It can skip, if the value was changed multiple times in the same rendering phase.

I see. That completely explains my issue then. Is there any way to get around this?

To render while you rendering? :) Not really. But you can split updates into multiple operations and use :flush-dom event metadata.

Okay, I see, I'll look it up, thanks.

Different problem, same solution: https://github.com/day8/re-frame/blob/master/docs/Solve-the-CPU-hog-problem.md

I'm not sure how this is related

I don't have any intesive work to do, I'm just trying to dispatch-sync a "http request is in progress" marker in the db to avoid a second request to run before the first one has completed

and as it turns out, dispatch-sync is not enough for that, the db gets updated, the souscription caches don't

maybe the issue is the 16ms thingy, tho

probably https://github.com/day8/re-frame/blob/master/docs/flow-mechanics.md#truth-interlude related

yep, flush was what I needed!

thanks for your help.

Are you per chance trying to do that dispatch within the event that is sending off the http request?

If so, please just write a function that will update your db with the loading flag to true and have the http request be in an fx vector

{:db (set-loading-flag db) :fx [[:http-xhrio ...]]}

That will be far easier to reason about and is actually atomic without relying on things like flush

I second @U3JH98J4R just set a loading flag to true from the event that dispatches the http request