Problem/Motivation
Split from #3257725: Add a cache prewarm API.
Once we have both #3257725: Add a cache prewarm API and #3425114: Add revolt/event-loop dependency to core (and maybe one more issue in-between, not sure), we can add a Drupal\Core\Async\usleepNonBlocking; method which will run down any pending event loop tasks while waiting for a lock to be released.
See the issue summary of #3257725: Add a cache prewarm API for more details.