Versioned context for layered entities questions

[hrstoyanov]

I am trying to make use of versioned layered entities, but have a few questions/concerns:

1. Using auto-incrementing (EntityVersionContext.AutoIncrementingLong()), which cannot be shared means that there is an overhead of one "hash-table-like" structure per every layered entity - is this correct?
2. Using mutable version context (EntityVersionContext.Mutable), which can be shared, does not add as much overhead as there is only one such structure for all layered entities?
3. How scalable is the approach of using one shared mutating context for the entire store graph - the documentation states this is possible?
4. Can the global mutable versioned context be stored and accessed in the store data root just like any other entity (I assume it can) rather than having to obtain it each time from an existing entities like this: EntityVersionContext.lookup(entity)?
5. While layer entities design implies thread safety (as it deals with immutable data objects), adding versioned context breaks this promise (both auto-incrementing or mutable)? For example, in this code from the docs:

EntityVersionContext.Mutable<String> versionContext = EntityVersionContext.Mutable();

versionContext.currentVersion("rev-1");

// Other thread can -re-set to a different current version, before john is created ?!

Person john = PersonCreator.New()
	.addLayer(versionContext)
	.firstName("John")
	.lastName("Doe")
	.create();

another thread can increment the versionContext concurrently, so by the time john is created the version is no longer "rev-1"?

[hrstoyanov]

Ok, I reviewed the source code and there is no guarantee for thread safety on the layered entities API at all.

[hrstoyanov]

@fh-ms the documentation states that layered entities can be used for logging, versioning and locking. Can you please provide examples of locking layer?

[hrstoyanov]

Thanks @fh-ms . Looking at the code of , adding a EntityVersionContext layer:

static ZGroupCreator creator() {
        return ZGroupCreator.New()
                .addLayer(ENTITY_LOGGER)
                .addLayer(EntityVersionContext.AutoIncrementingInstant());
    }

will make the entity thread-safe for later updates via :

var g = ZGroupUpdater.New(group);
g..name("whatever");
g.update();

because EntityLayerVersioning.updateEntityData(final Entity data ) is fully synchronized?

[fh-ms]

These are examples of what could be done in the logic layer.
We provide implementations for Logging and Versioning.