home/ []schmidt/pdf/ace-examples4.pdf · rds," i.e., so ck ets and tli, mak es po rtabilit y...

Developing E�cient and Portable

Communication Software with ACE and C++

Chris Gill and Douglas C. Schmidt

Distributed Object Computing Group

Computer Science Department, Washington University, St. Louis

[email protected]

http://www.cs.wustl.edu/�schmidt/ACE-examples4.ps.gz

ACE C++ Wrapper TutorialProblem: Software Evolution

DDIIAAGGNNOOSSTTIICC

SSTTAATTIIOONNSS

AATTMMMMAANN

AATTMMLLAANN

AATTMMLLAANN

MMOODDAALLIITTIIEESS

((CCTT,, MMRR,, CCRR)) CCEENNTTRRAALL

IIMMAAGGEESSTTOORREE

CCLLUUSSTTEERRIIMMAAGGEESSTTOORREE

DDXXIIMMAAGGEESSTTOORREE

� Key Challenges

{ Communication software

evolves over time

� Requirements change

� Platforms change

� New design forces emerge

{ It is essential to plan for

inevitable change

1

ACE C++ Wrapper Tutorial

Solution: Plan for Change Using Frameworks and

Patterns

Framework Framework

Tilde

FrameworkCached VirtualFilesystem

StrategyProtocol PipelineConcurrency

Expander

I/O Strategy

~/home/...

Mem

ento

Reactor/Proactor Strategy Singleton

Sta

teS

ervi

ce C

on

fig

ura

tor

Sta

te

StrategyActive ObjectPipes and Filters

Ad

apter

Service Configurator

ProtocolHandler

ProtocolFilter

Accep

tor

Event Dispatcher

Asynchronous Completion Token

� Solution Approach

{ Identify sources of

commonality and

variability

{ Use patterns to

identify reusable

design artifacts

{ Use frameworks to

\unify" variation in

code artifacts

2


Sources of Variation in Communication Software

WIDE AREA

NETWORK

SATELLITESSATELLITESTRACKINGTRACKINGSTATIONSTATION

PEERSPEERS

STATUS INFO

COMMANDS BULK DATA

TRANSFER

LOCAL AREA NETWORK

GROUNDSTATION

PEERS

GATEWAY

� Syntactic Variations

{ Unsupported non-essential APIs

{ Gratuitous di�erences in API

� Semantic Variations

{ Underlying platform di�erences

{ Framework must respect these

di�erences

� Complex Variations

{ Unsupported essential portions

of API

{ Emulation is necessary

3


ACE framework: Resolving Syntactic Variations

int ACE_OS::fstat (ACE_HANDLE handle,

struct stat *stp)

{#if defined (ACE_PSOS_LACKS_PHILE)

ACE_UNUSED_ARG (handle);

ACE_UNUSED_ARG (stp);

ACE_NOTSUP_RETURN (-1);

#elif defined (ACE_PSOS)

ACE_OSCALL_RETURN

(::fstat_f (handle, stp), int, -1);

#elseACE_OSCALL_RETURN

(::fstat (handle, stp), int, -1);

#endif /* ACE_PSOS_LACKS_PHILE */

}

� Examples

{ Unsupported

� Provide \no-op"

de�nitions

� Conditional compilation

{ Syntax

� Re-map function

parameters

4


ACE framework: Resolving Semantic Variations

int ACE_OS::clock_gettime

(clockid_t clockid, struct timespec *ts)

{#if defined (ACE_HAS_CLOCK_GETTIME)

ACE_OSCALL_RETURN (::clock_gettime

(clockid, ts), int, -1);

#elif defined (ACE_PSOS)

ACE_UNUSED_ARG (clockid);

ACE_PSOS_Time_t pt;

int result = ACE_PSOS_Time_t::get_system_time (pt);

*ts = ACE_static_cast (struct timespec, pt);

return result;

#elseACE_UNUSED_ARG (clockid);

ACE_UNUSED_ARG (ts);

ACE_NOTSUP_RETURN (-1);

#endif /* ACE_HAS_CLOCK_GETTIME */

}

� Examples

{ Underlying di�erences

� Time in clock ticks

� Ticks-per-second is

board-dependent

{ Framework must respect

these di�erences

� Provide a consistent

abstraction

� Intermediate wrappers

are useful for small,

coherent abstractions

5


ACE framework: Resolving Complex Variations

void *ACE_TSS_Emulation::tss_open

(void *ts_storage[ACE_TSS_KEYS_MAX])

{#if defined (ACE_PSOS)

u_long tss_base;

tss_base = (u_long) ts_storage;

t_setreg (0, PSOS_TASK_REG_TSS, tss_base);

void **tss_base_p = ts_storage;

for (u_int i = 0;

i < ACE_TSS_KEYS_MAX;

++i, ++tss_base_p)

*tss_base_p = 0;

return (void *) tss_base;

#elif defined (...)

// ...

� Examples

{ Unsupported but essential

portions of the API (e.g.,

thread-speci�c storage)

� Provided by POSIX, NT

� Not provided by

VxWorks, pSOS

� Emulation in user space is

necessary

{ Create a TSS emulation

class

{ Provide platform-speci�c

method implementations

6


Network Programming Alternatives

USER

SPACE

KERNEL

SPACE

DOC MIDDLEWAREDOC MIDDLEWARE

SOCKETS AND SOCKETS AND TLITLITLI

OPENOPEN///CLOSECLOSE///PUTMSGPUTMSG///GETMSGGETMSG

STREAMSSTREAMSSTREAMSFRAMEWORKFRAMEWORK

LE

VE

L O

F

AB

ST

RA

CT

ION

TPITPINPINPIDLPIDLPI

HI

LO

� Communication

software can be

programmed at

several levels of

abstraction

� Di�erent levels

are appropriate

for di�erent tasks

7


Navigating Through the Design Alternatives

Choosing the appropriate level of abstaction to program involves many

factors

� Performance

{ Higher levels may be less e�cient

� Functionality

{ Certain features, e.g., multicast, are not available at all levels

� Ease of programming

{ DOC middleware is typically easier to use

� Portability

{ The socket API is generally portable...

8

ACE C++ Wrapper TutorialOverview of DOC Middleware

INTERFACEINTERFACE

REPOSITORYREPOSITORY

IMPLEMENTATIONIMPLEMENTATION


IDLIDLCOMPILERCOMPILER

DIIDII ORBORBINTERFACEINTERFACE

ORBORB CORECORE

operation()operation()

OBJECTOBJECT

ADAPTERADAPTER

in argsin args

out args + return valueout args + return value

CLIENTCLIENT

GIOPGIOP//IIOPIIOP

OBJECTOBJECT((SERVANTSERVANT))

IDLIDLSTUBSSTUBS

STANDARD INTERFACESTANDARD INTERFACE STANDARD LANGUAGE MAPPINGSTANDARD LANGUAGE MAPPING

ORB-ORB-SPECIFIC INTERFACESPECIFIC INTERFACE STANDARD PROTOCOLSTANDARD PROTOCOL

INTERFACEINTERFACE


IMPLEMENTATIONIMPLEMENTATION


IDLIDLCOMPILERCOMPILER

IDLIDLSKELETONSKELETON

DSIDSI

www.cs.wustl.edu/�schmidt/corba.html

� Helps simplify

many types of

applications

� Lets developers

work at higher

levels of

abstraction

� Examples include

CORBA, DCOM,

Java RMI, DCE,

Sun RPC

9


Common DOC Middleware Features

� DOC middleware \stub/skeleton compiler" support

{ Automatically generate code to perform presentation layer conversions

� e.g., network byte-ordering and parameter marshaling

� DOC middleware runtime support

{ Handle network addressing and remote service identi�cation

{ Perform service registration, port monitoring, and service dispatching

{ Enforce authentication and security

{ Manage transport protocol selection and request delivery

{ Provide reliable operation delivery

{ Demultiplexing and dispatching

{ Concurrency and connection management

10

ACE C++ Wrapper TutorialDOC Middleware Limitations

� Some applications may need to access lower-level IPC mechanisms

directly to meet certain requirements

{ e.g., performance, functionality, portability, etc.

� Compared with direct use of sockets and TLI, DOC middleware may be

less e�cient due to

{ Presentation conversion processing and excessive data copying

{ Synchronous client-side and server-side stub behavior

{ Stop-and-wait ow control

{ Non-adaptive retransmission timer schemes

{ Non-optimized demultiplexing and concurrency models

11


Standard APIs for Network IPC

USER

SPACE

DISTRIBUTED

APPLICATION 1

DISTRIBUTED

APPLICATION 3

DISTRIBUTED

APPLICATION 2

KERNEL

SPACE

SYSTEM V

TLI API

SYSTEM V

TLI APIBSD SOCKET

API

SOCKET

API

APPLICATION

PROCESS 3592

APPLICATION

PROCESS 4183

APPLICATION

PROCESS 8729

OSOS KERNEL KERNEL

PROTOCOL SERVICESPROTOCOL SERVICES

((TCPTCP//IPIP,, OSI,OSI, ETC ETC.).)

NETWORK

INTERFACE

� Sockets and TLI allow

access to lower-level

IPC mechanisms, e.g.:

{ TCP/IP

{ XNS and Novell

IPX NetWare

protocols

{ UNIX domain

sockets

{ OSI protocols

12


Socket Taxonomy

LOCALLOCAL LOCALLOCAL//REMOTEREMOTE

ST

RE

AM

ST

RE

AM

ACTIVE

ACTIVE

PASSIVE

PASSIVE

DA

TA

DA

TA

GR

AM

GR

AM

CO

NN

EC

TE

DC

ON

NE

CT

ED

DA

TA

GR

AM

DA

TA

GR

AM

TY

PE

O

F

CO

MM

UN

ICA

TIO

N

SE

RV

ICE

TY

PE

O

F

CO

MM

UN

ICA

TIO

N

SE

RV

ICE

COMMUNICATION DOMAINCOMMUNICATION DOMAIN

CONNECTION

CONNECTION

ROLEROLE

accept(PF_UNIX)accept(PF_UNIX)listen() send()/recv()listen() send()/recv()

socket(PF_UNIX)socket(PF_UNIX)bind() sendto()bind() sendto()

socket(PF_UNX)socket(PF_UNX)bind() recvfrom()bind() recvfrom()

socket(PF_INET)socket(PF_INET)bind() recvfrom()bind() recvfrom()

socket(PF_INET)socket(PF_INET)bind() sendto()bind() sendto()

socket(PF_UNIX)socket(PF_UNIX)bind() connect() send()bind() connect() send()

socket(PF_UNIX)socket(PF_UNIX)bind() connect() recv()bind() connect() recv()

socket(PF_INET)socket(PF_INET) bind() connect() send() bind() connect() send()

socket(PF_INET)socket(PF_INET)bind() connect() recv()bind() connect() recv()

socket(PF_UNIX) bind()socket(PF_UNIX) bind()connect() send()/recv()connect() send()/recv()

accept(PF_INET)accept(PF_INET)listen() send()/recv()listen() send()/recv()

socket(PF_INET) bind()socket(PF_INET) bind()connect() send()/recv()connect() send()/recv()

� The Socket

API can be

classi�ed

along three

dimensions

13


Problem with Sockets: Lack of Type-safety

int buggy_echo_server (u_short port_num)

{ // Error checking omitted.

sockaddr_in s_addr;

int s_fd = socket (PF_UNIX, SOCK_DGRAM, 0);

s_addr.sin_family = AF_INET;

s_addr.sin_port = port_num;

s_addr.sin_addr.s_addr = INADDR_ANY;

bind (s_fd, (sockaddr *) &s_addr,

sizeof s_addr);

int n_fd = accept (s_fd, 0, 0);

for (;;) {

char buf[BUFSIZ];

ssize_t n = read (s_fd, buf, sizeof buf);

if (n <= 0) break;

write (n_fd, buf, n);

}}

� I/O handles are

not amenable to

strong type

checking at

compile-time

� The adjacent

code contains

many subtle,

common bugs

14


Problem with Sockets: Steep Learning Curve

Many socket/TLI API functions have complex semantics, e.g.:

� Multiple protocol families and address families

{ e.g., TCP, UNIX domain, OSI, XNS, etc.

� Infrequently used features, e.g.:

{ Broadcasting/multicasting

{ Passing open �le handles

{ Urgent data delivery and reception

{ Asynch I/O, non-blocking I/O, I/O-based and timer-based event

multiplexing

15

ACEC++

WrapperTutorial

Problem

withSockets:PoorlyStructured

socket()bind()connect()listen()accept()read()write()readv()writev()recv()send()recvfrom()sendto()recvmsg()sendmsg()setsockopt()getsockopt()getpeername()getsockname()gethostbyname()getservbyname()

�

NotethesocketAPIislinearratherthanhierarchical

{Thus,itgivesnohintsonhowtouseitcorrectly

�

Inaddition,thereisnoconsistencyamongnames...

16

ACEC++

WrapperTutorial

Problem

withSockets:Portability

�

Havingmultiple\standards,"i.e.,socketsandTLI,makesportability

di�cult,e.g.,

{Mayrequireconditionalcompilation

{Inaddition,relatedfunctionsarenotincludedinPOSIXstandards

�

e.g.,select,WaitForMultipleObjects,andpoll

�

PortabilitybetweenUNIXandWin32Socketsisproblematic,e.g.:

{Header�les

{Errornumbers

{Handlevs.descriptortypes

{Shutdownsemantics

{I/Ocontrolsandsocketoptions

17

ACEC++

WrapperTutorial

TheACEC++

IPCWrapperSolution

IPC

_S

AP A

SO

CK

_S

AP

TL

I_S

AP

FIF

O_S

AP

SP

IPE

_S

AP

SO

CK

ET

AP

I

TR

AN

SP

OR

T

LA

YE

R

INT

ER

FA

CE

AP

I

ST

RE

AM

PIP

E

AP

I

NA

ME

D P

IPE

AP

I

�

ACEprovidesC++\wrappers"thatencapsulateIPCprogramming

interfaceslikesocketsandTLI

{ThisisanexampleoftheWrapperFacadePattern

18

ACEC++

WrapperTutorial

IntentandStructureoftheWrapperFacadePattern

:Wrapper

:Wrapper

requ

est()1: req

uest ()

2: sp

ecific_req

uest()

:Wrappee

:Wrappee

specific_

request()

client

client

�

Intent

{Encapsulateslow-level,

stand-alonesystem

mechanismswithintype-safe,

modular,andportableclass

interfaces

�

ForcesResolved

{Avoidtedious,error-prone,

andnon-portablesystem

APIs

{Createcohesiveabstractions

19

ACEC++

WrapperTutorial

TheACEC++

SocketWrapperClassStructure

LO

CA

LL

OC

AL/R

EM

OT

E

STREAM

AC

TIV

E

PA

SSIV

E

DATAGRAM

CONNECTEDDATAGRAM

LO

CK

_C

on

necto

r L

SO

CK

_S

trea

m S

OC

K_

Co

nn

ecto

rS

OC

K_

Str

ea

m

SO

CK

_A

ccep

tor

SO

CK

_S

trea

m

SO

CK

_D

gra

m

LS

OC

K_

CO

Dg

ra

m S

OC

K_

CO

Dg

ra

m

LS

OC

K_

Dg

ra

m S

OC

K_

Dg

ra

m_

Bca

st

LS

OC

K_

Dg

ra

m S

OC

K_

Dg

ra

m

LS

OC

K_

Dg

ra

m

LS

OC

K_

Accep

tor

LS

OC

K_

Accep

tor

LS

OC

K_

Str

ea

mL

SO

CK

_S

trea

mSO

CK

_D

gra

m_

Mca

stS

OC

K_

Dg

ra

m_

Mca

st

SO

CK

_D

gra

m S

OC

K_

Dg

ra

m

TYPE OF COMMUNICATION SERVICE TYPE OF COMMUNICATION SERVICE

CO

MM

UN

ICA

TIO

N

DO

MA

INC

OM

MU

NIC

AT

ION

D

OM

AIN

CO

NN

EC

TIO

N

CO

NN

EC

TIO

N

RO

LE

RO

LE

�

Notehow

stand-alone

functionsare

replacedby

C++class

components

20

ACEC++

WrapperTutorial

SOCK

SAPFactoryClassInterfaces

classSOCK_Connector

{ public:

//Traits

typedefINET_AddrPEER_ADDR;

typedefSOCK_Stream

PEER_STREAM;

intconnect

(SOCK_Stream

&new_sap,

constINET_Addr

&raddr,

Time_Value*timeout,

constINET_Addr

&laddr);

//...

};

classSOCK_Acceptor

:publicSOCK

{ public:

//Traits


typedefSOCK_StreamPEER_STREAM;

SOCK_Acceptor

(constINET_Addr&local_addr);

intaccept

(SOCK_Stream

&new_sap,

INET_Addr*,

Time_Value*);

//...

};

21

ACEC++

WrapperTutorial

SOCK

SAPStream

andAddressingClassInterfaces

classSOCK_Stream

:publicSOCK

{ public:

//Trait.


ssize_tsend(constvoid*buf,

intn);

ssize_trecv(void*buf,

intn);

ssize_tsend_n(constvoid*buf,

intn);

ssize_trecv_n(void*buf,

intn);

intclose(void);

//...

};

classINET_Addr:publicAddr

{ public:

INET_Addr(u_shortport_number,

constcharhost[]);

u_shortget_port_number

(void);

int32get_ip_addr

(void);

//...

};

22

ACEC++

WrapperTutorial

OODesignInterlude

Q:WhydecoupletheSOCKAcceptorandtheSOCKConnectorfrom

SOCKStream?

A:ForthesamereasonsthatAcceptorandConnectoraredecoupled

fromSvcHandler,e.g.,

�

ASOCKStreamisonlyresponsiblefordatatransfer

{Regardlessofwhethertheconnectionisestablishedpassivelyor

actively

�

ThisensuresthattheSOCK*componentsarenotusedincorrectly...

{e.g.,youcan'taccidentallyreadorwriteonSOCKConnectorsor

SOCKAcceptors,etc.

23


ACE C++ Wrapper echo server

int echo_server (u_short port_num)

{// Error handling omitted.

INET_Addr my_addr (port_num);

SOCK_Acceptor acceptor (my_addr);

SOCK_Stream new_stream;

acceptor.accept (new_stream);

for (;;)

{char buf[BUFSIZ];

// Error caught at compile time!

ssize_t n = acceptor.recv (buf, sizeof buf);

new_stream.send_n (buf, n);

}}

24


A Generic Version of the Echo Server

template <class ACCEPTOR>

int echo_server (u_short port)

{// Local address of server (note use of traits).

ACCEPTOR::PEER_ADDR my_addr (port);

// Initialize the passive mode server.

ACCEPTOR acceptor (my_addr);

// Data transfer object (note use of traits).

ACCEPTOR::PEER_STREAM stream;

// Accept a new connection.

acceptor.accept (stream);

for (;;) {

char buf[BUFSIZ];

ssize_t n = stream.recv (buf, sizeof buf);

stream.send_n (buf, n);

}}

25


Socket vs. ACE C++ Socket Wrapper Example

� The following slides illustrate di�erences between using the Socket

interface vs. the ACE C++ Socket wrappers

� The example is a simple client/server \network pipe" application that

behaves as follows:

1. Starts an iterative daemon at a well-known server port

2. Client connects to the server and transmits its standard input to the

server

3. The server prints this data to its standard output

� The server portion of the \network pipe" application may actually run

either locally or remotely...

26

ACE C++ Wrapper TutorialNetwork Pipe with Sockets

SERVERSERVERCLIENTCLIENT

socket()bind() (optional)

connect()

send()/recv()

socket()bind()listen()accept()

send()/recv()

2: ACTIVE

ROLE

3: SERVICE

PROCESSINGclose()

close()

NETWORK

1: PASSIVE

ROLE

27


Network Pipe with ACE C++ Socket Wrappers

SERVERSERVERCLIENTCLIENT

SOCK_ConnectorSOCK_Stream

send()/recv()

SOCK_AcceptorSOCK_Stream

send()/recv()

2: ACTIVE

ROLE

3: SERVICE

PROCESSINGclose()

close()

NETWORK

1: PASSIVE

ROLE

28


Running the Network Pipe Program

� e.g.,

% ./server &

% echo "hello world" | ./client localhost

client localhost.cs.wustl.edu%: hello world

� Note that the ACE C++ Socket wrapper example:

{ Requires much less code (about 1/2 to 2/3 less)

{ Provides greater clarity and less potential for errors

{ Operates at no loss of e�ciency

� Complete example available at URL:

{ www.cs.wustl.edu/�schmidt/IPC SAP-92.ps.gz

29

AC

EC

++

Wra

pp

erT

uto

rial Socket

Client

#define

PORT_NUM

10000

int

main

(int

argc,

char

*argv[])

{

struct

sockaddr_in

saddr;

struct

hostent

*hp;

char

*host

=argc

>1

?argv[1]

:"tango.cs.wustl.edu"

;

u_short

port_num

=argc

>2

htons

(argc

>2

?atoi

(argv[2])

:PORT_NUM);

char

buf[BUFSIZ];

int

s_fd;

int

w_bytes;

int

r_bytes;

int

n;

/*

Create

alocal

endpoint

of

communication

*/

s_fd

=socket

(PF_INET,

SOCK_STREAM,

0);

/*

Determine

IP

address

of

the

server

*/

hp

=gethostbyname

(host);

30

AC

EC

++

Wra

pp

erT

uto

rial

Socket

Client

(cont'

d)

/*

Set

up

the

address

information

to

contact

the

server

*/

memset

((void

*)

&saddr,

0,

sizeof

saddr);

saddr.sin_family

=AF_INET;

saddr.sin_port

=port_num;

memcpy

(&saddr.sin_addr,

hp->h_addr,

hp->h_length);

/*

Establish

connection

with

remote

server

*/

connect

(s_fd,

(struct

sockaddr

*)

&saddr,

sizeof

saddr);

/*

Send

data

to

server

(correctly

handles

"incomplete

writes"

due

to

flow

control)

*/

while

((r_bytes

=read

(0,

buf,

sizeof

buf))

>0)

for

(w_bytes

=0;

w_bytes

<r_bytes;

w_bytes

+=

n)

n=

write

(s_fd,

buf

+w_bytes,

r_bytes

-w_bytes);

/*

Explicitly

close

the

connection

*/

close

(s_fd);

return

0;

} 31

ACEC++WrapperTutorial

C++SocketWrapperClient

constu_shortPORT_NUM=10000;

intmain(intargc,char*argv[])

{

charbuf[BUFSIZ];

char*host=argc>1?argv[1]:"ics.uci.edu";

u_shortport_num=

htons(argc>2?atoi(argv[2]):PORT_NUM);

INET_Addrserver_addr(port_num,host);

SOCK_Streamcli_stream;

SOCK_Connectorconnector.

//Establishtheconnectionwithserver.

connector.connect(cli_stream,server_addr);

32


C++SocketWrapperClient(cont'd)

//Senddatatoserver(correctlyhandles

//"incompletewrites").

for(;;){

ssize_tr_bytes=read(0,buf,sizeofbuf);

cli_stream.send_n(buf,r_bytes);

}

//Explicitlyclosetheconnection.

cli_stream.close();

return0;

}

33


SocketServer

#definePORT_NUM10000

int

main(intargc,char*argv[])

{

u_shortport_num=

htons(argc>1?atoi(argv[1]):PORT_NUM);

structsockaddr_insaddr;

ints_fd,n_fd;

/*Createalocalendpointofcommunication*/

s_fd=socket(PF_INET,SOCK_STREAM,0);

/*Setuptheaddressinformationto

becomeaserver*/

memset((void*)&saddr,0,sizeofsaddr);

saddr.sin_family=AF_INET;

saddr.sin_port=port_num;

saddr.sin_addr.s_addr=INADDR_ANY;

/*Associateaddresswithendpoint*/

bind(s_fd,(structsockaddr*)&saddr,

sizeofsaddr);

/*Makeendpointlistenforservicerequests*/

listen(s_fd,5);

34


SocketServer(cont'd)

/*Performstheiterativeserveractivities*/

for(;;){

charbuf[BUFSIZ];

structsockaddr_incli_addr;

intr_bytes,cli_addr_len=sizeofcli_addr;

structhostent*hp;

/*Createanewendpointofcommunication*/

while((n_fd=accept(s_fd,(structsockaddr*)

&cli_addr,

&cli_addr_len))==-1

&&errno==EINTR)

continue;

if(n_fd==-1)

continue;

hp=gethostbyaddr((char*)&cli_addr.sin_addr,

cli_addr_len,AF_INET);

printf("client%s:",hp->h_name),fflush(stdout);

/*Readdatafromclient(terminateonerror)*/

while((r_bytes=read(n_fd,buf,sizeofbuf))>0)

write(1,buf,r_bytes);

/*Closethenewendpoint

(listeningendpointremainsopen)*/

close(n_fd);

}

}

35


C++WrapperSocketServer

constu_shortPORT_NUM=10000;

//SOCK_SAPServer.

int

main(intargc,char*argv[])

{

u_shortport_num=

argc==1?PORT_NUM:::atoi(argv[1]);

//Createaserver.

SOCK_Acceptoracceptor((INET_Addr)port_num);

SOCK_Streamnew_stream;

INET_Addrcli_addr;

36


C++WrapperSocketServer(cont'd)

//Performstheiterativeserveractivities.

for(;;){

charbuf[BUFSIZ];

//CreateanewSOCK_Streamendpoint(note

//automaticrestartiferrno==EINTR).

acceptor.accept(new_stream,&cli_addr);

printf("client%s:",cli_addr.get_host_name());

fflush(stdout);

//Readdatafromclient(terminateonerror).

for(;;){

ssize_tr_bytes;

r_bytes=new_stream.recv(buf,sizeofbuf);

if(r_bytes<=0)break;

write(1,buf,r_bytes);

}

//Closenewendpoint(listening

//endpointstaysopen).

new_stream.close();

}

37

ACEC++

WrapperTutorial

ACEC++

WrapperDesignPrinciples

�

Enforcetypesafetyatcompile-time

�

Allowcontrolledviolationsoftypesafety

�

Simplifyforthecommoncase

�

Replaceone-dimensionalinterfaceswithhierarchicalclasscategories

�

Enhanceportabilitywithparameterizedtypes

�

Inlineperformancecriticalmethods

�

De�neauxiliaryclassestohideerror-pronedetails

38

ACEC++

WrapperTutorial

EnforceTypesafetyatCompile-Time

Socketscannotdetectcertainerrorsatcompile-time,e.g.,

ints_sd=socket(PF_INET,SOCK_STREAM,

0);

//...

bind(s_sd,...);//Bindaddress.

listen(s_sd);//Makeapassive-mode

socket.

//Errornotdetecteduntilrun-time.

read(s_sd,buf,sizeofbuf);

ACEenforcestype-safetyatcompile-timeviafactories,e.g.:

SOCK_Acceptor

acceptor(port);

//Error:recv()notamethodofSOCK_Acceptor.

acceptor.recv

(buf,sizeofbuf);

39

ACEC++

WrapperTutorial

AllowControlledViolationsofTypesafety

MakeiteasytousetheC++Socketwrapperscorrectly,hardtouseit

incorrectly,butnotimpossibletouseitinwaystheclassdesignersdidnot

anticipate

�

e.g.,itmaybenecessarytoretrievetheunderlyingsockethandle:

fd_setrd_sds;

FD_ZERO(&rd_sds);

FD_SET(acceptor.get_handle

(),&rd_sds);

select(acceptor.get_handle

()+1,&rd_sds,0,0,0);

40

ACEC++

WrapperTutorial SupplyDefaultParameters

SOCK_Connector

(SOCK_Stream

&new_stream,

constAddr&remote_sap,

ACE_Time_Value

*timeout=0,

constAddr&local_sap=Addr::sap_any,

intprotocol_family

=PF_INET,

intprotocol=0);

Theresultisextremelyconciseforthecommoncase:

SOCK_Stream

stream;

//Compilersuppliesdefaultvalues.

SOCK_Connector

con(stream,INET_Addr(port,host));

41

ACEC++

WrapperTutorial

De�neParsimoniousInterfaces

e.g.,useLSOCKtopasssockethandles:

LSOCK_Stream

stream;

LSOCK_Acceptor

acceptor("/tmp/foo");

acceptor.accept

(stream);

stream.send_handle

(stream.get_handle

());

versus

LSOCK::send_handle(constHANDLEsd)const{

u_chara[2];ioveciov;msghdrsend_msg;

a[0]=0xab,a[1]=0xcd;

iov.iov_base=(char*)a;iov.iov_len=sizeofa;

send_msg.msg_iov=&iov;send_msg.msg_iovlen=1;

send_msg.msg_name=(char*)0;

send_msg.msg_namelen=0;

send_msg.msg_accrights=(char*)&sd;

send_msg.msg_accrightslen=sizeofsd;

returnsendmsg(this->get_handle(),&send_msg,0);

42

ACEC++

WrapperTutorial

CombineMultipleOperationsintoOneOperation

Creatingaconventionalpassive-modesocketrequiresmultiplecalls:

ints_sd=socket(PF_INET,SOCK_STREAM,

0);

sockaddr_in

addr;

memset(&addr,0,sizeofaddr);

addr.sin_family

=AF_INET;

addr.sin_port

=htons(port);

addr.sin_addr.s_addr

=INADDR_ANY;

bind(s_sd,&addr,addr_len);

listen(s_sd);

//...

SOCKAcceptorcombinesthisintoasingleoperation:

SOCK_Acceptor

acceptor((INET_Addr)

port);

43


Create Hierarchical Class Categories

LSOCK LSOCKDgramDgram

SOCK SOCKDgramDgram

SOCK SOCKCODgramCODgram

LSOCK LSOCKCODgramCODgram

LSOCK LSOCKConnectorConnector

LSOCK LSOCKAcceptorAcceptor

SOCK SOCKAcceptorAcceptor

SOCK SOCKConnectorConnector

SOCK SOCK

AA

LSOCK LSOCK

AA

IPCIPCSAPSAP

AA

SOCK SOCKDgramDgramMcastMcast

SOCK SOCKDgramDgramBcastBcast

GROUPGROUP

COMMCOMM

DATAGRAMDATAGRAM

COMMCOMM

STREAMSTREAM

COMMCOMM

CONNECTIONCONNECTION

ESTABLISHMENTESTABLISHMENT

SOCKSOCKStreamStream

LSOCKLSOCKStreamStream

� Shared behavior is isolated in base classes

� Derived classes implement di�erent communication services,

communication domains, and connection roles

44


Enhance Portability with Parameterized Types

OSOS KERNEL KERNEL

PROTOCOL MECHANISMSPROTOCOL MECHANISMS

((TCPTCP//IPIP,, OSI,OSI, ETC ETC.).)

USERUSER

SPACESPACE

DISTRIBUTED

APPLICATION 1

APPLICATIONAPPLICATION11 DISTRIBUTED

APPLICATION 3

APPLICATIONAPPLICATION33DISTRIBUTED

APPLICATION 2

APPLICATIONAPPLICATION22

KERNELKERNEL

SPACESPACE

BSD SOCKET

API

COMMON INTERFACECOMMON INTERFACE

((PARAMETERIZED TYPESPARAMETERIZED TYPES))

SOCKETSOCKET

API

SOCK_SAP

BSD SOCKET

API

SYSTEM VTLI API

TLI_SAP

NETWORK

INTERFACE

45


Enhance Portability with Parameterized Types (cont'd)

Switching wholesale between sockets and TLI simply requires instantiating

a di�erent C++ wrapper, e.g.,

// Conditionally select IPC mechanism.

#if defined (USE_SOCKETS)

typedef SOCK_Acceptor PEER_ACCEPTOR;

#elif defined (USE_TLI)

typedef TLI_Acceptor PEER_ACCEPTOR;

#endif // USE_SOCKETS.

int main (void)

{// ...

// Invoke the echo_server with appropriate

// network programming interfaces.

echo_server<PEER_ACCEPTOR> (port);

}46


Inline Performance Critical Methods

Inlining is time and space e�cient since key methods are very short:

class SOCK_Stream : public SOCK

{public:

ssize_t send (const void *buf, size_t n)

{return ACE_OS::send (this->get_handle (), buf, n);

}ssize_t recv (void *buf, size_t n)

{return ACE_OS::recv (this->get_handle (), buf, n);

}};

47

ACEC++

WrapperTutorial

De�neAuxiliaryClassestoHideError-ProneDetails

StandardCsocketaddressingisawkwardanderror-prone

�

e.g.,easytoneglecttozero-outasockaddrinorconvertport

numberstonetworkbyte-order,etc.

ACEC++SocketWrappersde�neclassestohandlethesedetails

classINET_Addr:publicAddr{

public:

INET_Addr(u_shortport,longip_addr=0){

memset(&this->inet_addr_,

0,sizeofthis->inet_addr_);

this->inet_addr_.sin_family

=AF_INET;

this->inet_addr_.sin_port

=htons(port);

memcpy(&this->inet_addr_.sin_addr,

&ip_addr,sizeofip_addr);

} //...

private:

sockaddr_ininet_addr_;

};

48

ACEC++

WrapperTutorial

SummaryofACEC++

SocketWrapperDesign

Principles

�

Domainanalysisidenti�esandgroupsrelatedclassesofexistingAPI

behavior

{Examplesubdomainsinclude

�

Localcontextmanagementandoptions,datatransfer,

connection/terminationhandling,etc.

�

Datagramsvs.streams

�

Localvs.remoteaddressing

�

Activevs.passiveconnectionroles

�

Theserelationshipsaredirectlyre ectedintheACEC++Socket

wrapperinheritancehierarchy

49

ACEC++

WrapperTutorial

SummaryofACEC++

SocketWrapperDesign

Principles(cont'd)

�

TheACEC++Socketwrappersaredesignedtomaximizereusability

andsharingofcomponents

{Inheritanceisusedtofactoroutcommonalityanddecouplevariation

e.g.,

�

Pushcommonservices\upwards"intheinheritancehierarchy

�

Factoroutvariationsinclient/serverportionsofsocketAPI

�

Decoupledatagramvs.streamoperations,localvs.remote,etc.

{Inheritancealsosupports\functionalsubsetting"

�

e.g.,passingopen�lehandles...

50

ACEC++

WrapperTutorial

SummaryofACEC++

SocketWrapperDesign

Principles(cont'd)

�

Performanceimprovementstechniquesinclude:

{Inlinefunctionsareusedtoavoidadditionalfunctioncallpenalties

{Dynamicbindingisusedsparinglytoreducetime/spaceoverhead

�

i.e.,itiseliminatedforrecv/sendpath

�

Notethedi�erencebetweenthecompositionvs.

decomposition/compositionaspectsindesigncomplexity

{i.e.,ACEC++Socketwrappersareprimarilyanexercisein

compositionsincethebasiccomponentsalreadyexist

{MorecomplexOOdesignsinvolvebothaspects...

�

e.g.,theACEStreams,ServiceCon�gurator,andReactor

frameworks,etc.

51

ACEC++

WrapperTutorial

ConcludingRemarks

�

De�ningC++wrappersfornativeOSAPIssimpli�esthedevelopment

ofcorrect,portable,andextensibleapplications

{C++inlinefunctionsensurethatperformanceisn'tsacri�ced

�

ACEcontainsmanyC++wrappersthatencapsulateUNIX,Win32,and

RTOSAPIsinterfaces

{e.g.,sockets,TLI,namedpipes,STREAMpipes,etc.

�

ACEcanbeintegratedconvenientlywithCORBAandDCOMprovidea

exiblehigh-performance,real-timedevelopmentframework

52

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