diff --git a/lib/cpp/src/concurrency/ThreadManager.h b/lib/cpp/src/concurrency/ThreadManager.h
index f7c4b3c..cc13665 100644
--- a/lib/cpp/src/concurrency/ThreadManager.h
+++ b/lib/cpp/src/concurrency/ThreadManager.h
@@ -68,6 +68,8 @@
    * block until all the workers have finished their work. At that point
    * the ThreadManager will transition into the STOPPED state.
    */
+  virtual void join() = 0;
+
   enum STATE {
     UNINITIALIZED,
     STARTING,