Core Async Helpers

This crate contains helpers related to common asynchronous programming patterns used in nearcore:

• messaging: common interfaces for sending messages between components.
• test_loop: a event-loop-based test framework that can test multiple components together in a synchronous way.

Messaging

Sender<T> and AsyncSender<T> are abstractions of our Actix interfaces. When a component needs to send a message to another component, the component should keep a Sender<T> as a field and require it during construction, like:

struct MyComponent {
  downstream_component: Sender<DownstreamMessage>,
}

impl MyComponent {
  pub fn new(downstream_component: Sender<DownstreamMessage>) -> Self { ... }
}

The sender can then be used to send messages:

impl MyComponent {
  fn do_something(&mut self, args: ...) {
    self.downstream_component.send(DownstreamMessage::DataReady(...));
  }
}

To create a Sender<T>, we need any implementation of CanSend<T>. One way is to use an Actix address:

impl Handler<DownstreamMessage> for DownstreamActor {...}

impl DownstreamActor {
  pub fn spawn(...) -> Addr<DownstreamActor> {...}
}

fn setup_system() {
  let addr = DownstreamActor::spawn(...);
  let my_component = MyComponent::new(addr.into_sender());
}

In tests, the TestLoopBuilder provides the sender() function which also implements CanSend, see the examples directory under this crate.

AsyncSender<T> is similar, except that calling send_async returns a future that carries the response to the message.