InMemorySagaJournal

Reference implementation of SagaJournal backed by a ConcurrentHashMap with per-RunId locking.

Thread-safety model

Different RunIds may append concurrently without contention — each run has its own Mutex. Within a single RunId, appends are serialized by the per-run lock. Lock creation uses ConcurrentHashMap.computeIfAbsent, which is itself thread-safe.

Codec placement (D3)

This implementation stores payload P directly. PayloadCodec is never called here. Persistent adapters (Room, JDBC, file) accept a PayloadCodec in their own constructor and convert at persistence boundaries. This keeps in-memory usage fast and free of serialization concerns.

Usage

val journal = InMemorySagaJournal<OrderEvent>()

// Plug into a saga executor (T006 wires this):
val saga = sagaExecutor(journal = journal, runId = RunId("order-42")) { ... }

Parameters