22

✏️ Editing: corostream.pm

package DBD::Gofer::Transport::corostream;

use strict;
use warnings;

use Carp;

use Coro::Select; #  a slow but coro-aware replacement for CORE::select (global effect!)

use Coro;
use Coro::Handle;

use base qw(DBD::Gofer::Transport::stream);

# XXX ensure DBI_PUREPERL for parent doesn't pass to child
sub start_pipe_command {
    local $ENV{DBI_PUREPERL} = $ENV{DBI_PUREPERL_COROCHILD}; # typically undef
    my $connection = shift->SUPER::start_pipe_command(@_);
    return $connection;
}

__END__

=head1 NAME

DBD::Gofer::Transport::corostream - Async DBD::Gofer stream transport using Coro and AnyEvent

=head1 SYNOPSIS

DBI_AUTOPROXY="dbi:Gofer:transport=corostream" perl some-perl-script-using-dbi.pl

$dsn = ...; # the DSN for the driver and database you want to use
   $dbh = DBI->connect("dbi:Gofer:transport=corostream;dsn=$dsn", ...);

=head1 DESCRIPTION

The I<BIG WIN> from using L<Coro> is that it enables the use of existing
DBI frameworks like L<DBIx::Class>.

=head1 KNOWN ISSUES AND LIMITATIONS

- Uses Coro::Select so alters CORE::select globally
    Parent class probably needs refactoring to enable a more encapsulated approach.

- Doesn't prevent multiple concurrent requests
    Probably just needs a per-connection semaphore

- Coro has many caveats. Caveat emptor.

=head1 STATUS

THIS IS CURRENTLY JUST A PROOF-OF-CONCEPT IMPLEMENTATION FOR EXPERIMENTATION.

Please note that I have no plans to develop this code further myself.
I'd very much welcome contributions. Interested? Let me know!

=head1 AUTHOR

Tim Bunce, L<http://www.tim.bunce.name>

=head1 LICENCE AND COPYRIGHT

This module is free software; you can redistribute it and/or
modify it under the same terms as Perl itself. See L<perlartistic>.

=head1 SEE ALSO

L<DBD::Gofer::Transport::stream>

L<DBD::Gofer>

=head1 APPENDIX

Example code:

#!perl

use strict;
    use warnings;
    use Time::HiRes qw(time);

BEGIN { $ENV{PERL_ANYEVENT_STRICT} = 1; $ENV{PERL_ANYEVENT_VERBOSE} = 1; }

use AnyEvent;

BEGIN { $ENV{DBI_TRACE} = 0; $ENV{DBI_GOFER_TRACE} = 0; $ENV{DBD_GOFER_TRACE} = 0; };

use DBI;

$ENV{DBI_AUTOPROXY} = 'dbi:Gofer:transport=corostream';

my $ticker = AnyEvent->timer( after => 0, interval => 0.1, cb => sub {
        warn sprintf "-tick- %.2f\n", time
    } );

warn "connecting...\n";
    my $dbh = DBI->connect("dbi:NullP:");
    warn "...connected\n";

for (1..3) {
        warn "entering DBI...\n";
        $dbh->do("sleep 0.3"); # pseudo-sql understood by the DBD::NullP driver
        warn "...returned\n";
    }

warn "done.";

Example output:

$ perl corogofer.pl
    connecting...
    -tick- 1293631437.14
    -tick- 1293631437.14
    ...connected
    entering DBI...
    -tick- 1293631437.25
    -tick- 1293631437.35
    -tick- 1293631437.45
    -tick- 1293631437.55
    ...returned
    entering DBI...
    -tick- 1293631437.66
    -tick- 1293631437.76
    -tick- 1293631437.86
    ...returned
    entering DBI...
    -tick- 1293631437.96
    -tick- 1293631438.06
    -tick- 1293631438.16
    ...returned
    done. at corogofer.pl line 39.

You can see that the timer callback is firing while the code 'waits' inside the
do() method for the response from the database. Normally that would block.

=cut

MR SKB