Greg Stark <stark@mit.edu> writes:
> So I poked around a bit. It looks like Linux does send a SIGIO when a
> tcp connection is closed (with POLL_HUP if it's closed and POLL_IN if
> it's half-closed). So it should be possible to arrange to get a signal
> which CHECK_FOR_INTERRUPTS could handle the normal way.
> However this would mean getting a signal every time there's data
> available from the client. I don't know how inefficient that would be
> or how convenient it would be to turn it off and on all the time so we
> aren't constantly receiving useless signals.
That sounds like a mess --- race conditions all over the place,
even aside from efficiency worries.
> I'm not sure how portal this behaviour is either. There may well be
> platforms where having the socket closed doesn't generate a SIGIO.
AFAICS, the POSIX spec doesn't define SIGIO at all, so this worry is
probably very real.
What I *do* see standardized in POSIX is SIGURG (out-of-band data is
available). If that's delivered upon socket close, which unfortunately
POSIX doesn't say, then it'd avoid the race condition issue. We don't
use out-of-band data in the protocol and could easily say that we'll
never do so in future.
Of course the elephant in the room is Windows --- does it support
any of this stuff?
regards, tom lane
