diff --git a/notxv6/barrier.c b/notxv6/barrier.c
index 12793e8..277c3ee 100644
--- a/notxv6/barrier.c
+++ b/notxv6/barrier.c
@@ -31,6 +31,17 @@ barrier()
   // then increment bstate.round.
   //
   
+  pthread_mutex_lock(&bstate.barrier_mutex);
+  bstate.nthread += 1;
+  if (nthread == bstate.nthread) {
+    bstate.nthread = 0;
+    bstate.round += 1;
+    pthread_mutex_unlock(&bstate.barrier_mutex);
+    pthread_cond_broadcast(&bstate.barrier_cond);
+    return;
+  }
+  pthread_cond_wait(&bstate.barrier_cond, &bstate.barrier_mutex);
+  pthread_mutex_unlock(&bstate.barrier_mutex);
 }
 
 static void *