Carnegie Mellon University MSCF 1.NET Distributed Computing Notes from “Distributed.NET...

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.NET Distributed Computing

Notes from “Distributed .NET Programming in C#” byTom Barnaby and“.NET Programming” by Pradeep Tapadiya

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Remote Objects

• We can’t call methods on remote objects directly. We call methods on remote objects through a remote reference to that object.

• Parameters to and from the remote method are “marshaled”

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Marshaling Classification

• Marshal-by-value

• Marshal-by-reference

• Nonremotable

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Marshal-By-Value Objects

• Objects marked with the custom attribute [serializable] are pass-by-value objects

• The entire object is copied into the remote domain

• Any local change to the object is not reflected in the remote domain

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Marshal-By-Reference Object

• MBR objects derive from MarshalByRefObject

• The client of such an object is actually making calls on a proxy object created by the runtime

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MBR Objects (1)using System;using System.Threading;

public class Foo : MarshalByRefObject {

public void DisplayDomainInfo() {

String s = "Domain=" + AppDomain.CurrentDomain.FriendlyName + " Thread ID=" + AppDomain.GetCurrentThreadId() + " Context ID=" + Thread.CurrentContext.ContextID; Console.WriteLine(s); }}

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public class MyApp {

public static void Main() {

Foo fDefault = new Foo(); // No proxy is used because we are fDefault.DisplayDomainInfo(); // not crossing domains

}}

D:\..\46-690\MBRandMBV>mbvandmbr.exe

Domain=mbvandmbr.exe Thread ID=2284 Context ID=0

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MBR Objects (2)public class MyApp {

public static void Main() {

Foo fDefault = new Foo(); fDefault.DisplayDomainInfo(); // force a call by remote reference // fNew points to a proxy AppDomain ad = AppDomain.CreateDomain("MyNewAppDomain"); Foo fNew = (Foo) ad.CreateInstanceAndUnwrap("mbvandmbr", "Foo"); fNew.DisplayDomainInfo(); }}

D:\..\46-690\MBRandMBV>mbvandmbrDomain=mbvandmbr.exe Thread ID=2096 Context ID=0Domain=MyNewAppDomain Thread ID=2096 Context ID=0

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MBR Objects (3)using System;using System.Threading;

[Serializable] // make Serializable and remove MarshalByReferencepublic class Foo {

public void DisplayDomainInfo() {

String s = "Domain=" + AppDomain.CurrentDomain.FriendlyName + " Thread ID=" + AppDomain.GetCurrentThreadId() + " Context ID=" + Thread.CurrentContext.ContextID; Console.WriteLine(s); }}

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public class MyApp {

public static void Main() {

Foo fDefault = new Foo(); fDefault.DisplayDomainInfo();

AppDomain ad = AppDomain.CreateDomain("MyNewAppDomain"); Foo fNew = (Foo) ad.CreateInstanceAndUnwrap("mbvandmbr", "Foo"); fNew.DisplayDomainInfo(); }}

D:\...\46-690\MBRandMBV>mbvandmbrDomain=mbvandmbr.exe Thread ID=588 Context ID=0Domain=mbvandmbr.exe Thread ID=588 Context ID=0

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Remoting Model

REMOTING

LAYER

REMOTING

LAYER

Client Object Server Object

Proxy Channel

Namespaces:System.Runtime.Remoting.Channels.Tcp binary serializationSystem.Runtime.Remoting.Channels.Http uses Microsoft SOAP serializationClasses:TcpServerChannel, HttpServerChannel, TcpClientChannel, HttpClientChannel

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Remote Objects May Be

• Server-Activated Objects

(The server controls the lifetime)

• Client-Activated Objects

(The client controls the lifetime)

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Server Activated Objects Server activated objects – with a well-known name assigned on the server

The server code -- Registers a server side channel -- Registers the name of the remote object -- Provides a mechanism to keep the server alive -- Creates the object on the first call to the object trough the client side proxy The Client code -- Registers a client side channel -- Create a proxy with Activator.GetObject passing a type and a location -- Make calls on the proxy as though they were calls on the remote object

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Single-Call and Singletons

• Server Activated objects are published as either single-call or singleton objects

• Single-call => on each call from the client the object is created and then torn down

(WellKnownObjectMode.SingleCall)• Singleton => only one object exists and is

shared by callers (no synchronization)

(WellKnownObjectMode.Singleton)• Neither of these is appropriate for holding state

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Client Activated Objects

• The client requests that an instance be created on the server

• For each instance requested a proxy is returned to the client

• The client may store instance specific state in the object (through the proxy)

• The objects are garbage collected when their leases expire

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The Object To Be Served// A Remote Student Objectusing System;

public class RemoteStudent : MarshalByRefObject {

private int age; private String name;

public int getAge() { return age; } public String getName() { return name; }

public void setAge(int age) { this.age = age; } public void setName(string name) { this.name = name; } }

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Client Code (along with Student.dll)using System.Runtime.Remoting.Channels.Tcp;using System.Runtime.Remoting.Channels;using System.Runtime.Remoting;using System;using System.Runtime.Remoting.Activation;

class MyClient {

public static void Main() { ChannelServices.RegisterChannel(new TcpClientChannel());

RemoteStudent r = (RemoteStudent) Activator.CreateInstance( typeof(RemoteStudent),null, new object[] { new UrlAttribute( "tcp://localhost:6502") } );

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r.setName("Bob"); r.setAge(23); RemoteStudent s = (RemoteStudent) Activator.CreateInstance( typeof(RemoteStudent),null, new object[] { new UrlAttribute( "tcp://localhost:6502") } );

s.setName("Alice"); s.setAge(22);

Console.WriteLine("Name: " + s.getName() + " age " + s.getAge()); Console.WriteLine("Name: " + r.getName() + " age " + r.getAge()); }

}

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Server Code (with Student.dll)using System.Runtime.Remoting.Channels.Tcp;using System.Runtime.Remoting.Channels;using System.Runtime.Remoting;using System;

class MyApp {

public static void Main() {

ChannelServices.RegisterChannel( new TcpServerChannel(6502)); RemotingConfiguration.RegisterActivatedServiceType( Type.GetType("RemoteStudent, Student")); Console.WriteLine("Press a key to exit server"); Console.Read(); }}

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Output

..46-690\RemoteObjects3\client>MyClient

Name: Alice age 22

Name: Bob age 23

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Leases

• .NET uses a lease to manage the lifetime of remote (client activated) objects.

• A lease may be extended by the client

• When the lease expires the object is garbage collected and subsequent calls on the proxy will generate a RemotingException

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using System.Runtime.Remoting.Channels.Tcp;using System.Runtime.Remoting.Channels;using System.Runtime.Remoting;using System;using System.Runtime.Remoting.Activation;using System.Threading;

The Client Side Lets a Lease Expire

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class MyClient {

public static void Main() {

try { ChannelServices.RegisterChannel(new TcpClientChannel());

RemoteStudent r = (RemoteStudent) Activator.CreateInstance( typeof(RemoteStudent),null, new object[] { new UrlAttribute( "tcp://localhost:6502") } );

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r.setName("Bob"); r.setAge(23);

Thread.Sleep(45000); // wait 45 seconds after creating Bob RemoteStudent s = (RemoteStudent) Activator.CreateInstance( typeof(RemoteStudent),null, new object[] { new UrlAttribute( "tcp://localhost:6502") } ); s.setName("Alice"); s.setAge(22); Console.WriteLine("Name: " + s.getName() + " age " + s.getAge()); Console.WriteLine("Name: " + r.getName() + " age " + r.getAge()); } catch(RemotingException e) { Console.WriteLine("Caught exception " + e); // Bob causes trouble } }}

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A Student With A Lease// A Remote Student Objectusing System;using System.Runtime.Remoting.Lifetime;

public class RemoteStudent : MarshalByRefObject {

private int age; private String name;

public int getAge() { return age; } public String getName() { return name; }

public void setAge(int age) { this.age = age; } public void setName(string name) { this.name = name; }

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public override Object InitializeLifetimeService() {

Console.WriteLine("Lease code called"); // whenever called call base class method ILease lease = (ILease) base.InitializeLifetimeService();

// if first call make some changes if (lease.CurrentState == LeaseState.Initial) { lease.InitialLeaseTime = TimeSpan.FromSeconds(30); lease.RenewOnCallTime = TimeSpan.FromSeconds(10); } return lease; }}

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Same Server Codeusing System.Runtime.Remoting.Channels.Tcp;using System.Runtime.Remoting.Channels;using System.Runtime.Remoting;using System;

class MyApp {

public static void Main() {

ChannelServices.RegisterChannel( new TcpServerChannel(6502)); RemotingConfiguration.RegisterActivatedServiceType( Type.GetType("RemoteStudent, Student"));

Console.WriteLine("Press a key to exit server"); Console.Read(); }}

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..\46-690\RemoteObjects3\client>MyClientName: Alice age 22Caught exception System.Runtime.Remoting.RemotingException: No receiver registered

D:..\46-690\RemoteObjects3\server>ServerPress a key to exit serverLease code calledLease code called

Output

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The soapsuds tool

• Perhaps we do not want the client to have access to the Student code

• We only want the client to have access to meta information

• The soapsuds tool allows to download and then use meta information

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The server codeusing System.Runtime.Remoting.Channels.Http;using System.Runtime.Remoting.Channels;using System.Runtime.Remoting;using System;

class MyApp {

public static void Main() {

ChannelServices.RegisterChannel( new HttpServerChannel(6502));

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RemotingConfiguration.RegisterWellKnownServiceType( Type.GetType("RemoteStudent, Student"), "SomeStudent/Student.soap", WellKnownObjectMode.SingleCall);

Console.WriteLine("Press a key to exit server"); Console.Read(); }}

// Compile the server code// csc -t:library Student.cs// csc -r:Student.dll Server.cs

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The Client Codeusing System.Runtime.Remoting.Channels.Http;using System.Runtime.Remoting.Channels;using System.Runtime.Remoting;using System;

class MyClient {

public static void Main() {

ChannelServices.RegisterChannel(new HttpClientChannel());

RemoteStudent r = (RemoteStudent) Activator.GetObject( typeof(RemoteStudent), "http://localhost:6502/SomeStudent/Student.SOAP");

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String name = r.getName(); int age = r.getAge();

Console.WriteLine("Student Name: " + name + " Age: " + age); }

}

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Run The ClientBut this time we do not have the Student.dll available. So, MyClient.cscwill not compile.

1) Fetch the WSDL document from the server and generate the proxy class using soapsuds:

soapsuds -url:http://localhost:6502/SomeStudent/Student.soap?wsdl -oa:Student.dll

2) Compile and run the client: csc -r:Student.dll MyClient.cs MyClient Student Name: Mike Age: 23

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Web Services

“The internet is evolving from a collection of isolated web sites and applications into a general communication bus for distributed applications.”

From page 247 of the course text

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ASP.NET Web Services

0) Check if IIS is running by attempting to visit http://localhost

1) If it's not running click Start/Settings/Control

Panel/Add Remove Programs/

Add Remove Windows Components and

enable IIS.

2) If .NET was installed after IIS reconfigure IIS by running aspnet_regiis.exe /i from a command prompt.

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ASP.NET Web Services

Suppose we want to provide a student name

given a student ID

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ASP.NET Server Code <%@ WebService Language="C#" Class="Student.QueryService" %>

// CoolService.asmx

using System.Web.Services;using System.Collections;

namespace Student {

[WebService(Namespace="http://localhost/ACoolQueryService/")]

public class QueryService : WebService {

private static Hashtable nameValuePairs;

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static QueryService() {

nameValuePairs = new Hashtable(); nameValuePairs.Add("12345","Moe"); nameValuePairs.Add("01234","Curly Joe"); nameValuePairs.Add("54321","Larry"); }

[WebMethod] public string GetName(string id) { return (string)nameValuePairs[id]; } }}

// We can’t compile this code with csc.

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Create a virtual directory under IIS

• Start• Settings • Control Panel• Administrative Tools• Select Internet Information Services• Expand and select the default web site• Click Action/New/Virtual Directory• Provide a name (ACoolQueryService in this case) and

browse to the directory holding the .asmx file• Select everything but write

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Checking the service

• Visit the service with your browser• http://localhost/ACoolQueryService/CoolService.asmx

• HTML is generated that allows you to test the service via standard HTTP

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Testing With HTTP Get

Request

GET /ACoolQueryService/CoolService.asmx/GetName?id=string HTTP/1.1 Host: localhost HTTP/1.1 200 OK

Content-Type: text/xml;

charset=utf-8

Content-Length: length

Response

<?xml version="1.0" encoding="utf-8"?>

<string xmlns="http://localhost/ACoolQueryService/">string</string>

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Testing with SOAP POST /ACoolQueryService/CoolService.asmx HTTP/1.1 Host:

localhost Content-Type: text/xml; charset=utf-8 Content-Length: length of document SOAPAction: "http://localhost/ACoolQueryService/GetName"

<?xml version="1.0" encoding="utf-8"?> <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-

instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"

xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">

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<soap:Body> <GetName xmlns="http://localhost/ACoolQueryService/"> <id>string</id> </GetName> </soap:Body> </soap:Envelope>

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SOAP Response HTTP/1.1 200 OK Content-Type: text/xml; charset=utf-8 Content-Length: length <?xml version="1.0" encoding="utf-8"?> <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">

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<soap:Body> <GetNameResponse xmlns= "http://localhost/ACoolQueryService/"> <GetNameResult>string</GetNameResult> </GetNameResponse> </soap:Body></soap:Envelope>

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WSDL Structure

message operation(message)

message operation(message)

message operation(message)

typetype

{interface

• Operation names (method names)• Message types (parameters and return values)• Interfaces (groups of methods) are called ports• location of service

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Examine the WSDL

<?xml version="1.0" encoding="utf-8"?><definitions

xmlns:http="http://schemas.xmlsoap.org/wsdl/http/" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:s="http://www.w3.org/2001/XMLSchema" xmlns:s0="http://localhost/ACoolQueryService/" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:tm="http://microsoft.com/wsdl/mime/textMatching/" xmlns:mime="http://schemas.xmlsoap.org/wsdl/mime/" targetNamespace="http://localhost/ACoolQueryService/" xmlns="http://schemas.xmlsoap.org/wsdl/">

Namespaces disambiguate.

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<types>

<s:schema elementFormDefault="qualified" targetNamespace="http://localhost/ACoolQueryService/"> <s:element name="GetName"> <s:complexType> <s:sequence> <s:element minOccurs="0" maxOccurs="1" name="id" type="s:string" /> </s:sequence> </s:complexType> </s:element>

message type

<GetName>

<id> string</id>

</GetName

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<s:element name="GetNameResponse"> <s:complexType> <s:sequence> <s:element minOccurs="0" maxOccurs="1“ name="GetNameResult" type="s:string" /> </s:sequence> </s:complexType> </s:element> <s:element name="string" nillable="true" type="s:string" /> </s:schema> </types> Message type

<GetNameResponse> <GetNameResult>string</GetNameResult> </GetNameResponse>

Message type <string>string</string>

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<message name="GetNameSoapIn"> <part name="parameters" element="s0:GetName" /> </message> <message name="GetNameSoapOut"> <part name="parameters" element="s0:GetNameResponse" /> </message> <message name="GetNameHttpGetIn"> <part name="id" type="s:string" /> </message>

Message GetNameSoapIn : GetNameMessage GetNameSoapOut : GetNameResponseMessage GetNameHttpGetIn: { id : string}

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<message name="GetNameHttpGetOut"> <part name="Body" element="s0:string" /> </message> <message name="GetNameHttpPostIn"> <part name="id" type="s:string" /> </message> <message name="GetNameHttpPostOut"> <part name="Body" element="s0:string" /> </message>

Message GetNameHttpGetOut: { body : s0:string}Message GetNameHttpPostIn: { id : string}Message GetNameHttpPostOut: { body: s0string}

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<portType name="QueryServiceSoap"> <operation name="GetName"> <input message="s0:GetNameSoapIn" /> <output message="s0:GetNameSoapOut" /> </operation> </portType>

<portType name="QueryServiceHttpGet"> <operation name="GetName"> <input message="s0:GetNameHttpGetIn" /> <output message="s0:GetNameHttpGetOut" /> </operation> </portType>

Interface QueryServiceSoap So:GetNameSoapOut GetName(s0:GetNameSoapIn)Interface QueryServiceHttpGet S0:GetNameHttpGetOut GetName(s0:GetNameHttpGetIn)

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<portType name="QueryServiceHttpPost"> <operation name="GetName"> <input message="s0:GetNameHttpPostIn" /> <output message="s0:GetNameHttpPostOut" /> </operation> </portType>

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<binding name="QueryServiceSoap" type="s0:QueryServiceSoap"> <soap:binding transport="http://schemas.xmlsoap.org/soap/http" style="document" /> <operation name="GetName"> <soap:operation soapAction="http://localhost/ACoolQueryService/GetName" style="document" /> <input> <soap:body use="literal" /> </input> <output> <soap:body use="literal" /> </output> </operation> </binding>

Bind QueryServiceSOAP to the interface s0:QueryServiceSoapand describe how the data willlook on the wire

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<binding name="QueryServiceHttpGet" type="s0:QueryServiceHttpGet"> <http:binding verb="GET" /> <operation name="GetName"> <http:operation location="/GetName" /> <input> <http:urlEncoded /> </input> <output> <mime:mimeXml part="Body" /> </output> </operation> </binding>

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<binding name="QueryServiceHttpPost" type="s0:QueryServiceHttpPost"> <http:binding verb="POST" /> <operation name="GetName"> <http:operation location="/GetName" /> <input> <mime:content type="application/x-www-form-urlencoded" /> </input> <output> <mime:mimeXml part="Body" /> </output> </operation> </binding>

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<service name="QueryService"> <port name="QueryServiceSoap" binding="s0:QueryServiceSoap"> <soap:address location="http://localhost/ThreeStoogesTest/CoolService.asmx" /> </port> <port name="QueryServiceHttpGet" binding="s0:QueryServiceHttpGet"> <http:address location="http://localhost/ThreeStoogesTest/CoolService.asmx" /> </port> <port name="QueryServiceHttpPost" binding="s0:QueryServiceHttpPost"> <http:address location="http://localhost/ThreeStoogesTest/CoolService.asmx" /> </port> </service></definitions>

Provide addresses for each interface.

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Remoting Vs. Web Services

Characteristic .NET Remoting Web Services

Type system .NET Specific XML Schema

Client Platform .NET Any

Message Format

Binary, SOAP HTTP Post or Get Query strings or SOAP

Proxy building tool

Soapsuds.exe Wsdl.exe

Marshalling MBR or MBV MBV only

Interoperability No Yes