async queries in Perl and poll()/select() loop - how to make them work together?

[Alexander Farber <alexander.farber@xxxxxxxxx>]

Hello,

I'm using CentOS 5.5 Linux with stock perl v5.8.8
and have installed DBD-Pg-2.17.1 via CPAN shell
and I'm using postgresql-server-8.4.5-1PGDG.rhel5.

I've prepared a simple test case demonstrating
my problem - it is listed at the bottom. It works ok,
when I remove {pg_async => PG_ASYNC}.

I have a small multiplayer game, a non-forking daemon
reading/writing to sockets and running in a IO::Poll loop.

I'd like to add player statistics to it, so I was hoping
that I could call the simple INSERT/UPDATE
statements asynchronously from the loop and
I don't need to fetch any results of those queries,
because displaying statistics will be done by
web scripts, not by my game daemon.

I.e. I would like to "fire and forget" queries.

But unfortunately I get the error:
DBD::Pg::st execute failed: Cannot execute
until previous async query has finished
even though I'm not using PG_OLDQUERY_WAIT

Does anybody know what is wrong and
how would you use async queries with
poll()/select() loops anyway?

I can't even call "$dbh->pg_result if $sth->pg_ready",
on every loop iteration, because I can have
several queries running at that moment,
I don't want to iterate through a list of my $sth's...
This defeats my target of quick poll()-looping.

Regards
Alex

P.S. Here is my test case and it is also listed at
http://stackoverflow.com/questions/4065758/async-queries-with-dbdpg-fail-with-cannot-execute-until-previous-async-query-h

#!/usr/bin/perl -w

use strict;
use DBI;
use DBD::Pg qw(:async);

use constant DBNAME => 'snake';
use constant DBUSER => 'snake';
use constant DBPASS => 'snake';

use constant SQL_CREATE_TABLES => q{
        /*
        create table pref_users (
                id varchar(32) primary key,
                first_name varchar(32),
                last_name varchar(32),
                female boolean,
                avatar varchar(128),
                city varchar(32),
                lat real check (-90 <= lat and lat <= 90),
                lng real check (-90 <= lng and lng <= 90),
                last_login timestamp default current_timestamp,
                last_ip inet,
                medals smallint check (medals > 0)
        );

        create table pref_rate (
                obj varchar(32) references pref_users(id),
                subj varchar(32) references pref_users(id),
                good boolean,
                fair boolean,
                nice boolean,
                about varchar(256),
                last_rated timestamp default current_timestamp
        );

        create table pref_money (
                id varchar(32) references pref_users,
                yw char(7) default to_char(current_timestamp, 'YYYY-WW'),
                money real
        );
        create index pref_money_yw_index on pref_money(yw);

        create table pref_pass (
                id varchar(32) references pref_users
        );

        create table pref_misere (
                id varchar(32) references pref_users
        );
        */

        create or replace function pref_update_users(_id varchar,
            _first_name varchar, _last_name varchar, _female boolean,
            _avatar varchar, _city varchar, _last_ip inet) returns
void as $BODY$
                begin

                update pref_users set
                    first_name = _first_name,
                    last_name = _last_name,
                    female = _female,
                    avatar = _avatar,
                    city = _city,
                    last_ip = _last_ip
                where id = _id;

                if not found then
                        insert into pref_users(id, first_name,
                            last_name, female, avatar, city, last_ip)
                        values (_id, _first_name, _last_name,
                            _female, _avatar, _city, _last_ip);
                end if;
                end;
        $BODY$ language plpgsql;
};

eval {
        my $dbh = DBI->connect_cached('dbi:Pg:dbname=' .
            DBNAME, DBUSER, DBPASS, {
            AutoCommit => 1,
            PrintWarn => 1,
            PrintError => 1,
            RaiseError => 1,
            FetchHashKeyName => 'NAME_lc',
            pg_enable_utf8 => 1
        }, {pg_async => PG_ASYNC});

        $dbh->do(SQL_CREATE_TABLES, {pg_async => PG_ASYNC});
};
warn $@ if $@;

for my $i (1..10) {
        eval {
                my $dbh = DBI->connect_cached('dbi:Pg:dbname=' .
                    DBNAME, DBUSER, DBPASS, {
                    AutoCommit => 1,
                    PrintWarn => 1,
                    PrintError => 1,
                    RaiseError => 1,
                    FetchHashKeyName => 'NAME_lc',
                    pg_enable_utf8 => 1
                }, {pg_async => PG_ASYNC});

                #$dbh->pg_result;

                my $sth = $dbh->prepare_cached(
                    q{select pref_update_users(?, ?, ?, ?, ?, ?,
NULL)}, {pg_async => PG_ASYNC});

                $sth->execute('ID123', 'Alexander', 'Farber', undef,
undef, undef);
        };
        warn $@ if $@;
}

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