Hello Corinna, with the snapshot of cygwin1.dll and using bindresvport() from Cygwin for libtirpc (instead of the original bindresvport() from libtirpc) all my testcases work without error.
Many thanks Raimund -----Ursprüngliche Nachricht----- Von: cygwin-ow...@cygwin.com [mailto:cygwin-ow...@cygwin.com] Im Auftrag von Corinna Vinschen Gesendet: Montag, 5. Februar 2018 21:15 An: cygwin@cygwin.com Betreff: Re: RPC clnt_create() adress already in use 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
