8387751: G1: Remove volatile from G1CollectorState::_initiate_conc_mark_if_possible

Reviewed-by: aboldtch, ayang

src/hotspot/share/gc/g1/g1CollectorState.hpp

@@ -59,7 +59,7 @@ class G1CollectorState {
   // has been in progress when the request came in.
   //
   // This flag remembers that there is an unfullfilled request.
-  volatile bool _initiate_conc_mark_if_possible;
+  bool _initiate_conc_mark_if_possible;
 
 public:
   G1CollectorState() :

src/hotspot/share/gc/g1/g1CollectorState.inline.hpp

@@ -42,7 +42,7 @@ inline void G1CollectorState::set_in_full_gc() {
 
 inline void G1CollectorState::set_in_concurrent_start_gc() {
   _phase = Phase::YoungConcurrentStart;
-  _initiate_conc_mark_if_possible = false;
+  set_initiate_conc_mark_if_possible(false);
 }
 inline void G1CollectorState::set_in_prepare_mixed_gc() {
   _phase = Phase::YoungPrepareMixed;

src/hotspot/share/gc/g1/g1Policy.cpp

@@ -1253,6 +1253,7 @@ void G1Policy::update_survivors_policy() {
 }
 
 bool G1Policy::force_concurrent_start_if_outside_cycle(GCCause::Cause gc_cause) {
+  assert_at_safepoint_on_vm_thread();
   // Check whether a concurrent cycle is active, do not include the
   // reclamation/mixed phase. This means that we can schedule a concurrent cycle
   // even while in the mixed phase.

src/hotspot/share/gc/g1/g1Policy.hpp

@@ -335,9 +335,8 @@ private:
 
 public:
   // This sets the initiate_conc_mark_if_possible() flag to start a
-  // new cycle, as long as we are not already in one. It's best if it
-  // is called during a safepoint when the test whether a cycle is in
-  // progress or not is stable.
+  // new cycle, as long as we are not already in one. It is called
+  // at a safepoint.
   bool force_concurrent_start_if_outside_cycle(GCCause::Cause gc_cause);
 
   // Decide whether this garbage collection pause should be a concurrent start

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

@@ -144,7 +144,7 @@ public:
                    size_t allocation_word_size);
   void collect();
 
-  G1CollectorState next_state() const { return _next_state; }
+  const G1CollectorState next_state() const { return _next_state; }
   bool concurrent_operation_is_full_mark() const { return _concurrent_operation_is_full_mark; }
 };