[PATCH 2 of 4 RFC] chgcache: implement simple IPC mechanism

[Jun Wu]

Excerpts from Yuya Nishihara's message of 2017-02-14 22:49:34 +0900:
> On Mon, 13 Feb 2017 09:46:21 -0800, Jun Wu wrote:
> > Excerpts from Yuya Nishihara's message of 2017-02-13 23:00:25 +0900:
> > > Why not os.pipe()?
> > >
> > > We share the same (dup-ed) file descriptors. In this case, the write end can
> > > be used by many forked processes, but IIRC the read end can't. Only one
> > > reader can read out a message. So I think there's no reason to set up a
> > > full duplex IPC channel.
> > 
> > Duplex IRC is not needed. But I do want to use DGRAM.
> > 
> > DGRAM makes it impossible to send incomplete messages. I think that makes
> > the code simpler and maybe more efficient.
> 
> Ok.
> 
> Perhaps you won't need the suffix as datagram socket is message oriented?

Right. It's not needed if we can figure out the message length first.

That could be done via "fcntl.ioctl(fd, termios.FIONREAD, buf)", which won't
work on Windows. I think that's fine since we have so many non-Windows code
already.