Merge pull request 'Don't crash if ct_log/2 is called when app not running' (#4) from uw-ct_log-fallback into master

Reviewed-on: #4

src/gm_ctflow.erl

@@ -7,6 +7,7 @@
         ]).
 
 -export([ note_flow/1
+        , get_flow/0
         , ct_log/2          %% ct_log(Fmt, Args)
         , ct_log/3          %% ct_log(Flow, Fmt, Args)
         , timestamp/0 ]).
@@ -44,9 +45,14 @@ get(Key, Default) ->
 erase(Key) ->
     gm_ctflow_state:erase(Key).
 
-
+-spec note_flow(flow()) -> 'ok'.
 note_flow(Flow) ->
-    erlang:put({?MODULE, flow}, Flow).
+    erlang:put({?MODULE, flow}, Flow),
+    ok.
+
+-spec get_flow() -> flow() | 'undefined'.
+get_flow() ->
+    erlang:get({?MODULE, flow}).
 
 ct_log(Fmt, Args) ->
     ct_log(erlang:get({?MODULE, flow}), Fmt, Args).
@@ -55,13 +61,19 @@ ct_log(Flow, Fmt, Args) ->
     TS = timestamp(),
     case Flow of
         undefined ->
-            save_log(undefined, TS, Fmt, Args),
+            maybe_save_log_no_flow(TS, Fmt, Args),
             ct:log(Fmt, Args);
         Flow ->
             save_log(Flow, TS, Fmt, Args),
             ct:log("~p[~w]: " ++ Fmt, [Flow, self()|Args])
     end.
-    
+
+maybe_save_log_no_flow(TS, Fmt, Args) ->
+    try save_log(undefined, TS, Fmt, Args)
+    catch
+        error:_ ->
+            ok
+    end.
 
 save_log(Flow, TS, Fmt, Args) ->
     gm_ctflow_log:log(Flow, TS, Fmt, Args).
@@ -136,13 +148,20 @@ timestamp() ->
                                 [Year,Month,Day,Hour,Min,Sec,MilliSec])).
 
 spawn(F) ->
+    Flow = get_flow(),
     proc_lib:spawn(fun() ->
+                           maybe_inherit_flow(Flow),
                            ct_util:mark_process(),
                            F()
                    end).
 
 spawn_opt(F, Opts) ->
+    Flow = get_flow(),
     proc_lib:spawn_opt(fun() ->
-                                ct_util:mark_process(),
-                                F()
-                        end, Opts).
+                               maybe_inherit_flow(Flow),
+                               ct_util:mark_process(),
+                               F()
+                       end, Opts).
+
+maybe_inherit_flow(undefined) -> ok;
+maybe_inherit_flow(Flow)      -> note_flow(Flow).