在没有服务器调用“接受"的情况下，套接字上的“连接"调用能否成功返回? [英] Can 'connect' call on socket return successfully without server calling 'accept'?

问题描述

服务器创建了一个套接字并绑定到一个端口，并启动了一个循环接受连接的线程.稍后由于导致线程退出的异常而退出循环，但套接字仍然绑定到端口.现在，如果客户端连接"到此服务器，则成功.这怎么可能?如果我理解正确，连接"仅在服务器在侦听套接字上接受"后返回.我在这里遗漏了什么吗?

Server has created a socket and bound to a port and started a thread which is in loop to accept the connection. Sometime later loop exited due to an exception resulting in thread exit but socket is still bounded to port. Now if client does a 'connect' to this server, it is succeeding. How is it possible? If I understand correctly, 'connect' returns only after server does 'accept' on the listening socket. Am I missing something here?

推荐答案

如果我理解正确，'connect' 仅在服务器对侦听套接字执行 'accept' 后返回.我在这里遗漏了什么吗?

If I understand correctly, 'connect' returns only after server does 'accept' on the listening socket. Am I missing something here?

是的.TCP 在幕后建立连接 - 3 次握手 - 并在准备就绪时将其放入已完成的连接队列中.Accept() 从这个队列的前面返回下一个等待的连接.

Yes. TCP establishes the connection - the 3-way handshake - under the covers and puts it in a completed connection queue when it is ready. Accept() returns the next waiting connection from the front of this queue.

从客户端的角度来看，它是连接的"，但在服务器接受并开始处理之前它不会与任何人交谈.有点像当您致电公司并立即进入等待队列时.您已连接"，但在有人真正接听并开始说话之前，不会有任何业务进行.

From the client's perspective it is "connected" but it won't be talking to anyone until the server accepts and begins processing. Sort of like when you call a company and are immediately put in the hold queue. You are "connected" but no business is going to be done until someone actually picks up and starts talking.

您的单个​​线程可能已经死亡，但进程仍然存在并且文件描述符仍然打开，因此 TCP 不知道应用程序级别发生了什么.

Your individual thread may have died but the process is still alive and the file descriptor still open so TCP doesn't know what is going on at the application level.

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