gust-stdlib 0.4.1

Standard library of reusable Gust state machines (circuit breaker, retry, saga, rate limiter, and more)
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// Failure-threshold breaker with a time-based recovery probe.
//
// Every state field and the one effect are `i64`; the type parameter `T` this
// machine used to declare was referenced nowhere, and generated Rust that did
// not compile (E0392). If a breaker should carry a payload, put it in a state
// field so the parameter is actually used.
machine CircuitBreaker {
    state Closed(failures: i64, threshold: i64)
    state Open(opened_at: i64, timeout_ms: i64)
    state HalfOpen(successes: i64, needed: i64)

    transition fail: Closed -> Closed | Open
    transition check_open: Open -> Open | HalfOpen
    transition succeed_half: HalfOpen -> HalfOpen | Closed

    effect current_time_ms() -> i64

    on fail() {
        let next_failures = failures + 1;
        if next_failures >= threshold {
            goto Open(perform current_time_ms(), 60000);
        } else {
            goto Closed(next_failures, threshold);
        }
    }

    on check_open() {
        let elapsed = perform current_time_ms() - opened_at;
        if elapsed >= timeout_ms {
            goto HalfOpen(0, 3);
        } else {
            goto Open(opened_at, timeout_ms);
        }
    }

    on succeed_half() {
        let next = successes + 1;
        if next >= needed {
            goto Closed(0, 5);
        } else {
            goto HalfOpen(next, needed);
        }
    }
}