在 glib(mm) 中监控 UDP 套接字会占用 CPU 时间

发布于 2024-09-05 21:48:45 字数 1841 浏览 11 评论 0原文

我有一个 GTKmm Windows 应用程序(用 MinGW 构建),它接收 UDP 数据包(不发送)。套接字是本机的winsock,我使用glibmm IOChannel 将其连接到应用程序主循环。套接字是用recvfrom 读取的。

我的问题是:此设置在 3GHz 工作站上占用了 25% 的 CPU 时间。有人能告诉我为什么吗?

在这种情况下,应用程序处于空闲状态,如果我删除 UDP 代码,CPU 使用率会下降到几乎为零。由于应用程序必须执行一些 CPU 密集型任务,我可以想象更好的方法来花费这 25%

以下是一些代码摘录:(对 printf 感到抱歉;))


/* bind */
void UDPInterface::bindToPort(unsigned short port)
{
    struct sockaddr_in target;
    WSADATA wsaData;

    target.sin_family = AF_INET;
    target.sin_port = htons(port);
    target.sin_addr.s_addr = 0;

    if ( WSAStartup ( 0x0202, &wsaData ) )
    {
        printf("WSAStartup failed!\n");
        exit(0); // :)
        WSACleanup();
    }

    sock = socket( AF_INET, SOCK_DGRAM, 0 );
    if (sock == INVALID_SOCKET)
    {
        printf("invalid socket!\n");
        exit(0);
    }

    if (bind(sock,(struct sockaddr*) &target, sizeof(struct sockaddr_in) ) == SOCKET_ERROR)
    {
        printf("failed to bind to port!\n");
        exit(0);
    }

    printf("[UDPInterface::bindToPort] listening on port %i\n", port);
}

/* read */
bool UDPInterface::UDPEvent(Glib::IOCondition io_condition)
{
    recvfrom(sock, (char*)buf, BUF_SIZE*4, 0, NULL, NULL);
    /* process packet... */
}

/* glibmm connect */
Glib::RefPtr channel = Glib::IOChannel::create_from_win32_socket(udp.sock);
Glib::signal_io().connect( sigc::mem_fun(udp, &UDPInterface::UDPEvent), channel, Glib::IO_IN );

我已经在其他一些问题中以及 glib 文档中读到过(g_io_channel_win32_new_socket()) 表示套接字被置于非阻塞模式,这是“实现的副作用并且不可避免”。这是否解释了CPU的影响,我不清楚?

无论我使用 glib 访问套接字还是直接调用 recvfrom() 似乎都没有太大区别,因为 CPU 在任何数据包到达并调用读取处理程序之前就已用完。 glibmm 文档还指出,即使套接字被轮询(Glib::IOChannel::create_from_win32_socket()),也可以调用 recvfrom()

我已经尝试使用 -pg 编译程序并使用 gprof 创建了每个函数的 cpu 使用情况报告。这没有用,因为时间不是花在我的程序上,而是花在一些外部 glib/glibmm dll 上。

I have a GTKmm Windows application (built with MinGW) that receives UDP packets (no sending). The socket is native winsock and I use glibmm IOChannel to connect it to the application main loop. The socket is read with recvfrom.

My problem is: this setup eats 25% percent CPU time on a 3GHz workstation. Can somebody tell me why?

The application is idle in this case, and if I remove the UDP code, CPU usage drops down to almost zero. As the application has to perform some CPU intensive tasks, I could image better ways to spend that 25%

Here are some code excerpts: (sorry for the printf's ;) )


/* bind */
void UDPInterface::bindToPort(unsigned short port)
{
    struct sockaddr_in target;
    WSADATA wsaData;

    target.sin_family = AF_INET;
    target.sin_port = htons(port);
    target.sin_addr.s_addr = 0;

    if ( WSAStartup ( 0x0202, &wsaData ) )
    {
        printf("WSAStartup failed!\n");
        exit(0); // :)
        WSACleanup();
    }

    sock = socket( AF_INET, SOCK_DGRAM, 0 );
    if (sock == INVALID_SOCKET)
    {
        printf("invalid socket!\n");
        exit(0);
    }

    if (bind(sock,(struct sockaddr*) &target, sizeof(struct sockaddr_in) ) == SOCKET_ERROR)
    {
        printf("failed to bind to port!\n");
        exit(0);
    }

    printf("[UDPInterface::bindToPort] listening on port %i\n", port);
}

/* read */
bool UDPInterface::UDPEvent(Glib::IOCondition io_condition)
{
    recvfrom(sock, (char*)buf, BUF_SIZE*4, 0, NULL, NULL);
    /* process packet... */
}

/* glibmm connect */
Glib::RefPtr channel = Glib::IOChannel::create_from_win32_socket(udp.sock);
Glib::signal_io().connect( sigc::mem_fun(udp, &UDPInterface::UDPEvent), channel, Glib::IO_IN );

I've read here in some other question, and also in glib docs (g_io_channel_win32_new_socket()) that the socket is put into nonblocking mode, and it's "a side-effect of the implementation and unavoidable". Does this explain the CPU effect, it's not clear to me?

Whether or not I use glib to access the socket or call recvfrom() directly doesn't seem to make much difference, since CPU is used up before any packet arrives and the read handler gets invoked. Also glibmm docs state that it's ok to call recvfrom() even if the socket is polled (Glib::IOChannel::create_from_win32_socket())

I've tried compiling the program with -pg and created a per function cpu usage report with gprof. This wasn't usefull because the time is not spent in my program, but in some external glib/glibmm dll.

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