Refactor step #1, know current max_level

This refactoring just adds the stat to the
master gen_server of a Hanoi instance to 
know the current number of levels. Until now,
we've only held a reference to the current
top level.

src/hanoi.erl

@@ -41,7 +41,7 @@
 -include_lib("kernel/include/file.hrl").
 -include_lib("include/hanoi.hrl").
 
--record(state, { top, nursery, dir, opt }).
+-record(state, { top, nursery, dir, opt, max_level }).
 
 
 %% PUBLIC API
@@ -196,16 +196,17 @@ async_receive_fold_range(PID,Fun,Acc0,Ref,Range) ->
 init([Dir, Opts]) ->
     case file:read_file_info(Dir) of
         {ok, #file_info{ type=directory }} ->
-            {ok, TopLevel} = open_levels(Dir,Opts),
+            {ok, TopLevel, MaxLevel} = open_levels(Dir,Opts),
             {ok, Nursery} = hanoi_nursery:recover(Dir, TopLevel);
 
         {error, E} when E =:= enoent ->
             ok = file:make_dir(Dir),
-            {ok, TopLevel} = hanoi_level:open(Dir, ?TOP_LEVEL, undefined, Opts),
+            {ok, TopLevel} = hanoi_level:open(Dir, ?TOP_LEVEL, undefined, Opts, self()),
+            MaxLevel = ?TOP_LEVEL,
             {ok, Nursery} = hanoi_nursery:new(Dir)
     end,
 
-    {ok, #state{ top=TopLevel, dir=Dir, nursery=Nursery, opt=Opts }}.
+    {ok, #state{ top=TopLevel, dir=Dir, nursery=Nursery, opt=Opts, max_level=MaxLevel }}.
 
 
 
@@ -233,7 +234,7 @@ open_levels(Dir,Options) ->
 
     {TopLevel, MaxMerge} =
         lists:foldl( fun(LevelNo, {Prev, Max}) ->
-                             {ok, Level} = hanoi_level:open(Dir,LevelNo,Prev,Options),
+                             {ok, Level} = hanoi_level:open(Dir,LevelNo,Prev,Options,self()),
 
                              NextMax = max(Max, hanoi_level:unmerged_count(Level)),
 
@@ -250,7 +251,7 @@ open_levels(Dir,Options) ->
     %% second incremental merge blocks until the previous is done
     ok = hanoi_level:incremental_merge(TopLevel, 0),
 
-    {ok, TopLevel}.
+    {ok, TopLevel, MaxLevel}.
 
 parse_level(FileName) ->
     case re:run(FileName, "^[^\\d]+-(\\d+)\\.data$", [{capture,all_but_first,list}]) of
@@ -261,6 +262,9 @@ parse_level(FileName) ->
     end.
 
 
+handle_info({bottom_level, N}, State) when N > State#state.max_level ->
+    {noreply,State#state{ max_level = N }};
+
 handle_info(Info,State) ->
     error_logger:error_msg("Unknown info ~p~n", [Info]),
     {stop,bad_msg,State}.

src/hanoi_level.erl

@@ -42,7 +42,7 @@
 -behavior(plain_fsm).
 -export([data_vsn/0, code_change/3]).
 
--export([open/4, lookup/2, inject/2, close/1, snapshot_range/3, blocking_range/3,
+-export([open/5, lookup/2, inject/2, close/1, snapshot_range/3, blocking_range/3,
          incremental_merge/2, unmerged_count/1]).
 
 -include_lib("kernel/include/file.hrl").
@@ -50,16 +50,16 @@
 -record(state, {
           a, b, c, next, dir, level, inject_done_ref, merge_pid, folding = [],
           step_next_ref, step_caller, step_merge_ref,
-          opts = []
+          opts = [], owner
           }).
 
 %%%%% PUBLIC OPERATIONS
 
-open(Dir,Level,Next,Opts) when Level>0 ->
+open(Dir,Level,Next,Opts,Owner) when Level>0 ->
     PID = plain_fsm:spawn_link(?MODULE,
                               fun() ->
                                       process_flag(trap_exit,true),
-                                      initialize(#state{dir=Dir,level=Level,next=Next,opts=Opts})
+                                      initialize(#state{dir=Dir,level=Level,next=Next,opts=Opts,owner=Owner})
                               end),
     {ok, PID}.
 
@@ -481,7 +481,8 @@ main_loop(State = #state{ next=Next }) ->
             State1 =
                 if Next =:= undefined ->
                         {ok, PID} = ?MODULE:open(State#state.dir, State#state.level + 1, undefined,
-                                                 State#state.opts ),
+                                                 State#state.opts, State#state.owner ),
+                        State#state.owner ! { bottom_level, State#state.level + 1 },
                         State#state{ next=PID };
                    true ->
                         State