Commits on Apr 11, 2023

1. Remove JND delay for non-transition updates …

   Updates that are marked as part of a transition are allowed to block a
   render from committing. Generally, other updates cannot — however,
   there's one exception that's leftover from a previous iteration of our
   Suspense architecture. If an update is not the result of a known urgent
   event type — known as "Default" updates — then we allow it to suspend
   briefly, as long as the delay is short enough that the user won't
   notice. We refer to this delay as a "Just Noticable Difference" (JND)
   delay. To illustrate, if the user has already waited 400ms for an update
   to be reflected on the screen, the theory is that they won't notice if
   you wait an additional 100ms. So React can suspend for a bit longer in
   case more data comes in. The longer the user has already waited, the
   longer the JND.
   
   While we still believe this theory is sound from a UX perspective, we no
   longer think the implementation complexity is worth it. The main thing
   that's changed is how we handle Default updates. We used to render
   Default updates concurrently (i.e. they were time sliced, and were
   scheduled with postTask), but now they are blocking. Soon, they will
   also be scheduled with rAF, too, which means by the end of the next rAF,
   they will have either finished rendering or the main thread will be
   blocked until they do. There are various motivations for this but part
   of the rationale is that anything that can be made non-blocking should
   be marked as a Transition, anyway, so it's not worth adding
   implementation complexity to Default.
   
   This commit removes the JND delay for Default updates. They will now
   commit immediately once the render phase is complete, even if a
   component suspends.

   

   acdlite committed Apr 11, 2023
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