Timout await extension initialization, #28301 (#28340)

* use the existing creation-timeout config
* and error message about the typical mistake of accessing
  SerializationExtension from constructor of serializer
* mention in docs

akka-actor-tests/src/test/scala/akka/serialization/SerializeSpec.scala

@@ -532,6 +532,30 @@ class NoVerificationWarningOffSpec
   }
 }
 
+class SerializerDeadlockSpec extends AkkaSpec {
+
+  "SerializationExtension" must {
+
+    "not be accessed from constructor of serializer" in {
+      intercept[IllegalStateException] {
+        val sys = ActorSystem(
+          "SerializerDeadlockSpec",
+          ConfigFactory.parseString("""
+          akka {
+            actor {
+              creation-timeout = 1s
+              serializers {
+                test = "akka.serialization.DeadlockSerializer"
+              }
+            }
+          }
+          """))
+        shutdown(sys)
+      }.getMessage should include("SerializationExtension from its constructor")
+    }
+  }
+}
+
 protected[akka] class NoopSerializer extends Serializer {
   def includeManifest: Boolean = false
 
@@ -560,3 +584,17 @@ protected[akka] class NoopSerializer2 extends Serializer {
 protected[akka] final case class FakeThrowable(msg: String) extends Throwable(msg) with Serializable {
   override def fillInStackTrace = null
 }
+
+class DeadlockSerializer(system: ExtendedActorSystem) extends Serializer {
+
+  // not allowed
+  SerializationExtension(system)
+
+  def includeManifest: Boolean = false
+
+  def identifier = 9999
+
+  def toBinary(o: AnyRef): Array[Byte] = Array.empty[Byte]
+
+  def fromBinary(bytes: Array[Byte], clazz: Option[Class[_]]): AnyRef = null
+}

akka-actor/src/main/resources/reference.conf

@@ -119,7 +119,8 @@ akka {
     # In addition to the default there is akka.actor.StoppingSupervisorStrategy.
     guardian-supervisor-strategy = "akka.actor.DefaultSupervisorStrategy"
 
-    # Timeout for ActorSystem.actorOf
+    # Timeout for Extension creation and a few other potentially blocking
+    # initialization tasks.
     creation-timeout = 20s
 
     # Serializes and deserializes (non-primitive) messages to ensure immutability,
@@ -140,6 +141,7 @@ akka {
     # CallingThreadDispatcher for a top-level actor.
     unstarted-push-timeout = 10s
 
+    # TypedActor deprecated since 2.6.0.
     typed {
       # Default timeout for the depredated TypedActor (not the new actor APIs in 2.6) methods with non-void return type
       timeout = 5s

akka-actor/src/main/scala/akka/actor/ActorSystem.scala

@@ -31,6 +31,7 @@ import scala.util.control.{ ControlThrowable, NonFatal }
 import scala.util.{ Failure, Success, Try }
 
 import akka.event.Logging.DefaultLogger
+import akka.serialization.SerializationExtension
 
 object BootstrapSetup {
 
@@ -1133,7 +1134,13 @@ private[akka] class ActorSystemImpl(
   private def findExtension[T <: Extension](ext: ExtensionId[T]): T = extensions.get(ext) match {
     case c: CountDownLatch =>
       blocking {
-        c.await()
+        val awaitMillis = settings.CreationTimeout.duration.toMillis
+        if (!c.await(awaitMillis, TimeUnit.MILLISECONDS))
+          throw new IllegalStateException(
+            s"Initialization of [$ext] took more than [$awaitMillis ms]. " +
+            (if (ext == SerializationExtension)
+               "A serializer must not access the SerializationExtension from its constructor. Use lazy init."
+             else "Could be deadlock due to cyclic initialization of extensions."))
       }
       findExtension(ext) //Registration in process, await completion and retry
     case t: Throwable => throw t //Initialization failed, throw same again

akka-docs/src/main/paradox/serialization.md

@@ -127,6 +127,10 @@ bytes to different objects.
 Then you only need to fill in the blanks, bind it to a name in your configuration and then
 list which classes that should be serialized using it.
 
+The serializers are initialized eagerly by the `SerializationExtension` when the `ActorSystem` is started and
+therefore a serializer itself must not access the `SerializationExtension` from its constructor. Instead, it
+should access the `SerializationExtension` lazily.
+
 <a id="string-manifest-serializer"></a>
 ### Serializer with String Manifest
 

akka-docs/src/test/java/jdocs/serialization/SerializationDocTest.java

@@ -196,8 +196,7 @@ public class SerializationDocTest {
         akka.actor.typed.ActorSystem.create(Behaviors.empty(), "example");
 
     // Get the Serialization Extension
-    Serialization serialization =
+    Serialization serialization = SerializationExtension.get(system);
-        SerializationExtension.get(akka.actor.typed.javadsl.Adapter.toClassic(system));
     // #programmatic-typed
   }
 }

akka-docs/src/test/scala/docs/serialization/SerializationDocSpec.scala

@@ -214,12 +214,11 @@ package docs.serialization {
     def demonstrateTypedActorSystem(): Unit = {
       //#programmatic-typed
       import akka.actor.typed.ActorSystem
-      import akka.actor.typed.scaladsl.adapter._
 
       val system = ActorSystem(Behaviors.empty, "example")
 
       // Get the Serialization Extension
-      val serialization = SerializationExtension(system.toClassic)
+      val serialization = SerializationExtension(system)
       //#programmatic-typed
     }