start the event manager only if enabled_callbacks is passed

README.md

@@ -46,9 +46,9 @@ To start a new worker pool, you can either use `wpool:start_pool` (if you want t
 * **strategy**: Not the worker selection strategy (discussed below) but the supervisor flags to be used in the supervisor over the individual workers (`wpool_process_sup`). Defaults to `{one_for_one, 5, 60}`
 * **pool_sup_intensity** and **pool_sup_period**: The intensity and period for the supervisor that manages the worker pool system (`wpool_pool`). The strategy of this supervisor must be `one_for_all` but the intensity and period may be changed from their defaults of `5` and `60`.
 * **queue_type**: Order in which requests will be stored and handled by workers. This option can take values `lifo` or `fifo`. Defaults to `fifo`.
-* **callbacks**: List of callback modules implementing `wpool_process_callbacks` to be called on certain worker events.
 * **enable_callbacks**: A boolean value determining if `event_manager` should be started for callback modules.
-  If `callbacks` were specified, there is no need to set this option.
+* **callbacks**: Initial list of callback modules implementing `wpool_process_callbacks` to be called on certain worker events.
+  This options will only work if the `enable_callbacks` is set to **true**. Callbacks can be added and removed later by `wpool_pool:add_callback_module/2` and `wpool_pool:remove_callback_module/2`.
 
 #### Using the Workers
 Since the workers are `gen_server`s, messages can be `call`ed or `cast`ed to them. To do that you can use `wpool:call` and `wpool:cast` as you would use the equivalent functions on `gen_server`.

src/wpool_pool.erl

@@ -514,14 +514,10 @@ set_random_fun() ->
     end,
   application:set_env(worker_pool, random_fun, RndFun).
 
-maybe_event_manager(Options, Spec) ->
-  InitialCallbacks = proplists:get_value(callbacks, Options, undefined),
+maybe_event_manager(Options, Item) ->
   EnableEventManager = proplists:get_value(enable_callbacks, Options, false),
-  case {EnableEventManager, InitialCallbacks} of
-    {true, _} ->
-      [Spec];
-    {_, AList} when is_list(AList) ->
-      [Spec];
-    _ ->
-      []
+  case EnableEventManager of
+    true ->
+      [Item];
+    _ -> []
   end.

test/wpool_process_callbacks_SUITE.erl

@@ -41,6 +41,7 @@ complete_callback_passed_when_starting_pool(_Config) ->
   meck:expect(callbacks, handle_worker_creation, fun(_AWorkerName) -> ok end),
   meck:expect(callbacks, handle_worker_death, fun(_AWorkerName, _Reason) -> ok end),
   {ok, _Pid} = wpool:start_pool(Pool, [{workers, WorkersCount},
+                                       {enable_callbacks, true},
                                        {worker, {crashy_server, []}},
                                        {callbacks, [callbacks]}]),
 
@@ -64,6 +65,7 @@ partial_callback_passed_when_starting_pool(_Config) ->
   meck:expect(callbacks, handle_worker_creation, fun(_AWorkerName) -> ok end),
   meck:expect(callbacks, handle_worker_death, fun(_AWorkerName, _Reason) -> ok end),
   {ok, _Pid} = wpool:start_pool(Pool, [{workers, WorkersCount},
+                                       {enable_callbacks, true},
                                        {callbacks, [callbacks]}]),
   WorkersCount = ktn_task:wait_for(function_calls(callbacks, handle_worker_creation,
                                                   ['_']), WorkersCount),
@@ -120,6 +122,7 @@ crashing_callback_does_not_affect_others(_Config) ->
                                                       error(not_going_to_work) end),
   {ok, _Pid} = wpool:start_pool(Pool, [{workers, WorkersCount},
                                        {worker, {crashy_server, []}},
+                                       {enable_callbacks, true},
                                        {callbacks, [callbacks, callbacks2]}]),
 
   WorkersCount = ktn_task:wait_for(function_calls(callbacks, handle_worker_creation,