New couch_event:listen/4 API

This function doesn't return but allows a process to become an event
listener. Useful in RPC situations to avoid spawning an extra process
and doubling the message passing.

src/couch_event.erl

@@ -38,6 +38,10 @@ notify(DbName, Event) ->
     gen_server:cast(?DIST, {DbName, Event}).
 
 
+listen(Module, Function, State, Options) ->
+    couch_event_listener_mfa:enter_loop(Module, Function, State, Options).
+
+
 link_listener(Module, Function, State, Options) ->
     couch_event_listener_mfa:start_link(Module, Function, State, Options).
 

src/couch_event_listener_mfa.erl

@@ -16,7 +16,8 @@
 
 -export([
     start_link/4,
-    stop/1
+    enter_loop/4,
+    stop/1,
 ]).
 
 -export([
@@ -41,6 +42,15 @@ start_link(Mod, Func, State, Options) ->
     couch_event_listener:start_link(?MODULE, Arg, Options).
 
 
+enter_loop(Mod, Func, State, Options) ->
+    St = #st{
+        mod = Mod,
+        func = Func,
+        state = State
+    },
+    couch_event_listener:enter_loop(?MODULE, St, Options).
+
+
 stop(Pid) ->
     couch_event_listener:stop(Pid).