8247220: Make OopHandle constructor explicit

Fix null initializations to explicitly call the OopHandle constructor

Reviewed-by: lfoltan, kbarrett

src/hotspot/share/classfile/classLoaderData.cpp

@@ -183,7 +183,7 @@ ClassLoaderData::ChunkedHandleList::~ChunkedHandleList() {
   }
 }
 
-oop* ClassLoaderData::ChunkedHandleList::add(oop o) {
+OopHandle ClassLoaderData::ChunkedHandleList::add(oop o) {
   if (_head == NULL || _head->_size == Chunk::CAPACITY) {
     Chunk* next = new Chunk(_head);
     Atomic::release_store(&_head, next);
@@ -191,7 +191,7 @@ oop* ClassLoaderData::ChunkedHandleList::add(oop o) {
   oop* handle = &_head->_data[_head->_size];
   NativeAccess<IS_DEST_UNINITIALIZED>::oop_store(handle, o);
   Atomic::release_store(&_head->_size, _head->_size + 1);
-  return handle;
+  return OopHandle(handle);
 }
 
 int ClassLoaderData::ChunkedHandleList::count() const {
@@ -776,7 +776,7 @@ ClassLoaderMetaspace* ClassLoaderData::metaspace_non_null() {
 OopHandle ClassLoaderData::add_handle(Handle h) {
   MutexLocker ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
   record_modified_oops();
-  return OopHandle(_handles.add(h()));
+  return _handles.add(h());
 }
 
 void ClassLoaderData::remove_handle(OopHandle h) {

src/hotspot/share/classfile/classLoaderData.hpp

@@ -90,7 +90,7 @@ class ClassLoaderData : public CHeapObj<mtClass> {
 
     // Only one thread at a time can add, guarded by ClassLoaderData::metaspace_lock().
     // However, multiple threads can execute oops_do concurrently with add.
-    oop* add(oop o);
+    OopHandle add(oop o);
     bool contains(oop p);
     NOT_PRODUCT(bool owner_of(oop* p);)
     void oops_do(OopClosure* f);

src/hotspot/share/classfile/javaClasses.cpp

@@ -895,7 +895,7 @@ void java_lang_Class::fixup_mirror(Klass* k, TRAPS) {
       assert(present, "Missing archived mirror for %s", k->external_name());
       return;
     } else {
-      k->set_java_mirror_handle(NULL);
+      k->set_java_mirror_handle(OopHandle());
       k->clear_has_raw_archived_mirror();
     }
   }
@@ -1201,7 +1201,7 @@ oop java_lang_Class::archive_mirror(Klass* k, TRAPS) {
           ik->is_shared_app_class())) {
       // Archiving mirror for classes from non-builtin loaders is not
       // supported. Clear the _java_mirror within the archived class.
-      k->set_java_mirror_handle(NULL);
+      k->set_java_mirror_handle(OopHandle());
       return NULL;
     }
   }

src/hotspot/share/classfile/moduleEntry.hpp

@@ -79,9 +79,9 @@ private:
 
 public:
   void init() {
-    _module = NULL;
+    _module = OopHandle();
+    _pd = OopHandle();
     _loader_data = NULL;
-    _pd = NULL;
     _reads = NULL;
     _version = NULL;
     _location = NULL;

src/hotspot/share/classfile/systemDictionaryShared.cpp

@@ -61,9 +61,9 @@
 #include "utilities/stringUtils.hpp"
 
 
-OopHandle SystemDictionaryShared::_shared_protection_domains  =  NULL;
-OopHandle SystemDictionaryShared::_shared_jar_urls            =  NULL;
-OopHandle SystemDictionaryShared::_shared_jar_manifests       =  NULL;
+OopHandle SystemDictionaryShared::_shared_protection_domains;
+OopHandle SystemDictionaryShared::_shared_jar_urls;
+OopHandle SystemDictionaryShared::_shared_jar_manifests;
 DEBUG_ONLY(bool SystemDictionaryShared::_no_class_loading_should_happen = false;)
 
 class DumpTimeSharedClassInfo: public CHeapObj<mtClass> {

src/hotspot/share/oops/constantPool.cpp

@@ -283,7 +283,7 @@ void ConstantPool::archive_resolved_references(Thread* THREAD) {
         ik->is_shared_app_class())) {
     // Archiving resolved references for classes from non-builtin loaders
     // is not yet supported.
-    set_resolved_references(NULL);
+    set_resolved_references(OopHandle());
     return;
   }
 
@@ -315,7 +315,7 @@ void ConstantPool::archive_resolved_references(Thread* THREAD) {
     // resolved references will be created using the normal process
     // when there is no archived value.
     _cache->set_archived_references(archived);
-    set_resolved_references(NULL);
+    set_resolved_references(OopHandle());
   }
 }
 
@@ -389,7 +389,7 @@ void ConstantPool::remove_unshareable_info() {
   // If DynamicDumpSharedSpaces is enabled, clear the resolved references also
   // as java objects are not archived in the top layer.
   if (!HeapShared::is_heap_object_archiving_allowed() || DynamicDumpSharedSpaces) {
-    set_resolved_references(NULL);
+    set_resolved_references(OopHandle());
   }
 
   // Shared ConstantPools are in the RO region, so the _flags cannot be modified.

src/hotspot/share/oops/cpCache.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 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
@@ -767,7 +767,7 @@ void ConstantPoolCache::walk_entries_for_initialization(bool check_only) {
 void ConstantPoolCache::deallocate_contents(ClassLoaderData* data) {
   assert(!is_shared(), "shared caches are not deallocated");
   data->remove_handle(_resolved_references);
-  set_resolved_references(NULL);
+  set_resolved_references(OopHandle());
   MetadataFactory::free_array<u2>(data, _reference_map);
   set_reference_map(NULL);
 }

src/hotspot/share/oops/klass.cpp

@@ -555,7 +555,7 @@ void Klass::remove_java_mirror() {
     log_trace(cds, unshareable)("remove java_mirror: %s", external_name());
   }
   // Just null out the mirror.  The class_loader_data() no longer exists.
-  _java_mirror = NULL;
+  _java_mirror = OopHandle();
 }
 
 void Klass::restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, TRAPS) {
@@ -609,7 +609,7 @@ void Klass::restore_unshareable_info(ClassLoaderData* loader_data, Handle protec
 
     // No archived mirror data
     log_debug(cds, mirror)("No archived mirror data for %s", external_name());
-    _java_mirror = NULL;
+    _java_mirror = OopHandle();
     this->clear_has_raw_archived_mirror();
   }
 

src/hotspot/share/oops/oopHandle.hpp

@@ -42,7 +42,7 @@ private:
 
 public:
   OopHandle() : _obj(NULL) {}
-  OopHandle(oop* w) : _obj(w) {}
+  explicit OopHandle(oop* w) : _obj(w) {}
 
   inline static OopHandle create(oop obj);