Broadway v0.6.2 Broadway.Producer behaviour View Source

A Broadway.Producer is a GenStage producer that emits Broadway.Message as events.

Optionally, a Broadway.Producer can implement two optional Broadway callbacks: prepare_for_start/2 and c:prepare_for_draining/2, which are useful for booting up and shutting down Broadway topologies respectively.

Link to this section Summary

Callbacks

prepare_for_draining(state)

Invoked by the terminator right before Broadway starts draining in-flight messages during shutdown.

prepare_for_start(module, options)

Invoked once by Broadway during Broadway.start_link/2.

Link to this section Callbacks

prepare_for_draining(state)

(optional)

Specs

prepare_for_draining(state :: any()) ::
  {:noreply, [event], new_state}
  | {:noreply, [event], new_state, :hibernate}
  | {:stop, reason :: term(), new_state}
when new_state: term(), event: term()

Invoked by the terminator right before Broadway starts draining in-flight messages during shutdown.

This callback should be implemented by producers that need to do additional work before shutting down. That includes active producers like RabbitMQ that must ask the data provider to stop sending messages. It will be invoked for each producer stage.

prepare_for_start(module, options)

(optional)

Specs

prepare_for_start(module :: atom(), options :: keyword()) ::
  {[:supervisor.child_spec() | {module(), any()} | module()],
   options :: keyword()}

Invoked once by Broadway during Broadway.start_link/2.

The goal of this task is to manipulate the general topology options, if necessary at all, and introduce any new child specs that will be started before the ProducerSupervisor in Broadwday's supervision tree.

It is guaranteed to be invoked inside the Broadway main process.

The options include all of Broadway topology options.