From c5f1ee61a1a26f9be32191d12db67ac53c6be170 Mon Sep 17 00:00:00 2001
From: Coleen Phillimore <coleen.phillimore@oracle.com>
Date: Fri, 10 Jan 2025 16:17:56 +0000
Subject: [PATCH] 8347431: Update ObjectMonitor comments

---
 src/hotspot/share/runtime/objectMonitor.hpp | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/src/hotspot/share/runtime/objectMonitor.hpp b/src/hotspot/share/runtime/objectMonitor.hpp
index cf364cc012d39..3e1c97442cc09 100644
--- a/src/hotspot/share/runtime/objectMonitor.hpp
+++ b/src/hotspot/share/runtime/objectMonitor.hpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2025, 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
@@ -84,12 +84,6 @@ class ObjectWaiter : public CHeapObj<mtThread> {
 //
 // ObjectMonitor Layout Overview/Highlights/Restrictions:
 //
-// - The _metadata field must be at offset 0 because the displaced header
-//   from markWord is stored there. We do not want markWord.hpp to include
-//   ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This
-//   means that ObjectMonitor cannot inherit from any other class nor can
-//   it use any virtual member functions. This restriction is critical to
-//   the proper functioning of the VM.
 // - The _metadata and _owner fields should be separated by enough space
 //   to avoid false sharing due to parallel access by different threads.
 //   This is an advisory recommendation.
@@ -117,11 +111,7 @@ class ObjectWaiter : public CHeapObj<mtThread> {
 //
 // - See TEST_VM(ObjectMonitor, sanity) gtest for how critical restrictions are
 //   enforced.
-// - Adjacent ObjectMonitors should be separated by enough space to avoid
-//   false sharing. This is handled by the ObjectMonitor allocation code
-//   in synchronizer.cpp. Also see TEST_VM(SynchronizerTest, sanity) gtest.
 //
-// Futures notes:
 // - Separating _owner from the <remaining_fields> by enough space to
 //   avoid false sharing might be profitable. Given that the CAS in
 //   monitorenter will invalidate the line underlying _owner. We want
@@ -151,7 +141,7 @@ class ObjectMonitor : public CHeapObj<mtObjectMonitor> {
   // ParkEvent of unblocker thread.
   static ParkEvent* _vthread_unparker_ParkEvent;
 
-  // The sync code expects the metadata field to be at offset zero (0).
+  // Because of frequent access, the the metadata field is at offset zero (0).
   // Enforced by the assert() in metadata_addr().
   // * LM_LIGHTWEIGHT with UseObjectMonitorTable:
   // Contains the _object's hashCode.