8022887: Assertion hit while using class and redefining it with RedefineClasses simultaneously

Summary: Need to refetch each method from InstanceKlass after all safepoints.  Removed leaky PreviousVersionInfo code.
Reviewed-by: dcubed, sspitsyn

src/share/vm/memory/metaspaceShared.cpp

@@ -103,9 +103,10 @@ static void calculate_fingerprints() {
     if (k->oop_is_instance()) {
       InstanceKlass* ik = InstanceKlass::cast(k);
       for (int i = 0; i < ik->methods()->length(); i++) {
-        ResourceMark rm;
         Method* m = ik->methods()->at(i);
-        (new Fingerprinter(m))->fingerprint();
+        Fingerprinter fp(m);
+        // The side effect of this call sets method's fingerprint field.
+        fp.fingerprint();
       }
     }
   }

src/share/vm/oops/instanceKlass.cpp

@@ -2846,25 +2846,18 @@ void InstanceKlass::print_on(outputStream* st) const {
   st->print(BULLET"class type annotations:  "); class_type_annotations()->print_value_on(st); st->cr();
   st->print(BULLET"field annotations:       "); fields_annotations()->print_value_on(st); st->cr();
   st->print(BULLET"field type annotations:  "); fields_type_annotations()->print_value_on(st); st->cr();
-  {
-    ResourceMark rm;
-    // PreviousVersionInfo objects returned via PreviousVersionWalker
-    // contain a GrowableArray of handles. We have to clean up the
-    // GrowableArray _after_ the PreviousVersionWalker destructor
-    // has destroyed the handles.
   {
     bool have_pv = false;
-      PreviousVersionWalker pvw((InstanceKlass*)this);
-      for (PreviousVersionInfo * pv_info = pvw.next_previous_version();
-           pv_info != NULL; pv_info = pvw.next_previous_version()) {
+    PreviousVersionWalker pvw(Thread::current(), (InstanceKlass*)this);
+    for (PreviousVersionNode * pv_node = pvw.next_previous_version();
+         pv_node != NULL; pv_node = pvw.next_previous_version()) {
       if (!have_pv)
         st->print(BULLET"previous version:  ");
       have_pv = true;
-        pv_info->prev_constant_pool_handle()()->print_value_on(st);
+      pv_node->prev_constant_pool()->print_value_on(st);
     }
     if (have_pv) st->cr();
   } // pvw is cleaned up
-  } // rm is cleaned up
 
   if (generic_signature() != NULL) {
     st->print(BULLET"generic signature: ");
@@ -3395,7 +3388,7 @@ void InstanceKlass::add_previous_version(instanceKlassHandle ikh,
     PreviousVersionNode * pv_node = NULL;
     if (emcp_method_count == 0) {
       // non-shared ConstantPool gets a reference
-      pv_node = new PreviousVersionNode(cp_ref, !cp_ref->is_shared(), NULL);
+      pv_node = new PreviousVersionNode(cp_ref, NULL);
       RC_TRACE(0x00000400,
           ("add: all methods are obsolete; flushing any EMCP refs"));
     } else {
@@ -3416,7 +3409,7 @@ void InstanceKlass::add_previous_version(instanceKlassHandle ikh,
         }
       }
       // non-shared ConstantPool gets a reference
-      pv_node = new PreviousVersionNode(cp_ref, !cp_ref->is_shared(), method_refs);
+      pv_node = new PreviousVersionNode(cp_ref, method_refs);
     }
     // append new previous version.
     _previous_versions->append(pv_node);
@@ -3520,6 +3513,8 @@ Method* InstanceKlass::method_with_idnum(int idnum) {
         return m;
       }
     }
+    // None found, return null for the caller to handle.
+    return NULL;
   }
   return m;
 }
@@ -3536,10 +3531,9 @@ unsigned char * InstanceKlass::get_cached_class_file_bytes() {
 // Construct a PreviousVersionNode entry for the array hung off
 // the InstanceKlass.
 PreviousVersionNode::PreviousVersionNode(ConstantPool* prev_constant_pool,
-  bool prev_cp_is_weak, GrowableArray<Method*>* prev_EMCP_methods) {
+  GrowableArray<Method*>* prev_EMCP_methods) {
 
   _prev_constant_pool = prev_constant_pool;
-  _prev_cp_is_weak = prev_cp_is_weak;
   _prev_EMCP_methods = prev_EMCP_methods;
 }
 
@@ -3555,99 +3549,38 @@ PreviousVersionNode::~PreviousVersionNode() {
   }
 }
 
-
-// Construct a PreviousVersionInfo entry
-PreviousVersionInfo::PreviousVersionInfo(PreviousVersionNode *pv_node) {
-  _prev_constant_pool_handle = constantPoolHandle();  // NULL handle
-  _prev_EMCP_method_handles = NULL;
-
-  ConstantPool* cp = pv_node->prev_constant_pool();
-  assert(cp != NULL, "constant pool ref was unexpectedly cleared");
-  if (cp == NULL) {
-    return;  // robustness
-  }
-
-  // make the ConstantPool* safe to return
-  _prev_constant_pool_handle = constantPoolHandle(cp);
-
-  GrowableArray<Method*>* method_refs = pv_node->prev_EMCP_methods();
-  if (method_refs == NULL) {
-    // the InstanceKlass did not have any EMCP methods
-    return;
-  }
-
-  _prev_EMCP_method_handles = new GrowableArray<methodHandle>(10);
-
-  int n_methods = method_refs->length();
-  for (int i = 0; i < n_methods; i++) {
-    Method* method = method_refs->at(i);
-    assert (method != NULL, "method has been cleared");
-    if (method == NULL) {
-      continue;  // robustness
-    }
-    // make the Method* safe to return
-    _prev_EMCP_method_handles->append(methodHandle(method));
-  }
-}
-
-
-// Destroy a PreviousVersionInfo
-PreviousVersionInfo::~PreviousVersionInfo() {
-  // Since _prev_EMCP_method_handles is not C-heap allocated, we
-  // don't have to delete it.
-}
-
-
 // Construct a helper for walking the previous versions array
-PreviousVersionWalker::PreviousVersionWalker(InstanceKlass *ik) {
+PreviousVersionWalker::PreviousVersionWalker(Thread* thread, InstanceKlass *ik) {
+  _thread = thread;
   _previous_versions = ik->previous_versions();
   _current_index = 0;
-  // _hm needs no initialization
   _current_p = NULL;
-}
-
-
-// Destroy a PreviousVersionWalker
-PreviousVersionWalker::~PreviousVersionWalker() {
-  // Delete the current info just in case the caller didn't walk to
-  // the end of the previous versions list. No harm if _current_p is
-  // already NULL.
-  delete _current_p;
-
-  // When _hm is destroyed, all the Handles returned in
-  // PreviousVersionInfo objects will be destroyed.
-  // Also, after this destructor is finished it will be
-  // safe to delete the GrowableArray allocated in the
-  // PreviousVersionInfo objects.
+  _current_constant_pool_handle = constantPoolHandle(thread, ik->constants());
 }
 
 
 // Return the interesting information for the next previous version
 // of the klass. Returns NULL if there are no more previous versions.
-PreviousVersionInfo* PreviousVersionWalker::next_previous_version() {
+PreviousVersionNode* PreviousVersionWalker::next_previous_version() {
   if (_previous_versions == NULL) {
     // no previous versions so nothing to return
     return NULL;
   }
 
-  delete _current_p;  // cleanup the previous info for the caller
-  _current_p = NULL;  // reset to NULL so we don't delete same object twice
+  _current_p = NULL;  // reset to NULL
+  _current_constant_pool_handle = NULL;
 
   int length = _previous_versions->length();
 
   while (_current_index < length) {
     PreviousVersionNode * pv_node = _previous_versions->at(_current_index++);
-    PreviousVersionInfo * pv_info = new (ResourceObj::C_HEAP, mtClass)
-                                          PreviousVersionInfo(pv_node);
-
-    constantPoolHandle cp_h = pv_info->prev_constant_pool_handle();
-    assert (!cp_h.is_null(), "null cp found in previous version");
 
-    // The caller will need to delete pv_info when they are done with it.
-    _current_p = pv_info;
-    return pv_info;
+    // Save a handle to the constant pool for this previous version,
+    // which keeps all the methods from being deallocated.
+    _current_constant_pool_handle = constantPoolHandle(_thread, pv_node->prev_constant_pool());
+    _current_p = pv_node;
+    return pv_node;
   }
 
-  // all of the underlying nodes' info has been deleted
   return NULL;
 } // end next_previous_version()

src/share/vm/oops/instanceKlass.hpp

@@ -1136,21 +1136,11 @@ class BreakpointInfo;
 
 
 // A collection point for interesting information about the previous
-// version(s) of an InstanceKlass. This class uses weak references to
-// the information so that the information may be collected as needed
-// by the system. If the information is shared, then a regular
-// reference must be used because a weak reference would be seen as
-// collectible. A GrowableArray of PreviousVersionNodes is attached
-// to the InstanceKlass as needed. See PreviousVersionWalker below.
+// version(s) of an InstanceKlass.  A GrowableArray of PreviousVersionNodes
+// is attached to the InstanceKlass as needed. See PreviousVersionWalker below.
 class PreviousVersionNode : public CHeapObj<mtClass> {
  private:
-  // A shared ConstantPool is never collected so we'll always have
-  // a reference to it so we can update items in the cache. We'll
-  // have a weak reference to a non-shared ConstantPool until all
-  // of the methods (EMCP or obsolete) have been collected; the
-  // non-shared ConstantPool becomes collectible at that point.
-  ConstantPool*    _prev_constant_pool;  // regular or weak reference
-  bool    _prev_cp_is_weak;     // true if not a shared ConstantPool
+  ConstantPool*    _prev_constant_pool;
 
   // If the previous version of the InstanceKlass doesn't have any
   // EMCP methods, then _prev_EMCP_methods will be NULL. If all the
@@ -1159,7 +1149,7 @@ class PreviousVersionNode : public CHeapObj<mtClass> {
   GrowableArray<Method*>* _prev_EMCP_methods;
 
 public:
-  PreviousVersionNode(ConstantPool* prev_constant_pool, bool prev_cp_is_weak,
+  PreviousVersionNode(ConstantPool* prev_constant_pool,
                       GrowableArray<Method*>* prev_EMCP_methods);
   ~PreviousVersionNode();
   ConstantPool* prev_constant_pool() const {
@@ -1171,59 +1161,26 @@ public:
 };
 
 
-// A Handle-ized version of PreviousVersionNode.
-class PreviousVersionInfo : public ResourceObj {
- private:
-  constantPoolHandle   _prev_constant_pool_handle;
-  // If the previous version of the InstanceKlass doesn't have any
-  // EMCP methods, then _prev_EMCP_methods will be NULL. Since the
-  // methods cannot be collected while we hold a handle,
-  // _prev_EMCP_methods should never have a length of zero.
-  GrowableArray<methodHandle>* _prev_EMCP_method_handles;
-
-public:
-  PreviousVersionInfo(PreviousVersionNode *pv_node);
-  ~PreviousVersionInfo();
-  constantPoolHandle prev_constant_pool_handle() const {
-    return _prev_constant_pool_handle;
-  }
-  GrowableArray<methodHandle>* prev_EMCP_method_handles() const {
-    return _prev_EMCP_method_handles;
-  }
-};
-
-
-// Helper object for walking previous versions. This helper cleans up
-// the Handles that it allocates when the helper object is destroyed.
-// The PreviousVersionInfo object returned by next_previous_version()
-// is only valid until a subsequent call to next_previous_version() or
-// the helper object is destroyed.
+// Helper object for walking previous versions.
 class PreviousVersionWalker : public StackObj {
  private:
+  Thread*                               _thread;
   GrowableArray<PreviousVersionNode *>* _previous_versions;
   int                                   _current_index;
-  // Fields for cleaning up when we are done walking the previous versions:
-  // A HandleMark for the PreviousVersionInfo handles:
-  HandleMark                            _hm;
 
-  // It would be nice to have a ResourceMark field in this helper also,
-  // but the ResourceMark code says to be careful to delete handles held
-  // in GrowableArrays _before_ deleting the GrowableArray. Since we
-  // can't guarantee the order in which the fields are destroyed, we
-  // have to let the creator of the PreviousVersionWalker object do
-  // the right thing. Also, adding a ResourceMark here causes an
-  // include loop.
+  // A pointer to the current node object so we can handle the deletes.
+  PreviousVersionNode*                  _current_p;
 
-  // A pointer to the current info object so we can handle the deletes.
-  PreviousVersionInfo *                 _current_p;
+  // The constant pool handle keeps all the methods in this class from being
+  // deallocated from the metaspace during class unloading.
+  constantPoolHandle                    _current_constant_pool_handle;
 
  public:
-  PreviousVersionWalker(InstanceKlass *ik);
-  ~PreviousVersionWalker();
+  PreviousVersionWalker(Thread* thread, InstanceKlass *ik);
 
   // Return the interesting information for the next previous version
   // of the klass. Returns NULL if there are no more previous versions.
-  PreviousVersionInfo* next_previous_version();
+  PreviousVersionNode* next_previous_version();
 };
 
 

src/share/vm/prims/jvm.cpp

@@ -1835,16 +1835,27 @@ JVM_ENTRY(jobjectArray, JVM_GetClassDeclaredFields(JNIEnv *env, jclass ofClass,
 }
 JVM_END
 
-JVM_ENTRY(jobjectArray, JVM_GetClassDeclaredMethods(JNIEnv *env, jclass ofClass, jboolean publicOnly))
-{
-  JVMWrapper("JVM_GetClassDeclaredMethods");
+static bool select_method(methodHandle method, bool want_constructor) {
+  if (want_constructor) {
+    return (method->is_initializer() && !method->is_static());
+  } else {
+    return  (!method->is_initializer() && !method->is_overpass());
+  }
+}
+
+static jobjectArray get_class_declared_methods_helper(
+                                  JNIEnv *env,
+                                  jclass ofClass, jboolean publicOnly,
+                                  bool want_constructor,
+                                  Klass* klass, TRAPS) {
+
   JvmtiVMObjectAllocEventCollector oam;
 
   // Exclude primitive types and array types
   if (java_lang_Class::is_primitive(JNIHandles::resolve_non_null(ofClass))
       || java_lang_Class::as_Klass(JNIHandles::resolve_non_null(ofClass))->oop_is_array()) {
     // Return empty array
-    oop res = oopFactory::new_objArray(SystemDictionary::reflect_Method_klass(), 0, CHECK_NULL);
+    oop res = oopFactory::new_objArray(klass, 0, CHECK_NULL);
     return (jobjectArray) JNIHandles::make_local(env, res);
   }
 
@@ -1855,87 +1866,67 @@ JVM_ENTRY(jobjectArray, JVM_GetClassDeclaredMethods(JNIEnv *env, jclass ofClass,
 
   Array<Method*>* methods = k->methods();
   int methods_length = methods->length();
+
+  // Save original method_idnum in case of redefinition, which can change
+  // the idnum of obsolete methods.  The new method will have the same idnum
+  // but if we refresh the methods array, the counts will be wrong.
+  ResourceMark rm(THREAD);
+  GrowableArray<int>* idnums = new GrowableArray<int>(methods_length);
   int num_methods = 0;
 
-  int i;
-  for (i = 0; i < methods_length; i++) {
+  for (int i = 0; i < methods_length; i++) {
     methodHandle method(THREAD, methods->at(i));
-    if (!method->is_initializer() && !method->is_overpass()) {
+    if (select_method(method, want_constructor)) {
       if (!publicOnly || method->is_public()) {
+        idnums->push(method->method_idnum());
         ++num_methods;
       }
     }
   }
 
   // Allocate result
-  objArrayOop r = oopFactory::new_objArray(SystemDictionary::reflect_Method_klass(), num_methods, CHECK_NULL);
+  objArrayOop r = oopFactory::new_objArray(klass, num_methods, CHECK_NULL);
   objArrayHandle result (THREAD, r);
 
-  int out_idx = 0;
-  for (i = 0; i < methods_length; i++) {
-    methodHandle method(THREAD, methods->at(i));
-    if (!method->is_initializer() && !method->is_overpass()) {
-      if (!publicOnly || method->is_public()) {
-        oop m = Reflection::new_method(method, UseNewReflection, false, CHECK_NULL);
-        result->obj_at_put(out_idx, m);
-        ++out_idx;
+  // Now just put the methods that we selected above, but go by their idnum
+  // in case of redefinition.  The methods can be redefined at any safepoint,
+  // so above when allocating the oop array and below when creating reflect
+  // objects.
+  for (int i = 0; i < num_methods; i++) {
+    methodHandle method(THREAD, k->method_with_idnum(idnums->at(i)));
+    if (method.is_null()) {
+      // Method may have been deleted and seems this API can handle null
+      // Otherwise should probably put a method that throws NSME
+      result->obj_at_put(i, NULL);
+    } else {
+      oop m;
+      if (want_constructor) {
+        m = Reflection::new_constructor(method, CHECK_NULL);
+      } else {
+        m = Reflection::new_method(method, UseNewReflection, false, CHECK_NULL);
       }
+      result->obj_at_put(i, m);
     }
   }
-  assert(out_idx == num_methods, "just checking");
+
   return (jobjectArray) JNIHandles::make_local(env, result());
 }
+
+JVM_ENTRY(jobjectArray, JVM_GetClassDeclaredMethods(JNIEnv *env, jclass ofClass, jboolean publicOnly))
+{
+  JVMWrapper("JVM_GetClassDeclaredMethods");
+  return get_class_declared_methods_helper(env, ofClass, publicOnly,
+                                           /*want_constructor*/ false,
+                                           SystemDictionary::reflect_Method_klass(), THREAD);
+}
 JVM_END
 
 JVM_ENTRY(jobjectArray, JVM_GetClassDeclaredConstructors(JNIEnv *env, jclass ofClass, jboolean publicOnly))
 {
   JVMWrapper("JVM_GetClassDeclaredConstructors");
-  JvmtiVMObjectAllocEventCollector oam;
-
-  // Exclude primitive types and array types
-  if (java_lang_Class::is_primitive(JNIHandles::resolve_non_null(ofClass))
-      || java_lang_Class::as_Klass(JNIHandles::resolve_non_null(ofClass))->oop_is_array()) {
-    // Return empty array
-    oop res = oopFactory::new_objArray(SystemDictionary::reflect_Constructor_klass(), 0 , CHECK_NULL);
-    return (jobjectArray) JNIHandles::make_local(env, res);
-  }
-
-  instanceKlassHandle k(THREAD, java_lang_Class::as_Klass(JNIHandles::resolve_non_null(ofClass)));
-
-  // Ensure class is linked
-  k->link_class(CHECK_NULL);
-
-  Array<Method*>* methods = k->methods();
-  int methods_length = methods->length();
-  int num_constructors = 0;
-
-  int i;
-  for (i = 0; i < methods_length; i++) {
-    methodHandle method(THREAD, methods->at(i));
-    if (method->is_initializer() && !method->is_static()) {
-      if (!publicOnly || method->is_public()) {
-        ++num_constructors;
-      }
-    }
-  }
-
-  // Allocate result
-  objArrayOop r = oopFactory::new_objArray(SystemDictionary::reflect_Constructor_klass(), num_constructors, CHECK_NULL);
-  objArrayHandle result(THREAD, r);
-
-  int out_idx = 0;
-  for (i = 0; i < methods_length; i++) {
-    methodHandle method(THREAD, methods->at(i));
-    if (method->is_initializer() && !method->is_static()) {
-      if (!publicOnly || method->is_public()) {
-        oop m = Reflection::new_constructor(method, CHECK_NULL);
-        result->obj_at_put(out_idx, m);
-        ++out_idx;
-      }
-    }
-  }
-  assert(out_idx == num_constructors, "just checking");
-  return (jobjectArray) JNIHandles::make_local(env, result());
+  return get_class_declared_methods_helper(env, ofClass, publicOnly,
+                                           /*want_constructor*/ true,
+                                           SystemDictionary::reflect_Constructor_klass(), THREAD);
 }
 JVM_END
 

src/share/vm/prims/jvmtiImpl.cpp

@@ -273,25 +273,17 @@ void JvmtiBreakpoint::each_method_version_do(method_action meth_act) {
 
   // add/remove breakpoint to/from versions of the method that
   // are EMCP. Directly or transitively obsolete methods are
-  // not saved in the PreviousVersionInfo.
+  // not saved in the PreviousVersionNodes.
   Thread *thread = Thread::current();
   instanceKlassHandle ikh = instanceKlassHandle(thread, _method->method_holder());
   Symbol* m_name = _method->name();
   Symbol* m_signature = _method->signature();
 
-  {
-    ResourceMark rm(thread);
-    // PreviousVersionInfo objects returned via PreviousVersionWalker
-    // contain a GrowableArray of handles. We have to clean up the
-    // GrowableArray _after_ the PreviousVersionWalker destructor
-    // has destroyed the handles.
-    {
   // search previous versions if they exist
-      PreviousVersionWalker pvw((InstanceKlass *)ikh());
-      for (PreviousVersionInfo * pv_info = pvw.next_previous_version();
-           pv_info != NULL; pv_info = pvw.next_previous_version()) {
-        GrowableArray<methodHandle>* methods =
-          pv_info->prev_EMCP_method_handles();
+  PreviousVersionWalker pvw(thread, (InstanceKlass *)ikh());
+  for (PreviousVersionNode * pv_node = pvw.next_previous_version();
+       pv_node != NULL; pv_node = pvw.next_previous_version()) {
+    GrowableArray<Method*>* methods = pv_node->prev_EMCP_methods();
 
     if (methods == NULL) {
       // We have run into a PreviousVersion generation where
@@ -308,7 +300,7 @@ void JvmtiBreakpoint::each_method_version_do(method_action meth_act) {
     }
 
     for (int i = methods->length() - 1; i >= 0; i--) {
-          methodHandle method = methods->at(i);
+      Method* method = methods->at(i);
       // obsolete methods that are running are not deleted from
       // previous version array, but they are skipped here.
       if (!method->is_obsolete() &&
@@ -319,13 +311,11 @@ void JvmtiBreakpoint::each_method_version_do(method_action meth_act) {
           method->name()->as_C_string(),
           method->signature()->as_C_string()));
 
-            ((Method*)method()->*meth_act)(_bci);
+        (method->*meth_act)(_bci);
         break;
       }
     }
   }
-    } // pvw is cleaned up
-  } // rm is cleaned up
 }
 
 void JvmtiBreakpoint::set() {

src/share/vm/prims/jvmtiRedefineClasses.cpp

@@ -2807,18 +2807,12 @@ void VM_RedefineClasses::AdjustCpoolCacheAndVtable::do_klass(Klass* k) {
                                         &trace_name_printed);
       }
     }
-    {
-      ResourceMark rm(_thread);
-      // PreviousVersionInfo objects returned via PreviousVersionWalker
-      // contain a GrowableArray of handles. We have to clean up the
-      // GrowableArray _after_ the PreviousVersionWalker destructor
-      // has destroyed the handles.
-      {
+
     // the previous versions' constant pool caches may need adjustment
-        PreviousVersionWalker pvw(ik);
-        for (PreviousVersionInfo * pv_info = pvw.next_previous_version();
-             pv_info != NULL; pv_info = pvw.next_previous_version()) {
-          other_cp = pv_info->prev_constant_pool_handle();
+    PreviousVersionWalker pvw(_thread, ik);
+    for (PreviousVersionNode * pv_node = pvw.next_previous_version();
+         pv_node != NULL; pv_node = pvw.next_previous_version()) {
+      other_cp = pv_node->prev_constant_pool();
       cp_cache = other_cp->cache();
       if (cp_cache != NULL) {
         cp_cache->adjust_method_entries(_matching_old_methods,
@@ -2827,8 +2821,6 @@ void VM_RedefineClasses::AdjustCpoolCacheAndVtable::do_klass(Klass* k) {
                                         &trace_name_printed);
       }
     }
-      } // pvw is cleaned up
-    } // rm is cleaned up
   }
 }
 
@@ -2942,10 +2934,9 @@ void VM_RedefineClasses::check_methods_and_mark_as_obsolete(
       // obsolete methods need a unique idnum
       u2 num = InstanceKlass::cast(_the_class_oop)->next_method_idnum();
       if (num != ConstMethod::UNSET_IDNUM) {
-//      u2 old_num = old_method->method_idnum();
         old_method->set_method_idnum(num);
-// TO DO: attach obsolete annotations to obsolete method's new idnum
       }
+
       // With tracing we try not to "yack" too much. The position of
       // this trace assumes there are fewer obsolete methods than
       // EMCP methods.

src/share/vm/runtime/handles.hpp

@@ -136,7 +136,7 @@ DEF_HANDLE(typeArray        , is_typeArray        )
 // Specific Handles for different oop types
 #define DEF_METADATA_HANDLE(name, type)          \
   class name##Handle;                            \
-  class name##Handle {                           \
+  class name##Handle : public StackObj {         \
     type*     _value;                            \
     Thread*   _thread;                           \
    protected:                                    \
@@ -175,7 +175,7 @@ DEF_METADATA_HANDLE(constantPool, ConstantPool)
 // Writing this class explicitly, since DEF_METADATA_HANDLE(klass) doesn't
 // provide the necessary Klass* <-> Klass* conversions. This Klass
 // could be removed when we don't have the Klass* typedef anymore.
-class KlassHandle {
+class KlassHandle : public StackObj {
   Klass* _value;
  protected:
    Klass* obj() const          { return _value; }

src/share/vm/runtime/handles.inline.hpp

@@ -79,6 +79,7 @@ inline name##Handle::name##Handle(const name##Handle &h) {             \
     } else {                                                           \
       _thread = Thread::current();                                     \
     }                                                                  \
+    assert (_thread->is_in_stack((address)this), "not on stack?");     \
     _thread->metadata_handles()->push((Metadata*)_value);              \
   } else {                                                             \
     _thread = NULL;                                                    \
@@ -95,6 +96,7 @@ inline name##Handle& name##Handle::operator=(const name##Handle &s) {  \
     } else {                                                           \
       _thread = Thread::current();                                     \
     }                                                                  \
+    assert (_thread->is_in_stack((address)this), "not on stack?");     \
     _thread->metadata_handles()->push((Metadata*)_value);              \
   } else {                                                             \
     _thread = NULL;                                                    \