一种IPC通信机制Gdbus详解

一、DBus介绍

常规进程间通信有管道，消息队列，共享内存，以及socket等，每个都有优劣，这次我们介绍一种高阶的进程间通信方式DBus。
DBus通信是IPC通信机制的一种方式，本身是建立在socket机制之上，它支持远程函数调用和信号传递。
它有两种模式，分别为：session(会话模式)、system(总线模式)
总线模式（system bus）：采用总线模式时，系统需要维护一个DBus Daemon，每个DBus的请求通过DBus Daemon转发。这种模式Server只需要维护一个与DBus Daemon的链接，结构清晰，可以通过广播的方式发送消息到各个Client。
会话模式（session bus）：这种模式一般称之为点对点的星型结构，Client与Server之间是直接的Peer2Peer的连接，少了DBus Daemon的中转，因此性能较好。

二、DBus API

glib API中有两种可以用的，分别是dbus-glib和gdbus，dbus-glib是一种老的API，现在不推荐使用了，gdbus是从glib2.26开始添加的，目前推荐使用。gdbus和glib-dbus都是GNU组织开发的，gdbus可以认为是dbus-glib的升级版，其编程过程比起dbus-glib来要简单得多。

三、DBus 开发

多进程之间需要通信，可能有一对一，可能有一对多，多对多的通信方式。为简单起见，我们假设某个系统中就只有两个进程需要通信——我们称之为Server和Client。基于GDBus的进程间通信，首先就是要定义好Server和Client之间的通信接口。在GDBus编程框架下，我们使用xml文件来描述接口，然后通过GDbus提供的工具生成对应的C/C++代码。
通常应用的组织形式如下，服务端发布的时候同时提供接口库供其他客户端程序调用，客户端连接接口库即可，像正常的接口调用，如下图，下面我们通过一个设置、获取一个人姓名和年龄，并且设置完姓名和年龄后会广播给所有客户端的程序来学习一下GDBus。

interface_people.xml

<?xml version="1.0" encoding="UTF-8"?>
<node><interface name="gdbus.demo.people"><method name="set_name"><arg name="name" type="s" direction="in"/><arg name="ret" type="b" direction="out"/></method><method name="get_name"><arg name="name" type="s" direction="out"/></method><method name="set_age"><arg name="age" type="i" direction="in"/><arg name="ret" type="b" direction="out"/></method><method name="get_age"><arg name="age" type="i" direction="out"/></method><signal name="send_info"><arg name="name" type="s"/><arg name="age" type="i"/></signal></interface>
</node>

四、数据类型介绍

上面XML中使用了一些数据类型，对应关系如下表。
1、基本数据类型

2、复杂数据类型

五、程序运行

gdbus运行需要先运行deamon和环境变量
方法一：
1、运行下面脚本，生成地址，同时这个daemon要跑着

dbus-daemon --config-file=/etc/dbus-1/session.conf --print-address

2、生成的地址替换掉下面的地址部分

export DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-4z6nMwqewd,guid=e6359f4ef81d07fc7185fb8b6059d267

3、在需要运行程序的终端中设置上面的环境变量
方法二：
1、执行完下面脚本，然后在同一终端运行Server和Client

eval dbus-launch --auto-syntax

方法三：

export DBUS_SESSION_BUS_ADDRESS="unix:abstract=/tmp/dbus-cwrMdqoyqU,guid=4780330fcb5755ab1492ce8800000024"
dbus-daemon --config-file=/etc/dbus-1/session.conf --address=$DBUS_SESSION_BUS_ADDRESS

六、代码附录

文件结构如下

重点代码
client.cpp

#include <iostream>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>#include "interface.h"using namespace std;int main(void)
{string name = "";int age = 0;interface iface;iface.initDBusCommunication();name = "dongdong.fan";iface.set_name(name);iface.set_age(30);name = iface.get_name();age = iface.get_age();cout << "Have a people name:" << name << "age:" << age;while (1){sleep(10);}return 0;
}

service.cpp

#include <unistd.h>#include "people.h"
#include "gdbusServer.h"int main()
{initDBusCommunication();while (1){sleep(10);}return 0;
}

gdbusServer.cpp

#include "gdbusServer.h"#include <ctype.h>
#include <gio/gio.h>
#include <glib.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>#include "gdbusCommon.h"
#include "people.h"
#include "people_gen_interface.h"static guint g_own_id = 0;
static GMainLoop *g_pLoop = NULL;
static GdbusDemoPeople *g_pSkeleton = NULL;
static people g_people;// start
static gboolean set_name_method(GdbusDemoPeople *object,GDBusMethodInvocation *invocation,const gchar *in_arg,gpointer user_data) {my_printf("Server set_name_method is call, arg is : %s.\n", in_arg);bool ret = 0;string strTemp = in_arg;ret = g_people.set_name(strTemp);gdbus_demo_people_complete_set_name(object, invocation, ret);// 同时广播gdbus_demo_people_emit_send_info(object,g_people.get_name().c_str(),g_people.get_age());return TRUE;
}static gboolean get_name_method(GdbusDemoPeople *object,GDBusMethodInvocation *invocation,const gchar *in_arg,gpointer user_data) {my_printf("Server get_name_method is call.\n");string strTemp = g_people.get_name();gdbus_demo_people_complete_get_name(object, invocation, strTemp.c_str());return TRUE;
}static gboolean set_age_method(GdbusDemoPeople *object,GDBusMethodInvocation *invocation,gint in_arg,gpointer user_data) {my_printf("Server set_age_method is call, arg is : %d.\n", in_arg);bool ret = 0;ret = g_people.set_age(in_arg);gdbus_demo_people_complete_set_age(object, invocation, ret);// 同时广播gdbus_demo_people_emit_send_info(object,g_people.get_name().c_str(),g_people.get_age());return TRUE;
}static gboolean get_age_method(GdbusDemoPeople *object,GDBusMethodInvocation *invocation,gpointer user_data) {my_printf("Server get_age_method is call.\n");int age = g_people.get_age();gdbus_demo_people_complete_get_age(object, invocation, age);return TRUE;
}
// endstatic void GBusAcquired_Callback(GDBusConnection *connection,const gchar *name,gpointer user_data) {GError *pError = NULL;g_pSkeleton = gdbus_demo_people_skeleton_new();// Attach to dbus signals// start(void)g_signal_connect(g_pSkeleton, "handle-set-name", G_CALLBACK(set_name_method), NULL);(void)g_signal_connect(g_pSkeleton, "handle-get-name", G_CALLBACK(get_name_method), NULL);(void)g_signal_connect(g_pSkeleton, "handle-set-age", G_CALLBACK(set_age_method), NULL);(void)g_signal_connect(g_pSkeleton, "handle-get-age", G_CALLBACK(get_age_method), NULL);// end(void)g_dbus_interface_skeleton_export(G_DBUS_INTERFACE_SKELETON(g_pSkeleton),connection,GDBUS_DEMO_PEOPLE_OBJECT_PATH,&pError);if (pError == 0) {my_printf("skeleton export successfully. \n");} else {my_printf("Error: Failed to export object. Reason: %s.\n", pError->message);g_error_free(pError);g_main_loop_quit(g_pLoop);return;}
}static void GBusNameAcquired_Callback(GDBusConnection *connection,const gchar *name,gpointer user_data) {my_printf("GBusNameAcquired_Callback, Acquired bus name: %s \n", GDBUS_DEMO_PEOPLE_NAME);
}static void GBusNameLost_Callback(GDBusConnection *connection,const gchar *name,gpointer user_data) {if (connection == NULL) {my_printf("GBusNameLost_Callback, Error: Failed to connect to dbus. \n");} else {my_printf("GBusNameLost_Callback, Error: Failed to get dbus name : %s\n", GDBUS_DEMO_PEOPLE_NAME);}g_main_loop_quit(g_pLoop);
}static void *run_callback(void *arg) {g_main_loop_run(g_pLoop);return NULL;
}bool initDBusCommunication(void) {bool ret = false;pthread_t tid;g_pLoop = g_main_loop_new(NULL, FALSE);if (NULL == g_pLoop) {my_printf("g_pLoop is NULL\n");goto LEAVE;}g_own_id = g_bus_own_name(G_BUS_TYPE_SESSION,GDBUS_DEMO_PEOPLE_NAME,G_BUS_NAME_OWNER_FLAGS_NONE,&GBusAcquired_Callback,&GBusNameAcquired_Callback,&GBusNameLost_Callback,NULL,NULL);pthread_create(&tid, NULL, run_callback, NULL);ret = true;
LEAVE:return ret;
}bool uinitDBusCommunication(void) {g_bus_unown_name(g_own_id);g_main_loop_unref(g_pLoop);return true;
}

gdbusServer.cpp

#ifndef _GDBUS_SERVER_H_
#define _GDBUS_SERVER_H_bool initDBusCommunication(void);
bool uinitDBusCommunication(void);#endif

people.cpp

#include "people.h"people::people()
{m_name = "default";m_age = 20;
}people::~people()
{//todo
}bool people::set_name(string &name)
{m_name = name;return true;
}string people::get_name()
{return m_name;
}bool people::set_age(int age)
{m_age = age;return true;
}int people::get_age()
{return m_age;
}

people.hpp

#ifndef _PEOPLE_H_
#define _PEOPLE_H_#include <string>using namespace std;class people
{public:people();~people();bool set_name(string &name);string get_name();bool set_age(int age);int get_age();private:string m_name;     // 姓名int m_age;         // 年龄  
};#endif

interface.hpp

#ifndef  _INTERFACE_H_
#define  _INTERFACE_H_#include <string>class interface
{public:interface();virtual ~interface();bool initDBusCommunication(void);//peoplebool set_name(std::string &name);std::string get_name();bool set_age(int age);int get_age();
};#endif