Remove expired Node weak pointers regularly,
in a way that ensures that:
* every expired pointer gets eventually cleaned up
* expired pointer ratio remains reasonably low
* no cleanup pass blocks the node for too long,
* impact on performance is negligible
Impact on performance:
Every N insertions, at most N nodes are tested by iterating the map
-> performance impact in O(1) (constant).
Expiring nodes on cache destruction allow to cancel
any remaining request before the dht instance is destructed,
since Node instances might remain alive after the dht instance
is destroyed.
Since bootstrapSearch was rewritten to use the node cache, it made it clear that
refill should be rewritten as such. However, then bootstrapSearch becomes
irrelevant.
An enhancement to refill is that it will let insertNode review its whole list
of nodes and then let it insert nodes up to SEARCH_NODES nodes. The previous
method would not garantee this behavior since, most of the times, it would pass
less than SEARCH_NODES nodes to insertNode.
Adrien Béraud
Simon Désaulniers
kaldoran