MB-46279 make sure that file:rename doesn't happen when we wait

...for memcached to complete configuration request

This is needed because memcached configuration request might lock
the file causing simultaneous rename to fail

Change-Id: I4d853273f959eb7f9f14b5503ef03412baff4210
Reviewed-on: http://review.couchbase.org/c/ns_server/+/156369
Well-Formed: Build Bot <build@couchbase.com>
Tested-by: Artem Stemkovski <artem@couchbase.com>
Tested-by: Build Bot <build@couchbase.com>
Reviewed-by: Steve Watanabe <steve.watanabe@couchbase.com>

src/memcached_cfg.erl

@@ -163,7 +163,7 @@ write_cfg(#state{path = Path,
 rename_and_refresh(#state{path = Path,
                           tmp_path = TmpPath,
                           module = Module}, Tries, SleepTime) ->
-    case file:rename(TmpPath, Path) of
+    case memcached_refresh:apply_to_file(TmpPath, Path) of
         ok ->
             ok = Module:refresh(),
             ?log_debug("Successfully renamed ~p to ~p", [TmpPath, Path]);

src/memcached_refresh.erl

@@ -13,7 +13,7 @@
 
 -behaviour(gen_server).
 
--export([start_link/0, refresh/1]).
+-export([start_link/0, refresh/1, apply_to_file/2]).
 
 -include("ns_common.hrl").
 
@@ -27,6 +27,9 @@ start_link() ->
 refresh(Item) ->
     gen_server:cast(?MODULE, {refresh, Item}).
 
+apply_to_file(TmpPath, Path) ->
+    gen_server:call(?MODULE, {apply_to_file, TmpPath, Path}).
+
 init([]) ->
     ToRestart =
         case ns_ports_manager:find_port(ns_server:get_babysitter_node(), memcached) of
@@ -42,6 +45,9 @@ init([]) ->
 code_change(_OldVsn, State, _) -> {ok, State}.
 terminate(_Reason, _State) -> ok.
 
+handle_call({apply_to_file, TmpPath, Path}, _From, State) ->
+    ?log_debug("File rename from ~p to ~p is requested", [TmpPath, Path]),
+    {reply, file:rename(TmpPath, Path), State};
 handle_call(_Msg, _From, State) ->
     {reply, not_implemented, State}.