Programming WCF Services, 2nd Edition

Custom Service Synchronization Contexts

While a synchronization context is a general-purpose pattern, out of the box, .NET only implements a single useful one: the Windows Forms synchronization context (there is also the default implementation that uses the .NET thread pool). As it turns out, the ability to automatically marshal calls to a custom synchronization context is one of the most powerful extensibility mechanisms in WCF.

The Thread Pool Synchronizer

There are two aspects to developing a custom service synchronization context: the first is implementing a custom synchronization context, and the second is installing it or even applying it declaratively on the service. ServiceModelEx contains my ThreadPoolSynchronizer class, defined as:

public class ThreadPoolSynchronizer : SynchronizationContext,IDisposable
{
   public ThreadPoolSynchronizer(uint poolSize);
   public ThreadPoolSynchronizer(uint poolSize,string poolName);

   public void Dispose(  );
   public void Close(  );
   public void Abort(  );

   protected Semaphore CallQueued
   {get;}
}

Implementing a custom synchronization context has nothing to do with WCF and is therefore not discussed in this book, although the implementation code is available with ServiceModelEx.

ThreadPoolSynchronizer marshals all calls to a custom thread pool, where the calls are first queued up, then multiplexed on the available threads. The size of the pool is provided as a construction parameter. If the pool is maxed out, any calls that come in will remain pending in ...