1. Introduction

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(hEv
ent, 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-9A
9F-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 doesnt have to deal with
• Concurrency
• Reliability
• Security
• Persistence
• Extensibility
• Interoperability
• Scale and complexity
• Configuration management

Distribution
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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
• Doesnt 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 doesnt 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 dont 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
  programsonly 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?

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Consistency/isolation models

• Distributed computation good performance
  requires caching, else 10s 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

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Plan

• Read mix of recent and classic papers on related
  topics
• Security, concurrency, reliability, persistence,
  extensibility
• 12 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

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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

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Wednesday

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