[MapProxy] Tile Locks

[Oliver Tonnhofer]

On 07.01.2013, at 05:33, Keith Moss wrote:

> Hi list,
>  
> I've got a bit of a bizarre issue with MapServer holding locks on MapProxy tiles.
>  
> Our setup is: 4 x Windows Server 2008 running MapProxy 1.5.0 via WSGI in Apache, 1 x Windows Server 2008 running mapproxy-seed.exe in scheduled tasks, 1 x Windows Server 2008 storing the .yaml config files.
>  
> Our four MapProxy instances are using sources of the WMS type that point back to the MapServer .exe locally i.e. http://localhost/cgi-bin/mapserv.exe?map=something.map
>  
> In our log files from MapProxy and from mapproxy-seed we're periodically getting errors from lock.py line 124, e.g.
> [...]
> WindowsError: [Error 32] The process cannot access the file because it is being
> used by another process: '\\\\10.0.0.70\\c_drive\\mapproxy\\cache\\layer7_fhs_la
> st_0_72.shp_EPSG900913\\tile_locks\\1d5b8827382a79fba940cc62e989aead-14883-6072-
> 14.lck'

And all servers access the same tiles via a remote share?
The locking does not work well with most networked file systems.


> Using Process Explorer I've managed to track the file locks down to the mapserv.exe process. In a typical case mapserv.exe will have locks on a PNG and a few of the .lck files. My understanding was that there's no link between the sources and the PNG tiles that MapProxy creates, so I'm at somewhat of a loss as to how mapserv.exe can come to have any knowledge of these PNG and .lck files.

MapProxy starts mapserv.exe when using the mapserver source and (I assume that) this process inherits the open file handles. This is what you see in the process explorer, but the MapProxy process actually handles the lock files. 


Regards,
Oliver

-- 
Oliver Tonnhofer    | Omniscale GmbH & Co KG    | http://omniscale.com
http://mapproxy.org | https://github.com/olt    | @oltonn