From c46d60af17256b2475c2413c0e72bae3ea28a8dc Mon Sep 17 00:00:00 2001
From: Annabelle Huo <Annabelle.Huo@ibm.com>
Date: Tue, 21 Mar 2023 14:31:54 -0400
Subject: [PATCH] Remove setImmutableField on currentThread for JDK19 and up

`Thread.currentThread` can be changed by JCL in
JDK19 and up. Set it as volatile for JDK19 and up.

Add `isJ9VMThreadCurrentThreadImmutable` in FrontEnd
to query whether or not `Thread.currentThread` is
immutable based on `JAVA_SPEC_VERSION`.

Fixes #16258

Co-authored-by: Daryl Maier <maier@ca.ibm.com>
Signed-off-by: Annabelle Huo <Annabelle.Huo@ibm.com>
---
 runtime/compiler/compile/J9SymbolReferenceTable.cpp |  9 ++++++++-
 runtime/compiler/env/VMJ9.cpp                       | 10 ++++++++++
 runtime/compiler/env/VMJ9.h                         |  7 +++++++
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/runtime/compiler/compile/J9SymbolReferenceTable.cpp b/runtime/compiler/compile/J9SymbolReferenceTable.cpp
index 4d34b810d84..cbbe1428122 100644
--- a/runtime/compiler/compile/J9SymbolReferenceTable.cpp
+++ b/runtime/compiler/compile/J9SymbolReferenceTable.cpp
@@ -1356,7 +1356,14 @@ J9::SymbolReferenceTable::findOrCreateCurrentThreadSymbolRef()
       TR_J9VMBase *fej9 = (TR_J9VMBase *)(fe());
       TR::Symbol * sym = TR::RegisterMappedSymbol::createMethodMetaDataSymbol(trHeapMemory(), "CurrentThread");
       sym->setDataType(TR::Address);
-      sym->setImmutableField();
+      if (fej9->isJ9VMThreadCurrentThreadImmutable())
+         {
+         sym->setImmutableField();
+         }
+      else
+         {
+         sym->setVolatile();
+         }
       element(currentThreadSymbol) = new (trHeapMemory()) TR::SymbolReference(self(), currentThreadSymbol, sym);
       element(currentThreadSymbol)->setOffset(fej9->thisThreadGetCurrentThreadOffset());
       }
diff --git a/runtime/compiler/env/VMJ9.cpp b/runtime/compiler/env/VMJ9.cpp
index 00cd757aad1..55d7b154b80 100644
--- a/runtime/compiler/env/VMJ9.cpp
+++ b/runtime/compiler/env/VMJ9.cpp
@@ -9376,6 +9376,16 @@ TR_J9VMBase::isSnapshotModeEnabled()
 #endif /* defined(J9VM_OPT_CRIU_SUPPORT) */
    }
 
+bool
+TR_J9VMBase::isJ9VMThreadCurrentThreadImmutable()
+   {
+#if JAVA_SPEC_VERSION >= 19
+   return false;
+#else
+   return true;
+#endif /* JAVA_SPEC_VERSION >= 19 */
+   }
+
 // Native method bodies
 //
 #if defined(TR_HOST_X86)
diff --git a/runtime/compiler/env/VMJ9.h b/runtime/compiler/env/VMJ9.h
index b03ea9bc64c..60563a91ba2 100644
--- a/runtime/compiler/env/VMJ9.h
+++ b/runtime/compiler/env/VMJ9.h
@@ -1361,6 +1361,13 @@ class TR_J9VMBase : public TR_FrontEnd
     */
    bool isSnapshotModeEnabled();
 
+   /**
+    * \brief Answers whether or not Thread.currentThread() is immutable.
+    *
+    * \return True if Thread.currentThread() is immutable.
+    */
+   virtual bool isJ9VMThreadCurrentThreadImmutable();
+
 protected:
 
    enum // _flags