HalfOpen

State of the CircuitBreaker in which the circuit breaker has already allowed a task to go through, as a reset attempt, in order to test the connection.

Contract:

• The first task when Open has expired is allowed through without failing fast, just before the circuit breaker is evolved into the HalfOpen state
• All tasks attempted in HalfOpen fail-fast with an exception just as in Open state
• If that task attempt succeeds, the breaker is reset back to the Closed state, with the resetTimeout and the failures count also reset to initial values
• If the first call fails, the breaker is tripped again into the Open state (the resetTimeout is passed to the backoff function)