AnyEvent weirdness w/ open() and/or ``'s

pprocacci has asked for the wisdom of the Perl Monks concerning the following question:

Monks,

Firstly, thank you in advance for taking your time to read through my question.

The below `heavily modified` perl code works flawlessly without the call to retr_connected_users. Once I add that subroutine, perl gets hung on the `select` syscall *after* it's first interation through the code. I suspect it has something to do with the `some command` code, and I have tried variations like open/<>/close, but I cannot get past the first iteration.

My question is can AnyEvent effect the underlying file descriptors in a way that would cause this strange behavior and is there any way to read external data from pipes/file descriptors synchronously that perhaps I am just missing entirely?

use AnyEvent::XMPP::Ext::MUC;

sub retr_connected_users {
        my @data = map { chomp; s/@.*//; $_ } (`some command`);
        return @data;
}

$muc->reg_cb(
        message => sub {
                my ( undef, undef, $msg ) = @_;

                my @inter = retr_connected_users();
                foreach my $user(@inter){
                        AnyEvent::XMPP::IM::Message->new (
                                body => construct_body($msg->body, $fr
+om),
                                to   => "$user\@" . HOST,
                                type => "chat",
                        )->send($conn);
                }
        },
);
[download]

Thanks for your time.

Comment on AnyEvent weirdness w/ open() and/or ``'s Download Code

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Re: AnyEvent weirdness w/ open() and/or ``'s by james2vegas (Chaplain) on Nov 02, 2013 at 17:06 UTC
Why do you need to read your data synchronously? Why not read lines from your command asynchronously, and create the messages in a callback? There are many AnyEvent modules to make running and getting output back from external commands easy, but there is also AnyEvent::Util::fork_call (which serialises the whole output of your command before calling the callback). Alternatively, you could probably use an IO watcher like this: `open my $fh, '-\|', 'some command'; my $w; $w = AnyEvent->io( fh => $fh, poll => 'r', cb => sub { chomp(my $user = $fh->getline); AnyEvent::XMPP::IM::Message->new( body => construct_body( $msg->body, $from ), to => "$user\@" . HOST, type => "chat", )->send($conn); undef $w if eof($fh); } );` [download]	[reply] [d/l]
Re^2: AnyEvent weirdness w/ open() and/or ``'s by pprocacci (Initiate) on Nov 03, 2013 at 07:30 UTC
James, I appreciate your response. My familiarity w/ AnyEvent isn't too great and your response has helped greatly. What I ended up doing which I believe to look extremely ugly follows my comments. (again heavily modified) To provide further details to hopefully paint a full picture .... I have two sources. One is from a command, and another is from a file. Both sources are pulled into an array and what I believe the below achieves is sending messages to the intersection of the arrays. The below works with my limited testing and I appreciate the guidance thus far you've provided. I don't need further help unless of coarse you see something glaringly wrong, but until then, thanks James. $muc->reg_cb( message => sub { my ( undef, undef, $msg ) = @_; my @connected_users = (); open my $fh, '-\|', 'command_that_outputs_users' or die $!; my $w; $w = AnyEvent->io( fh => $fh, poll => 'r', cb => sub { my $user = $fh->getline; return if !defined($user); chomp($user); push(@connected_users, $user); if(eof($fh)){ close($fh); undef $w; open($fh, "< $file") or die $!; my $w2; $w2 = AnyEvent->io( fh => $fh, poll => 'r', cb => sub { my $user = $fh->getline; return if !defined($user); chomp($user); if($user ~~ @connected_users){ AnyEvent::XMPP::IM::Message->new( body => construct_body( $msg->body, $from ), to => "$user\@" . HOST, type => "chat", )->send($conn); close($fh); undef $w2; } } ); } } ); }, ); [download]	[reply] [d/l]