Perl 5 and C have the select call that lets you determine which of a group of file-descriptor are ready for reading and writing. I thought it might be useful here.
https://en.wikipedia.org/wiki/Select_(Unix) I've found a module by Tadzik, https://github.com/tadzik/IO-Select, but it's looking defunct and Parrot specifc. Are we missing a working 'select' call? - David On Fri, Jul 28, 2017 at 12:04 PM, Brandon Allbery <allber...@gmail.com> wrote: > On Thu, Jul 27, 2017 at 7:49 PM, Norman Gaywood <ngayw...@gmail.com> > wrote: > >> my $input = q:to/EOS/; >> line of text >> another line >> EOS >> >> my $cat = run 'cat', '-n', :in($input.print), :out; >> my $output = $cat.out.get; >> $cat.in.close; >> $cat.out.close; >> >> say "done"; >> say $output; >> >> But that is not correct. I seem to be missing something. >> > > :in, :out, :err want a filehandle (or will create one if you specify True, > which is what pair syntax gives you if you specify one of them without a > filehandle). Not a string; and .print applied to a Str does not turn the > string into a filehandle, it sends the string to the filehandle in $*OUT. > > my $cat = run 'cat', '-n', :in, :out; > $cat.in.print($input); # this .print, on IO::Handle, prints the string to > that handle > $cat.in.close; > my $output = $cat.out.slurp: :close; > > Note that you need to be very careful to avoid the "open3" deadlock: pipes > have limited buffers, and if you do this all in one thread when the data is > large enough to block on write, and the receiving program then blocks on > write back to you, you will deadlock. No language can protect you from > this. The solution is that either the writer or the reader (or both) needs > to be in its own thread so that if one blocks, the other can keep running > and eventually clear the block. > > -- > brandon s allbery kf8nh sine nomine > associates > allber...@gmail.com > ballb...@sinenomine.net > unix, openafs, kerberos, infrastructure, xmonad > http://sinenomine.net >
