[PPT] - Non-In trusiv e Ob jet In trosp etion in C++: Ar hiteture PowerPoint Presentation

SLIDE 1 Non-In trusiv e Ob je t In trosp e tion in C++: Ar hite ture and Appli ation T yng-Ruey Ch uang Institute

f

Information S ien e A ademia Sini a Nank ang, T aip ei 115, T aiw an Join t w

rk

with Chin-Ch uan Hsu, Ch uan-Chieh Jung, W en-Min Kuan, Y. S. Kuo, W ei-Hsueh Lai, and Chien-Min W ang. 1

SLIDE 2 Outline

Ob

je t in trosp e tion

The

problems with C++

Non-in

trusiv e

b

je t in trosp e tion in C++

Implemen

tation issues

Appli ations

2

SLIDE 3 Dynami Appli ations

They

deal with

b

je ts whose t yp es are kno wn

nly

at run-time.

Examples

in lude dynami library loaders, program debuggers,

b

je t serialization routines, et .

They

mak e external

b

je ts \ ome aliv e" whenev er they are needed, and no matter what they are.

Sev

eral OO languages ha v e builtin supp

rts,

su h as late-binding, for dev eloping dynami appli ations.

CLOS,

Ja v a, Ob je tiv e C, and Smalltalk, for example, all allo w late-binding metho d alls to

b

je ts. 3

SLIDE 4 Ob je t In trosp e tion

It

is the abilit y to query and

p

erate an

b

je t without kno wing its t yp e stati ally . In trosp e tiv e

p

erations are still t yp e- he k ed, ho w ev er, to ex lude illegal a esses.

It

greatly helps the dev elopmen t

f

dynami appli ations.

Example:

Ja v a

re

ree tion API.

No

builtin supp

rt

for

b

je t in trosp e tion in C++. C++'s virtual fun tion and Run-Time T yp e Information (R TTI) me hanism an b e to

restri tiv

e. 4

SLIDE 5 Example

C++
b

je ts: BSTree *p = new BSTree; p->insert("Sini a ");

In

trosp e tiv e C++

b

je ts: void *p; Klass bstree = getClass("BSTree" ); p = bstree.new(); Method insert = getMethod(bstree , "insert"); void* argv[℄ = {"Sini a", 0}; bstree.invoke(p, insert, argv); 5

SLIDE 6 Curren t C++ Solutions

Appli ation

framew

rk:

lasses deriv ed from pre-dened framew

rk

re eiv e additional in trosp e tiv e supp

rts.

Examples: System Ob je t Mo del (SOM) from IBM, and Common Ob je t Mo del (COM) from Mi rosoft.

New

language seman ti s and implemen tation: Mak e all

b

je ts in trosp e tiv e b y default.

Systemati

augmen tation to lass denitions: Instan es

f

the augmen ted lasses b e ome in trosp e tiv e. 6

SLIDE 7 Issues

f

In terop erabilit y

T

ypi al problem: Ob je ts pro du ed b y third-part y lass library need in trosp e tion as w ell.

Third-part

y library ma y ha v e its

wn

lass hierar hi al stru ture (i.e., framew

rk).

It is diÆ ult to t it in to another appli ation framew

rk.
The

library is dev elop ed using

ld

seman ti s and implemen tation. New C++ seman ti s and implemen tation do not help.

The

augmen ted lass denitions will pro du e

b

je ts in ompatible with the existing library (a \bla k b

x").
Summary:

urren t solutions are in trusiv e to existing lass denitions. 7

SLIDE 8 Goals: Non-In trusiv e Ob je t In trosp e tiv e in C++

Mak

e

b

je ts in trosp e tiv e, as long as

ne

has a ess to their lass denitions in adv an e.

Non-in

trusiv e. F

r

an y giv en lass, its in trosp e tiv e instan es are

mpatible

with non-in trosp e tiv e instan es.

Easy

to use. Automati to

ls

are used to mak e instan es from a lass in trosp e tiv e.

Comprehensiv

e supp

rts.

The to

l

should

v

er as man y C++ lass features as p

ssible.

8

SLIDE 9 A Meta Ob je t Ar hite ture (I)

F
r

ea h lass, a

rresp
nding

application source application binary application binary class declarations class libraries ("black boxes") class libraries ("black boxes") meta objects (one for each class) Introspective Run-Time Environment Stand-alone Executable Run-Time declarations meta class meta class supporting libraries meta class supporting libraries meta object code generator code to generate meta objects Compile-Time Link-Time

Example: Appli ations that needs C++

b

je t input/output. 11

SLIDE 12 Lo

sely-Coupled

Mo del

application source application binary application binary class declarations class libraries ("black boxes") meta objects (one for each class) class libraries ("black boxes") Compile-Time Run-Time Executable (Client) Dynamically Loaded Libraries (Servers) declarations meta class meta class supporting libraries meta class supporting libraries Link-Time meta objects code to generate Script (Meta Object Generation) meta object code generator

Example: Bro wsers that load and exer ise C++ lasses

n

demand. 12

SLIDE 13 Meta Class Supp

rting

Library

Meta

lasses: Klass, Method, et . for represen ting fun tionalit y pro vided b y an y C++ lass and metho d (e.g., ea h meta

b

je t an instan e

f

Klass). Most metho ds in the meta lasses are virtual fun tions.

P
lymorphi
b

je t referen es: In trosp e tiv e

b

je ts all ha v e stati t yp e void*, ho w do es

ne

dis o v er their dynami t yp es? W e need virtual

nst

har

nst

*dynami Type (void

nst

*self) { return typeid(*(B *) self).name(); } in the meta

b

je t for lass B.

Similar

problems with

n

v ersion routines b et w een base and deriv ed lasses. 13

SLIDE 14 Meta Ob je t Generation Routines

They

are automati ally generated b y parsing the lass de larations.

They

ma y b e applied in t w

stages:

the generator exe ute at appli ation dev elopmen t time, but the

de

so generated exe ute at appli ation run-time. Hen e the need for

de

lik e

ffset_of_a_in_A

= ( har *) &(((A *) 64)->a)

( har

*) ((A *) 64) for prop er memory la y

ut
f

lass A.

Ob

je t

mpatibilit

y: W e ma y need to augmen t a lass de laration to gain a ess, but nev er augmen t it in w a ys that will hange its

b

je t la y

ut.

F

r

example, inserting friend fun tions is OK, but adding new virtual fun tions is not. 14

SLIDE 15 Tw

In

trosp e tiv e Appli ations

Obje

tStr e am: A soft w are to

l

for pro viding automati I/O supp

rts

for

mplex

C++

b

je ts. Tigh tly- oupled mo del.

R

unClass: An appli ation for in tera tiv e exe ution

f

dynami ally loaded C++ lass library . Lo

sely- oupled

mo del.

Ob

je tStream helps sa v e dev elopmen t time and a v

id

man ual

ding

error.

RunClass

helps p erform lass-based soft w are testing, and helps

ne

familiarize with new lass library . 15

SLIDE 16 RunClass

It

allo ws users to reate

b

je ts for giv en lasses, exe ute metho ds up

n

sp e i

b

je ts, and examine their

n

ten ts in tera tiv ely .

It

has easy-to-use graphi user in terfa e.

A

user's

mmand

sequen e, and its ee t, an b e logged, and repla y ed later for regression testing

n

new er v ersions

f

a lass library . 16

SLIDE 17 RunClass S reen Shot Note: Being sho wn to exer ise Mi rosoft F

undation

Classes. 17

SLIDE 18 Ob je tStream

C++

I/O

p

erators lik e << and >> are made to w

rk
n

instan es

f

an y user-dened lass. In header le

f

the supp

rting

library: template < lass T> Uostream &operator<<(Uostre am &os, T &obj) { Uwrite(os, (void*) &obj, typeid(T).name()); return

s;

} template < lass T> Uistream &operator>>(Uistre am &is, T *&obj){ Uread (is, (void *)

bj,

typeid(T).name()); return is; }

Ob

je tStream is used to

nstru t

an in tera tiv e bro wser for

b

je ts stored in external media/format. It is also in orp

rated

in to RunClass for

b

je t equalit y test. 18

SLIDE 19 Design

f

Ob je tStream

User{pro

vided lass header les are parsed to extra t lass information (su h as

b

je t la y

ut

and lass hierar h y).

Co

de is generated to build up a

lle tion
f

lass information based

n

the extra tions.

C++

I/O

p

erators, >> and <<, are

v

erloaded to supp

rt

user-dened lasses.

A

generi I/O library is used b y the I/O

p

erators to

nstru t/tra

v el

b

je ts, based

n

lass information previously

lle ted

and

n

run-time t yp e information from C++. 19

SLIDE 20 F rom A User's P ersp e tiv e

ObjectStream code generator application source code class declaration augmented class declarations ObjectStream C++ compiler C++ compiler application binary code class-specific class-specific class definition binary code linker stand-alone executable main.cpp class.h main.obj generic I/O library class.obj main.exe

The shell script will automat the working in the dotted box. ObjectStream

class.h initialization binary initialization source classInit.obj classInit.cpp ustream.lib configuration file class.cfg ustream.h ObjectStream header file header file

20

SLIDE 21 T e hni al Issues

Flexible

and extendible univ ersal stream fa ilit y .

A urate

mapping

f

p

lymorphi
b

je ts | an

b

je t's dynami (run-time) format not ne essarily depi ted b y its stati ( ompile-time) de laration.

Cross{referen es

among and within

b

je ts | A graph tra v ersal problem (as in \garbage

lle tion").
Am

biguities in the language. (void*, union, et .) and anar hi language features (m ultiple inheritan e, lo al lass de larations. et .). 21

SLIDE 22 Limitations

f

Curren t Approa h

Need

a ess to lass de larations.

Cannot

deal with am biguities in C++

b

je ts: void*, union, et .

In ur

run-time

v

erhead in t yp e- he king in trosp e tiv e

p

erations. 22

SLIDE 23 Con luding Remarks

Non-in

trusiv ely

b

je t in trosp e tion in C++ is p

ssible.
Our

system ar hite ture is based

n