PPAPI: Reduce string copying in SerializedVar.

ppapi/proxy/serialized_var.h

 // 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.
 
 #ifndef PPAPI_PROXY_SERIALIZED_VAR_H_
 #define PPAPI_PROXY_SERIALIZED_VAR_H_
 
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
 #include "ppapi/c/pp_var.h"
 #include "ppapi/proxy/ppapi_proxy_export.h"
 
 namespace IPC {
 class Message;
 }
 
 namespace ppapi {
 namespace proxy {
 
@@ skipping 57 matching lines @@
   friend class SerializedVarReturnValue;
   friend class SerializedVarOutParam;
   friend class SerializedVarSendInput;
   friend class SerializedVarTestConstructor;
   friend class SerializedVarVectorReceiveInput;
 
   class PPAPI_PROXY_EXPORT Inner : public base::RefCounted<Inner> {
    public:
     Inner();
     Inner(VarSerializationRules* serialization_rules);
-    Inner(VarSerializationRules* serialization_rules, const PP_Var& var);
     ~Inner();
 
     VarSerializationRules* serialization_rules() {
       return serialization_rules_;
     }
     void set_serialization_rules(VarSerializationRules* serialization_rules) {
       serialization_rules_ = serialization_rules;
     }
 
     // See outer class's declarations above.
     PP_Var GetVar() const;
     PP_Var GetIncompleteVar() const;
     void SetVar(PP_Var var);
-    const std::string& GetString() const;
-    std::string* GetStringPtr();
+    void SetString(scoped_ptr<std::string> str);
+    // Return a new string with the contents of the string referenced by Inner.
+    // The string referenced by the Inner will be empty after this.
+    scoped_ptr<std::string> GetStringDestructive();
+    // Return a pointer to our internal string pointer. This is so that the
+    // caller will be able to make this Inner point to a string that's owned
+    // elsewhere (i.e., in the tracker).
+    const std::string** GetStringPtrPtr();
 
     // For the SerializedVarTestConstructor, this writes the Var value as if
     // it was just received off the wire, without any serialization rules.
     void ForceSetVarValueForTest(PP_Var value);
     void ForceSetStringValueForTest(const std::string& str);
 
     void WriteToMessage(IPC::Message* m) const;
     bool ReadFromMessage(const IPC::Message* m, void** iter);
 
     // Sets the cleanup mode. See the CleanupMode enum below. These functions
@@ skipping 14 matching lines @@
       // The serialized var will call EndReceiveCallerOwned in the destructor.
       END_RECEIVE_CALLER_OWNED
     };
 
     // Rules for serializing and deserializing vars for this process type.
     // This may be NULL, but must be set before trying to serialize to IPC when
     // sending, or before converting back to a PP_Var when receiving.
     VarSerializationRules* serialization_rules_;
 
     // If this is set to VARTYPE_STRING and the 'value.id' is 0, then the
-    // string_value_ contains the string. This means that the caller hasn't
+    // string_from_ipc_ holds the string. This means that the caller hasn't
     // called Deserialize with a valid Dispatcher yet, which is how we can
     // convert the serialized string value to a PP_Var string ID.
     //
     // This var may not be complete until the serialization rules are set when
     // reading from IPC since we'll need that to convert the string_value to
     // a string ID. Before this, the as_id will be 0 for VARTYPE_STRING.
     PP_Var var_;
 
-    // Holds the literal string value to/from IPC. This will be valid if the
-    // var_ is VARTYPE_STRING.
-    std::string string_value_;
+    // If valid, this is a pointer to a string owned by the VarTracker. When our
+    // outer SerializedVar gets serialized, it will write the string directly
+    // from the tracker so we do not need to make any unnecessary copies. This
+    // should only be valid on the sender side.
+    const std::string* tracker_string_ptr_;
+
+    // If valid, this is a string received from IPC which needs to be inserted
+    // in to the var tracker. When we provide it to the tracker, we pass
+    // ownership so that there are no unnecessary copies. This should only ever
+    // be valid on the receiver side.
+    scoped_ptr<std::string> string_from_ipc_;
 
     CleanupMode cleanup_mode_;
 
     // The dispatcher saved for the call to EndSendPassRef for the cleanup.
     // This is only valid when cleanup_mode == END_SEND_PASS_REF.
     Dispatcher* dispatcher_for_end_send_pass_ref_;
 
 #ifndef NDEBUG
     // When being sent or received over IPC, we should only be serialized or
     // deserialized once. These flags help us assert this is true.
     mutable bool has_been_serialized_;
     mutable bool has_been_deserialized_;
 #endif
 
     DISALLOW_COPY_AND_ASSIGN(Inner);
   };
 
   SerializedVar(VarSerializationRules* serialization_rules);
-  SerializedVar(VarSerializationRules* serialization, const PP_Var& var);
 
   mutable scoped_refptr<Inner> inner_;
 };
 
 // Helpers for message sending side --------------------------------------------
 
 // For sending a value to the remote side.
 //
 // Example for API:
 //   void MyFunction(PP_Var)
@@ skipping 265 matching lines @@
 // For tests that want to read what's in a SerializedVar.
 class PPAPI_PROXY_EXPORT SerializedVarTestReader : public SerializedVar {
  public:
   explicit SerializedVarTestReader(const SerializedVar& var);
 
   // The "incomplete" var is the one sent over the wire. Strings and object
   // IDs have not yet been converted, so this is the thing that tests will
   // actually want to check.
   PP_Var GetIncompleteVar() const { return inner_->GetIncompleteVar(); }
 
-  const std::string& GetString() const { return inner_->GetString(); }
+  const std::string* GetTrackerStringPtr() const {
+    return *inner_->GetStringPtrPtr();
+  }
 };
 
 }  // namespace proxy
 }  // namespace ppapi
 
 #endif  // PPAPI_PROXY_SERIALIZED_VAR_H_