Linux，套接字，非阻塞连接 [英] Linux, sockets, non-blocking connect

问题描述

我想创建一个非阻塞连接. 像这样:

I want to create a non-blocking connect. Like this:

socket.connect(); // returns immediately

为此，我使用了另一个线程，无限循环和Linux epoll.像这样(伪代码):

For this, I use another thread, an infinite loop and Linux epoll. Like this(pseudocode):

// in another thread
{
  create_non_block_socket();
  connect();

  epoll_create();
  epoll_ctl(); // subscribe socket to all events
  while (true)
  {
    epoll_wait(); // wait a small time(~100 ms)
    check_socket(); // check on EPOLLOUT event
  }
}

如果我先运行服务器，然后运行客户端，则所有工作正常.如果我先运行客户端，请稍等一会儿，再运行服务器，然后客户端将无法连接.

If I run a server and then a client, all it works. If I first run a client, wait a some small time, run a server, then the client doesn't connect.

我做错了什么?也许可以做不同的事情吗?

What am I doing wrong? Maybe it can be done differently?

推荐答案

对于异步连接，您应该使用以下步骤:

You should use the following steps for an async connect:

• 使用socket(..., SOCK_NONBLOCK, ...)
创建套接字
• 与connect(fd, ...)
开始连接
• 如果返回值既不是0也不是EINPROGRESS，则中止并出现错误
• 等待直到发信号通知fd准备输出
• 使用getsockopt(fd, SOL_SOCKET, SO_ERROR, ...)
检查套接字的状态
• 完成

• create socket with socket(..., SOCK_NONBLOCK, ...)
• start connection with connect(fd, ...)
• if return value is neither 0 nor EINPROGRESS, then abort with error
• wait until fd is signalled as ready for output
• check status of socket with getsockopt(fd, SOL_SOCKET, SO_ERROR, ...)
• done

没有循环-除非您想处理EINTR.

No loops - unless you want to handle EINTR.

如果首先启动客户端，则应该在最后一步看到错误ECONNREFUSED.如果发生这种情况，请关闭插座并从头开始.

If the client is started first, you should see the error ECONNREFUSED in the last step. If this happens, close the socket and start from the beginning.

在不查看更多详细信息的情况下很难分辨代码出了什么问题.我想，您不会因check_socket操作中的错误而中止.

It is difficult to tell what's wrong with your code, without seeing more details. I suppose, that you do not abort on errors in your check_socket operation.

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