Serialization issues

[vyazelenko]

I've found several issues with how Serializable is used in the project:

• No classes that are Serializable declare serialVersionUID fields (e.g. AsciiNumberFormatException, Int2ObjectHashMap etc.).

  The classes should declare serialVersionUID field but it must be compatible with the old code, i.e. the value of the serialVersionUID field must match values at least from the latest released versions of Agrona on JDK 8 to avoid breaking existing code. This needs to also work for generated classes.

• Some serializable classes contain non-serializable fields:

  • Externally assigned fields - for example IntLruCache takes two parameters one java.util.function.IntFunction and another java.util.function.Consumer neither of which are serializable by default and assigns them to the non-transient fields.

    The easiest solution would be to mark the corresponding fields transient if it would not break the internal logic of the class. Otherwise the solution is require provided functions to be serializable. For example in case of IntLruCache the constructor signature will change to this:

         public <FACTORY extends IntFunction<E> & Serializable, CONSUMER extends Consumer<E> & Serializable> IntLruCache(
            @DoNotSub final int capacity,
            final FACTORY factory,
            final CONSUMER closer)
         {
            ...
         }

    Or maybe simple instanceof Serializable check when creating object would suffice.

  • Internal fields - for example Int2ObjectCache caches KeySet, ValueCollection and EntrySet none of which are serializable. In this case we can either mark fields as transient or make the corresponding classes serializable.

[mjpt777]

I was against added Serializable but some people convince me it was just for testing. We should not need to be backwards compatible between versions with a serialVersionUID change.

[vyazelenko]

@mjpt777 I guess we keep non-serializable lambdas as is, i.e. they render the corresponding collections non-serializable despite those implementing Serializable interface.

Possible solutions:

• Drop Serializable from the collections that accept lambda as the constructor argument.
• Add run-time check to ensure that provided lambda is serializable. Will break all existing code!
• Add compile-time check check to ensure that provided lambda is serializable. Will break all existing code!
• Add run-time check when serializing to ensure that use gets a nicer exception.
• Do nothing - let it burn when someone tries to serialize.

[mjpt777]

If things cannot be seralized then we should remove it. Which classes are impacted?

[vyazelenko]

@mjpt777 Updated #224 to use serialVersionUID instead of @SuppressWarnings("serial").

[vyazelenko]

Impacted classes:

• org.agrona.collections.Int2ObjectCache
• org.agrona.collections.IntLruCache
• org.agrona.collections.UnmodifiableCollectionView

And the generated classes from them.

[mjpt777]

We can remove Serializable from them.

[vyazelenko]

Ok, will do in my PR/

[vyazelenko]

The rest of this issues should be fixed with #224.

[guidomedina]

I'm too late to this discussion but the reason there were Serializable was because of this issue #110