circuit_breaker

Circuit breaker — closed, open, half-open state machine.

Implements the classic circuit breaker pattern for fault tolerance. Transitions: Closed (normal) → Open (failing) → HalfOpen (recovering).

Usage

let config = circuit_breaker.CircuitConfig(
  failure_threshold: 5,
  recovery_timeout_ms: 30_000,
  half_open_max_calls: 2,
)
let cb = circuit_breaker.new("my_service", config)

// Before calling the service:
case circuit_breaker.is_call_allowed(cb, config) {
  True  -> // proceed
  False -> // fail fast
}

// After success / failure:
let cb = circuit_breaker.record_success(cb, config)
let cb = circuit_breaker.record_failure(cb, config)

Types

CircuitBreaker

</>

pub type CircuitBreaker {
  CircuitBreaker(
    name: String,
    state: CircuitState,
    failure_count: Int,
    success_count: Int,
    last_failure_time_ms: Int,
    cooldown_ms: Int,
  )
}

Constructors

CircuitBreaker(
  name: String,
  state: CircuitState,
  failure_count: Int,
  success_count: Int,
  last_failure_time_ms: Int,
  cooldown_ms: Int,
)

CircuitConfig

</>

pub type CircuitConfig {
  CircuitConfig(
    failure_threshold: Int,
    recovery_timeout_ms: Int,
    half_open_max_calls: Int,
  )
}

Constructors

CircuitConfig(
  failure_threshold: Int,
  recovery_timeout_ms: Int,
  half_open_max_calls: Int,
)

CircuitState

</>

pub type CircuitState {
  CircuitClosed
  CircuitOpen
  CircuitHalfOpen
}

Constructors

```
CircuitClosed
```
```
CircuitOpen
```
```
CircuitHalfOpen
```

Values

is_call_allowed

</>

pub fn is_call_allowed(
  breaker: CircuitBreaker,
  config: CircuitConfig,
) -> Bool

Returns True if the circuit allows a call through.

Closed: always allowed.
Open: allowed only after the recovery timeout has elapsed (transitions to HalfOpen).
HalfOpen: allowed while success_count < half_open_max_calls.

new

</>

pub fn new(name: String, config: CircuitConfig) -> CircuitBreaker

Create a new circuit breaker in the Closed state.

record_failure

</>

pub fn record_failure(
  breaker: CircuitBreaker,
  config: CircuitConfig,
) -> CircuitBreaker

Record a failed call. Transitions Closed → Open at threshold, HalfOpen → Open immediately.

record_success

</>

pub fn record_success(
  breaker: CircuitBreaker,
  config: CircuitConfig,
) -> CircuitBreaker

Record a successful call. Transitions HalfOpen → Closed once enough successes.

state_name

</>

pub fn state_name(state: CircuitState) -> String

Return the state name as a string.