Re: Two way pipe

[Neil Jerram <neil@ossau.uklinux.net>]

ludovic.courtes@laas.fr (Ludovic Courtès) writes:

> Doesn't `OPEN_BOTH' do what you want? 

Yes, indeed.  Believe it or not, I was looking at a 1.6 distribution
and didn't think to check 1.8 or CVS.  (Newbie alert! :-))

> However, the manual reads:
>
>    Care should be taken with `OPEN_BOTH', a deadlock will occur if
>    both parent and child are writing, and waiting until the write
>    completes before doing any reading.  Each direction has `PIPE_BUF'
>    bytes of buffering (*note Ports and File Descriptors::), which
>    will be enough for small writes, but not for say putting a big
>    file through a filter.

So far I've been playing with (open-input-pipe "mplayer -slave ..."),
but not bothering to select on and read from the pipe.  If the track
being played is longer than about 3 minutes, mplayer crashes - and I
assume that's because its write to stdout is failing unexpectedly.  So
for some programs, it seems that filling up the pipe buffer can be a
problem even if in only one direction.

When I implement things fully this won't be a problem, because the
Guile app will be reading any available data from the pipe as soon as
it's there, and only very rarely writing anything.

Many thanks,

     Neil



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