Reuse the waiting monitor when a worker exits

Fixes #61.

src/poolboy.erl

@@ -307,10 +307,9 @@ handle_worker_exit(Pid, State) ->
            monitors = Monitors,
            overflow = Overflow} = State,
     case queue:out(State#state.waiting) of
-        {{value, {{FromPid, _} = From, _}}, LeftWaiting} ->
-            MonitorRef = erlang:monitor(process, FromPid),
+        {{value, {From, Ref}}, LeftWaiting} ->
             NewWorker = new_worker(State#state.supervisor),
-            true = ets:insert(Monitors, {NewWorker, MonitorRef}),
+            true = ets:insert(Monitors, {NewWorker, Ref}),
             gen_server:reply(From, NewWorker),
             State#state{waiting = LeftWaiting};
         {empty, Empty} when Overflow > 0 ->

test/poolboy_tests.erl

@@ -65,6 +65,9 @@ pool_test_() ->
             },
             {<<"Check FIFO strategy">>,
                 fun fifo_strategy/0
+            },
+            {<<"Pool reuses waiting monitor when a worker exits">>,
+                fun reuses_waiting_monitor_on_worker_exit/0
             }
         ]
     }.
@@ -465,6 +468,25 @@ fifo_strategy() ->
     Worker1 = poolboy:checkout(Pid),
     poolboy:stop(Pid).
 
+reuses_waiting_monitor_on_worker_exit() ->
+    {ok, Pool} = new_pool(1,0),
+
+    Self = self(),
+    Pid = spawn(fun() ->
+        Worker = poolboy:checkout(Pool),
+        Self ! {worker, Worker},
+        poolboy:checkout(Pool),
+        receive ok -> ok end
+    end),
+
+    Worker = receive {worker, Worker} -> Worker end,
+    exit(Worker, kill),
+
+    ?assertEqual(1, length(get_monitors(Pool))),
+
+    Pid ! ok,
+    ok = pool_call(Pool, stop).
+
 get_monitors(Pid) ->
     [{monitors, Monitors}] = erlang:process_info(Pid, [monitors]),
     Monitors.