Ensure ORM's 2LC Caffeine instance runs eviction tasks on the eventlo…

…op by default

extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/service/QuarkusRegionFactoryInitiator.java

@@ -3,6 +3,9 @@
 import static java.lang.Boolean.FALSE;
 
 import java.util.Map;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ForkJoinPool;
+import java.util.function.Supplier;
 
 import org.hibernate.boot.registry.StandardServiceInitiator;
 import org.hibernate.cache.internal.NoCachingRegionFactory;
@@ -12,6 +15,10 @@
 import org.hibernate.service.spi.ServiceRegistryImplementor;
 import org.infinispan.quarkus.hibernate.cache.QuarkusInfinispanRegionFactory;
 
+import io.quarkus.arc.Arc;
+import io.quarkus.arc.InstanceHandle;
+import io.vertx.core.Vertx;
+
 public final class QuarkusRegionFactoryInitiator implements StandardServiceInitiator<RegionFactory> {
 
     public static final QuarkusRegionFactoryInitiator INSTANCE = new QuarkusRegionFactoryInitiator();
@@ -44,7 +51,38 @@ public RegionFactory initiateService(Map configurationValues, ServiceRegistryImp
             }
         }
 
-        return new QuarkusInfinispanRegionFactory();
+        return new QuarkusInfinispanRegionFactory(getCacheExecutor());
+    }
+
+    private Supplier<Executor> getCacheExecutor() {
+        String propertyName = "io.quarkus.hibernate-orm.2lc.caffeineexecutor";
+        //Undocumented property for now: TODO benchmark and decide if it's worth to expose as user facing options?
+        final String executorStrategy = System.getProperty(propertyName, "ON_EVENTLOOP");
+        switch (executorStrategy) {
+            case "ON_EVENTLOOP": //We expect this to perform best, so it's the current default in Quarkus.
+                return () -> getVertxCacheExecutor();
+            case "INLINE":
+                return () -> Runnable::run;
+            case "ON_FORKJOIN":
+                return () -> ForkJoinPool.commonPool(); //default in Caffeine: same as returning null
+            default:
+                throw new IllegalArgumentException(
+                        "Unrecognized property value for '" + propertyName + "'='" + executorStrategy + "'");
+        }
+        //For a full explanation, see https://github.com/quarkusio/quarkus/issues/32317#issuecomment-1492698253
+    }
+
+    private static Executor getVertxCacheExecutor() {
+        final Vertx vertx = retrieveVertxInstance();
+        return vertx.nettyEventLoopGroup();
+    }
+
+    private static Vertx retrieveVertxInstance() {
+        InstanceHandle<Vertx> vertxHandle = Arc.container().instance(Vertx.class);
+        if (!vertxHandle.isAvailable()) {
+            throw new IllegalStateException("No Vert.x instance has been registered in ArC ?");
+        }
+        return vertxHandle.get();
     }
 
 }