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% Copyright 2010 Cloudant
%
% Licensed under the Apache License, Version 2.0 (the "License"); you may not
% use this file except in compliance with the License. You may obtain a copy of
% the License at
%
% http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
% License for the specific language governing permissions and limitations under
% the License.
-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, get_node_info/2]).
-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).
get_node_info(Node, Key) ->
gen_server:call(?MODULE, {get_node_info, Node, Key}).
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, lists:sort(dict:fetch_keys(State#state.nodes)), State};
handle_call({get_node_info, Node, Key}, _From, State) ->
case dict:find(Node, State#state.nodes) of
{ok, NodeInfo} ->
{reply, couch_util:get_value(Key, NodeInfo), State};
error ->
{reply, error, State}
end;
handle_call({add_node, Node, NodeInfo}, _From, #state{nodes=Nodes} = State) ->
gen_event:notify(mem3_events, {add_node, Node}),
{reply, ok, State#state{nodes = dict:store(Node, NodeInfo, Nodes)}};
handle_call({remove_node, Node}, _From, #state{nodes=Nodes} = State) ->
gen_event:notify(mem3_events, {remove_node, Node}),
{reply, ok, State#state{nodes = dict:erase(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) ->
twig:log(notice, "~p changes listener died ~p", [?MODULE, Reason]),
StartSeq = State#state.update_seq,
Seq = case Reason of {seq, EndSeq} -> EndSeq; _ -> StartSeq end,
erlang:send_after(5000, self(), 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", "node_db", "nodes"),
{ok, Db} = mem3_util:ensure_exists(DbName),
{ok, _, {_, Nodes0}} = couch_btree:fold(Db#db.id_tree, fun first_fold/3,
{Db, dict:new()}, []),
% add self if not already present
case dict:find(node(), Nodes0) of
{ok, _} ->
Nodes = Nodes0;
error ->
Doc = #doc{id = couch_util:to_binary(node())},
{ok, _} = couch_db:update_doc(Db, Doc, []),
Nodes = dict:store(node(), [], Nodes0)
end,
couch_db:close(Db),
{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}=DocInfo, _, {Db, Dict}) ->
{ok, #doc{body={Props}}} = couch_db:open_doc(Db, DocInfo),
{ok, {Db, dict:store(mem3_util:to_atom(Id), Props, Dict)}}.
listen_for_changes(Since) ->
DbName = couch_config:get("mem3", "node_db", "nodes"),
{ok, Db} = mem3_util: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).
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 ->
{Props} = couch_util:get_value(doc, Change),
gen_server:call(?MODULE, {add_node, mem3_util:to_atom(Node), Props});
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}.
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