netdev - RE: [Bug 106241] New: shutdown(3)/close(3) behaviour is incorrect for sockets in accept(3)

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Date:	Fri, 30 Oct 2015 17:43:21 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'David Holland' <dholland-tech@...bsd.org>,
	Alan Burlison <Alan.Burlison@...cle.com>
CC:	"Casper.Dik@...cle.com" <Casper.Dik@...cle.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	David Miller <davem@...emloft.net>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	"stephen@...workplumber.org" <stephen@...workplumber.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [Bug 106241] New: shutdown(3)/close(3) behaviour is incorrect
 for sockets in accept(3)

From: David Holland
> Sent: 29 October 2015 14:59
> On Tue, Oct 27, 2015 at 10:52:46AM +0000, Alan Burlison wrote:
>  > >But in general, this is basically a problem with the application: the file
>  > >descriptor space is shared between threads and having one thread sniping
>  > >at open files, you do have a problem and whatever the kernel does in that
>  > >case perhaps doesn't matter all that much: the application needs to be
>  > >fixed anyway.
>  >
>  > The scenario in Hadoop is that the FD is being used by a thread that's
>  > waiting in accept and another thread wants to shut it down, e.g. because
>  > the application is terminating and needs to stop all threads cleanly.
> 
> ISTM that the best way to do this is to post a signal to the thread so
> accept bails with EINTR, at which point it can check to see if it's
> supposed to be exiting.

Actually, just send it a connect indication.

ISTM that the correct call should be listen(fd, 0);
Although that doesn't help a thread stuck in recvmsg() for a datagram.

It is also tempting to think that close(fd) should sleep until all
io activities using that fd have completed - whether or not blocking
calls are woken.

	David

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