8202578: Revisit location for class unload events

Summary: Use notify_unload_class() to post JFR class unload events instead of doing a separate traversal of the class loader data graph
Reviewed-by: lfoltan, coleenp, mgronlun, egahlin

src/share/vm/classfile/classLoaderData.cpp

@@ -64,11 +64,6 @@
 #include "utilities/growableArray.hpp"
 #include "utilities/macros.hpp"
 #include "utilities/ostream.hpp"
-#include "utilities/ticks.hpp"
-#if INCLUDE_JFR
-#include "jfr/jfr.hpp"
-#include "jfr/jfrEvents.hpp"
-#endif
 
 ClassLoaderData * ClassLoaderData::_the_null_class_loader_data = NULL;
 
@@ -753,29 +748,6 @@ bool ClassLoaderDataGraph::contains_loader_data(ClassLoaderData* loader_data) {
 }
 #endif // PRODUCT
 
-#if INCLUDE_JFR
-static Ticks class_unload_time;
-static void post_class_unload_event(Klass* const k) {
-  assert(k != NULL, "invariant");
-  EventClassUnload event(UNTIMED);
-  event.set_endtime(class_unload_time);
-  event.set_unloadedClass(k);
-  event.set_definingClassLoader(k->class_loader_data());
-  event.commit();
-}
-
-static void post_class_unload_events() {
-  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint!");
-  if (Jfr::is_enabled()) {
-    if (EventClassUnload::is_enabled()) {
-      class_unload_time = Ticks::now();
-      ClassLoaderDataGraph::classes_unloading_do(&post_class_unload_event);
-    }
-    Jfr::on_unloading_classes();
-  }
-}
-#endif // INCLUDE_JFR
-
 // Move class loader data from main list to the unloaded list for unloading
 // and deallocation later.
 bool ClassLoaderDataGraph::do_unloading(BoolObjectClosure* is_alive_closure, bool clean_alive) {
@@ -815,10 +787,6 @@ bool ClassLoaderDataGraph::do_unloading(BoolObjectClosure* is_alive_closure, boo
     ClassLoaderDataGraph::clean_metaspaces();
   }
 
-  if (seen_dead_loader) {
-    JFR_ONLY(post_class_unload_events();)
-  }
-
   return seen_dead_loader;
 }
 

src/share/vm/classfile/systemDictionary.cpp

@@ -138,6 +138,9 @@ bool SystemDictionary::is_internal_format(Symbol* class_name) {
   }
 }
 
+#endif
+#if INCLUDE_JFR
+#include "jfr/jfr.hpp"
 #endif
 
 // ----------------------------------------------------------------------------
@@ -1749,6 +1752,7 @@ bool SystemDictionary::do_unloading(BoolObjectClosure* is_alive, bool clean_aliv
   // First, mark for unload all ClassLoaderData referencing a dead class loader.
   bool unloading_occurred = ClassLoaderDataGraph::do_unloading(is_alive, clean_alive);
   if (unloading_occurred) {
+    JFR_ONLY(Jfr::on_unloading_classes();)
     dictionary()->do_unloading();
     constraints()->purge_loader_constraints();
     resolution_errors()->purge_resolution_errors();

src/share/vm/oops/instanceKlass.cpp

@@ -78,6 +78,10 @@
 #ifdef COMPILER1
 #include "c1/c1_Compiler.hpp"
 #endif
+#if INCLUDE_JFR
+#include "jfr/jfrEvents.hpp"
+#endif
+
 
 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
 
@@ -2526,6 +2530,14 @@ void InstanceKlass::notify_unload_class(InstanceKlass* ik) {
 
   // notify ClassLoadingService of class unload
   ClassLoadingService::notify_class_unloaded(ik);
+
+#if INCLUDE_JFR
+  assert(ik != NULL, "invariant");
+  EventClassUnload event;
+  event.set_unloadedClass(ik);
+  event.set_definingClassLoader(ik->class_loader_data());
+  event.commit();
+#endif
 }
 
 void InstanceKlass::release_C_heap_structures(InstanceKlass* ik) {