linux - socket::accept continual to return EGAIN -

i use nonblocking socket receive new connection. code repeatedly fails accept().

int sockfd = ::socket(family, sock_stream | sock_nonblock | sock_cloexec, ipproto_tcp); ::bind(sockfd, bind_addr, static_cast<socklen_t>(sizeof(struct sockaddr_in6))); ret = ::listen(sockfd, somaxconn);  while (true) {     ::poll(&*pollfds_.begin(), pollfds_.size(), timeoutms);     struct sockaddr_in6 addr;     bzero(&addr, sizeof addr);     socklen_t addrlen = static_cast<socklen_t>(sizeof *addr);     int connfd = ::accept4(sockfd, sockaddr_cast(addr),                          &addrlen, sock_nonblock | sock_cloexec); } 

errno eagain.

from manpage accept(2):

eagain or ewouldblock

the socket marked nonblocking , no connections present accepted. posix.1-2001 allows either error returned case, , not require these constants have same value, portable application should check both possibilities.

this means call accept made before client has connected.