Registry.dispatch

You're seeing just the function dispatch, go back to Registry module for more information.
Link to this function

dispatch(registry, key, mfa_or_fun, opts \\ [])

View Source (since 1.4.0)

Specs

dispatch(registry(), key(), dispatcher, keyword()) :: :ok
when dispatcher:
       (entries :: [{pid(), value()}] -> term()) | {module(), atom(), [any()]}

Invokes the callback with all entries under key in each partition for the given registry.

The list of entries is a non-empty list of two-element tuples where the first element is the PID and the second element is the value associated to the PID. If there are no entries for the given key, the callback is never invoked.

If the registry is partitioned, the callback is invoked multiple times per partition. If the registry is partitioned and parallel: true is given as an option, the dispatching happens in parallel. In both cases, the callback is only invoked if there are entries for that partition.

See the module documentation for examples of using the dispatch/3 function for building custom dispatching or a pubsub system.