Set pointers to NULL after shutdown, so the shutdown function can be called for multiple times.

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

@@ -857,12 +857,14 @@ GenerateDefaultInstanceInitializer(io::Printer* printer) {
 void MessageGenerator::
 GenerateShutdownCode(io::Printer* printer) {
   printer->Print(
-    "delete $classname$::default_instance_;\n",
+    "delete $classname$::default_instance_;\n"
+    "$classname$::default_instance_ = NULL;\n",
     "classname", classname_);
 
   if (HasDescriptorMethods(descriptor_->file())) {
     printer->Print(
-      "delete $classname$_reflection_;\n",
+      "delete $classname$_reflection_;\n"
+      "$classname$_reflection_ = NULL;\n",
       "classname", classname_);
   }
 

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

@@ -251,7 +251,8 @@ void StringFieldGenerator::
 GenerateShutdownCode(io::Printer* printer) const {
   if (!descriptor_->default_value_string().empty()) {
     printer->Print(variables_,
-      "delete $classname$::$default_variable$;\n");
+      "delete $classname$::$default_variable$;\n"
+      "$classname$::$default_variable$ = NULL;\n");
   }
 }
 

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

@@ -115,11 +115,17 @@ void protobuf_RegisterTypes(const ::std::string&) {
 
 void protobuf_ShutdownFile_google_2fprotobuf_2fcompiler_2fplugin_2eproto() {
   delete CodeGeneratorRequest::default_instance_;
+  CodeGeneratorRequest::default_instance_ = NULL;
   delete CodeGeneratorRequest_reflection_;
+  CodeGeneratorRequest_reflection_ = NULL;
   delete CodeGeneratorResponse::default_instance_;
+  CodeGeneratorResponse::default_instance_ = NULL;
   delete CodeGeneratorResponse_reflection_;
+  CodeGeneratorResponse_reflection_ = NULL;
   delete CodeGeneratorResponse_File::default_instance_;
+  CodeGeneratorResponse_File::default_instance_ = NULL;
   delete CodeGeneratorResponse_File_reflection_;
+  CodeGeneratorResponse_File_reflection_ = NULL;
 }
 
 void protobuf_AddDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto() {

src/google/protobuf/descriptor.pb.cc

@@ -518,45 +518,85 @@ void protobuf_RegisterTypes(const ::std::string&) {
 
 void protobuf_ShutdownFile_google_2fprotobuf_2fdescriptor_2eproto() {
   delete FileDescriptorSet::default_instance_;
+  FileDescriptorSet::default_instance_ = NULL;
   delete FileDescriptorSet_reflection_;
+  FileDescriptorSet_reflection_ = NULL;
   delete FileDescriptorProto::default_instance_;
+  FileDescriptorProto::default_instance_ = NULL;
   delete FileDescriptorProto_reflection_;
+  FileDescriptorProto_reflection_ = NULL;
   delete DescriptorProto::default_instance_;
+  DescriptorProto::default_instance_ = NULL;
   delete DescriptorProto_reflection_;
+  DescriptorProto_reflection_ = NULL;
   delete DescriptorProto_ExtensionRange::default_instance_;
+  DescriptorProto_ExtensionRange::default_instance_ = NULL;
   delete DescriptorProto_ExtensionRange_reflection_;
+  DescriptorProto_ExtensionRange_reflection_ = NULL;
   delete FieldDescriptorProto::default_instance_;
+  FieldDescriptorProto::default_instance_ = NULL;
   delete FieldDescriptorProto_reflection_;
+  FieldDescriptorProto_reflection_ = NULL;
   delete EnumDescriptorProto::default_instance_;
+  EnumDescriptorProto::default_instance_ = NULL;
   delete EnumDescriptorProto_reflection_;
+  EnumDescriptorProto_reflection_ = NULL;
   delete EnumValueDescriptorProto::default_instance_;
+  EnumValueDescriptorProto::default_instance_ = NULL;
   delete EnumValueDescriptorProto_reflection_;
+  EnumValueDescriptorProto_reflection_ = NULL;
   delete ServiceDescriptorProto::default_instance_;
+  ServiceDescriptorProto::default_instance_ = NULL;
   delete ServiceDescriptorProto_reflection_;
+  ServiceDescriptorProto_reflection_ = NULL;
   delete MethodDescriptorProto::default_instance_;
+  MethodDescriptorProto::default_instance_ = NULL;
   delete MethodDescriptorProto_reflection_;
+  MethodDescriptorProto_reflection_ = NULL;
   delete FileOptions::default_instance_;
+  FileOptions::default_instance_ = NULL;
   delete FileOptions_reflection_;
+  FileOptions_reflection_ = NULL;
   delete MessageOptions::default_instance_;
+  MessageOptions::default_instance_ = NULL;
   delete MessageOptions_reflection_;
+  MessageOptions_reflection_ = NULL;
   delete FieldOptions::default_instance_;
+  FieldOptions::default_instance_ = NULL;
   delete FieldOptions_reflection_;
+  FieldOptions_reflection_ = NULL;
   delete EnumOptions::default_instance_;
+  EnumOptions::default_instance_ = NULL;
   delete EnumOptions_reflection_;
+  EnumOptions_reflection_ = NULL;
   delete EnumValueOptions::default_instance_;
+  EnumValueOptions::default_instance_ = NULL;
   delete EnumValueOptions_reflection_;
+  EnumValueOptions_reflection_ = NULL;
   delete ServiceOptions::default_instance_;
+  ServiceOptions::default_instance_ = NULL;
   delete ServiceOptions_reflection_;
+  ServiceOptions_reflection_ = NULL;
   delete MethodOptions::default_instance_;
+  MethodOptions::default_instance_ = NULL;
   delete MethodOptions_reflection_;
+  MethodOptions_reflection_ = NULL;
   delete UninterpretedOption::default_instance_;
+  UninterpretedOption::default_instance_ = NULL;
   delete UninterpretedOption_reflection_;
+  UninterpretedOption_reflection_ = NULL;
   delete UninterpretedOption_NamePart::default_instance_;
+  UninterpretedOption_NamePart::default_instance_ = NULL;
   delete UninterpretedOption_NamePart_reflection_;
+  UninterpretedOption_NamePart_reflection_ = NULL;
   delete SourceCodeInfo::default_instance_;
+  SourceCodeInfo::default_instance_ = NULL;
   delete SourceCodeInfo_reflection_;
+  SourceCodeInfo_reflection_ = NULL;
   delete SourceCodeInfo_Location::default_instance_;
+  SourceCodeInfo_Location::default_instance_ = NULL;
   delete SourceCodeInfo_Location_reflection_;
+  SourceCodeInfo_Location_reflection_ = NULL;
 }
 
 void protobuf_AddDesc_google_2fprotobuf_2fdescriptor_2eproto() {