1 files changed, 120 insertions, 0 deletions
diff --git a/apps/mem3/src/mem3_nodes.erl b/apps/mem3/src/mem3_nodes.erl
new file mode 100644
index 00000000..6cbf3d9a
--- /dev/null
+++ b/apps/mem3/src/mem3_nodes.erl
@@ -0,0 +1,120 @@
+-module(mem3_nodes).
+-behaviour(gen_server).
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, 
+    code_change/3]).
+
+-export([start_link/0, get_nodelist/0]).
+
+-include("mem3.hrl").
+-include_lib("couch/include/couch_db.hrl").
+
+-record(state, {changes_pid, update_seq, nodes}).
+
+start_link() ->
+    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
+
+get_nodelist() ->
+    gen_server:call(?MODULE, get_nodelist).
+
+init([]) ->
+    {Nodes, UpdateSeq} = initialize_nodelist(),
+    {Pid, _} = spawn_monitor(fun() -> listen_for_changes(UpdateSeq) end),
+    {ok, #state{changes_pid = Pid, update_seq = UpdateSeq, nodes = Nodes}}.
+
+handle_call(get_nodelist, _From, State) ->
+    {reply, State#state.nodes, State};
+handle_call({add_node, Node}, _From, #state{nodes=Nodes} = State) ->
+    gen_event:notify(mem3_events, {add_node, Node}),
+    {reply, ok, State#state{nodes = lists:umerge([Node], Nodes)}};
+handle_call({remove_node, Node}, _From, #state{nodes=Nodes} = State) ->
+    gen_event:notify(mem3_events, {remove_node, Node}),
+    {reply, ok, State#state{nodes = lists:delete(Node, Nodes)}};
+handle_call(_Call, _From, State) ->
+    {noreply, State}.
+
+handle_cast(_Msg, State) ->
+    {noreply, State}.
+
+handle_info({'DOWN', _, _, Pid, Reason}, #state{changes_pid=Pid} = State) ->
+    ?LOG_INFO("~p changes listener died ~p", [?MODULE, Reason]),
+    StartSeq = State#state.update_seq,
+    Seq = case Reason of {seq, EndSeq} -> EndSeq; _ -> StartSeq end,
+    timer:send_after(5000, start_listener),
+    {noreply, State#state{update_seq = Seq}};
+handle_info(start_listener, #state{update_seq = Seq} = State) ->
+    {NewPid, _} = spawn_monitor(fun() -> listen_for_changes(Seq) end),
+    {noreply, State#state{changes_pid=NewPid}};
+handle_info(_Info, State) ->
+    {noreply, State}.
+
+terminate(_Reason, _State) ->
+    ok.
+
+code_change(_OldVsn, State, _Extra) ->
+    {ok, State}.
+
+%% internal functions
+
+initialize_nodelist() ->
+    DbName = couch_config:get("mem3", "nodedb", "nodes"),
+    {ok, Db} = ensure_exists(DbName),
+    {ok, _, Nodes0} = couch_btree:fold(Db#db.id_tree, fun first_fold/3, [], []),
+    % add self if not already present
+    case lists:member(node(), Nodes0) of
+    true ->
+        Nodes = Nodes0;
+    false ->
+        Doc = #doc{id = couch_util:to_binary(node())},
+        {ok, _} = couch_db:update_doc(Db, Doc, []),
+        Nodes = [node() | Nodes0]
+    end,
+    couch_db:close(Db),
+    {lists:sort(Nodes), Db#db.update_seq}.
+
+first_fold(#full_doc_info{id = <<"_design/", _/binary>>}, _, Acc) ->
+    {ok, Acc};
+first_fold(#full_doc_info{deleted=true}, _, Acc) ->
+    {ok, Acc};
+first_fold(#full_doc_info{id=Id}, _, Acc) ->
+    {ok, [mem3_util:to_atom(Id) | Acc]}.
+
+listen_for_changes(Since) ->
+    DbName = ?l2b(couch_config:get("mem3", "nodedb", "nodes")),
+    {ok, Db} = ensure_exists(DbName),
+    Args = #changes_args{
+        feed = "continuous",
+        since = Since,
+        heartbeat = true,
+        include_docs = true
+    },
+    ChangesFun = couch_changes:handle_changes(Args, nil, Db),
+    ChangesFun(fun changes_callback/2).
+
+ensure_exists(DbName) when is_list(DbName) ->
+    ensure_exists(list_to_binary(DbName));
+ensure_exists(DbName) ->
+    Options = [{user_ctx, #user_ctx{roles=[<<"_admin">>]}}],
+    case couch_db:open(DbName, Options) of
+    {ok, Db} ->
+        {ok, Db};
+    _ -> 
+        couch_server:create(DbName, Options)
+    end.
+
+changes_callback(start, _) ->
+    {ok, nil};
+changes_callback({stop, EndSeq}, _) ->
+    exit({seq, EndSeq});
+changes_callback({change, {Change}, _}, _) ->
+    Node = couch_util:get_value(<<"id">>, Change),
+    case Node of <<"_design/", _/binary>> -> ok; _ ->
+        case couch_util:get_value(deleted, Change, false) of
+        false ->
+            gen_server:call(?MODULE, {add_node, mem3_util:to_atom(Node)});
+        true ->
+            gen_server:call(?MODULE, {remove_node, mem3_util:to_atom(Node)})
+        end
+    end,
+    {ok, couch_util:get_value(<<"seq">>, Change)};
+changes_callback(timeout, _) ->
+    {ok, nil}.