InstanceContextMode Enumeration


Specifies the number of service instances available for handling calls that are contained in incoming messages.

Namespace:   System.ServiceModel
Assembly:  System.ServiceModel (in System.ServiceModel.dll)

public enum InstanceContextMode

Member nameDescription

A new InstanceContext object is created prior to and recycled subsequent to each call. If the channel does not create a session this value behaves as if it were PerCall.


A new InstanceContext object is created for each session.


Only one InstanceContext object is used for all incoming calls and is not recycled subsequent to the calls. If a service object does not exist, one is created.

The System.ServiceModel.InstanceContext manages the association between the channel and the user-defined service objects. Use the InstanceContextMode enumeration with the ServiceBehaviorAttribute.InstanceContextMode property to specify the lifetime of the InstanceContext object. Windows Communication Foundation (WCF) can create a new InstanceContext object for every call, every session or specify that the InstanceContext object is bound to a single service object. For a working example, see the Instancing.

The Single value specifies that a single InstanceContext object should be used for the lifetime of the service.


If the InstanceContextMode value is set to Single the result is that your service can only process one message at a time unless you also set the ConcurrencyMode value to Multiple.

The following code illustrates how to set the InstanceContextMode for a service class:

// Service class which implements the service contract.
public class CalculatorService : ICalculator
    public double Add(double n1, double n2)
        return n1 + n2;

    public double Subtract(double n1, double n2)
        return n1 - n2;

    public double Multiply(double n1, double n2)
        return n1 * n2;

    public double Divide(double n1, double n2)
        return n1 / n2;

.NET Framework
Available since 3.0
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