From e6110b0e9ebf7817418ce1e913432a16ecc4ac8f Mon Sep 17 00:00:00 2001
From: Zaiming Shi <zmstone@gmail.com>
Date: Tue, 27 Jul 2021 16:03:55 +0200
Subject: [PATCH] fix(emqx_app): stop listeners in application prep_stop
 callback

Application:stop is call after the root supervisor is stopped,
in our case, prior to this fix, emqx_sup is stopped before
the listeners (hence the emqx_connection processes).

This causes shutdown to emit a lot of error logs
e.g. emqx_broker pool is down, but emqx_connection process is still
trying to call the pool
---
 apps/emqx/src/emqx_app.erl | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/apps/emqx/src/emqx_app.erl b/apps/emqx/src/emqx_app.erl
index a3978ad90..3a2e2b123 100644
--- a/apps/emqx/src/emqx_app.erl
+++ b/apps/emqx/src/emqx_app.erl
@@ -19,6 +19,7 @@
 -behaviour(application).
 
 -export([ start/2
+        , prep_stop/1
         , stop/1
         , get_description/0
         , get_release/0
@@ -63,12 +64,13 @@ start(_Type, _Args) ->
     print_vsn(),
     {ok, Sup}.
 
--spec(stop(State :: term()) -> term()).
-stop(_State) ->
+prep_stop(_State) ->
     ok = emqx_alarm_handler:unload(),
     emqx_boot:is_enabled(listeners)
       andalso emqx_listeners:stop().
 
+stop(_State) -> ok.
+
 set_backtrace_depth() ->
     Depth = emqx_config:get([node, backtrace_depth]),
     _ = erlang:system_flag(backtrace_depth, Depth),