Cst556 Distributed Applications for .NET with Mono 4 ...pooh.poly.asu.edu/Cst556/ClassNotes/cnRemoting.pdf · applications to be developed at the object level rather than via TCP

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cnRemoting.fm Course Review Notes

with Mono

Distributed Applications for Windows © T. Lindquist 2019 February 2019

Cst556 Distributed Applications for .NET

4. Remoting with .NET

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eferences

uted applications #? Remoting nt and server.

ows distributed than via TCP data

ngleton and Client-pplications best ations that utilize

ifetimes of Remote

ter and return types


4.a .NET Remoting: Outcomes and R

4.a.1 Motivation and Outcomes• What is .NET Remoting and how can I develop distrib

using Remoting Object Servers and their Clients in Cprovides for object-level communication between clie

• Section Outcomes

- To understand what it means to say that remoting allapplications to be developed at the object level ratherprotocols.

- To understand the differences between SingleCall, SiActivated remote object servers and the distributed asuited for each. To be able to develop C# .NET appliceach.

- To understand the leasing mechanism for controlling lObjects.

- To understand limitations on and handling of paramefor remoting applications.

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Remoting

ft Press, Chapter 15


4.a.2 References for .NET Remoting• C# Web Services (course textbook) Chapter 6 on .NET

Architecture• C# for Java Developers by Jones and Freeman, Microso

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emotingivated Pencil

d Pencil Servervated PencilServerg Example with

moting Examplefor notification:


4.a.3 Index to Example Programs for .NET R- Server-activated: Section 4.d.4 Example Server-Act

Server- Single-call: Section 4.d.4 Example Server-Activate- Client-activated: Section 4.d.6 Example Client-Acti- User-defined parameter types: Section 4.f.2 Remotin

User-Defined Parameter Types- Using leases: Section 4.f.4 Leases in GroupMgr Re- Remote Server that Registers and calls-back clients

Section 4.g.2 Solution Approach

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jects

allow components level. and/or on different application.mail client and

riented way, guments for the e. are all handled by

ote machine:ts with data

n, enhance, and use.


4.b Introduction to Distributed Ob4.b.1 What are Distributed Objects?

• Distributed objects as realized through .NET Remotingof distributed applications to communicate at the object- Components, which may reside in different processes

machines are viewed as separate executing parts of an- Example components are browser and http server, e

imap server, as well as their subparts.- Components send each other messages in an object-o

consisting of a method to be invoked together with armethod. The result of a message may be a return valu

- Arguments, call synchronization and return valuesplatform; not by the application developer.

• Without distributed objects, sending a message to a rem- Current protocols (http, ftp, telnet) use stream socke

protocols, or RPC- Current protocols are data centric, difficult to maintai

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objects.

r each other and

d/or follow mobile .

gister themselves the registry and ompeting) services.

middleware issues

nchronization?


4.b.2 Vision of Distributed Object Computing

• Applications are federations of cooperating distributed

- Configuration may be dynamic - objects can discovecommunicate to perform some service for each other.

- Distributed Objects can survive network outages anparadigms where connectivity is constantly changing

- Distributed Objects may be service providers that rewith multiple registries. Potential clients may contactdiscover information about compatible (and maybe c

• View the Internet as an Object Bus

• Distributed Object technologies remove the underlying from applications and their developers.

- How to implement message passing and argument sy

- What if objects are not “in-process”?

- Distinction between objects within LAN versus WAN

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ice Competitors

bject model

ent Group

n) hindered usage.

tomatic dynamic each application.bage collection.web server-specific


4.b.3 .NET Remoting and ASP.NET Web Serv• Distributed COM and its evolutions by Microsoft

- Multi-language, single platform- constrained functionally by not including complete o

• Common Object Request Broker by Object Managem- Multi-language, multi-platform,- Sacrificed ease of use and functionality.- Lagging Pass-By-Value implementations (serializatio

• Remote Method Invocation in SUN’s Java- Single language, multiple platform- Easy to use and conceptually clean, although with au

class loading security must be carefully addressed for- Incurs burdon of net-wide reference counting and gar- Lots of Intranet application including J2EE and other

support applications.

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motinguted application

he cliente as fast as web eroperability).

AP and HTTP

SOAP)xample, Java client


4.b.4 ASP.NET Web Services versus .NET Re• .NET Framework includes two mechanisms for distrib

development:- ASP.NET Web Services- .NET Remoting

• Remoting can use different transport mechanisms- A native binary TCP based protocol- SOAP and HTTP- Object references and a proxy object are utilized by t- Remoting is a fast (binary formatted remoting is twic

services) solution for .NET clients and servers (no int

• ASP.NET Web Services expose web methods using SOthrough an IIS web server.- Developed based on open standards (WSDL, UDDI,- Intended to allow across development platforms (for e

accessing an ASP.NET Web Service).

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tions

ng system processample) is achieved

or each application.age runtime’s pplication.

machine within a

gram control.ins (code not data),

bjects in another


4.c Background of .NET Applica4.c.1 View of ASP.NET Remoting

• Multiple .NET applications can run in the same operati- Application isolation (for transactions, security, for ex

by defining Application Domains within a process f- An Application Domain is the .NET common langu

version of a “light weight” process for executing an a- See the System.AppDomain class

• ASP.NET hosts all ASP.NET applications on a given single process.

• Each Application Domain consists of Assemblies- Assemblies can be loaded under program control.- The Application Domain can be unloaded under pro- An Assembly can be shared by all Application Doma

which is called a Domain-Neutral Assembly• Objects in one Application Domain can’t interact with o

except through Remoting.

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ssemblys outside the core

services such as:

t called the Contextssociated with a its execution.


4.c.2 .NET Base Class Library• The Base Class Library is spread over two assemblies

- MSCorLib.dll- System.dll

• MSCorLib.dll is always loaded as a domain neutral a- To keep it as small as possible, there are no reference

library.

• .NET provides that classes can be configured to require- synchronization,- security,- just-in-time activation, and- transactions

• These available services make up a runtime environmen- Classes (objects) within an Application Domain are a

Context that defines the resources and constraints on

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Domainuires eitherjectsote objects

limited to the

arked [Serializable]ng the object - a stream.n by deserializing.

pplication Domain,

nal object.eiving results

plication domain.


4.c.3 Communication outside the Application• Any communication outside the application domain req

- Marshal by Value Objects, which are serializable ob- Marshal by Reference Objects, which are called rem

• Any objects that are neither remote nor serializable areapplication domain in which they are created.

• Serializable objects -implement ISerializable or are m- Marshalled as they leave an Application by serializi

(creating a copy) and then transporting them through - Unmarshalled on entering a new Application Domai

• Remote objects- Extend System.MarshalByRefObject- When a remote object reference is imported into an A

a proxy object is created in the receiving Domain.- The proxy has a method for each method in the origi- Proxy object methods handle calling methods and rec

utilizing a Tcp or Http channel to another process/ap

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ing layer, which formation to the el.

shals the call and turns the results.

n Domain

oting Layer

te Object Server


4.c.4 Calling a Remote Object’s Methods• Client method calls resolve to the proxy object.

- The proxy object directs the call through the Remotmarshals the parameters and communicates all call inreceiving application domain through a defined chann

- On the object server side, the Remoting layer unmararguments, calls the method and then marshals and re

Application Domain

Remoting Layer

Applicatio

Rem

Channel

Client

Proxy

Remo

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own Objectsl known to client), associating it with

ndle requests from e displayed in ultiple servers.

le each client call. ervice is to be a function, such as

d used to service

tiple calls, such as


4.d Implementing with .NET4.d.1 Types of .NET Remote Objects

• Server-Activated remote objects - also called Well Kn- The client must have a URL naming the object (wel- A server may create and register the remote object

either a TCP or HTTP channel for cummunication.• Two types of Server-Activated objects

- Singleton object - one object exists and is used to haall clients. Used when one client’s information may banother, such as a chat server. Hard to scale across m

- Single Call object - a new object is created to handUsed for stateless remote objects where an isolated sperformed for each client call. For example calculatingthe energy consumed by an air conditioner.

• Client-Activated objects - A single object is created anmultiple calls from a single client.- Used to retain client session information through mul

shopping cart applications.

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emoting

e exposed to the

nterfaces or proxies ients.

on the appropriate or http) and remote

rvice) to register the

and are to be sor the lease

. Provide their user-


4.d.2 Developing an Application with .NET R• Server

- Define the server-side classes and methods that will binternet (published).

- Provide implementations of the classes and develop ithat isolate the server implementation classes from cl

• Registering the server-type- Based on the characteristics of the application, decide

deployment paradigm - communication platform (tcpobject type (Server-Activated or Client-Activated)

- Create a separate console application (or Windows Seserver channels and type(s)

• Consider server object lifetime - if leases are involvedmanually maintained, create a client application to spon

• Client- Define the client applications that will use the service

interface as well as connection to server code.

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icate between the

ce. Use Http when ttp channels have TP makes

ormance benefit but nternet proxies.

channel Group Server:

through TCP with::8888/GrpSrv”)


4.d.3 Publishing a Server-Activated Singleton• Either (or both) HTTP and TCP can be used to commun

client and the server.- Http channels use SOAP and have slower performan

clients and server are located on different networks. Hspecific support for using proxies and SOAP over HTtraversing Internet proxies easier.

- Tcp channels use binary encoding which offers a perfis less likely to be succesfully transmitted across all I

• A single Application Domain may define more than one- For Example, publishing a server-activated singleton

TcpChannel tcpChan = new TcpChannel(8888);ChannelServices.RegisterChannel(tcpChan);HttpChannel httpChan = new HttpChannel(8889);ChannelServices.RegisterChannel(httpChan);RemotingConfiguration.RegisterWellKnowServiceType(typeof(GrpMgr),

“GrpSrv”,WellKnownObjectMode.Singleton)...

- A client may obtain a reference to the group managerGrpMgr gm=(GrpMgr)Activator.GetObject(typeof(GrpMgr),”tcp://localhost

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y contacting the

emotingPencil.jar

pl.csver object

er.csdme.txtnd running the ated singleton and


4.d.4 Example Server-Activated Pencil Server• Suppose we have a pencil server. Clients share pencils b

server to borrow or return some number of pencils.• Here’s a jar file containing the entire example: dotNetR• Create the server implementation class as a library.

- See: PencilServerImpl.cs in the jar file. - msc /t:library /out:PencilServer.dll PencilServerIm

• Create an application to register and initiate a single ser- See: RegisterPencilServer.cs in the jar file. - msc /reference:PencilServer.dll RegisterPencilServ

• The example comes with an Ant build.xml file and rea- See the readme.txt file for instructions on building a

example. Note that this example includes server activsingle call as well as client activated (session).

http://pooh.poly.asu.edu/Cst556/Examples/Remote/dotNetRemotingPencil.jar

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Objectsr each method call.

e a new object.tion, the remote leton or single-call

e same as:

is initiated in the lls.

or.CreateInstance:ull,


4.d.5 SingleCall and Client-Activated Remote• Server-Activated SingleCall - Activates a new object fo

Client calls a method which initiates server to instantiat- The object is activated for a single call. Upon comple

object is released. Registration indicates the type singHttpChannel httpChan = new HttpChannel(8889);ChannelServices.RegisterChannel(httpChan);RemotingConfiguration.RegisterWellKnowServiceType( typeof(GroupMgr), “GroupServer”, WellKnownObjectMode.SingleCall)

- On the client side, obtaining an object may be done thChannelServices.RegisterChannel(new HttpClientChannel());GroupMgr gm = (GroupMgr)Activator.GetObject( typeof(GroupMgr), "http://localhost:8090/GroupServer");

• Client-Activated - Server registers the type; activation client. A single object instance serves all of a client’s ca

ChannelServices.RegisterChannel(new TcpServerChannel(8889));RemotingConfiguration.RegisterActivatedServiceType(typeof(GroupMgr));

- One way a client can create the object is using ActivatGroupMgr gm = (GroupMgr)Activator.CreateInstance(typeof(GroupMgr), n new object[] { new UrlAttribute(“tcp://localhost:8889”) } );

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see:

ent-activated.

ext create two or ote that each client

of pencils.)hes the life-time of

compiles:pl.cser.cs

ilServer.dll in the y from the server.


4.d.6 Example Client-Activated PencilServer• Download the Ant project (same as the prior example),

dotNetRemotingPencil.jar- Follow the directions in the readme.txt file to run cli

• Differences and Observations:- Observe session functionality by starting the server. N

more clients in separate command prompt windows. Nhas its own remote server object (and its own supply

- The life-time of a client-activated remote object matcthe client’s remote reference to the server.

• Directly building the application requires the following- msc /t:library /out:PencilServer.dll PencilServerIm- msc /reference:PencilServer.dll RegisterPencilServ- msc /reference:PencilServer.dll PencilClient.cs- Attempting to deploy PencilClient.exe without Penc

folder will result in an attempt to download the librar

http://pooh.poly.asu.edu/Cst556/Examples/Remote/dotNetRemotingPencil.jar

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ecify L from a file.cts of the

d the application. GroupConfig.xml

jectUri=”GroupServer”/>

nfiguration with:


4.d.7 Configuration by XML• Instead of using method calls and their parameters to sp

RemotingConfiguration, it can be done by reading XM- Reading from an XML file allows for modifying aspe

configuration without having to recompile and rebuil- Suppose the Server-Activated configuration is in file:

<configuration> <system.runtime.remoting> <application> <service> <wellknown mode=”Singleton” type=”GroupMgr, GroupMgr” ob </service> <channels> <channel ref=”http” port=”8889”/> </channels> </application> </system.runtime.remoting></configuration>

- The server registration program could specify this coRemotingConfiguration.Configure(“GroupConfig.xml”);

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ote Servers

active forever,

utes of inactivity.y calls a method on

verhead of network

time that is limited tialized to service a etes.

a Client-Activated

m calls the vice, which returns


4.e Lifetimes for Server-Activated Rem4.e.1 Lifetime of Remote Objects

• Client-Activated and Server-Activated objects aren’t unless explicitly specified this way by the developer.- Default idle period is 5 minutes. Released after 5 min- A new object is instantiated when a client subsequentl

the object.- Leases are used to manage lifetime, which avoids the o

wide reference counting of remote object references.

• Server-Activated SingleCall remote objects have a lifeto the duration of a single method call. The object is inisingle method call and released after the method compl

• How is the lifetime of a Server-Activated Singleton andremote object determined?- When a new instance is created, the Remoting Syste

MarshalByRefObject method InitializeLifetimeSeran object implementing ILease

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rvice method to

bject) contains the s implementation nctionality.iated object will

will exist after a

ours of idle time till release method call extend 10 mins

figures the object

eSpan.Zero


4.e.2 Manually Controlling Leases• A Remote object can override the InitializeLifetimeSe

control aspects of the lease.- The remote server’s base class (MarshalByReference O

method InitializeLifetimeService. The remote server’can override this method to provide server-specific fu

- InitialLeaseTime determines how long a server-activexist when its initially registered.

- RenewOnCallTime determines how long the object client makes a method call.

public override object InitializeLifetimeService() { ILease myROLease = (ILease)base.InitializeLifetimeService(); if (myROLease.CurrentState == LeaseState.Initial){ myROLease.InitialLeaseTime = TimeSpan.FromHours(3); //initially 3 h myROLease.RenewOnCallTime = TimeSpan.FromMinutes(10); //after a } return myROLease;}

• Returning null or setting InitialLeaseTime to zero, conwith a never expiring lease.- For example: myROLease.InitialLeaseTime = Tim

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.

ase expiration

ehalf of the remote

the service.

se expires. It returns extended.

bject class

nsor is used as an

opied to the server

separate client.

s.jar


4.e.3 Sponsoring a Lease• A client of a remote object can sponsor the objects lease

• Sponsors implement ISponsor and register interest in le

- The sponsor is a client that manages lease renewal on bobject.

ILease myROLease = (ILease)RemotingServices.GetLifetimeService(myRO);myROLease.Register(this); //this code may appear in a method that publishes

- the ISponsor.Renewal method is called before the leaa TimeSpan indicating how long the lease should be

• The sponsor must be a serializable or a MarshalByRefO

- When registering the sponsor with remoting, the Spoargument to a method in the Remoting Server.

- When the Sponsor is serializable, it is serialized and cand subsequently executed on the server.

- When the sponsor is a remote object, then it acts as a

- Example of a server registered with a lease: userParm

http://pooh.poly.asu.edu/Cst556/Examples/Remote/userParms.jar

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etersjectste Object Calls?

y/value, such as rshalling and

lByRefObjectrovide class lass must be ccess to the proxy.


4.f .NET Remoting Method Param4.f.1 Arguments and Returns for Remote Ob

• What are the valid parameter and return types for Remo- Primitive values, such as int and boolean.- .NET defined Serializable objects are passed by cop

String or Array classes. They are serialized upon madeserialized when unmarshalled.

- Remote objects. Classes that extend System.Marsha- User-Defined serializable or remote classes. Must p

information to the client. For serializable, the entire cavailable to the client. For remotes, the client needs a

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arameter Typesation on groups of

erParms.jar

and their referencesng information n be seen by all.plications, such as

gr.dll

blic class RegisterGroupMgr{/neither serializable//nor remote

sterGroupMgr.exe


4.f.2 Remoting Example with User-Defined P• Consider the problem of representing and serving inform

people, such as Cst556, Faculty, and Students. See: us

• The diagram above shows assemblies in this application• Example with multiple clients accessing and manipulati

about groups of persons. Changes made by one client ca- Characteristic of a class of problems in distributed ap

email, listserves, and chatrooms.

GroupM

public class GroupMgr{ //remote}public class Group { //remote}GroupMgrClient.exe

public class GroupMgrClient { //neither serializable //nor remote}

pu / }

Regi

public class Person { //serializable}

public class SponsorGr { //serializable}

Person.dll


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oting includes:k (GroupMgr).ut are not published.erson)

roupMgrClient ces GroupMgr.dll

serializable class as Person. By design, ass definition. They ss. For example,

ined classes as one on for user-defined stub promotes all ethods; Person’s


4.f.3 Comments on the GroupMgr Example• Implementation of this group application in .NET Rem

- Singleton object published in the remoting framewor- A number of remote Groups live in the application, b- Serialized objects are copied and passed to clients (P

• Constraint in deploying with .NET Remoting Clients. Gdoes not bind a Proxy for the remotes. Instead it referenand Person.dll libraries.- A distributed application may include a user-defined

a parameter or return from a Remote method, such as the client and the server may need access to the full clmay be designed to rely on methods of the shared claPerson’s Age property get and set methods.

- The soapsuds tool does not treat serializable user-defwould hope. Soapsuds generates a stub-class definitiserializable parameter (or return) types (Person). Theproperties to public visibility, and does not include mAge property get and set methods, for example.

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ell know type. sponsor for

r managing groupsethod call) lease

gr object to manage

ept that the sponsor

vide a TimeSpanwhen you run the


4.f.4 Leases in GroupMgr Remoting Example• The example consists of three console applications

- RegisterGroupMgr - registers the GroupMgr as a wSponsorGroupMgr object is created as the renewal GroupMgr

- GroupMgrClient - provides a client user interface fo• Upon instantiation, GroupMgr sets its initial (and on m

times to 15 seconds. It also creates the SponsorGroupMits lease.- After 15 seconds of idle time, the object is released exc

has been registered to renew the lease.- Whenever the lease expires, Renewal is called to pro- Observe what happens to the state of defined groups

client without (comment out) the sponsor.- See: userParms.jar


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e

mote object types? another machine

ponding names?

ations.

jects as parameters

es appear (client or ssed person they do?

rsion of required

g the library ant implementation solution?


4.f.5 Notes and Issues on GroupMgr Exampl

• Consider the following points related to the example

- How is name management handled for registered reCan a registered type be unregistered? Can a client onobtain a listing of all registered types and their corres

• Controlling where methods execute in distributed applic

- Serializable objects versus marshal-by-reference oband return values.

- Note the windows in which the two following messagserver): new group for myGroup created, and acceminiMe’s age property. Why do they appear where

• Using a proxy versus distributing the code or library veclasses:

- Note that the GroupMgr example builds clients usincontaining code for the server. Assuming we don’t wcode on the client, how could we better structure the

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s.

singleton server

rvice each arriving ared data?

sses should be

read safe. Observe Group and ed synchronization read safe.

y way to allocate uests arrive? Object applications that


4.f.6 Threads and Thread-Safe Server Object• Server-activated singleton objects should be thread-safe

- What happens if multiple requests for method(s) in a object arrive at the same time?

- The remoting subsystem creates distinct threads to serequest. What is the implication on any underlying sh

- As a practical guideline, all marshal-by-reference clathread-safe.

• In the Group Manager example:

- The singleton GroupMgr object was not coded as ththat multiple threads (one for each client) can executeGroupMgr methods concurrently. There is no enforcof these threads. Good exercise to make the classes th

- For SingleCall server-activated remoting, is there anobjects from an existing pool of remote objects as reqpooling is a common approach to scaling the types ofSingleCall objects are intended to address.

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ient

persistent state that

ssage servers.me aspect of the

the state, then all

plication.each client displays

splayed on all other

of the supply desk hange has occurred rver calls the client y.


4.g Call-Backs from Server to Cl4.g.1 The Problem

• Consider distributed applications where the server has amay be accessed and modified by multiple clients.- Characteristics of group-ware, email or threaded me- Multiple clients may be simultaneously displaying so

server’s current state.- If one client requests a server operation that modifies

other clients may display out-of-date information.• For example, consider the PencilServer supply desk ap

- Suppose clients are graphical user interfaces in which the current total of pencils in the supply desk.

- If one client adds pencils to the supply, then the total diclients will be out-of-date.

• Solution: The server acts as a client whenever the statechanges. It calls all active clients notifying them that a cin the supply desk (a modify event has occurred). The se(commonly called a callback) so it can update its displa

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the Remote e server, such as terface includes a

ctivatable, or rtObject method to

encilModified.elegate with a llBackPencil.jar

er; also the private or each client call.as a listener; on exit t of listeners.


4.g.2 Solution Approach• In Java with RMI:

- The client becomes a remote object by implementinginterface. It also implements an interface known to thPencilChangeListener. The PencilChangeListener inmethod, such as notifyPencilSupplyChanged.

- The client either extends one of the remote classes (AUnicastRemoteObject) or it performs the static Expolet the RMI system know its a remote object.

• In C# .NET Remoting:- The server defines a public delegate, such as NotifyP- The client creates a delegate object, associating the d

method defined in the client. See example project: ca• In both the C# and Java solutions, the server:

- Implements methods: addListener and removeListenmethod callListener. CallListener creates a thread f

- In the client constructor, it calls the server to add itself the client calls the server to remove itself from the se

http://pooh.poly.asu.edu/Cst556/Examples/Remote/callBackPencil.jar

Cst556 Distributed Applications for .NET with Mono 4 ...pooh.poly.asu.edu/Cst556/ClassNotes/cnRemoting.pdf · applications to be developed at the object level rather than via TCP

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