dbus-glib 和 GDBus 的區別

http://people.freedesktop.org/~david/gio-gdbus-codegen-20110412/ch29.html

Conceptual differences(概念上的區別)

The central concepts of D-Bus are modelled in a very similar way in dbus-glib and GDBus. Both have a objects representing connections, proxies and method invocations. But there are some important differences:

D-Bus最重要的概念在dbus-glib和GDBus中都是相似的.都用對象表示連接,代理 和 方法執行,但也有一些重要的不同點:

• dbus-glib uses the libdbus reference implementation, GDBus doesn't. Instead, it relies on GIO streams as transport layer, and has its own implementation for the the D-Bus connection setup and authentication. Apart from using streams as transport, avoiding libdbus also lets GDBus avoid some thorny multithreading issues.

        dbus-glib使用 libdbus reference implementation,GDBus不使用,而是依賴GIO流作為傳輸層,並且擁有一套自己實現的D-Bus連接設置和授權的方法.暫且不說GDBus使用流傳輸,

        不使用libdbus可以使GDBus避免一些多線程方面的問題.

• dbus-glib uses the GObject type system for method arguments and return values, including a homegrown container specialization mechanism. GDBus relies on the GVariant type system which is explicitly designed to match D-Bus types.

       dbus-glib的方法參數和返回值使用Gobject類型系統,其中包含了一個特定結構的自有容器.GDBus依賴專為匹配D-Bus類型而設計的GVariant類型系統.

• dbus-glib models only D-Bus interfaces and does not provide any types for objects. GDBus models both D-Bus interfaces (via the GDBusInterface, GDBusProxy and GDBusInterfaceStub types) and objects (via the GDBusObject, GDBusObjectStub and GDBusObjectProxy types).

       dbus-glib 只能提供D-Bus接口,不為對象提供任何類型,

       GDBus同時提供D-Bus接口(通過GDBusInterface, GDBusProxy 和 GDBusInterfaceStub 類型)和對象接口(通過GDBusObject, GDBusObjectStub 和 GDBusObjectProxy 類型)

• GDBus includes native support for the org.freedesktop.DBus.Properties (via the GDBusProxy type) and org.freedesktop.DBus.ObjectManager D-Bus interfaces, dbus-glib doesn't.

       GDBus 為org.freedesktop.DBus.Properties (通過 GDBusProxy 類型) 和 org.freedesktop.DBus.ObjectManager D-Bus接口,包含了本地支持,dbus-glib沒有.

• The typical way to export an object in dbus-glib involves generating glue code from XML introspection data using dbus-binding-tool. GDBus provides a similar tool called gdbus-codegen that can also generate Docbook D-Bus interface documentation. 

       dbus-glib中導出對象的典型方法是使用dbus-binding-tool根據XML內省數據生成代碼,GDBus也提供了一個類似的工具叫做gdbus-codegen,這個工具也可以生成Docbook D-Bus接口文件.        

• dbus-glib doesn't provide any convenience API for owning and watching bus names, GDBus provides the g_bus_own_name() and g_bus_watch_name() family of convenience functions.

       dbus-glib不提供戰友和監視總線名字的方便的API,GDBus提供了g_bus_own_name() 和g_bus_watch_name() 系列的方便函數.

• GDBus provides API to parse, generate and work with Introspection XML, dbus-glib doesn't.

        GDBus提供API來解析、生成 和 工作的內省XML，dbus-glib不提供。

 

API comparison

　　　　　　　　　　　　　　　　　　　　　　　　Table. dbus-glib APIs and their GDBus counterparts

dbus-glib	GDBus
DBusGConnection	GDBusConnection
DBusGProxy	GDBusProxy, GDBusInterface - also see GDBusObjectProxy
DBusGObject	GDBusInterfaceStub, GDBusInterface - also see GDBusObjectStub
DBusGMethodInvocation	GDBusMethodInvocation
dbus_g_bus_get()	g_bus_get_sync(), also see g_bus_get()
dbus_g_proxy_new_for_name()	g_dbus_proxy_new_sync() and g_dbus_proxy_new_for_bus_sync(), also see g_dbus_proxy_new()
dbus_g_proxy_add_signal()	not needed, use the generic "g-signal"
dbus_g_proxy_connect_signal()	use g_signal_connect() with "g-signal"
dbus_g_connection_register_g_object()	g_dbus_connection_register_object() - also see g_dbus_object_manager_server_export()
dbus_g_connection_unregister_g_object()	g_dbus_connection_unregister_object() - also see g_dbus_object_manager_server_unexport()
dbus_g_object_type_install_info()	introspection data is installed while registering an object, see g_dbus_connection_register_object()
dbus_g_proxy_begin_call()	g_dbus_proxy_call()
dbus_g_proxy_end_call()	g_dbus_proxy_call_finish()
dbus_g_proxy_call()	g_dbus_proxy_call_sync()
dbus_g_error_domain_register()	g_dbus_error_register_error_domain()
dbus_g_error_has_name()	no direct equivalent, see g_dbus_error_get_remote_error()
dbus_g_method_return()	g_dbus_method_invocation_return_value()
dbus_g_method_return_error()	g_dbus_method_invocation_return_error() and variants
dbus_g_method_get_sender()	g_dbus_method_invocation_get_sender()

 

Owning bus names

Using dbus-glib, you typically call RequestName manually to own a name, like in the following excerpt:

使用dbus-glib來占有一個總線名字的典型做法是手動調用RequestName ,像下面的例子:

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error = NULL; res = dbus_g_proxy_call (system_bus_proxy, "RequestName", &error, G_TYPE_STRING, NAME_TO_CLAIM, G_TYPE_UINT, DBUS_NAME_FLAG_ALLOW_REPLACEMENT, G_TYPE_INVALID, G_TYPE_UINT, &result, G_TYPE_INVALID); if (!res) { if (error != NULL) { g_warning ("Failed to acquire %s: %s", NAME_TO_CLAIM, error->message); g_error_free (error); } else { g_warning ("Failed to acquire %s", NAME_TO_CLAIM); } goto out; } if (result != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER) { if (error != NULL) { g_warning ("Failed to acquire %s: %s", NAME_TO_CLAIM, error->message); g_error_free (error); } else { g_warning ("Failed to acquire %s", NAME_TO_CLAIM); } exit (1); } dbus_g_proxy_add_signal (system_bus_proxy, "NameLost", G_TYPE_STRING, G_TYPE_INVALID); dbus_g_proxy_connect_signal (system_bus_proxy, "NameLost", G_CALLBACK (on_name_lost), NULL, NULL); /* further setup ... */

 

While you can do things this way with GDBus too, using g_dbus_proxy_call_sync(), it is much nicer to use the high-level API for this:

當然你可以使用GDBus的方式,調用函數g_dbus_proxy_call_sync()來完成同樣的功能,但是使用高級的API(g_bus_own_name)是更好地方式.

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static void on_name_acquired (GDBusConnection *connection, const gchar *name, gpointer user_data) { /* further setup ... */ } /* ... */ owner_id = g_bus_own_name (G_BUS_TYPE_SYSTEM, NAME_TO_CLAIM, G_BUS_NAME_OWNER_FLAGS_ALLOW_REPLACEMENT, on_bus_acquired, on_name_acquired, on_name_lost, NULL, NULL); g_main_loop_run (loop); g_bus_unown_name (owner_id);

Note that g_bus_own_name() works asynchronously and requires you to enter your mainloop to await the on_name_aquired() callback. Also note that in order to avoid race conditions (e.g. when your service is activated by a method call), you have to export your manager object before acquiring the name. The on_bus_acquired() callback is the right place to do such preparations.

需要注意的是g_bus_own_name 工作方式是異步的,並且需要你進入mainloop來等待on_name_aquired()這個callback被調用.還需要注意的是為了防止條件競爭(例如你的服務是同方法調用來啟動的),你必須在就on_name_aquired()回調之前導出管理對象,on_bus_acquired()這個callback中是導出管理對象的正確位置.

Creating proxies for well-known names

dbus-glib lets you create proxy objects for well-known names, like the following example:

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proxy = dbus_g_proxy_new_for_name (system_bus_connection, "org.freedesktop.Accounts", "/org/freedesktop/Accounts", "org.freedesktop.Accounts");

For a DBusGProxy constructed like this, method calls will be sent to the current owner of the name, and that owner can change over time.

The same can be achieved with GDBusProxy:

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error = NULL; proxy = g_dbus_proxy_new_for_bus_sync (G_BUS_TYPE_SYSTEM, G_DBUS_PROXY_FLAGS_NONE, NULL, /* GDBusInterfaceInfo */ "org.freedesktop.Accounts", "/org/freedesktop/Accounts", "org.freedesktop.Accounts", NULL, /* GCancellable */ &error);

For an added layer of safety, you can specify what D-Bus interface the proxy is expected to conform to by using the GDBusInterfaceInfo type. Additionally, GDBusProxy loads, caches and tracks changes to the D-Bus properties on the remote object. It also sets up match rules so D-Bus signals from the remote object are delivered locally.

The GDBusProxy type normally isn't used directly - instead proxies subclassing GDBusProxy generated by gdbus-codegen is used, see the section called “Using gdbus-codegen”

 

 

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