Fix list_buckets

List buckets was blocking riak, because file-level
range folds sends too many values. This makes
range fold stable towards such cases.

src/hanoi.erl

@@ -211,12 +211,14 @@ drain_worker_and_throw(MRef, PID, ExitTuple) ->
         ?CAST(_,{fold_done, PID}) ->
             erlang:demonitor(MRef, [flush]),
             raise(ExitTuple)
+    after 0 ->
+            raise(ExitTuple)
     end.
 
 drain_worker_and_return(MRef, PID, Value) ->
     receive
         ?CALL(_From,{fold_result, PID, _, _}) ->
-            drain_worker_and_throw(MRef, PID, Value);
+            drain_worker_and_return(MRef, PID, Value);
         {'DOWN', MRef, _, _, _} ->
             Value;
         ?CAST(_,{fold_limit, PID, _}) ->
@@ -225,6 +227,8 @@ drain_worker_and_return(MRef, PID, Value) ->
         ?CAST(_,{fold_done, PID}) ->
             erlang:demonitor(MRef, [flush]),
             Value
+    after 0 ->
+            Value
     end.
 
 

src/riak_kv_hanoi_backend.erl

@@ -196,7 +196,7 @@ delete(Bucket, PrimaryKey, IndexSpecs, #state{tree=Tree}=State) ->
 fold_buckets(FoldBucketsFun, Acc, Opts, #state{tree=Tree}) ->
     BucketFolder =
         fun() ->
-                fold_list_buckets(<<>>, Tree, FoldBucketsFun, Acc)
+                fold_list_buckets(undefined, Tree, FoldBucketsFun, Acc)
         end,
     case proplists:get_bool(async_fold, Opts) of
         true ->
@@ -207,8 +207,8 @@ fold_buckets(FoldBucketsFun, Acc, Opts, #state{tree=Tree}) ->
 
 
 fold_list_buckets(PrevBucket, Tree, FoldBucketsFun, Acc) ->
-
-    case Acc of
+    ?log("fold_list_buckets prev=~p~n", [PrevBucket]),
+    case PrevBucket of
         undefined ->
             RangeStart = to_object_key(<<>>, '_');
         _ ->