Implement shared class array containing IdentityObject

src/hotspot/share/classfile/classFileParser.cpp

@@ -5057,6 +5057,11 @@ static Array<InstanceKlass*>* compute_transitive_interfaces(const InstanceKlass*
     // length will be less than the max_transitive_size if duplicates were removed
     const int length = result->length();
     assert(length <= max_transitive_size, "just checking");
+
+    if (length == 1 && result->at(0) == SystemDictionary::IdentityObject_klass()) {
+      return Universe::the_single_IdentityObject_klass_array();
+    }
+
     Array<InstanceKlass*>* const new_result =
       MetadataFactory::new_array<InstanceKlass*>(loader_data, length, CHECK_NULL);
     for (int i = 0; i < length; i++) {
@@ -6396,6 +6401,10 @@ void ClassFileParser::fill_instance_klass(InstanceKlass* ik, bool changed_by_loa
   // it's official
   set_klass(ik);
 
+  if (ik->name() == vmSymbols::java_lang_IdentityObject()) {
+    Universe::initialize_the_single_IdentityObject_klass_array(ik, CHECK);
+  }
+
   debug_only(ik->verify();)
 }
 
@@ -7047,6 +7056,8 @@ void ClassFileParser::post_process_parsed_stream(const ClassFileStream* const st
   int itfs_len = _temp_local_interfaces->length();
   if (itfs_len == 0) {
     _local_interfaces = Universe::the_empty_instance_klass_array();
+  } else if (itfs_len == 1 && _temp_local_interfaces->at(0) == SystemDictionary::IdentityObject_klass()) {
+    _local_interfaces = Universe::the_single_IdentityObject_klass_array();
   } else {
     _local_interfaces = MetadataFactory::new_array<InstanceKlass*>(_loader_data, itfs_len, NULL, CHECK);
     for (int i = 0; i < itfs_len; i++) {

src/hotspot/share/memory/universe.cpp

@@ -139,6 +139,7 @@ Array<int>* Universe::_the_empty_int_array            = NULL;
 Array<u2>* Universe::_the_empty_short_array           = NULL;
 Array<Klass*>* Universe::_the_empty_klass_array     = NULL;
 Array<InstanceKlass*>* Universe::_the_empty_instance_klass_array  = NULL;
+Array<InstanceKlass*>* Universe::_the_single_IdentityObject_klass_array = NULL;
 Array<Method*>* Universe::_the_empty_method_array   = NULL;
 
 // These variables are guarded by FullGCALot_lock.
@@ -224,6 +225,7 @@ void Universe::metaspace_pointers_do(MetaspaceClosure* it) {
   it->push(&_the_empty_instance_klass_array);
   it->push(&_the_empty_method_array);
   it->push(&_the_array_interfaces_array);
+  it->push(&_the_single_IdentityObject_klass_array);
 
   _finalizer_register_cache->metaspace_pointers_do(it);
   _loader_addClass_cache->metaspace_pointers_do(it);
@@ -262,6 +264,7 @@ void Universe::serialize(SerializeClosure* f) {
   f->do_ptr((void**)&_the_empty_method_array);
   f->do_ptr((void**)&_the_empty_klass_array);
   f->do_ptr((void**)&_the_empty_instance_klass_array);
+  f->do_ptr((void**)&_the_single_IdentityObject_klass_array);
   _finalizer_register_cache->serialize(f);
   _loader_addClass_cache->serialize(f);
   _throw_illegal_access_error_cache->serialize(f);
@@ -343,6 +346,8 @@ void Universe::genesis(TRAPS) {
       assert(_the_array_interfaces_array->at(2) ==
                    SystemDictionary::IdentityObject_klass(), "u3");
 
+      assert(_the_single_IdentityObject_klass_array->at(0) ==
+          SystemDictionary::IdentityObject_klass(), "u3");
     } else
 #endif
     {
@@ -471,6 +476,14 @@ void Universe::initialize_basic_type_mirrors(TRAPS) {
   //_mirrors[T_ARRAY]   = _object_klass->java_mirror();
 }
 
+void Universe::initialize_the_single_IdentityObject_klass_array(InstanceKlass* ik, TRAPS) {
+    assert(_the_single_IdentityObject_klass_array == NULL, "Must not be initialized twice");
+    assert(ik->name() == vmSymbols::java_lang_IdentityObject(), "Must be");
+    Array<InstanceKlass*>* array = MetadataFactory::new_array<InstanceKlass*>(ik->class_loader_data(), 1, NULL, CHECK);
+    array->at_put(0, ik);
+    _the_single_IdentityObject_klass_array = array;
+  }
+
 void Universe::fixup_mirrors(TRAPS) {
   // Bootstrap problem: all classes gets a mirror (java.lang.Class instance) assigned eagerly,
   // but we cannot do that for classes created before java.lang.Class is loaded. Here we simply

src/hotspot/share/memory/universe.hpp

@@ -136,6 +136,7 @@ class Universe: AllStatic {
   static Array<u2>*             _the_empty_short_array;          // Canonicalized short array
   static Array<Klass*>*         _the_empty_klass_array;          // Canonicalized klass array
   static Array<InstanceKlass*>* _the_empty_instance_klass_array; // Canonicalized instance klass array
+  static Array<InstanceKlass*>* _the_single_IdentityObject_klass_array;
   static Array<Method*>*        _the_empty_method_array;         // Canonicalized method array
 
   static Array<Klass*>*  _the_array_interfaces_array;
@@ -312,6 +313,12 @@ class Universe: AllStatic {
   static Array<Method*>*         the_empty_method_array() { return _the_empty_method_array; }
   static Array<Klass*>*          the_empty_klass_array()  { return _the_empty_klass_array; }
   static Array<InstanceKlass*>*  the_empty_instance_klass_array() { return _the_empty_instance_klass_array; }
+  static Array<InstanceKlass*>*  the_single_IdentityObject_klass_array() {
+    assert(_the_single_IdentityObject_klass_array != NULL, "Must be initialized before use");
+    assert(_the_single_IdentityObject_klass_array->length() == 1, "Sanity check");
+    return _the_single_IdentityObject_klass_array;
+  }
+  static void initialize_the_single_IdentityObject_klass_array(InstanceKlass* ik, TRAPS);
 
   // OutOfMemoryError support. Returns an error with the required message. The returned error
   // may or may not have a backtrace. If error has a backtrace then the stack trace is already

src/hotspot/share/oops/instanceKlass.cpp

@@ -537,14 +537,16 @@ void InstanceKlass::deallocate_interfaces(ClassLoaderData* loader_data,
     // check that the interfaces don't come from super class
     Array<InstanceKlass*>* sti = (super_klass == NULL) ? NULL :
                     InstanceKlass::cast(super_klass)->transitive_interfaces();
-    if (ti != sti && ti != NULL && !ti->is_shared()) {
+    if (ti != sti && ti != NULL && !ti->is_shared() &&
+        ti != Universe::the_single_IdentityObject_klass_array()) {
       MetadataFactory::free_array<InstanceKlass*>(loader_data, ti);
     }
   }
 
   // local interfaces can be empty
   if (local_interfaces != Universe::the_empty_instance_klass_array() &&
-      local_interfaces != NULL && !local_interfaces->is_shared()) {
+      local_interfaces != NULL && !local_interfaces->is_shared() &&
+      local_interfaces != Universe::the_single_IdentityObject_klass_array()) {
     MetadataFactory::free_array<InstanceKlass*>(loader_data, local_interfaces);
   }
 }