.NET REMOTING

1. .NET REMOTING CertSIG Tom Perkins

2. FUNDAMENTALS

3. Distributed Applications Process B • Objects can communicate across process boundaries • Objects may be on same computer, different computers, or Internet • Heterogeneous architectures allowed • Some processes can run even though others busy or have failed • Application divided into tiers (layers) – gives increased flexibility and scalability Process A Process C

4. Process Boundaries • Good News … • Windows creates “process boundary” to isolate processes • Keeps one process from affecting others • Each process has its own • virtual address space • Executable code • Data • One process cannot access code or data of another process • If process crashes it doesn’t affect others Process B Process A Bad News … Takes a lot of resources to create, monitor, and terminate processes Switching processes is expensive Many apps have many short-lived processes

5. Application Domains CLR • Provides managed execution • Services: • Cross-language integration • Code access security • Object lifetime management • Debugging • Profiling support • Application can run in CLR in application domain • Smallest execution unit in .NET • Class System.AppDomain • Several app domains can run in a Windows process • App domain boundary similar to process boundary, but much cheaper • Can run multiple apps in same Windows process Process A Application Domain A Application Domain B

6. 3 Ways to develop Distributed Applications • Standalone listeners • Custom protocol handlers • Requires good understanding of network programming System.Net Namespace • Classes in this chapter • Allows communication between objects in different app domains • May be on separate computers • Simple way for processes to communicate • Key characteristics: flexibility and extensibility System.Runtime.Remoting Namespace • Classes make up ASP.NET Web Services • Objects exchange messages in HTML and SOAP • Key characteristics: simplicity and interoperability with other systems System.web services namespace System.Web.Services

7. What is .NET Remoting? • .Net Remoting allows objects in different application domains to talk to one another • It handles the details of network communication transparently

8. What about this business of no direct calls across application domain boundaries? • Remoting uses indirect approach • Creates proxy objects

9. .Net Remoting Architecture Client object Server Object Proxy Channel Remoting System Remoting System Client App Domain Server App Domain

10. Marshalling • Process of packaging and sending method calls among objects • Uses serialization and deserialization

11. Remotable Objects • Definition – objects that can be marshalled across application domains • All other objects – non-remotable objects • Two types of Remotable Objects • Marshal-by-value (MBV) • Copied from server domain to client app domain • Marshal-by-reference (MBR) • Uses proxy to access objects on client side • Clients hold just a reference to these objects

12. Marshal-by-Value Objects Faster performance Fewer network roundtrips Large objects slow to move Doesn’t run in (better) server environment 1. Object resides here Client invokes a method on MBV object 2. 3. Object is serialized, transferred over network,restored on client as exact copy 4, MBV object available on client; No proxy, no marshalling Create by declaring class serializable [Serializable] Public class MyMBVObject Server App Domain Client App Domain

13. Marshal-by-Reference Objects Increases number of network roundtrips Use when objects are large Or functionality available only on server 1. Object always resides, executes here Client invokes a method on object 2. . 3, Local proxy holds reference to object Server App Domain Client App Domain public class MyMBRObject : MarshalByRefObject

14. Channels • Objects that transport messages across application boundaries (computers, etc) • When client calls method on server, info transferred through channel • Info back through same channel • Channels must be registered before they can be used

15. More about Channels • Channel has 2 endpoints • Receiving end (server) listens to particular protocol through specified port number • Sending end (client) sends info using protocol and port number specified by server • Receiving end  must implement IChannelReceiver Interface • Sending end  must implement IChannelSender Interface • Protocols • HTTP • TCP

16. Formatters • Defn- objects used to serialize and deserialize data into messages before they are transmitted over a channel • 2 Formatters • SOAP – SOAPFormatter class • Binary – BinaryFormatter class • Defaults • HTTP Channel SOAP formatter • TCP Channel Binary formatter

17. Remote Object Activation • Only MBR objects can be activated remotely • 2 Categories of Activate objects • Server-activated objects • Client-activated objects Server object Client object

18. Server-activated Objects (SOAs) • Object Lifetime controlled directly by server • Remote object instantiated only when client calls a method on proxy object Client object Server Object Proxy object This guy controls its own lifetime

19. 2 Activation Modes for SOAs • Single-Call activation • Object instantiated only for purpose of fulfilling one client request • .NET then deletes and reclaims memory • Singleton Activation mode • At most one remote object, regardless of how may clients may be using it • State can be maintained • Lifetime Lease determines its lifetime

20. When to use • Single-Call activation • When it doesn’t cost much to create an object • No object state required • Server needs to support large number of requests for object • Load balancing environment • (retrieve inventory level for an item, display shipment info, etc) • Singleton Activation • Use when it costs a lot to create an object • State required over a long period of time • Several clients need to work on the shared state • (Chat server – multiple people talk to same remote object and share data with one another)

21. Client-Activated Objects (CAOs) Client object • Lifetime is controlled by the client • CAOs are instantiated on server as soon as the client requests the object to be created. • Object creation is not delayed until first method is called by client. Server Object Proxy object This guy controls this guy’s lifetime.

22. CAO Activation Client object Server Object 3. Server creates object 1. Client attempts to create an instance of the server object. 5. Client uses ObjRef object to build proxy Proxy 2. Activation request sent to remote server Channel Remoting System Remoting System 4. Server return ObjRef object to client – info to build proxy object Client App Domain Server App Domain

23. CAO Characteristics • Serves only client responsible for its creation • Doesn’t get discarded with each request • Can maintain state with client it is serving • Unlike Singleton CAO’s, different CAOs cannot share a common state.

24. When to Use CAOs • Clients want to maintain a private session with the remote object • Clients want to have control over how the object is created and how long it should live. • Example: a complex purchase order involving many roundtrips and clients want to maintain their own private state with the remote object

25. Comparing Object Activation Techniques Maximum scalability; remote object uses resources for min time; server can handle many clients Maximum flexibility; you have complete control over remote object construction and lifetime

26. Lifetime Leases • Definition – the period of time a particular object will be in memory before deletion and garbage collection • Used by Singleton SAOs and CAOs • Object must implement Ilease interface in the System.Runtime.Remoting.Lifetime namespace

27. DEMO – 1.Create a Remotable class • Must inherit from MarshalByRefObject class. • This demo creates DbConnect class (will produce a remote server object) • Purpose: connects to a SQL Server database • Allows you to execute a SELECT statement to return a dataset – ExecuteQuery() method on the server object. • Walkthru, then class is in DLL (bin\Debug) • Still need to connect to Remoting Framework Remotable class Server object Client object SQL SELECT query ExecuteQuery() dataset

28. Server Program • Connects to .Net Remoting Framework • Listens to the client request • Instantiates the remote object • Invokes calls on remote object as requested by client Server Program Listens to client requests Remote object

29. Creating a Server-Activated Object (SAO) Remotable class Remoting Framework Remoting Server Program DbConnect Activation requests Channel 1. create server channel – listens on particular port for activation requests from other application domains TcpServerChannel channel = new TcpServerChannel(1234) // port 1234 2. Register the channel with .Net Remoting 3 Register the remotable class RemotingConfiguration.RegisterWellKnownServiceType( typeof(dbConnect), // type of class “DbConnect”, // URI of remotable class WellKnownObject Mode.SingleCall) // activation mode – c.b. Singleton Remote object can be accessed through all registered channels

30. DEMO – 2. Create a Server-Activated Object (SingleCall) • Exposes the remotable class through the remoting framework • Long running process • No interface • Listens for incoming client requests on a channel • This example uses a Console application • (Should be a Windows service or IIS) • Walkthru – StepByStep3_2 • Creates a remoting host that listens on port 1234

31. DEMO – 3. Instantiate and Invoke a Server-Activated Object • We’re building a Remoting Client • We want to send messages to Remoting Server to activate the Remote object. • Steps • Create and register a client channel to send messages to server; type s.b. compatible (TCP or HTTP) • Register the remotable class in the client’s app domain. • Instantiate the server object DbConnect dbc = new DbConnect();

32. StepByStep3_3 • Windows application • Accepts SQL SELECT string from user • Passes it to remotable object • Returned rows are displayed in datagrid