Allow subscribing to node down events from the node monitor.

src/rabbit_node_monitor.erl

@@ -24,7 +24,7 @@
          write_cluster_status/1, read_cluster_status/0,
          update_cluster_status/0, reset_cluster_status/0]).
 -export([notify_node_up/0, notify_joined_cluster/0, notify_left_cluster/1]).
--export([partitions/0]).
+-export([partitions/0, subscribe/1]).
 
 %% gen_server callbacks
 -export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2,
@@ -33,7 +33,7 @@
 -define(SERVER, ?MODULE).
 -define(RABBIT_UP_RPC_TIMEOUT, 2000).
 
--record(state, {monitors, partitions}).
+-record(state, {monitors, partitions, subscribers}).
 
 %%----------------------------------------------------------------------------
 
@@ -54,6 +54,7 @@
 -spec(notify_left_cluster/1 :: (node()) -> 'ok').
 
 -spec(partitions/0 :: () -> {node(), [{atom(), node()}]}).
+-spec(subscribe/1 :: (pid()) -> 'ok').
 
 -endif.
 
@@ -179,6 +180,9 @@ notify_left_cluster(Node) ->
 partitions() ->
     gen_server:call(?SERVER, partitions, infinity).
 
+subscribe(Pid) ->
+    gen_server:cast(?SERVER, {subscribe, Pid}).
+
 %%----------------------------------------------------------------------------
 %% gen_server callbacks
 %%----------------------------------------------------------------------------
@@ -190,8 +194,9 @@ init([]) ->
     %% happen.
     process_flag(trap_exit, true),
     {ok, _} = mnesia:subscribe(system),
-    {ok, #state{monitors   = pmon:new(),
-                partitions = []}}.
+    {ok, #state{monitors    = pmon:new(),
+                subscribers = pmon:new(),
+                partitions  = []}}.
 
 handle_call(partitions, _From, State = #state{partitions = Partitions}) ->
     {reply, {node(), Partitions}, State};
@@ -232,17 +237,24 @@ handle_cast({left_cluster, Node}, State) ->
     write_cluster_status({del_node(Node, AllNodes), del_node(Node, DiscNodes),
                           del_node(Node, RunningNodes)}),
     {noreply, State};
+handle_cast({subscribe, Pid}, State = #state{subscribers = Subscribers}) ->
+    {noreply, State#state{subscribers = pmon:monitor(Pid, Subscribers)}};
 handle_cast(_Msg, State) ->
     {noreply, State}.
 
 handle_info({'DOWN', _MRef, process, {rabbit, Node}, _Reason},
-            State = #state{monitors = Monitors}) ->
+            State = #state{monitors = Monitors, subscribers = Subscribers}) ->
     rabbit_log:info("rabbit on node ~p down~n", [Node]),
     {AllNodes, DiscNodes, RunningNodes} = read_cluster_status(),
     write_cluster_status({AllNodes, DiscNodes, del_node(Node, RunningNodes)}),
     ok = handle_dead_rabbit(Node),
+    [P ! {node_down, Node} || P <- pmon:monitored(Subscribers)],
     {noreply, State#state{monitors = pmon:erase({rabbit, Node}, Monitors)}};
 
+handle_info({'DOWN', _MRef, process, Pid, _Reason},
+            State = #state{subscribers = Subscribers}) ->
+    {noreply, State#state{subscribers = pmon:erase(Pid, Subscribers)}};
+
 handle_info({mnesia_system_event,
              {inconsistent_database, running_partitioned_network, Node}},
             State = #state{partitions = Partitions}) ->