From b59f49a1c3e370f794291a1f948e67d2651ece11 Mon Sep 17 00:00:00 2001
From: Axel Boldt-Christmas <aboldtch@openjdk.org>
Date: Mon, 26 Jan 2026 14:28:39 +0000
Subject: [PATCH] 8374680: ZGC: Convert zGeneration to use Atomic<T>

Reviewed-by: stefank, tschatzl
---
 src/hotspot/share/gc/z/zGeneration.cpp | 21 ++++++++++-----------
 src/hotspot/share/gc/z/zGeneration.hpp |  9 +++++----
 2 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/src/hotspot/share/gc/z/zGeneration.cpp b/src/hotspot/share/gc/z/zGeneration.cpp
index a8c646bf895..27f352a624f 100644
--- a/src/hotspot/share/gc/z/zGeneration.cpp
+++ b/src/hotspot/share/gc/z/zGeneration.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 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
@@ -56,7 +56,6 @@
 #include "logging/log.hpp"
 #include "memory/universe.hpp"
 #include "prims/jvmtiTagMap.hpp"
-#include "runtime/atomicAccess.hpp"
 #include "runtime/continuation.hpp"
 #include "runtime/handshake.hpp"
 #include "runtime/safepoint.hpp"
@@ -298,33 +297,33 @@ bool ZGeneration::is_relocate_queue_active() const {
 
 void ZGeneration::reset_statistics() {
   assert(SafepointSynchronize::is_at_safepoint(), "Should be at safepoint");
-  _freed = 0;
-  _promoted = 0;
-  _compacted = 0;
+  _freed.store_relaxed(0u);
+  _promoted.store_relaxed(0u);
+  _compacted.store_relaxed(0u);
 }
 
 size_t ZGeneration::freed() const {
-  return _freed;
+  return _freed.load_relaxed();
 }
 
 void ZGeneration::increase_freed(size_t size) {
-  AtomicAccess::add(&_freed, size, memory_order_relaxed);
+  _freed.add_then_fetch(size, memory_order_relaxed);
 }
 
 size_t ZGeneration::promoted() const {
-  return _promoted;
+  return _promoted.load_relaxed();;
 }
 
 void ZGeneration::increase_promoted(size_t size) {
-  AtomicAccess::add(&_promoted, size, memory_order_relaxed);
+  _promoted.add_then_fetch(size, memory_order_relaxed);
 }
 
 size_t ZGeneration::compacted() const {
-  return _compacted;
+  return _compacted.load_relaxed();;
 }
 
 void ZGeneration::increase_compacted(size_t size) {
-  AtomicAccess::add(&_compacted, size, memory_order_relaxed);
+  _compacted.add_then_fetch(size, memory_order_relaxed);
 }
 
 ConcurrentGCTimer* ZGeneration::gc_timer() const {
diff --git a/src/hotspot/share/gc/z/zGeneration.hpp b/src/hotspot/share/gc/z/zGeneration.hpp
index 3b700361460..1371865958b 100644
--- a/src/hotspot/share/gc/z/zGeneration.hpp
+++ b/src/hotspot/share/gc/z/zGeneration.hpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 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
@@ -37,6 +37,7 @@
 #include "gc/z/zWeakRootsProcessor.hpp"
 #include "gc/z/zWorkers.hpp"
 #include "memory/allocation.hpp"
+#include "runtime/atomic.hpp"
 
 class ThreadClosure;
 class ZForwardingTable;
@@ -70,9 +71,9 @@ protected:
   ZRelocate             _relocate;
   ZRelocationSet        _relocation_set;
 
-  volatile size_t       _freed;
-  volatile size_t       _promoted;
-  volatile size_t       _compacted;
+  Atomic<size_t>        _freed;
+  Atomic<size_t>        _promoted;
+  Atomic<size_t>        _compacted;
 
   Phase                 _phase;
   uint32_t              _seqnum;