8374328: Convert simple AtomicAccess uses in gc/shared to use Atomic<T>

Reviewed-by: dholmes, tschatzl

src/hotspot/share/gc/shared/barrierSetNMethod.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -33,6 +33,7 @@
 #include "memory/universe.hpp"
 #include "oops/access.inline.hpp"
 #include "oops/method.inline.hpp"
+#include "runtime/atomic.hpp"
 #include "runtime/frame.inline.hpp"
 #include "runtime/javaThread.hpp"
 #include "runtime/threads.hpp"
@@ -196,8 +197,8 @@ int BarrierSetNMethod::nmethod_stub_entry_barrier(address* return_address_ptr) {
     // Diagnostic option to force deoptimization 1 in 10 times. It is otherwise
     // a very rare event.
     if (DeoptimizeNMethodBarriersALot && !nm->is_osr_method()) {
-      static volatile uint32_t counter=0;
-      if (AtomicAccess::add(&counter, 1u) % 10 == 0) {
+      static Atomic<uint32_t> counter{0};
+      if (counter.add_then_fetch(1u) % 10 == 0) {
         may_enter = false;
       }
     }

src/hotspot/share/gc/shared/concurrentGCThread.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -23,7 +23,7 @@
  */
 
 #include "gc/shared/concurrentGCThread.hpp"
-#include "runtime/atomicAccess.hpp"
+#include "runtime/atomic.hpp"
 #include "runtime/init.hpp"
 #include "runtime/jniHandles.hpp"
 #include "runtime/mutexLocker.hpp"
@@ -48,7 +48,7 @@ void ConcurrentGCThread::run() {
 
   // Signal thread has terminated
   MonitorLocker ml(Terminator_lock);
-  AtomicAccess::release_store(&_has_terminated, true);
+  _has_terminated.release_store(true);
   ml.notify_all();
 }
 
@@ -57,21 +57,21 @@ void ConcurrentGCThread::stop() {
   assert(!has_terminated(), "Invalid state");
 
   // Signal thread to terminate
-  AtomicAccess::release_store_fence(&_should_terminate, true);
+  _should_terminate.release_store_fence(true);
 
   stop_service();
 
   // Wait for thread to terminate
   MonitorLocker ml(Terminator_lock);
-  while (!_has_terminated) {
+  while (!_has_terminated.load_relaxed()) {
     ml.wait();
   }
 }
 
 bool ConcurrentGCThread::should_terminate() const {
-  return AtomicAccess::load_acquire(&_should_terminate);
+  return _should_terminate.load_acquire();
 }
 
 bool ConcurrentGCThread::has_terminated() const {
-  return AtomicAccess::load_acquire(&_has_terminated);
+  return _has_terminated.load_acquire();
 }

src/hotspot/share/gc/shared/concurrentGCThread.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -25,14 +25,15 @@
 #ifndef SHARE_GC_SHARED_CONCURRENTGCTHREAD_HPP
 #define SHARE_GC_SHARED_CONCURRENTGCTHREAD_HPP
 
+#include "runtime/atomic.hpp"
 #include "runtime/javaThread.hpp"
 #include "runtime/nonJavaThread.hpp"
 #include "utilities/debug.hpp"
 
 class ConcurrentGCThread: public NamedThread {
 private:
-  volatile bool _should_terminate;
-  volatile bool _has_terminated;
+  Atomic<bool> _should_terminate;
+  Atomic<bool> _has_terminated;
 
 protected:
   void create_and_start(ThreadPriority prio = NearMaxPriority);

src/hotspot/share/gc/shared/gcLocker.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -28,7 +28,7 @@
 #include "logging/log.hpp"
 #include "memory/resourceArea.hpp"
 #include "memory/universe.hpp"
-#include "runtime/atomicAccess.hpp"
+#include "runtime/atomic.hpp"
 #include "runtime/interfaceSupport.inline.hpp"
 #include "runtime/javaThread.inline.hpp"
 #include "runtime/safepoint.hpp"
@@ -60,16 +60,13 @@ public:
 };
 
 Monitor* GCLocker::_lock;
-volatile bool GCLocker::_is_gc_request_pending;
+Atomic<bool> GCLocker::_is_gc_request_pending{false};
 
-DEBUG_ONLY(uint64_t GCLocker::_verify_in_cr_count;)
+DEBUG_ONLY(Atomic<uint64_t> GCLocker::_verify_in_cr_count{0};)
 
 void GCLocker::initialize() {
   assert(JNICritical_lock != nullptr, "inv");
   _lock = JNICritical_lock;
-  _is_gc_request_pending = false;
-
-  DEBUG_ONLY(_verify_in_cr_count = 0;)
 }
 
 bool GCLocker::is_active() {
@@ -84,11 +81,11 @@ bool GCLocker::is_active() {
 void GCLocker::block() {
   // _lock is held from the beginning of block() to the end of of unblock().
   _lock->lock();
-  assert(AtomicAccess::load(&_is_gc_request_pending) == false, "precondition");
+  assert(_is_gc_request_pending.load_relaxed() == false, "precondition");
 
   GCLockerTimingDebugLogger logger("Thread blocked to start GC.");
 
-  AtomicAccess::store(&_is_gc_request_pending, true);
+  _is_gc_request_pending.store_relaxed(true);
 
   // The _is_gc_request_pending and _jni_active_critical (inside
   // in_critical_atomic()) variables form a Dekker duality. On the GC side, the
@@ -112,14 +109,14 @@ void GCLocker::block() {
 #ifdef ASSERT
   // Matching the storestore in GCLocker::exit.
   OrderAccess::loadload();
-  assert(AtomicAccess::load(&_verify_in_cr_count) == 0, "inv");
+  assert(_verify_in_cr_count.load_relaxed() == 0, "inv");
 #endif
 }
 
 void GCLocker::unblock() {
-  assert(AtomicAccess::load(&_is_gc_request_pending) == true, "precondition");
+  assert(_is_gc_request_pending.load_relaxed() == true, "precondition");
 
-  AtomicAccess::store(&_is_gc_request_pending, false);
+  _is_gc_request_pending.store_relaxed(false);
   _lock->unlock();
 }
 
@@ -139,7 +136,7 @@ void GCLocker::enter_slow(JavaThread* current_thread) {
     // Same as fast path.
     OrderAccess::fence();
 
-    if (!AtomicAccess::load(&_is_gc_request_pending)) {
+    if (!_is_gc_request_pending.load_relaxed()) {
       return;
     }
 

src/hotspot/share/gc/shared/gcLocker.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -27,6 +27,7 @@
 
 #include "gc/shared/gcCause.hpp"
 #include "memory/allStatic.hpp"
+#include "runtime/atomic.hpp"
 #include "runtime/mutex.hpp"
 
 // GCLocker provides synchronization between the garbage collector (GC) and
@@ -43,11 +44,11 @@
 
 class GCLocker: public AllStatic {
   static Monitor* _lock;
-  static volatile bool _is_gc_request_pending;
+  static Atomic<bool> _is_gc_request_pending;
 
 #ifdef ASSERT
   // Debug-only: to track the number of java threads in critical-region.
-  static uint64_t _verify_in_cr_count;
+  static Atomic<uint64_t> _verify_in_cr_count;
 #endif
   static void enter_slow(JavaThread* current_thread);
 

src/hotspot/share/gc/shared/gcLocker.inline.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -38,13 +38,13 @@ void GCLocker::enter(JavaThread* current_thread) {
     // Matching the fence in GCLocker::block.
     OrderAccess::fence();
 
-    if (AtomicAccess::load(&_is_gc_request_pending)) {
+    if (_is_gc_request_pending.load_relaxed()) {
       current_thread->exit_critical();
       // slow-path
       enter_slow(current_thread);
     }
 
-    DEBUG_ONLY(AtomicAccess::add(&_verify_in_cr_count, (uint64_t)1);)
+    DEBUG_ONLY(_verify_in_cr_count.add_then_fetch(1u);)
   } else {
     current_thread->enter_critical();
   }
@@ -55,7 +55,7 @@ void GCLocker::exit(JavaThread* current_thread) {
 
 #ifdef ASSERT
   if (current_thread->in_last_critical()) {
-    AtomicAccess::add(&_verify_in_cr_count, (uint64_t)-1);
+    _verify_in_cr_count.sub_then_fetch(1u);
     // Matching the loadload in GCLocker::block.
     OrderAccess::storestore();
   }

src/hotspot/share/gc/shared/pretouchTask.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -25,7 +25,7 @@
 #include "gc/shared/gc_globals.hpp"
 #include "gc/shared/pretouchTask.hpp"
 #include "logging/log.hpp"
-#include "runtime/atomicAccess.hpp"
+#include "runtime/atomic.hpp"
 #include "runtime/globals.hpp"
 #include "runtime/os.hpp"
 #include "utilities/align.hpp"
@@ -52,11 +52,11 @@ size_t PretouchTask::chunk_size() {
 
 void PretouchTask::work(uint worker_id) {
   while (true) {
-    char* cur_start = AtomicAccess::load(&_cur_addr);
+    char* cur_start = _cur_addr.load_relaxed();
     char* cur_end = cur_start + MIN2(_chunk_size, pointer_delta(_end_addr, cur_start, 1));
     if (cur_start >= cur_end) {
       break;
-    } else if (cur_start == AtomicAccess::cmpxchg(&_cur_addr, cur_start, cur_end)) {
+    } else if (cur_start == _cur_addr.compare_exchange(cur_start, cur_end)) {
       os::pretouch_memory(cur_start, cur_end, _page_size);
     } // Else attempt to claim chunk failed, so try again.
   }

src/hotspot/share/gc/shared/pretouchTask.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -26,9 +26,11 @@
 #define SHARE_GC_SHARED_PRETOUCH_HPP
 
 #include "gc/shared/workerThread.hpp"
+#include "runtime/atomic.hpp"
+#include "utilities/globalDefinitions.hpp"
 
 class PretouchTask : public WorkerTask {
-  char* volatile _cur_addr;
+  Atomic<char*> _cur_addr;
   char* const _end_addr;
   size_t _page_size;
   size_t _chunk_size;

src/hotspot/share/gc/shared/suspendibleThreadSet.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -30,7 +30,7 @@
 
 uint          SuspendibleThreadSet::_nthreads          = 0;
 uint          SuspendibleThreadSet::_nthreads_stopped  = 0;
-volatile bool SuspendibleThreadSet::_suspend_all       = false;
+Atomic<bool>  SuspendibleThreadSet::_suspend_all{false};
 double        SuspendibleThreadSet::_suspend_all_start = 0.0;
 
 static Semaphore* _synchronize_wakeup = nullptr;
@@ -96,7 +96,7 @@ void SuspendibleThreadSet::synchronize() {
   {
     MonitorLocker ml(STS_lock, Mutex::_no_safepoint_check_flag);
     assert(!should_yield(), "Only one at a time");
-    AtomicAccess::store(&_suspend_all, true);
+    _suspend_all.store_relaxed(true);
     if (is_synchronized()) {
       return;
     }
@@ -127,6 +127,6 @@ void SuspendibleThreadSet::desynchronize() {
   MonitorLocker ml(STS_lock, Mutex::_no_safepoint_check_flag);
   assert(should_yield(), "STS not synchronizing");
   assert(is_synchronized(), "STS not synchronized");
-  AtomicAccess::store(&_suspend_all, false);
+  _suspend_all.store_relaxed(false);
   ml.notify_all();
 }

src/hotspot/share/gc/shared/suspendibleThreadSet.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -26,7 +26,7 @@
 #define SHARE_GC_SHARED_SUSPENDIBLETHREADSET_HPP
 
 #include "memory/allocation.hpp"
-#include "runtime/atomicAccess.hpp"
+#include "runtime/atomic.hpp"
 
 // A SuspendibleThreadSet is a set of threads that can be suspended.
 // A thread can join and later leave the set, and periodically yield.
@@ -43,7 +43,7 @@ class SuspendibleThreadSet : public AllStatic {
 private:
   static uint          _nthreads;
   static uint          _nthreads_stopped;
-  static volatile bool _suspend_all;
+  static Atomic<bool>  _suspend_all;
   static double        _suspend_all_start;
 
   static bool is_synchronized();
@@ -59,7 +59,7 @@ private:
 
 public:
   // Returns true if an suspension is in progress.
-  static bool should_yield() { return AtomicAccess::load(&_suspend_all); }
+  static bool should_yield() { return _suspend_all.load_relaxed(); }
 
   // Suspends the current thread if a suspension is in progress.
   static void yield() {

src/hotspot/share/gc/shared/workerThread.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -42,7 +42,7 @@ WorkerTaskDispatcher::WorkerTaskDispatcher() :
 void WorkerTaskDispatcher::coordinator_distribute_task(WorkerTask* task, uint num_workers) {
   // No workers are allowed to read the state variables until they have been signaled.
   _task = task;
-  _not_finished = num_workers;
+  _not_finished.store_relaxed(num_workers);
 
   // Dispatch 'num_workers' number of tasks.
   _start_semaphore.signal(num_workers);
@@ -51,9 +51,12 @@ void WorkerTaskDispatcher::coordinator_distribute_task(WorkerTask* task, uint nu
   _end_semaphore.wait();
 
   // No workers are allowed to read the state variables after the coordinator has been signaled.
-  assert(_not_finished == 0, "%d not finished workers?", _not_finished);
+#ifdef ASSERT
+  uint not_finished = _not_finished.load_relaxed();
+  assert(not_finished == 0, "%u not finished workers?", not_finished);
+#endif // ASSERT
   _task = nullptr;
-  _started = 0;
+  _started.store_relaxed(0);
 }
 
 void WorkerTaskDispatcher::worker_run_task() {
@@ -61,7 +64,7 @@ void WorkerTaskDispatcher::worker_run_task() {
   _start_semaphore.wait();
 
   // Get and set worker id.
-  const uint worker_id = AtomicAccess::fetch_then_add(&_started, 1u);
+  const uint worker_id = _started.fetch_then_add(1u);
   WorkerThread::set_worker_id(worker_id);
 
   // Run task.
@@ -70,7 +73,7 @@ void WorkerTaskDispatcher::worker_run_task() {
 
   // Mark that the worker is done with the task.
   // The worker is not allowed to read the state variables after this line.
-  const uint not_finished = AtomicAccess::sub(&_not_finished, 1u);
+  const uint not_finished = _not_finished.sub_then_fetch(1u);
 
   // The last worker signals to the coordinator that all work is completed.
   if (not_finished == 0) {

src/hotspot/share/gc/shared/workerThread.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2002, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2002, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -27,6 +27,7 @@
 
 #include "gc/shared/gcId.hpp"
 #include "memory/allocation.hpp"
+#include "runtime/atomic.hpp"
 #include "runtime/nonJavaThread.hpp"
 #include "runtime/semaphore.hpp"
 #include "utilities/debug.hpp"
@@ -58,8 +59,8 @@ class WorkerTaskDispatcher {
   // The task currently being dispatched to the WorkerThreads.
   WorkerTask* _task;
 
-  volatile uint _started;
-  volatile uint _not_finished;
+  Atomic<uint> _started;
+  Atomic<uint> _not_finished;
 
   // Semaphore used to start the WorkerThreads.
   Semaphore _start_semaphore;