Deferred rendering calls not cancelled when scrolling fast in a list/grid

[Olivier Tilloy]

This is more visible in plugins that do some calls to remote servers to render thumbnails for example.

Steps to reproduce (with the Flickr plugin):

1) Clear your cache directories (~/.moovida/flickr_cache and ~/.moovida/pictures_cache).
2) Start Moovida, go to Internet Media > Images > Flickr > Last 7 Days Interesting.
3) Wait for half of the grid to be rendered and scroll fast to the right.

Expected result: the thumbnails for the range of photos in the grid's window load correctly (and start loading straight away).

Current result: wrong thumbnails are displayed for some photos (proceeding from non cancelled requests for previous photos) and then are replaced by correct thumbnails.

[Florian Boucault (fboucault)]

This is very likely due to a very improper use of _render_calls dictionary in pigment/widgets/list.py where different keys are used, sometimes the widget, sometimes the item.

[Florian Boucault (fboucault)]

After experimentation, my last comment was wrong.

[Florian Boucault (fboucault)]

The bug is not specific to the grid mode. It also happens in the vertical list mode.

[Florian Boucault (fboucault)]

The explanation is in fact pretty straightforward: calls to get metadata (thumbnail, etc.) in poblesec.base.list are not cancelled.
Plan is to make node_renderer return a cancellable deferred that will be called at the appropriate time = a newly written cleaner function passed to the list widget.

[Florian Boucault (fboucault)]

My last comment is wrong. Some deferreds, notably the thumbnail retrieval one, are registered for later cancellation.

[Florian Boucault (fboucault)]

Merge request available:

https://www.moovida.com/quality/review/request/%<email address hidden>%3E