Mojo::UserAgent non-blocking vs blocking performance - perl

Question

I have the following code:
my $ua = Mojo::UserAgent->new ();
my #ids = qw(id1 id2 id3);
foreach (#ids) {
my $input = $_;
my $res = $ua->get('http://my_site/rest/id/'.$input.'.json' => sub {
my ($ua, $res) = #_;
print "$input =>" . $res->result->json('/net/id/desc'), "\n";
});
}
Mojo::IOLoop->start unless Mojo::IOLoop->is_running;
Why when I run the above code (non-blocking) does it take about 6 seconds while when running the code as blocking, i.e. inside the loop something like:
my $res = $ua->get('http://my_site/rest/id/'.$input.'.json');
print "$input =>" . $res->result->json('/net/id/desc'), "\n";
without the latest line it takes about 1 second?
Why is the blocking code faster than the non-blocking code?

Answer 1

The first thing to check when things happened. I couldn't get the same delay. Remember to try each way several times to spot outliers where there's a network hiccup. Note that the second argument to the non-blocking sub is a transaction object, normally written as $tx, where the response object is normally written res:
use Mojo::Util qw(steady_time);
say "Begin: " . steady_time();
END { say "End: " . steady_time() }
my $ua = Mojo::UserAgent->new ();
my #ids = qw(id1 id2 id3);
foreach (#ids) {
my $input = $_;
my $res = $ua->get(
$url =>
sub {
my ($ua, $tx) = #_;
print "Fetched\n";
}
);
}
One possibility is that keep-alive is holding an open connection. What happens if you turn that off?
my $res = $ua->get(
$url =>
{ Connection => 'close' }
sub {
my ($ua, $tx) = #_;
print "Fetched\n";
}
);
Here's a version that uses promises, which you'll want to get used to as more Mojo stuff moves to it:
use feature qw(signatures);
no warnings qw(experimental::signatures);
use Mojo::Promise;
use Mojo::Util qw(steady_time);
use Mojo::UserAgent;
my $ua = Mojo::UserAgent->new;
say "Begin: " . steady_time();
END { say "End: " . steady_time() }
my #ids = qw(id1 id2 id3);
my #gets = map {
$ua->get_p( 'http://www.perl.com' )->then(
sub ( $tx ) { say "Fetched: " . steady_time() },
sub { print "Error: #_" }
);
} #ids;
Mojo::Promise->all( #gets )->wait;