From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: RPC clnt_create() adress already in use
Date: Mon, 05 Feb 2018 13:34:00 -0000 [thread overview]
Message-ID: <20180205133450.GJ2912@calimero.vinschen.de> (raw)
In-Reply-To: <20180205112617.GB2912@calimero.vinschen.de>
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On Feb 5 12:26, Corinna Vinschen wrote:
> On Feb 5 02:29, Mark Geisert wrote:
> > Using Cygwin's bindresvport() is the best solution because Cygwin keeps
> > track of the last port number it has allocated *to any Cygwin program*.
> > This is the only approach that can deal with multiple programs and multiple
> > calls in one program. So we need to nail down why it doesn't seem to work
> > for you.
>
> Apart from all the above, there may still be a problem in the given scenario.
>
> 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.
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
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next prev parent reply other threads:[~2018-02-05 13:34 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-05 8:19 PAULUS, Raimund, TI-ABN
2018-02-05 10:29 ` Mark Geisert
2018-02-05 11:26 ` Corinna Vinschen
2018-02-05 13:34 ` Corinna Vinschen [this message]
2018-02-05 14:06 ` Corinna Vinschen
2018-02-05 20:15 ` Corinna Vinschen
-- strict thread matches above, loose matches on Subject: below --
2018-03-08 11:44 PAULUS, Raimund, TI-ABN
2018-03-08 15:24 ` Corinna Vinschen
2018-03-08 23:00 ` Mark Geisert
2018-03-02 10:39 PAULUS, Raimund, TI-ABN
2018-02-27 9:54 PAULUS, Raimund, TI-ABN
2018-02-27 10:37 ` Corinna Vinschen
2018-02-28 6:00 ` Mark Geisert
2018-02-06 11:29 PAULUS, Raimund, TI-ABN
2018-02-06 14:20 ` Corinna Vinschen
2018-02-07 6:54 ` Mark Geisert
2018-02-05 14:58 PAULUS, Raimund, TI-ABN
2018-02-02 12:58 PAULUS, Raimund, TI-ABN
2018-01-30 10:07 PAULUS, Raimund, TI-ABN
2018-01-31 8:15 ` Mark Geisert
2018-01-31 9:11 ` Corinna Vinschen
2018-01-31 9:35 ` Mark Geisert
2018-02-02 8:11 ` Mark Geisert
2018-01-30 7:01 PAULUS, Raimund, TI-ABN
2018-01-30 9:05 ` Mark Geisert
2017-12-19 16:13 PAULUS, Raimund, TI-ABN
2017-12-28 0:03 ` Mark Geisert
2017-09-29 9:52 PAULUS, Raimund, TI-ABN
2017-09-29 17:36 ` Mark Geisert
2017-09-27 12:51 PAULUS, Raimund, TI-ABN
2017-09-25 6:44 PAULUS, Raimund, TI-ABN
2017-09-27 9:50 ` Mark Geisert
2017-09-22 7:22 PAULUS, Raimund, TI-ABN
2017-09-24 9:49 ` Mark Geisert
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