8364925: G1: Improve program flow around incremental collection set building

Reviewed-by: ayang, iwalulya

Author: Thomas Schatzl

src/hotspot/share/gc/g1/g1CollectionSet.cpp

@@ -38,6 +38,15 @@
 #include "utilities/globalDefinitions.hpp"
 #include "utilities/quickSort.hpp"
 
+uint G1CollectionSet::selected_groups_cur_length() const {
+  assert(_inc_build_state == CSetBuildType::Inactive, "must be");
+  return _collection_set_groups.length();
+}
+
+uint G1CollectionSet::collection_groups_increment_length() const {
+  return selected_groups_cur_length() - _selected_groups_inc_part_start;
+}
+
 G1CollectorState* G1CollectionSet::collector_state() const {
   return _g1h->collector_state();
 }
@@ -54,7 +63,6 @@ G1CollectionSet::G1CollectionSet(G1CollectedHeap* g1h, G1Policy* policy) :
   _collection_set_cur_length(0),
   _collection_set_max_length(0),
   _collection_set_groups(),
-  _selected_groups_cur_length(0),
   _selected_groups_inc_part_start(0),
   _eden_region_length(0),
   _survivor_region_length(0),
@@ -122,9 +130,23 @@ void G1CollectionSet::add_old_region(G1HeapRegion* hr) {
 
 void G1CollectionSet::start_incremental_building() {
   assert(_collection_set_cur_length == 0, "Collection set must be empty before starting a new collection set.");
+  assert(selected_groups_cur_length() == 0, "Collection set groups must be empty before starting a new collection set.");
+  assert(_optional_groups.length() == 0, "Collection set optional gorups must be empty before starting a new collection set.");
+
+  continue_incremental_building();
+}
+
+void G1CollectionSet::continue_incremental_building() {
   assert(_inc_build_state == Inactive, "Precondition");
 
-  update_incremental_marker();
+  _inc_part_start = _collection_set_cur_length;
+  _selected_groups_inc_part_start = selected_groups_cur_length();
+
+  _inc_build_state = CSetBuildType::Active;
+}
+
+void G1CollectionSet::stop_incremental_building() {
+  _inc_build_state = Inactive;
 }
 
 void G1CollectionSet::finalize_incremental_building() {
@@ -343,9 +365,6 @@ static int compare_region_idx(const uint a, const uint b) {
 void G1CollectionSet::finalize_old_part(double time_remaining_ms) {
   double non_young_start_time_sec = os::elapsedTime();
 
-  _selected_groups_cur_length = 0;
-  _selected_groups_inc_part_start = 0;
-
   if (!candidates()->is_empty()) {
     candidates()->verify();
 
@@ -363,13 +382,8 @@ void G1CollectionSet::finalize_old_part(double time_remaining_ms) {
     log_debug(gc, ergo, cset)("No candidates to reclaim.");
   }
 
-  _selected_groups_cur_length = collection_set_groups()->length();
-  stop_incremental_building();
-
   double non_young_end_time_sec = os::elapsedTime();
   phase_times()->record_non_young_cset_choice_time_ms((non_young_end_time_sec - non_young_start_time_sec) * 1000.0);
-
-  QuickSort::sort(_collection_set_regions, _collection_set_cur_length, compare_region_idx);
 }
 
 static void print_finish_message(const char* reason, bool from_marking) {
@@ -670,16 +684,21 @@ void G1CollectionSet::add_region_to_collection_set(G1HeapRegion* r) {
 }
 
 void G1CollectionSet::finalize_initial_collection_set(double target_pause_time_ms, G1SurvivorRegions* survivor) {
+  assert(_inc_part_start == 0, "must be");
+  assert(_selected_groups_inc_part_start == 0, "must be");
+
   double time_remaining_ms = finalize_young_part(target_pause_time_ms, survivor);
   finalize_old_part(time_remaining_ms);
+
+  stop_incremental_building();
+  QuickSort::sort(_collection_set_regions, _collection_set_cur_length, compare_region_idx);
 }
 
 bool G1CollectionSet::finalize_optional_for_evacuation(double remaining_pause_time) {
-  update_incremental_marker();
+  continue_incremental_building();
 
   uint num_regions_selected = select_optional_collection_set_regions(remaining_pause_time);
 
-  _selected_groups_cur_length = collection_set_groups()->length();
   stop_incremental_building();
 
   _g1h->verify_region_attr_remset_is_tracked();

src/hotspot/share/gc/g1/g1CollectionSet.hpp

@@ -149,9 +149,7 @@ class G1CollectionSet {
   // Old gen groups selected for evacuation.
   G1CSetCandidateGroupList _collection_set_groups;
 
-  // Groups are added to the collection set in increments when performing optional evacuations.
-  // We use the value below to track these increments.
-  uint _selected_groups_cur_length;
+  uint selected_groups_cur_length() const;
   uint _selected_groups_inc_part_start;
 
   uint _eden_region_length;
@@ -258,14 +256,10 @@ class G1CollectionSet {
 
   // Initialize incremental collection set info.
   void start_incremental_building();
-  // Start a new collection set increment.
-  void update_incremental_marker() {
-    _inc_build_state = Active;
-    _inc_part_start = _collection_set_cur_length;
-    _selected_groups_inc_part_start = _selected_groups_cur_length;
-  }
+  // Start a new collection set increment, continuing the incremental building.
+  void continue_incremental_building();
   // Stop adding regions to the current collection set increment.
-  void stop_incremental_building() { _inc_build_state = Inactive; }
+  void stop_incremental_building();
 
   // Iterate over the current collection set increment applying the given G1HeapRegionClosure
   // from a starting position determined by the given worker id.
@@ -276,7 +270,7 @@ class G1CollectionSet {
   // Returns the length of the whole current collection set in number of regions
   size_t cur_length() const { return _collection_set_cur_length; }
 
-  uint collection_groups_increment_length() const { return _selected_groups_cur_length - _selected_groups_inc_part_start; }
+  uint collection_groups_increment_length() const;
 
   // Iterate over the entire collection set (all increments calculated so far), applying
   // the given G1HeapRegionClosure on all of them.