DSF ID Loader

To be Reviewed By: October 8, 2021

Authors: Jens Deppe

Status: Draft | Discussion | Active | Dropped | Superseded

Superseded by: N/A

Related: N/A

Problem

To facilitate backwards compatibility, Geode has a concept known as Data Serializable Fixed ID (DSFID) which allows serializable objects to evolve over time using an API that allows newer versions of the classes to still be deserialized by older versions of Geode. This is a core capability of Geode that is primarily intended for internal classes but is also utilized by various modules, notably WAN, Lucene and Redis.

To use DSFIDs, a class needs to register itself so that it is known by the serialization framework. Many core classes register in DSFIDFactory . The modules, mentioned before, register during their service loader discovery and initialization phase. Under some situations, however, Geode will require knowledge of the DSFID very early on during member startup. If a member receives a message with an unknown DSFID it will throw a DSFIDNotFoundException. Without introducing module circular dependencies, there is no way for a module to register its required DSFIDs early enough to avoid this issue.

Anti-Goals

What is outside the scope of what the proposal is trying to solve?None identified.

Solution

The proposed solution includes introducing a Service Loader interface - DSFIDLoader - which will allow DSFIDs to be automatically discovered and will be initialized as part of the static class initialization already existing in InternalDataSerializer .has 2 parts:

Currently, the DSFIDSerializer  interface exposes a registerDSFID(int dsfid, Class<?> dsfidClass) method. This method will be moved into a new interface ( DataSerializerFixedIdRegistrant ) and DSFIDSerialzer  will extend this interface:

interface DataSerializeableFixedIdRegistry {
  register(int id, Class<? extends DataSerializableFixedId> clazz);
}

This will reduce the API surface area required by the following new service provider interface which would perform the actual Fixed Id registration:

public interface DSFIDLoaderDataSerializeableFixedIdRegistrant {
  void registerDSFIDsregister(DSFIDSerializerDataSerializableFixedIdRegistry serializerregistry);
}

This SPI will be initialized as part of the static class initialization already existing in InternalDataSerializer .

In order to use this, a module will need to:

• Include a provider configuration resource file: resources/META-INF/services/org.apache.geode.internal.serialization.DataSerializabledFixedIdRegistrant
• This file will contain one or more fully qualified class names which implement the above interface

The result will be that DSFIDs will be registered and available when the core serialization framework is instantiated.

Error Conditions

Currently, an IllegalArgumentException  is thrown, during registration, if the given class does not have a zero-argument constructor. This should be expanded to also produce an IllegalArgumentException  if a registration is attempted for a previously registered ID will be added to the geode-serialization module.

Changes and Additions to Public Interfaces

...

No backwards compatibility impact.

Prior Art

N/A

FAQ

Answers to questions you’ve commonly been asked after requesting comments for this proposalNone yet.

Errata

What are minor adjustments that had to be made to the proposal since it was approved?None yet.