D-Bus

lazycat posted @ 2012年3月05日 14:43 in linux , 5333 阅读

D-Bus 也是一个用于进程间通信的框架。

简单介绍一下如何编写一个helloworld通信例子。

0. 下载源码

http://www.freedesktop.org/wiki/Software/dbus#Download.

1. ./configure

这时候可能会出现问题：

configure: error: Could not find expat.h, check config.log for failed attempts

可以通过

sudo apt-get install libexpat1-dev

来解决

2. make

3. make install

其中可能遇到的编译问题

1. fatal error: dbus/dbus.h: No such file or directory

把/usr/local/include/dbus-1.0/dbus/拷贝到/usr/include/dbus

2. fatal error: dbus/dbus-arch-deps.h: No such file or directory

把/usr/local/lib/dbus-1.0/include/dbus/dbus-arch-deps.h拷贝到/usr/include/dbus

3. 链接错误 collect2: ld returned 1 exit status

添加链接选项 -l dbus-1

测试代码

服务端接收消息

/* server.c */

#include <dbus/dbus.h>
#include <stdbool.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

static DBusHandlerResult
filter_func(DBusConnection *connection, DBusMessage *message, void *usr_data)
{
    dbus_bool_t handled = false;
    char *word = NULL;
    DBusError dberr;

    if (dbus_message_is_signal(message, "client.signal.Type", "Test")) {
        dbus_error_init(&dberr);
        dbus_message_get_args(message, &dberr, DBUS_TYPE_STRING,
            &word, DBUS_TYPE_INVALID);
        if (dbus_error_is_set(&dberr)) {
            dbus_error_free(&dberr);
        } else {
            printf("receive message %s\n", word);
            handled = true;
        }
    }
    return (handled ? DBUS_HANDLER_RESULT_HANDLED : DBUS_HANDLER_RESULT_NOT_YET_HANDLED);
}

int main(int argc, char *argv[])
{
    DBusError dberr;
    DBusConnection *dbconn;

    dbus_error_init(&dberr);

    dbconn = dbus_bus_get(DBUS_BUS_SESSION, &dberr);
    if (dbus_error_is_set(&dberr)) {
        dbus_error_free(&dberr);
        return -1;
    }

    if (!dbus_connection_add_filter(dbconn, filter_func, NULL, NULL)) {
        return -1;
    }

    dbus_bus_add_match(dbconn, "type='signal',interface='client.signal.Type'", &dberr);
    if (dbus_error_is_set(&dberr)) {
        dbus_error_free(&dberr);
        return -1;
    }

    while(dbus_connection_read_write_dispatch(dbconn, -1)) {
        /* loop */
    }
    return 0;
}

客户端发送消息

#include <dbus/dbus.h>
#include <stdbool.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

int db_send(DBusConnection *dbconn)
{
    DBusMessage *dbmsg;
    char *word;
    int i;

    dbmsg = dbus_message_new_signal("/client/signal/Object", // object name of the signal
                                  "client.signal.Type",      // interface name of the signal
                                  "Test");                   // name of the signal
    if (!dbmsg) {
        return -1;
    }

    word = "hello world";
    if (!dbus_message_append_args(dbmsg, DBUS_TYPE_STRING, &word, DBUS_TYPE_INVALID)) {
        return -1;
    }

    if (!dbus_connection_send(dbconn, dbmsg, NULL)) {
        return -1;
    }
    dbus_connection_flush(dbconn);
    printf("send message %s\n", word);

    dbus_message_unref(dbmsg);
    return 0;
}

int main(int argc, char *argv[])
{
    DBusError dberr;
    DBusConnection *dbconn;
    int i;

    dbus_error_init(&dberr);

    dbconn = dbus_bus_get(DBUS_BUS_SESSION, &dberr);
    if (dbus_error_is_set(&dberr)) {
        return -1;
    }

    db_send(dbconn);

    dbus_connection_unref(dbconn);

    return 0;
}

测试结果如下

root@ubuntu:~/dbus# gcc -o client client.c -l dbus-1

root@ubuntu:~/dbus# gcc -o server server.c -l dbus-1

root@ubuntu:~/dbus# ./listen

receive message hello world

root@ubuntu:~/dbus# ./send

send message hello world

很多API和具体实现还没搞清楚，有待深入研究。

D-Bus的性能会比linux自带的send,recv高么?

http://pvanhoof.be/blog/index.php/2010/05/13/ipc-performance-the-report

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