From 6e1a55e9eda0d732b1427acb16ccc76dc1410c91 Mon Sep 17 00:00:00 2001
From: Zaiming Shi <zmstone@gmail.com>
Date: Mon, 29 Mar 2021 11:14:57 +0200
Subject: [PATCH] perf(emqx_connection): no priority receive

Prior to this change the main message receive loop of emqx_connection
is a priority receive which selects system messages and parent EXIT
signals prior to other message.
This accidental (not intended) design may cause the receive operation
to scan potentially large mail box.
---
 src/emqx_connection.erl | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/src/emqx_connection.erl b/src/emqx_connection.erl
index 28ea67bf8..92778f7a8 100644
--- a/src/emqx_connection.erl
+++ b/src/emqx_connection.erl
@@ -269,17 +269,20 @@ exit_on_sock_error(Reason) ->
 
 recvloop(Parent, State = #state{idle_timeout = IdleTimeout}) ->
     receive
-        {system, From, Request} ->
-            sys:handle_system_msg(Request, From, Parent, ?MODULE, [], State);
-        {'EXIT', Parent, Reason} ->
-            terminate(Reason, State);
         Msg ->
-            process_msg([Msg], Parent, ensure_stats_timer(IdleTimeout, State))
+            handle_recv(Msg, Parent, State)
     after
         IdleTimeout + 100 ->
             hibernate(Parent, cancel_stats_timer(State))
     end.
 
+handle_recv({system, From, Request}, Parent, State) ->
+    sys:handle_system_msg(Request, From, Parent, ?MODULE, [], State);
+handle_recv({'EXIT', Parent, Reason}, Parent, State) ->
+    terminate(Reason, State);
+handle_recv(Msg, Parent, State = #state{idle_timeout = IdleTimeout}) ->
+    process_msg([Msg], Parent, ensure_stats_timer(IdleTimeout, State)).
+
 hibernate(Parent, State) ->
     proc_lib:hibernate(?MODULE, wakeup_from_hib, [Parent, State]).