On 27/10/2015 13:59, David Miller wrote:
From: Alan Burlison <alan.burli...@oracle.com>
Date: Tue, 27 Oct 2015 13:37:26 +0000
If you took that argument to it's logical extreme they you'd never
make any changes that made changes to existing behaviour, and that's
patently not the case.
You know exactly what I mean, and what you're saying here is just a
scarecrow distracting the discussion from the real issue.
I think you probably mean "a straw man".
The problematic case is MT applications that don't manage sharing of FDs
in a sensible way and need to have a way of terminating any accept() in
other threads. On Linux that's currently done with a shutdown()+close(),
on other platforms you can use open()+dup2(). However the Linux
shutdown() mechanism relies on bending the POSIX semantics and the
dup2() mechanism doesn't work on Linux as it also doesn't kick other
threads off accept().
At the moment, on Linux you have to explicitly call shutdown() on a
socket on which another thread may be sat in accept(). If closing the
socket in one thread terminated any accept()s in other threads, in the
same way that an explicit shutdown() does, then the explicit shutdown()
wouldn't be needed for more sensibly written apps that weren't prone to
FD recycling races. As far as I can tell, that would work cross-platform.
Ideally there'd be a single way of doing this that worked
cross-platform, at the moment there isn't. And yes, even if such a
mechanism was available now it would be some time before it could be
assumed to be available everywhere. I don't know enough about the Linux
implementation to know if there is a practical way around this, and of
course even if such a change were made, potential breakage of existing
code would be a concern. If there's a better, cross-platform way of
doing this then I'm all ears.
--
Alan Burlison
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