Replace kEmptyString wth OnceInit initialized string*

src/google/protobuf/compiler/cpp/cpp_string_field.cc

@@ -53,7 +53,7 @@ void SetStringVariables(const FieldDescriptor* descriptor,
   (*variables)["default_length"] =
       SimpleItoa(descriptor->default_value_string().length());
   (*variables)["default_variable"] = descriptor->default_value_string().empty()
-      ? "&::google::protobuf::internal::kEmptyString"
+      ? "&::google::protobuf::internal::GetEmptyString()"
       : "_default_" + FieldName(descriptor) + "_";
   (*variables)["pointer_type"] =
       descriptor->type() == FieldDescriptor::TYPE_BYTES ? "void" : "char";

src/google/protobuf/compiler/plugin.pb.cc

@@ -184,7 +184,7 @@ CodeGeneratorRequest::CodeGeneratorRequest(const CodeGeneratorRequest& from)
 
 void CodeGeneratorRequest::SharedCtor() {
   _cached_size_ = 0;
-  parameter_ = const_cast< ::std::string*>(&::google::protobuf::internal::kEmptyString);
+  parameter_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
   ::memset(_has_bits_, 0, sizeof(_has_bits_));
 }
 
@@ -193,7 +193,7 @@ CodeGeneratorRequest::~CodeGeneratorRequest() {
 }
 
 void CodeGeneratorRequest::SharedDtor() {
-  if (parameter_ != &::google::protobuf::internal::kEmptyString) {
+  if (parameter_ != &::google::protobuf::internal::GetEmptyString()) {
     delete parameter_;
   }
   if (this != default_instance_) {
@@ -224,7 +224,7 @@ CodeGeneratorRequest* CodeGeneratorRequest::New() const {
 void CodeGeneratorRequest::Clear() {
   if (_has_bits_[1 / 32] & (0xffu << (1 % 32))) {
     if (has_parameter()) {
-      if (parameter_ != &::google::protobuf::internal::kEmptyString) {
+      if (parameter_ != &::google::protobuf::internal::GetEmptyString()) {
         parameter_->clear();
       }
     }
@@ -501,9 +501,9 @@ CodeGeneratorResponse_File::CodeGeneratorResponse_File(const CodeGeneratorRespon
 
 void CodeGeneratorResponse_File::SharedCtor() {
   _cached_size_ = 0;
-  name_ = const_cast< ::std::string*>(&::google::protobuf::internal::kEmptyString);
-  insertion_point_ = const_cast< ::std::string*>(&::google::protobuf::internal::kEmptyString);
-  content_ = const_cast< ::std::string*>(&::google::protobuf::internal::kEmptyString);
+  name_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+  insertion_point_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+  content_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
   ::memset(_has_bits_, 0, sizeof(_has_bits_));
 }
 
@@ -512,13 +512,13 @@ CodeGeneratorResponse_File::~CodeGeneratorResponse_File() {
 }
 
 void CodeGeneratorResponse_File::SharedDtor() {
-  if (name_ != &::google::protobuf::internal::kEmptyString) {
+  if (name_ != &::google::protobuf::internal::GetEmptyString()) {
     delete name_;
   }
-  if (insertion_point_ != &::google::protobuf::internal::kEmptyString) {
+  if (insertion_point_ != &::google::protobuf::internal::GetEmptyString()) {
     delete insertion_point_;
   }
-  if (content_ != &::google::protobuf::internal::kEmptyString) {
+  if (content_ != &::google::protobuf::internal::GetEmptyString()) {
     delete content_;
   }
   if (this != default_instance_) {
@@ -549,17 +549,17 @@ CodeGeneratorResponse_File* CodeGeneratorResponse_File::New() const {
 void CodeGeneratorResponse_File::Clear() {
   if (_has_bits_[0 / 32] & (0xffu << (0 % 32))) {
     if (has_name()) {
-      if (name_ != &::google::protobuf::internal::kEmptyString) {
+      if (name_ != &::google::protobuf::internal::GetEmptyString()) {
         name_->clear();
       }
     }
     if (has_insertion_point()) {
-      if (insertion_point_ != &::google::protobuf::internal::kEmptyString) {
+      if (insertion_point_ != &::google::protobuf::internal::GetEmptyString()) {
         insertion_point_->clear();
       }
     }
     if (has_content()) {
-      if (content_ != &::google::protobuf::internal::kEmptyString) {
+      if (content_ != &::google::protobuf::internal::GetEmptyString()) {
         content_->clear();
       }
     }
@@ -839,7 +839,7 @@ CodeGeneratorResponse::CodeGeneratorResponse(const CodeGeneratorResponse& from)
 
 void CodeGeneratorResponse::SharedCtor() {
   _cached_size_ = 0;
-  error_ = const_cast< ::std::string*>(&::google::protobuf::internal::kEmptyString);
+  error_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
   ::memset(_has_bits_, 0, sizeof(_has_bits_));
 }
 
@@ -848,7 +848,7 @@ CodeGeneratorResponse::~CodeGeneratorResponse() {
 }
 
 void CodeGeneratorResponse::SharedDtor() {
-  if (error_ != &::google::protobuf::internal::kEmptyString) {
+  if (error_ != &::google::protobuf::internal::GetEmptyString()) {
     delete error_;
   }
   if (this != default_instance_) {
@@ -879,7 +879,7 @@ CodeGeneratorResponse* CodeGeneratorResponse::New() const {
 void CodeGeneratorResponse::Clear() {
   if (_has_bits_[0 / 32] & (0xffu << (0 % 32))) {
     if (has_error()) {
-      if (error_ != &::google::protobuf::internal::kEmptyString) {
+      if (error_ != &::google::protobuf::internal::GetEmptyString()) {
         error_->clear();
       }
     }

src/google/protobuf/descriptor.cc

@@ -139,8 +139,6 @@ const int FieldDescriptor::kLastReservedNumber;
 
 namespace {
 
-const string kEmptyString;
-
 string ToCamelCase(const string& input) {
   bool capitalize_next = false;
   string result;
@@ -2757,7 +2755,7 @@ Symbol DescriptorBuilder::NewPlaceholder(const string& name,
     placeholder_name = tables_->AllocateString(
       placeholder_full_name->substr(dotpos + 1));
   } else {
-    placeholder_package = &kEmptyString;
+    placeholder_package = &::google::protobuf::internal::GetEmptyString();
     placeholder_name = placeholder_full_name;
   }
 
@@ -2843,7 +2841,7 @@ const FileDescriptor* DescriptorBuilder::NewPlaceholderFile(
   memset(placeholder, 0, sizeof(*placeholder));
 
   placeholder->name_ = tables_->AllocateString(name);
-  placeholder->package_ = &kEmptyString;
+  placeholder->package_ = &::google::protobuf::internal::GetEmptyString();
   placeholder->pool_ = pool_;
   placeholder->options_ = &FileOptions::default_instance();
   placeholder->tables_ = &FileDescriptorTables::kEmpty;
@@ -3485,7 +3483,7 @@ void DescriptorBuilder::BuildFieldOrExtension(const FieldDescriptorProto& proto,
           result->default_value_enum_ = NULL;
           break;
         case FieldDescriptor::CPPTYPE_STRING:
-          result->default_value_string_ = &kEmptyString;
+          result->default_value_string_ = &::google::protobuf::internal::GetEmptyString();
           break;
         case FieldDescriptor::CPPTYPE_MESSAGE:
           break;

src/google/protobuf/generated_message_reflection.cc

@@ -68,7 +68,7 @@ bool ParseNamedEnum(const EnumDescriptor* descriptor,
 
 const string& NameOfEnum(const EnumDescriptor* descriptor, int value) {
   const EnumValueDescriptor* d = descriptor->FindValueByNumber(value);
-  return (d == NULL ? kEmptyString : d->name());
+  return (d == NULL ? GetEmptyString() : d->name());
 }
 
 // ===================================================================
@@ -771,7 +771,7 @@ string GeneratedMessageReflection::GetString(
     }
 
     GOOGLE_LOG(FATAL) << "Can't get here.";
-    return kEmptyString;  // Make compiler happy.
+    return GetEmptyString();  // Make compiler happy.
   }
 }
 
@@ -790,7 +790,7 @@ const string& GeneratedMessageReflection::GetStringReference(
     }
 
     GOOGLE_LOG(FATAL) << "Can't get here.";
-    return kEmptyString;  // Make compiler happy.
+    return GetEmptyString();  // Make compiler happy.
   }
 }
 
@@ -832,7 +832,7 @@ string GeneratedMessageReflection::GetRepeatedString(
     }
 
     GOOGLE_LOG(FATAL) << "Can't get here.";
-    return kEmptyString;  // Make compiler happy.
+    return GetEmptyString();  // Make compiler happy.
   }
 }
 
@@ -850,7 +850,7 @@ const string& GeneratedMessageReflection::GetRepeatedStringReference(
     }
 
     GOOGLE_LOG(FATAL) << "Can't get here.";
-    return kEmptyString;  // Make compiler happy.
+    return GetEmptyString();  // Make compiler happy.
   }
 }
 

src/google/protobuf/generated_message_util.cc

@@ -47,7 +47,12 @@ double NaN() {
   return std::numeric_limits<double>::quiet_NaN();
 }
 
-const ::std::string kEmptyString;
+const ::std::string* empty_string_;
+ProtobufOnceType empty_string_once_init_;
+
+void InitEmptyString() {
+  empty_string_ = new std::string;
+}
 
 }  // namespace internal
 }  // namespace protobuf

src/google/protobuf/generated_message_util.h

@@ -41,6 +41,7 @@
 #include <string>
 
 #include <google/protobuf/stubs/common.h>
+#include <google/protobuf/stubs/once.h>
 namespace google {
 namespace protobuf {
 namespace internal {
@@ -59,8 +60,17 @@ namespace internal {
 LIBPROTOBUF_EXPORT double Infinity();
 LIBPROTOBUF_EXPORT double NaN();
 
-// Constant used for empty default strings.
-LIBPROTOBUF_EXPORT extern const ::std::string kEmptyString;
+// Default empty string object. Don't use the pointer directly. Instead, call
+// GetEmptyString() to get the reference.
+LIBPROTOBUF_EXPORT extern const ::std::string* empty_string_;
+LIBPROTOBUF_EXPORT extern ProtobufOnceType empty_string_once_init_;
+
+LIBPROTOBUF_EXPORT void InitEmptyString();
+
+LIBPROTOBUF_EXPORT inline const ::std::string& GetEmptyString() {
+  GoogleOnceInit(&empty_string_once_init_, &InitEmptyString);
+  return *empty_string_;
+}
 
 // Defined in generated_message_reflection.cc -- not actually part of the lite
 // library.

src/google/protobuf/repeated_field.h

@@ -383,7 +383,7 @@ class LIBPROTOBUF_EXPORT StringTypeHandlerBase {
   static void Clear(string* value) { value->clear(); }
   static void Merge(const string& from, string* to) { *to = from; }
   static const Type& default_instance() {
-    return ::google::protobuf::internal::kEmptyString;
+    return ::google::protobuf::internal::GetEmptyString();
   }
 };