Re: piping from external program not working..

[muppet <scott asofyet org>]

On Saturday, June 5, 2004, at 06:30 AM, Jan Hudec wrote:

> On Fri, Jun 04, 2004 at 16:38:03 -0400, muppet wrote:
> > On Friday, June 4, 2004, at 03:18 PM, Jan Hudec wrote:
> >
> > > I really wish perl IO descriptors had a 'buffer' method. It would 
> > > return the internal buffer as a (read-only) string.

there is one, at the C level --- PerlIO_get_base().  see perlapio.


> > > Then we could have Glib::IO watchers properly generating 'in' event 
> > > when the perlio descriptor (not the underlying file) have some data 
> > > to read!

how would you have it work?  while the buffer is non-empty, keep firing 
the 'in' condition?  (that is, multiple 'in' dispatches for a single 
file descriptor read.)  or return the new data to the sub?

even if we see how many bytes are actually available, it's up the the 
handler to decide if and how to read them, so the handler will still 
have to do filehandle io carefully.  also, how would you handle the 
output situation?  (e.g., the 'out' condition, when it's safe to write 
to the socket.)


> > the old gtk-perl used some interesting MAGIC vtable tricks to allow 
> > subs to be called whenever a scalar is changed.  perhaps we should 
> > modify Glib::IO::add_watch() to use a similar mechanism?
>
> The vtable MAGIC was about the scalars. The interface to glib is not 
> magic at all. And for watching perlio objects, you don't need the 
> vtable magic.
>
> On the glib side, it means to implement an object based on GSource 
> structure. It has a "vtable" GSourceFuncs with four functions -- 
> prepare, check, dispatch and finalize.

yeah, i understand all of that.  what i was referring to was in 
Gtk-Perl/Gtk/xs/Gtk.xs, the implementation of Gtk::watch_add(), which 
creates a GSource containing functions that watch magical SVs.  this 
caused the main loop to wake up whenever anything happened to that 
scalar.

i forgot that the old version of Glib::IO::add_watch() was 
Gtk::Gdk::input_add(); for some reason i thought that the magical 
scalar implementation of watch_add would handle io events as well.  
note that the old version (input_add()) used plain file descriptors, as 
well.

> prepare is called before poll. It must look whether there are data in 
> the buffer. This is actualy the hardest part, at least for me, since I 
> don't understand internals of perlio. prepare returns true if the 
> source is ready (buffer not empty).

there's a macro to get the number of bytes in the buffer, 
PerlIO_get_cnt().


--
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  -- Neal, circa 1996, referring to a movie released in 1984.