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1;
__END__

=pod

=head1 NAME

Bot::Cobalt::DB - Locking Berkeley DBs with serialization

=head1 SYNOPSIS

  use Bot::Cobalt::DB;

  ## ... perhaps in a Cobalt_register ...
  my $db_path = $core->var ."/MyDatabase.db";
  my $db = Bot::Cobalt::DB->new(
    file => $db_path,
  );

  ## Open (and lock):
  $db->dbopen;

  ## Do some work:
  $db->put( SomeKey => $some_deep_structure );

  for my $key ($db->dbkeys) {
    my $this_hash = $db->get($key);
  }

  ## Close and unlock:
  $db->dbclose;


=head1 DESCRIPTION

B<Bot::Cobalt::DB> provides a simple object-oriented interface to basic
L<DB_File> (Berkeley DB 1.x) usage.

BerkDB is a fast and simple key/value store. This module uses JSON to
store nested Perl data structures, providing easy database-backed
storage for L<Bot::Cobalt> plugins.

=head2 Constructor

B<new()> is used to create a new Bot::Cobalt::DB object representing your
Berkeley DB:

  my $db = Bot::Cobalt::DB->new(
    file => $path_to_db,

   ## Optional arguments:

    # Database file mode
    perms => $octal_mode,

    ## Locking timeout in seconds
    ## Defaults to 5s:
    timeout => 10,

    ## Normally, references are serialized transparently.
    ## If raw is enabled, no serialization filter is used and you're
    ## on your own.
    raw => 0,
  );

=head2 Opening and closing

Database operations should be contained within a dbopen/dbclose:

  ## open, put, close:
  $db->dbopen || croak "dbopen failure";
  $db->put($key, $data);
  $db->dbclose;

  ## open for read-only, read, close:
  $db->dbopen(ro => 1) || croak "dbopen failure";
  my $data = $db->get($key);
  $db->dbclose;

Methods will fail if the DB is not open.

If the DB for this object is open when the object is DESTROY'd, Bot::Cobalt::DB
will attempt to close it safely.

=head2 Locking

Proper locking is done -- that means the DB is 're-tied' after a lock is
granted and state cannot change between database open and lock time.

The attempt to gain a lock will time out after five seconds (and
L</dbopen> will return boolean false).

The lock is cleared on L</dbclose>.

If the Bot::Cobalt::DB object is destroyed, it will attempt to dbclose
for you, but it is good practice to keep track of your open/close
calls and attempt to close as quickly as possible.


=head2 Methods

=head3 dbopen

B<dbopen> opens and locks the database. If 'ro => 1' is specified,
this is a LOCK_SH shared (read) lock; otherwise it is a LOCK_EX
exclusive (write) lock.

Try to call a B<dbclose> as quickly as possible to reduce locking
contention.

dbopen() will return false (and possibly warn) if the database could
not be opened (probably due to lock timeout).

=head3 is_open

Returns a boolean value representing whether or not the DB is currently
open and locked.

=head3 dbclose