NotSerializableException in AsyncCacheAPI#getOrElseUpdate

Are you filing an issue? Please follow these checklists and provide us all the possible information to speed up the process.

Reporting a bug?

1. Version of play-redis: 2.0.1
2. Version of Scala: 2.12.4
3. Version of Play: 2.6.6
4. Describe the environment if applies (usually in cloud etc.) Local

So I was working on play-redis 1.6.1 but as soon as I migrated to 2.0.1 I faced two different problems using the method getOrElseUpdate.

When I use this method for the first time, they key is not found on redis, so the method does the update and store in redis before returning the value. The second time I ask for this key, I am getting the following error:

java.io.NotSerializableException: No configured serialization-bindings for class [java.lang.Object]
        at akka.serialization.Serialization.serializerFor(Serialization.scala:238)
        at akka.serialization.Serialization.$anonfun$deserialize$3(Serialization.scala:204)
        at scala.util.Try$.apply(Try.scala:209)
        at akka.serialization.Serialization.deserialize(Serialization.scala:204)
        at play.api.cache.redis.connector.AkkaDecoder.binaryToAnyRef(AkkaSerializer.scala:122)
        at play.api.cache.redis.connector.AkkaDecoder.$anonfun$stringToAnyRef$2(AkkaSerializer.scala:126)
        at scala.Function1.$anonfun$andThen$1(Function1.scala:52)
        at play.api.cache.redis.connector.AkkaDecoder.stringToAnyRef(AkkaSerializer.scala:126)
        at play.api.cache.redis.connector.AkkaDecoder.untypedDecode(AkkaSerializer.scala:113)
        at play.api.cache.redis.connector.AkkaDecoder.decode(AkkaSerializer.scala:97)

The second issue that I have is a problem that was solved on 1.6.1. Again, the java context is lost in getOrElseUpdate with the last version.

[KarelCemus]

It takes usually several hours to sync

[KarelCemus]

Great example, I reproduced the serialization issue. Unfortunately, I don’t know how to fix it right now. The issue lies in the Java erasure of runtime types and occurs only with Java version of AsyncCacheApi. More specifically, the issue is directly in Play, see the code. Here, Scala.classTag returns Object and I believe that’s due to runtime type erasure.

Explanation

When you miss on cache, you compute the actual value and then serialize it, which works as it asks the value itself for its type.

However, when you hit, it considers the ClassTag given by Scala.classTag, which is wrong.

In the previous version of Play, i.e., Play 2.5 and earlier, Play’s API didn’t support type parameter T and I used a workaround of caching besides the value also its type to be able to deserialize it later. However, since Play 2.6, I use this given type T, which works pretty well with the synchronous API, as the main type is not erased. But oviously, it doesn’t work with async API as CompletedStage<T> gets erased to CompletedStage<Object>.

So, it seems the issue is not in play-redis but I have to investigate it more to see how to deal with it.