8374876: Epsilon: Convert to use Atomic<T>

Reviewed-by: tschatzl, stefank

src/hotspot/share/gc/epsilon/epsilonHeap.cpp

@@ -62,8 +62,6 @@ jint EpsilonHeap::initialize() {
 
   // Enable monitoring
   _monitoring_support = new EpsilonMonitoringSupport(this);
-  _last_counter_update = 0;
-  _last_heap_print = 0;
 
   // Install barrier set
   BarrierSet::set_barrier_set(new EpsilonBarrierSet());
@@ -156,17 +154,17 @@ HeapWord* EpsilonHeap::allocate_work(size_t size) {
   // At this point, some diagnostic subsystems might not yet be initialized.
   // We pretend the printout happened either way. This keeps allocation path
   // from obsessively checking the subsystems' status on every allocation.
-  size_t last_counter = AtomicAccess::load(&_last_counter_update);
+  size_t last_counter = _last_counter_update.load_relaxed();
   if ((used - last_counter >= _step_counter_update) &&
-      AtomicAccess::cmpxchg(&_last_counter_update, last_counter, used) == last_counter) {
+      _last_counter_update.compare_set(last_counter, used)) {
     if (_monitoring_support->is_ready()) {
       _monitoring_support->update_counters();
     }
   }
 
-  size_t last_heap = AtomicAccess::load(&_last_heap_print);
+  size_t last_heap = _last_heap_print.load_relaxed();
   if ((used - last_heap >= _step_heap_print) &&
-      AtomicAccess::cmpxchg(&_last_heap_print, last_heap, used) == last_heap) {
+      _last_heap_print.compare_set(last_heap, used)) {
     print_heap_info(used);
     if (Metaspace::initialized()) {
       print_metaspace_info();

src/hotspot/share/gc/epsilon/epsilonHeap.hpp

@@ -31,6 +31,7 @@
 #include "gc/shared/collectedHeap.hpp"
 #include "gc/shared/space.hpp"
 #include "memory/virtualspace.hpp"
+#include "runtime/atomic.hpp"
 #include "services/memoryManager.hpp"
 
 class EpsilonHeap : public CollectedHeap {
@@ -45,8 +46,8 @@ private:
   size_t _step_counter_update;
   size_t _step_heap_print;
   int64_t _decay_time_ns;
-  volatile size_t _last_counter_update;
-  volatile size_t _last_heap_print;
+  Atomic<size_t> _last_counter_update;
+  Atomic<size_t> _last_heap_print;
 
   void print_tracing_info() const override;
   void stop() override {};

src/hotspot/share/gc/epsilon/epsilonMonitoringSupport.cpp

@@ -96,7 +96,6 @@ public:
 EpsilonMonitoringSupport::EpsilonMonitoringSupport(EpsilonHeap* heap) {
   _heap_counters  = new EpsilonGenerationCounters(heap);
   _space_counters = new EpsilonSpaceCounters("Heap", 0, heap->max_capacity(), 0, _heap_counters);
-  _ready = false;
 }
 
 void EpsilonMonitoringSupport::update_counters() {
@@ -114,9 +113,9 @@ void EpsilonMonitoringSupport::update_counters() {
 }
 
 bool EpsilonMonitoringSupport::is_ready() {
-  return AtomicAccess::load_acquire(&_ready);
+  return _ready.load_acquire();
 }
 
 void EpsilonMonitoringSupport::mark_ready() {
-  return AtomicAccess::release_store(&_ready, true);
+  _ready.release_store(true);
 }

src/hotspot/share/gc/epsilon/epsilonMonitoringSupport.hpp

@@ -26,6 +26,7 @@
 #define SHARE_GC_EPSILON_EPSILONMONITORINGSUPPORT_HPP
 
 #include "memory/allocation.hpp"
+#include "runtime/atomic.hpp"
 
 class EpsilonGenerationCounters;
 class EpsilonSpaceCounters;
@@ -35,7 +36,7 @@ class EpsilonMonitoringSupport : public CHeapObj<mtGC> {
 private:
   EpsilonGenerationCounters* _heap_counters;
   EpsilonSpaceCounters* _space_counters;
-  volatile bool _ready;
+  Atomic<bool> _ready;
 
 public:
   EpsilonMonitoringSupport(EpsilonHeap* heap);