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1. Introduction 2 September 02

1. Introduction 2 September 02. Writing “Hello World”. Written by a CS 100 programmer: print “Hello world!”. By a CS 211 programmer: public class Hello { static void main (String[] argv) { System.out.println(“Hello world!”); } }. Written by an expert:. …

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1. Introduction 2 September 02

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  1. 1. Introduction 2 September 02

  2. Writing “Hello World” • Written by a CS 100 programmer: print “Hello world!” • By a CS 211 programmer: • public class Hello { • static void main (String[] argv) { • System.out.println(“Hello world!”); • } • }

  3. Written by an expert: … int _cdecl main(int argc, char * argv[]) { ULONG ulRef; DWORD dwRegistration; CHelloCF *pCF = new CHelloCF(); hEvent = CreateEvent(NULL, FALSE, FALSE, NULL); // Initialize the OLE libraries CoInitializeEx(NULL, COINIT_MULTITHREADED); CoRegisterClassObject(CLSID_CHello, pCF, CLSCTX_LOCAL_SERVER, REGCLS_MULTIPLEUSE, &dwRegistration); // wait on an event to stop WaitForSingleObject(hEvent, INFINITE); // revoke and release the class object CoRevokeClassObject(dwRegistration); ulRef = pCF-Release(); // Tell OLE we are going away. CoUninitialize(); return(0); } … [ uuid(2573F8F4-CFEE-101A-9A9F-00AA00342820) ] library LHello { // bring in the master library importlib("actimp.tlb"); importlib("actexp.tlb"); // bring in my interfaces #include "pshlo.idl" [ uuid(2573F8F5-CFEE-101A-9A9F-00AA00342820) ] cotype THello { interface IHello; interface IPersistFile; }; }; [ exe, uuid(2573F890-CFEE-101A-9A9F-00AA00342820) ]

  4. Perils of writing software • After 30+ years of research and engineering, have to know too much! • Protocols • OLE, COM, Corba, RMI, IP, DNS, TCP, HTTP, Corba, JavaBeans, ‘serialization’… • Languages • Java, C, Perl, sh, Javascript, Visual Basic, make, C++, HTML, XML… • Library/OS interfaces • Unix, X Windows, AWT, Swing, WINNT, …

  5. Problems Stuff CS 211 doesn’t have to deal with: • Concurrency • Reliability • Security • Persistence • Extensibility • Interoperability • Scale and complexity • Configuration management Distribution

  6. Does it have to be this bad? • Lots of (visible) stuff underneath (and above!) your code • Every layer has itsown semantics IDE autoconf Ant/make CVS m4 Application code sh “look-and-feel” lib XML UI base RMI HTTP Serialization JIT compiler Reflection window system file system virtual mem TCP/IP stack m-kernel OS

  7. Cost • Cost of computing systems is: • software development • customization to local environment • training • maintenance • Not: • hardware • The (single-machine) performance problem is solved

  8. Language-based solution • Idea: program in a language expressive enough to hide most of the cruft • existing layer semantics can be embedded in language, made less onerous • Advantages: • Programmers learn one language • Power: some features (e.g., transparent persistence) impossible to provide through procedural interface • Domain-specific languages

  9. Transparency • End-user is given increasingly transparent interface • web sites transparently distributed • files transparently distributed • documents mapped onto file system • differences between content hidden (web pages, files) • content seamlessly encapsulated • Programmers need transparency too • Simple programming model, sophisticated implementation • But what to expose?

  10. An attempt: Java • Some support for concurrency, distribution, security, extensibility • Doesn’t address: reliability, persistence, scale, resource management • Visual Basic, Javascript…

  11. Security • Access control provided by OS (NT) or language (Java) • Language-based: application-specific access rights • Security = data confidentiality, integrity • (D)AC doesn’t enforce system-wide security • access but not propagation • No simple way to validate AC settings • Must prevent improper information flow

  12. Static information flow • Information flows in program analyzed statically • Programs that might violate security are rejected at compile time • Lots of unsolved problems : concurrency, distribution, covert channels, dynamic security policies [Sabelfeld and Myers]

  13. Persistence • What is the right programming (& data) model for accessing persistent data? • Usual persistent data formats don’t look much like popular programming language models of data! • No pointers or object identity, weak referential integrity, no garbage collection, weak or absent types • Considered important for writing correct programs…only needed for volatile data?

  14. Transparent Persistence? • Want safe, fine-grained data sharing across applications, network • Orthogonal persistence: objects transparently persistent or volatile • System makes persistent objects arrive in memory when needed • Result: simpler programming; more robust code; better performance! • Problems: data evolution, software upgrades, distributed computing

  15. Distributed computing • Correct concurrent programs are hard • Distribution is harder: failure-prone components, high-latency communication • Need failure-tolerant programs • automatic failure recovery

  16. Distributed performance • Function shipping: data has home computer, computation moves to data • Data shipping: data moves to host computer • Transfer data or control? Both! • Function shipping (RMI) is good when data is large, bad when control flow is complex (overhead, fragility) • Data shipping good when computation is complex • Can we figure it out automatically?

  17. Consistency/isolation models • Distributed computation: good performance requires caching, else 10’s of ms access time • Caching  stale data  inconsistency • Programmer needs isolation model to write code that works in face of update • Expose transactions in the programming model? • Weak or strong consistency model? • Explicit versioning?

  18. Extensibility • High software development, customization costs  reusable, extensible code • Parametric polymorphism helps • Object-oriented programming helps more • subtyping • inheritance • Still not enough! • multimethods, mixins, open classes, … • linking languages, reflection

  19. Plan • Read mix of recent and classic papers on related topics • Security, concurrency, reliability, persistence, extensibility • 1–2 papers per 50-minute lecture • Participation  Presentation • Come prepared to talk • Read the paper(s) • Discussion is as important as presentation • Outrageous (polite) opinions welcome

  20. Reading • new papers: • PLDI ‘02 • OOPSLA ‘02 • ASPLOS ‘02 • POPL ‘03 (when available) + timeless papers • Some pure PL, some systems + PL. • Paper suggestions welcome • Sign up by sending me mail

  21. Presentation suggestions • Computer projector and laptop will be available. • Aim for a 25-minute talk without interruptions. • Practice your talk at least once before. • Can go over slides with me.

  22. Project • For credit: write a short (4-5k words) paper • project on related topics • survey of work in area

  23. Wednesday • Start talking about security – three papers to read on foundations of information flow www.cs.cornell.edu/andru/cs711

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