WCF is all about communication objects – channels, listeners, factories, all implement the ICommunicationObject interface (some through the CommunicationObject class). This provides a base implementation for the basic state machine states and transitions common to all communication-oriented object.

At any given point in time, the communication objects find themselves in a CommunicationState. Here is a diagram with the states and the transitions:

image

When we look at a communication object in a debugger, we see something like this (some columns and internal objects removed for brevity reasons):

Name: System.ServiceModel.Channels.ServiceChannel

Fields:

Type VT Value Name
System.Boolean 1 0 aborted
System.Boolean 1 0 closeCalled
System.Boolean 1 0 onClosingCalled
System.Boolean 1 0 onClosedCalled
System.Boolean 1 1 onOpeningCalled
System.Boolean 1 1 onOpenedCalled
System.Boolean 1 0 raisedClosed
System.Boolean 1 0 raisedClosing
System.Boolean 1 0 raisedFaulted
System.Boolean 1 0 traceOpenAndClose
System.Object 0 000000000131d8e0 eventSender
System.Int32 1 2 state
System.EventHandler 0 0 Closed
System.EventHandler 0 0 Closing
System.EventHandler 0 0 Faulted
System.EventHandler 0 0 Opened
System.EventHandler 0 0 Opening


In our example, the communication object is in state 2. How does that translate to the actual states? To tell you the truth, I always take some time to map the number to the state, so I started using this cheat sheet:

public enum CommunicationState
{
    Created = 0,
    Opening = 1,
    Opened = 2,
    Closing = 3,
    Closed = 4,
    Faulted = 5
}

So in our case, the ServiceChannel is Opened. We could identify the state by looking at the other variable – if close called or aborted was called, we can only by in state 4 or 5 and so on. But the cheat sheet makes it simple.

Hope you find it useful!