WCF and Hosting - Advanced hosting features
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The ICommunicationObject interface supported by ServiceHostoffers some advanced features, listed in Example 1-4.
Example 1-4. The ICommunicationObject interface
public interface ICommunicationObject
{
void Open();
void Close();
void Abort();
event EventHandler Closed;
event EventHandler Closing;
event EventHandler Faulted;
event EventHandler Opened;
event EventHandler Opening;
IAsyncResult BeginClose(AsyncCallback callback,object state);
IAsyncResult BeginOpen(AsyncCallback callback,object state);
void EndClose(IAsyncResult result);
void EndOpen(IAsyncResult result);
CommunicationState State
{get;}
//More members
}
public enum CommunicationState
{
Created,
Opening,
Opened,
Closing,
Closed,
Faulted
}
If opening or closing the host is a lengthy operation, you can do so asynchronously with theBeginOpen()andBeginClose()methods. You can subscribe to hosting events such as state changes or faults, and you can use theStateproperty to query for the host status. Finally, theServiceHostclass also implements theAbort()method.Abort()is an ungraceful exit—when called, it immediately aborts all service calls in progress and shuts down the host. Active clients will get an exception.
The ServiceHost<T> class
You can improve on the WCF-provided ServiceHost class by defining the ServiceHost<T>class, as shown in Example 1-5.
Example 1-5. The ServiceHost<T> class
public class ServiceHost<T> : ServiceHost
{
public ServiceHost() : base(typeof(T))
{}
public ServiceHost(params string[] baseAddresses) :
base(typeof(T),Convert(baseAddresses))
{}
public ServiceHost(params Uri[] baseAddresses) :
base(typeof(T),baseAddresses)
{}
static Uri[] Convert(string[] baseAddresses)
{
Converter<string,Uri> convert = delegate(string address)
{
return new Uri(address);
};
return Array.ConvertAll(baseAddresses,convert);
}
}
ServiceHost<T>provides simple constructors that do not require the service type as a construction parameter, and can operate on raw strings instead of the cumbersomeUri. I’ll add quite a few extensions, features, and capabilities toServiceHost<T>in the rest of the book.
WAS Hosting
The Windows Activation Service (WAS) is a system service available with Windows Vista. WAS is part of IIS7, but can be installed and configured separately. To use the WAS for hosting your WCF service, you need to supply a .svcfile, just as with IIS. The main difference between IIS and WAS is that the WAS is not limited to HTTP and can be used with any of the available WCF transports, ports, and queues.
WAS offers many advantages over self-hosting, including application pooling, recycling, idle time management, identity management, and isolation, and is the host process of choice when available; that is, when you can target either a Vista Server machine for scalability or a Vista client machine used as a server machine for a handful of clients only.
Still, the self-hosted process offers singular advantages such as in-proc hosting, dealing with unknown customer environments, and easy programmatic access to the advanced hosting features described previously.
Next: Bindings >>
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 This article is excerpted from chapter one of Programming WCF Services, written by Juval Lowy (O'Reilly, 2007; ISBN: 0596526997). Check it out today at your favorite bookstore. Buy this book now.
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