Simplify call sequence for fold

Now hanoi:fold_range/4 creates the fold worker;
which makes the callee and not the hanoi main
gen_server be ancestor for the worker.

src/hanoi.erl

@@ -117,13 +117,14 @@ fold(Ref,Fun,Acc0) ->
 
 -spec fold_range(hanoi(),kv_fold_fun(),any(),key_range()) -> any().
 fold_range(Ref,Fun,Acc0,Range) ->
+    {ok, FoldWorkerPID} = hanoi_fold_worker:start(self()),
     if Range#btree_range.limit < 10 ->
-            {ok, PID} = gen_server:call(Ref, {blocking_range, self(), Range}, infinity);
+            ok = gen_server:call(Ref, {blocking_range, FoldWorkerPID, Range}, infinity);
        true ->
-            {ok, PID} = gen_server:call(Ref, {snapshot_range, self(), Range}, infinity)
+            ok = gen_server:call(Ref, {snapshot_range, FoldWorkerPID, Range}, infinity)
     end,
-    MRef = erlang:monitor(process, PID),
-    receive_fold_range(MRef, PID,Fun,Acc0).
+    MRef = erlang:monitor(process, FoldWorkerPID),
+    receive_fold_range(MRef, FoldWorkerPID, Fun, Acc0).
 
 receive_fold_range(MRef, PID,Fun,Acc0) ->
     receive
@@ -308,14 +309,12 @@ code_change(_OldVsn, State, _Extra) ->
 
 
 
-handle_call({snapshot_range, Sender, Range}, _From, State=#state{ top=TopLevel, nursery=Nursery }) ->
-    {ok, FoldWorkerPID} = hanoi_fold_worker:start(Sender),
+handle_call({snapshot_range, FoldWorkerPID, Range}, _From, State=#state{ top=TopLevel, nursery=Nursery }) ->
     hanoi_nursery:do_level_fold(Nursery, FoldWorkerPID, Range),
     Result = hanoi_level:snapshot_range(TopLevel, FoldWorkerPID, Range),
     {reply, Result, State};
 
-handle_call({blocking_range, Sender, Range}, _From, State=#state{ top=TopLevel, nursery=Nursery }) ->
-    {ok, FoldWorkerPID} = hanoi_fold_worker:start(Sender),
+handle_call({blocking_range, FoldWorkerPID, Range}, _From, State=#state{ top=TopLevel, nursery=Nursery }) ->
     hanoi_nursery:do_level_fold(Nursery, FoldWorkerPID, Range),
     Result = hanoi_level:blocking_range(TopLevel, FoldWorkerPID, Range),
     {reply, Result, State};

src/hanoi_fold_worker.erl

@@ -75,7 +75,8 @@ start(SendTo) ->
                                   process_flag(trap_exit,true),
                                   link(SendTo),
 try
-                                  initialize(#state{sendto=SendTo}, [])
+                                  initialize(#state{sendto=SendTo}, []),
+                                  unlink(SendTo)
 catch
     Class:Ex ->
         error_logger:error_msg("Unexpected: ~p:~p ~p~n", [Class, Ex, erlang:get_stacktrace()]),
@@ -227,7 +228,6 @@ emit_next(State, [{FirstPID,FirstKV}|Rest]=Values, Queues) ->
     end.
 
 end_of_fold(State) ->
-    unlink(State#state.sendto),
     ok.
 
 data_vsn() ->

src/hanoi_level.erl

@@ -128,12 +128,12 @@ destroy(Ref) ->
 snapshot_range(Ref, FoldWorkerPID, Range) ->
     {ok, Folders} = plain_rpc:call(Ref, {init_snapshot_range_fold, FoldWorkerPID, Range, []}),
     FoldWorkerPID ! {initialize, Folders},
-    {ok, FoldWorkerPID}.
+    ok.
 
 blocking_range(Ref, FoldWorkerPID, Range) ->
     {ok, Folders} = plain_rpc:call(Ref, {init_blocking_range_fold, FoldWorkerPID, Range, []}),
     FoldWorkerPID ! {initialize, Folders},
-    {ok, FoldWorkerPID}.
+    ok.
 
 %%%%% INTERNAL