[erlang-questions] gen_statem next_event and appending to the event queue

[Frans Schneider]

 > On Wed, Oct 04, 2017 at 11:03:33AM +0200, Frans Schneider wrote:
 >> Dear list,
 >>
 >> I have a state machine which implements the RTPS reader locator [1].
 >> Basically, it has a list of unsent changes which should be send one by
 >> one to some transport. If the list is empty, the state becomes idle,
 >> otherwise it keeps the state pushing and uses the state callback action
 >> {next_event, internal, can_send} to process the next change from the 
list.
 >> However, the state machine also has to respond to some other events like
 >> the one which will replace the list with unsent changes with a new one
 >> (this is according to the specs.) But, since the callback action
 >> next_event inserts events in front of the event queue, an event like
 >> (re)setting the unsent changes list is only processed after all internal
 >> events have been processed.
 >> Adding events to the back of the queue can of course be done using a
 >> gen_statem:cast or a simple '!', but I would like to use a callback
 >> action for this as well, which looks tidier and feels better. What about
 >> adding an action {add_event, EventType, EventContent}?
 >
 > The gen_statem {next_event,,} event queue is not intended to solve all
 > possible event queue problems, and in particular not intended to be a
 > complete event execution model which would create a language within
 > the language.  One may handle this with a specific queue in the state
 > e.g with the module 'queue'.
 >
 > That said, there is a trick that might solve this problem, and that is to
 > use a timeout 0.  It is guaranteed to be handled by the state machine
 > before all external events.

Actualy, I don't want the event _before_ the external events but just 
added at the _end_ of the event queue. If I put it before external 
events, it would still process the can_send events before the (re)set 
events which are external.

 >
 >>
 >> Frans
 >>
 >> [1] http://www.omg.org/spec/DDSI-RTPS/2.2/
 >