This is the first step towards more type-safety in Actor interactions,
comprising:
* generic ActorRef[T] that only accepts T messages
* generic ActorSystem[T] extends ActorRef[T] (sending to the guardian,
whose Props[T] are provided for ActorSystem construction)
* removed the Actor trait: everything in there has been made into
messages and signals
* new Behavior[T] abstraction that consumes messages (of type T) or
Signals (lifecycle hooks, Terminated, ReceiveTimeout, Failed),
producing the next Behavior[T] as the result each time
* the ask pattern is provided and yields properly typed Futures
* variants of ActorContext are provided for synchronous testing of
Behaviors
All of this is implemented without touching code outside akka-typed
(apart from making guardianProps configurable), creating wrapper objects
around ActorRef, ActorContext, ActorSystem, Props and providing an Actor
implementation that just runs a Behavior.
The most prominent changes compared to eventsourced are:
- No central processor and channel registry any more
- Auto-recovery of processors on start and restart (can be disabled)
- Recovery of processor networks doesn't require coordination
- Explicit channel activation not needed any more
- Message sequence numbers generated per processor (no gaps)
- Sender references are journaled along with messages
- Processors can determine their recovery status
- No custom API on extension object, only messages
- Journal created by extension from config, not by application
- Applications only interact with processors and channels via messages
- Internal design prepared for having processor-specific journal actors (for later optimization possibilities)
Further additions and changes during review:
- Allow processor implementation classes to use inherited stash
- Channel support to resolve (potentially invalid) sender references
- Logical intead of physical deletion of messages
- Pinned dispatcher for LevelDB journal
- Processor can handle failures during recovery
- Message renamed to Persistent
This prototype has the following limitations:
- Serialization of persistent messages and their payload via JavaSerializer only (will be configurable later)
- The LevelDB journal implementation based on a LevelDB Java port, not the native LevelDB (will be configurable later)
The following features will be added later using separate tickets:
- Snapshot-based recovery
- Reliable channels
- Journal plugin API
- Optimizations
- ...
