What are the different instance management modes available in WCF?

Question

ICSM Computer · Answer

In WCF (Windows Communication Foundation), instance management defines
how service objects are created and maintained for client requests. WCF provides three main
instance context modes, configured using the [ServiceBehavior] attribute's
InstanceContextMode property.
1. PerCall (default)
A new service instance is created for each client request.No state is maintained between calls.Ideal for stateless services.
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)]
public class MyService : IMyService
{
    // A new instance is created per request
}
Pros:
High scalability.No need for synchronization.Low memory usage.
Cons:
Cannot maintain service-level state.
2. PerSession
One service instance is created per client session (requires session-enabled binding like
NetTcpBinding or WSHttpBinding with reliable session).State is preserved throughout the session.
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]
public class MyService : IMyService
{
    // Maintains state per client session
}
Pros:
Maintains state for a specific client.Useful for multi-call workflows.
Cons:
Increased memory per client.Requires bindings that support sessions.
3. Single (Singleton)
A single service instance serves all client requests.Shared state across all clients.
[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)]
public class MyService : IMyService
{
    // Shared instance for all clients
}
Pros:
Easy to maintain shared state.Suitable for centralized services.
Cons:
Must handle concurrency (ConcurrencyMode.Multiple or Reentrant).Potential bottleneck if not managed correctly.
Summary Table
Mode
Instance per
State Preservation
Concurrency Consideration
PerCall
Call
No
Not needed
PerSession
Session
Yes (per client)
Needed if multiple calls overlap
Single
Application
Yes (shared)
Must handle explicitly
You can configure it like this:
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]
public class MyService : IMyService
{
    // Implementation
}

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What are the different instance management modes available in WCF?

ICSM Computer

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1 Answers

1. PerCall (default)

2. PerSession

3. Single (Singleton)

Summary Table

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Mode	Instance per	State Preservation	Concurrency Consideration
PerCall	Call	No	Not needed
PerSession	Session	Yes (per client)	Needed if multiple calls overlap
Single	Application	Yes (shared)	Must handle explicitly