walsender stuck in wait_for_standby_confirmation.

[Manju050]

wal_sender_timeout = 360 secs
1.I am trying to test pg_failover_slots in unique case scenario when standby is down .According to flow of code walsender process will wait in latch defined in wait_for_standby_confirmation() function because standby is lagging.
2.Now I tried to restart subscriber to connect again which resulting in error stating that slot is active for another PID.It seems likes previous walsender process is not able to process the shutdown message ('X') because he is waiting in wait_for_standby_confirmation.Because of this behaviour subscriber needs to wait for wal_sender_timeout to connect again.

Any possibilities of handling subscriber messages while looping in wait_for_standby_confirmation() function?