MemBus extension points

20 Sep 2010 in software-development | patterns | csharp | membus |

ISubscription

public interface ISubscription
{
    void Push(object message);
    Type Handles { get; }
}

This is the basic structure of a subscription. There is also a typed version:

    public interface IHandles<T> : ISubscription
    {
        void Push(T message);
    }

If you want to write a handler, you can inherit from the Handles class:

class MsgAHandler : Handles<MessageA> {
  protected override void push(MessageA msg) {
    // Do stuff.
  }
}

How can you introduce subscriptions into MemBus apart from method-based subscriptions? In the setup, either directly through _IConfigurableBus.AddSubscription(ISubscription subscription) _or more universal by adding an implementation of

ISubscriptionResolver

    public interface ISubscriptionResolver
    {
        IEnumerable<ISubscription> GetSubscriptionsFor(object message);
        bool Add(ISubscription subscription);
    }

A resolver must provide subscriptions for a given message and it may accept subscriptions. The boolean return value states whether the subscription was accepted or not.

IPublishPipelineMember

public class PublishToken
{
    public object Message { get; private set; }
    public IEnumerable<ISubscription> Subscriptions { get; private set; }
    ...
}

public interface IPublishPipelineMember
{
    void LookAt(PublishToken token);
}

The “act” of publishing is the execution of the publish pipeline, which may consist of many pipeline members. You can participate in the publishing pipeline by implementing the above interface.

ISubscriptionShaper

public interface ISubscriptionShaper
{
    ISubscription EnhanceSubscription(ISubscription subscription);
}

This allows you to provide instances that “shape” subscriptions. This interface is best explained by an example:

public class ShapeToFilter<M> : ISubscriptionShaper
{
    private readonly Func<M, bool> filter;

    public ShapeToFilter(Func<M,bool> filter)
    {
        this.filter = filter;
    }

    public ISubscription EnhanceSubscription(ISubscription subscription)
    {
        return new FilteredSubscription<M>(filter, subscription);
    }
}

Consider that a subscription can interact with another instance implementing ISubscription in the “Push” method. A shaper is the abstraction of enhacing an existing subscription. It is used internally for making a subscription disposable, making it filtered, making it dispatch on the UI, etc.

Chronology

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