Help: Perl/Mapscript Bug?

[Sean Gillies]

On May 5, 2005, at 11:21 AM, Stephen Woodbridge wrote:

> Hi all,
>
> I have run into an interesting but NASTY problem with Perl/Mapscript
> running in a fcgi process on Linux.
>
> Does anyone have any ideas?
> Is this a bug that has been fixed in a later release?
>
> Particulars:
>
> Debian Woody and Mapserver 4.01 - yes it is old, but it is a production
> system and we are concerned about the performance issues are in the
> later releases.
>
> The problem is that this script is running as an apache fcgi process
> and
> it is consuming all the system resources. An lsof shows that the
> shapefiles are not getting closed after each hit. We have tried to
> close
> the layer and undef the mapObj, but it does not fix the problem. It
> seems mapscript is not closing the file handles!!!
>
> We are going to try and test this under 4.4.1 and 4.4.2 and see what
> happens
>
> Any ideas?
>    -Steve W.
>

Steve,

I don't even keep the 4.0 source around anymore, so I'm looking at 4.2.
  I don't think maplayer.c had too many changes in between.

I suspect your problem is with the multiple calls to layerObj::open().
On the second call, a new shapefileObj will be allocated and the
layer's info pointer will be pointed to it, but it doesn't look like
the pre-existing one is ever freed.  My comments continue below ...


> the Perl code is like:
>
> sub query {
>      my $latitude = shift;
>      my $longitude = shift;
>
>      ## create new mapscript objec using appropriate mapfile
>      my $map = new mapscript::mapObj($mapfile);
>      return error("Can not open Mapfile: $mapfile") if not $map;
>
>      ## get streets layer
>      my $layer = $map->getLayerByName('data');
>      return error("Can not open Layer: data") if not $layer;
>      $layer->{status} = $mapscript::MS_ON;
>
>      ## open the layer or the query will fail
>      ## WHY DOES THIS NEED TO BE DONE HERE!
>      $layer->open();
>

This is not necessary, and is probably the source of the leak.  I've
never had problems querying a closed layer.

>      ## build point obj using lat/lon
>      my $point = new mapscript::pointObj();
>      $point->{y} = $latitude;
>      $point->{x} = $longitude;
>
>      ## now query the layer object using lat/longs
>      $layer->queryByPoint($map, $point, $mapscript::MS_SINGLE, -1.0);
>
>      ## reopen layer to get results,
>      ## you can't close it or it will lose the query info
>      $layer->open();
>      my $res = $layer->getResult(0);
>

Right.  Open the layer only to get the results.


>      ## get shape obj
>      my $shp = new mapscript::shapeObj($layer->{type});
>      $layer->getShape($shp, $res->{tileindex}, $res->{shapeindex});
>
>      my $data;
>      my $polyline = get_shp_xy($shp);
>
>      ## do stuff with polyline put results into $data
>
>      ## we tried   $layer->close() and undef $map here
>      ## but it did not make a difference
>
>      return($data);
> }
>
>

Hope that helps,


--
Sean Gillies
sgillies at frii dot com
http://zcologia.com