8013160: NPG: Remove unnecessary mark stack draining after CodeCache::do_unloading

Reviewed-by: coleenp, mgerdin

hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp

@@ -6007,26 +6007,23 @@ void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
                                         &cmsDrainMarkingStackClosure,
                                         NULL);
     }
-    verify_work_stacks_empty();
   }
 
+  // This is the point where the entire marking should have completed.
+  verify_work_stacks_empty();
+
   if (should_unload_classes()) {
     {
       TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
 
-      // Follow SystemDictionary roots and unload classes
+      // Unload classes and purge the SystemDictionary.
       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
 
-      // Follow CodeCache roots and unload any methods marked for unloading
+      // Unload nmethods.
       CodeCache::do_unloading(&_is_alive_closure, purged_class);
 
-      cmsDrainMarkingStackClosure.do_void();
-      verify_work_stacks_empty();
-
-      // Update subklass/sibling/implementor links in KlassKlass descendants
+      // Prune dead klasses from subklass/sibling/implementor lists.
       Klass::clean_weak_klass_links(&_is_alive_closure);
-      // Nothing should have been pushed onto the working stacks.
-      verify_work_stacks_empty();
     }
 
     {
@@ -6040,11 +6037,10 @@ void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
   // Need to check if we really scanned the StringTable.
   if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
     TraceTime t("scrub string table", PrintGCDetails, false, gclog_or_tty);
-    // Now clean up stale oops in StringTable
+    // Delete entries for dead interned strings.
     StringTable::unlink(&_is_alive_closure);
   }
 
-  verify_work_stacks_empty();
   // Restore any preserved marks as a result of mark stack or
   // work queue overflow
   restore_preserved_marks_if_any();  // done single-threaded for now

hotspot/src/share/vm/gc_implementation/g1/g1MarkSweep.cpp

@@ -144,29 +144,25 @@ void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
                                     &GenMarkSweep::follow_stack_closure,
                                     NULL);
 
-  // Follow system dictionary roots and unload classes
+
+  // This is the point where the entire marking should have completed.
+  assert(GenMarkSweep::_marking_stack.is_empty(), "Marking should have completed");
+
+  // Unload classes and purge the SystemDictionary.
   bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
-  assert(GenMarkSweep::_marking_stack.is_empty(),
-         "stack should be empty by now");
 
-  // Follow code cache roots (has to be done after system dictionary,
-  // assumes all live klasses are marked)
+  // Unload nmethods.
   CodeCache::do_unloading(&GenMarkSweep::is_alive, purged_class);
-  GenMarkSweep::follow_stack();
 
-  // Update subklass/sibling/implementor links of live klasses
+  // Prune dead klasses from subklass/sibling/implementor lists.
   Klass::clean_weak_klass_links(&GenMarkSweep::is_alive);
-  assert(GenMarkSweep::_marking_stack.is_empty(),
-         "stack should be empty by now");
 
-  // Visit interned string tables and delete unmarked oops
+  // Delete entries for dead interned strings.
   StringTable::unlink(&GenMarkSweep::is_alive);
+
   // Clean up unreferenced symbols in symbol table.
   SymbolTable::unlink();
 
-  assert(GenMarkSweep::_marking_stack.is_empty(),
-         "stack should be empty by now");
-
   if (VerifyDuringGC) {
     HandleMark hm;  // handle scope
     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);

hotspot/src/share/vm/gc_implementation/parallelScavenge/psMarkSweep.cpp

@@ -517,23 +517,23 @@ void PSMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
       is_alive_closure(), mark_and_push_closure(), follow_stack_closure(), NULL);
   }
 
-  // Follow system dictionary roots and unload classes
+  // This is the point where the entire marking should have completed.
+  assert(_marking_stack.is_empty(), "Marking should have completed");
+
+  // Unload classes and purge the SystemDictionary.
   bool purged_class = SystemDictionary::do_unloading(is_alive_closure());
 
-  // Follow code cache roots
+  // Unload nmethods.
   CodeCache::do_unloading(is_alive_closure(), purged_class);
-  follow_stack(); // Flush marking stack
 
-  // Update subklass/sibling/implementor links of live klasses
-  Klass::clean_weak_klass_links(&is_alive);
-  assert(_marking_stack.is_empty(), "just drained");
+  // Prune dead klasses from subklass/sibling/implementor lists.
+  Klass::clean_weak_klass_links(is_alive_closure());
 
-  // Visit interned string tables and delete unmarked oops
+  // Delete entries for dead interned strings.
   StringTable::unlink(is_alive_closure());
+
   // Clean up unreferenced symbols in symbol table.
   SymbolTable::unlink();
-
-  assert(_marking_stack.is_empty(), "stack should be empty by now");
 }
 
 

hotspot/src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.cpp

@@ -2354,22 +2354,24 @@ void PSParallelCompact::marking_phase(ParCompactionManager* cm,
   }
 
   TraceTime tm_c("class unloading", print_phases(), true, gclog_or_tty);
+
+  // This is the point where the entire marking should have completed.
+  assert(cm->marking_stacks_empty(), "Marking should have completed");
+
   // Follow system dictionary roots and unload classes.
   bool purged_class = SystemDictionary::do_unloading(is_alive_closure());
 
-  // Follow code cache roots.
+  // Unload nmethods.
   CodeCache::do_unloading(is_alive_closure(), purged_class);
-  cm->follow_marking_stacks(); // Flush marking stack.
 
-  // Update subklass/sibling/implementor links of live klasses
+  // Prune dead klasses from subklass/sibling/implementor lists.
   Klass::clean_weak_klass_links(is_alive_closure());
 
-  // Visit interned string tables and delete unmarked oops
+  // Delete entries for dead interned strings.
   StringTable::unlink(is_alive_closure());
+
   // Clean up unreferenced symbols in symbol table.
   SymbolTable::unlink();
-
-  assert(cm->marking_stacks_empty(), "marking stacks should be empty");
 }
 
 void PSParallelCompact::follow_klass(ParCompactionManager* cm, Klass* klass) {

hotspot/src/share/vm/memory/genMarkSweep.cpp

@@ -223,23 +223,23 @@ void GenMarkSweep::mark_sweep_phase1(int level,
       &is_alive, &keep_alive, &follow_stack_closure, NULL);
   }
 
-  // Follow system dictionary roots and unload classes
+  // This is the point where the entire marking should have completed.
+  assert(_marking_stack.is_empty(), "Marking should have completed");
+
+  // Unload classes and purge the SystemDictionary.
   bool purged_class = SystemDictionary::do_unloading(&is_alive);
 
-  // Follow code cache roots
+  // Unload nmethods.
   CodeCache::do_unloading(&is_alive, purged_class);
-  follow_stack(); // Flush marking stack
 
-  // Update subklass/sibling/implementor links of live klasses
+  // Prune dead klasses from subklass/sibling/implementor lists.
   Klass::clean_weak_klass_links(&is_alive);
-  assert(_marking_stack.is_empty(), "just drained");
 
-  // Visit interned string tables and delete unmarked oops
+  // Delete entries for dead interned strings.
   StringTable::unlink(&is_alive);
+
   // Clean up unreferenced symbols in symbol table.
   SymbolTable::unlink();
-
-  assert(_marking_stack.is_empty(), "stack should be empty by now");
 }