8278923: Document Klass::is_loader_alive

Reviewed-by: dholmes, iklam

src/hotspot/share/oops/klass.inline.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2022, 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
@@ -44,6 +44,10 @@ inline bool Klass::is_non_strong_hidden() const {
 // Iff the class loader (or mirror for non-strong hidden classes) is alive the
 // Klass is considered alive. This is safe to call before the CLD is marked as
 // unloading, and hence during concurrent class unloading.
+// This returns false if the Klass is unloaded, or about to be unloaded because the holder of
+// the CLD is no longer strongly reachable.
+// The return value of this function may change from true to false after a safepoint. So the caller
+// of this function must ensure that a safepoint doesn't happen while interpreting the return value.
 inline bool Klass::is_loader_alive() const {
   return class_loader_data()->is_alive();
 }