Changing ImageReader::refreshCount() invalidates all ImageReader caches, not just the current

[HughMacdonald]

It appears that when refreshCountPlug() on ImageReader is changed, it causes ImageReader to call

imageCache()->invalidate_all( true );

This will clear the cache for every single ImageReader node, rather than just for the current one.

[johnhaddon]

Note though that in the face of multiple contexts there is no such thing as "the current one". If I have an image sequence and hit refresh and then hit play, I expect all the frames to be refreshed. That's the simple case - the more complex one involves arbitrary ${variable} substitutions in the filename.

I think the best we can aim for is to take the longest substitution-free prefix from the unsubstituted filename, and then remove all images with that prefix from the cache. Do we have the ability to query the current list of cached files from OIIO? I guess we could track the queries we've made ourselves if we really had to?