Lab6: add barrier demo code

lab6/demos/barriers.c

@@ -0,0 +1,37 @@
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define NUM_THREADS 3
+
+pthread_barrier_t barrier;
+
+void *thread_func(void *arg) {
+    int thread_id = *(int*) arg;
+
+    printf("Thread %d is waiting at the barrier\n", thread_id);
+    pthread_barrier_wait(&barrier);
+    printf("Thread %d has passed the barrier\n", thread_id);
+
+    return NULL;
+}
+
+int main() {
+    pthread_t threads[NUM_THREADS];
+    int thread_ids[NUM_THREADS];
+
+    pthread_barrier_init(&barrier, NULL, NUM_THREADS);
+
+    for (int i = 0; i < NUM_THREADS; i++) {
+        thread_ids[i] = i;
+        pthread_create(threads + i, NULL, thread_func, &thread_ids[i]);
+    }
+    for (int i = 0; i < NUM_THREADS; i++) {
+        pthread_join(threads[i], NULL);
+    }
+
+    pthread_barrier_destroy(&barrier);
+
+    return 0;
+}
+