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Callbacks in async code

by Adamba (Sexton)
on Jun 19, 2013 at 10:02 UTC ( #1039754=perlquestion: print w/ replies, xml ) Need Help??
Adamba has asked for the wisdom of the Perl Monks concerning the following question:

I'm trying to make a Queue Manager that get jobs when files are created in a specific folder. I've created my code using AnyEvent so it's async.

My problem is, i'm trying to deliver a return value from the subroutines add_route, and del_route, using callbacks, but the AE::timer won't stop, and the value that the callback gets, won't saved in the variable $return_code. Where have I gone wrong?

#!/usr/bin/perl use strict; use warnings; use AnyEvent; use AnyEvent::Filesys::Notify; use Const::Fast; use DDP; use File::Basename; use File::Copy; use File::Slurp; use FindBin '$Bin'; use List::Util qw(first); use Regexp::Common qw(net); use v5.10.1; const my $true => 1; const my $false => 0; my $cv = AE::cv; my $jobs_folder_path = $Bin . '/jobs'; my $interval = 5; my $after = 10; my %jobs_folders = ( "new" => "$jobs_folder_path/new", "progress" => "$jobs_folder_path/progress", "failed" => "$jobs_folder_path/failed", ); my $notifier = AnyEvent::Filesys::Notify->new( dirs => [ $jobs_folders{'new'} ], interval => $interval, cb => sub { my (@events) = @_; for my $event (@events) { if ($event->is_created) { process_new_job($event->path); } } } ); my $timer = AE::timer $after, $interval, sub { my @files = read_dir($jobs_folders{'progress'}, prefix => $true); if (@files) { foreach my $file (@files) { my $file_name = basename($file); my $line = read_file($file); for ($file_name) { when (/add/) { my ($ip_address, $next_hop) = split(/ /, $line); my $return_code; my $cb = sub { my $ret_val = shift; $return_code = $ret_val; }; add_route($ip_address, $next_hop, $cb); print $return_code; #post_job_process($return_code, $file_name); } when (/del/) { my ($ip_address) = $line; my $return_code; my $cb = sub { my $ret_val = shift; $return_code = $ret_val; }; del_route($ip_address, $cb); print $return_code, "\n"; #post_job_process($return_code, $file_name); } } } } }; $cv->recv; sub process_new_job { my ($new_job) = shift; my $file_name = basename($new_job); move("$jobs_folders{'new'}/$file_name", "$jobs_folders{'progress'} +/$file_name"); } sub post_job_process { my ($return_code, $file_name) = @_; if ($return_code == $false) { move("$jobs_folders{'progress'}/$file_name", "$jobs_folders{'f +ailed'}/$file_name"); send_email(); } } sub send_email { print "Sending Email...\n"; } sub add_route { my ($ip_address, $next_hop, $cb) = @_; my $attempt = 0; my $sleep = 10; my $add_timer; $add_timer = AE::timer 0, $sleep, sub { if ($attempt++ >= 3) { undef $add_timer; $cb->($false); } print "$attempt. Adding Route $ip_address via $next_hop\n"; my @addresses = get_routing_table(); my ($comparable_ip) = $ip_address =~ /($RE{net}{IPv4})\/32$/; my $is_in_routing_table = first { $_->{'ip_address'} eq $compa +rable_ip } @addresses; if ($is_in_routing_table) { undef $add_timer; $cb->($true); } }; } sub del_route { my ($ip_address, $cb) = @_; my $attempt = 0; my $sleep = 10; my $delete_timer; $delete_timer = AE::timer 0, $sleep, sub { if ($attempt++ >= 3) { undef $delete_timer; $cb->($false); } print "$attempt. Deleting Route $ip_address\n"; my @addresses = get_routing_table(); my ($comparable_ip) = $ip_address =~ /^($RE{net}{IPv4})\/32/; my $is_in_routing_table = first { $_->{'ip_address'} eq $compa +rable_ip } @addresses; if (not $is_in_routing_table) { undef $delete_timer; $cb->($true); } }; } sub get_routing_table { #my @routing_table = `ip ro`; my @routing_table = ( ' dev lo proto kernel scope link src', ' via dev eth0 proto baba', ); my @ret_val; foreach my $line (@routing_table) { my ($ip_address, $next_hop) = $line =~ /^($RE{net}{IPv4}) via +($RE{net}{IPv4}) .*proto baba$/; if (defined ($ip_address) and defined ($next_hop)) { push @ret_val, { ip_address => $ip_address, next_hop => $n +ext_hop }; } } return @ret_val; }

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Re: Callbacks in async code
by Corion (Pope) on Jun 19, 2013 at 12:11 UTC

    You seem to be confused about the order of execution here:

    ... my $return_code; my $cb = sub { my $ret_val = shift; $return_code = $ret_val; }; add_route($ip_address, $next_hop, $cb); print $return_code; #post_job_process($return_code, $file_name); ...

    add_route() will basically return immediately, and you print out $return_code immediately. What you seem to want is to print out $return_code in your callback instead.

    As an alternative to printing in the callback, you might want to ->send the return code using a condvar, and ->recv that somewhere up the call stack where you actually need it.

Re: Callbacks in async code
by choroba (Chancellor) on Jun 19, 2013 at 12:03 UTC
    Crossposted at StackOverflow. It is considered polite to inform about crossposting, so that people not attending both sites do not waste their efforts solving a problem already solved at the other end of the wires.
    لսႽ ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

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