tor/changes/decouple_conn_attach

  o Code simplification and refactorings:
    - Decouple the list of streams needing to be attached to circuits
      from the overall connection list. This change makes it possible to
      attach streams quickly while both simplifying Tor's callgraph and
      avoiding O(N) scans of the entire connection list.  Closes ticket
      17590.
Decouple ..attach_circuit() from most of its callers. Long ago we used to call connection_ap_handshake_attach_circuit() only in a few places, since connection_ap_attach_pending() attaches all the pending connections, and does so regularly. But this turned out to have a performance problem: it would introduce a delay to launching or connecting a stream. We couldn't just call connection_ap_attach_pending() every time we make a new connection, since it walks the whole connection list. So we started calling connection_ap_attach_pending all over, instead! But that's kind of ugly and messes up our callgraph. So instead, we now have connection_ap_attach_pending() use a list only of the pending connections, so we can call it much more frequently. We have a separate function to scan the whole connection array to see if we missed adding anything, and log a warning if so. Closes ticket #17590 2015-11-13 19:38:01 +01:00			`o Code simplification and refactorings:`
			`- Decouple the list of streams needing to be attached to circuits`
			`from the overall connection list. This change makes it possible to`
			`attach streams quickly while both simplifying Tor's callgraph and`
			`avoiding O(N) scans of the entire connection list. Closes ticket`
			`17590.`