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    $pool->_check_queue;
}


package AnyEvent::Pg::Pool::Watcher;

sub _new {
    my ($class, $obj) = @_;
    my $watcher = \$obj;
    bless $watcher, $class;
}

sub DESTROY {
    my $watcher = shift;
    my $obj = $$watcher // {};
    $obj->{canceled} = 1;
}

package AnyEvent::Pg::Pool::QueryWatcher;
our @ISA = ('AnyEvent::Pg::Pool::Watcher');

sub DESTROY {
    my $watcher = shift;
    my $obj = $$watcher // {};
    $obj->{canceled} = 1;
    # delete also the watcher for the slave query sent to the conn
    # object:
    delete $obj->{watcher};
}

package AnyEvent::Pg::Pool::ListenerWatcher;
our @ISA = ('AnyEvent::Pg::Pool::Watcher');


1;

=head1 NAME

AnyEvent::Pg::Pool

=head1 SYNOPSIS

  my $pool = AnyEvent::Pg::Pool->new($conninfo,
                                     on_connect_error => \&on_db_is_dead);

  my $qw = $pool->push_query(query => 'select * from foo',
                             on_result => sub { ... });

  my $lw = $pool->listen('bar',
                         on_notify => sub { ... });

=head1 DESCRIPTION

  *******************************************************************
  ***                                                             ***
  *** NOTE: This is a very early release that may contain lots of ***
  *** bugs. The API is not stable and may change between releases ***
  ***                                                             ***
  *******************************************************************

This module handles a pool of databases connections, and transparently
handles reconnection and reposting queries when network and server
errors occur.

=head2 API

The following methods are provided:

=over 4

=item $pool = AnyEvent::Pg::Pool->new($conninfo, %opts)

Creates a new object.

Accepts the following options:

=over 4

=item size => $size

Maximum number of database connections that can be simultaneously
established with the server.

=item connection_retries => $n

Maximum number of attempts to establish a new database connection
before calling the C<on_connect_error> callback when there is no other
connection alive on the pool.

=item connection_delay => $seconds

When establishing a new connection fails, this setting allows to
configure the number of seconds to delay before trying to connect
again.

=item timeout => $seconds

When some active connection does not report activity for the given
number of seconds, it is considered dead and closed.

=item global_timeout => $seconds

When all the connections to the database become broken and it is not
possible to establish a new connection for the given time period the
pool is considered dead and the C<on_error> callback will be called.

Note that this timeout is approximate. It is checked every time a new
connection attempt fails but its expiration will not cause the
abortion of an in-progress connection.

=item on_error => $callback

When some error happens that can not be automatically handled by the
module (for instance, by requeuing the current query), this callback
is invoked.

=item on_connect_error => $callback

When the number of failed reconnection attempts goes over the limit,
this callback is called. The pool object and the L<AnyEvent::Pg>
object representing the last failed attempt are passed as arguments.