reached end of a block of journal items or read all of journal items. lfjour_cleanup_hook() can clean only journal items every recipient has processed,
so it was often called uselessly.
This commit restricts most of the unusefull scheduling. Only some consumers are given a token alowing them to try to schedule the lfjour_cleanup_hook().
When a consumer wants to schedule the lfjour_cleanup_hook(), it checks whether it has a token. If yes, it decrements number of tokens the journal has given (issued_tokens)
and discards its own token. If issued_tokens reaches zero, the consumer is allowed do schedule the lfjour_cleanup_hook().
There is a maximum number of tokens a journal can give to its customers (max_tokens). A new customer is given a token in its init, if the maximum number of tokens was not reached.
The rest of tokens is given to customers in lfjour_cleanup_hook(). In lf_jour_cleanup_hook(), it is increased the issued_tokens number in order not to call the hook
before it finishes. Then, tokens are given to the slowest recipients (but never to more than max_token recipients). Before leaving lfjour_cleanup_hook(),
the issued_tokens number is decreased. If no other tokens are given, we have to make sure the lfjour_cleanup_hook will be called again. If every item in journal
was read by every recipient, tokens are given to random recipients. If all recipients with tokens managed to finish until now, we give the token to first
unfinished customer we find or we call the hook again.
the sync is actually needed when the pages get freed, not precisely
after every item cleanup, as the data technically stays intact until the
deferred free's are called.
Introducing a new omnipotent internal API to just pass route updates
from whatever point wherever we want.
From now on, all the exports should be processed by RT_WALK_EXPORTS
macro, and you can also issue a separate feed-only request to just get a
feed and finish.
The exporters can now also stop and the readers must expect that to
happen and recover. Main tables don't stop, though.
