fhew has asked for the wisdom of the Perl Monks concerning the following question:
What I'm seeing is that the child (at random) stops getting the indication (in a 'select') that there is data to read, so once it gets into this 'mode', I never see any more data from the parent even though its there (as proven when I blindly do a read some time in the future.)
I've narrowed down my problem to the shortest test code I can, but due to timing issues, it may or may not fail the same on your machine. If you remove the 'time-waster', it works, but the more stuff you do in the child (it doesn't matter what), the worse it gets.
Or is the problem when 'there was more than one write to the pipe before the other end reads it'? If so... a) thats silly, and b) how would you get around it?
Here is a (annotated) sample run that fails: (Note that messages 4, 5, 6, 7, 8 never got picked up via the select, but later when I just read STDIN explicitly, the data _is_ there.)
Here is the test code. Can anyone tell me what I'm doing wrong?# ./mon1 waiting for more data waiting for more data Tx: ADD I 1 1 50.0.5.1 Rx: ADD I 1 1 50.0.5.1 => Done waiting for more data Tx: ADD I 1 2 50.0.5.2 Rx: ADD I 1 2 50.0.5.2 => Done Tx: ADD I 1 3 50.0.5.3 Tx: ADD I 1 4 50.0.5.4 Tx: ADD I 1 5 50.0.5.5 Tx: ADD I 1 6 50.0.5.6 Tx: ADD I 1 7 50.0.5.7 Tx: ADD I 1 8 50.0.5.8 waiting for more data Rx: ADD I 1 3 50.0.5.3 => Done waiting for more data waiting for more data waiting for more data waiting for more data waiting for more data waiting for more data waiting for more data ALSO READ: ADD I 1 4 50.0.5.4 waiting for more data waiting for more data ...
#!/usr/bin/perl use IO::Select; if ($::child_pid = open (CHILD, "|-")) { { my $h = select(CHILD); $|=1; select($h); } sleep 1; # allow the child's select mechnanism to start for (1..8) { my $s = "ADD I 1 $_ 50.0.5.$_\n"; print CHILD $s; print "Tx: $s"; } while (1) { sleep 1; } } else { my $select = IO::Select->new(\*STDIN); while (1) { print "waiting for more data\n"; foreach my $client ($select->can_read(1)) { $_ = <$client>; chomp; print "\tRx: $_ => "; for (1..5) { # time for my $foo (keys %::) { # waster $zub = \&{$::{$foo}}; # to } # induce } # problem print "\tDone\n"; } if ($::i++ == 10) { my $a = <STDIN>; print "ALSO READ: $a\n"; } } }
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Re: Interprocess pipe doesn't reliably deliver data
by bluto (Curate) on Mar 16, 2006 at 18:20 UTC | |
Re: Interprocess pipe doesn't reliably deliver data
by traveler (Parson) on Mar 16, 2006 at 18:34 UTC | |
by fhew (Beadle) on Mar 16, 2006 at 18:40 UTC | |
by traveler (Parson) on Mar 16, 2006 at 18:55 UTC |