This means tightening types from Duration to FiniteDuration in several
places; a good thing, since we replace runtime complaints by compile
time errors.
* Uses finite state machine for three states: Closed, Open, Half-Open
* Closed state allows calls through, and on sequential failures exceeding the max# set - transitions to Open state. Intervening successes cause the failure count to reset to 0
* Open state throws a CircuitOpenException on every call until the reset timeout is reached which causes a transition to Half-Open state
* Half-Open state will allow the next single call through, if it succeeds - transition to Closed state, if it fails - transition back to Open state, starting the reset timer again
* Allow configuration for the call and reset timeouts, as well as the maximum number of sequential failures before opening
* Supports async or synchronous call protection
* Callbacks are supported for state entry into Closed, Open, Half-Open. These are run in the supplied execution context
* Both thrown exceptions and calls exceeding max call time are considered failures
* Uses akka scheduler for timer events
* Integrated into File-Based durable mailbox
* Sample documented for other durable mailboxes
- replace ActorRef.stop() by ActorRefFactory.stop(child) everywhere
- ActorCell “optimizes” this to remove the child from its childrenRefs
in order to allow immediate recycling of the name
- the lost soul must have a place, for which the Locker has been
created, where Davy Jones will happily rebind the soul to his ship
(i.e. set “parent” to the locker to avoid mem leak) and periodically
revisit it (.stop(), in case of that being lost in comm failure,
similar .watch() to re-check liveness)
