# `Ash.Signals.Delivery`
[🔗](https://github.com/ash-project/ash/blob/v3.36.1/lib/ash/signals/delivery.ex#L5)

A behaviour for delivering signals to their listeners.

Each listener declares how signals reach it, with its `delivery` option. The default,
`Ash.Signals.Delivery.Inline`, runs the listener immediately, during the phase in which the
signal is emitted. Other deliveries can, for example, enqueue a job, so that the listener runs
after the emitting action's transaction commits.

```elixir
signals_in do
  from MyApp.Shop.Signals do
    on :order_placed, :send_receipt, delivery: {MyApp.JobDelivery, queue: :mailers}
  end
end
```

When a signal is emitted, during the signal's phase and after every payload has been cast,
`c:deliver/4` is called once for each delivery and options its listeners use, with those
listeners. To run a listener, immediately or later, use `Ash.Signals.run_listener/3`, which does
exactly what the inline delivery does. A delivery that runs listeners later can store signals
with `Ash.Signals.dump/3`, load them with `Ash.Signals.load/3`, and find the listener again
with `Ash.Resource.Info.signal_listener/2`.

# `deliver`

```elixir
@callback deliver(
  signals :: [struct()],
  listeners :: [Ash.Resource.SignalListener.t()],
  opts :: Keyword.t(),
  context :: Ash.Signals.Delivery.Context.t()
) :: :ok | {:error, term()}
```

Delivers signals to the given listeners.

`signals` are the signal structs emitted together, `listeners` are the listeners of the signal
that use this delivery with these options, and `opts` are the options given to the delivery in
their `delivery` option. Returning an error fails the emit.

# `verify_listener`
*optional* 

```elixir
@callback verify_listener(
  listener :: Ash.Resource.SignalListener.t(),
  signal :: Ash.Signals.Signal.t(),
  opts :: Keyword.t(),
  dsl_state :: Spark.Dsl.t()
) :: :ok | {:error, String.t()}
```

Verifies a listener that uses this delivery, when the listening resource is compiled. Receives
the signal it listens to, and the options given to the delivery.

---

*Consult [api-reference.md](api-reference.md) for complete listing*