8377701: Shenandoah: Convert ShenandoahEvacOOMHandler to use Atomic<T>

Reviewed-by: shade, xpeng, wkemper, phh

src/hotspot/share/gc/shenandoah/shenandoahEvacOOMHandler.cpp

@@ -37,22 +37,22 @@ ShenandoahEvacOOMCounter::ShenandoahEvacOOMCounter() :
 void ShenandoahEvacOOMCounter::decrement() {
   assert(unmasked_count() > 0, "sanity");
   // NOTE: It's ok to simply decrement, even with mask set, because unmasked value is positive.
-  AtomicAccess::dec(&_bits);
+  _bits.fetch_then_sub(1);
 }
 
 void ShenandoahEvacOOMCounter::clear() {
   assert(unmasked_count() == 0, "sanity");
-  AtomicAccess::release_store_fence(&_bits, (jint)0);
+  _bits.release_store_fence((jint)0);
 }
 
 void ShenandoahEvacOOMCounter::set_oom_bit(bool decrement) {
-  jint threads_in_evac = AtomicAccess::load_acquire(&_bits);
+  jint threads_in_evac = _bits.load_acquire();
   while (true) {
     jint newval = decrement
       ? (threads_in_evac - 1) | OOM_MARKER_MASK
       : threads_in_evac | OOM_MARKER_MASK;
 
-    jint other = AtomicAccess::cmpxchg(&_bits, threads_in_evac, newval);
+    jint other = _bits.compare_exchange(threads_in_evac, newval);
     if (other == threads_in_evac) {
       // Success: wait for other threads to get out of the protocol and return.
       break;
@@ -65,7 +65,7 @@ void ShenandoahEvacOOMCounter::set_oom_bit(bool decrement) {
 
 bool ShenandoahEvacOOMCounter::try_increment()
 {
-  jint threads_in_evac = AtomicAccess::load_acquire(&_bits);
+  jint threads_in_evac = _bits.load_acquire();
 
   while (true) {
     // Cannot enter evacuation if OOM_MARKER_MASK is set.
@@ -73,7 +73,7 @@ bool ShenandoahEvacOOMCounter::try_increment()
       return false;
     }
 
-    jint other = AtomicAccess::cmpxchg(&_bits, threads_in_evac, threads_in_evac + 1);
+    jint other = _bits.compare_exchange(threads_in_evac, threads_in_evac + 1);
     if (other == threads_in_evac) {
       // Success: caller may safely enter evacuation
       return true;

src/hotspot/share/gc/shenandoah/shenandoahEvacOOMHandler.hpp

@@ -27,6 +27,7 @@
 
 #include "gc/shenandoah/shenandoahPadding.hpp"
 #include "memory/allocation.hpp"
+#include "runtime/atomic.hpp"
 #include "runtime/javaThread.hpp"
 #include "utilities/globalDefinitions.hpp"
 
@@ -36,7 +37,7 @@
 class ShenandoahEvacOOMCounter {
 private:
   // Combination of a 31-bit counter and 1-bit OOM marker.
-  volatile jint _bits;
+  Atomic<jint> _bits;
 
   // This class must be at least a cache line in size to prevent false sharing.
   shenandoah_padding_minus_size(0, sizeof(jint));

src/hotspot/share/gc/shenandoah/shenandoahEvacOOMHandler.inline.hpp

@@ -29,14 +29,13 @@
 
 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
 #include "gc/shenandoah/shenandoahThreadLocalData.hpp"
-#include "runtime/atomicAccess.hpp"
 
 jint ShenandoahEvacOOMCounter::load_acquire() {
-  return AtomicAccess::load_acquire(&_bits);
+  return _bits.load_acquire();
 }
 
 jint ShenandoahEvacOOMCounter::unmasked_count() {
-  return AtomicAccess::load_acquire(&_bits) & ~OOM_MARKER_MASK;
+  return _bits.load_acquire() & ~OOM_MARKER_MASK;
 }
 
 void ShenandoahEvacOOMHandler::enter_evacuation(Thread* thr) {