【dbus】invalid pointer

目的：利用dbus进行IPC
源码来源：http://www.ibm.com/developerworks/cn/linux/l-dbus.html
环境：桌面系统（因为在CLI情况下报错：** (process:5725): WARNING **: Failed to connect to the D-BUS deamon: /bin/dbus-launch terminated abnormally with the following error: Autolaunch error: X11 initialization failed.）

清单 1. dbus-ping-send.c

#include <glib.h>
#include <dbus/dbus-glib.h>
static gboolean send_ping (DBusConnection *bus);
int
main (int argc, char **argv)
{
  GMainLoop *loop;
  DBusConnection *bus;
  DBusError error;
  /* Create a new event loop to run in */
  loop = g_main_loop_new (NULL, FALSE);
  /* Get a connection to the session bus */
  dbus_error_init (&error);
  bus = dbus_bus_get (DBUS_BUS_SESSION, &error);
  if (!bus) {
    g_warning ("Failed to connect to the D-BUS daemon: %s", error.message);
    dbus_error_free (&error);
    return 1;
  }
  /* Set up this connection to work in a GLib event loop */
  dbus_connection_setup_with_g_main (bus, NULL);
  /* Every second call send_ping() with the bus as an argument*/
  g_timeout_add (1000, (GSourceFunc)send_ping, bus);
  /* Start the event loop */
  g_main_loop_run (loop);
  return 0;
}
static gboolean
send_ping (DBusConnection *bus)
{
  DBusMessage *message;
  /* Create a new signal "Ping" on the "com.burtonini.dbus.Signal" interface,
   * from the object "/com/burtonini/dbus/ping". */
  message = dbus_message_new_signal ("/com/burtonini/dbus/ping",
                                     "com.burtonini.dbus.Signal", "Ping");
  /* Append the string "Ping!" to the signal */
  dbus_message_append_args (message,
                            DBUS_TYPE_STRING, "Ping!",
                            DBUS_TYPE_INVALID);
  /* Send the signal */
  dbus_connection_send (bus, message, NULL);
  /* Free the signal now we have finished with it */
  dbus_message_unref (message);
  /* Tell the user we send a signal */
  g_print("Ping!\n");
  /* Return TRUE to tell the event loop we want to be called again */
  return TRUE;
}

清单 2. dbus-ping-listen.c

#include <glib.h>
#include <dbus/dbus-glib.h>
static DBusHandlerResult signal_filter
      (DBusConnection *connection, DBusMessage *message, void *user_data);
int
main (int argc, char **argv)
{
  GMainLoop *loop;
  DBusConnection *bus;
  DBusError error;
  loop = g_main_loop_new (NULL, FALSE);
  dbus_error_init (&error);
  bus = dbus_bus_get (DBUS_BUS_SESSION, &error);
  if (!bus) {
    g_warning ("Failed to connect to the D-BUS daemon: %s", error.message);
    dbus_error_free (&error);
    return 1;
  }
  dbus_connection_setup_with_g_main (bus, NULL);
  /* listening to messages from all objects as no path is specified */
  dbus_bus_add_match (bus, "type='signal',interface='com.burtonini.dbus.Signal'");
  dbus_connection_add_filter (bus, signal_filter, loop, NULL);
  g_main_loop_run (loop);
  return 0;
}
static DBusHandlerResult
signal_filter (DBusConnection *connection, DBusMessage *message, void *user_data)
{
  /* User data is the event loop we are running in */
  GMainLoop *loop = user_data;
  /* A signal from the bus saying we are about to be disconnected */
  if (dbus_message_is_signal
        (message, DBUS_INTERFACE_ORG_FREEDESKTOP_LOCAL, "Disconnected")) {
    /* Tell the main loop to quit */
    g_main_loop_quit (loop);
    /* We have handled this message, don't pass it on */
    return DBUS_HANDLER_RESULT_HANDLED;
  }
  /* A Ping signal on the com.burtonini.dbus.Signal interface */
  else if (dbus_message_is_signal (message, "com.burtonini.dbus.Signal", "Ping")) {
    DBusError error;
    char *s;
    dbus_error_init (&error);
    if (dbus_message_get_args
       (message, &error, DBUS_TYPE_STRING, &s, DBUS_TYPE_INVALID)) {
      g_print("Ping received: %s\n", s);
      dbus_free (s);
    } else {
      g_print("Ping received, but error getting message: %s\n", error.message);
      dbus_error_free (&error);
    }
    return DBUS_HANDLER_RESULT_HANDLED;
  }
  return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
}

编译：
gcc dbus-ping-send.c -ldbus-glib-1 -o send
gcc dbus-ping-listen.c -ldbus-glib-1 -o listen
各自编译通过
终端1执行./listen
终端2执行./send后：
终端1报错：*** glibc detected *** ./listen: free(): invalid pointer: 0x0804846c ***
经查，是dbus_free(s)一行（清单2第47行）产生的错误。
上网搜索关键词：“free(): invalid pointer:”，集中在两种情况：
可能的情况1：gcc版本问题；
可能的情况2：char *s这个指针指向的内存空间不是通过malloc分配的（malloc分配五大区中的堆区，free只能释放堆区的内存），无法用free函数释放。

情况1不大可靠；
针对情况2，把dbus_free(s)一行删除后，通过send函数无限发送消息给listen，查看listen进程占用的内存：# ps -e|grep listen
5677 pts/4    00:00:01 listen
# top -p 5677

显示该进程内存占用率一直上升，说明内存不断泄漏。

实在不知道该怎么解决了，于是在源代码的基础上，把char *s设为全局变量，并删除dbus_free(s)一行。无限发送消息测试，内存不存在泄漏问题。
算是绕个弯解决了问题。