PerfMon::MemStats Node1 PerfMon::MemStats + enable() + installHooks() + uninstallHooks() + saveHooks() + enabled() + nbytes() + nmallocs() + nfrees() + start() + stop() Node2 std::atomic< bool > + ptr Node2->Node1 +m_enabled Node3 long Node3->Node1 +ATLAS_THREAD_SAFE