9.72 Startable Facility

Startable facility allows objects to be "Started" after they are created, and/or to be "Stopped" once they are released. The objects are instantiated eagerly, that means container will create the first instance without you having to explicitly call container.Resolve. This is mostly useful for singleton background services that you want to have running for the entire lifespan of your application.

Starting with version 2.5 of Windsor, the facility offers two modes of working - aggressive (default, same as in previous versions) and new - optimized for usage of single install call.

Following code samples assume that the kernel with registered facility is in scope

using Castle.Facilities.Startable;
IKernel container = new DefaultKernel();

Making components startable

Component need not to be changed at all to become a startable. The only thing required is to call Start extention method during component's registration

container.Register(
   Component.For<PocoComponent>()
      .Start()
);

After such a registration component will be resolved by Windsor and will not be destroyed by Garbage Collector until the end of it's container lifecycle (if the component implements IDisposable it's Dispose method will then be invoked automatically during container's deinitialization).

Dedicated start/stop methods

Sometimes component have complex initialization and constructor is not enough for the job (e.g. configuring through IConfiguration object or properties setters. In such a case component may introduce special method(s).

container.Register(
    Component.For<PocoComponent>().DependsOn(Property.ForKey("Name").Eq("John"))
        .StartUsingMethod("Begin")
        .StopUsingMethod("End")
);

In this example PocoComponent's Begin method will be called at the end of initialization (i.e. than the Name property is set to "John") whereas End method will be called during container's utilization phase.

Both StartUsingMethod and StopUsingMethod are extension methods living in facility's namespace.

You can skip either Start or Stop method if you don't need it.

:information_source: Requirements: Stop and Start methods have to be public, have return type of 'void' and zero parameters.

Strongly typed POCO

You can also use strongly typed version of the above code:

container.Register(
   Component.For<PocoComponent>().DependsOn(Property.ForKey<string>().Eq("init value"))
      .StartUsingMethod(c => c.Begin)
      .StopUsingMethod(c => c.End)
);

IStartable interface

Another option to make component startable is to implement the Castle.Core.IStartable interface

public interface IStartable
{
    void Start();
    void Stop();
}

When component implements it you can register the component just like any other usual component. Facility will automatically register it's Start() and Stop() methods.

XML configuration

As most facilities, you can also configure Startable Facility via XML config file

If you don't register the facility in code, you can register it in config file:

<facility id="startable"
    type="Castle.Facilities.Startable.StartableFacility, Castle.Windsor" / >

And register your startable components using additional startable attributes:

<component id="mycomponent"
    type="Namespace.MyComponent, Assembly"
    startable="true" startMethod="StartListener" stopMethod="StopListener" / >

You need to specify startable="true" (which is equivalent to Start extension method discussed above) and optionally either startMethod, stopMethod or both.

Aggressive (old) mode

For backward compatibility this mode is the default, so you just need to add the facility to the container.

container.AddFacility<StartableFacility>();

Assuming we have a startable component, that prints out every step of its lifetime to the console like this...

public class Startable : IStartable
{
   public Startable()
   {
      Console.WriteLine("Created!");
   }

   public void Start()
   {
      Console.WriteLine("Started!");
   }

   public void Stop()
   {
      Console.WriteLine("Stopped!");
   }
}

// later in code
container.Register(Component.For<Startable>());
Console.WriteLine("Registered!");

container.Dispose();
Console.WriteLine("Released!");

If we execute this code, the following will be printed out:

Created!
Started!
Registered!
Stopped!
Released!

:information_source: Notice: Notice that component was instantiated and started during its registration and that we didn't resolve the component explicitly.

Deferred mode - Optimized for single call to Install

If you're using three step approach to interacting with Windsor and registering all your components during a single call to container.Install you can take another route with the facility, which offers better performance and behaves differently.

:information_source: Prefer deferred mode: Due to backward compatibility the deferred mode is off by default. However when possible you should prefer this mode over the old one.

When using this approach the facility is not trying aggressively to instantiate your components right on the spot, but instead waits for the end of the call to Install. Only at this point it will resolve and start all the startable components.

:information_source: Deferred mode will thrown when component can't be resolved: Using optimized mode, it is assumed that when the call to Install ends all components should be correctly configured and resolvable so that if Windsor can't resolve a component it will consider this an error and throw an exception, and not silently wait for the missing dependency to appear, like the old mode. When for some reasons you want to disable the exception and let the component just silently not start you can use DeferredTryStart method.

How to activate it

The optimized mode is not the default so you need to enable it explicitly when registering the facility:

container.AddFacility<StartableFacility>(f => f.DeferredStart());

If you want to disable the fail fast behavior, which throws exception when the component can not be started, you can do it by calling DeferredTryStart method.

container.AddFacility<StartableFacility>(f => f.DeferredTryStart());

External resources

• Blog post by Mike Hadlow about the facility (Jan 16, 2010)
• Blog post by Alex Henderson about the facility (Apr 29, 2007) - written long ago but still accurate