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Message Bus

The TMessageBus class provides in-process, generic publish/subscribe messaging with wildcard topic matching.

Overview​

TMessageBus lives in Nidus.Message.Bus. It holds a TDictionary<String, TValue> of named callbacks, where TValue wraps a TCallback<T> anonymous method. Events are dispatched synchronously on the calling thread.

Registering a listener​

var LBus := TMessageBus.Create;

// Exact topic
LBus.RegisterEvent<TOrderCreated>('order.created',
  procedure(const E: TOrderCreated)
  begin
    WriteLn('Order created: ', E.Id);
  end);

// Wildcard prefix — matches 'order.created', 'order.cancelled', etc.
LBus.RegisterEvent<TOrderEvent>('order.*',
  procedure(const E: TOrderEvent)
  begin
    WriteLn('Any order event');
  end);

TCallback<T> = reference to procedure(const Value: T) — defined in Nidus.Message.Bus.

Publishing an event​

var LEvent := TOrderCreated.Create(42);
LBus.Notify<TOrderCreated>('order.created', LEvent);

Wildcard dispatch rules​

Notify<T>(AName, AValue):

  1. If AName exists verbatim in the registry → invoke that callback and exit.
  2. If AName ends with * → strip the * to form LPattern; invoke all keys that start with LPattern.
  3. Otherwise use AName as LPattern and match all keys that start with it.

Example: Notify<TOrderEvent>('order.*', E) invokes all callbacks whose key starts with 'order.'.

Unregistering a listener​

LBus.UnregisterEvent('order.created');

Integration with Nidus modules​

TMessageBus is a standalone class — it is not automatically wired into the DI container. Register it as a singleton in your module if you want DI resolution:

procedure TEventModule.Configure(const ABuilder: IModuleBuilder);
begin
  ABuilder
    .AddProvider(TBind<TMessageBus>.Singleton)
    .Export(TMessageBus);
end;

Then resolve normally:

var LBus := GetNidus.Get<TMessageBus>;
note

The Nidus.Message.Bus.Module unit (Nidus.Message.Bus.Module.pas) provides a pre-built module definition for the message bus. The class is TMessageBusModule (extends TModule) and exports TMessageBus as a singleton bind.

Lifecycle​

TMessageBus owns no external resources. Destroy clears and frees the internal dictionary. No thread-safety is provided — if you publish from multiple threads, wrap calls in a TCriticalSection.