监听 dbus 信号

Posted 2023-04-14

【中文标题】监听 dbus 信号

【英文标题】：Listening to dbus signals

【发布时间】：2016-07-16 13:08:57

【问题描述】：

我正在尝试从 c 代码中收听 dbus-event。我可以通过 dbus-monitor 事件捕获它们。

dbus-monitor --session --monitor "type='signal',interface='org.jwz.XScreensaver'"

signal sender=org.freedesktop.DBus -> dest=:1.146 serial=2 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameAcquired
   string ":1.146"

signal sender=:1.96 -> dest=(null destination) serial=40 path=/org/jwz/XScreensaver; interface=org.jwz.XScreensaver; member=ScreensaverStarted
signal sender=:1.96 -> dest=(null destination) serial=41 path=/org/jwz/XScreensaver; interface=org.jwz.XScreensaver; member=ScreensaverStopped

当我从 c 代码尝试时相同，不可见。不确定我在哪里丢失了回调没有签名然后事件是预期的，或者我的路径/接口是错误的。这是代码

static void
test_hint_signal_handler (DBusGProxy * proxy,
       gpointer user_data)

  printf("I am here");


gint
main (gint argc, gchar *argv[])

  printf("In Main\n");
  DBusGConnection *dbus_glib_connection = NULL;
  GMainLoop *loop = NULL;
  GError *error = NULL;
  DBusGProxy *control_proxy = NULL;

  g_type_init ();

  loop = g_main_loop_new (NULL, FALSE);

  dbus_glib_connection = dbus_g_bus_get (DBUS_BUS_SYSTEM, &error);
  if (error != NULL)
    
      g_warning ("Failed connecting to system bus: %s", error->message);
      dbus_glib_connection = NULL;
      g_error_free (error);
    
  if (dbus_glib_connection != NULL)
    
      control_proxy = dbus_g_proxy_new_for_name( dbus_glib_connection,
            "org.jwz.XScreensaver",
            "/org/jwz/XScreensaver",
            "org.jwz.XScreensaver"
            );
      if (control_proxy == NULL)
    
      g_warning ("Failed to get proxy");
    
    
  if (control_proxy != NULL)
    
        dbus_g_proxy_add_signal( control_proxy,
            "ScreensaverStarted",
            G_TYPE_INVALID
            );

    dbus_g_proxy_connect_signal( control_proxy,
            "ScreensaverStarted",
            G_CALLBACK(test_hint_signal_handler),
            NULL,
            NULL
            );

    

  g_debug("Starting mainloop");
  g_main_loop_run (loop);

  return 0;

编辑：代码没有退出。它正在等待事件的到来。这是编译时警告

dbus-test-client.c: In function ‘main’:
dbus-test-client.c:20:3: warning: ‘g_type_init’ is deprecated [-Wdeprecated-declarations]
   g_type_init ();
   ^
In file included from /usr/include/glib-2.0/gobject/gobject.h:24:0,
                 from /usr/include/glib-2.0/gobject/gbinding.h:29,
                 from /usr/include/glib-2.0/glib-object.h:23,
                 from /usr/include/dbus-1.0/dbus/dbus-glib.h:27,
                 from dbus-test-client.c:2:
/usr/include/glib-2.0/gobject/gtype.h:681:23: note: declared here
 void                  g_type_init                    (void);
                       ^

【问题讨论】：

你能在主循环之后添加一些g_debug 调用，以确保你没有退出它。您在编译或执行时收到警告了吗？

在问题本身中添加了评论

【参考方案1】：

在顶部代码中您添加了 --session 参数（您正在使用会话总线），而在底部 C 代码中您正在连接到 SYSTEM 总线 (DBUS_BUS_SYSTEM)。用C代码把SYSTEM总线切换到SESSION总线（DBUS_BUS_SESSION）就可以了：

dbus_glib_connection = dbus_g_bus_get (DBUS_BUS_SESSION, &error);