[mapguide-internals] TileService cache Question

[UV]

Thanks!
I also found the recursive mutex a bit further down which should delay a 
competing thread until the requested tile has been rendered.
A 2 layered approach with lockfile and mutex....

Trevor Wekel wrote:
> Hi UV,
>
> If MgServerTileService::DetectTileLockFile finds an existing lock file, it waits for 120 seconds for the lock to free up before returning.  If the lock has not freed up after two minutes, then the render has probably failed and it is reasonable to blow the lock away and retry.
>
> Regards,
> Trevor
>
> -----Original Message-----
> From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-internals-bounces at lists.osgeo.org] On Behalf Of UV
> Sent: March 15, 2010 9:45 AM
> To: MapGuide Internals Mail List
> Subject: [mapguide-internals] TileService cache Question
>
> Trying to understand parallel overlapping tile requests to the tile 
> service in preparation of meta tiling.
>
> line 321-326 ServerTileService.cpp:
>    // If there is a dangling lock file, then attempt to remove it.
>     if (DetectTileLockFile(lockPathname))
>     {
>         // TODO: Handle the exception by displaying a tile with an error 
> message?
>         MgFileUtil::DeleteFile(lockPathname, true);
>     }
>
>
> I dont understand this logic... If someone has made the request for my 
> tile already should I not wait instead of removing the lockfile?
> Checking the time stamp of the lockfile would be a practical way to 
> determine if its worth waiting......
>
> The logic shown above seems to assume that it is an erroneous state to 
> request a tile while it is computed.
> In a multi-threaded server I can easily create scenarios where this 
> could happen and a retry would be a smarter reaction to a found lockfile.
>
> Any ideas?
>
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