better locking

Author: stephen-derosa

src/subscription_thread_dispatcher.cpp

@@ -668,16 +668,25 @@ std::thread SubscriptionThreadDispatcher::startDataReaderLocked(DataFrameCallbac
     stream = subscribe_result.value();
     LK_LOG_INFO("Data reader thread: subscribed to \"{}\" track=\"{}\"", identity, track_name);
 
+    bool cancelled = false;
     {
       const std::scoped_lock<std::mutex> guard(reader->sub_mutex);
       // A replacement or teardown may have cancelled this reader while the
-      // subscribe was in flight. Close the fresh stream and bail so we do not
-      // leave a second live subscription behind.
+      // subscribe was in flight. Close the fresh stream so we do not leave a
+      // second live subscription behind.
       if (reader->cancelled.load()) {
+        cancelled = true;
         stream->close();
-        return;
+      } else {
+        reader->stream = stream;
       }
-      reader->stream = stream;
+    }
+    if (cancelled) {
+      // Mirror the normal-exit cleanup below. Done outside sub_mutex to keep the
+      // lock_ -> sub_mutex order and avoid inversion; a no-op unless this reader
+      // still owns its slot.
+      eraseDataReaderIfCurrent(id, reader);
+      return;
     }
 
     DataTrackFrame frame;