From owner-freebsd-java@FreeBSD.ORG  Wed Dec 13 12:10:54 2006
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From: David Xu <davidxu@freebsd.org>
To: freebsd-java@freebsd.org,
 Daniel Eischen <deischen@freebsd.org>
Date: Wed, 13 Dec 2006 20:10:49 +0800
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Cc: Kostik Belousov <kostikbel@gmail.com>,
	Poul-Henning Kamp <phk@phk.freebsd.dk>, "Arne H. Juul" <arnej@pvv.ntnu.no>,
	Bruce Evans <bde@zeta.org.au>, freebsd-arch@freebsd.org
Subject: Re: close() of active socket does not work on FreeBSD 6
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On Wednesday 13 December 2006 04:49, Daniel Eischen wrote:
> On Tue, 12 Dec 2006, Poul-Henning Kamp wrote:
> > In message <20061212160016.W56465@delplex.bde.org>, Bruce Evans writes:
> >> On Mon, 11 Dec 2006, Daniel Eischen wrote:
> >>
> >> It's probably a nightmare in the kernel too.  close() starts looking
> >> like revoke(), and revoke() has large problems and bugs in this area.
> >
> > There is the distinctive difference that revoke() operates on a name
> > and close() on a filedescriptor, but otherwise I agree.
>
> Well, if threads waiting on IO are interruptable by signals,
> can't we make a new signal that's only used by the kernel
> and send it to all threads waiting on IO for that descriptor?
> When it gets out to actually setup the signal handler, it
> just resumes like it is returning from an SA_RESTART signal
> handler (which according to another posting would reissue
> the IO command and get EBADF).

Even if you have implemented the close() with the interruption, another
thread openning a file still can reuse the file handle immediately,
according to specifications, the lowest free file handle will be returned, 
if SA_RESTART is used, the interrupted thread restart the syscall,
it will be using a wrong file, I think even if we have implemented the
feature in kernel, useland threads still has serious race to fix.

David Xu