Mojo C++ bindings: remove the lock in MultiplexRouter if it only serves a single interface.

mojo/public/cpp/bindings/lib/multiplex_router.h

 // Copyright 2015 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 MOJO_PUBLIC_CPP_BINDINGS_LIB_MULTIPLEX_ROUTER_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_MULTIPLEX_ROUTER_H_
 
 #include <stdint.h>
 
 #include <deque>
@@ skipping 38 matching lines @@
 // while the others are safe to call from any threads. Please see the method
 // comments for more details.
 //
 // NOTE: CloseMessagePipe() or PassMessagePipe() MUST be called on |runner|'s
 // thread before this object is destroyed.
 class MultiplexRouter
     : public MessageReceiver,
       public AssociatedGroupController,
       public PipeControlMessageHandlerDelegate {
  public:
+  enum Config {
+    // There is only the master interface running on this router. Please note
+    // that because of interface versioning, the other side of the message pipe
+    // may use a newer master interface definition which passes associated
+    // interfaces. In that case, this router may still receive pipe control
+    // messages or messages targetting associated interfaces.
+    SINGLE_INTERFACE,
+    // There may be associated interfaces running on this router.
+    MULTI_INTERFACE
+  };
+
   // If |set_interface_id_namespace_bit| is true, the interface IDs generated by
   // this router will have the highest bit set.
-  MultiplexRouter(bool set_interface_id_namespace_bit,
-                  ScopedMessagePipeHandle message_pipe,
+  MultiplexRouter(ScopedMessagePipeHandle message_pipe,
+                  Config config,
+                  bool set_interface_id_namespace_bit,
                   scoped_refptr<base::SingleThreadTaskRunner> runner);
 
   // Sets the master interface name for this router. Only used when reporting
   // message header or control message validation errors.
   void SetMasterInterfaceName(const std::string& name);
 
   // ---------------------------------------------------------------------------
   // The following public methods are safe to call from any threads.
 
   // AssociatedGroupController implementation:
@@ skipping 125 matching lines @@
   // been closed, removes it from |endpoints_|.
   // NOTE: The method may invalidate |endpoint|.
   enum EndpointStateUpdateType { ENDPOINT_CLOSED, PEER_ENDPOINT_CLOSED };
   void UpdateEndpointStateMayRemove(InterfaceEndpoint* endpoint,
                                     EndpointStateUpdateType type);
 
   void RaiseErrorInNonTestingMode();
 
   InterfaceEndpoint* FindOrInsertEndpoint(InterfaceId id, bool* inserted);
 
+  void AssertLockAcquired();
+
   // Whether to set the namespace bit when generating interface IDs. Please see
   // comments of kInterfaceIdNamespaceMask.
   const bool set_interface_id_namespace_bit_;
 
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
 
   // Owned by |filters_| below.
   MessageHeaderValidator* header_validator_;
 
   FilterChain filters_;
   Connector connector_;
 
   base::ThreadChecker thread_checker_;
 
   // Protects the following members.
-  mutable base::Lock lock_;
+  // Sets to nullptr in Config::SINGLE_INTERFACE mode.
+  std::unique_ptr<base::Lock> lock_;
   PipeControlMessageHandler control_message_handler_;
   PipeControlMessageProxy control_message_proxy_;
 
   std::map<InterfaceId, scoped_refptr<InterfaceEndpoint>> endpoints_;
   uint32_t next_interface_id_value_;
 
   std::deque<std::unique_ptr<Task>> tasks_;
   // It refers to tasks in |tasks_| and doesn't own any of them.
   std::map<InterfaceId, std::deque<Task*>> sync_message_tasks_;
 
   bool posted_to_process_tasks_;
   scoped_refptr<base::SingleThreadTaskRunner> posted_to_task_runner_;
 
   bool encountered_error_;
 
   bool paused_;
 
   bool testing_mode_;
 
   DISALLOW_COPY_AND_ASSIGN(MultiplexRouter);
 };
 
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_MULTIPLEX_ROUTER_H_