
+    int i;
+
+    // sync init
+    pthread_mutex_init(&mutex, NULL);
+    sem_init(&wrt, 0, 1);  // binary semaphore init
+
+    // reader thread creation
+    for (i = 0; i < NUM_READERS; i++) {
+        reader_ids[i] = i + 1;
+        if (pthread_create(&readers[i], NULL, reader, &reader_ids[i]) != 0) {
+            perror("Failed to create reader thread");
+            exit(EXIT_FAILURE);
+        }
+    }
+
+    // writer thread creation
+    for (i = 0; i < NUM_WRITERS; i++) {
+        writer_ids[i] = i + 1;
+        if (pthread_create(&writers[i], NULL, writer, &writer_ids[i]) != 0) {
+            perror("Failed to create writer thread");
+            exit(EXIT_FAILURE);
+        }
+    }
+
+    // thread joining
+    for (i = 0; i < NUM_READERS; i++) {
+        pthread_join(readers[i], NULL);
+    }
+    for (i = 0; i < NUM_WRITERS; i++) {
+        pthread_join(writers[i], NULL);
+    }
+
+    // cleanup
+    pthread_mutex_destroy(&mutex);
+    sem_destroy(&wrt);
+
+    return 0;
+}