added optimised OS codes

OS/C/Week7/q2.c

@@ -6,106 +6,100 @@
 #include <semaphore.h>
 #include <unistd.h>
 
-#define NUM_READERS 3
+#define NR 3 // NUM_READERS
-#define NUM_WRITERS 2
+#define NW 2 // NUM_WRITERS
 
 // shared data structure - simple integer
-int shared_data = 0;
+int sd = 0; // shared_data
 
 // sync variables
-pthread_mutex_t mutex;  // mutex for read_count protection
+pthread_mutex_t m;  // mutex for rc protection
-sem_t wrt;             // semaphore for writer access control
+sem_t w;             // semaphore for writer access control
-int read_count = 0;    // tracks active readers
+int rc = 0;    // read_count: tracks active readers
 
-void* reader(void* arg) {
+void* r(void* arg) { // reader
     int id = *((int*)arg);
     while (1) {
         // read delay sim
         sleep(1);
 
         // critical section entry
-        pthread_mutex_lock(&mutex);
+        pthread_mutex_lock(&m);
-        read_count++;
+        rc++;
-        if (read_count == 1) {
+        if (rc == 1) {
             // first reader blocks writers
-            sem_wait(&wrt);
+            sem_wait(&w);
         }
-        pthread_mutex_unlock(&mutex);
+        pthread_mutex_unlock(&m);
 
         // critical section
-        printf("Reader %d is reading shared_data = %d\n", id, shared_data);
+        printf("Reader %d is reading sd = %d\n", id, sd);
         sleep(2);  // read time sim
 
         // critical section exit
-        pthread_mutex_lock(&mutex);
+        pthread_mutex_lock(&m);
-        read_count--;
+        rc--;
-        if (read_count == 0) {
+        if (rc == 0) {
             // last reader unblocks writers
-            sem_post(&wrt);
+            sem_post(&w);
         }
-        pthread_mutex_unlock(&mutex);
+        pthread_mutex_unlock(&m);
     }
     pthread_exit(NULL);
 }
 
-void* writer(void* arg) {
+void* w_func(void* arg) { // writer
     int id = *((int*)arg);
     while (1) {
         // write delay sim
         sleep(3);
 
         // critical section entry
-        sem_wait(&wrt);  // exclusive access control
+        sem_wait(&w);  // exclusive access control
 
         // critical section
-        shared_data += 1;
+        sd++; // shared_data modification
-        printf("Writer %d is writing: shared_data becomes %d\n", id, shared_data);
+        printf("Writer %d is writing: sd becomes %d\n", id, sd);
         sleep(2);  // write time sim
 
         // critical section exit
-        sem_post(&wrt);
+        sem_post(&w);
     }
     pthread_exit(NULL);
 }
 
 int main(void) {
-    pthread_t readers[NUM_READERS], writers[NUM_WRITERS];
+    pthread_t rts[NR], wts[NW]; // reader/writer threads
-    int reader_ids[NUM_READERS], writer_ids[NUM_WRITERS];
+    int rids[NR], wids[NW]; // reader/writer ids
     int i;
 
     // sync init
-    pthread_mutex_init(&mutex, NULL);
+    pthread_mutex_init(&m, NULL);
-    sem_init(&wrt, 0, 1);  // binary semaphore init
+    sem_init(&w, 0, 1);  // binary semaphore init
 
     // reader thread creation
-    for (i = 0; i < NUM_READERS; i++) {
+    for (i = 0; i < NR; i++) {
-        reader_ids[i] = i + 1;
+        rids[i] = i + 1;
-        if (pthread_create(&readers[i], NULL, reader, &reader_ids[i]) != 0) {
+        pthread_create(&rts[i], NULL, r, &rids[i]);
-            perror("Failed to create reader thread");
-            exit(EXIT_FAILURE);
-        }
     }
 
     // writer thread creation
-    for (i = 0; i < NUM_WRITERS; i++) {
+    for (i = 0; i < NW; i++) {
-        writer_ids[i] = i + 1;
+        wids[i] = i + 1;
-        if (pthread_create(&writers[i], NULL, writer, &writer_ids[i]) != 0) {
+        pthread_create(&wts[i], NULL, w_func, &wids[i]);
-            perror("Failed to create writer thread");
-            exit(EXIT_FAILURE);
-        }
     }
 
     // thread joining
-    for (i = 0; i < NUM_READERS; i++) {
+    for (i = 0; i < NR; i++) {
-        pthread_join(readers[i], NULL);
+        pthread_join(rts[i], NULL);
     }
-    for (i = 0; i < NUM_WRITERS; i++) {
+    for (i = 0; i < NW; i++) {
-        pthread_join(writers[i], NULL);
+        pthread_join(wts[i], NULL);
     }
 
     // cleanup
-    pthread_mutex_destroy(&mutex);
+    pthread_mutex_destroy(&m);
-    sem_destroy(&wrt);
+    sem_destroy(&w);
 
     return 0;
 }