tree 034f3c2be25534aa36af135a77fb1210554c9fa3
parent 8a44b78e66cd448be192627413403fc514bb8399
author Pavlin Radoslavov <pavlin@onlab.us> 1407470236 -0700
committer Pavlin Radoslavov <pavlin@onlab.us> 1407784093 -0700

ONOS-1871: Send Topology MastershipEvent info to Topology listeners.

The MastershipEvent info is needed by applications such as the GUI
(via the Websocket client).

NOTE: Previously, the Mastership Events were sent only when there
was any change, but no Mastership Events were sent when a listener
has just subscribed.

The solution is to add a mechanism for creating and sending Topology
Snapshot event to new listeners, and that event also includes
the Mastership Events.

The modifications are:

 * Renamed and updated the ITopologyService API for adding/removing
   Topology listeners:
   OLD: registerTopologyListener() and deregisterTopologyListener()
   NEW: addListener() and removeListener()

   Also, addListener() has a second argument:
       "boolean startFromSnapshot"
   If that argument is true, and if the topology is not empty, the first
   (expected) event to that listener should be a snapshot of the current
   topology.

 * Added TopologyEvents() constructor for ADDED events only. Such event
   can be used to represent a snapshot of the topology.

 * Added new APIs to TopologyInternal:
   getAllSwitchEvents(), getAllPortEvents(), get AllLinkEvents(),
   getAllHostEvents()
   Those APIs are needed for creating a snapshot of the topology.

 * Added a mechanism for creating empty (NO-OP) TopologyEvent instance,
   and use that mechanism to "wake-up" the EventHandler processing thread
   when it needs to send Topology Snapshot to a new listener.
   This solution is (kind-of) a hack.

Change-Id: Ie1eb52242f58682aac61f54af29c3b5d291ac0bd