On Feb 5 15:06, Corinna Vinschen wrote: > On Feb 5 14:34, Corinna Vinschen wrote: > > On Feb 5 12:26, Corinna Vinschen wrote: > > > To reiterate the problem we observe: > > > > > > - socket() > > > - setsockopt (SO_REUSEADDR) > > > - bind() succeeds > > > - connect() fails with EADDRINUSE while socket is still in TIME_WAIT > > > > > > using bindresvport in place of bind only marginally changes the > > > situation, in particular if the second parameter is set and requests a > > > port number != 0. What happens in that case is that bindresvport calls > > > bind with this port number and checks if bind returns EADDRINUSE. > > > > > > Only then it tries to bind other port numbers in the reserved range. > > > But we now know that bind will never return EADDINUSE if the SO_REUSEADDR > > > socket option has been set. > > > > > > Even assuming the process calls bindresvport(sock, NULL) we may end up > > > returning a port number already in use if the process is the only Cygwin > > > process on the system. The reason is that Cygwin uses a round robin > > > approach which relies on having a globally shared value called > > > last_used_bindresvport. If the process is the only Cygwin process on > > > the system, this information is lost after exiting the process, so the > > > next process will start with the same start port number and bind will > > > again fail to notice the client with EADDRINUSE. > > > > > > What potential solutions to this problem do we have? > > > > > > - bindresvport could enforce SO_EXCLUSIVEADDRUSE temporarily to make > > > sure bind fails. > > > > Nope, no way. Even enforcing SO_EXCLUSIVEADDRUSE results in the > > second bind succeeding and the subsequent connect failing. The > > entire SO_REUSEADDR/SO_EXCLUSIVEADDRUSE semantics only works as > > desired on the server side apparently > > > > > - bindresvport could check every local address for being free prior > > > to calling bind. However, there's a potential race here. > > > > > > - DisconnectEx? Never tried this Winsock extension but it might be > > > worth a shot. > > I think I have a very simple solution for the scenario which calls > bindresvport with port number. Still looking for a solution for > the second problem...
I've pushed a few patches and uploaded new developer snapshots to https://cygwin.com/snapshots. Please give them a try. Thanks, Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat
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