Merge pull request #28 from rabbitmq/work-around-race-in-cover-is_compiled

horus: Work around race in `cover:is_compiled/1`

Author: dumbbell

src/horus.erl

@@ -1998,7 +1998,7 @@ get_object_code(Module) ->
 %% @private
 
 do_get_object_code(Module) ->
-    case cover:is_compiled(Module) of
+    case is_cover_compiled(Module) of
         false ->
             get_object_code_from_code_server(Module);
         {file, Filename} ->
@@ -2008,6 +2008,18 @@ do_get_object_code(Module) ->
             erpc:call(CoverMainNode, ?MODULE, do_get_object_code, [Module])
     end.
 
+is_cover_compiled(Module) ->
+    try
+        cover:is_compiled(Module)
+    catch
+        error:{badmatch, {error, {already_started, _}}} ->
+            %% The code in `cover' that checks if the cover server is started
+            %% seem racy. We get an exception if it thinks it has to start it
+            %% but it is already started. In this case, we retry the call.
+            timer:sleep(100),
+            cover:is_compiled(Module)
+    end.
+
 get_object_code_from_code_server(Module) ->
     case code:get_object_code(Module) of
         {Module, Beam, Filename} ->