Make logging not crash when lager is not running

include/lager.hrl

@@ -25,6 +25,7 @@
 -define(CRITICAL, 2).
 -define(ALERT, 1).
 -define(EMERGENCY, 0).
+-define(LOG_NONE, -1).
 
 -define(LEVEL2NUM(Level),
     case Level of
@@ -51,7 +52,7 @@
     end).
 
 -define(SHOULD_LOG(Level),
-    ?LEVEL2NUM(Level) =< lager_mochiglobal:get(loglevel, ?DEBUG)).
+    ?LEVEL2NUM(Level) =< lager_mochiglobal:get(loglevel, ?LOG_NONE)).
 
 %% internal non-blocking logging call
 -define(INT_LOG(Level, Format, Args),

src/lager.erl

@@ -48,30 +48,26 @@ log(Level, Module, Function, Line, Pid, Time, Message) ->
     Timestamp = lager_util:format_time(Time),
     Msg = [io_lib:format("[~p] ~p@~p:~p:~p ", [Level, Pid, Module,
                 Function, Line]),  string:strip(lists:flatten(Message), right, $\n)],
-    gen_event:sync_notify(lager_event, {log, lager_util:level_to_num(Level),
-            Timestamp, Msg}).
+    safe_notify(lager_util:level_to_num(Level), Timestamp, Msg).
 
 %% @private
 log(Level, Module, Function, Line, Pid, Time, Format, Args) ->
     Timestamp = lager_util:format_time(Time),
     Msg = [io_lib:format("[~p] ~p@~p:~p:~p ", [Level, Pid, Module,
                 Function, Line]), string:strip(lists:flatten(io_lib:format(Format, Args)), right, $\n)],
-    gen_event:sync_notify(lager_event, {log, lager_util:level_to_num(Level),
-            Timestamp, Msg}).
+    safe_notify(lager_util:level_to_num(Level), Timestamp, Msg).
 
 %% @doc Manually log a message into lager without using the parse transform.
 log(Level, Pid, Message) ->
     Timestamp = lager_util:format_time(),
     Msg = [io_lib:format("[~p] ~p ", [Level, Pid]), string:strip(lists:flatten(Message), right, $\n)],
-    gen_event:sync_notify(lager_event, {log, lager_util:level_to_num(Level),
-            Timestamp, Msg}).
+    safe_notify(lager_util:level_to_num(Level), Timestamp, Msg).
 
 %% @doc Manually log a message into lager without using the parse transform.
 log(Level, Pid, Format, Args) ->
     Timestamp = lager_util:format_time(),
     Msg = [io_lib:format("[~p] ~p ", [Level, Pid]), string:strip(lists:flatten(io_lib:format(Format, Args)), right, $\n)],
-    gen_event:sync_notify(lager_event, {log, lager_util:level_to_num(Level),
-            Timestamp, Msg}).
+    safe_notify(lager_util:level_to_num(Level), Timestamp, Msg).
 
 %% @doc Set the loglevel for a particular backend.
 set_loglevel(Handler, Level) when is_atom(Level) ->
@@ -109,3 +105,13 @@ minimum_loglevel([]) ->
     -1; %% lower than any log level, logging off
 minimum_loglevel(Levels) ->
     erlang:hd(lists:reverse(lists:sort(Levels))).
+
+safe_notify(Level, Timestamp, Msg) ->
+    case whereis(lager_event) of
+        undefined ->
+            %% lager isn't running
+            {error, lager_not_running};
+        Pid ->
+            gen_event:sync_notify(Pid, {log, Level, Timestamp, Msg})
+    end.
+

src/lager_transform.erl

@@ -67,7 +67,7 @@ transform_statement({call, Line, {remote, Line1, {atom, Line2, lager},
                     {op,Line,'>=',
                         {call,Line,
                             {remote,Line,{atom,Line,lager_mochiglobal},{atom,Line,get}},
-                            [{atom,Line,loglevel},{integer,Line,0}]},
+                            [{atom,Line,loglevel},{integer,Line,?LOG_NONE}]},
                         {integer, Line, ?LEVEL2NUM(Severity)}},
                     [{clause,Line,
                             [{atom,Line,true}], %% yes, we log!

test/lager_test_backend.erl

@@ -81,6 +81,9 @@ count() ->
 count_ignored() ->
     gen_event:call(lager_event, ?MODULE, count_ignored).
 
+not_running_test() ->
+    ?assertEqual({error, lager_not_running}, lager:log(info, wtf, "not running")).
+
 lager_test_() ->
     {foreach,
         fun setup/0,