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.NET REMOTING. CertSIG Tom Perkins. FUNDAMENTALS. Distributed Applications. Process B. Objects can communicate across process boundaries Objects may be on same computer, different computers, or Internet Heterogeneous architectures allowed

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Net remoting

.NET REMOTING

CertSIG

Tom Perkins



Distributed applications
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


Process boundaries
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


Application domains
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


3 ways to develop distributed applications
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


What is net remoting
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
What about this business of no direct calls across application domain boundaries?

  • Remoting uses indirect approach

  • Creates proxy objects


Net remoting architecture
.Net Remoting Architecture application domain boundaries?

Client object

Server Object

Proxy

Channel

Remoting System

Remoting System

Client App Domain

Server App Domain


Marshalling
Marshalling application domain boundaries?

  • Process of packaging and sending method calls among objects

  • Uses serialization and deserialization


Remotable objects
Remotable Objects application domain boundaries?

  • 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
Marshal-by-Value Objects application domain boundaries?

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


Marshal by reference objects
Marshal-by-Reference Objects application domain boundaries?

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


Channels
Channels application domain boundaries?

  • 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
More about Channels application domain boundaries?

  • 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
Formatters application domain boundaries?

  • 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
Remote Object Activation application domain boundaries?

  • Only MBR objects can be activated remotely

  • 2 Categories of Activate objects

    • Server-activated objects

    • Client-activated objects

Server object

Client object


Server activated objects soas
Server-activated Objects (SOAs) application domain boundaries?

  • 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


2 activation modes for soas
2 Activation Modes for SOAs application domain boundaries?

  • 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
When to use application domain boundaries?

  • 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
Client-Activated Objects (CAOs) application domain boundaries?

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.


Cao activation
CAO Activation application domain boundaries?

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


Cao characteristics
CAO Characteristics application domain boundaries?

  • 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
When to Use CAOs application domain boundaries?

  • 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
Comparing Object Activation Techniques application domain boundaries?

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
Lifetime Leases application domain boundaries?

  • 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
DEMO – 1.Create a Remotable class application domain boundaries?

  • 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


Server program
Server Program application domain boundaries?

  • 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


Creating a server activated object sao
Creating a Server-Activated Object (SAO) application domain boundaries?

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


Demo 2 create a server activated object singlecall
DEMO – 2. Create a Server-Activated Object (SingleCall) application domain boundaries?

  • 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
DEMO – 3. Instantiate and Invoke a Server-Activated Object application domain boundaries?

  • 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();


Stepbystep3 3
StepByStep3_3 application domain boundaries?

  • Windows application

  • Accepts SQL SELECT string from user

  • Passes it to remotable object

  • Returned rows are displayed in datagrid


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