8290814: Hide G1RootRegions behind G1ConcurrentMark

Reviewed-by: sangheki, iwalulya

src/hotspot/share/gc/g1/g1CollectedHeap.cpp

@@ -984,14 +984,6 @@ void G1CollectedHeap::print_heap_after_full_collection() {
 }
 
 bool G1CollectedHeap::abort_concurrent_cycle() {
-  // If we start the compaction before the CM threads finish
-  // scanning the root regions we might trip them over as we'll
-  // be moving objects / updating references. So let's wait until
-  // they are done. By telling them to abort, they should complete
-  // early.
-  _cm->root_regions()->abort();
-  _cm->root_regions()->wait_until_scan_finished();
-
   // Disable discovery and empty the discovered lists
   // for the CM ref processor.
   _ref_processor_cm->disable_discovery();
@@ -3279,7 +3271,7 @@ void G1CollectedHeap::retire_gc_alloc_region(HeapRegion* alloc_region,
 
   bool const during_im = collector_state()->in_concurrent_start_gc();
   if (during_im && allocated_bytes > 0) {
-    _cm->root_regions()->add(alloc_region->top_at_mark_start(), alloc_region->top());
+    _cm->add_root_region(alloc_region);
   }
   _hr_printer.retire(alloc_region);
 }

src/hotspot/share/gc/g1/g1ConcurrentMark.cpp

@@ -1006,6 +1006,14 @@ void G1ConcurrentMark::scan_root_regions() {
   }
 }
 
+bool G1ConcurrentMark::wait_until_root_region_scan_finished() {
+  return root_regions()->wait_until_scan_finished();
+}
+
+void G1ConcurrentMark::add_root_region(HeapRegion* r) {
+  root_regions()->add(r->top_at_mark_start(), r->top());
+}
+
 void G1ConcurrentMark::concurrent_cycle_start() {
   _gc_timer_cm->register_gc_start();
 
@@ -2018,6 +2026,14 @@ void G1ConcurrentMark::print_stats() {
 }
 
 bool G1ConcurrentMark::concurrent_cycle_abort() {
+  // If we start the compaction before the CM threads finish
+  // scanning the root regions we might trip them over as we'll
+  // be moving objects / updating references. So let's wait until
+  // they are done. By telling them to abort, they should complete
+  // early.
+  root_regions()->abort();
+  root_regions()->wait_until_scan_finished();
+
   // We haven't started a concurrent cycle no need to do anything; we might have
   // aborted the marking because of shutting down though. In this case the marking
   // might have already completed the abort (leading to in_progress() below to

src/hotspot/share/gc/g1/g1ConcurrentMark.hpp

@@ -285,6 +285,7 @@ class G1ConcurrentMark : public CHeapObj<mtGC> {
   friend class G1CMKeepAliveAndDrainClosure;
   friend class G1CMRefProcProxyTask;
   friend class G1CMRemarkTask;
+  friend class G1CMRootRegionScanTask;
   friend class G1CMTask;
   friend class G1ConcurrentMarkThread;
 
@@ -497,8 +498,6 @@ public:
   size_t partial_mark_stack_size_target() const { return _global_mark_stack.capacity() / 3; }
   bool mark_stack_empty() const                 { return _global_mark_stack.is_empty(); }
 
-  G1CMRootMemRegions* root_regions() { return &_root_regions; }
-
   void concurrent_cycle_start();
   // Abandon current marking iteration due to a Full GC.
   bool concurrent_cycle_abort();
@@ -557,10 +556,17 @@ public:
   // Scan all the root regions and mark everything reachable from
   // them.
   void scan_root_regions();
+  bool wait_until_root_region_scan_finished();
+  void add_root_region(HeapRegion* r);
+
+private:
+  G1CMRootMemRegions* root_regions() { return &_root_regions; }
 
   // Scan a single root MemRegion to mark everything reachable from it.
   void scan_root_region(const MemRegion* region, uint worker_id);
 
+public:
+
   // Do concurrent phase of marking, to a tentative transitive closure.
   void mark_from_roots();
 
@@ -608,7 +614,6 @@ private:
   void rebuild_and_scrub();
 
   uint needs_remembered_set_rebuild() const { return _needs_remembered_set_rebuild; }
-
 };
 
 // A class representing a marking task.

src/hotspot/share/gc/g1/g1YoungCollector.cpp

@@ -245,7 +245,7 @@ void G1YoungCollector::wait_for_root_region_scanning() {
   // root regions as it's the only way to ensure that all the
   // objects on them have been correctly scanned before we start
   // moving them during the GC.
-  bool waited = concurrent_mark()->root_regions()->wait_until_scan_finished();
+  bool waited = concurrent_mark()->wait_until_root_region_scan_finished();
   Tickspan wait_time;
   if (waited) {
     wait_time = (Ticks::now() - start);