Module API: does not provide a way to invalidate caches in other workers

[MatMaul]

Currently if we use @cached() on a function on a module there is no cache invalidation happening between workers.

[clokep]

This sounds awfully low-level for a module to care about -- and very likely for things to be implemented improperly by modules. Would it be possible to provide a higher level feature to support what the module needs?

[MatMaul]

Currently modules that want to use @cached() already can and have to invalidate manually through cached_function.invalidate(). This however only invalidates locally, and the invalidation is not replicated through workers. The planned fix involves a new module API that allows to invalidate locally and replicate the invalidation to other workers.

Current WIP can be found here:
https://github.com/matrix-org/synapse/tree/mv/module-cache-invalidation

[reivilibre]

+1 to noting that this is intended for modules to invalidate their own caches. I was quite scared from the title but the justification makes sense :)