Tom Lane wrote:
> I said:
> > But the backends would only have the socket open, they'd not be actively
> > listening to it. So how could you tell whether anyone had the socket
> > open or not?
>
> Oh, I take that back, I see how you could do it: the postmaster opens
> the socket *for writing*, but never actually writes. All its child
> processes inherit that same open file descriptor and just keep it
> around. Then, to tell if anyone's home, you open the socket *for
> reading* and try to read in O_NONBLOCK mode. You get an EOF indication
> if and only if no one has the socket open for writing; otherwise you
> get an EAGAIN error.
>
> That would work ... but is it more portable than depending on SysV
> shmem connection counts? ISTR that some of the platforms we support
> don't have Unix-style sockets at all.
I think what you describe is a named pipe, not a socket. The underlying implementation might be a socketpair,
but the behaviour of named pipes is exactly that since Version 7 at least. This worked under Minix already.
>
> regards, tom lane
Jan
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