From b1aea5520592e835e33762e349615fe616576103 Mon Sep 17 00:00:00 2001
From: Axel Boldt-Christmas <aboldtch@openjdk.org>
Date: Tue, 27 Jan 2026 10:26:29 +0000
Subject: [PATCH] 8374695: ZGC: Convert zTLABUsage to use Atomic<T>

Reviewed-by: stefank, tschatzl
---
 src/hotspot/share/gc/z/zTLABUsage.cpp | 11 +++++------
 src/hotspot/share/gc/z/zTLABUsage.hpp |  7 ++++---
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/src/hotspot/share/gc/z/zTLABUsage.cpp b/src/hotspot/share/gc/z/zTLABUsage.cpp
index c2e3db6bedf..d3613cf8632 100644
--- a/src/hotspot/share/gc/z/zTLABUsage.cpp
+++ b/src/hotspot/share/gc/z/zTLABUsage.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2025, 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
@@ -23,24 +23,23 @@
 
 #include "gc/z/zTLABUsage.hpp"
 #include "logging/log.hpp"
-#include "runtime/atomicAccess.hpp"
 
 ZTLABUsage::ZTLABUsage()
   : _used(0),
     _used_history() {}
 
 void ZTLABUsage::increase_used(size_t size) {
-  AtomicAccess::add(&_used, size, memory_order_relaxed);
+  _used.add_then_fetch(size, memory_order_relaxed);
 }
 
 void ZTLABUsage::decrease_used(size_t size) {
-  precond(size <= _used);
+  precond(size <= _used.load_relaxed());
 
-  AtomicAccess::sub(&_used, size, memory_order_relaxed);
+  _used.sub_then_fetch(size, memory_order_relaxed);
 }
 
 void ZTLABUsage::reset() {
-  const size_t used = AtomicAccess::xchg(&_used, (size_t) 0);
+  const size_t used = _used.exchange(0u);
 
   // Avoid updates when nothing has been allocated since the last YC
   if (used == 0) {
diff --git a/src/hotspot/share/gc/z/zTLABUsage.hpp b/src/hotspot/share/gc/z/zTLABUsage.hpp
index 3d1b084fe16..68c7620c26e 100644
--- a/src/hotspot/share/gc/z/zTLABUsage.hpp
+++ b/src/hotspot/share/gc/z/zTLABUsage.hpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2025, 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
@@ -24,6 +24,7 @@
 #ifndef SHARE_GC_Z_ZTLABUSAGE_HPP
 #define SHARE_GC_Z_ZTLABUSAGE_HPP
 
+#include "runtime/atomic.hpp"
 #include "utilities/globalDefinitions.hpp"
 #include "utilities/numberSeq.hpp"
 
@@ -42,9 +43,9 @@
 class ZTLABUsage {
 private:
   // Accounting TLAB used until the next GC cycle
-  volatile size_t _used;
+  Atomic<size_t> _used;
   // Sequence of historic used values
-  TruncatedSeq    _used_history;
+  TruncatedSeq   _used_history;
 
 public:
   ZTLABUsage();