Deadlock risk while register sticky event

[tangnan526]

When we register event listener by sticky, there is a risk of deadlock.
Because when register a sticky event, it may invoke the event handler method, if the event handler method tries to acquire a lock to do something, at the same time another thread already acquires the lock and try to post an event, deadlock happend.

If we can optimize the register code to avoid this risk, that will be great!!