Re: [TUHS] V6 networking & alarm syscall

[Dave Horsfall <dave@horsfall.org>]

On Fri, 11 Jan 2019, Noel Chiappa wrote:

[ ... ]

>         ioctl (0, FIONREAD, &nch);
>                        if (nch == 0) {
>                                tk_yield ();
>                                continue;
>                        }
>                }
>                if ((c = getchar()) == EOF) {
>
> so that ioctl() must look to see if there is any data waiting in the 
> terminal input buffer (I'm too lazy to go see what FIONREAD does, right 
> at the moment).

As I dimly recall (because I'm too sick/lazy to look it up), it returns 
the number of characters in the input queue (at that time) so that you 
won't block (and time out, if you wrote it thus).

It was quite useful, if you didn't like the horrible semantics of 
select(), or, for that matter, SysV poll() (?) which was only slightly 
better.

Of course, FIONREAD wasn't always reliable, because by the time you got to 
using it the keyboard (l)user could have deleted some characters etc, and 
you *could* be left there hanging on a timeout (with signals, which for 
some reason I hate with a passion, as I've posted here before, as they 
are just too brutal).

No doubt someone here will tell me that Plan9 did it right :-)  I really 
must run it up some time, before I finally kark it (I'm in my late 60s).

-- Dave