PPAPI: Reduce string copying in SerializedVar.

ppapi/proxy/serialized_var.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ppapi/proxy/serialized_var.h"
 
 #include "base/logging.h"
 #include "ipc/ipc_message_utils.h"
 #include "ppapi/proxy/dispatcher.h"
 #include "ppapi/proxy/interface_proxy.h"
 #include "ppapi/proxy/ppapi_param_traits.h"
 #include "ppapi/proxy/var_serialization_rules.h"
 
 namespace ppapi {
 namespace proxy {
 
 // SerializedVar::Inner --------------------------------------------------------
 
 SerializedVar::Inner::Inner()
     : serialization_rules_(NULL),
       var_(PP_MakeUndefined()),
+      tracker_string_ptr_(NULL),
       cleanup_mode_(CLEANUP_NONE),
       dispatcher_for_end_send_pass_ref_(NULL) {
 #ifndef NDEBUG
   has_been_serialized_ = false;
   has_been_deserialized_ = false;
 #endif
 }
 
 SerializedVar::Inner::Inner(VarSerializationRules* serialization_rules)
     : serialization_rules_(serialization_rules),
       var_(PP_MakeUndefined()),
+      tracker_string_ptr_(NULL),
       cleanup_mode_(CLEANUP_NONE),
       dispatcher_for_end_send_pass_ref_(NULL) {
 #ifndef NDEBUG
-  has_been_serialized_ = false;
-  has_been_deserialized_ = false;
-#endif
-}
-
-SerializedVar::Inner::Inner(VarSerializationRules* serialization_rules,
-                            const PP_Var& var)
-    : serialization_rules_(serialization_rules),
-      var_(var),
-      cleanup_mode_(CLEANUP_NONE),
-      dispatcher_for_end_send_pass_ref_(NULL) {
-#ifndef NDEBUG
   has_been_serialized_ = false;
   has_been_deserialized_ = false;
 #endif
 }
 
 SerializedVar::Inner::~Inner() {
   switch (cleanup_mode_) {
     case END_SEND_PASS_REF:
       DCHECK(dispatcher_for_end_send_pass_ref_);
       serialization_rules_->EndSendPassRef(var_,
@@ skipping 21 matching lines @@
   return var_;
 }
 
 void SerializedVar::Inner::SetVar(PP_Var var) {
   // Sanity check, when updating the var we should have received a
   // serialization rules pointer already.
   DCHECK(serialization_rules_);
   var_ = var;
 }
 
-const std::string& SerializedVar::Inner::GetString() const {
+scoped_ptr<std::string> SerializedVar::Inner::GetStringDestructive() {
   DCHECK(serialization_rules_);
-  return string_value_;
+  return string_from_ipc_.Pass();
 }
 
-std::string* SerializedVar::Inner::GetStringPtr() {
+const std::string** SerializedVar::Inner::GetStringPtrPtr() {
   DCHECK(serialization_rules_);
-  return &string_value_;
+  // The caller will set our string pointer, and we promise not to change it.
+  // This path is taken for the "Send" side of SerializedVars, and we will only
+  // read the string in those cases, so it's safe for us to point directly to a
+  // string in the VarTracker.
+  return &tracker_string_ptr_;
 }
 
 void SerializedVar::Inner::ForceSetVarValueForTest(PP_Var value) {
   var_ = value;
 }
 
 void SerializedVar::Inner::ForceSetStringValueForTest(const std::string& str) {
-  string_value_ = str;
+  // We don't need to change tracker_string_ptr_, as that is only used for
+  // serializing, and we're emulating a SerializedVar that was received from
+  // IPC.
+  string_from_ipc_.reset(new std::string(str));
 }
 
 void SerializedVar::Inner::WriteToMessage(IPC::Message* m) const {
   // When writing to the IPC messages, a serization rules handler should
   // always have been set.
   //
   // When sending a message, it should be difficult to trigger this if you're
   // using the SerializedVarSendInput class and giving a non-NULL dispatcher.
   // Make sure you're using the proper "Send" helper class.
   //
   // It should be more common to see this when handling an incoming message
   // that returns a var. This means the message handler didn't write to the
   // output parameter, or possibly you used the wrong helper class
   // (normally SerializedVarReturnValue).
   DCHECK(serialization_rules_);
 
 #ifndef NDEBUG
   // We should only be serializing something once.
   DCHECK(!has_been_serialized_);
   has_been_serialized_ = true;
 #endif
 
   // If the var is not a string type, we should not have ended up with any
   // string data.
-  DCHECK(var_.type == PP_VARTYPE_STRING || string_value_.empty());
+  DCHECK(var_.type == PP_VARTYPE_STRING || !tracker_string_ptr_);
 
   m->WriteInt(static_cast<int>(var_.type));
   switch (var_.type) {
     case PP_VARTYPE_UNDEFINED:
     case PP_VARTYPE_NULL:
       // These don't need any data associated with them other than the type we
       // just serialized.
       break;
     case PP_VARTYPE_BOOL:
       m->WriteBool(PP_ToBool(var_.value.as_bool));
       break;
     case PP_VARTYPE_INT32:
       m->WriteInt(var_.value.as_int);
       break;
     case PP_VARTYPE_DOUBLE:
       IPC::ParamTraits<double>::Write(m, var_.value.as_double);
       break;
     case PP_VARTYPE_STRING:
       // TODO(brettw) in the case of an invalid string ID, it would be nice
       // to send something to the other side such that a 0 ID would be
       // generated there. Then the function implementing the interface can
       // handle the invalid string as if it was in process rather than seeing
       // what looks like a valid empty string.
-      m->WriteString(string_value_);
+      m->WriteString(tracker_string_ptr_ ? *tracker_string_ptr_
+                                           : std::string());
       break;
     case PP_VARTYPE_ARRAY_BUFFER:
       // TODO(dmichael): Proxy ArrayBuffer.
       NOTIMPLEMENTED();
       break;
     case PP_VARTYPE_OBJECT:
       m->WriteInt64(var_.value.as_id);
       break;
     case PP_VARTYPE_ARRAY:
     case PP_VARTYPE_DICTIONARY:
@@ skipping 36 matching lines @@
       var_.value.as_bool = PP_FromBool(bool_value);
       break;
     }
     case PP_VARTYPE_INT32:
       success = m->ReadInt(iter, &var_.value.as_int);
       break;
     case PP_VARTYPE_DOUBLE:
       success = IPC::ParamTraits<double>::Read(m, iter, &var_.value.as_double);
       break;
     case PP_VARTYPE_STRING:
-      success = m->ReadString(iter, &string_value_);
+      DCHECK(!tracker_string_ptr_ && !string_from_ipc_.get());
+      string_from_ipc_.reset(new std::string);
+      success = m->ReadString(iter, string_from_ipc_.get());
       var_.value.as_id = 0;
       break;
     case PP_VARTYPE_OBJECT:
       success = m->ReadInt64(iter, &var_.value.as_id);
       break;
     case PP_VARTYPE_ARRAY:
     case PP_VARTYPE_DICTIONARY:
       // TODO(brettw) when these types are supported, implement this.
       NOTIMPLEMENTED();
       break;
@@ skipping 24 matching lines @@
 
 // SerializedVar ---------------------------------------------------------------
 
 SerializedVar::SerializedVar() : inner_(new Inner) {
 }
 
 SerializedVar::SerializedVar(VarSerializationRules* serialization_rules)
     : inner_(new Inner(serialization_rules)) {
 }
 
-SerializedVar::SerializedVar(VarSerializationRules* serialization_rules,
-                             const PP_Var& var)
-    : inner_(new Inner(serialization_rules, var)) {
-}
-
 SerializedVar::~SerializedVar() {
 }
 
 // SerializedVarSendInput ------------------------------------------------------
 
 SerializedVarSendInput::SerializedVarSendInput(Dispatcher* dispatcher,
                                                const PP_Var& var)
     : SerializedVar(dispatcher->serialization_rules()) {
   inner_->SetVar(dispatcher->serialization_rules()->SendCallerOwned(
-      var, inner_->GetStringPtr()));
+      var, inner_->GetStringPtrPtr()));
 }
 
 // static
 void SerializedVarSendInput::ConvertVector(Dispatcher* dispatcher,
                                            const PP_Var* input,
                                            size_t input_count,
                                            std::vector<SerializedVar>* output) {
-  output->resize(input_count);
-  for (size_t i = 0; i < input_count; i++) {
-    SerializedVar& cur = (*output)[i];
-    cur = SerializedVar(dispatcher->serialization_rules());
-    cur.inner_->SetVar(dispatcher->serialization_rules()->SendCallerOwned(
-        input[i], cur.inner_->GetStringPtr()));
-  }
+  output->reserve(input_count);
+  for (size_t i = 0; i < input_count; i++)
+    output->push_back(SerializedVarSendInput(dispatcher, input[i]));
 }
 
 // ReceiveSerializedVarReturnValue ---------------------------------------------
 
 ReceiveSerializedVarReturnValue::ReceiveSerializedVarReturnValue() {
 }
 
 ReceiveSerializedVarReturnValue::ReceiveSerializedVarReturnValue(
     const SerializedVar& serialized)
     : SerializedVar(serialized) {
 }
 
 PP_Var ReceiveSerializedVarReturnValue::Return(Dispatcher* dispatcher) {
   inner_->set_serialization_rules(dispatcher->serialization_rules());
   inner_->SetVar(inner_->serialization_rules()->ReceivePassRef(
-      inner_->GetIncompleteVar(), inner_->GetString(), dispatcher));
+      inner_->GetIncompleteVar(), inner_->GetStringDestructive(), dispatcher));
   return inner_->GetVar();
 }
 
 // ReceiveSerializedException --------------------------------------------------
 
 ReceiveSerializedException::ReceiveSerializedException(Dispatcher* dispatcher,
                                                        PP_Var* exception)
     : SerializedVar(dispatcher->serialization_rules()),
       dispatcher_(dispatcher),
       exception_(exception) {
 }
 
 ReceiveSerializedException::~ReceiveSerializedException() {
   if (exception_) {
     // When an output exception is specified, it will take ownership of the
     // reference.
-    inner_->SetVar(inner_->serialization_rules()->ReceivePassRef(
-        inner_->GetIncompleteVar(), inner_->GetString(), dispatcher_));
+    inner_->SetVar(
+        inner_->serialization_rules()->ReceivePassRef(
+            inner_->GetIncompleteVar(),
+            inner_->GetStringDestructive(),
+            dispatcher_));
     *exception_ = inner_->GetVar();
   } else {
     // When no output exception is specified, the browser thinks we have a ref
     // to an object that we don't want (this will happen only in the plugin
     // since the browser will always specify an out exception for the plugin to
     // write into).
     //
     // Strings don't need this handling since we can just avoid creating a
     // Var from the std::string in the first place.
     if (inner_->GetVar().type == PP_VARTYPE_OBJECT)
@@ skipping 53 matching lines @@
   serialized_.inner_->set_serialization_rules(
       dispatcher->serialization_rules());
 
   // Ensure that when the serialized var goes out of scope it cleans up the
   // stuff we're making in BeginReceiveCallerOwned.
   serialized_.inner_->SetCleanupModeToEndReceiveCallerOwned();
 
   serialized_.inner_->SetVar(
       serialized_.inner_->serialization_rules()->BeginReceiveCallerOwned(
           serialized_.inner_->GetIncompleteVar(),
-          serialized_.inner_->GetStringPtr(),
+          serialized_.inner_->GetStringDestructive(),
           dispatcher));
   return serialized_.inner_->GetVar();
 }
 
 // SerializedVarVectorReceiveInput ---------------------------------------------
 
 SerializedVarVectorReceiveInput::SerializedVarVectorReceiveInput(
     const std::vector<SerializedVar>& serialized)
     : serialized_(serialized) {
 }
@@ skipping 10 matching lines @@
   deserialized_.resize(serialized_.size());
   for (size_t i = 0; i < serialized_.size(); i++) {
     // The vectors must be able to clean themselves up after this call is
     // torn down.
     serialized_[i].inner_->set_serialization_rules(
         dispatcher->serialization_rules());
 
     serialized_[i].inner_->SetVar(
         serialized_[i].inner_->serialization_rules()->BeginReceiveCallerOwned(
             serialized_[i].inner_->GetIncompleteVar(),
-            serialized_[i].inner_->GetStringPtr(),
+            serialized_[i].inner_->GetStringDestructive(),
             dispatcher));
     deserialized_[i] = serialized_[i].inner_->GetVar();
   }
 
   *array_size = static_cast<uint32_t>(serialized_.size());
   return deserialized_.empty() ? NULL : &deserialized_[0];
 }
 
 // SerializedVarReturnValue ----------------------------------------------------
 
 SerializedVarReturnValue::SerializedVarReturnValue(SerializedVar* serialized)
     : serialized_(serialized) {
 }
 
 void SerializedVarReturnValue::Return(Dispatcher* dispatcher,
                                       const PP_Var& var) {
   serialized_->inner_->set_serialization_rules(
       dispatcher->serialization_rules());
 
   // Var must clean up after our BeginSendPassRef call.
   serialized_->inner_->SetCleanupModeToEndSendPassRef(dispatcher);
 
   serialized_->inner_->SetVar(
       dispatcher->serialization_rules()->BeginSendPassRef(
           var,
-          serialized_->inner_->GetStringPtr()));
+          serialized_->inner_->GetStringPtrPtr()));
 }
 
 // static
 SerializedVar SerializedVarReturnValue::Convert(Dispatcher* dispatcher,
                                                 const PP_Var& var) {
   // Mimic what happens in the normal case.
   SerializedVar result;
   SerializedVarReturnValue retvalue(&result);
   retvalue.Return(dispatcher, var);
   return result;
 }
 
 // SerializedVarOutParam -------------------------------------------------------
 
 SerializedVarOutParam::SerializedVarOutParam(SerializedVar* serialized)
     : serialized_(serialized),
       writable_var_(PP_MakeUndefined()),
       dispatcher_(NULL) {
 }
 
 SerializedVarOutParam::~SerializedVarOutParam() {
   if (serialized_->inner_->serialization_rules()) {
     // When unset, OutParam wasn't called. We'll just leave the var untouched
     // in that case.
     serialized_->inner_->SetVar(
         serialized_->inner_->serialization_rules()->BeginSendPassRef(
-            writable_var_, serialized_->inner_->GetStringPtr()));
+            writable_var_, serialized_->inner_->GetStringPtrPtr()));
 
     // Normally the current object will be created on the stack to wrap a
     // SerializedVar and won't have a scope around the actual IPC send. So we
     // need to tell the SerializedVar to do the begin/end send pass ref calls.
     serialized_->inner_->SetCleanupModeToEndSendPassRef(dispatcher_);
   }
 }
 
 PP_Var* SerializedVarOutParam::OutParam(Dispatcher* dispatcher) {
   dispatcher_ = dispatcher;
@@ skipping 53 matching lines @@
   inner_->ForceSetStringValueForTest(str);
 }
 
 SerializedVarTestReader::SerializedVarTestReader(const SerializedVar& var)
     : SerializedVar(var) {
 }
 
 }  // namespace proxy
 }  // namespace ppapi