DOCSLIB.ORG

Acceptor-Connector an Object Creational Pattern for Connecting and Initializing Communication Services

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Acceptor-Connector an Object Creational Pattern for Connecting and Initializing Communication Services Acceptor-Connector An Object Creational Pattern for Connecting and Initializing Communication Services Douglas C. Schmidt [email protected] Department of Computer Science Washington University St. Louis, MO 63130, USA An earlier version of this paper appeared in a chapter in TRACKING the book Pattern Languages of Program Design 3, edited SATELLITES STATION by Robert Martin, Frank Buschmann, and Dirke Riehle pub- PEERS lished by Addison-Wesley, 1997. 1Intent STATUS INFO The Acceptor-Connector design pattern decouples connec- WIDE AREA NETWORK tion establishment and service initialization in a distributed COMMANDS BULK DATA system from the processing performed once a service is ini- TRANSFER tialized. This decoupling is achieved with three compo- nents: acceptors, connectors,andservice handlers. A con- GATEWAY nector actively establishes a connection with a remote ac- ceptor component and initializes a service handler to pro- cess data exchanged on the connection. Likewise, an ac- LOCAL AREA NETWORK ceptor passively waits for connection requests from remote GROUND connectors, establishing a connection upon arrival of such a STATION PEERS request, and initializing a service handler to process data ex- changed on the connection. The initialized service handlers Figure 1: The Physical Architecture of a Connection- then perform application-specific processing and communi- oriented Application-level Gateway cate via the connection established by the connector and ac- ceptor components. The Gateway transmits data between its Peers using the connection-oriented TCP/IP protocol [1]. In our exam- 2 Example ple network configuration, each service is bound to a con- nection endpoint designated by an IP host address and a TCP To illustrate the Acceptor-Connector pattern, consider the port number. The port number uniquely identifies the type of multi-service, application-level Gateway shown in Fig- service. Maintaining separate connections for each type of ure 1. In general, a Gateway decouples cooperating com- service/port increases the flexibility of routing strategies and ponents in a distributed system and allows them to interact provides more robust error handling if network connections without having direct dependencies on each other. The par- shutdown unexpectedly. ticular Gateway in Figure 1 routes data between different In our distributed application, Gateway and Peers must service endpoints running on remote Peers used to mon- be able to change their connection roles to support different itor and control a satellite constellation. Each service in use-cases. In particular, either may initiate a connection ac- the Peers sends and receives several types of data via the tively or may wait passively for connection requests. For Gateway, such as status information, bulk data, and com- example, in one configuration, the Gateway may actively mands. In general, Peers can be distributed throughout lo- initiate connections to remote Peers in order to route data cal area networks (LANs) and wide-area networks (WANs). to them. In another configuration, the Gateway may pas- The Gateway is a router that coordinates the communi- sively receive connection requests from Peers which then cation among its PeersFrom˙ the Gateway’s perspective, route data through the Gateway to another Peer.Like- the Peer services whose data it routes differ solely in terms wise, Peers may be active connection initiators in one use- of their application-level communication protocols, which case and then be passive connection acceptors in another use- may use different framing formats and payload types. case. 1 Due to the nature of our distributed application, con- may be necessary to extend the Gateway to interoper- ventional designs that designate connection establishment ate with a directory service that runs over the IPX/SPX and service initialization roles a priori and hard-code them communication protocol, rather than TCP/IP.. into the Gateway and Peer components are too inflexi- It should be possible to decouple (1) the connection ble. Such a design overly couples the connection establish- roles, i.e., which process initiates a connection vs. ac- ment, service initialization, and service processing compo- cepts the connection, from (2) the communication roles, nents. This tight coupling make it hard to change connection i.e., which service endpoint is the client or the server. In roles independently of the communication roles. general, the distinction between “client” and “server” refer to communication roles, which may be orthogo- 3 Context nal to connection roles. For instance, clients often play the active role when initiating connections with a pas- A client/server application in a distributed system that uti- sive server. However, these connection roles can be re- lizes connection-oriented protocols to communicate between versed. For example, a client that plays an active com- service endpoints. munication role may wait passively for another process to connect to it. The example in Section 2 illustrates this latter use-case. 4Problem It should be possible to write communication software that is portable to many OS platforms in order to max- Distributed applications often contain complex code that per- imize availability and market share. Many low-level forms connection establishment and service initialization. In network programming APIs have semantics that are general, the processing of data exchanged between service only superficially different. Therefore, it hard to write endpoints in a distributed application is largely independent portable application using low-level APIs, such as sock- of configuration issues such as (1) which endpoint initiated ets and TLI, due to syntactic incompatibilities. the connection, i.e.,theconnection role vs. the communca- tion role and (2) the connection management protocol vs. the It should be possible to shield programmers from the network programming API. These issues are outlined below: lack of typesafety in low-level network programming APIs like sockets or TLI. For example, connection es- Connection role vs. communication role: Connection establishment roles are inherently asymmetrical, i.e., the pas- tablishment code should be completely decoupled from sive service endpoint waits and the active service endpoint subsequent data transport code to ensure that endpoints initiates the connection. Once the connection is established, are used correctly. Without this strong decoupling, for however, the communication role can be orthogonal to the instance, services may mistakenly read or write data on connection role. Thus, data can be transferred between ser- passive-mode transport endpoint factories that should vice endpoints in any manner that obeys the service’s com- only be used to accept connections. munication protocol. Common communication protocols in- It should be possible to reduce connection latency by clude peer-to-peer, request-response, and oneway streaming. using OS features like asynchronous connection es- tablishment. For instance, applications with a large The connection management protocol vs. the network programming API: Different network programming in- number of peers may need to asynchronously establish terfaces, such as sockets or TLI, provide different APIs to many connections concurrently. Efficient and scalable establish connections using various connection management connection establishment is particularly important for protocols. Regardless of the protocol used to establish a con- applications that run over long-latency WANs. nection, however, data can be transferred between endpoints It should be possible to reuse as much general-purpose using uniform message passing operations, e.g., send/recv connection establishment and service initialization soft- calls. ware as possible in order to leverage prior development In general, the strategies for connection establishment and effort. service initialization change much less frequently than ap- plication service implementations and communication pro- tocols. Thus, decoupling these aspects so that they can vary 5 Solution independently is essential for developing and maintaining distributed applications. The following forces impact the so- For each service offered by a distributed application, use the lution to the problem of separating the connection and ini- Acceptor-Connector pattern to decouple connection estab- tialization protocols from the communication protocol: lishment and service initialization from subsequent process- ing performed by the two endpoints of a service once they It should be easy to add new types of services, new ser- are connected and initialized. vice implementations, and new communication proto- Introduce two factories that produce connected and ini- cols without affecting the existing connection establish- tialized service handlers, which implement the application ment and service initialization software. For instance, it services. The first factory, called acceptor, creates and ini- 2 Service Handler Service Service Handler Connector Handler ACTIVATES Acceptor connect(sh, addr) n 1 peer_acceptor_ ACTIVATES peer_stream_ complete() open() accept() 1 n open() NOTIFY WHEN NOTIFY WHEN CONNECTION COMPLETES CONNECTION ARRIVES Dispatcher Figure 2: Structure of Participants in the Acceptor-Connector Pattern tializes a transport endpoint that passively listens at a par- Handler and uses its transport endpoint factory to accept a ticular address for connection requests from remote connec- new connection into the Service Handler.
Load more

Recommended publications
  • Design Pattern Interview Questions
    DDEESSIIGGNN PPAATTTTEERRNN -- IINNTTEERRVVIIEEWW QQUUEESSTTIIOONNSS http://www.tutorialspoint.com/design_pattern/design_pattern_interview_questions.htm Copyright © tutorialspoint.com Dear readers, these Design Pattern Interview Questions have been designed specially to get you acquainted with the nature of questions you may encounter during your interview for the subject of Design Pattern. As per my experience good interviewers hardly plan to ask any particular question during your interview, normally questions start with some basic concept of the subject and later they continue based on further discussion and what you answer: What are Design Patterns? Design patterns represent the best practices used by experienced object-oriented software developers. Design patterns are solutions to general problems that software developers faced during software development. These solutions were obtained by trial and error by numerous software developers over quite a substantial period of time. What is Gang of Four GOF? In 1994, four authors Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides published a book titled Design Patterns - Elements of Reusable Object-Oriented Software which initiated the concept of Design Pattern in Software development. These authors are collectively known as Gang of Four GOF. Name types of Design Patterns? Design patterns can be classified in three categories: Creational, Structural and Behavioral patterns. Creational Patterns - These design patterns provide a way to create objects while hiding the creation logic, rather than instantiating objects directly using new opreator. This gives program more flexibility in deciding which objects need to be created for a given use case. Structural Patterns - These design patterns concern class and object composition. Concept of inheritance is used to compose interfaces and define ways to compose objects to obtain new functionalities.
    [Show full text]
  • Learning Javascript Design Patterns
    Learning JavaScript Design Patterns Addy Osmani Beijing • Cambridge • Farnham • Köln • Sebastopol • Tokyo Learning JavaScript Design Patterns by Addy Osmani Copyright © 2012 Addy Osmani. All rights reserved. Revision History for the : 2012-05-01 Early release revision 1 See http://oreilly.com/catalog/errata.csp?isbn=9781449331818 for release details. ISBN: 978-1-449-33181-8 1335906805 Table of Contents Preface ..................................................................... ix 1. Introduction ........................................................... 1 2. What is a Pattern? ...................................................... 3 We already use patterns everyday 4 3. 'Pattern'-ity Testing, Proto-Patterns & The Rule Of Three ...................... 7 4. The Structure Of A Design Pattern ......................................... 9 5. Writing Design Patterns ................................................. 11 6. Anti-Patterns ......................................................... 13 7. Categories Of Design Pattern ............................................ 15 Creational Design Patterns 15 Structural Design Patterns 16 Behavioral Design Patterns 16 8. Design Pattern Categorization ........................................... 17 A brief note on classes 17 9. JavaScript Design Patterns .............................................. 21 The Creational Pattern 22 The Constructor Pattern 23 Basic Constructors 23 Constructors With Prototypes 24 The Singleton Pattern 24 The Module Pattern 27 iii Modules 27 Object Literals 27 The Module Pattern
    [Show full text]
  • Creational Patterns
    9. Creational Pattern Venkat Subramaniam CDP-1 Creational Patterns • Abstracts instantiation process • Makes system independent of how its objects are œ created œ composed œ represented • Encapsulates knowledge about which concrete classes the system uses • Hides how instances of these classes are created and put together Venkat Subramaniam CDP-2 Abstract Factory Provide an interface for creating families of related or dependent objects without specifying their concrete classes Venkat Subramaniam CDP-3 Example that would benefit from Abstract Factory ComputerModelA MemoryType A CPUTypeA ModemTypeA BuildComputer(ComputerModelA& comp) { comp.Add(new MemoryTypeA); comp.Add(new CPUTypeA); comp.Add(new ModemTypeA); } What if I want to build a Computer of Model B with Model B Memory,CPU and Modem? Venkat Subramaniam CDP-4 Using Abstract Factory ComputerFactory Client Computer createComputer() createMemory() createCPU() Computer Computer createModem() ModelA ModelB Memory CompFactoryB CompFactoryA createComputer() createComputer() Memory Memory createMemory() createMemory() ModelA ModelB createCPU() createCPU() createModem() createModem() Venkat Subramaniam CDP-5 Using Abstract Factory... BuildComputer(Computer& comp, ComputerFactory& compFactory) { comp.Add(compFactory.createMemory()) ; comp.Add(compFactory.createCPU()); comp.Add(compFactory.createModem()); } Venkat Subramaniam CDP-6 .hen to use Abstract Factory? • Use Abstract Factory when: œ system should be independent of how its products are created, composed and represented œ system should
    [Show full text]
  • Java Design Patterns I
    Java Design Patterns i Java Design Patterns Java Design Patterns ii Contents 1 Introduction to Design Patterns 1 1.1 Introduction......................................................1 1.2 What are Design Patterns...............................................1 1.3 Why use them.....................................................2 1.4 How to select and use one...............................................2 1.5 Categorization of patterns...............................................3 1.5.1 Creational patterns..............................................3 1.5.2 Structural patterns..............................................3 1.5.3 Behavior patterns...............................................3 2 Adapter Design Pattern 5 2.1 Adapter Pattern....................................................5 2.2 An Adapter to rescue.................................................6 2.3 Solution to the problem................................................7 2.4 Class Adapter..................................................... 11 2.5 When to use Adapter Pattern............................................. 12 2.6 Download the Source Code.............................................. 12 3 Facade Design Pattern 13 3.1 Introduction...................................................... 13 3.2 What is the Facade Pattern.............................................. 13 3.3 Solution to the problem................................................ 14 3.4 Use of the Facade Pattern............................................... 16 3.5 Download the Source Code.............................................
    [Show full text]
  • Design Patterns Chapter 3
    A Brief Introduction to Design Patterns Jerod Weinman Department of Computer Science Grinnell College [email protected] Contents 1 Introduction 2 2 Creational Design Patterns 4 2.1 Introduction ...................................... 4 2.2 Factory ........................................ 4 2.3 Abstract Factory .................................... 5 2.4 Singleton ....................................... 8 2.5 Builder ........................................ 8 3 Structural Design Patterns 10 3.1 Introduction ...................................... 10 3.2 Adapter Pattern .................................... 10 3.3 Façade ......................................... 11 3.4 Flyweight ....................................... 12 3.5 Proxy ......................................... 13 3.6 Decorator ....................................... 14 4 Behavioral Design Patterns 20 4.1 Introduction ...................................... 20 4.2 Chain of Responsibility ................................ 20 4.3 Observer ........................................ 20 4.4 Visitor ......................................... 22 4.5 State .......................................... 25 1 Chapter 1 Introduction As you have probably experienced by now, writing correct computer programs can sometimes be quite a challenge. Writing the programs is fairly easy, it can be the “correct” part that maybe is a bit hard. One of the prime culprits is the challenge in understanding a great number of complex interactions. We all have probably experienced the crash of some application program
    [Show full text]
  • A Study of Patterns in an ATC System
    Department of Mathematics, Statistics and Computer Science Reports from MASDA - Rapporter från MASDA A Study of Patterns in an ATC System Mattias Blåman Robert Pratz Aug MASDA Report 9984 1999 Växjö University ISSN 1400-1942 S-351 95 VÄXJÖ ISRN VXU/MASDA/DA/E/--9984--SE Abstract The differences between an experienced software developer and a novice are knowledge and experience. There has always been a need for an effective way of passing along the knowledge and experiences of senior software developers to novices. A remedy to this problem lies in the use of patterns. Patterns help software developers build systems on the collective experience of expert software developers. Patterns encapsulate well-proven design solutions in software development in a reusable way and help to promote good design practice. Patterns distill and provide a means to reuse the design knowledge gained by experienced software developers. The importance and extent of software in defense systems constantly increases. FMV, the Swedish Defense Material Administration, has an interest in decreasing the costs of software system development and saving time and money. An attempt to achieve this is to introduce the use of patterns in the associated software development organizations. As an initial step in this project, FMV is examining a number of existing defense systems developed by different suppliers. One of these suppliers is Enator Telub AB in Växjö, which has developed the ATC (Air Traffic Control) system SIGMA/AMP. In this master thesis, we examine the SIGMA/AMP system to investigate whether patterns have been used during the development work or not.
    [Show full text]
  • Digital Notes on Design Patterns (R15a0528)
    DIGITAL NOTES ON DESIGN PATTERNS (R15A0528) B.TECH IV YEAR - I SEM (2019-20) DEPARTMENT OF INFORMATION TECHNOLOGY MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) (Affiliated to JNTUH, Hyderabad, Approved by AICTE - Accredited by NBA & NAAC – ‘A’ Grade - ISO 9001:2015 Certified) Maisammaguda, Dhulapally (Post Via. Hakimpet), Secunderabad – 500100, Telangana State, INDIA. Design Patterns Page 1 MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY DEPARTMENT OF INFORMATION TECHNOLOGY IV Year B.Tech IT – I Sem L T /P/D C 4 - / - / - 3 (R15A0528) DESIGN PATTERNS (Elective IV) OBJECTIVES: 1. Design patterns are a systematic approach that focus and describe abstract systems of interaction between classes, objects, and communication flow 2. Given OO design heuristics, patterns or published guidance, evaluate a design for applicability, reasonableness, and relation to other design criteria. 3. Comprehend the nature of design patterns by understanding a small number of examples from different pattern categories, and to be able to apply these patterns in creating an OO design. 4. Good knowledge on the documentation effort required for designing the patterns. UNIT I: Introduction: What Is a Design Pattern? Design Patterns in Smalltalk MVC, Describing Design Patterns, The Catalog of Design Patterns, Organizing the Catalog, How Design Patterns Solve Design Problems, How to Select a Design Pattern, How to Use a Design Pattern. UNIT II: A Case Study: Designing a Document Editor: Design Problems, Document Structure, Formatting, Embellishing the User Interface, and Supporting Multiple Look – and - Feel Standards, Supporting Multiple Window Systems, User Operations Spelling Checking and Hyphenation, Summary. UNIT III: Creational Patterns: Abstract Factory, Builder, Factory Method, Prototype, Singleton, Discussion of Creational Patterns.
    [Show full text]
  • Chap 5. Patterns
    Chap 5. Patterns 1. Introduction 2. Pattern Description and Application 3. Design Patterns 4. Architectural Patterns 5. Appendix: Other Patterns 1 1. Introduction Motivating Example Problem: You are building a quote application, which contains a class that is responsible for managing all of the quotes in the system. It is important that all quotes interact with one and only one instance of this class. How do you structure your design so that only one instance of this class is accessible within the application? Simple solution: ÷Create a QuoteManager class with a private constructor so that no other class can instantiate it. ÷This class contains a static instance of QuoteManager that is returned with a static method named GetInstance(). public class QuoteManager { //NOTE: For single threaded applications only private static QuoteManager _Instance = null; private QuoteManager() {} public static QuoteManager GetInstance() { if (_Instance==null) { _Instance = new QuoteManager (); } return _Instance; Recurring problems like this kind have } been observed by experienced developers //... functions provided by QuoteManager and a common solution has been distilled,2 } as the Singleton pattern. Pattern Overview - A classical engineering rule of thumb consists of reusing extensively available knowledge base for any kind of problem solving that occurs during system design. Method ÷ When the knowledge doesn't exist for the problem at hand,Theft Intuition then intuition takes the lead. ÷ Architectural styles or patterns define experience-based classes of designs along with their known characteristics. Classical system Method Theft Intuition - A pattern is a solution to a problem in a context •A pattern codifies specific knowledge collected from experience in a domain Unprecedented system •There are three kinds of patterns –Idioms: provide a solution for specific programming issues in given language.
    [Show full text]
  • Proceedings Template
    Supporting the Evolution of Service Oriented Web Applications using Design Patterns Manolis Tzagarakis Michalis Vaitis Nikos Karousos Computer Technology Institute University of the Aegean University of Patras 26500 Rion University Hill, GR-811 00 Mytilene 26500 Rion Greece Greece Greece +30 2610 960482 +30 22510 36433 +30 2610 960482 [email protected] [email protected] [email protected] ABSTRACT "Web systems that are kept running via continual stream of Web applications make increasingly use of services that are Patches or upgrades developed without systematic approaches” provided by external information systems to deliver advanced The problems are even more complicated, when web applications functionalities to end users. However, many issues regarding how are built upon service oriented architectures (SOA) that differ these services are integrated into web applications and how greatly fom traditional client server architectures. SOA exhibit service oriented web applications evolve, are reengineered and great flexibility with respect to services and require new refactored are still addressed in an ad hoc manner. In this paper, approaches to service integration. Within the hypermedia field, we present how design patterns can lessen the efforts required to Component-Based Hypermedia Systems (CB-OHS)[15] have integrate hypermedia services into web applications. In particular emerged, consisting of an underlying set of infrastructure services we present how evolution and maintenance issues are addressed that support the development and operation of an open set of within Callimachus, a CB-OHS that web applications need to components (called structure servers), providing structure services integrate in order to provide hypertext functionality to end users. for specific application domains.
    [Show full text]
  • Unit-Iii Pattern
    SOFTWARE ARCHITECTURE AND DESIGN PATTERN UNIT-III PATTERN: PATTERN DESCRIPTION Software patterns are reusable solutions to recurring problems that occur during software development. In general, a pattern has four essential elements: The pattern name is a handle we can use to describe a design problem, its solutions,andconsequencesinawordortwo.Namingapatternimmediatelyincreasesour designvocabulary.Itletsusdesignatahigherlevelofabstraction.Havingavocabularyfor patterns lets us talk about them with our colleagues, in our documentation, and even to ourselves.Itmakesiteasiertothinkaboutdesignsandtocommunicatethemandtheirtrade- offs to others. Finding good names has been one of the hardest parts of developing our catalog. Theproblem describes when to apply the pattern. It explains the problem and its context. It mightdescribespecificdesignproblemssuchashowtorepresentalgorithmsasobjects.It mightdescribeclassorobjectstructuresthataresymptomaticofaninflexibledesign. Sometimestheproblemwillincludealistofconditionsthatmustbemetbeforeitmakes sensetoapplythepattern. The solution describes the elements that make up the design, their relationships, responsibilities,andcollaborations.Thesolutiondoesn'tdescribeaparticularconcretedesign orimplementation,becauseapatternislikeatemplatethatcanbeappliedinmanydifferent situations.Instead,thepatternprovidesanabstractdescriptionofadesignproblemandhow ageneralarrangementofelements(classesandobjectsinourcase)solvesit. The consequences are the results and trade-offs of applying the pattern .Though consequences are
    [Show full text]
  • Factory Method Design Pattern Real World Example
    Factory Method Design Pattern Real World Example Preponderating and tasty Tyson wallpapers his calvities precools bratticed preposterously. Shannan is fixative: she unplait Jewishly and exploiter her quarrians. Startling Lucian overlooks or misuse some sabotages individualistically, however parentless Parrnell breveting humanly or silenced. Abhishek is not parameterized. The Factory Method defines an interface for creating objects but lets. Let's why how appropriate use the Abstract Factory hand to design this kind of system. Design Patterns for Humans Developer Roadmaps. ValueOf method is good praise which caches true whereas false boolean value. So cannot have to design in an a serve to reuse the Director to create rather complex objects I wait looking foe a practical example to mint this. The child class method's can facilitate different implementation depends on the. Factory Design Pattern in Java JournalDev. Abstract factory inside a creational design pattern which allows us to. Its methods to real world example of this method is a number of your post dedicated class at hand, how to add new values that? Factory method but you might believe because in real world examples and an earlier saved state and java is considered good examples to be in a lot. Design Patterns The pickle Factory Pattern. Simple factory and turn responsible to real factory world pattern example, you can apply the target class with composition over toppings array to! Finally we have just made my factory is that you, these techniques like you know about capturing and type of such a product type. Diagrams applicable scenarios java example showing usage of javautil.
    [Show full text]
  • Security Patterns
    Security Patterns Ronald Wassermann and Betty H.C. Cheng¤ Software Engineering and Network Systems Laboratory Department of Computer Science and Engineering Michigan State University East Lansing, Michigan 48824, USA Email: fwasser17,[email protected] Abstract Design patterns propose generic solutions to recurring design problems. Commonly, they present a solution in a well-structured form that facilitates its reuse in a di®erent context. Re- cently, there has been growing interest in identifying pattern-based designs for the domain of system security termed Security Patterns. Currently, those patterns lack comprehensive struc- ture that conveys essential information inherent to security engineering. This paper describes research into investigating an appropriate template for Security Patterns that is tailored to meet the needs of secure system development. In order to maximize comprehensibility, we make use of well-known notations such as the Uni¯ed Modeling Language (UML) to represent structural and behavioral aspects of design. Furthermore, we investigate how veri¯cation can be enabled by adding formal constraints to the patterns. ¤Please contact B. Cheng for all correspondences. i Contents 1 Introduction 1 2 Background 2 2.1 Viega's and McGraw's ten principles . 2 2.1.1 Principle 1: Secure the weakest link. 3 2.1.2 Principle 2: Practice defense in depth. 3 2.1.3 Principle 3: Fail securely. 3 2.1.4 Principle 4: Follow the principle of least privilege. 4 2.1.5 Principle 5: Compartmentalize. 4 2.1.6 Principle 6: Keep it simple. 4 2.1.7 Principle 7: Promote privacy. 5 2.1.8 Principle 8: Remember that hiding secrets is hard.
    [Show full text]