Re: Implementing file-locking *control* in DBD::File

2009/12/3 H.Merijn Brand <[email protected]>:
> Any objections to me committing below change?

While the originator of this request updates his ticket, maybe a smarter
implementation is reasonable:

I could modify S::S opentable() to request opening for reading/writing,
so you could differ between LOCK_SH and LOCK_EX automatically.
Further, it could be suitable to or LOCK_NB, which allows to avoid deadlocks.

Sorry for generating extra wishes ;)

/Jens

> --8<---
> --- DBI-svn/lib/DBD/File.pm   2009-12-03 17:47:15.000000000 +0100
> +++ DBI-svn/lib/DBD/File.pm   2009-12-03 17:49:20.000000000 +0100
> @@ -162,6 +162,7 @@ sub connect ($$;$$$)
>            f_ext       => 1, # file extension
>            f_schema    => 1, # schema name
>            f_tables    => 1, # base directory
> +           f_lock      => 1, # Table locking mode
>            };
>         $this->{sql_valid_attrs} = {
>            sql_handler           => 1, # Nano or S:S
> @@ -725,12 +726,17 @@ sub open_table ($$$$$)
>        }
>     $fh and binmode $fh;
>     if ($locking and $fh) {
> -       if ($lockMode) {
> +       my $lm = defined $data->{Database}{f_lock}
> +                     && $data->{Database}{f_lock} =~ m/^[012]$/
> +                      ? $data->{Database}{f_lock}
> +                      : $lockMode ? 2 : 1;
> +       if ($lm == 2) {
>            flock $fh, 2 or croak "Cannot obtain exclusive lock on $file: $!";
>            }
> -       else {
> +       elsif ($lm == 1) {
>            flock $fh, 1 or croak "Cannot obtain shared lock on $file: $!";
>            }
> +       # $lm = 0 is forced no locking at all
>        }
>     my $columns = {};
>     my $array   = [];
> @@ -929,6 +935,29 @@ tables into the same (or no) schema:
>  Defining f_schema to the empty string is equal to setting it to C<undef>,
>  this to enable the DSN to be C<dbi:CSV:f_schema=;f_dir=.>.
>
> +=item f_lock
> +
> +With this attribute, you can force locking mode (if locking is supported
> +at all) for opening tables. By default, tables are opened with a shared
> +lock for reading, and with an exclusive lock for writing. The supported
> +modes are:
> +
> +=over 2
> +
> +=item 0
> +
> +Force no locking at all.
> +
> +=item 1
> +
> +Only shared locks will be used.
> +
> +=item 2
> +
> +Only exclusive locks will be used.
> +
> +=back
> +
>  =back
>
>  =head2 Driver private methods
> -->8---
>
> --
> H.Merijn Brand  http://tux.nl      Perl Monger  http://amsterdam.pm.org/
> using & porting perl 5.6.2, 5.8.x, 5.10.x, 5.11.x on HP-UX 10.20, 11.00,
> 11.11, 11.23, and 11.31, OpenSuSE 10.3, 11.0, and 11.1, AIX 5.2 and 5.3.
> http://mirrors.develooper.com/hpux/           http://www.test-smoke.org/
> http://qa.perl.org      http://www.goldmark.org/jeff/stupid-disclaimers/
>