Re: HAVE_POLL is not enough

["Philippe De Muyter" <phdm at macqel dot be>]

First of all, sorry for the long delay for answers, but I am really busy
(and more) with my day-hours work.

> Elena Zannoni wrote:
> > 
> > Philippe De Muyter writes:
> >  > With the gdb cvs tree of 2000-02-19, on m68k-motorola-sys, configure
> >  > correctly detect  that we have `poll', but gdb incorrectly assumes that
> >  > `poll' can be used to wait for `stdin'.  On m68k-motorola-sysv, tty's
> >  > are not stream-based and not `poll'able.  Should the configure test
> >  > be enhanced ? I don't think so if we need to run a target program to check
> >  > that, because it would fail if we cross-compile gdb, but if it can be
> >  > determined by other ways, like the presence of some constants in some
> >  > header files then I would agree.  We could also always compile in the `poll'
> >  > version if HAVE_POLL, but switch to the the fall-back method at run time if
> >  > poll fails with POLLNVAL.
> >  >
> > 
> > Right now the decision on whether to run gdb with or without the event
> > loop is determined by the user as start up, and it is not detected
> > neither by configure or at run time. The easiest thing to do for now

I did not ask explicitly to start gdb with or without the event-loop, and it
tried automatically to use the event-loop.  I don't know why but that seems
to invalidate Elena's statement that `it is determined by the user as start up'.

> > is probably tell the user what happened and switch to
> > non-event-loop mode.  Maybe some configury work could be done to
> > determine whether the tty's can be pollable, I am not familiar with
> > your system enough to know whether this is anything feasible.  Sorry I
> > cannot be of more help here.
> > How about the 'target async' part, would that work?
> 
> As far as I know, this problem is still present.
> 
> Following on from Elena's comment.  Is there any known work around or
> other hack available?
> 
> If we get really desparate there is always the option of putting:
> 
> 	HOST_POLL_BROKEN
> 
> in
> 
> 	config/m68k/xm-m68kv4.h
> 
> :-( (And yes, I'm about to get really desperate).
> 
> Philippe, if GDB is forced to use select, does it work?

If we never use poll, and always use select if it is available, I think
we'll then have the inverse problem : platforms where some channels are
`poll'-able, but not `select'-able.

So, my idea is : at gdb startup, first poll the needed fd's one by one with
a null or small timeout, and if one is not `poll'-able, then switch to `select'.
I know that on m68k-motorola-sysv, `stdin' is `select'-able, so this scheme
would work.

Sorry, no time for a patch at the moment.

> 
> 	Andrew
>