[GitHub] markusthoemmes commented on a change in pull request #2414: SPI approach for pluggable implementations

[gi...@git.apache.org]

markusthoemmes commented on a change in pull request #2414: SPI approach for pluggable implementations
URL: https://github.com/apache/incubator-openwhisk/pull/2414#discussion_r124871176
 
 

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 File path: common/scala/src/main/scala/whisk/spi/SpiProvider.scala
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 @@ -0,0 +1,195 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package whisk.spi
+
+import java.util.ServiceLoader
+
+import akka.actor.ActorSystem
+import akka.actor.ExtendedActorSystem
+import akka.actor.Extension
+import akka.actor.ExtensionId
+import akka.actor.ExtensionIdProvider
+import scaldi.Binding
+import scaldi.DynamicModule
+import scaldi.Identifier
+import scaldi.ImmutableWrapper
+import scaldi.Injectable
+import scaldi.Injector
+import scaldi.MutableInjector
+
+import scala.collection.JavaConverters._
+import scala.collection.mutable.ListBuffer
+import scala.reflect.ClassTag
+import scala.reflect.runtime.universe._
+
+/**
+  * An Spi (Service Provider Interface) is an extension point.
+  * At runtime, multiple Spi implementations may exist in the classpath, but only a single implementation
+  * will be available for consumers to use. The specific implementation available at runtime is governed by the
+  * configKey specified in the SpiProvider
+  */
+trait Spi  extends Extension {
+
+}
+
+/**
+  * Spi implementations must extend SpiModule to register a factory for their implementation.
+  * The SpiModule implementations will be loaded at runtime via ServiceLoader
+  * @param tag
+  * @param classTag
+  * @tparam SpiImpl
+  */
+abstract class SpiModule[SpiImpl <: Spi ](implicit tag:TypeTag[SpiImpl], classTag:ClassTag[SpiImpl])  {
+  //lazy so that we can FIRST load the module, but THEN setup injectables and finally THEN initialize the instance
+  // (we call getInstance exactly once per module!)
+  lazy val spiImplInstance:SpiImpl = getInstance
+  val spiTypeName:String = classTag.runtimeClass.getName
+  protected [spi] def getInstance:SpiImpl
+}
+
+/**
+  * An extended SpiModule that will register a factory that uses an Injector for binding additional dependencies
+  * during instantiation of the Spi implementation
+  * @param ev$1
+  * @param tag
+  * @tparam SpiImpl
+  */
+abstract class SpiFactoryModule[SpiImpl <: Spi : TypeTag](implicit tag:ClassTag[SpiImpl])
+  extends SpiModule[SpiImpl] with Injectable{
+  protected [spi] final def getInstance:SpiImpl = getInstance(SharedModules.sharedModulesInjector)
+  protected [spi] def getInstance(implicit injector:Injector): SpiImpl
+}
+
+/**
+  * Spi providers must extend SpiProvider to expose an Extension for accessing the Spi impl
+  *
+  * @param configKey an key in application.conf which indicates which impl will be used at runtime
+  * @param tag
+  * @param classTag
+  * @tparam T
+  */
+abstract class SpiProvider[T <: Spi](configKey: String)(implicit tag: TypeTag[T], classTag:ClassTag[T])extends ExtensionId[T] with ExtensionIdProvider {
+
+  override def apply(system: ActorSystem): T = {
 
 Review comment:
   Why is this dependent on the `ActorSystem`?
 
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