Here's what's going on with the noticed odd-good/even-bad behavior:

#!/usr/bin/perl

use common::sense;
use AnyEvent::HTTP;
use Data::Dumper;

sub do {
    my $iter = shift;

    my $cv = AnyEvent->condvar;
    $cv->begin;
    http_get
        'https://imasheep.hurrdurr.org/category/about.html',
        timeout => 2,
        # out-comment to get the even/odd behavior
        persistent => 0,
        sub {
            my ($body, $hdr) = @_;
            say "$iter $hdr->{Status}";
            unless ($hdr->{Status} == 200) {
                warn Data::Dumper->Dump([$hdr],['hdr']);
            }
            $cv->end;
        }
    ;
    $cv->recv;
}

for (1..4) {
    &do($_);
    sleep(5);
}
[download]

The documentation for that 'persistent' reads as follows:

        persistent => $boolean
               Try to create/reuse a persistent connection. When this flag is set (default: true for idempotent
               requests, false for all others), then "http_request" tries to re-use an existing (previously-created)
               persistent connection to the host and, failing that, tries to create a new one.

               Requests failing in certain ways will be automatically retried once, which is dangerous for non-
               idempotent requests, which is why it defaults to off for them. The reason for this is because the bozos
               who designed HTTP/1.1 made it impossible to distinguish between a fatal error and a normal connection
               timeout, so you never know whether there was a problem with your request or not.

               When reusing an existent connection, many parameters (such as TLS context) will be ignored. See the
               "session" parameter for a workaround.

This default persistence for idempotent requests conflicts with your 5 seconds sleeps - and that's why only every second connection attempt succeeds.


Krambambuli
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