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Compatible grains

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When an existing grain activation is about to process a request, the runtime will check if the version in the request and the actual version of the grain are compatible. Orleans does not infer at runtime which policy to use. The default behavior to determine if two versions are compatible is determined by Orleans.Versions.Compatibility.CompatibilityStrategy.

Backward compatible (default)

Definition

A grain interface version Vn can be backward compatible with Vm if:

  • The name of the interface didn't change (or the overridden typecode).
  • All public methods present in the Vm version are in the Vn version. It is important that the signatures of the methods inherited from Vm are not modified: since Orleans use an internal built-in serializer, modifying/renaming a field (even private) can make the serialization to break.

Since Vn can have added methods compared to Vm, Vm is not compatible with Vn.

Example

If in the cluster we have two versions of a given interface, V1 and V2 and that V2 is backward compatible with V1:

  • If the current activation is a V2 and the requested version is V1, the current activation will be able to process the request normally
  • If the current activation is a V1 and the requested version is V2, the current activation will be deactivated and a new activation compatible with V2 will be created (see version selector strategy).

Fully compatible

Definition

A grain interface version Vn can be fully compatible with Vm if:

  • Vn is backward compatible with Vm
  • No public methods were added in the Vn version

If Vn is fully compatible with Vm then Vm is also fully compatible with Vn.

Example

If in the cluster we have two versions of a given interface, V1 and V2 and that V2 is fully compatible with V1:

  • If the current activation is a V2 and the requested version is V1, the current activation will be able to process the request normally
  • If the current activation is a V1 and the requested version is V2, the current activation will also be able to process the request normally