refactor(sessds): Introduce macros for the timers

apps/emqx/src/emqx_persistent_session_ds.erl

@@ -120,7 +120,11 @@
 -type clientinfo() :: emqx_types:clientinfo().
 -type conninfo() :: emqx_session:conninfo().
 -type replies() :: emqx_session:replies().
--type timer() :: pull | get_streams | bump_last_alive_at.
+
+-define(TIMER_PULL, timer_pull).
+-define(TIMER_GET_STREAMS, timer_get_streams).
+-define(TIMER_BUMP_LAST_ALIVE_AT, timer_bump_last_alive_at).
+-type timer() :: ?TIMER_PULL | ?TIMER_GET_STREAMS | ?TIMER_BUMP_LAST_ALIVE_AT.
 
 -define(STATS_KEYS, [
     subscriptions_cnt,
@@ -399,7 +403,7 @@ deliver(_ClientInfo, _Delivers, Session) ->
     {ok, replies(), session()} | {ok, replies(), timeout(), session()}.
 handle_timeout(
     _ClientInfo,
-    pull,
+    ?TIMER_PULL,
     Session = #{id := Id, inflight := Inflight0, receive_maximum := ReceiveMaximum}
 ) ->
     {Publishes, Inflight} = emqx_persistent_message_ds_replayer:poll(
@@ -422,13 +426,13 @@ handle_timeout(
             [_ | _] ->
                 0
         end,
-    ensure_timer(pull, Timeout),
+    ensure_timer(?TIMER_PULL, Timeout),
     {ok, Publishes, Session#{inflight := Inflight}};
-handle_timeout(_ClientInfo, get_streams, Session) ->
+handle_timeout(_ClientInfo, ?TIMER_GET_STREAMS, Session) ->
     renew_streams(Session),
-    ensure_timer(get_streams),
+    ensure_timer(?TIMER_GET_STREAMS),
     {ok, [], Session};
-handle_timeout(_ClientInfo, bump_last_alive_at, Session0) ->
+handle_timeout(_ClientInfo, ?TIMER_BUMP_LAST_ALIVE_AT, Session0) ->
     %% Note: we take a pessimistic approach here and assume that the client will be alive
     %% until the next bump timeout.  With this, we avoid garbage collecting this session
     %% too early in case the session/connection/node crashes earlier without having time
@@ -436,7 +440,7 @@ handle_timeout(_ClientInfo, bump_last_alive_at, Session0) ->
     BumpInterval = emqx_config:get([session_persistence, last_alive_update_interval]),
     EstimatedLastAliveAt = now_ms() + BumpInterval,
     Session = session_set_last_alive_at_trans(Session0, EstimatedLastAliveAt),
-    ensure_timer(bump_last_alive_at),
+    ensure_timer(?TIMER_BUMP_LAST_ALIVE_AT),
     {ok, [], Session}.
 
 -spec replay(clientinfo(), [], session()) ->
@@ -958,9 +962,9 @@ export_record(_, _, [], Acc) ->
 %% TODO: find a more reliable way to perform actions that have side
 %% effects. Add `CBM:init' callback to the session behavior?
 ensure_timers() ->
-    ensure_timer(pull),
-    ensure_timer(get_streams),
-    ensure_timer(bump_last_alive_at).
+    ensure_timer(?TIMER_PULL),
+    ensure_timer(?TIMER_GET_STREAMS),
+    ensure_timer(?TIMER_BUMP_LAST_ALIVE_AT).
 
 -spec ensure_timer(timer()) -> ok.
 ensure_timer(bump_last_alive_at = Type) ->