Distributed Embedded Systems

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Distributed

Embedded Systems

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1. Motivation

2. An Overview of Distributed Software Architecture Approaches

2.1 Pro & Contra Middleware

2.2 Message-Based Architectures

2.3 Service-Based Architectures

2.4 Subscribe-Based Architectures

2.5 Component-Based Architectures

3. Inter-Process-Communication (IPC) in Unix

4. Example: MPI

5. Example: Web Services

6. Example: OPC UA

7. Critical Sections and Deadlocks

8. Example: DDS

9. Example: OSGi

10. Redundancy and Consistency

11. MultiCore Programming and Synchronous Languages

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Introduction

Web Services

Web services:

• service-based middleware optimized for the internet • flexible calling of remote services via the internet

• creation of complex applications by the composition of services

Internet Web Application Server UDDI Service Registry/Broker Client PC

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Introduction

Web Services

Using web services

Internet Web Application Server UDDI Service Registry/Broker Client PC 1: Send service description WSDL File 2: return service handle UDDI protocol 3: Send SOAP request SOAP XML 4: Send SOAP answer SOAP XML e.g. HTTP protocol

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UDDI

Web Services

Founded by IBM, Ariba, and Microsoft Service publishing and discovery

Based on other web service technologies:

HTTP, ftp, IIOP, etc. SOAP WSDL UDDI WSFL network protocol XM-based messaging service description service publishing & discovery service interactions

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UDDI

Web Services

Categorization of services using predefined taxonomies

UDDI defines the protocol used to communicate with a service registry/broker

UDDI messages are defined in XML, wrapped in a SOAP frame and send via HTTP

UDDI Service Registry/ Broker SW Companies, Standardization bodies, etc. 1: publish tModels Businesses 2: publish services 3: UDDI assigns a unique UUID to each

tModel and each service _{4: Applications} request the services

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UDDI

Web Services

The UDDI Service Registry/Broker uses a standardized data model to specify a registered service: 1. businessEntity:

• description of publishing party 2. businessService:

• service description 3. bindingTemplate:

• description of a service’s API

• used to access the service on a technical level 4. tModels:

• categories and taxonomies

• used by the other parts of the data model

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UDDI

Web Services

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UDDI Example 1

Web Services

<tModel xmlns="urn:uddi-org:api" tModelKey="UUID:AAAAAAAA-AAAA-AAAA-AAAA-AAAAAAAAAAAA">

<description xml:lang="en">Add the (sic) number</description> <overviewDoc> <overviewURL>http://schema.com/add42.wsdl</overviewURL> </overviewDoc> <categoryBag> <keyedReference tModelKey="UUID:CD253352-186B-4532-C53F-6BDAD766635" keyName="Number adding services"

keyValue="84.14.16.01.00"/> <keyedReference tModelKey="UUID:C1ACF26D-9672-4404-9D70-39B756E62AB4" keyName="types" keyValue="Nonsense sevices"/> </categoryBag> </tModel>

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UDDI Example 1

Web Services

<tModel xmlns="urn:uddi-org:api" tModelKey="UUID:AAAAAAAA-AAAA-AAAA-AAAA-AAAAAAAAAAAA">

<description xml:lang="en">Add the (sic) number</description> <overviewDoc> <overviewURL>http://schema.com/add42.wsdl</overviewURL> </overviewDoc> <categoryBag> <keyedReference tModelKey="UUID:CD253352-186B-4532-C53F-6BDAD766635" keyName="Number adding services"

keyValue="84.14.16.01.00"/> <keyedReference tModelKey="UUID:C1ACF26D-9672-4404-9D70-39B756E62AB4" keyName="types" keyValue="Nonsense sevices"/> </categoryBag> </tModel> The WSDL reference

The pointer to an element in a user-defined taxonomy

The pointer to an element in the "wsdlSpec" type in the uddi-org:types (UUID:C1ACF26D...)

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tModels

Web Services

Predefined taxonomies (tModels):

1. ISO 3166 Geographic Taxonomy: Geographical locations

2. Universal Standard Products and Services Classification (UNSPSC) <businessEntity businessKey=...

...

<!-- Categorize this businessEntity as serving California using the ISO 3166

taxonomy -->

<keyedReference keyName="Domestic Air Cargo Transport" keyValue="78.10.15.01.00"

tModelKey = "uuid:CD153257-086A-4237-B336-6BDCBDCC6634"/> </categoryBag>

...

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UDDI Example 1

Web Services

<businessService

businessKey="BBBBBBBB-BBBB-BBBB-BBBB-BBBBBBBBBBBB" serviceKey="CCCCCCCC-CCCC-CCCC-CCCC-CCCCCCCCCCCC"> <name>OWL Add 42 Instance</name>

<bindingTemplates> <bindingTemplate serviceKey="CCCCCCCC-CCCC-CCCC-CCCC-CCCCCCCCCCCC" bindingKey="DDDDDDDD-DDDD-DDDD-DDDD-DDDDDDDDDDDD"> <accessPoint URLType="https">https://hs-owl.de/add42</ accessPoint> <tModelInstanceDetails> <tModelInstanceInfo tModelKey="UUID:AAAAAAAA-AAAA-AAAA-AAAA-AAAAAAAAAAAA"/> <tModelInstanceDetails> </bindingTemplate> </bindingTemplates </businessService>

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Stub/Proxy/Skeleton Pattern

Web Services

Processor Communication System Middleware Communication Driver Processor Communication Driver Client Proxy Middleware Server Skeleton Dispatcher

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Stub/Proxy/Skeleton Pattern

Web Services

The client is just your everyday program; nothing related to distributed systems is used.

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Stub/Proxy/Skeleton Pattern

Web Services

The proxy replaces the server component the

client side. From the client point of view, the proxy is the the server component.

It(de-)serializes the method calls and object

accesses. It also translates between middleware API and proxy.

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Stub/Proxy/Skeleton Pattern

Web Services

The dispatcher chooses the right server components, i.e. its skeleton.

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Stub/Proxy/Skeleton Pattern

Web Services

The skeleton translates between server API and middleware. It also handles parallel accesses.

The skeleton (de-)serializes the method calls and object accesses.

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Stub/Proxy/Skeleton Pattern

Web Services

The server is just your everyday program; nothing related to distributed systems is used.

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Stub/Proxy/Skeleton Pattern

Web Services

Proxy and/or skeletons are often also called stubs.

The binding between client and server can either be static or dynamic:

Static binding means that the references between client and servers are statically defined at compile-time. Dynamic binding means that references are established at run-time via a broker/repository.

Distributed system may either use compile-time or run-time objects. Compile-time objects are instances of classes/ interfaces which have been defined at compile-time. Run-time objects are constructed at run-time via reflection mechanisms.

If distributed systems are cross-language (e.g. CORBA), object adapters are used to translate between the languages.

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Introduction

SOAP

Protocol for the exchange of structured data. Data is expressed in form of an XML document.

SOAP normally used TCP and HTTP/HTTPS as underlying protocols.

SOAP defines how data can be expressed and how remote calls are modeled History:

• Dave Winer and Microsoft developed 1998 XML-RPC • SOAP V1.0 1999

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Message Structure

SOAP

<?xml version="1.0"?> <s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope"> <s:Header> </s:Header> <s:Body> </s:Body> </s:Envelope>

Messages are transmitted in an “envelope”

The header comprises application-specific meta information about a message (transaction IDs, authentication, etc.).

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Message Structure

SOAP

Example: Ask a database if a specific wine is on storage

Request: Answer: <?xml version="1.0"?> <s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope"> <s:Body> <m:BottleInStorage xmlns:m="http://www.wine-store.de/soap"> Brunello di Montalcino </m: BottleInStorage> </s:Body> </s:Envelope> <?xml version="1.0"?> <s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope"> <s:Header>

<m:RequestID xmlns:m="http://www.wine-store.de/soap">c4f7d603e</m:RequestID> </s:Header>

<s:Body>

<m:DbResponse xmlns:m="http://www.wine-store.de/soap"> <m:title value="Brunello di Montalcino">

<m:Choice value="1">Il Poggione, 1998</m:Choice> <m:Choice value="2">Castello Banfi, 1999</m:Choice> </m:title>

</m:DbResponse> </s:Body>

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Introduction

WSDL

WSDL (Web Service Description Language) is an XML Schema to describe web services. WSDL V2.0 is a W3C recommendation

Structure of a WSDL 2.0 document:

1. Abstract Section: Meta-Level

1.1 Types (aka messages): Data Types described as an XML Schema 1.2 Interfaces (aka portType): Interfaces implemented by the services

1.2.1 Operation: Operations/methods including input and output parameters, parameters types are defined in 1.1

2. Concrete Section: Instance-Level

2.1 Binding: Interfaces from 1.2 used by the service, transport protocol 2.2 Service

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Example

WSDL

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Example

WSDL

<?xml version="1.0" encoding="UTF-8" standalone="no"?>

<wsdl:definitions xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:tns="http://

www.example.org/FindWine/" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/" xmlns:xsd="http:// www.w3.org/2001/XMLSchema" name="FindWine" targetNamespace="http://www.example.org/FindWine/"> <wsdl:types>

<xsd:schema targetNamespace="http://www.example.org/FindWine/"> <xsd:element name="findWine">

<xsd:complexType> <xsd:sequence>

<xsd:element name="in" type="xsd:string"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="findWineResponse"> <xsd:complexType> <xsd:sequence>

<xsd:element name="out" type="xsd:string"/> </xsd:sequence>

</xsd:complexType> </xsd:element>

<xsd:element name="findWine" type="xsd:string"></xsd:element> </xsd:schema>

</wsdl:types>

<wsdl:message name="findWineRequest">

<wsdl:part element="tns:findWine" name="parameters"/> </wsdl:message>

<wsdl:message name="findWineResponse">

<wsdl:part element="tns:findWineResponse" name="parameters"/> </wsdl:message>

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Example

WSDL

<wsdl:portType name="FindWine"> <wsdl:operation name="findWine"> <wsdl:input message="tns:findWineRequest"/> <wsdl:output message="tns:findWineResponse"/> </wsdl:operation> </wsdl:portType>

<wsdl:binding name="FindWineSOAP" type="tns:FindWine">

<soap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http"/> <wsdl:operation name="findWine"> <soap:operation soapAction="http://www.example.org/FindWine/findWine"/> <wsdl:input> <soap:body use="literal"/> </wsdl:input> <wsdl:output> <soap:body use="literal"/> </wsdl:output> </wsdl:operation> </wsdl:binding> <wsdl:service name="FindWine">

<wsdl:port binding="tns:FindWineSOAP" name="FindWineSOAP"> <soap:address location="http://www.example.org/"/>

</wsdl:port> </wsdl:service> </wsdl:definitions>

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SOAP & Eclipse

SOAP

Install Eclipse JEE Edition

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SOAP & Eclipse

SOAP

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SOAP & Eclipse

SOAP

Create WebServices for this class. Eclipse can do this by invoking the “WebService” context menu on the Java class.

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SOAP & Eclipse

SOAP

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SOAP & Eclipse

SOAP

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The generated server application knows about the mapping between our Java program and the service.

SOAP & Eclipse

SOAP

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For the generated client application, several java classes have been generated.

SOAP & Eclipse

SOAP

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General structure on the client side (simplified!):

SOAP & Eclipse

SOAP

Client Application AddClass Interface AddClassProxy implements uses AddClassServiceLocator

ask for SOAP dispatcher

AddClassSoapBindingStub

return handle to

AddClassSoapBindingStub uses

SOAP Middleware (Axis)

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Client application implemented in JavaServer Pages (JSP): Result.jsp

SOAP & Eclipse

SOAP

<jsp:useBean id="sampleAddClassProxyid" scope="session" class="DefaultNamespace.AddClassProxy" /> <%

if (request.getParameter("endpoint") != null && request.getParameter("endpoint").length() > 0) sampleAddClassProxyid.setEndpoint(request.getParameter("endpoint"));

%> ....

case 13:

gotMethod = true;

String x_1id= request.getParameter("x16"); int x_1idTemp = Integer.parseInt(x_1id);

int add_4213mtemp = sampleAddClassProxyid.add_42(x_1idTemp);

String tempResultreturnp14 = org.eclipse.jst.ws.util.JspUtils.markup(String.valueOf(add_4213mtemp)); %>

<%= tempResultreturnp14 %> <%

break;

Connect to Java class

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AddClass.java:

SOAP & Eclipse

SOAP

/**

* AddClass.java *

* This file was auto-generated from WSDL

* by the Apache Axis 1.4 Apr 22, 2006 (06:55:48 PDT) WSDL2Java emitter. */

package DefaultNamespace;

public interface AddClass extends java.rmi.Remote {

public int add_42(int x) throws java.rmi.RemoteException; }

Our server class is now an interface on the client side.

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AddClassProxy.java: Proxy Class

SOAP & Eclipse

SOAP

public class AddClassProxy implements DefaultNamespace.AddClass { private DefaultNamespace.AddClass addClass = null;

...

private void _initAddClassProxy() { try {

addClass = (new DefaultNamespace.AddClassServiceLocator()).getAddClass(); if (addClass != null) { if (_endpoint != null) ((javax.xml.rpc.Stub)addClass)._setProperty("javax.xml.rpc.service.endpoint.address", _endpoint); else _endpoint = (String)((javax.xml.rpc.Stub)addClass)._getProperty("javax.xml.rpc.service.endpoint.address"); } }

catch (javax.xml.rpc.ServiceException serviceException) {} }

...

public int add_42(int x) throws java.rmi.RemoteException{ if (addClass == null)

_initAddClassProxy();

return addClass.add_42(x); }}

This class implements the interface, it is the proxy for the server class on the client side.

Get SOAP stub class.

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public class AddClassServiceLocator extends org.apache.axis.client.Service implements DefaultNamespace.AddClassService {

...

// Use to get a proxy class for AddClass

private java.lang.String AddClass_address =

"http://localhost:8080/WebServiceProject/services/AddClass";

public java.lang.String getAddClassAddress() { return AddClass_address;

}

// The WSDD service name defaults to the port name.

private java.lang.String AddClassWSDDServiceName = "AddClass";

SOAP & Eclipse

SOAP

AddClassServiceLocator.java: SOAP-specific dispatcher class

The URI

Service Name

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SOAP & Eclipse

SOAP

AddClassServiceLocator.java

public DefaultNamespace.AddClass getAddClass() throws javax.xml.rpc.ServiceException { java.net.URL endpoint;

try {

endpoint = new java.net.URL(AddClass_address); }

catch (java.net.MalformedURLException e) {

throw new javax.xml.rpc.ServiceException(e); }

return getAddClass(endpoint); }

public DefaultNamespace.AddClass getAddClass(java.net.URL portAddress) throws javax.xml.rpc.ServiceException {

try {

DefaultNamespace.AddClassSoapBindingStub _stub = new

DefaultNamespace.AddClassSoapBindingStub(portAddress, this); _stub.setPortName(getAddClassWSDDServiceName()); return _stub; } catch (org.apache.axis.AxisFault e) { return null; } }

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SOAP & Eclipse

SOAP

AddClassSoapBindingStub.java

public int add_42(int x) throws java.rmi.RemoteException { ...

org.apache.axis.client.Call _call = createCall(); _call.setOperation(_operations[0]);

_call.setUseSOAPAction(true); _call.setSOAPActionURI(""); _call.setEncodingStyle(null);

_call.setProperty(org.apache.axis.client.Call.SEND_TYPE_ATTR, Boolean.FALSE); _call.setProperty(org.apache.axis.AxisEngine.PROP_DOMULTIREFS, Boolean.FALSE); _call.setSOAPVersion(org.apache.axis.soap.SOAPConstants.SOAP11_CONSTANTS);

_call.setOperationName(new javax.xml.namespace.QName("http://DefaultNamespace", "add_42"));

setRequestHeaders(_call); setAttachments(_call);

try { java.lang.Object _resp =

_call.invoke(new java.lang.Object[]{new java.lang.Integer(x)}); if (_resp instanceof java.rmi.RemoteException) {

throw (java.rmi.RemoteException)_resp; } else {

extractAttachments(_call); try {

return ((java.lang.Integer) _resp).intValue(); } catch (java.lang.Exception _exception) {

return ((java.lang.Integer) org.apache.axis.utils.JavaUtils.convert(_resp, int.class)).intValue(); Dispatcher for method