trigger handle_DOWN callback when a new leader is elected if the prev…

…ious one is down.

Since the handle_DOWN callback is only called in the leader, when the leader goes down, that callback is never called.
So the way to solve this is to keep track of the previous leader so that when a new one is elected, the handke_DOWN callback can be called if the previous leader is still down.

src/gen_leader.erl

@@ -117,6 +117,7 @@
 
 -record(election, {
           leader = none,
+          previous_leader = none,
           name,
           leadernode = none,
           candidate_nodes = [],
@@ -520,6 +521,7 @@ safe_loop(#server{mod = Mod, state = State} = Server, Role,
                     NewE1 = mon_node(E, From, Server),
                     NewE = NewE1#election{leader = From,
                                           leadernode = node(From),
+                                          previous_leader = E#election.leader,
                                           worker_nodes = Workers,
                                           status = norm,
                                           cand_timer=undefined},
@@ -610,6 +612,7 @@ safe_loop(#server{mod = Mod, state = State} = Server, Role,
             case Node == E#election.leadernode of
                 true ->
                     NewE = E#election{ leader = none, leadernode = none,
+                                       previous_leader = E#election.leader,
                                        status = waiting_worker,
                                        monitored = []};
                 false ->
@@ -1178,6 +1181,7 @@ continStage2(E, Server) ->
                                                 % io:format("I am the leader (Node ~w) ~n", [node()]),
             E#election{leader = self(),
                        leadernode = node(),
+                       previous_leader = E#election.leader,
                        status = norm}
     end.
 
@@ -1252,8 +1256,26 @@ hasBecomeLeader(E,Server,Msg) ->
             %% io:format("==> I am the leader! (acks: ~200p)\n", [E#election.acks]),
             %% Set the internal timeout (corresponds to Periodically)
             timer:send_after(E#election.cand_timer_int, {heartbeat, node()}),
+
+            %% trigger handle_DOWN callback if previous leader is down
+            PrevLeader = E#election.previous_leader,
+            {NewState2, NewE2} =
+              case PrevLeader of
+                  none -> {NewState, NewE};
+                  Pid when is_pid(Pid) ->
+                    case lists:member(node(PrevLeader), down(E)) of
+                        false -> {NewState, NewE};
+                        true ->
+                          case (Server#server.mod):handle_DOWN(node(PrevLeader), NewState, NewE) of
+                              {ok, NS} -> {NS, NewE};
+                              {ok, Synch2, NS} ->
+                                {NS, broadcast({from_leader, Synch2}, NewE)}
+                          end
+                    end
+              end,
+
             %%    (It's meaningful only when I am the leader!)
-            loop(Server#server{state = NewState},elected,NewE,Msg);
+            loop(Server#server{state = NewState2},elected,NewE2,Msg);
         false ->
             safe_loop(Server,candidate,E,Msg)
     end.