Merge pull request ceph#64764 from badone/wip-tracker-72337-mgr-drop-daemonstateindex-lock

mgr/DaemonState: Minimise time we hold the DaemonStateIndex lock

Reviewed-by: Radoslaw Zarzynski <[email protected]>

Author: yuriw

src/mgr/DaemonState.h

@@ -261,9 +261,12 @@ class DaemonStateIndex
   template<typename Callback, typename...Args>
   auto with_daemons_by_server(Callback&& cb, Args&&... args) const ->
     decltype(cb(by_server, std::forward<Args>(args)...)) {
-    std::shared_lock l{lock};
-    
-    return std::forward<Callback>(cb)(by_server, std::forward<Args>(args)...);
+    const decltype(by_server) by_server_copy = [&] {
+      // Don't hold the lock any longer than necessary
+      std::shared_lock l{lock};
+      return by_server;
+    }();
+    return std::forward<Callback>(cb)(by_server_copy, std::forward<Args>(args)...);
   }
 
   template<typename Callback, typename...Args>