Log warning when threadpool for cache maintenance is null

Signed-off-by: owenhalpert <ohalpert@gmail.com>

Author: owenhalpert

src/main/java/org/opensearch/knn/index/memory/NativeMemoryCacheManager.java

@@ -110,8 +110,11 @@ private void initialize(NativeMemoryCacheManagerDto nativeMemoryCacheDTO) {
         cacheCapacityReached = new AtomicBoolean(false);
         accessRecencyQueue = new ConcurrentLinkedDeque<>();
         cache = cacheBuilder.build();
+
         if (threadPool != null) {
             startMaintenance(cache);
+        } else {
+            logger.warn("ThreadPool is null during NativeMemoryCacheManager initialization. Maintenance will not be started.");
         }
     }
 

src/main/java/org/opensearch/knn/quantization/models/quantizationState/QuantizationStateCache.java

@@ -78,8 +78,11 @@ private void buildCache() {
             )
             .removalListener(this::onRemoval)
             .build();
+
         if (threadPool != null) {
             startMaintenance(cache);
+        } else {
+            log.warn("ThreadPool is null during QuantizationStateCache initialization. Maintenance will not be started.");
         }
     }