From c619263486ac7ef31c730a09b7ad273423d38525 Mon Sep 17 00:00:00 2001
From: Andrew Thompson <andrew@hijacked.us>
Date: Wed, 26 Oct 2011 17:44:18 -0400
Subject: [PATCH] Cleanup unused handlers when a trace is removed,
 documentation

---
 README.org                    |  9 +++++++++
 src/lager.erl                 | 30 +++++++++++++++++++++++++-----
 src/lager_console_backend.erl |  4 ++--
 src/lager_file_backend.erl    |  2 +-
 4 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/README.org b/README.org
index 56daa23..22369b8 100644
--- a/README.org
+++ b/README.org
@@ -198,3 +198,12 @@
 
   To view the active log backends and traces, you can use the lager:status()
   function. To clear all active traces, you can use lager:clear_all_traces().
+
+  To delete a specific trace, store a handle for the trace when you create it,
+  that you later pass to lager:stop_trace/1:
+
+#+BEGIN_EXAMPLE
+  {ok, Trace} = lager:trace_file("log/error.log", [{module, mymodule}]),
+  ...
+  lager:stop_trace(Trace)
+#+END_EXAMPLE
diff --git a/src/lager.erl b/src/lager.erl
index 5462495..807a5ca 100644
--- a/src/lager.erl
+++ b/src/lager.erl
@@ -137,16 +137,36 @@ trace_console(Filter, Level) ->
             Error
     end.
 
-stop_trace(Trace) ->
+stop_trace({_Filter, _Level, Target} = Trace) ->
     {MinLevel, Traces} = lager_mochiglobal:get(loglevel),
-    lager_mochiglobal:put(loglevel, {MinLevel, lists:delete(Trace, Traces)}),
-    %% TODO - somehow determine if the handler is safe to stop, its not
-    %$ straightforward to tell.
+    NewTraces =  lists:delete(Trace, Traces),
+    lager_mochiglobal:put(loglevel, {MinLevel, NewTraces}),
+    case get_loglevel(Target) of
+        none ->
+            %% check no other traces point here
+            case lists:keyfind(Target, 3, NewTraces) of
+                false ->
+                    gen_event:delete_handler(lager_event, Target, []);
+                _ ->
+                    ok
+            end;
+        _ ->
+            ok
+    end,
     ok.
 
 clear_all_traces() ->
     {MinLevel, _Traces} = lager_mochiglobal:get(loglevel),
-    lager_mochiglobal:put(loglevel, {MinLevel, []}).
+    lager_mochiglobal:put(loglevel, {MinLevel, []}),
+    [begin
+                case get_loglevel(Handler) of
+                    none ->
+                        gen_event:delete_handler(lager_event, Handler, []);
+                    _ ->
+                        ok
+                end
+        end || Handler <- gen_event:which_handlers(lager_event)],
+    ok.
 
 status() ->
     Handlers = gen_event:which_handlers(lager_event),
diff --git a/src/lager_console_backend.erl b/src/lager_console_backend.erl
index 710d164..cc85e13 100644
--- a/src/lager_console_backend.erl
+++ b/src/lager_console_backend.erl
@@ -183,7 +183,7 @@ console_log_test_() ->
                             500 ->
                                 ?assert(true)
                         end,
-                        ok = lager:trace_console([{module, ?MODULE}]),
+                        {ok, _} = lager:trace_console([{module, ?MODULE}]),
                         lager:debug("Test message"),
                         receive
                             {io_request, From1, ReplyAs1, {put_chars, unicode, Msg1}} ->
@@ -210,7 +210,7 @@ console_log_test_() ->
                             500 ->
                                 ?assert(true)
                         end,
-                        ok = lager:trace_console([{module, ?MODULE}]),
+                        {ok, _} = lager:trace_console([{module, ?MODULE}]),
                         lager:error("Test message"),
                         receive
                             {io_request, From1, ReplyAs1, {put_chars, unicode, Msg1}} ->
diff --git a/src/lager_file_backend.erl b/src/lager_file_backend.erl
index 6845aff..286937f 100644
--- a/src/lager_file_backend.erl
+++ b/src/lager_file_backend.erl
@@ -376,7 +376,7 @@ filesystem_test_() ->
             {"tracing to a dedicated file should work",
                 fun() ->
                         file:delete("foo.log"),
-                        lager:trace_file("foo.log", [{module, ?MODULE}]),
+                        {ok, _} = lager:trace_file("foo.log", [{module, ?MODULE}]),
                         lager:error("Test message"),
                         {ok, Bin3} = file:read_file("foo.log"),
                         ?assertMatch([_, _, "[error]", _, "Test message\n"], re:split(Bin3, " ", [{return, list}, {parts, 5}]))