The Center for Distributed Object Computing DOC Center ...schmidt/PDF/doc-overview4.pdf · MD110...

The Center for Distributed Object Computing

Research Synopsis

David L. Levinewww.cs.wustl.edu/ �levine/

Director, Center for Computer Science Dept.Distributed Object Computing Washington University, St. Louis

SponsorsNSF, DARPA, Bellcore/Telcordia, BBN, Boeing, CDI/GDIS, Comverse, Hughes,

Kodak, Lockheed, Lucent, Microsoft, Motorola, Nokia, Nortel, OCI,OTI, Raytheon, SAIC, Siemens SCR, Siemens MED, Siemens ZT, Sprint, USENIX

24 November 1999

DOC Center Washington University, St. Louis

Motivation: the Communication Software Crisis

www.arl.wustl.edu/arl/� Symptoms

Communication hardware getssmaller, faster, cheaper

– Communication software gets larger,slower, more expensive

� Culprits

– Inherent and accidental complexity

� Solution Approach

– Standard communicationmiddleware

1


DOC Center Research Focus

HighPerformance

Real-TimeCORBA

DistributedConfigurable

Systems

Adaptive Communication Environment (ACE)

The ACE Orb (TAO)

Patte

rns,

Pat

tern

Lan

guag

es, a

nd F

ram

ewor

ks

SimulationandEmbeddedSystems

MissionCritical

Communication

2


DOC Center Members� David L. Levine, Director

� Fred Kuhns, Associate Director

� Douglas C. Schmidt, Former Director

� Full-time staff: C. Gill, C. O’Ryan, J. Parsons, I. Pyarali, N. Wang

� PhD students: C. Gill, J. Hu, C. O’Ryan, O. Othman, I. Pyarali, N.Wang

� Masters students: L. Baker, D. Brunsch, P. Gore, V. Kachroo, Y.Krishnamurthy, B. Natarajan, K. Parameswaran, J. Parsons, M.Spivak

� Undergrads: K. Pathayapura

3


DOC Center Sponsors

Bellcore/Telcordia MotorolaBBN NokiaBoeing NortelCDI/GDIS NSFComverse OCIDARPA OTIHughes RaytheonKodak SAICLockheed Martin SiemensLucent SprintMicrosoft USENIX

4


Problem: Lack of QoS-enabled Middleware

HHOOSSTT IINNFFRRAASSTTRRUUCCTTUURREE MMIIDDDDLLEEWWAARREE

DDIISSTTRRIIBBUUTTIIOONN MMIIDDDDLLEEWWAARREE

CCOOMMMMOONN MMIIDDDDLLEEWWAARREE SSEERRVVIICCEESS

AAPPPPLLIICCAATTIIOONNSS

HHAARRDDWWAARREE DDEEVVIICCEESS

WWTTSSHHUUDD

NNaavv

AAVVIIOONNIICCSSRREEPPLLIICCAATTIIOONN

SSEERRVVIICCEEDDOOMMAAIINN--SSPPEECCIIFFIICC MMIIDDDDLLEEWWAARREE SSEERRVVIICCEESS

OOPPEERRAATTIINNGG SSYYSSTTEEMMSS && PPRROOTTOOCCOOLLSS

EEVVEENNTTCCHHAANNNNEELL

CCoonnssCCoonnss

CCoonnss

� Many applications require QoSguarantees

– e.g., avionics, telecom, WWW,medical, high-energy physics

� Building these applicationsmanually is hard

� Existing middleware doesn’tsupport QoS effectively

– e.g., CORBA, DCOM, DCE, Java� Solutions must be integrated

horizontally & vertically

5


Candidate Solution: CORBA

INTERFACE

REPOSITORY

IMPLEMENTATION

REPOSITORY

IDLCOMPILER

DII ORBINTERFACE

ORBORB CORECORE GIOPGIOP//IIOPIIOP//ESIOPSESIOPS

IDLIDLSTUBSSTUBS

operation()operation()in args

out args + return value

CLIENTOBJECT(SERVANT)

OBJ

REF

STANDARD INTERFACE STANDARD LANGUAGE MAPPING

ORB-SPECIFIC INTERFACE STANDARD PROTOCOL

INTERFACE

REPOSITORY

IMPLEMENTATION

REPOSITORY

IDLCOMPILER

IDLSKELETON

DSI

OBJECT

ADAPTER

www.cs.wustl.edu/�schmidt/corba.html

Goals of CORBA

� Simplify distributionby automating

– Object location &activation

– Parametermarshaling

– Demultiplexing– Error handling

� Provide foundationfor higher-levelservices

6 DO

CC

ente

rW

ashi

ngto

nU

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Cav

eat:

Req

uire

men

ts/L

imita

tions

ofC

OR

BA

for

QoS

-ena

bled

Sys

tem

s

NE

TW

OR

KN

ET

WO

RK

OP

ER

AT

ION

SO

PE

RA

TIO

NS

CE

NT

ER

CE

NT

ER

HSM

HSM

AR

CH

IVE

AR

CH

IVE

SE

RV

ER

SE

RV

ER

AG

EN

TA

GE

NT

INT

ER

AC

TIV

EIN

TE

RA

CT

IVE

AU

DIO

AU

DIO

//VID

EO

VID

EO

AG

EN

TA

GE

NT

AR

CH

ITE

CT

UR

EA

RC

HIT

EC

TU

RE

SP

CS

PC

HA

RD

WA

RE

HA

RD

WA

RE

EM

BE

DD

ED

EM

BE

DD

ED

TA

OT

AO

MIB

MIB

AG

EN

TA

GE

NT

ww

w.c

s.w

ustl.

edu/

�

schm

idt/R

T-O

RB

.ps.

gz

Req

uire

men

ts

�

Loca

tion

tran

spar

ency

�

Per

form

ance

tran

spar

ency

�

Pre

dict

abili

tytr

ansp

aren

cy

�

Rel

iabi

lity

tran

pare

ncy

Lim

itatio

ns

�

Lack

ofQ

oSsp

ecifi

catio

ns

�

Lack

ofQ

oSen

forc

emen

t

�

Lack

ofre

al-t

ime

prog

ram

min

gfe

atur

es

�

Lack

ofpe

rform

ance

optim

izat

ions


Problem: Optimizing Complex Software

DIAGNOSTIC STATIONSDIAGNOSTIC STATIONS

ATMATMMANMAN

ATM

LAN

ATM

LAN

MODALITIES

(CT, MR, CR) CENTRAL

BLOB STORE

CLUSTER

BLOB

STORE

DX

BLOB

STORE

www.cs.wustl.edu/�schmidt/JSAC-99.ps.gz

Common Problems !

� Optimizing complex softwareis hard

� Small “mistakes” can be costly

Solution Approach (Iterative) !

� Pinpoint overhead viawhite-box metrics– e.g., Quantify and

VMEtro

� Apply patterns and frameworkcomponents

� Revalidate via white-box andblack-box metrics

8


Solution 1: Patterns and Framework Components

ACCEPTORCONNECTOR

ABSTRACTFACTORY

SERVANTCLIENT

OS KERNELOS KERNEL

LEADER /FOLLOWERS

THREAD -SPECIFICSTORAGE

COMPONENTCONFIGURATOR

REACTOR

WRAPPER FACADES

STRATEGY

www.cs.wustl.edu/�schmidt/ORB-patterns.ps.gz

Definitions

� Pattern

– A solution to a problem ina context

� Framework

– A “semi-complete”application built withcomponents

� Components

– Self-contained, “pluggable”ADTs

9

DO

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ente

rW

ashi

ngto

nU

n

Sol

utio

n2:

OR

BO

ptim

izat

ion

Prin

cipl

eP

atte

rns

Defi

nitio

n

�

Opt

imiz

atio

npr

inci

ple

patte

rns

docu

men

tru

les

for

avoi

ding

com

mon

desi

gnan

dim

plem

enta

tion

prob

lem

sth

atca

nde

grad

eth

eef

ficie

ncy,

scal

abili

ty,a

ndpr

edic

tabi

lity

ofco

mpl

exsy

stem

s

Key

Prin

cipl

eP

atte

rns

Use

din

TAO

#P

rinci

ple

Pat

tern

1O

ptim

ize

for

the

com

mon

case

2R

emov

egr

atui

tous

was

te3

Rep

lace

inef

ficie

ntge

nera

l-pur

pose

func

tions

with

effic

ient

spec

ial-p

urpo

seon

es4

Shi

ftco

mpu

tatio

nin

time,

e.g.

,pre

com

pute

5S

tore

redu

ndan

tsta

teto

spee

d-up

expe

nsiv

eop

erat

ions

6P

ass

hint

sbe

twee

nla

yers

and

com

pone

nts

7D

on’t

betie

dto

refe

renc

eim

plem

enta

tions

/mod

els

8U

seef

ficie

nt/p

redi

ctab

leda

tast

ruct

ures


Patterns for Communication Middleware

EventPatterns

ConcurrencyPatterns

ExternalPolymorphism

WrapperFacade

Connector

Acceptor

ThreadPool

Thread-perSession

Thread-perRequest

AsynchronousCompletion

Token

ThreadSpecificStorage

ActiveObject

Half-Sync/Half-Async

Leader/Followers

ServiceConfigurator

Object LifetimeManager

Reactor

Proactor

DoubleCheckedLocking

Thread-Safe

Interface

ScopedLocking

StrategizedLocking

InitializationPatterns

SynchronizationPatterns

� Observation

– Failures rarely resultfrom unknown scientificprinciples, but fromfailing to apply provenengineering practicesand patterns

� Benefits of Patterns

– Facilitate design reuse– Preserve crucial design

information– Guide design choices

11


The ADAPTIVE Communication Environment (ACE)

PROCESSES/THREADS

DYNAMICLINKING

SHAREDMEMORY

SELECT/IO COMP

FILE SYSAPIS

WIN32 NAMEDPIPES & UNIXSTREAM PIPES

UNIXFIFOS

CCAAPPIISS

SOCKETS/TLI

CCOOMMMMUUNNIICCAATTIIOONNSSUUBBSSYYSSTTEEMM

VVIIRRTTUUAALL MMEEMMOORRYY && FFIILLEESSUUBBSSYYSSTTEEMM

GGEENNEERRAALL OOPPEERRAATTIINNGG SSYYSSTTEEMM SSEERRVVIICCEESS

PPRROOCCEESSSS//TTHHRREEAADDSSUUBBSSYYSSTTEEMM

FFRRAAMMEEWWOORRKKLLAAYYEERR

AACCCCEEPPTTOORR CCOONNNNEECCTTOORR

NNEETTWWOORRKKEEDDSSEERRVVIICCEE

CCOOMMPPOONNEENNTTSSLLAAYYEERR

NAMESERVER

TOKENSERVER

LOGGINGSERVER

GATEWAYSERVER

SOCK SAP/TLI SAP

FIFOSAP

LOGMSG

SSEERRVVIICCEEHHAANNDDLLEERR

TIMESERVER

CC++++WWRRAAPPPPEERRFFAACCAADDEELLAAYYEERR SPIPE

SAP

CCOORRBBAAHHAANNDDLLEERR

FILESAP

SHAREDMALLOC

THE ACE ORB(TAO)

JAWS ADAPTIVEWEB SERVER

SSTTAANNDDAARRDDSS--BBAASSEEDD MMIIDDDDLLEEWWAARREE

RREEAACCTTOORR//PPRROOAACCTTOORR

PROCESS/THREADMANAGERS

SSTTRREEAAMMSS

SSEERRVVIICCEECCOONNFFIIGG--UURRAATTOORR

SYNCHWRAPPERS

MEMMAP

OOSS AADDAAPPTTAATTIIOONN LLAAYYEERR

www.cs.wustl.edu/�schmidt/ACE.html

� ACE Overview– Concurrent OO

networkingframework

– Available for C++and Java

– Ported to POSIX,Win32, VxWorks,Chorus, PharLapTNT, et al.

12 DO

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rW

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ngto

nU

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The

AC

EO

RB

(TA

O)

and

ItsC

OR

BA

Obj

ectS

ervi

ces

SC

HE

DU

LIN

G

PR

OP

ER

TY

EV

EN

T/

NO

TIF

ICA

TIO

NT

RA

DIN

G

NA

MIN

GC

ON

CU

RR

EN

CY

TIM

E

A/V

ST

RE

AM

ING

NE

TW

OR

K

OR

B Q

OS

INT

ER

FA

CE

RID

LS

TU

BS

RID

LS

KE

LE

TO

N

CL

IEN

T

OS

KE

RN

EL

OS

I/

O S

UB

SY

ST

EM

NE

TW

OR

K A

DA

PT

ER

S

OS

KE

RN

EL

OS

I/

O S

UB

SY

ST

EM

NE

TW

OR

K A

DA

PT

ER

S

GIO

P/R

IOP

OB

JE

CT

(SE

RV

AN

T)

LO

GG

ING

CORBA SERVICES

IDL

CO

MP

ILE

R

RE

AL-T

IME

OR

B C

OR

E

AC

EC

OM

PO

NE

NT

S

LIF

EC

YC

LE

RE

AL-T

IME

OB

JE

CT

AD

AP

TE

R


ACE and TAO Statistics

� Over 30 person-years of effort

– ACE > 200,000 LOC– TAO > 125,000 LOC– TAO IDL compiler > 100,000 LOC– TAO CORBA Object Services >

150,000 LOC

� Ported to POSIX, Win32, VxWorks,et al.

� Large user community

– www.cs.wustl.edu/�schmidt/ACE-users.html

� Currently used by dozensof companies

– Bellcore, Boeing,Ericsson, Kodak,Lockheed, Lucent,Motorola, Nokia, Nortel,Raytheon, SAIC,Siemens, etc.

� Supported commercially

– ACE !

www.riverace.com– TAO !

www.theaceorb.com

14


Real-time Optimizations in TAO

NETWORKNETWORK

OS KERNELOS KERNEL

OS IOS I//O SUBSYSTEMO SUBSYSTEM

NETWORK INTERFACESNETWORK INTERFACES

ORBORBINTERFACEINTERFACE

ORBORBCORECORE

operation()operation()

IDLIDLSTUBSSTUBS

OBJECTOBJECT

ADAPTERADAPTER

IDLIDLSKELETONSKELETON

in argsin args

out args + return valueout args + return value

CLIENT

GIOP

OBJECT(SERVANT)

CONCURRENCY

MODELS

TRANSPORT

PROTOCOLS

I/OSUBSYSTEM

NETWORK

ADAPTER

PRESENTATION

LAYER

SCHEDULING,DEMUXING, &DISPATCHING

DATA COPYING

& MEMORY

ALLOCATION

CONNECTION

MANAGEMENT

OS KERNEL

OS I/O SUBSYSTEM

NETWORK INTERFACES

OBJ

REF

15


New TAO Features and Optimizations

STANDARD

SYNCHRONIZERS

END-TO-END

PRIORITY

PROPAGATION

ORB CORE

OBJECT

ADAPTER

CLIENTOBJECT(SERVANT)

THREAD

POOLS

EXPLICIT

BINDING

NETWORK

OS KERNEL

NETWORK INTERFACE

OS I/O SUBSYSTEM

OS KERNEL

NETWORK INTERFACE

OS I/O SUBSYSTEM

PLUGGABLEPROTOCOLS &

PROPERTIES

GIOP GIOP

� New Features

– Real-time CORBA– Minimum CORBA– CORBA Messaging– Fault Tolerance

� URL

– �schmidt/TAO-status.html

16


Integrating TAO with ATM I/O Subsystem

REACTOR

(20 HZ)

REACTOR

(10 HZ)

REACTOR

(5 HZ)

REACTOR

(1 HZ)

ORB CORE

APIC ATM DRIVER

I/OSUBSYSTEM

PER-VC

SOCKET

QUEUES

APIC PACING

QUEUES

Z

E

R

O

C

O

P

Y

B

U

F

F

E

R

S

�schmidt/RIO.ps.gz

Features

� Vertical integration of QoSthrough ORB, OS, and ATMnetwork

� Real-time I/O enhancementsto Solaris kernel

� Provides rate-based QoSend-to-end

� Leverages APIC features forcell pacing and zero-copybuffering

17


Strategized Scheduling Framework ssttrruucctt RRTT__IInnffoo {{ wwcc__eexxeecc__ttiimmee__;; ppeerr iioodd__;; ccrr iittiiccaalliittyy__;; iimmppoorr ttaannccee__;; ddeeppeennddeenncciieess__;; }};;

SSCCHHEEDDUULLIINNGG

SSTTRRAATTEEGGYY

RRTT__IINNFFOO

RREEPPOOSSII TTOORRYY

OOFFFF--LL II NNEE

SSTTRRAATTEEGGIIZZEEDD

SSCCHHEEDDUULLEERR

OOFFFF--LLIINNEE

OONN--LLIINNEE

RRTT__IINNFFOO

RREEPPOOSSII TTOORRYY

RRUUNN--TTIIMMEE

SSCCHHEEDDUULLEERR

11.. SSPPEECCIIFFYY RRTT__OOPPEERRAATTIIOONN

CCHHAARRAACCTTEERRIISSTTIICCSS AANNDD

DDEEPPEENNDDEENNCCIIEESS

55.. AASSSSEESSSS SSCCHHEEDDUULLAABBIILL IITTYY

33.. AASSSSII GGNN SSTTAATTIICC PPRRIIOORRIITTYY AANNDD SSTTAATTIICC SSUUBBPPRRIIOORRIITTYY

44.. MMAAPP SSTTAATTIICC PPRRIIOORRIITTYY,, DDYYNNAAMMII CC SSUUBBPPRRII OORRII TTYY,, AANNDD

SSTTAATTIICC SSUUBBPPRRIIOORRIITTYY II NNTTOO DDIISSPPAATTCCHHIINNGG PPRRIIOORRIITTYY

AANNDD DDIISSPPAATTCCHHIINNGG SSUUBBPPRRIIOORRIITTYY

66.. AASSSSIIGGNN DDIISSPPAATTCCHHIINNGG QQUUEEUUEE CCOONNFFIIGGUURRAATTIIOONN

22.. PPOOPPUULLAATTEE

RRTT__IINNFFOO

RREEPPOOSSIITTOORRYY

77.. SSUUPPPPLLYY DDIISSPPAATTCCHHIINNGG QQUUEEUUEE

CCOONNFFIIGGUURRAATTIIOONN TTOO TTHHEE OORRBB

RRTTOOppeerraattiioonn



II //OO SSUUBBSSYYSSTTEEMM

OORRBB CCOORREE

OOBBJJEECCTT AADDAAPPTTEERR

99.. SSUUPPPPLLYY SSTTAATTIICC PPOORRTTIIOONNSS OOFF

DDIISSPPAATTCCHHIINNGG PPRRIIOORRIITTYY AANNDD

DDIISSPPAATTCCHHIINNGG SSUUBBPPRRIIOORRIITTYY

TTOO TTHHEE OORRBB

((SSCCHHEEDDUULLEERR''SS OOUUTTPPUUTT

IINNTTEERRFFAACCEE))

((SSCCHHEEDDUULLEERR''SS IINNPPUUTT

IINNTTEERRFFAACCEE))

88.. CCOONNFFIIGGUURREE QQUUEEUUEESS BBAASSEEDD

OONN DDIISSPPAATTCCHHIINNGG QQUUEEUUEE

CCOONNFFIIGGUURRAATTIIOONN

1100.. DDYYNNAAMMIICC QQUUEEUUEESS AASSSSIIGGNN

DDYYNNAAMMIICC PPOORRTTIIOONNSS OOFF

DDIISSPPAATTCCHHIINNGG SSUUBBPPRRIIOORRIITTYY

((AANNDD PPOOSSSSIIBBLLYY

DDIISSPPAATTCCHHIINNGG PPRRIIOORRIITTYY)) OORRBB EENNDDSSYYSSTTEEMM

18 DO

CC

ente

rW

ashi

ngto

nU

n

Use

-cas

esfo

rA

CE

and

TAO

' &

$ %' &

$ %

Dom

ains

�

Ele

ctro

nic

med

ical

imag

ing

�

Net

wor

km

anag

emen

t

�

Wire

less

pers

onal

com

mun

icat

ion

syst

ems

(PC

S)

�

Rea

l-tim

eav

ioni

csm

issi

onco

mut

ing

�

Mul

timed

iase

rvic

es

�

Dis

trib

uted

inte

ract

ive

sim

ulat

ion


Applying ACE and TAO to Medical Imaging

DIAGNOSTIC STATIONSDIAGNOSTIC STATIONS

ATMATMMANMAN

ATM

LAN

ATM

LAN

MODALITIES

(CT, MR, CR) CENTRAL

BLOB STORE

CLUSTER

BLOB

STORE

DX

BLOB

STORE

� Domain Challenges

– Large volume of “Blob”data

� e.g., 10 to 40 Mbps– “Lossy compression”

isn’t viable– Prioritization of

requests

� URLs

– �schmidt/COOTS-96.ps.gz

– �schmidt/av.ps.gz– �schmidt/NMVC.html

20


Applying ACE to Network Management

Session RouterModule

PresentationModule

Event FilterModule

Event AnalysisModule

PresentationModule

Switch RouterModule

Reactor

MD110MD110 ERICSSONERICSSON

TELECOMTELECOM

SWITCHESSWITCHES

SUPERSUPER

VISORSVISORS



SUPERSUPER

VISORSVISORS

SUPERSUPER

VISORSVISORS

Switch IO

Session IO


– Low latency– Multi-platform– Family of related

services� URLs

– �schmidt/DSEJ-94.ps.gz

– �schmidt/ECOOP-95.ps.gz

21


Applying ACE to Global PCS

WIDE AREA

NETWORK

SATELLITESSATELLITESTRACKINGTRACKINGSTATIONSTATION

PEERSPEERS

STATUS INFO

COMMANDS BULK DATA

TRANSFER

LOCAL AREA NETWORK

GROUNDSTATION

PEERS

GATEWAY


– Long latency satellite links– High reliability– Prioritization

� URL

– �schmidt/TAPOS-95.ps.gz

22


Applying TAO to Real-time Avionics

REPLICATION

SERVICE

OBJECT REQUEST BROKER

1: SENSORS

GENERATE

DATA

FLIRGPS IFF

3:PUSH (EVENTS)

2: SENSOR PROXIES DEMARSHAL DATA

& PASS TO EVENT CHANNEL

3:PUSH (EVENTS)

EVENT

CHANNEL

HUD NavAir

FrameWTS

4: PULL(DATA)


– Real-time periodicprocessing

– Complexdependencies

– Very low latency

� URL

–�levine/research/JSAC-98.ps.gz

23


Open ATM Signaling & Control

MANAGE

MIBTAO

RIO

APIC

NETWORK OPERATIONS

CENTER - ENDSYSTEM

GET STATSRECONFIG

SWITCH STATUS

CHANGE

RIO

APIC

TAO objB

objA

LOW LATENCY

CONTROLHIGH - BANDWIDTH

VIDEO/AUDIO DATA

ENDSYSTEM A

ENDSYSTEM B

HIGH - BANDWIDTH

BULK DATA

ENDSYSTEM C

HIGH -BANDWIDTH

VIDEO/AUDIO

MULTICAST

NETWORK

SERVICE

PROCESSOR

SPC

WUGS

SPC

SPC

SPC

SPC

SPC

SC

CLASSIFIER /ROUTER

ACTIVE NETWORK

RESOURCE CONTROLLER

NATIVE ATM BYPASSES THROUGH APIC

ATM PORT INTERCONNECT CONTROLLER (APIC)

USER

KERNEL

NSP

HIGH -PERFORMANCE

NETWORK ELEMENT

WEIGHTED

FAIR

QUEUING

IP FLOW

CLASSIFICATION

AND ROUTING

TAO

WUGS

OBJECT

SIGNALING

SERVERTAO

RESOURE

MANAGER

SWITCH

MANAGER

SWITCH CONTROLLER

HIGH -PERFORMANCE NETWORK ELEMENT

QOSMANAGER

TAO

PORT

CONTROLLER

SMART

PORT

CARD

24 DO

CC

ente

rW

ashi

ngto

nU

n

Aud

io/V

ideo

Str

eam

ing

End

-poi

ntFl

ow d

ata

Ada

ptor

Stre

am

(Sou

rce)

Flow

dat

a

Ada

ptor

Obj

ects

And

Man

agem

ent

Obj

ect

Con

trol

Inte

rfac

e

OR

B C

OR

E

POA

End

-poi

nt

Stre

am

Con

trol

Inte

rfac

e

Obj

ect

Stre

am

Stre

am POA

Con

trol

(Sin

k)

MU

LT

IME

DIA

STR

EA

M

Effi

cien

cy

�

Soc

kets

for

data

tran

sfer

toge

thig

hpe

rfor

man

ce

Fle

xibi

lity

�

Use

sC

OR

BA

for

cont

rol

mes

sage

san

dpr

oper

ties


Concluding Remarks

� Researchers and developers of distributed, real-time applicationsconfront many common challenges

– e.g., service initialization and distribution, error handling, flow control,scheduling, event demultiplexing, concurrency control, persistence, faulttolerance

� Successful researchers and developers apply patterns,frameworks, and components to resolve these challenges

� Careful application of patterns can yield efficient, predictable,scalable, and flexible middleware

– i.e., middleware performance is largely an “implementation detail”

� Next-generation ORBs will be highly QoS-enabled, though manyresearch challenges remain

26

The Center for Distributed Object Computing DOC Center ...schmidt/PDF/doc-overview4.pdf · MD110...

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