AnyEvent is fairly portable

Really? Does it work with files and pipes under Windows?

Does AnyEvent::DBI work on Windows? Cos you certainly wouldn't think so looking at the source:

   my $pid = fork;

   if ($pid) {
      # parent
      close $server;
   } elsif (defined $pid) {
      # child
      my $serv_fno = fileno $server;

      if ($self->{exec_server}) {
         fcntl $server, &Fcntl::F_SETFD, 0; # don't close the server s
+ide
         exec {$^X}
              "$0 dbi slave",
              -e => "require shift; AnyEvent::DBI::serve_fd ($serv_fno
+, $VERSION)",
              $INC{"AnyEvent/DBI.pm"};
         POSIX::_exit 124;
      } else {
         ($_ != $serv_fno) && POSIX::close $_
            for $^F+1..$FD_MAX;
         serve_fh $server, $VERSION;

         # no other way on the broken windows platform, even this leak
+s
         # memory and might fail.
         kill 9, $$
            if AnyEvent::WIN32;

         # and this kills the parent process on windows
         POSIX::_exit 0;
      }
   } else {
      croak "fork: $!";
   }

   $self->{child_pid} = $pid;

   $self->_req (
      ($self->{on_connect} ? $self->{on_connect} : sub { }),
      (caller)[1,2],
      req_open => $dbi, $user, $pass, %dbi_args
   );

   $self
}
[download]

has a solution to blocking APIs like DBI. ... it spawns an external process which executes the fetch and then passes the results back via IPC.

I guess I could have said "don't have a good solution", but I don't consider starting a new process for each query and then having to squeeze potentially large amounts of structured data through a byte stream, a solution worthy of the name.