问题描述
我正试图在套接字上调用select,我不明白自己在做什么错.
setup_server_socket调用bind和listen并将套接字设置为非阻塞模式.
似乎在select上的以下代码块被调用,而不是前进到FD_ISSET.我尝试连接客户端,但似乎成功,但select从未返回任何内容.
执行此操作的正确方法是什么?
... int listenfd = setup_server_socket( serverPort ); if( -1 == listenfd ) return 1; fd_set read_fds; FD_ZERO(&read_fds); int fdmax = listenfd; // loop forever while( 1 ) { if (select(fdmax+1, &read_fds, NULL,NULL,NULL) == -1){ perror("select"); exit(4); } for (int i = 0; i<= fdmax; i++){ printf("Testing: %d, %d\n", i, FD_ISSET(i,&read_fds)); }return 0; ...
阅读多次选择(2),投票(2 (顺便说一句,您应该更喜欢poll而不是过时的select,后者不处理大于__FD_SETSIZE的文件描述符,即在我的Linux/Debian/x86-64系统上为1024). >
然后:
fd_set read_fds; FD_ZERO(&read_fds); int fdmax = listenfd; FD_SET(listenfd, &read_fds);
在调用select之前,应该进入循环内的 .顺便说一句,我建议使用poll代替select
还请阅读有关 C10k问题
别忘了select正在更改其给定的fd_set -s(通常希望它们为非空)...
也许使用 strace(1)
也请阅读高级Linux编程(这是一本免费的书,您也可以在纸上阅读,也可以从中下载其他几个地方,例如此等...)
I'm trying to wrap my head around calling select on sockets and I can't understand what I'm doing wrong.
setup_server_socket calls bind and listen and sets the socket to nonblocking mode.
The following code blocks on the select call it seems, not moving forward to FD_ISSET. I tried connecting a client and it seems to succeed but select never returns anything.
What's the proper way to do this?
... int listenfd = setup_server_socket( serverPort ); if( -1 == listenfd ) return 1; fd_set read_fds; FD_ZERO(&read_fds); int fdmax = listenfd; // loop forever while( 1 ) { if (select(fdmax+1, &read_fds, NULL,NULL,NULL) == -1){ perror("select"); exit(4); } for (int i = 0; i<= fdmax; i++){ printf("Testing: %d, %d\n", i, FD_ISSET(i,&read_fds)); }return 0; ...
Read several times select(2), poll(2) (BTW, you should prefer poll to the obsolete select, which don't handle file descriptors bigger than __FD_SETSIZE, i.e. 1024 on my Linux/Debian/x86-64 system).
Then:
fd_set read_fds; FD_ZERO(&read_fds); int fdmax = listenfd; FD_SET(listenfd, &read_fds);
should go inside the while(1) loop, before calling select. BTW, I recommend using poll instead of select
Read also about the C10k problem
Don't forget that select is changing its given fd_set-s (and usually wants them to be non-empty)...
Perhaps use strace(1)
Read also Advanced Linux Programming (it is a free book that you could also read on paper, or download from several other places, e.g. this etc...)
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