Cleanups suggested by @mshonle

src/lager.erl

@@ -78,13 +78,13 @@ dispatch_log(Severity, Metadata, Format, Args, Size) when is_atom(Severity)->
                                 _ ->
                                     Format
                             end,
+                            LagerMsg = lager_msg:new(Msg, Timestamp,
+                                Severity, Metadata, Destinations),
                             case lager_config:get(async, false) of
                                 true ->
-                                    gen_event:notify(Pid, {log, lager_msg:new(Msg, Timestamp,
-                                                Severity, Metadata, Destinations)});
+                                    gen_event:notify(Pid, {log, LagerMsg});
                                 false ->
-                                    gen_event:sync_notify(Pid, {log, lager_msg:new(Msg, Timestamp,
-                                                Severity, Metadata, Destinations)})
+                                    gen_event:sync_notify(Pid, {log, LagerMsg})
                             end;
                         false ->
                             ok

src/lager_app.erl

@@ -39,10 +39,11 @@ start(_StartType, _StartArgs) ->
     case application:get_env(lager, async_threshold) of
         undefined ->
             ok;
-        {ok, Threshold} when is_integer(Threshold), Threshold > 0 ->
-            _ = supervisor:start_child(lager_handler_watcher_sup, [lager_event, lager_backend_throttle, [Threshold]]);
-        {ok, _BadVal} ->
-            ok
+        {ok, Threshold} when is_integer(Threshold), Threshold >= 0 ->
+            _ = supervisor:start_child(lager_handler_watcher_sup, [lager_event, lager_backend_throttle, Threshold]);
+        {ok, BadVal} ->
+            error_logger:error_msg("Invalid value for 'async_threshold': ~p~n", [BadVal]),
+            throw({error, bad_config})
     end,
 
     Handlers = case application:get_env(lager, handlers) of

src/lager_backend_throttle.erl

@@ -1,3 +1,25 @@
+%% Copyright (c) 2011-2012 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").
@@ -12,7 +34,7 @@
         async = true
     }).
 
-init([Hwm]) ->
+init(Hwm) ->
     lager_config:set(async, true),
     {ok, #state{hwm=Hwm}}.