[MapProxy] Tile Locks

[Keith Moss]

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.



[12:17:04]  7  75.00% 13775786.98567, -5465442.18332, 15654303.39280, -5009377.0
8570 (477 tiles) ETA: 2013-01-07-12:17:25
Exception in thread Thread-2:
Traceback (most recent call last):
  File "C:\Python27\Lib\threading.py", line 554, in __bootstrap_inner
    self.run()
  File "c:\pythonenv\mapproxy-srss\lib\site-packages\mapproxy-1.5.0a_20130107-py
2.7.egg\mapproxy\seed\seeder.py", line 92, in run
    self.work_loop()
  File "c:\pythonenv\mapproxy-srss\lib\site-packages\mapproxy-1.5.0a_20130107-py
2.7.egg\mapproxy\seed\seeder.py", line 104, in work_loop
    exceptions=(SourceError, IOError), ignore_exceptions=(LockTimeout, ))
  File "c:\pythonenv\mapproxy-srss\lib\site-packages\mapproxy-1.5.0a_20130107-py
2.7.egg\mapproxy\seed\util.py", line 222, in exp_backoff
    result = func(*args, **kw)
  File "c:\pythonenv\mapproxy-srss\lib\site-packages\mapproxy-1.5.0a_20130107-py
2.7.egg\mapproxy\cache\tile.py", line 126, in load_tile_coords
    created_tiles = creator.create_tiles(uncached_tiles)
  File "c:\pythonenv\mapproxy-srss\lib\site-packages\mapproxy-1.5.0a_20130107-py
2.7.egg\mapproxy\cache\tile.py", line 227, in create_tiles
    created_tiles = self._create_meta_tiles(meta_tiles)
  File "c:\pythonenv\mapproxy-srss\lib\site-packages\mapproxy-1.5.0a_20130107-py
2.7.egg\mapproxy\cache\tile.py", line 300, in _create_meta_tiles
    created_tiles.extend(self._create_meta_tile(meta_tile))
  File "c:\pythonenv\mapproxy-srss\lib\site-packages\mapproxy-1.5.0a_20130107-py
2.7.egg\mapproxy\cache\tile.py", line 307, in _create_meta_tile
    with self.tile_mgr.lock(main_tile):
  File "c:\pythonenv\mapproxy-srss\lib\site-packages\mapproxy-1.5.0a_20130107-py
2.7.egg\mapproxy\cache\tile.py", line 143, in lock
    return self.cache.lock(tile)
  File "c:\pythonenv\mapproxy-srss\lib\site-packages\mapproxy-1.5.0a_20130107-py
2.7.egg\mapproxy\cache\base.py", line 115, in lock
    cleanup_lockdir(self.lock_dir, force=False)
  File "c:\pythonenv\mapproxy-srss\lib\site-packages\mapproxy-1.5.0a_20130107-py
2.7.egg\mapproxy\platform\cpython\lock.py", line 124, in cleanup_lockdir
    raise e
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'



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.



One pretty out-there thought we've had was that perhaps it's something to do with mapproxy-seed, Apache, and MapProxy all using the same user account and somehow because of that there's some shared file handle issue.



Am I missing something obvious here? :)



Cheers,



Keith



__________________________________
Keith Moss
Satellite Remote Sensing Services
Operations
Landgate
65 Brockway Road, FLOREAT WA 6014
PO Box 741 Wembley WA 6913
Ph. (08) 9387 0332 | Fx. (08) 9383 7142
keith.moss at landgate.wa.gov.au<mailto:keith.moss at landgate.wa.gov.au>
http://www.landgate.wa.gov.au/

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