From 6fda44172e955d4e1d181598a97902ed5b16c57b Mon Sep 17 00:00:00 2001
From: Axel Boldt-Christmas <aboldtch@openjdk.org>
Date: Tue, 27 Jan 2026 08:42:44 +0000
Subject: [PATCH] 8374690: ZGC: Convert zRelocate to use Atomic<T>

Reviewed-by: stefank, tschatzl
---
 src/hotspot/share/gc/z/zRelocate.cpp | 26 +++++++++++++-------------
 src/hotspot/share/gc/z/zRelocate.hpp |  7 ++++---
 2 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/src/hotspot/share/gc/z/zRelocate.cpp b/src/hotspot/share/gc/z/zRelocate.cpp
index da07f67d859..d51cf5abbae 100644
--- a/src/hotspot/share/gc/z/zRelocate.cpp
+++ b/src/hotspot/share/gc/z/zRelocate.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 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
@@ -64,31 +64,31 @@ ZRelocateQueue::ZRelocateQueue()
     _needs_attention(0) {}
 
 bool ZRelocateQueue::needs_attention() const {
-  return AtomicAccess::load(&_needs_attention) != 0;
+  return _needs_attention.load_relaxed() != 0;
 }
 
 void ZRelocateQueue::inc_needs_attention() {
-  const int needs_attention = AtomicAccess::add(&_needs_attention, 1);
+  const int needs_attention = _needs_attention.add_then_fetch(1);
   assert(needs_attention == 1 || needs_attention == 2, "Invalid state");
 }
 
 void ZRelocateQueue::dec_needs_attention() {
-  const int needs_attention = AtomicAccess::sub(&_needs_attention, 1);
+  const int needs_attention = _needs_attention.sub_then_fetch(1);
   assert(needs_attention == 0 || needs_attention == 1, "Invalid state");
 }
 
 void ZRelocateQueue::activate(uint nworkers) {
-  _is_active = true;
+  _is_active.store_relaxed(true);
   join(nworkers);
 }
 
 void ZRelocateQueue::deactivate() {
-  AtomicAccess::store(&_is_active, false);
+  _is_active.store_relaxed(false);
   clear();
 }
 
 bool ZRelocateQueue::is_active() const {
-  return AtomicAccess::load(&_is_active);
+  return _is_active.load_relaxed();
 }
 
 void ZRelocateQueue::join(uint nworkers) {
@@ -453,7 +453,7 @@ static void retire_target_page(ZGeneration* generation, ZPage* page) {
 class ZRelocateSmallAllocator {
 private:
   ZGeneration* const _generation;
-  volatile size_t    _in_place_count;
+  Atomic<size_t>     _in_place_count;
 
 public:
   ZRelocateSmallAllocator(ZGeneration* generation)
@@ -463,7 +463,7 @@ public:
   ZPage* alloc_and_retire_target_page(ZForwarding* forwarding, ZPage* target) {
     ZPage* const page = alloc_page(forwarding);
     if (page == nullptr) {
-      AtomicAccess::inc(&_in_place_count);
+      _in_place_count.add_then_fetch(1u);
     }
 
     if (target != nullptr) {
@@ -493,7 +493,7 @@ public:
   }
 
   size_t in_place_count() const {
-    return _in_place_count;
+    return _in_place_count.load_relaxed();
   }
 };
 
@@ -503,7 +503,7 @@ private:
   ZConditionLock      _lock;
   ZRelocationTargets* _shared_targets;
   bool                _in_place;
-  volatile size_t     _in_place_count;
+  Atomic<size_t>      _in_place_count;
 
 public:
   ZRelocateMediumAllocator(ZGeneration* generation, ZRelocationTargets* shared_targets)
@@ -539,7 +539,7 @@ public:
       ZPage* const to_page = alloc_page(forwarding);
       _shared_targets->set(partition_id, to_age, to_page);
       if (to_page == nullptr) {
-        AtomicAccess::inc(&_in_place_count);
+        _in_place_count.add_then_fetch(1u);
         _in_place = true;
       }
 
@@ -579,7 +579,7 @@ public:
   }
 
   size_t in_place_count() const {
-    return _in_place_count;
+    return _in_place_count.load_relaxed();
   }
 };
 
diff --git a/src/hotspot/share/gc/z/zRelocate.hpp b/src/hotspot/share/gc/z/zRelocate.hpp
index 038efba83eb..d25536e1bce 100644
--- a/src/hotspot/share/gc/z/zRelocate.hpp
+++ b/src/hotspot/share/gc/z/zRelocate.hpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 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
@@ -28,6 +28,7 @@
 #include "gc/z/zPageAge.hpp"
 #include "gc/z/zRelocationSet.hpp"
 #include "gc/z/zValue.hpp"
+#include "runtime/atomic.hpp"
 
 class ZForwarding;
 class ZGeneration;
@@ -42,8 +43,8 @@ private:
   uint                 _nworkers;
   uint                 _nsynchronized;
   bool                 _synchronize;
-  volatile bool        _is_active;
-  volatile int         _needs_attention;
+  Atomic<bool>         _is_active;
+  Atomic<int>          _needs_attention;
 
   bool needs_attention() const;
   void inc_needs_attention();