IMap memoizers and concurrency

Three APIs share the same storage pattern

Each memoizer reads an IMap, evaluates on a miss, and stores with putIfAbsent. If another JVM has already stored a value, that value wins.

val scores: IMap<String, Score> = hazelcast.getMap("scores-v1")

val sync = scores.memoizer { key -> calculateScore(key) }
val future = scores.asyncMemoizer { key -> calculateScore(key) }
val suspend = scores.suspendMemoizer { key -> calculateScoreSuspend(key) }

The synchronous evaluator runs on the calling thread. The async evaluator runs in CompletableFuture.supplyAsync’s default executor. The suspend evaluator runs in the calling coroutine. Make CPU and blocking expectations explicit inside the evaluator.

Single-flight is local to one JVM

Each memoizer instance keeps a ConcurrentHashMap<K, ...> named inFlight. Release tests verify one evaluator call for concurrent requests to the same key in one JVM.

Another JVM has another map, so this is not cluster-wide single-flight. Two members can evaluate the same miss, after which IMap.putIfAbsent selects one result. Evaluators with side effects must tolerate duplicate execution or use a stronger cluster coordination boundary.

Failures allow the next call to retry

Sync, async, and suspend implementations remove failed in-flight entries. Async and suspend tests verify that the first failed evaluation is followed by a successful re-evaluation.

Failures are not cached. A hot key that keeps failing can repeatedly hit the source, so apply retry and concurrency limits outside the memoizer.

Clear does not cancel active evaluation

clear calls IMap.clear(). The async implementation also clears its local in-flight map but does not cancel futures already running. Sync and suspend implementations do not explicitly clear their in-flight maps. An evaluator completing after clear can store a value again.

For a live schema migration or force purge, switching to a new map name avoids this race more reliably.

Sources and tests

• HazelcastMemoizer.kt
• HazelcastAsyncMemoizer.kt
• HazelcastSuspendMemoizer.kt
• HazelcastAsyncMemoizerTest.kt
• HazelcastSuspendMemoizerTest.kt