Struct failsafe::StateMachine

pub struct StateMachine<POLICY, INSTRUMENT> { /* private fields */ }

A circuit breaker implementation backed by state machine.

It is implemented via a finite state machine with three states: Closed, Open and HalfOpen. The state machine does not know anything about the backend’s state by itself, but uses the information provided by the method via on_success and on_error events. Before communicating with the backend, the the permission to do so must be obtained via the method is_call_permitted.

The state of the state machine changes from Closed to Open when the FailurePolicy reports that the failure rate is above a (configurable) threshold. Then, all access to the backend is blocked for a time duration provided by FailurePolicy.

After the time duration has elapsed, the state changes from Open to HalfOpen and allows calls to see if the backend is still unavailable or has become available again. If the circuit breaker receives a failure on the next call, the state will change back to Open. Otherwise it changes to Closed.

Implementations

impl<POLICY, INSTRUMENT> StateMachine<POLICY, INSTRUMENT>where
    POLICY: FailurePolicy,
    INSTRUMENT: Instrument,

pub fn new(failure_policy: POLICY, instrument: INSTRUMENT) -> Self

Creates a new state machine with given failure policy and instrument.

pub fn is_call_permitted(&self) -> bool

Requests permission to call.

It returns true if a call is allowed, or false if prohibited.

pub fn on_success(&self)

Records a successful call.

This method must be invoked when a call was success.

pub fn on_error(&self)

Records a failed call.

This method must be invoked when a call failed.

Trait Implementations

impl<POLICY, INSTRUMENT> CircuitBreaker for StateMachine<POLICY, INSTRUMENT>where
    POLICY: FailurePolicy,
    INSTRUMENT: Instrument,

fn is_call_permitted(&self) -> bool

Requests permission to call.

fn call_with<P, F, E, R>(&self, predicate: P, f: F) -> Result<R, Error<E>>where
    P: FailurePredicate<E>,
    F: FnOnce() -> Result<R, E>,

Executes a given function within circuit breaker.

fn call<F, E, R>(&self, f: F) -> Result<R, Error<E>>where
    F: FnOnce() -> Result<R, E>,

Executes a given function within circuit breaker.

impl<POLICY, INSTRUMENT> CircuitBreaker for StateMachine<POLICY, INSTRUMENT>where
    POLICY: FailurePolicy + Send + Sync,
    INSTRUMENT: Instrument + Send + Sync,

fn is_call_permitted(&self) -> bool

Requests permission to call.

fn call_with<F, P>(
    &self,
    predicate: P,
    f: F
) -> ResponseFuture<F, Self::FailurePolicy, Self::Instrument, P>where
    F: Future,
    P: FailurePredicate<F::Error>,

Executes a given future within circuit breaker.

fn call<F>(
    &self,
    f: F
) -> ResponseFuture<F, Self::FailurePolicy, Self::Instrument, Any>where
    F: Future,

Executes a given future within circuit breaker.

impl<POLICY, INSTRUMENT> Clone for StateMachine<POLICY, INSTRUMENT>

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<POLICY, INSTRUMENT> Debug for StateMachine<POLICY, INSTRUMENT>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.