Allow fold worker to send {fold_results, PID, KVs}

Not just individual KVs, but lists of KVs

src/lsm_btree.erl

@@ -79,6 +79,8 @@ sync_fold_range(Ref,Fun,Acc0,Range) ->
 
 sync_receive_fold_range(MRef, PID,Fun,Acc0) ->
     receive
+
+        %% receive one K/V from fold_worker
         {fold_result, PID, K,V} ->
             case
                 try
@@ -96,6 +98,25 @@ sync_receive_fold_range(MRef, PID,Fun,Acc0) ->
                     erlang:exit(PID, kill),
                     drain_worker_and_throw(MRef,PID,Exit)
             end;
+
+        %% receive multiple KVs from fold_worker
+        {fold_results, PID, KVs} ->
+            case
+                try
+                    {ok, kvfoldl(Fun,Acc0,KVs)}
+                catch
+                    Class:Exception ->
+                        lager:warning("Exception in lsm_btree fold: ~p", [Exception]),
+                        {'EXIT', Class, Exception, erlang:get_stacktrace()}
+                end
+            of
+                {ok, Acc1} ->
+                    sync_receive_fold_range(MRef, PID, Fun, Acc1);
+                Exit ->
+                    %% kill the fold worker ...
+                    erlang:exit(PID, kill),
+                    drain_worker_and_throw(MRef,PID,Exit)
+            end;
         {fold_limit, PID, _} ->
             erlang:demonitor(MRef, [flush]),
             Acc0;
@@ -106,6 +127,13 @@ sync_receive_fold_range(MRef, PID,Fun,Acc0) ->
             error({fold_worker_died, Reason})
     end.
 
+kvfoldl(_Fun,Acc0,[]) ->
+    Acc0;
+kvfoldl(Fun,Acc0,[{K,V}|T]) ->
+    kvfoldl(Fun, Fun(K,V,Acc0), T).
+
+
+
 raise({'EXIT', Class, Exception, Trace}) ->
     erlang:raise(Class, Exception, Trace).
 
@@ -113,6 +141,8 @@ drain_worker_and_throw(MRef, PID, ExitTuple) ->
     receive
         {fold_result, PID, _, _} ->
             drain_worker_and_throw(MRef, PID, ExitTuple);
+        {fold_results, PID, _} ->
+            drain_worker_and_throw(MRef, PID, ExitTuple);
         {'DOWN', MRef, _, _, _} ->
             raise(ExitTuple);
         {fold_limit, PID, _} ->