Don't call AddDesc() at static init time in LITE_RUNTIME mode.

This patch makes the generation of StaticDescriptorInitializer_$filename$
depend on whether LITE_RUNTIME is enabled. Note that this works only when
extensions are not used.

This lets us significantly decrease the number of static initializers generated
by protoc in LITE_RUNTIME mode (used in Chromium).
In LITE_RUNTIME mode, $adddescriptorsname$() is called the first time that
default_instance() is called (rather than being called during static init).

To benefit from this patch in LITE_RUNTIME mode without extensions, compile
with -DGOOGLE_PROTOBUF_NO_STATIC_INIT.

BUG=351

5 files changed, 201 insertions, 35 deletions

diff --git a/src/google/protobuf/compiler/cpp/cpp_file.cc b/src/google/protobuf/compiler/cpp/cpp_file.cc
index 312ebc86..f4930610 100644
--- a/src/google/protobuf/compiler/cpp/cpp_file.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_file.cc
@@ -381,11 +381,12 @@ void FileGenerator::GenerateSource(io::Printer* printer) {
 
 void FileGenerator::GenerateBuildDescriptors(io::Printer* printer) {
   // AddDescriptors() is a file-level procedure which adds the encoded
-  // FileDescriptorProto for this .proto file to the global DescriptorPool
-  // for generated files (DescriptorPool::generated_pool()).  It always runs
-  // at static initialization time, so all files will be registered before
-  // main() starts.  This procedure also constructs default instances and
-  // registers extensions.
+  // FileDescriptorProto for this .proto file to the global DescriptorPool for
+  // generated files (DescriptorPool::generated_pool()). It either runs at
+  // static initialization time (by default) or when default_instance() is
+  // called for the first time (in LITE_RUNTIME mode with
+  // GOOGLE_PROTOBUF_NO_STATIC_INITIALIZER flag enabled). This procedure also
+  // constructs default instances and registers extensions.
   //
   // Its sibling, AssignDescriptors(), actually pulls the compiled
   // FileDescriptor from the DescriptorPool and uses it to populate all of
@@ -489,22 +490,27 @@ void FileGenerator::GenerateBuildDescriptors(io::Printer* printer) {
 
   printer->Outdent();
   printer->Print(
-    "}\n");
+    "}\n\n");
 
   // -----------------------------------------------------------------
 
   // Now generate the AddDescriptors() function.
-  printer->Print(
-    "\n"
+  PrintHandlingOptionalStaticInitializers(
+    file_, printer,
+    // With static initializers.
+    // Note that we don't need any special synchronization in the following code
+    // because it is called at static init time before any threads exist.
     "void $adddescriptorsname$() {\n"
-    // We don't need any special synchronization here because this code is
-    // called at static init time before any threads exist.
     "  static bool already_here = false;\n"
     "  if (already_here) return;\n"
     "  already_here = true;\n"
-    "  GOOGLE_PROTOBUF_VERIFY_VERSION;\n"
-    "\n",
+    "  GOOGLE_PROTOBUF_VERIFY_VERSION;\n",
+    // Without.
+    "void $adddescriptorsname$_impl() {\n"
+    "  GOOGLE_PROTOBUF_VERIFY_VERSION;\n",
+    // Vars.
     "adddescriptorsname", GlobalAddDescriptorsName(file_->name()));
+
   printer->Indent();
 
   // Call the AddDescriptors() methods for all of our dependencies, to make
@@ -572,17 +578,27 @@ void FileGenerator::GenerateBuildDescriptors(io::Printer* printer) {
     "shutdownfilename", GlobalShutdownFileName(file_->name()));
 
   printer->Outdent();
-
   printer->Print(
     "}\n"
-    "\n"
+    "\n");
+
+  PrintHandlingOptionalStaticInitializers(
+    file_, printer,
+    // With static initializers.
     "// Force AddDescriptors() to be called at static initialization time.\n"
     "struct StaticDescriptorInitializer_$filename$ {\n"
     "  StaticDescriptorInitializer_$filename$() {\n"
     "    $adddescriptorsname$();\n"
     "  }\n"
-    "} static_descriptor_initializer_$filename$_;\n"
-    "\n",
+    "} static_descriptor_initializer_$filename$_;\n",
+    // Without.
+    "::google::protobuf::GoogleOnceType $adddescriptorsname$_once_ =\n"
+    "    GOOGLE_PROTOBUF_ONCE_INIT;\n"
+    "void $adddescriptorsname$() {\n"
+    "  ::google::protobuf::GoogleOnceInit(&$adddescriptorsname$_once_,\n"
+    "                 &$adddescriptorsname$_impl);\n"
+    "}\n",
+    // Vars.
     "adddescriptorsname", GlobalAddDescriptorsName(file_->name()),
     "filename", FilenameIdentifier(file_->name()));
 }
diff --git a/src/google/protobuf/compiler/cpp/cpp_helpers.cc b/src/google/protobuf/compiler/cpp/cpp_helpers.cc
index 25b05a85..c4b868c2 100644
--- a/src/google/protobuf/compiler/cpp/cpp_helpers.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_helpers.cc
@@ -33,10 +33,12 @@
 //  Sanjay Ghemawat, Jeff Dean, and others.
 
 #include <limits>
+#include <map>
 #include <vector>
 #include <google/protobuf/stubs/hash.h>
 
 #include <google/protobuf/compiler/cpp/cpp_helpers.h>
+#include <google/protobuf/io/printer.h>
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/stubs/strutil.h>
 #include <google/protobuf/stubs/substitute.h>
@@ -105,6 +107,20 @@ string UnderscoresToCamelCase(const string& input, bool cap_next_letter) {
   return result;
 }
 
+// Returns whether the provided descriptor has an extension. This includes its
+// nested types.
+bool HasExtension(const Descriptor* descriptor) {
+  if (descriptor->extension_count() > 0) {
+    return true;
+  }
+  for (int i = 0; i < descriptor->nested_type_count(); ++i) {
+    if (HasExtension(descriptor->nested_type(i))) {
+      return true;
+    }
+  }
+  return false;
+}
+
 }  // namespace
 
 const char kThickSeparator[] =
@@ -341,6 +357,50 @@ string EscapeTrigraphs(const string& to_escape) {
   return StringReplace(to_escape, "?", "\\?", true);
 }
 
+bool StaticInitializersForced(const FileDescriptor* file) {
+  if (HasDescriptorMethods(file) || file->extension_count() > 0) {
+    return true;
+  }
+  for (int i = 0; i < file->message_type_count(); ++i) {
+    if (HasExtension(file->message_type(i))) {
+      return true;
+    }
+  }
+  return false;
+}
+
+void PrintHandlingOptionalStaticInitializers(
+    const FileDescriptor* file, io::Printer* printer,
+    const char* with_static_init, const char* without_static_init,
+    const char* var1, const string& val1,
+    const char* var2, const string& val2) {
+  map<string, string> vars;
+  if (var1) {
+    vars[var1] = val1;
+  }
+  if (var2) {
+    vars[var2] = val2;
+  }
+  PrintHandlingOptionalStaticInitializers(
+      vars, file, printer, with_static_init, without_static_init);
+}
+
+void PrintHandlingOptionalStaticInitializers(
+    const map<string, string>& vars, const FileDescriptor* file,
+    io::Printer* printer, const char* with_static_init,
+    const char* without_static_init) {
+  if (StaticInitializersForced(file)) {
+    printer->Print(vars, with_static_init);
+  } else {
+    printer->Print(vars, (string(
+      "#ifdef GOOGLE_PROTOBUF_NO_STATIC_INITIALIZER\n") +
+      without_static_init +
+      "#else\n" +
+      with_static_init +
+      "#endif\n").c_str());
+  }
+}
+
 }  // namespace cpp
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/cpp/cpp_helpers.h b/src/google/protobuf/compiler/cpp/cpp_helpers.h
index b13d53be..662a7c31 100644
--- a/src/google/protobuf/compiler/cpp/cpp_helpers.h
+++ b/src/google/protobuf/compiler/cpp/cpp_helpers.h
@@ -35,12 +35,18 @@
 #ifndef GOOGLE_PROTOBUF_COMPILER_CPP_HELPERS_H__
 #define GOOGLE_PROTOBUF_COMPILER_CPP_HELPERS_H__
 
+#include <map>
 #include <string>
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/descriptor.pb.h>
 
 namespace google {
 namespace protobuf {
+
+namespace io {
+class Printer;
+}
+
 namespace compiler {
 namespace cpp {
 
@@ -150,6 +156,22 @@ inline bool HasFastArraySerialization(const FileDescriptor* file) {
   return file->options().optimize_for() == FileOptions::SPEED;
 }
 
+// Returns whether we have to generate code with static initializers.
+bool StaticInitializersForced(const FileDescriptor* file);
+
+// Prints 'with_static_init' if static initializers have to be used for the
+// provided file. Otherwise emits both 'with_static_init' and
+// 'without_static_init' using #ifdef.
+void PrintHandlingOptionalStaticInitializers(
+    const FileDescriptor* file, io::Printer* printer,
+    const char* with_static_init, const char* without_static_init,
+    const char* var1 = NULL, const string& val1 = "",
+    const char* var2 = NULL, const string& val2 = "");
+
+void PrintHandlingOptionalStaticInitializers(
+    const map<string, string>& vars, const FileDescriptor* file,
+    io::Printer* printer, const char* with_static_init,
+    const char* without_static_init);
 
 }  // namespace cpp
 }  // namespace compiler
diff --git a/src/google/protobuf/compiler/cpp/cpp_message.cc b/src/google/protobuf/compiler/cpp/cpp_message.cc
index c4e6fb2c..1c158be0 100644
--- a/src/google/protobuf/compiler/cpp/cpp_message.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_message.cc
@@ -493,6 +493,19 @@ GenerateClassDefinition(io::Printer* printer) {
     "static const $classname$& default_instance();\n"
     "\n");
 
+  if (!StaticInitializersForced(descriptor_->file())) {
+    printer->Print(vars,
+      "#ifdef GOOGLE_PROTOBUF_NO_STATIC_INITIALIZER\n"
+      "// Returns the internal default instance pointer. This function can\n"
+      "// return NULL thus should not be used by the user. This is intended\n"
+      "// for Protobuf internal code. Please use default_instance() declared\n"
+      "// above instead.\n"
+      "static inline const $classname$* internal_default_instance() {\n"
+      "  return default_instance_;\n"
+      "}\n"
+      "#endif\n"
+      "\n");
+  }
 
   printer->Print(vars,
     "void Swap($classname$* other);\n"
@@ -660,11 +673,17 @@ GenerateClassDefinition(io::Printer* printer) {
   // Declare AddDescriptors(), BuildDescriptors(), and ShutdownFile() as
   // friends so that they can access private static variables like
   // default_instance_ and reflection_.
-  printer->Print(
+  PrintHandlingOptionalStaticInitializers(
+    descriptor_->file(), printer,
+    // With static initializers.
     "friend void $dllexport_decl$ $adddescriptorsname$();\n",
+    // Without.
+    "friend void $dllexport_decl$ $adddescriptorsname$_impl();\n",
+    // Vars.
     "dllexport_decl", dllexport_decl_,
     "adddescriptorsname",
-      GlobalAddDescriptorsName(descriptor_->file()->name()));
+    GlobalAddDescriptorsName(descriptor_->file()->name()));
+
   printer->Print(
     "friend void $assigndescriptorsname$();\n"
     "friend void $shutdownfilename$();\n"
@@ -981,8 +1000,12 @@ GenerateSharedDestructorCode(io::Printer* printer) {
                      .GenerateDestructorCode(printer);
   }
 
-  printer->Print(
-    "if (this != default_instance_) {\n");
+  PrintHandlingOptionalStaticInitializers(
+    descriptor_->file(), printer,
+    // With static initializers.
+    "if (this != default_instance_) {\n",
+    // Without.
+    "if (this != &default_instance()) {\n");
 
   // We need to delete all embedded messages.
   // TODO(kenton):  If we make unset messages point at default instances
@@ -1034,10 +1057,16 @@ GenerateStructors(io::Printer* printer) {
 
     if (!field->is_repeated() &&
         field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
-      printer->Print(
-          "  $name$_ = const_cast< $type$*>(&$type$::default_instance());\n",
-          "name", FieldName(field),
-          "type", FieldMessageTypeName(field));
+      PrintHandlingOptionalStaticInitializers(
+        descriptor_->file(), printer,
+        // With static initializers.
+        "  $name$_ = const_cast< $type$*>(&$type$::default_instance());\n",
+        // Without.
+        "  $name$_ = const_cast< $type$*>(\n"
+        "      $type$::internal_default_instance());\n",
+        // Vars.
+        "name", FieldName(field),
+        "type", FieldMessageTypeName(field));
     }
   }
   printer->Print(
@@ -1093,8 +1122,20 @@ GenerateStructors(io::Printer* printer) {
   }
 
   printer->Print(
-    "const $classname$& $classname$::default_instance() {\n"
-    "  if (default_instance_ == NULL) $adddescriptorsname$();"
+    "const $classname$& $classname$::default_instance() {\n",
+    "classname", classname_);
+
+  PrintHandlingOptionalStaticInitializers(
+    descriptor_->file(), printer,
+    // With static initializers.
+    "  if (default_instance_ == NULL) $adddescriptorsname$();\n",
+    // Without.
+    "  $adddescriptorsname$();\n",
+    // Vars.
+    "adddescriptorsname",
+    GlobalAddDescriptorsName(descriptor_->file()->name()));
+
+  printer->Print(
     "  return *default_instance_;\n"
     "}\n"
     "\n"
@@ -1106,7 +1147,6 @@ GenerateStructors(io::Printer* printer) {
     "classname", classname_,
     "adddescriptorsname",
     GlobalAddDescriptorsName(descriptor_->file()->name()));
-
 }
 
 void MessageGenerator::
@@ -1377,11 +1417,22 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
     // Special-case MessageSet.
     printer->Print(
       "bool $classname$::MergePartialFromCodedStream(\n"
-      "    ::google::protobuf::io::CodedInputStream* input) {\n"
+      "    ::google::protobuf::io::CodedInputStream* input) {\n",
+      "classname", classname_);
+
+    PrintHandlingOptionalStaticInitializers(
+      descriptor_->file(), printer,
+      // With static initializers.
       "  return _extensions_.ParseMessageSet(input, default_instance_,\n"
-      "                                      mutable_unknown_fields());\n"
-      "}\n",
+      "                                      mutable_unknown_fields());\n",
+      // Without.
+      "  return _extensions_.ParseMessageSet(input, &default_instance(),\n"
+      "                                      mutable_unknown_fields());\n",
+      // Vars.
       "classname", classname_);
+
+    printer->Print(
+      "}\n");
     return;
   }
 
@@ -1541,12 +1592,21 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
     }
     printer->Print(") {\n");
     if (HasUnknownFields(descriptor_->file())) {
-      printer->Print(
+      PrintHandlingOptionalStaticInitializers(
+        descriptor_->file(), printer,
+        // With static initializers.
         "  DO_(_extensions_.ParseField(tag, input, default_instance_,\n"
+        "                              mutable_unknown_fields()));\n",
+        // Without.
+        "  DO_(_extensions_.ParseField(tag, input, &default_instance(),\n"
         "                              mutable_unknown_fields()));\n");
     } else {
-      printer->Print(
-        "  DO_(_extensions_.ParseField(tag, input, default_instance_));\n");
+      PrintHandlingOptionalStaticInitializers(
+        descriptor_->file(), printer,
+        // With static initializers.
+        "  DO_(_extensions_.ParseField(tag, input, default_instance_));\n",
+        // Without.
+        "  DO_(_extensions_.ParseField(tag, input, &default_instance()));\n");
     }
     printer->Print(
       "  continue;\n"
diff --git a/src/google/protobuf/compiler/cpp/cpp_message_field.cc b/src/google/protobuf/compiler/cpp/cpp_message_field.cc
index 23e75b87..7c785e7e 100644
--- a/src/google/protobuf/compiler/cpp/cpp_message_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_message_field.cc
@@ -82,8 +82,16 @@ GenerateAccessorDeclarations(io::Printer* printer) const {
 void MessageFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
   printer->Print(variables_,
-    "inline const $type$& $classname$::$name$() const {\n"
-    "  return $name$_ != NULL ? *$name$_ : *default_instance_->$name$_;\n"
+    "inline const $type$& $classname$::$name$() const {\n");
+
+  PrintHandlingOptionalStaticInitializers(
+    variables_, descriptor_->file(), printer,
+    // With static initializers.
+    "  return $name$_ != NULL ? *$name$_ : *default_instance_->$name$_;\n",
+    // Without.
+    "  return $name$_ != NULL ? *$name$_ : *default_instance().$name$_;\n");
+
+  printer->Print(variables_,
     "}\n"
     "inline $type$* $classname$::mutable_$name$() {\n"
     "  set_has_$name$();\n"