Bug: Review of thumbnail caching and loading strategy

[cxallan]

OMERO.web makes use of the single thumbnail loading mechanisms of the thumbnail service. When there are rendering settings changes behind the scenes of OMERO.web (or with multiple tabs, windows or logins; case in point the image viewer), due to its usage of the same thumbnail service and a lack of close() calls thumbnails can be rendered with stale state.

We should make an overarching review of the thumbnail load semantics in these multi-user and multi-view contexts so that no stale state is used. Furthermore, due to browser caching semantics it will be important to ensure that the "right" thumbnails are cached by the browser.

[atarkowska]

Once this is resolved #6100 should be fixed.

[wmoore]

Problem with closing all thumbnailstores in ImageWrapper.saveDefaults() is that you get Ice Object Not Exist exceptions from the other thumbnail store proxy object wrappers.
After discussion with Chris and Ola:
Better to simply close TB proxy at the end of each getThumbnail().

[Will Moore <will@…>]

(In [7b09f46d5a8fdb0ce290c2f82cfc0332e0f75a6a/ome.git] on branch develop) ImageWrapper?.getThumbnail() closes TB store proxy every time. See #6116

[wmoore]

Seems that recent changes to webgateway/views.py d8c06ecf52cc9fccaf403b43fcd2970a77f955e5 has fixed caching of thumbnails and cache is cleared when any changes are made to rendering settings.

Only issue now is to set a default location for cache #6314.