Now timeout option is 0:

local SYNC_MUTEX_OPTS = { name = "get_delta", timeout = 0, }

So how the error timeout will happen? Or it will always be timeout?

@chronolaw This is a locked operation, where timeout = 0 means it will fail instantly if the lock can not be acquired. By tolerating timeout in this case, we allow sync_once to actually retry instead of giving up when another coroutine holds the lock

Do you mean that it will always get a timeout error?

@chronolaw No. When the callback fails or errors out it will emit a different error. That is what we count for a real error

I.e, if we have no error but the version still does not match, we count it as 1 trial; if it's a real failure (internal or external), we still count it as 1 trial. This way we prevent it from looping forever; but meanwhile we do not want a running coroutine to block the sync_once call and make it quickly exhaust all the chances, so we do not count timeouts(lock failure)