8379404: G1: Hide ConcurrentMarkThread reference from outside ConcurrentMark

Reviewed-by: stefank, iwalulya

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

@@ -1652,21 +1652,13 @@ jint G1CollectedHeap::initialize() {
   return JNI_OK;
 }
 
-bool G1CollectedHeap::concurrent_mark_is_terminating() const {
-  assert(_cm != nullptr, "_cm must have been created");
-  assert(_cm->is_fully_initialized(), "thread must exist in order to check if mark is terminating");
-  return _cm->cm_thread()->should_terminate();
-}
-
 void G1CollectedHeap::stop() {
   // Stop all concurrent threads. We do this to make sure these threads
   // do not continue to execute and access resources (e.g. logging)
   // that are destroyed during shutdown.
   _cr->stop();
   _service_thread->stop();
-  if (_cm->is_fully_initialized()) {
-    _cm->cm_thread()->stop();
-  }
+  _cm->stop();
 }
 
 void G1CollectedHeap::safepoint_synchronize_begin() {
@@ -1857,12 +1849,12 @@ void G1CollectedHeap::increment_old_marking_cycles_completed(bool concurrent,
     record_whole_heap_examined_timestamp();
   }
 
-  // We need to clear the "in_progress" flag in the CM thread before
+  // We need to tell G1ConcurrentMark to update the state  before
   // we wake up any waiters (especially when ExplicitInvokesConcurrent
   // is set) so that if a waiter requests another System.gc() it doesn't
   // incorrectly see that a marking cycle is still in progress.
   if (concurrent) {
-    _cm->cm_thread()->set_idle();
+    _cm->notify_concurrent_cycle_completed();
   }
 
   // Notify threads waiting in System.gc() (with ExplicitGCInvokesConcurrent)
@@ -2565,11 +2557,9 @@ void G1CollectedHeap::start_concurrent_cycle(bool concurrent_operation_is_full_m
   assert(!_cm->in_progress(), "Can not start concurrent operation while in progress");
   MutexLocker x(G1CGC_lock, Mutex::_no_safepoint_check_flag);
   if (concurrent_operation_is_full_mark) {
-    _cm->post_concurrent_mark_start();
-    _cm->cm_thread()->start_full_mark();
+    _cm->start_full_concurrent_cycle();
   } else {
-    _cm->post_concurrent_undo_start();
-    _cm->cm_thread()->start_undo_mark();
+    _cm->start_undo_concurrent_cycle();
   }
   G1CGC_lock->notify();
 }

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

@@ -915,9 +915,6 @@ public:
   // specified by the policy object.
   jint initialize() override;
 
-  // Returns whether concurrent mark threads (and the VM) are about to terminate.
-  bool concurrent_mark_is_terminating() const;
-
   void safepoint_synchronize_begin() override;
   void safepoint_synchronize_end() override;
 

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

@@ -581,6 +581,11 @@ PartialArrayStateManager* G1ConcurrentMark::partial_array_state_manager() const
   return _partial_array_state_manager;
 }
 
+G1ConcurrentMarkThread* G1ConcurrentMark::cm_thread() const {
+  assert(is_fully_initialized(), "must be");
+  return _cm_thread;
+}
+
 void G1ConcurrentMark::reset() {
   _has_aborted.store_relaxed(false);
 
@@ -715,7 +720,6 @@ public:
 private:
   // Heap region closure used for clearing the _mark_bitmap.
   class G1ClearBitmapHRClosure : public G1HeapRegionClosure {
-  private:
     G1ConcurrentMark* _cm;
     G1CMBitMap* _bitmap;
     bool _suspendible; // If suspendible, do yield checks.
@@ -959,7 +963,7 @@ void G1ConcurrentMark::pre_concurrent_start(GCCause::Cause cause) {
   _gc_tracer_cm->set_gc_cause(cause);
 }
 
-void G1ConcurrentMark::post_concurrent_mark_start() {
+void G1ConcurrentMark::start_full_concurrent_cycle() {
   // Start Concurrent Marking weak-reference discovery.
   ReferenceProcessor* rp = _g1h->ref_processor_cm();
   rp->start_discovery(false /* always_clear */);
@@ -976,10 +980,26 @@ void G1ConcurrentMark::post_concurrent_mark_start() {
   // when marking is on. So, it's also called at the end of the
   // concurrent start pause to update the heap end, if the heap expands
   // during it. No need to call it here.
+
+  // Signal the thread to start work.
+  cm_thread()->start_full_mark();
 }
 
-void G1ConcurrentMark::post_concurrent_undo_start() {
+void G1ConcurrentMark::start_undo_concurrent_cycle() {
   root_regions()->cancel_scan();
+
+  // Signal the thread to start work.
+  cm_thread()->start_undo_mark();
+}
+
+void G1ConcurrentMark::notify_concurrent_cycle_completed() {
+  cm_thread()->set_idle();
+}
+
+void G1ConcurrentMark::stop() {
+  if (is_fully_initialized()) {
+    cm_thread()->stop();
+  }
 }
 
 /*
@@ -1943,7 +1963,7 @@ bool G1ConcurrentMark::concurrent_cycle_abort() {
   // has been signalled is already rare), and this work should be negligible compared
   // to actual full gc work.
 
-  if (!is_fully_initialized() || (!cm_thread()->in_progress() && !_g1h->concurrent_mark_is_terminating())) {
+  if (!is_fully_initialized() || (!cm_thread()->in_progress() && !cm_thread()->should_terminate())) {
     return false;
   }
 

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

@@ -352,6 +352,7 @@ class G1ConcurrentMark : public CHeapObj<mtGC> {
   friend class G1CMRemarkTask;
   friend class G1CMRootRegionScanTask;
   friend class G1CMTask;
+  friend class G1ClearBitMapTask;
   friend class G1ConcurrentMarkThread;
 
   G1ConcurrentMarkThread* _cm_thread;     // The thread doing the work
@@ -524,6 +525,9 @@ class G1ConcurrentMark : public CHeapObj<mtGC> {
   Atomic<HeapWord*>* _top_at_rebuild_starts;
   // True when Remark pause selected regions for rebuilding.
   bool _needs_remembered_set_rebuild;
+
+  G1ConcurrentMarkThread* cm_thread() const;
+
 public:
   // To be called when an object is marked the first time, e.g. after a successful
   // mark_in_bitmap call. Updates various statistics data.
@@ -602,8 +606,6 @@ public:
                    G1RegionToSpaceMapper* bitmap_storage);
   ~G1ConcurrentMark();
 
-  G1ConcurrentMarkThread* cm_thread() { return _cm_thread; }
-
   G1CMBitMap* mark_bitmap() const { return (G1CMBitMap*)&_mark_bitmap; }
 
   // Calculates the number of concurrent GC threads to be used in the marking phase.
@@ -632,8 +634,15 @@ public:
   // These two methods do the work that needs to be done at the start and end of the
   // concurrent start pause.
   void pre_concurrent_start(GCCause::Cause cause);
-  void post_concurrent_mark_start();
-  void post_concurrent_undo_start();
+
+  // Start the particular type of concurrent cycle. After this call threads may be running.
+  void start_full_concurrent_cycle();
+  void start_undo_concurrent_cycle();
+
+  void notify_concurrent_cycle_completed();
+
+  // Stop active components/the concurrent mark thread.
+  void stop();
 
   // Scan all the root regions and mark everything reachable from
   // them.