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diff --git a/deps/lager/src/lager_backend_throttle.erl b/deps/lager/src/lager_backend_throttle.erl
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+%% Copyright (c) 2011-2013 Basho Technologies, Inc.  All Rights Reserved.
+%%
+%% This file is provided to you under the Apache License,
+%% Version 2.0 (the "License"); you may not use this file
+%% except in compliance with the License.  You may obtain
+%% a copy of the License at
+%%
+%%   http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing,
+%% software distributed under the License is distributed on an
+%% "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+%% KIND, either express or implied.  See the License for the
+%% specific language governing permissions and limitations
+%% under the License.
+
+%% @doc A simple gen_event backend used to monitor mailbox size and
+%% switch log messages between synchronous and asynchronous modes.
+%% A gen_event handler is used because a process getting its own mailbox
+%% size doesn't involve getting a lock, and gen_event handlers run in their
+%% parent's process.
+
+-module(lager_backend_throttle).
+
+-include("lager.hrl").
+
+-behaviour(gen_event).
+
+-export([init/1, handle_call/2, handle_event/2, handle_info/2, terminate/2,
+        code_change/3]).
+
+%%
+%% Allow test code to verify that we're doing the needful.
+-ifdef(TEST).
+-define(ETS_TABLE, async_threshold_test).
+-define(TOGGLE_SYNC(), test_increment(sync_toggled)).
+-define(TOGGLE_ASYNC(), test_increment(async_toggled)).
+-else.
+-define(TOGGLE_SYNC(), true).
+-define(TOGGLE_ASYNC(), true).
+-endif.
+
+-record(state, {
+        sink :: atom(),
+        hwm :: non_neg_integer(),
+        window_min :: non_neg_integer(),
+        async = true :: boolean()
+    }).
+
+init([{sink, Sink}, Hwm, Window]) ->
+    lager_config:set({Sink, async}, true),
+    {ok, #state{sink=Sink, hwm=Hwm, window_min=Hwm - Window}}.
+
+
+handle_call(get_loglevel, State) ->
+    {ok, {mask, ?LOG_NONE}, State};
+handle_call({set_loglevel, _Level}, State) ->
+    {ok, ok, State};
+handle_call(_Request, State) ->
+    {ok, ok, State}.
+
+handle_event({log, _Message},State) ->
+    {message_queue_len, Len} = erlang:process_info(self(), message_queue_len),
+    case {Len > State#state.hwm, Len < State#state.window_min, State#state.async} of
+        {true, _, true} ->
+            %% need to flip to sync mode
+            ?TOGGLE_SYNC(),
+            lager_config:set({State#state.sink, async}, false),
+            {ok, State#state{async=false}};
+        {_, true, false} ->
+            %% need to flip to async mode
+            ?TOGGLE_ASYNC(),
+            lager_config:set({State#state.sink, async}, true),
+            {ok, State#state{async=true}};
+        _ ->
+            %% nothing needs to change
+            {ok, State}
+    end;
+handle_event(_Event, State) ->
+    {ok, State}.
+
+handle_info(_Info, State) ->
+    {ok, State}.
+
+%% @private
+terminate(_Reason, _State) ->
+    ok.
+
+%% @private
+code_change(_OldVsn, State, _Extra) ->
+    {ok, State}.
+
+-ifdef(TEST).
+test_get(Key) ->
+    get_default(ets:lookup(?ETS_TABLE, Key)).
+
+test_increment(Key) ->
+    ets:insert(?ETS_TABLE,
+               {Key, test_get(Key) + 1}).
+
+get_default([]) ->
+    0;
+get_default([{_Key, Value}]) ->
+    Value.
+-endif.