GeoServer/Image mosaic jdbc reader not thread safe (blank images)
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Key: GEOS-3216
URL: http://jira.codehaus.org/browse/GEOS-3216
Project: GeoServer
Issue Type: Bug
Components: Image mosaic JDBC
Affects Versions: 1.7.5
Reporter: Arnoud de Bruijn
Assignee: Andrea Aime
Hi everyone!
We''ve been using the ImageMosaicJDBC plug in GeoServer 1.7.5. When requesting several images at the same time, some of the images come back blank when they shouldn't. After some debugging I found out the following: GeoServer seems to use the same ImageMosiacJDBCReader object for processing all (i.e. all except for the first set of) simultaneous requests. This, in turn, causes ImageMosaicJDBCReader.loadTiles to pass on private member 'tileQueue' to threads processing different requests. In some cases this leads to an end marker being written in the tile queue and an ImageComposer-thread exiting without having processed any queue objects (it's decoder threads are presumably still busy), the 'image' variable is null and is reset to the ImageMosaicJDBCReader.DEFAULT_IMAGE_TYPE.
The question is: what is the contract between GeoServer and its plugins? i.e. should the plugin be thread safe or should GeoServer deal with thread safe issues? I've looked into ResourcePool.java.getGridCoverageReader@anonymised.com : the coverage reader is cached per CoverageStoreInfo and is being reused for every incoming request (except for when no reader has been previously cached: the synchronize only guards the 'put' and not the 'get' so in that case the threads are waiting in line to create and cache a reader), so this would suggest the plugin should be thread safe. I've temporarily disabled coverage reader caching because we need it to work for a demo 
Does anyone have any thoughts on the matter?
Cheers,
Arnoud de Bruijn
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