.NET REMOTING

CertSIG

Tom Perkins

FUNDAMENTALS

Distributed Applications

Process A

Process B

Process C

•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 Boundaries

Process A Process B

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

Bad News …

Takes a lot of resources to create, monitor, and terminate processes

Switching processes is expensive

Many apps have many short-lived processes

Application Domains

Process A

Application Domain

A

Application Domain

B

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

3 Ways to develop Distributed Applications

System.Net Namespace

•Standalone listeners•Custom protocol handlers•Requires good understanding of network programming

System.Runtime.Remoting

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.Web.ServicesSystem.web services

namespace

•Classes make up ASP.NET Web Services•Objects exchange messages in HTML and SOAP•Key characteristics: simplicity and interoperability with other systems

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

What about this business of no direct calls across application

domain boundaries?

• Remoting uses indirect approach

• Creates proxy objects

.Net Remoting Architecture

Client object

Client App Domain Server App Domain

Proxy

Remoting SystemRemoting System

Server Object

Channel

Marshalling

• Process of packaging and sending method calls among objects

• Uses serialization and deserialization

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

Marshal-by-Value Objects

Client App DomainServer App Domain

Object resides hereClient invokes a

method on MBV object

1.

3.

2.

Object is serialized, transferred over network,restored on client as exact copy

MBV object available on client;

No proxy, no marshalling

4,

Faster performance

Fewer network roundtrips

Large objects slow to move

Doesn’t run in (better) server environment

Create by declaring class serializable

[Serializable]

Public class MyMBVObject

Marshal-by-Reference Objects

Client App DomainServer App Domain

Object always resides,

executes here

Client invokes a method on

object

1.

.

2.

Local proxy holds reference to object

3,

Increases number of network roundtrips

Use when objects are large

Or functionality available only on server

public class MyMBRObject : MarshalByRefObject

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

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

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

Remote Object Activation

• Only MBR objects can be activated remotely

• 2 Categories of Activate objects– Server-activated objects– Client-activated objects

Client objectServer object

Server-activated Objects (SOAs)

• Object Lifetime controlled directly by server

• Remote object instantiated only when client calls a method on proxy object

Client object

Proxy object

Server Object

This guy controls its own lifetime

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

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)

Client-Activated Objects (CAOs)

• 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.

Client object

Proxy object

Server Object

This guy controls this guy’s lifetime.

CAO Activation

Client object

Client App Domain Server App Domain

Proxy

Remoting SystemRemoting System

Server Object

Channel

1. Client attempts to create an instance of the server object.

2. Activation request sent to remote server

3. Server creates object

4. Server return ObjRef object to client – info to build proxy object

5. Client uses ObjRef object to build proxy

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.

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

Comparing Object Activation Techniques

Activation Type Flexibility Scalability

Single-Call Server Activation

Singleton Server activation

Client Activation

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

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

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

Client object Server object

ExecuteQuery()

SQL SELECT query

dataset

Remotable class

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

Remote object

Listens to client

requests

Creating a Server-Activated Object (SAO)

Remoting Server Program

Channel

Remoting

Framework DbConnect

Remotable class

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

Activation requests

Remote object can be accessed through all registered channels

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

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 objectDbConnect dbc = new DbConnect();

StepByStep3_3

• Windows application

• Accepts SQL SELECT string from user

• Passes it to remotable object

• Returned rows are displayed in datagrid