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The Cell View

The Cell view answers:

What happens when my Cell receives a Message?

A step-by-step view of message processing inside one Myrmic Cell

1. A Message waits in the Mailbox​

Commands, Events, callbacks, and timer wake-ups enter the Cell through its Mailbox.

The Mailbox separates Message arrival from the moment the Cell is ready to process it.

2. One Handler runs​

The Cell processes one Message at a time.

The Handler reads the Cell's State, applies Application logic, and stages any Messages it wants to send. A slow Handler delays the work behind it, so Handlers should remain short.

3. The Handler stages one unit of work​

For a Command Handler, that unit groups:

  • consuming the inbound Message,
  • updating the Cell's State,
  • writing outbound Messages.

The current transaction boundary, including what happens if the Handler fails or the destination lives on another Node, is stated on the Guarantees page.

Messages continue the workflow​

An outbound Message enters another Cell's Mailbox. A result returns as a callback Message to the caller's Mailbox rather than as a blocking Cell-to-Cell call.

External effects sit outside​

HTTP calls, MQTT publishes, and actuator writes sit outside the Cell transaction. Applications must make these effects idempotent, use a sink that supports deduplication or fencing, or accept at-least-once behaviour.

Two design rules​

  • Make every Handler safe to run twice.
  • Rely on order inside one Cell, never on a global order across Cells.

See also​

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