Re: XForms: Async I/O

Steve Lamont (spl@szechuan.ucsd.edu)
Fri, 9 Apr 99 06:58:54 PDT

# To subscribers of the xforms list from spl@szechuan.ucsd.edu (Steve Lamont) :

> I'm having difficulty with fl_set_io_callback( ... FL_WRITE ... ) on Linux
> 2.0.35 xforms 0.89.
>
> What I find is that if I make the fl_set_io_callback call followed by
> fl_do_forms then I get continuous invocations of the callback even though
> there is no I/O activity.
>
> The manual says that the callback is invoked when the Tx buffer is available
> (which, pedantically, could be continuous) but I would have thought that the
> CB would be called just once on write completion i.e. at the transition
> between unavailable and available. The continuous calling of the CB looks
> like a problem to me.

The IO callback mechanism isn't really much more than a wrapper around
a select() call. If the file descriptor is writable (which will be
pretty much continuously in most cases), then it's going to trigger
the callback.

Refer to the man page for select -- this should clarify matters.

spl

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