Glossary

Kevlar uses a small vocabulary consistently across strategies, diagnostics, and documentation. These definitions are conceptual; links point to the API or guide where the behavior becomes concrete.

Ambient handling

The exception and result predicates currently inherited by strategies added to a fluent chain. Calling When... starts an ambient handling clause; Or... extends it. Each reactive strategy captures the clause that exists when that strategy is added. See Handling failures.

Proactive strategy

A strategy that acts before an operation produces an outcome. Timeouts, rate limits, concurrency limits, and hedging are proactive: they budget, admit, or schedule work. They do not need an exception or result predicate to decide whether to start.

Reactive strategy

A strategy that reacts after an attempt produces an exception or handled result. Retry, circuit breaker, and fallback are reactive. Their handling clause defines which outcomes affect them; unhandled outcomes pass through unchanged.

Outcome

A success value or an exception represented without throwing between pipeline layers. Public Outcome and Outcome<T> APIs support no-throw execution; ordinary Execute... methods throw the terminal exception only at the caller boundary.

Strategy

One resilience behavior in a shield. A fluent chain builds an immutable linked sequence of strategies. The first strategy added is outermost, so it observes everything performed by the strategies added after it.

Shield

An immutable, thread-safe resilience pipeline. Shield protects operations without results; Shield<T> can also judge results. A built shield may be safely shared when callers should share breaker, limiter, or retry-related state.

Judge

To evaluate an exception or result against a handling predicate. Benchmark descriptions use “judging” for this predicate cost; it does not imply throwing or changing the outcome.

Seal

To end inheritance of an ambient handling clause across a composition boundary. Wrap and Compose seal the wrapped pipeline: strategies appended afterward return to default handling until another When... clause is declared. Sealing prevents a caller's clause from silently changing a library-owned pipeline.

Attempt

One invocation of the protected delegate. Retries and hedges create additional attempts. Retry counts use additional-attempt semantics: Retry(3) permits the original plus three retries. Event models document their own attempt-number convention.

Terminal outcome

The value or exception selected after every strategy finishes. Superseded retry results and losing hedge results are pipeline-owned and disposed; the selected terminal result remains caller-owned.

Operation key

A bounded diagnostic label carried by KevlarContext. It identifies an operation within a named shield without changing strategy state. Avoid unbounded values such as request IDs.

Snapshot

An immutable view captured at a defined boundary. Options and routing collections are snapshotted when documented, and testing snapshots copy live state so later executions cannot mutate an assertion already obtained.

Partition

Independent strategy state selected by a key through PartitionedShield. Partitions isolate tenants or endpoints while sharing one pipeline definition; capacity and eviction keep retained state bounded. See Partitioning.