Implement Bus and ObjectProxy classes for our D-Bus library.

dbus/bus.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 DBUS_BUS_H_
+#define DBUS_BUS_H_
+#pragma once
+
+#include <set>
+#include <string>
+#include <dbus/dbus.h>
+
+#include "base/callback.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/tracked_objects.h"
+
+class MessageLoop;
+
+namespace base {
+class Thread;
+}
+
+namespace dbus {
+
+class ExportedObject;
+class ObjectProxy;
+
+// Bus is used to establish a connection with D-Bus, create object
+// proxies, and export objects.
+//
+// For asynchronous operations such as an asynchronous method call, the
+// bus object will use a message loop to monitor the underlying file
+// descriptor used for D-Bus communication. By default, the bus will use
+// the current thread's MessageLoopForIO. If |dbus_thread| option is
+// specified, the bus will use the D-Bus thread's message loop.
+//
+// THREADING
+//
+// In the D-Bus library, we use the two threads:
+//
+// - The origin thread: the thread that created the Bus object.
+// - The D-Bus thread: the thread supplifed by |dbus_thread| option.
+//
+// The origin thread is usually Chrome's UI thread. The D-Bus thread is
+// usually a dedicated thread for the D-Bus library.
+//
+// BLOCKING CALLS
+//
+// Functions that issue blocking calls are marked "BLOCKING CALL" and
+// these functions should be called in the D-Bus thread (if
+// supplied). AssertOnDBusThread() is placed in these functions.
+//
+// Note that it's hard to tell if a libdbus function is actually blocking
+// or not (ex. dbus_bus_request_name() internally calls
+// dbus_connection_send_with_reply_and_block(), which is a blocking
+// call). To err on the side, we consider all libdbus functions that deal
+// with the connection to dbus-damoen to be blocking.
+//
+// EXAMPLE USAGE:
+//
+// Synchronous method call:
+//
+//   dbus::Bus::Options options;
+//   // Set up the bus options here.
+//   ...
+//   dbus::Bus bus(options);
+//
+//   dbus::ObjectProxy* object_proxy =
+//       bus.GetObjectProxy(service_name, object_path);
+//
+//   dbus::MethodCall method_call(interface_name, method_name);
+//   dbus::Response response;
+//   bool success =
+//       object_proxy.CallMethodAndBlock(&method_call, timeout_ms, &response);
+//
+// Asynchronous method call:
+//
+//   void OnResponse(dbus::Response* response) {
+//     // response is NULL if the method call failed.
+//     if (!response)
+//       return;
+//     // Do something with response here, and delete it.
+//     delete response;
+//   }
+//
+//   ...
+//   object_proxy.CallMethod(&method_call, timeout_ms,
+//                           base::Bind(&OnResponse));
+//
+// Exporting a method:
+//
+//   Response* Echo(dbus::MethodCall* method_call) {
+//     // Do something with method_call.
+//     Response* response = Response::FromMethodCall(method_call);
+//     // Build response here.
+//     return response;
+//   }
+//
+//   void OnExported(const std::string& interface_name,
+//                   const std::string& object_path,
+//                   bool success) {
+//     // success is true if the method was exported successfully.
+//   }
+//
+//   ...
+//   dbus::ExportedObject* exported_object =
+//       bus.GetExportedObject(service_name, object_path);
+//   exported_object.ExportMethod(interface_name, method_name,
+//                                base::Bind(&Echo),
+//                                base::Bind(&OnExported));
+//
+// WHY IS THIS A REF COUNTED OBJECT?
+//
+// Bus is a ref counted object, to ensure that |this| of the object is
+// alive when callbacks referencing |this| are called. However, after
+// Shutdown() is called, |connection_| can be NULL. Hence, calbacks should
+// not rely on that |connection_| is alive.
+class Bus : public base::RefCountedThreadSafe<Bus> {
+ public:
+  // Specifies the bus type. SESSION is used to communicate with per-user
+  // services like GNOME applications. SYSTEM is used to communicate with
+  // system-wide services like NetworkManager.
+  enum BusType {
+    SESSION = DBUS_BUS_SESSION,
+    SYSTEM  = DBUS_BUS_SYSTEM,
+  };
+
+  // Specifies the connection type. PRIVATE should usually be used unless
+  // you are sure that SHARED is safe for you, which is unlikely the case
+  // in Chrome.
+  //
+  // PRIVATE gives you a private connection, that won't be shared with
+  // other Bus objects.
+  //
+  // SHARED gives you a connection shared among other Bus objects, which
+  // is unsafe if the connection is shared with multiple threads.
+  enum ConnectionType {
+    PRIVATE,
+    SHARED,
+  };
+
+  // Options used to create a Bus object.
+  struct Options {
+    Options();
+    ~Options();

[stevenjb, 2011/08/10 19:40:07]

nit: a struct shouldn't need a destructor, and I find it is better to inline the
constructor so that it is self-documenting (i.e. the default comments next to
the members below become unnecessary).

[satorux1, 2011/08/10 21:14:27]

I agree with you that it'd be nicer to inline the constructor. The reason I put
the definition in .cc file was that I was bitten by the clang bot more than once
where they raised an error for "complex" constructor and destructor:

http://www.chromium.org/developers/coding-style/chromium-style-checker-errors

Here, we are safe, but we'll be bitten by the clang bot, if we add more members,
so I'd keep the definition in .cc file.

[stevenjb, 2011/08/10 21:31:18]

Meh. I didn't realize clang would trigger on number of members. The whole point
of a struct is that it shouldn't have any logic, which is why I prefer inline
constructors, but whatever. Given clang's behavior, your reasoning is sound.

+
+    BusType bus_type;  // SESSION by default.
+    ConnectionType connection_type;  // PRIVATE by default.
+    // If the thread is set, the bus object will use the message loop
+    // attached to the thread to process asynchronous operations.
+    //
+    // The thread should meet the following requirements:
+    // 1) Already running.
+    // 2) Has a MessageLoopForIO.
+    // 3) Outlives the bus.
+    base::Thread* dbus_thread;  // NULL by default.
+  };
+
+  // Called when shutdown is done. Used for Shutdown().
+  typedef base::Callback<void ()> OnShutdownCallback;
+
+  // Creates a Bus object. The actual connection will be established when
+  // Connect() is called.
+  explicit Bus(const Options& options);
+
+  // Gets the object proxy for the given service name and the object path.
+  // The caller must not delete the returned object. The bus will own the
+  // object. Never returns NULL.
+  //
+  // The object proxy is used to call remote methods.
+  //
+  // |service_name| looks like "org.freedesktop.NetworkManager", and
+  // |object_path| looks like "/org/freedesktop/NetworkManager/Devices/0".
+  //
+  // Must be called in the origin thread.
+  virtual ObjectProxy* GetObjectProxy(const std::string& service_name,
+                                      const std::string& object_path);
+
+  // Gets the exported object for the given service name and the object
+  // path. The caller must not delete the returned object. The bus will
+  // own the object. Never returns NULL.
+  //
+  // The exported object is used to export objects to other D-Bus clients.
+  //
+  // Must be called in the origin thread.
+  virtual ExportedObject* GetExportedObject(const std::string& service_name,
+                                            const std::string& object_path);
+
+  // Shutdowns the bus and blocks until it's done. More specifically, this

[stevenjb, 2011/08/10 19:40:07]

nit: Shuts down

[satorux1, 2011/08/10 21:14:27]

Done.

+  // function does the followings:

[stevenjb, 2011/08/10 19:40:07]

nit: following

[satorux1, 2011/08/10 21:14:27]

Done.

+  //
+  // - Unregisters the object paths
+  // - Releases the service names
+  // - Close the connection to dbus-daemon.

[stevenjb, 2011/08/10 19:40:07]

nit: Closes

[satorux1, 2011/08/10 21:14:27]

Done.

+  //
+  // BLOCKING CALL.
+  virtual void ShutdownAndBlock();
+
+  // Shutdowns the bus in the D-Bus thread. |callback| will be called in

[stevenjb, 2011/08/10 19:40:07]

nit: Shuts down

[satorux1, 2011/08/10 21:14:27]

Done.

+  // the origin thread.
+  //
+  // Must be called in the origin thread.
+  virtual void Shutdown(OnShutdownCallback callback);
+
+  //
+  // The public functions below are not intended to be used in client
+  // code. These are used to implement ObjectProxy and ExportedObject.
+  //
+
+  // Connects the bus to the dbus-daemon.
+  // Returns true on success, or the bus is already connected.
+  //
+  // BLOCKING CALL.
+  virtual bool Connect();
+
+  // Requests the ownership of the given service name.
+  // Returns true on success, or the the service name is already obtained.
+  //
+  // BLOCKING CALL.
+  virtual bool RequestOwnership(const std::string& service_name);
+
+  // Releases the ownership of the given service name.
+  // Returns true on success.
+  //
+  // BLOCKING CALL.
+  virtual bool ReleaseOwnership(const std::string& service_name);
+
+  // Sets up async operations.
+  // Returns true on success, or it's already set up.
+  // This function needs to be called before starting async operations.
+  //
+  // BLOCKING CALL.
+  virtual bool SetUpAsyncOperations();
+
+  // Sends a message to the bus and blocks until the response is
+  // received. Used to implement synchronous method calls.
+  //
+  // BLOCKING CALL.
+  virtual DBusMessage* SendWithReplyAndBlock(DBusMessage* request,
+                                             int timeout_ms,
+                                             DBusError* error);
+
+  // Requests to send a message to the bus.
+  //
+  // BLOCKING CALL.
+  virtual void SendWithReply(DBusMessage* request,
+                             DBusPendingCall** pending_call,
+                             int timeout_ms);
+
+  // Tries to register the object path.
+  //
+  // BLOCKING CALL.
+  virtual bool TryRegisterObjectPath(const std::string& object_path,
+                                     const DBusObjectPathVTable* vtable,
+                                     void* user_data,
+                                     DBusError* error);
+
+  // Unregister the object path.
+  //
+  // BLOCKING CALL.
+  virtual bool UnregisterObjectPath(const std::string& object_path);
+
+  // Posts the task to the message loop of the thread that created the bus.
+  virtual void PostTaskToOriginThread(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task);
+
+  // Posts the task to the message loop of the D-Bus thread. If D-Bus
+  // thread is not supplied, the message loop of the origin thread will be
+  // used.
+  virtual void PostTaskToDBusThread(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task);
+
+  // Posts the delayed task to the message loop of the D-Bus thread. If
+  // D-Bus thread is not supplied, the message loop of the origin thread
+  // will be used.
+  virtual void PostDelayedTaskToDBusThread(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task,
+      int delay_ms);
+
+  // Check whether the current thread is on the origin thread (the thread
+  // that created the bus). If not, DCHECK will fail.
+  virtual void AssertOnOriginThread();
+
+  // Check whether the current thread is on the D-Bus thread. If not,
+  // DCHECK will fail. If the D-Bus thread is not supplied, it calls
+  // AssertOnOriginThread().
+  virtual void AssertOnDBusThread();
+
+  // Returns true if the bus has the D-Bus thread.
+  virtual bool has_dbus_thread() { return dbus_thread_ != NULL; }
+
+ private:
+  friend class base::RefCountedThreadSafe<Bus>;
+  virtual ~Bus();
+
+  // Helper function used for Shutdown().
+  void ShutdownInternal(OnShutdownCallback callback);
+
+  // Processes the all incoming data to the connection, if any.
+  //
+  // BLOCKING CALL.
+  void ProcessAllIncomingDataIfAny();
+
+  // Called when a watch object is added. Used to start monitoring the
+  // file descriptor used for D-Bus communication.
+  dbus_bool_t OnAddWatch(DBusWatch* raw_watch);
+
+  // Called when a watch object is removed.
+  void OnRemoveWatch(DBusWatch* raw_watch);
+
+  // Called when the "enabled" status of |raw_watch| is toggled.
+  void OnToggleWatch(DBusWatch* raw_watch);
+
+  // Called when a timeout object is added. Used to start monitoring
+  // timeout for method calls.
+  dbus_bool_t OnAddTimeout(DBusTimeout* raw_timeout);
+
+  // Called when a timeout object is removed.
+  void OnRemoveTimeout(DBusTimeout* raw_timeout);
+
+  // Called when the "enabled" status of |raw_timeout| is toggled.
+  void OnToggleTimeout(DBusTimeout* raw_timeout);
+
+  // Called when the dispatch status (i.e. if any incoming data is
+  // available) is changed.
+  void OnDispatchStatusChanged(DBusConnection* connection,
+                               DBusDispatchStatus status);
+
+  // Callback helper functions. Redirects to the corresponding member function.
+  static dbus_bool_t OnAddWatchThunk(DBusWatch* raw_watch, void* data);
+  static void OnRemoveWatchThunk(DBusWatch* raw_watch, void* data);
+  static void OnToggleWatchThunk(DBusWatch* raw_watch, void* data);
+  static dbus_bool_t OnAddTimeoutThunk(DBusTimeout* raw_timeout, void* data);
+  static void OnRemoveTimeoutThunk(DBusTimeout* raw_timeout, void* data);
+  static void OnToggleTimeoutThunk(DBusTimeout* raw_timeout, void* data);
+  static void OnDispatchStatusChangedThunk(DBusConnection* connection,
+                                           DBusDispatchStatus status,
+                                           void* data);

[stevenjb, 2011/08/10 19:40:07]

Can these be declared in a local namespace inside the .cc file?

[satorux1, 2011/08/10 21:14:27]

These need to be static member functions, as these call private non-static
member functions like:

dbus_bool_t Bus::OnAddWatchThunk(DBusWatch* raw_watch, void* data) {
  Bus* self = static_cast<Bus*>(data);
  return self->OnAddWatch(raw_watch);  // OnAddWatch() is private.

[stevenjb, 2011/08/10 21:31:18]

That makes sense.

+  const BusType bus_type_;
+  const ConnectionType connection_type_;
+  base::Thread* dbus_thread_;
+  DBusConnection* connection_;
+
+  MessageLoop* origin_loop_;
+  base::PlatformThreadId origin_thread_id_;
+  base::PlatformThreadId dbus_thread_id_;
+
+  std::set<std::string> owned_service_names_;
+  std::vector<dbus::ObjectProxy*> object_proxies_;
+  std::vector<dbus::ExportedObject*> exported_objects_;
+
+  bool async_operations_are_set_up_;
+
+  DISALLOW_COPY_AND_ASSIGN(Bus);
+};
+
+}  // namespace dbus
+
+#endif  // DBUS_BUS_H_