8244997: Convert the JavaThread::_threadObj oop to use OopStorage

Move the oop and handle releasing it in the service thread.  Remove Universe::oops_do from callers.

Co-authored-by: Erik Osterlund <erik.osterlund@oracle.com>
Co-authored-by: Tom Rodriguez <tom.rodriguez@oracle.com>
Reviewed-by: dholmes, zgu, eosterlund, cjplummer

src/hotspot/cpu/aarch64/c1_LIR_aarch64.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2020, 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
@@ -48,7 +48,7 @@ LIR_Opr LIR_OprFact::double_fpu(int reg1, int reg2) {
 void LIR_Address::verify() const {
   assert(base()->is_cpu_register(), "wrong base operand");
   assert(index()->is_illegal() || index()->is_double_cpu() || index()->is_single_cpu(), "wrong index operand");
-  assert(base()->type() == T_OBJECT || base()->type() == T_LONG || base()->type() == T_METADATA,
+  assert(base()->type() == T_ADDRESS || base()->type() == T_OBJECT || base()->type() == T_LONG || base()->type() == T_METADATA,
          "wrong type for addresses");
 }
 #endif // PRODUCT

src/hotspot/cpu/arm/c1_LIR_arm.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2010, 2020, 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
@@ -52,12 +52,12 @@ void LIR_Address::verify() const {
   // be handled by the back-end or will be rejected if not.
 #ifdef _LP64
   assert(index()->is_illegal() || index()->is_double_cpu(), "wrong index operand");
-  assert(base()->type() == T_OBJECT || base()->type() == T_LONG || base()->type() == T_METADATA,
+  assert(base()->type() == T_ADDRESS || base()->type() == T_OBJECT || base()->type() == T_LONG || base()->type() == T_METADATA,
          "wrong type for addresses");
 #else
   assert(base()->is_single_cpu(), "wrong base operand");
   assert(index()->is_illegal() || index()->is_single_cpu(), "wrong index operand");
-  assert(base()->type() == T_OBJECT || base()->type() == T_INT || base()->type() == T_METADATA,
+  assert(base()->type() == T_ADDRESS || base()->type() == T_OBJECT || base()->type() == T_INT || base()->type() == T_METADATA,
          "wrong type for addresses");
 #endif
 }

src/hotspot/cpu/ppc/c1_LIR_ppc.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2020, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2016 SAP SE. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
@@ -52,12 +52,12 @@ void LIR_Address::verify() const {
 #ifdef _LP64
   assert(base()->is_cpu_register(), "wrong base operand");
   assert(index()->is_illegal() || index()->is_double_cpu(), "wrong index operand");
-  assert(base()->type() == T_OBJECT || base()->type() == T_LONG || base()->type() == T_METADATA,
+  assert(base()->type() == T_ADDRESS || base()->type() == T_OBJECT || base()->type() == T_LONG || base()->type() == T_METADATA,
          "wrong type for addresses");
 #else
   assert(base()->is_single_cpu(), "wrong base operand");
   assert(index()->is_illegal() || index()->is_single_cpu(), "wrong index operand");
-  assert(base()->type() == T_OBJECT || base()->type() == T_INT || base()->type() == T_METADATA,
+  assert(base()->type() == T_ADDRESS || base()->type() == T_OBJECT || base()->type() == T_INT || base()->type() == T_METADATA,
          "wrong type for addresses");
 #endif
 }

src/hotspot/cpu/s390/c1_LIR_s390.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2020, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2016 SAP SE. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
@@ -51,7 +51,7 @@ LIR_Opr LIR_OprFact::double_fpu(int reg1, int reg2) {
 void LIR_Address::verify() const {
   assert(base()->is_cpu_register(), "wrong base operand");
   assert(index()->is_illegal() || index()->is_double_cpu(), "wrong index operand");
-  assert(base()->type() == T_OBJECT || base()->type() == T_LONG || base()->type() == T_METADATA,
+  assert(base()->type() == T_ADDRESS || base()->type() == T_OBJECT || base()->type() == T_LONG || base()->type() == T_METADATA,
          "wrong type for addresses");
 }
 #endif // PRODUCT

src/hotspot/cpu/x86/c1_LIR_x86.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2020, 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
@@ -62,12 +62,12 @@ void LIR_Address::verify() const {
 #ifdef _LP64
   assert(base()->is_cpu_register(), "wrong base operand");
   assert(index()->is_illegal() || index()->is_double_cpu(), "wrong index operand");
-  assert(base()->type() == T_OBJECT || base()->type() == T_LONG || base()->type() == T_METADATA,
+  assert(base()->type() == T_ADDRESS || base()->type() == T_OBJECT || base()->type() == T_LONG || base()->type() == T_METADATA,
          "wrong type for addresses");
 #else
   assert(base()->is_single_cpu(), "wrong base operand");
   assert(index()->is_illegal() || index()->is_single_cpu(), "wrong index operand");
-  assert(base()->type() == T_OBJECT || base()->type() == T_INT || base()->type() == T_METADATA,
+  assert(base()->type() == T_ADDRESS || base()->type() == T_OBJECT || base()->type() == T_INT || base()->type() == T_METADATA,
          "wrong type for addresses");
 #endif
 }

src/hotspot/share/c1/c1_LIRGenerator.cpp

@@ -1315,8 +1315,12 @@ void LIRGenerator::do_isPrimitive(Intrinsic* x) {
 // Example: Thread.currentThread()
 void LIRGenerator::do_currentThread(Intrinsic* x) {
   assert(x->number_of_arguments() == 0, "wrong type");
+  LIR_Opr temp = new_register(T_ADDRESS);
   LIR_Opr reg = rlock_result(x);
-  __ move_wide(new LIR_Address(getThreadPointer(), in_bytes(JavaThread::threadObj_offset()), T_OBJECT), reg);
+  __ move(new LIR_Address(getThreadPointer(), in_bytes(JavaThread::threadObj_offset()), T_ADDRESS), temp);
+  // threadObj = ((OopHandle)_threadObj)->resolve();
+  access_load(IN_NATIVE, T_OBJECT,
+              LIR_OprFact::address(new LIR_Address(temp, T_OBJECT)), reg);
 }
 
 

src/hotspot/share/gc/g1/g1GCPhaseTimes.cpp

@@ -58,7 +58,6 @@ G1GCPhaseTimes::G1GCPhaseTimes(STWGCTimer* gc_timer, uint max_gc_threads) :
 
   // Root scanning phases
   _gc_par_phases[ThreadRoots] = new WorkerDataArray<double>("ThreadRoots", "Thread Roots (ms):", max_gc_threads);
-  _gc_par_phases[UniverseRoots] = new WorkerDataArray<double>("UniverseRoots", "Universe Roots (ms):", max_gc_threads);
   _gc_par_phases[ObjectSynchronizerRoots] = new WorkerDataArray<double>("ObjectSynchronizerRoots", "ObjectSynchronizer Roots (ms):", max_gc_threads);
   _gc_par_phases[CLDGRoots] = new WorkerDataArray<double>("CLDGRoots", "CLDG Roots (ms):", max_gc_threads);
   AOT_ONLY(_gc_par_phases[AOTCodeRoots] = new WorkerDataArray<double>("AOTCodeRoots", "AOT Root Scan (ms):", max_gc_threads);)

src/hotspot/share/gc/g1/g1GCPhaseTimes.hpp

@@ -48,7 +48,6 @@ class G1GCPhaseTimes : public CHeapObj<mtGC> {
     GCWorkerStart,
     ExtRootScan,
     ThreadRoots,
-    UniverseRoots,
     ObjectSynchronizerRoots,
     CLDGRoots,
     AOT_ONLY(AOTCodeRoots COMMA)

src/hotspot/share/gc/g1/g1RootProcessor.cpp

@@ -43,7 +43,6 @@
 #include "gc/shared/oopStorageSetParState.inline.hpp"
 #include "gc/shared/referenceProcessor.hpp"
 #include "memory/allocation.inline.hpp"
-#include "memory/universe.hpp"
 #include "runtime/mutex.hpp"
 #include "utilities/macros.hpp"
 
@@ -181,13 +180,6 @@ void G1RootProcessor::process_vm_roots(G1RootClosures* closures,
                                        uint worker_id) {
   OopClosure* strong_roots = closures->strong_oops();
 
-  {
-    G1GCParPhaseTimesTracker x(phase_times, G1GCPhaseTimes::UniverseRoots, worker_id);
-    if (_process_strong_tasks.try_claim_task(G1RP_PS_Universe_oops_do)) {
-      Universe::oops_do(strong_roots);
-    }
-  }
-
   {
     G1GCParPhaseTimesTracker x(phase_times, G1GCPhaseTimes::ObjectSynchronizerRoots, worker_id);
     if (_process_strong_tasks.try_claim_task(G1RP_PS_ObjectSynchronizer_oops_do)) {

src/hotspot/share/gc/parallel/psParallelCompact.cpp

@@ -2008,10 +2008,6 @@ static void mark_from_roots_work(ParallelRootType::Value root_type, uint worker_
   PCMarkAndPushClosure mark_and_push_closure(cm);
 
   switch (root_type) {
-    case ParallelRootType::universe:
-      Universe::oops_do(&mark_and_push_closure);
-      break;
-
     case ParallelRootType::object_synchronizer:
       ObjectSynchronizer::oops_do(&mark_and_push_closure);
       break;
@@ -2225,7 +2221,6 @@ void PSParallelCompact::adjust_roots(ParCompactionManager* cm) {
   PCAdjustPointerClosure oop_closure(cm);
 
   // General strong roots.
-  Universe::oops_do(&oop_closure);
   Threads::oops_do(&oop_closure, NULL);
   ObjectSynchronizer::oops_do(&oop_closure);
   OopStorageSet::strong_oops_do(&oop_closure);

src/hotspot/share/gc/parallel/psRootType.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2020, 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
@@ -34,7 +34,6 @@ public:
   // The order reflects the order these roots are to be processed,
   // We do not want any holes in the enum as we enumerate these values by incrementing them.
   enum Value {
-    universe,
     object_synchronizer,
     class_loader_data,
     code_cache,

src/hotspot/share/gc/parallel/psScavenge.cpp

@@ -92,10 +92,6 @@ static void scavenge_roots_work(ParallelRootType::Value root_type, uint worker_i
   PSPromoteRootsClosure  roots_to_old_closure(pm);
 
   switch (root_type) {
-    case ParallelRootType::universe:
-      Universe::oops_do(&roots_closure);
-      break;
-
     case ParallelRootType::object_synchronizer:
       ObjectSynchronizer::oops_do(&roots_closure);
       break;

src/hotspot/share/gc/shared/c2/barrierSetC2.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2020, 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
@@ -141,6 +141,7 @@ Node* BarrierSetC2::load_at_resolved(C2Access& access, const Type* val_type) con
   bool control_dependent = (decorators & C2_CONTROL_DEPENDENT_LOAD) != 0;
   bool unknown_control = (decorators & C2_UNKNOWN_CONTROL_LOAD) != 0;
   bool unsafe = (decorators & C2_UNSAFE_ACCESS) != 0;
+  bool immutable = (decorators & C2_IMMUTABLE_MEMORY) != 0;
 
   bool in_native = (decorators & IN_NATIVE) != 0;
 
@@ -153,10 +154,14 @@ Node* BarrierSetC2::load_at_resolved(C2Access& access, const Type* val_type) con
     GraphKit* kit = parse_access.kit();
     Node* control = control_dependent ? kit->control() : NULL;
 
-    if (in_native) {
+    if (immutable) {
-      load = kit->make_load(control, adr, val_type, access.type(), mo, dep,
+      assert(!requires_atomic_access, "can't ensure atomicity");
-                            requires_atomic_access, unaligned,
+      Compile* C = Compile::current();
+      Node* mem = kit->immutable_memory();
+      load = LoadNode::make(kit->gvn(), control, mem, adr,
+                            adr_type, val_type, access.type(), mo, dep, unaligned,
                             mismatched, unsafe, access.barrier_data());
+      load = kit->gvn().transform(load);
     } else {
       load = kit->make_load(control, adr, val_type, access.type(), adr_type, mo,
                             dep, requires_atomic_access, unaligned, mismatched, unsafe,

src/hotspot/share/gc/shared/c2/barrierSetC2.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2020, 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
@@ -54,6 +54,8 @@ const DecoratorSet C2_READ_ACCESS            = DECORATOR_LAST << 8;
 const DecoratorSet C2_TIGHTLY_COUPLED_ALLOC  = DECORATOR_LAST << 9;
 // Loads and stores from an arraycopy being optimized
 const DecoratorSet C2_ARRAY_COPY             = DECORATOR_LAST << 10;
+// Loads from immutable memory
+const DecoratorSet C2_IMMUTABLE_MEMORY       = DECORATOR_LAST << 11;
 
 class Compile;
 class ConnectionGraph;

src/hotspot/share/gc/shared/genCollectedHeap.cpp

@@ -817,10 +817,6 @@ void GenCollectedHeap::process_roots(StrongRootsScope* scope,
   bool is_par = scope->n_threads() > 1;
   Threads::possibly_parallel_oops_do(is_par, strong_roots, roots_from_code_p);
 
-  if (_process_strong_tasks->try_claim_task(GCH_PS_Universe_oops_do)) {
-    Universe::oops_do(strong_roots);
-  }
-
   if (_process_strong_tasks->try_claim_task(GCH_PS_ObjectSynchronizer_oops_do)) {
     ObjectSynchronizer::oops_do(strong_roots);
   }

src/hotspot/share/gc/shared/genCollectedHeap.hpp

@@ -105,7 +105,6 @@ protected:
 
   // The set of potentially parallel tasks in root scanning.
   enum GCH_strong_roots_tasks {
-    GCH_PS_Universe_oops_do,
     GCH_PS_ObjectSynchronizer_oops_do,
     GCH_PS_OopStorageSet_oops_do,
     GCH_PS_ClassLoaderDataGraph_oops_do,

src/hotspot/share/gc/shared/oopStorageSet.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2020, 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
@@ -37,7 +37,7 @@ class OopStorageSet : public AllStatic {
 
 public:
   // Must be updated when new OopStorages are introduced
-  static const uint strong_count = 2;
+  static const uint strong_count = 3;
   static const uint weak_count = 4 JFR_ONLY(+ 1);
   static const uint all_count = strong_count + weak_count;
 

src/hotspot/share/gc/shenandoah/shenandoahPhaseTimings.hpp

@@ -37,7 +37,6 @@ class outputStream;
   f(CNT_PREFIX ## TotalWork,                DESC_PREFIX "<total>")                     \
   f(CNT_PREFIX ## ThreadRoots,              DESC_PREFIX "Thread Roots")                \
   f(CNT_PREFIX ## CodeCacheRoots,           DESC_PREFIX "Code Cache Roots")            \
-  f(CNT_PREFIX ## UniverseRoots,            DESC_PREFIX "Universe Roots")              \
   f(CNT_PREFIX ## VMStrongRoots,            DESC_PREFIX "VM Strong Roots")             \
   f(CNT_PREFIX ## VMWeakRoots,              DESC_PREFIX "VM Weak Roots")               \
   f(CNT_PREFIX ## ObjectSynchronizerRoots,  DESC_PREFIX "Synchronizer Roots")          \

src/hotspot/share/gc/shenandoah/shenandoahRootProcessor.cpp

@@ -37,7 +37,6 @@
 #include "gc/shenandoah/shenandoahVMOperations.hpp"
 #include "memory/iterator.hpp"
 #include "memory/resourceArea.hpp"
-#include "memory/universe.hpp"
 #include "runtime/thread.hpp"
 
 ShenandoahSerialRoot::ShenandoahSerialRoot(ShenandoahSerialRoot::OopsDo oops_do,
@@ -53,12 +52,10 @@ void ShenandoahSerialRoot::oops_do(OopClosure* cl, uint worker_id) {
 }
 
 ShenandoahSerialRoots::ShenandoahSerialRoots(ShenandoahPhaseTimings::Phase phase) :
-  _universe_root(&Universe::oops_do, phase, ShenandoahPhaseTimings::UniverseRoots),
   _object_synchronizer_root(&ObjectSynchronizer::oops_do, phase, ShenandoahPhaseTimings::ObjectSynchronizerRoots) {
 }
 
 void ShenandoahSerialRoots::oops_do(OopClosure* cl, uint worker_id) {
-  _universe_root.oops_do(cl, worker_id);
   _object_synchronizer_root.oops_do(cl, worker_id);
 }
 

src/hotspot/share/gc/shenandoah/shenandoahRootProcessor.hpp

@@ -51,7 +51,6 @@ public:
 
 class ShenandoahSerialRoots {
 private:
-  ShenandoahSerialRoot  _universe_root;
   ShenandoahSerialRoot  _object_synchronizer_root;
 public:
   ShenandoahSerialRoots(ShenandoahPhaseTimings::Phase phase);

src/hotspot/share/gc/shenandoah/shenandoahRootVerifier.cpp

@@ -37,7 +37,6 @@
 #include "gc/shared/oopStorage.inline.hpp"
 #include "gc/shared/oopStorageSet.hpp"
 #include "gc/shared/weakProcessor.inline.hpp"
-#include "memory/universe.hpp"
 #include "runtime/thread.hpp"
 #include "utilities/debug.hpp"
 
@@ -75,7 +74,6 @@ void ShenandoahRootVerifier::oops_do(OopClosure* oops) {
 
   if (verify(SerialRoots)) {
     shenandoah_assert_safepoint();
-    Universe::oops_do(oops);
     ObjectSynchronizer::oops_do(oops);
   }
 
@@ -119,7 +117,6 @@ void ShenandoahRootVerifier::roots_do(OopClosure* oops) {
   CLDToOopClosure clds(oops, ClassLoaderData::_claim_none);
   ClassLoaderDataGraph::cld_do(&clds);
 
-  Universe::oops_do(oops);
   JNIHandles::oops_do(oops);
   ObjectSynchronizer::oops_do(oops);
   Universe::vm_global()->oops_do(oops);
@@ -145,7 +142,6 @@ void ShenandoahRootVerifier::strong_roots_do(OopClosure* oops) {
   CLDToOopClosure clds(oops, ClassLoaderData::_claim_none);
   ClassLoaderDataGraph::roots_cld_do(&clds, NULL);
 
-  Universe::oops_do(oops);
   JNIHandles::oops_do(oops);
   ObjectSynchronizer::oops_do(oops);
   Universe::vm_global()->oops_do(oops);

src/hotspot/share/gc/z/zRootsIterator.cpp

@@ -54,7 +54,6 @@
 static const ZStatSubPhase ZSubPhasePauseRootsSetup("Pause Roots Setup");
 static const ZStatSubPhase ZSubPhasePauseRoots("Pause Roots");
 static const ZStatSubPhase ZSubPhasePauseRootsTeardown("Pause Roots Teardown");
-static const ZStatSubPhase ZSubPhasePauseRootsUniverse("Pause Roots Universe");
 static const ZStatSubPhase ZSubPhasePauseRootsObjectSynchronizer("Pause Roots ObjectSynchronizer");
 static const ZStatSubPhase ZSubPhasePauseRootsJVMTIWeakExport("Pause Roots JVMTIWeakExport");
 static const ZStatSubPhase ZSubPhasePauseRootsVMThread("Pause Roots VM Thread");
@@ -185,7 +184,6 @@ void ZJavaThreadsIterator::threads_do(ThreadClosure* cl) {
 ZRootsIterator::ZRootsIterator(bool visit_jvmti_weak_export) :
     _visit_jvmti_weak_export(visit_jvmti_weak_export),
     _java_threads_iter(),
-    _universe(this),
     _object_synchronizer(this),
     _jvmti_weak_export(this),
     _vm_thread(this),
@@ -213,11 +211,6 @@ ZRootsIterator::~ZRootsIterator() {
   COMPILER2_OR_JVMCI_PRESENT(DerivedPointerTable::update_pointers());
 }
 
-void ZRootsIterator::do_universe(ZRootsIteratorClosure* cl) {
-  ZStatTimer timer(ZSubPhasePauseRootsUniverse);
-  Universe::oops_do(cl);
-}
-
 void ZRootsIterator::do_object_synchronizer(ZRootsIteratorClosure* cl) {
   ZStatTimer timer(ZSubPhasePauseRootsObjectSynchronizer);
   ObjectSynchronizer::oops_do(cl);
@@ -248,7 +241,6 @@ void ZRootsIterator::do_code_cache(ZRootsIteratorClosure* cl) {
 
 void ZRootsIterator::oops_do(ZRootsIteratorClosure* cl) {
   ZStatTimer timer(ZSubPhasePauseRoots);
-  _universe.oops_do(cl);
   _object_synchronizer.oops_do(cl);
   _vm_thread.oops_do(cl);
   _java_threads.oops_do(cl);

src/hotspot/share/gc/z/zRootsIterator.hpp

@@ -110,14 +110,12 @@ private:
   const bool           _visit_jvmti_weak_export;
   ZJavaThreadsIterator _java_threads_iter;
 
-  void do_universe(ZRootsIteratorClosure* cl);
   void do_object_synchronizer(ZRootsIteratorClosure* cl);
   void do_jvmti_weak_export(ZRootsIteratorClosure* cl);
   void do_vm_thread(ZRootsIteratorClosure* cl);
   void do_java_threads(ZRootsIteratorClosure* cl);
   void do_code_cache(ZRootsIteratorClosure* cl);
 
-  ZSerialOopsDo<ZRootsIterator, &ZRootsIterator::do_universe>            _universe;
   ZSerialOopsDo<ZRootsIterator, &ZRootsIterator::do_object_synchronizer> _object_synchronizer;
   ZSerialOopsDo<ZRootsIterator, &ZRootsIterator::do_jvmti_weak_export>   _jvmti_weak_export;
   ZSerialOopsDo<ZRootsIterator, &ZRootsIterator::do_vm_thread>           _vm_thread;

src/hotspot/share/jfr/leakprofiler/chains/rootSetClosure.cpp

@@ -34,7 +34,6 @@
 #include "jfr/leakprofiler/chains/edgeQueue.hpp"
 #include "jfr/leakprofiler/chains/rootSetClosure.hpp"
 #include "jfr/leakprofiler/utilities/unifiedOopRef.inline.hpp"
-#include "memory/universe.hpp"
 #include "oops/access.inline.hpp"
 #include "oops/oop.inline.hpp"
 #include "runtime/synchronizer.hpp"
@@ -73,7 +72,6 @@ void RootSetClosure<Delegate>::process() {
   // We don't follow code blob oops, because they have misaligned oops.
   Threads::oops_do(this, NULL);
   ObjectSynchronizer::oops_do(this);
-  Universe::oops_do(this);
   OopStorageSet::strong_oops_do(this);
   AOTLoader::oops_do(this);
 }

src/hotspot/share/jfr/leakprofiler/checkpoint/rootResolver.cpp

@@ -33,7 +33,6 @@
 #include "jfr/leakprofiler/checkpoint/rootResolver.hpp"
 #include "jfr/utilities/jfrThreadIterator.hpp"
 #include "memory/iterator.hpp"
-#include "memory/universe.hpp"
 #include "oops/klass.hpp"
 #include "oops/oop.hpp"
 #include "prims/jvmtiThreadState.hpp"
@@ -97,7 +96,6 @@ class ReferenceToRootClosure : public StackObj {
 
   bool do_cldg_roots();
   bool do_object_synchronizer_roots();
-  bool do_universe_roots();
   bool do_oop_storage_roots();
   bool do_string_table_roots();
   bool do_aot_loader_roots();
@@ -138,13 +136,6 @@ bool ReferenceToRootClosure::do_object_synchronizer_roots() {
   return rlc.complete();
 }
 
-bool ReferenceToRootClosure::do_universe_roots() {
-  assert(!complete(), "invariant");
-  ReferenceLocateClosure rlc(_callback, OldObjectRoot::_universe, OldObjectRoot::_type_undetermined, NULL);
-  Universe::oops_do(&rlc);
-  return rlc.complete();
-}
-
 bool ReferenceToRootClosure::do_oop_storage_roots() {
   int i = 0;
   for (OopStorageSet::Iterator it = OopStorageSet::strong_iterator(); !it.is_end(); ++it, ++i) {
@@ -185,11 +176,6 @@ bool ReferenceToRootClosure::do_roots() {
     return true;
   }
 
-  if (do_universe_roots()) {
-   _complete = true;
-    return true;
-  }
-
   if (do_oop_storage_roots()) {
    _complete = true;
     return true;

src/hotspot/share/jvmci/vmStructs_jvmci.cpp

@@ -170,7 +170,7 @@
   nonstatic_field(JVMCICompileState,           _jvmti_can_post_on_exceptions,                 jbyte)                                 \
   nonstatic_field(JVMCICompileState,           _jvmti_can_pop_frame,                          jbyte)                                 \
                                                                                                                                      \
-  nonstatic_field(JavaThread,                  _threadObj,                                    oop)                                   \
+  nonstatic_field(JavaThread,                  _threadObj,                                    OopHandle)                             \
   nonstatic_field(JavaThread,                  _anchor,                                       JavaFrameAnchor)                       \
   nonstatic_field(JavaThread,                  _vm_result,                                    oop)                                   \
   volatile_nonstatic_field(JavaThread,         _exception_oop,                                oop)                                   \

src/hotspot/share/memory/universe.cpp

@@ -223,11 +223,6 @@ void Universe::basic_type_classes_do(KlassClosure *closure) {
   }
 }
 
-void Universe::oops_do(OopClosure* f) {
-
-  ThreadsSMRSupport::exiting_threads_oops_do(f);
-}
-
 void LatestMethodCache::metaspace_pointers_do(MetaspaceClosure* it) {
   it->push(&_klass);
 }

src/hotspot/share/memory/universe.hpp

@@ -328,12 +328,6 @@ class Universe: AllStatic {
   static bool        should_fill_in_stack_trace(Handle throwable);
   static void check_alignment(uintx size, uintx alignment, const char* name);
 
-  // Iteration
-
-  // Apply "f" to the addresses of all the direct heap pointers maintained
-  // as static fields of "Universe".
-  static void oops_do(OopClosure* f);
-
   // CDS support
   static void serialize(SerializeClosure* f);
 

src/hotspot/share/opto/graphKit.cpp

@@ -1614,7 +1614,7 @@ Node* GraphKit::access_load(Node* adr,   // actual adress to load val at
     return top(); // Dead path ?
   }
 
-  C2AccessValuePtr addr(adr, NULL);
+  C2AccessValuePtr addr(adr, adr->bottom_type()->is_ptr());
   C2ParseAccess access(this, decorators | C2_READ_ACCESS, bt, NULL, addr);
   if (access.is_raw()) {
     return _barrier_set->BarrierSetC2::load_at(access, val_type);

src/hotspot/share/opto/library_call.cpp

@@ -1096,9 +1096,10 @@ Node* LibraryCallKit::generate_current_thread(Node* &tls_output) {
   const Type* thread_type  = TypeOopPtr::make_from_klass(thread_klass)->cast_to_ptr_type(TypePtr::NotNull);
   Node* thread = _gvn.transform(new ThreadLocalNode());
   Node* p = basic_plus_adr(top()/*!oop*/, thread, in_bytes(JavaThread::threadObj_offset()));
-  Node* threadObj = _gvn.transform(LoadNode::make(_gvn, NULL, immutable_memory(), p, p->bottom_type()->is_ptr(), thread_type, T_OBJECT, MemNode::unordered));
   tls_output = thread;
-  return threadObj;
+  Node* thread_obj_handle = LoadNode::make(_gvn, NULL, immutable_memory(), p, p->bottom_type()->is_ptr(), TypeRawPtr::NOTNULL, T_ADDRESS, MemNode::unordered);
+  thread_obj_handle = _gvn.transform(thread_obj_handle);
+  return access_load(thread_obj_handle, thread_type, T_OBJECT, IN_NATIVE | C2_IMMUTABLE_MEMORY);
 }
 
 

src/hotspot/share/opto/memnode.cpp

@@ -811,7 +811,9 @@ bool LoadNode::is_immutable_value(Node* adr) {
   return (adr->is_AddP() && adr->in(AddPNode::Base)->is_top() &&
           adr->in(AddPNode::Address)->Opcode() == Op_ThreadLocal &&
           (adr->in(AddPNode::Offset)->find_intptr_t_con(-1) ==
-           in_bytes(JavaThread::osthread_offset())));
+           in_bytes(JavaThread::osthread_offset()) ||
+           adr->in(AddPNode::Offset)->find_intptr_t_con(-1) ==
+           in_bytes(JavaThread::threadObj_offset())));
 }
 #endif
 

src/hotspot/share/prims/jvmtiTagMap.cpp

@@ -3030,7 +3030,7 @@ inline bool VM_HeapWalkOperation::collect_simple_roots() {
   // Many of these won't be visible but others (such as instances of important
   // exceptions) will be visible.
   blk.set_kind(JVMTI_HEAP_REFERENCE_OTHER);
-  Universe::oops_do(&blk);
+  Universe::vm_global()->oops_do(&blk);
   if (blk.stopped()) {
     return false;
   }

src/hotspot/share/runtime/serviceThread.cpp

@@ -31,6 +31,7 @@
 #include "gc/shared/oopStorage.hpp"
 #include "gc/shared/oopStorageSet.hpp"
 #include "memory/universe.hpp"
+#include "oops/oopHandle.inline.hpp"
 #include "runtime/handles.inline.hpp"
 #include "runtime/interfaceSupport.inline.hpp"
 #include "runtime/javaCalls.hpp"
@@ -53,6 +54,29 @@ JvmtiDeferredEvent* ServiceThread::_jvmti_event = NULL;
 // to add this field to the per-JavaThread event queue.  TODO: fix this sometime later
 JvmtiDeferredEventQueue ServiceThread::_jvmti_service_queue;
 
+// Defer releasing JavaThread OopHandle to the ServiceThread
+class OopHandleList : public CHeapObj<mtInternal> {
+  OopHandle      _handle;
+  OopHandleList* _next;
+ public:
+   OopHandleList(OopHandle h, OopHandleList* next) : _handle(h), _next(next) {}
+   ~OopHandleList() {
+     _handle.release(JavaThread::thread_oop_storage());
+   }
+   OopHandleList* next() const { return _next; }
+};
+
+static OopHandleList* _oop_handle_list = NULL;
+
+static void release_oop_handles() {
+  assert_lock_strong(Service_lock);
+  while (_oop_handle_list != NULL) {
+    OopHandleList* l = _oop_handle_list;
+    _oop_handle_list = l->next();
+    delete l;
+  }
+}
+
 void ServiceThread::initialize() {
   EXCEPTION_MARK;
 
@@ -139,6 +163,7 @@ void ServiceThread::service_thread_entry(JavaThread* jt, TRAPS) {
               (thread_id_table_work = ThreadIdTable::has_work()) |
               (protection_domain_table_work = SystemDictionary::pd_cache_table()->has_work()) |
               (oopstorage_work = OopStorage::has_cleanup_work_and_reset()) |
+              (_oop_handle_list != NULL) |
               (deflate_idle_monitors = ObjectSynchronizer::is_async_deflation_needed())
              ) == 0) {
         // Wait until notified that there is some work to do.
@@ -152,6 +177,11 @@ void ServiceThread::service_thread_entry(JavaThread* jt, TRAPS) {
         jvmti_event = _jvmti_service_queue.dequeue();
         _jvmti_event = &jvmti_event;
       }
+
+      // Release thread OopHandles in lock
+      if (_oop_handle_list != NULL) {
+        release_oop_handles();
+      }
     }
 
     if (stringtable_work) {
@@ -238,3 +268,10 @@ void ServiceThread::nmethods_do(CodeBlobClosure* cf) {
     _jvmti_service_queue.nmethods_do(cf);
   }
 }
+
+void ServiceThread::add_oop_handle_release(OopHandle handle) {
+  MutexLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
+  OopHandleList* new_head = new OopHandleList(handle, _oop_handle_list);
+  _oop_handle_list = new_head;
+  Service_lock->notify_all();
+}

src/hotspot/share/runtime/serviceThread.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2020, 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
@@ -52,6 +52,7 @@ class ServiceThread : public JavaThread {
 
   // Add event to the service thread event queue.
   static void enqueue_deferred_event(JvmtiDeferredEvent* event);
+  static void add_oop_handle_release(OopHandle handle);
 
   // GC support
   void oops_do(OopClosure* f, CodeBlobClosure* cf);

src/hotspot/share/runtime/thread.cpp

@@ -37,6 +37,8 @@
 #include "gc/shared/barrierSet.hpp"
 #include "gc/shared/gcId.hpp"
 #include "gc/shared/gcLocker.inline.hpp"
+#include "gc/shared/oopStorage.hpp"
+#include "gc/shared/oopStorageSet.hpp"
 #include "gc/shared/workgroup.hpp"
 #include "interpreter/interpreter.hpp"
 #include "interpreter/linkResolver.hpp"
@@ -1055,12 +1057,12 @@ static Handle create_initial_thread_group(TRAPS) {
   return main_instance;
 }
 
-// Creates the initial Thread
+// Creates the initial Thread, and sets it to running.
-static oop create_initial_thread(Handle thread_group, JavaThread* thread,
+static void create_initial_thread(Handle thread_group, JavaThread* thread,
                                  TRAPS) {
   InstanceKlass* ik = SystemDictionary::Thread_klass();
   assert(ik->is_initialized(), "must be");
-  instanceHandle thread_oop = ik->allocate_instance_handle(CHECK_NULL);
+  instanceHandle thread_oop = ik->allocate_instance_handle(CHECK);
 
   // Cannot use JavaCalls::construct_new_instance because the java.lang.Thread
   // constructor calls Thread.current(), which must be set here for the
@@ -1069,7 +1071,7 @@ static oop create_initial_thread(Handle thread_group, JavaThread* thread,
   java_lang_Thread::set_priority(thread_oop(), NormPriority);
   thread->set_threadObj(thread_oop());
 
-  Handle string = java_lang_String::create_from_str("main", CHECK_NULL);
+  Handle string = java_lang_String::create_from_str("main", CHECK);
 
   JavaValue result(T_VOID);
   JavaCalls::call_special(&result, thread_oop,
@@ -1078,8 +1080,12 @@ static oop create_initial_thread(Handle thread_group, JavaThread* thread,
                           vmSymbols::threadgroup_string_void_signature(),
                           thread_group,
                           string,
-                          CHECK_NULL);
+                          CHECK);
-  return thread_oop();
+
+  // Set thread status to running since main thread has
+  // been started and running.
+  java_lang_Thread::set_thread_status(thread_oop(),
+                                      java_lang_Thread::RUNNABLE);
 }
 
 char java_runtime_name[128] = "";
@@ -1187,6 +1193,23 @@ static void call_postVMInitHook(TRAPS) {
   }
 }
 
+// Initialized by VMThread at vm_global_init
+static OopStorage* _thread_oop_storage = NULL;
+
+oop  JavaThread::threadObj() const    {
+  return _threadObj.resolve();
+}
+
+void JavaThread::set_threadObj(oop p) {
+  assert(_thread_oop_storage != NULL, "not yet initialized");
+  _threadObj = OopHandle(_thread_oop_storage, p);
+}
+
+OopStorage* JavaThread::thread_oop_storage() {
+  assert(_thread_oop_storage != NULL, "not yet initialized");
+  return _thread_oop_storage;
+}
+
 void JavaThread::allocate_threadObj(Handle thread_group, const char* thread_name,
                                     bool daemon, TRAPS) {
   assert(thread_group.not_null(), "thread group should be specified");
@@ -1653,7 +1676,6 @@ void JavaThread::initialize() {
   // Initialize fields
 
   set_saved_exception_pc(NULL);
-  set_threadObj(NULL);
   _anchor.clear();
   set_entry_point(NULL);
   set_jni_functions(jni_functions());
@@ -1758,7 +1780,7 @@ void JavaThread::interrupt() {
 bool JavaThread::is_interrupted(bool clear_interrupted) {
   debug_only(check_for_dangling_thread_pointer(this);)
 
-  if (threadObj() == NULL) {
+  if (_threadObj.peek() == NULL) {
     // If there is no j.l.Thread then it is impossible to have
     // been interrupted. We can find NULL during VM initialization
     // or when a JNI thread is still in the process of attaching.
@@ -1871,6 +1893,9 @@ JavaThread::JavaThread(ThreadFunction entry_point, size_t stack_sz) :
 
 JavaThread::~JavaThread() {
 
+  // Ask ServiceThread to release the threadObj OopHandle
+  ServiceThread::add_oop_handle_release(_threadObj);
+
   // JSR166 -- return the parker to the free list
   Parker::Release(_parker);
   _parker = NULL;
@@ -1971,7 +1996,7 @@ void JavaThread::run() {
 
 void JavaThread::thread_main_inner() {
   assert(JavaThread::current() == this, "sanity check");
-  assert(this->threadObj() != NULL, "just checking");
+  assert(_threadObj.peek() != NULL, "just checking");
 
   // Execute thread entry point unless this thread has a pending exception
   // or has been stopped before starting.
@@ -3015,7 +3040,6 @@ void JavaThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
 
   // Traverse instance variables at the end since the GC may be moving things
   // around using this function
-  f->do_oop((oop*) &_threadObj);
   f->do_oop((oop*) &_vm_result);
   f->do_oop((oop*) &_exception_oop);
   f->do_oop((oop*) &_pending_async_exception);
@@ -3717,13 +3741,7 @@ void Threads::initialize_java_lang_classes(JavaThread* main_thread, TRAPS) {
   Handle thread_group = create_initial_thread_group(CHECK);
   Universe::set_main_thread_group(thread_group());
   initialize_class(vmSymbols::java_lang_Thread(), CHECK);
-  oop thread_object = create_initial_thread(thread_group, main_thread, CHECK);
+  create_initial_thread(thread_group, main_thread, CHECK);
-  main_thread->set_threadObj(thread_object);
-
-  // Set thread status to running since main thread has
-  // been started and running.
-  java_lang_Thread::set_thread_status(thread_object,
-                                      java_lang_Thread::RUNNABLE);
 
   // The VM creates objects of this class.
   initialize_class(vmSymbols::java_lang_Module(), CHECK);
@@ -3886,6 +3904,9 @@ jint Threads::create_vm(JavaVMInitArgs* args, bool* canTryAgain) {
   }
 #endif // INCLUDE_JVMCI
 
+  // Initialize OopStorage for threadObj
+  _thread_oop_storage = OopStorageSet::create_strong("Thread OopStorage");
+
   // Attach the main thread to this os thread
   JavaThread* main_thread = new JavaThread();
   main_thread->set_thread_state(_thread_in_vm);

src/hotspot/share/runtime/thread.hpp

@@ -92,6 +92,8 @@ class JVMCIPrimitiveArray;
 class Metadata;
 class ResourceArea;
 
+class OopStorage;
+
 DEBUG_ONLY(class ResourceMark;)
 
 class WorkerThread;
@@ -1017,7 +1019,7 @@ class JavaThread: public Thread {
   friend class ThreadsSMRSupport; // to access _threadObj for exiting_threads_oops_do
  private:
   bool           _on_thread_list;                // Is set when this JavaThread is added to the Threads list
-  oop            _threadObj;                     // The Java level thread object
+  OopHandle      _threadObj;                     // The Java level thread object
 
 #ifdef ASSERT
  private:
@@ -1277,8 +1279,8 @@ class JavaThread: public Thread {
 
   // Thread oop. threadObj() can be NULL for initial JavaThread
   // (or for threads attached via JNI)
-  oop threadObj() const                          { return _threadObj; }
+  oop threadObj() const;
-  void set_threadObj(oop p)                      { _threadObj = p; }
+  void set_threadObj(oop p);
 
   // Prepare thread and add to priority queue.  If a priority is
   // not specified, use the priority of the thread object. Threads_lock
@@ -2112,6 +2114,7 @@ public:
   void interrupt();
   bool is_interrupted(bool clear_interrupted);
 
+  static OopStorage* thread_oop_storage();
 };
 
 // Inline implementation of JavaThread::current

src/hotspot/share/runtime/threadSMR.cpp

@@ -41,9 +41,6 @@
 #include "utilities/resourceHash.hpp"
 #include "utilities/vmError.hpp"
 
-// List of exiting threads
-ThreadsSMRSupport::Holder* ThreadsSMRSupport::_exiting_threads = NULL;
-
 // The '_cnt', '_max' and '_times" fields are enabled via
 // -XX:+EnableThreadSMRStatistics:
 
@@ -927,8 +924,6 @@ void ThreadsSMRSupport::release_stable_list_wake_up(bool is_nested) {
 
 void ThreadsSMRSupport::remove_thread(JavaThread *thread) {
 
-  ThreadsSMRSupport::add_exiting_thread(thread);
-
   if (ThreadIdTable::is_initialized()) {
     jlong tid = SharedRuntime::get_java_tid(thread);
     ThreadIdTable::remove_thread(tid);
@@ -998,7 +993,6 @@ void ThreadsSMRSupport::wait_until_not_protected(JavaThread *thread) {
         // This is the common case.
         ThreadsSMRSupport::clear_delete_notify();
         ThreadsSMRSupport::delete_lock()->unlock();
-        ThreadsSMRSupport::remove_exiting_thread(thread);
         break;
       }
       if (!has_logged_once) {
@@ -1188,47 +1182,3 @@ void ThreadsSMRSupport::print_info_elements_on(outputStream* st, ThreadsList* t_
     cnt++;
   }
 }
-
-void ThreadsSMRSupport::add_exiting_thread(JavaThread* thread) {
-  assert(thread == JavaThread::current(), "invariant");
-  assert(Threads_lock->owned_by_self(), "invariant");
-  assert(!contains_exiting_thread(thread), "invariant");
-  Holder* h = new Holder(thread, _exiting_threads);
-  _exiting_threads = h;
-}
-
-void ThreadsSMRSupport::remove_exiting_thread(JavaThread* thread) {
-  assert(thread == JavaThread::current(), "invariant");
-  assert(Threads_lock->owned_by_self(), "invariant");
-  // If a thread fails to initialize fully it can be deleted immediately
-  // so we won't remove it from the ThreadsList and so never add it to the
-  // exiting thread list - so we can't assert(contains_exiting_thread(p)) here.
-
-  for (Holder* current = _exiting_threads, **prev_next = &_exiting_threads;
-       current != NULL;
-       prev_next = &current->_next, current = current->_next) {
-    if (current->_thread == thread) {
-      *prev_next = current->_next;
-      delete current;
-      break;
-    }
-  }
-}
-
-#ifdef ASSERT
-bool ThreadsSMRSupport::contains_exiting_thread(JavaThread* thread) {
-  for (Holder* current = _exiting_threads; current != NULL; current = current->_next) {
-    if (current->_thread == thread) {
-      return true;
-    }
-  }
-  return false;
-}
-#endif
-
-void ThreadsSMRSupport::exiting_threads_oops_do(OopClosure* f) {
-  assert_locked_or_safepoint(Threads_lock);
-  for (Holder* current = _exiting_threads; current != NULL; current = current->_next) {
-    f->do_oop((oop*) &current->_thread->_threadObj);
-  }
-}

src/hotspot/share/runtime/threadSMR.hpp

@@ -82,33 +82,12 @@ class ThreadClosure;
 // but that target JavaThread * will not be deleted until it is no
 // longer protected by a ThreadsListHandle.
 //
-// Once a JavaThread has removed itself from the main ThreadsList it is
-// no longer visited by GC. To ensure that thread's threadObj() oop remains
-// valid while the thread is still accessible from a ThreadsListHandle we
-// maintain a special list of exiting threads:
-// - In remove() we add the exiting thread to the list (under the Threads_lock).
-// - In wait_until_not_protected() we remove it from the list (again under the
-//   Threads_lock).
-// - Universe::oops_do walks the list (at a safepoint so VMThread holds
-//   Threads_lock) and visits the _threadObj oop of each JavaThread.
-
 // SMR Support for the Threads class.
 //
 class ThreadsSMRSupport : AllStatic {
   friend class VMStructs;
   friend class SafeThreadsListPtr;  // for _nested_thread_list_max, delete_notify(), release_stable_list_wake_up() access
 
-  // Helper class for the exiting thread list
-  class Holder : public CHeapObj<mtInternal> {
-   public:
-    JavaThread* _thread;
-    Holder* _next;
-    Holder(JavaThread* thread, Holder* next) : _thread(thread), _next(next) {}
-  };
-
-  // The list of exiting threads
-  static Holder* _exiting_threads;
-
   // The coordination between ThreadsSMRSupport::release_stable_list() and
   // ThreadsSMRSupport::smr_delete() uses the delete_lock in order to
   // reduce the traffic on the Threads_lock.
@@ -170,12 +149,6 @@ class ThreadsSMRSupport : AllStatic {
   static void smr_delete(JavaThread *thread);
   static void update_tlh_stats(uint millis);
 
-  // Exiting thread list maintenance
-  static void add_exiting_thread(JavaThread* thread);
-  static void remove_exiting_thread(JavaThread* thread);
-  DEBUG_ONLY(static bool contains_exiting_thread(JavaThread* thread);)
-  static void exiting_threads_oops_do(OopClosure* f);
-
   // Logging and printing support:
   static void log_statistics();
   static void print_info_elements_on(outputStream* st, ThreadsList* t_list);

src/hotspot/share/runtime/vmStructs.cpp

@@ -740,7 +740,7 @@ typedef HashtableEntry<InstanceKlass*, mtClass>  KlassHashtableEntry;
   nonstatic_field(Thread,                      _current_waiting_monitor,                      ObjectMonitor*)                        \
   nonstatic_field(NamedThread,                 _name,                                         char*)                                 \
   nonstatic_field(NamedThread,                 _processed_thread,                             JavaThread*)                           \
-  nonstatic_field(JavaThread,                  _threadObj,                                    oop)                                   \
+  nonstatic_field(JavaThread,                  _threadObj,                                    OopHandle)                             \
   nonstatic_field(JavaThread,                  _anchor,                                       JavaFrameAnchor)                       \
   nonstatic_field(JavaThread,                  _vm_result,                                    oop)                                   \
   nonstatic_field(JavaThread,                  _vm_result_2,                                  Metadata*)                             \

src/hotspot/share/services/heapDumper.cpp

@@ -1859,8 +1859,9 @@ void VM_HeapDumper::work(uint worker_id) {
   // HPROF_GC_ROOT_JNI_GLOBAL
   JNIGlobalsDumper jni_dumper(writer());
   JNIHandles::oops_do(&jni_dumper);
-  Universe::oops_do(&jni_dumper);  // technically not jni roots, but global roots
+  // technically not jni roots, but global roots
   // for things like preallocated throwable backtraces
+  Universe::vm_global()->oops_do(&jni_dumper);
 
   // HPROF_GC_ROOT_STICKY_CLASS
   // These should be classes in the NULL class loader data, and not all classes

src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/runtime/JavaThread.java

@@ -43,7 +43,7 @@ import sun.jvm.hotspot.utilities.Observer;
 public class JavaThread extends Thread {
   private static final boolean DEBUG = System.getProperty("sun.jvm.hotspot.runtime.JavaThread.DEBUG") != null;
 
-  private static sun.jvm.hotspot.types.OopField threadObjField;
+  private static long          threadObjFieldOffset;
   private static AddressField  anchorField;
   private static AddressField  lastJavaSPField;
   private static AddressField  lastJavaPCField;
@@ -85,7 +85,8 @@ public class JavaThread extends Thread {
     Type type = db.lookupType("JavaThread");
     Type anchorType = db.lookupType("JavaFrameAnchor");
 
-    threadObjField    = type.getOopField("_threadObj");
+    threadObjFieldOffset = type.getField("_threadObj").getOffset();
+
     anchorField       = type.getAddressField("_anchor");
     lastJavaSPField   = anchorType.getAddressField("_last_Java_sp");
     lastJavaPCField   = anchorType.getAddressField("_last_Java_pc");
@@ -347,7 +348,9 @@ public class JavaThread extends Thread {
   public Oop getThreadObj() {
     Oop obj = null;
     try {
-      obj = VM.getVM().getObjectHeap().newOop(threadObjField.getValue(addr));
+      Address addr = getAddress().addOffsetTo(threadObjFieldOffset);
+      VMOopHandle vmOopHandle = VMObjectFactory.newObject(VMOopHandle.class, addr);
+      obj = vmOopHandle.resolve();
     } catch (Exception e) {
       e.printStackTrace();
     }

src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/GraalHotSpotVMConfig.java

@@ -375,7 +375,19 @@ public class GraalHotSpotVMConfig extends GraalHotSpotVMConfigAccess {
     public final int threadTlabOffset = getFieldOffset("Thread::_tlab", Integer.class, "ThreadLocalAllocBuffer");
     public final int javaThreadAnchorOffset = getFieldOffset("JavaThread::_anchor", Integer.class, "JavaFrameAnchor");
     public final int javaThreadShouldPostOnExceptionsFlagOffset = getFieldOffset("JavaThread::_should_post_on_exceptions_flag", Integer.class, "int", Integer.MIN_VALUE, JVMCI || JDK >= 12);
-    public final int threadObjectOffset = getFieldOffset("JavaThread::_threadObj", Integer.class, "oop");
+
+    public final boolean threadObjectFieldIsHandle;
+    public final int threadObjectOffset;
+    {
+        if (JDK <= 15) {
+            threadObjectFieldIsHandle = false;
+            threadObjectOffset = getFieldOffset("JavaThread::_threadObj", Integer.class, "oop");
+        } else {
+            threadObjectFieldIsHandle = true;
+            threadObjectOffset = getFieldOffset("JavaThread::_threadObj", Integer.class, "OopHandle");
+        }
+    }
+
     public final int osThreadOffset = getFieldOffset("JavaThread::_osthread", Integer.class, "OSThread*");
     public final int threadIsMethodHandleReturnOffset = getFieldOffset("JavaThread::_is_method_handle_return", Integer.class, "int");
     public final int threadObjectResultOffset = getFieldOffset("JavaThread::_vm_result", Integer.class, "oop");

src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/meta/HotSpotGraphBuilderPlugins.java

@@ -30,6 +30,7 @@ import static org.graalvm.compiler.hotspot.GraalHotSpotVMConfigAccess.JDK;
 import static org.graalvm.compiler.hotspot.HotSpotBackend.BASE64_ENCODE_BLOCK;
 import static org.graalvm.compiler.hotspot.HotSpotBackend.GHASH_PROCESS_BLOCKS;
 import static org.graalvm.compiler.hotspot.meta.HotSpotAOTProfilingPlugin.Options.TieredAOT;
+import static org.graalvm.compiler.hotspot.replacements.HotSpotReplacementsUtil.JAVA_THREAD_THREAD_OBJECT_HANDLE_LOCATION;
 import static org.graalvm.compiler.hotspot.replacements.HotSpotReplacementsUtil.JAVA_THREAD_THREAD_OBJECT_LOCATION;
 import static org.graalvm.compiler.java.BytecodeParserOptions.InlineDuringParsing;
 
@@ -427,12 +428,21 @@ public class HotSpotGraphBuilderPlugins {
                 AddressNode address = b.add(new OffsetAddressNode(thread, offset));
                 // JavaThread::_threadObj is never compressed
                 ObjectStamp stamp = StampFactory.objectNonNull(TypeReference.create(b.getAssumptions(), metaAccess.lookupJavaType(Thread.class)));
-                b.addPush(JavaKind.Object, new ReadNode(address, JAVA_THREAD_THREAD_OBJECT_LOCATION, stamp, BarrierType.NONE));
+                ReadNode value = b.add(new ReadNode(address, JAVA_THREAD_THREAD_OBJECT_LOCATION,
+                                config.threadObjectFieldIsHandle ? StampFactory.forKind(wordTypes.getWordKind()) : stamp, BarrierType.NONE));
+                if (config.threadObjectFieldIsHandle) {
+                    ValueNode handleOffset = ConstantNode.forIntegerKind(wordTypes.getWordKind(), 0, b.getGraph());
+                    AddressNode handleAddress = b.add(new OffsetAddressNode(value, handleOffset));
+                    value = b.add(new ReadNode(handleAddress, JAVA_THREAD_THREAD_OBJECT_HANDLE_LOCATION, stamp, BarrierType.NONE));
+                }
+                b.push(JavaKind.Object, value);
                 return true;
             }
         });
 
         if (config.osThreadInterruptedOffset != Integer.MAX_VALUE) {
+            // This substitution is no longer in use when threadObj is a handle
+            assert !config.threadObjectFieldIsHandle;
             r.registerMethodSubstitution(ThreadSubstitutions.class, "isInterrupted", Receiver.class, boolean.class);
         }
 

src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/replacements/HotSpotReplacementsUtil.java

@@ -308,6 +308,8 @@ public class HotSpotReplacementsUtil {
      */
     public static final LocationIdentity JAVA_THREAD_THREAD_OBJECT_LOCATION = NamedLocationIdentity.immutable("JavaThread::_threadObj");
 
+    public static final LocationIdentity JAVA_THREAD_THREAD_OBJECT_HANDLE_LOCATION = NamedLocationIdentity.immutable("JavaThread::_threadObj handle");
+
     @Fold
     public static int threadObjectOffset(@InjectedParameter GraalHotSpotVMConfig config) {
         return config.threadObjectOffset;

test/hotspot/jtreg/gc/g1/TestGCLogMessages.java

@@ -121,7 +121,6 @@ public class TestGCLogMessages {
         new LogMessageWithLevel("LAB Undo Waste", Level.DEBUG),
         // Ext Root Scan
         new LogMessageWithLevel("Thread Roots", Level.TRACE),
-        new LogMessageWithLevel("Universe Roots", Level.TRACE),
         new LogMessageWithLevel("ObjectSynchronizer Roots", Level.TRACE),
         new LogMessageWithLevel("CLDG Roots", Level.TRACE),
         new LogMessageWithLevel("CM RefProcessor Roots", Level.TRACE),

test/jdk/jdk/jfr/event/gc/collection/TestG1ParallelPhases.java

@@ -91,10 +91,10 @@ public class TestG1ParallelPhases {
         Set<String> allPhases = of(
             "ExtRootScan",
             "ThreadRoots",
-            "UniverseRoots",
             "ObjectSynchronizerRoots",
             "VM Global",
             "JNI Global",
+            "Thread OopStorage",
             "CLDGRoots",
             "CMRefRoots",
             "MergeER",