Motivation: the Distributed Software Crisis Symptoms Hardware gets smaller, cheaper faster, Software gets larger, slower, more expensive Culprits Acci

Transcription

1 Using the ACE Framework and Patterns to Develop OO Communication Software University, St. Louis Washington Sponsors DARPA, Bellcore, Boeing, CDI/GDIS, NSF, Kodak, Lockheed, Lucent, Microsoft, Motorola, OTI, SAIC, Siemens SCR, Siemens MED, Siemens ZT, Sprint

2 Motivation: the Distributed Software Crisis Symptoms Hardware gets smaller, cheaper faster, Software gets larger, slower, more expensive Culprits Accidental and inherent complexity Solutions Frameworks, components, and patterns Washington University, St. Louis 1

3 Frameworks Reusable, \semi-complete" Architecture Families of related patterns Distributed Object Computing Group for Improving Software Techniques and Productivity Quality Proven solutions Components Self-contained, \pluggable" ADTs applications Patterns Problem/solution pairs in a context and components Washington University, St. Louis 2

4 Distributed Object Computing Group Why We Need Communication Middleware System call-level programming is wrong abstraction for developers application Too low-level! error codes, endless reinvention Error-prone! HANDLEs lack type-safety, thread cancellation woes Mechanisms do not scale! Win32 TLS Steep learning curve! Win32 Named Pipes Non-portable! socket bugs Inecient! i.e., tedious for humans GUI frameworks are inadequate for communication software Inecient! excessive use of virtual methods Lack of features! minimal threading and synchronization no network services mechanisms, Washington University, St. Louis 3

5 The ADAPTIVE Communication Environment (ACE) ACE Overview A concurrent OO networking framework Available in C++ Java and Ported to POSIX, VxWorks, and Win32 Related work x-kernel SysV STREAMS Washington University, St. Louis 4

6 Distributed Object Computing Group ACE Statistics ACE contain > 135,000 lines of C++ Over 15 person-years of eort Ported to UNIX, Win32, MVS, and platforms embedded e.g., VxWorks, LynxOS, psos Large user community users.html Currently used by dozens companies of Bellcore, Boeing, Kodak, Ericsson, Lucent, Lockheed, SAIC, Motorola, Siemens, StorTek, etc. Supported commercially Washington University, St. Louis 5

7 unknown scientic from but from principles, to apply proven failing practices and engineering Distributed Object Computing Group Patterns for Communication Middleware Observation Failures rarely result patterns Benets of Patterns Facilitate design reuse Preserve crucial design information Guide design choices Washington University, St. Louis 6

8 Active Objects with ACE Tasks ACE Task Features Queueing Event demultiplexing Concurrency Dynamic linking Washington University, St. Louis 7

9 The ACE Stream Class Category ACE Stream Features Layered service composition Synchronous and messaging asynchronous Dynamic conguration Washington University, St. Louis 8

10 Alternative Concurrency Models Message-based Evaluation Low overhead Harder to program Task-based Features Higher overhead Easier to program Washington University, St. Louis 9

11 Use-cases for ACE Domains Medical imaging Network management Wireless communications Real-time avionics Multimedia services Washington University, St. Louis 10

12 DX IMAGE STORE Applying ACE to Medical Imaging Domain Challenges Large volume of \Blob" ATM LAN DIAGNOSTIC STATIONS data e.g., 10 to 40 Mbps ATM MAN ATM LAN CLUSTER IMAGE STORE \Lossy compression" viable isn't Prioritization of requests schmidt/coots-96.ps.gz schmidt/av.ps.gz MODALITIES (CT, MR, CR) CENTRAL IMAGE STORE Washington University, St. Louis 11

13 Domain Challenges Low latency Multi-platform Family of related services schmidt/dsej- 94.ps.gz Applying ACE to Network Management Washington University, St. Louis 12

14 Applying ACE to Global PCS Domain Challenges Long latency satellite links High reliability Prioritization schmidt/tapos-95.ps.gz Washington University, St. Louis 13

15 Consumers Applying ACE to Real-time Avionics I/O Facade I/O Facade I/O Facade Domain Challenges Real-time periodic 3: push (demarshaled data) processing Complex dependencies Event Channel Very low latency schmidt/jsac- 2: push (demarshaled data) Suppliers 98.ps.gz Sensor Proxy Sensor Proxy Sensor Proxy Sensor Proxy 1: I/O via interrupts Aircraft Sensors Washington University, St. Louis 14

16 schmidt/tao.html Distributed Object Computing Group TAO Overview High-performance, The ACE ORB (TAO) ORB real-time Networking and focus avionics Leverages ACE Runs on VxWorks, and Win32 POSIX, Washington University, St. Louis 15

17 JAWS Adaptive Web Server JAWS Overview A high-performance server Web Flexible and concurrency dispatching event mechanisms Full HTTP 1.0 and support CGI Leverages the ACE framework Ported to most OS platforms jxh/research/ Washington University, St. Louis 16

18 schmidt/jace.html schmidt/medjava.ps.gz Distributed Object Computing Group DISTRIBUTED SERVICES AND COMPONENTS TOKEN SERVER LOGGING SERVER NAME SERVER TIME SERVER Java ACE Java ACE Overview A version of ACE FRAMEWORKS AND CLASS CATEGORIES ACCEPTOR CONNECTOR SERVICE HANDLER ADAPTIVE SERVICE EXECUTIVE (ASX) in Java written Used for medical JAVA WRAPPERS SYNCH WRAPPERS SOCK_SAP THREAD MANAGER LOG MSG TIMER QUEUE SERVICE CONFIGURATOR JAVA VIRTUAL MACHINE (JVM) imaging prototype schmidt/c++2java.html Washington University, St. Louis 17

19 Distributed Object Computing Group Lessons Learned Building ACE Good components, frameworks, and software architectures take time to develop Reuse-in-the-large works best when: The marketplace is competitive The domain is complex Building middleware in-house costs too much Corporate culture is supportive Produce reusable components by generalizing from working applications i.e., don't build components in isolation The best components (and systems research) come from solving real problems Washington University, St. Louis 18

20 Distributed Object Computing Group Concluding Remarks Developers of communication software confront recurring challenges are largely application-independent that e.g., service initialization and distribution, error handling, ow event demultiplexing, concurrency control control, Successful developers resolve these challenges by applying appropriate patterns to create communication frameworks design Application frameworks are an eective way to achieve broad reuse of software Washington University, St. Louis 19

21 Distributed Object Computing Group Obtaining ACE ACE is an OO framework that reies key communication software patterns All source code for ACE is freely available Mailing lists Newsgroup comp.soft-sys.ace Washington University, St. Louis 20