C++ network programming. Vol. 2 Systematic reuse with ACE and frameworks

372 Pages·2.083 MB·English

by  Schmidt, Douglas C;Huston, Stephen D

C++ Network Programming
Volume 2
The C++ In-Depth Series
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C++ Network Programming
Volume 2
Systematic Reuse with ACE and Frameworks
Douglas C. Schmidt
Stephen D. Huston
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C++networkprogramming/DouglasC.Schmidt,StephenD.Huston.
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Includesbibliographicalreferencesandindex.
Contents:Vol.2.SystematicreusewithACEandframeworks.
ISBN0-201-79525-6(v.2:pbk.)
1.C++(Computerprogramlanguage)2.Object-orientedprogramming(Computer
science)3.Computernetworks.I.Huston,StephenD.II.Title.
QA76.73.C153S3682002
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Second printing, February 2005
Contents
Foreword vii
AboutThisBook xi
Chapter1 Object-OrientedFrameworksforNetworkProgramming 1
1.1 AnOverviewofObject-OrientedFrameworks 1
1.2 ComparingSoftwareDevelopmentandReuseTechniques 4
1.3 ApplyingFrameworkstoNetworkProgramming 12
1.4 ATourthroughtheACEFrameworks 14
1.5 Example: ANetworkedLoggingService 19
1.6 Summary 21
Chapter2 ServiceandConfigurationDesignDimensions 23
2.1 ServiceandServerDesignDimensions 24
2.2 ConfigurationDesignDimensions 34
2.3 Summary 38
Chapter3 TheACEReactorFramework 39
3.1 Overview 39
3.2 TheACE Time ValueClass 42
3.3 TheACE Event HandlerClass 46
3.4 TheACETimerQueueClasses 61
3.5 TheACE ReactorClass 70
3.6 Summary 86
Chapter4 ACEReactorImplementations 87
4.1 Overview 87
4.2 TheACE Select ReactorClass 89
4.3 TheACE TP ReactorClass 99
v
vi CONTENTS
4.4 TheACE WFMO ReactorClass 103
4.5 Summary 113
Chapter5 TheACEServiceConfiguratorFramework 115
5.1 Overview 115
5.2 TheACE Service ObjectClass 118
5.3 TheACE Service RepositoryClasses 126
5.4 TheACE Service ConfigClass 138
5.5 Summary 154
Chapter6 TheACETaskFramework 155
6.1 Overview 155
6.2 TheACE Message QueueClass 157
6.3 TheACE TaskClass 183
6.4 Summary 202
Chapter7 TheACEAcceptor-ConnectorFramework 203
7.1 Overview 203
7.2 TheACE Svc HandlerClass 206
7.3 TheACE AcceptorClass 216
7.4 TheACE ConnectorClass 229
7.5 Summary 256
Chapter8 TheACEProactorFramework 257
8.1 Overview 257
8.2 TheAsynchronousI/OFactoryClasses 261
8.3 TheACE HandlerClass 270
8.4 TheProactiveAcceptor-ConnectorClasses 278
8.5 TheACE ProactorClass 286
8.6 Summary 296
Chapter9 TheACEStreamsFramework 297
9.1 Overview 297
9.2 TheACE ModuleClass 299
9.3 TheACE StreamClass 314
9.4 Summary 318
Glossary 319
Bibliography 329
Index 337
Foreword
TheADAPTIVECommunicationEnvironment(ACE)toolkithasachievedenormoussuc-
cess in the area of middleware for networked computing. Due to its flexibility, perfor-
mance, platform coverage, and other key properties, ACE enjoys broad acceptance by the
networkedapplicationsoftwarecommunity,asevidencedbyitsuseinthousandsofapplica-
tions,inscoresofcountries,andindozensofdomains. ACEhasalsoreceivedconsiderable
attentionbeyondthemiddlewarecommunitysinceit’sanopen-sourcerolemodelforhigh-
qualityandwell-designedpattern-orientedsoftwarearchitectures.
ButwhyisACEsosuccessful? Addressingthisquestionproperlytakessomethought.
To start off, let’s reconsider the Foreword from C++ Network Programming: Mastering
Complexity with ACE and Patterns (C++NPv1) and resume the mass transit analogy pre-
sented there by my colleague Steve Vinoski. Steve’s right that a high-quality mass transit
system consists of more than just aircraft, airports, trains, train stations, and rails. It also
needs less obvious infrastructure, such as scheduling, routing, ticketing, maintenance, and
monitoring. But even a complete collection of ingredients is still not sufficient to develop
aneffectivemasstransitsystem. Arrangingtheseingredientssotheyseamlesslyfulfilltheir
primaryobjective—fastandreliabletransportationofpeople—isequallyimportant. Would
you use a mass transit system whose ticketing was located in a train maintenance location
oranairporthangar,orwhoseplannedandactualschedulingandroutingweren’tavailable
tothepublic? Idoubtit!
Thesuccessofmasstransitsystemsdependsonmorethantheknowledgeoftheinfra-
structurepartsthatareprovided—itdependsonhowthesedifferentpartsmustbeconnected
and integrated with their environment. This knowledge enables architects of mass transit
systemstointegrateindividualpartsintohigher-levelbuildingblocksandtoconnectthese
buildingblockseffectively. Forexample,ticketing,informationpoints,baggageoffices,and
boarding are integrated in train stations located at city centers or major suburban centers.
Likewise, airports are often located near large cities and connected by frequent express
trains.
vii
viii Foreword
Even mass transit centers themselves are arranged so that activities can be performed
effectively. Forexample,whenyouenteratrainstationorairportviathemainentrance,you
find ticket agents, information centers, and timetables. You also find shops to satisfy your
travelneeds. Asyouenterthemaintrainhallorairportconcourse,youfindotherinforma-
tion centers, up-to-date scheduling information, and the platforms and gates for boarding
the trains and planes. Mass transit centers thus not only provide all necessary services
to begin and end a journey, they also organize their internal “control flows” effectively.
While the core structures and control flows in most train stations and airports are similar,
their concrete realization can differ widely. Yet we all recognize these mass transit center
patterns immediately since they follow key invariants that we’ve learned through years of
experience.
Sowhat’stheconnectionbetweensuccessfulmasstransitsystemdesignandthesuccess
ofACE?Theanswerissimple: Inadditiontothebasicnetworkcomputingingredients(the
wrapper facades that Doug and Steve introduced in C++NPv1), ACE also includes use-
ful object-oriented frameworks that build upon these wrapper facades and provide useful
higher-level communication services, such as event demultiplexing and dispatching, con-
nectionmanagement,serviceconfiguration,concurrency,andhierarchicallylayeredstream
processing. The ACE framework services satisfy many networked software needs by or-
ganizing the structures and internal control flows of your applications effectively via key
patternslearnedthroughyearsofexperience.
TheACEframeworksofferyouanumberofimportantbenefits:
• Youneedn’tdevelopthecapabilitiesprovidedbyACE,whichwillsaveconsiderable
time and effort. You can therefore focus on your key responsibility: implementing
theapplicationfunctionalityrequiredbyyourcustomersandendusers.
• TheACEframeworksreifytheextensivenetworkprogrammingexpertisethatDoug,
Steve,andtheircolleagueshavegainedoverseveraldecades. Inparticular,theACE
frameworksefficientlyimplementthecanonicalclasses,classrelationships,andcon-
trol flows common to networked applications. The ACE frameworks are tested reg-
ularly by thousands of users from around the world, which has yielded many useful
corrections and improvements. As an ACE user, you can directly leverage the cor-
rectness,effectiveness,andefficiencyoftheACEframeworksinyourapplications.
• A framework isn’t a framework if it can’t be adapted to specific user needs. This
means you can adapt the ACE frameworks at key points of variation in networked
applications. For example, the ACE Reactor framework can be adapted to use dif-
ferent event demultiplexer functions, such as WaitForMultipleObjects() or
select(). Likewise, the ACE Acceptor-Connector framework can be configured
with different IPC mechanisms. While this adaptability is beneficial by itself, ACE
goes a step further: for many adaptations you can configure the desired strategies
fromavailableandinterchangeableimplementations. InadditiontothedifferentRe-
Foreword ix
actorimplementationsmentionedabove,forinstance,ACEprovideswrapperfacades
forvariousIPCmechanisms,suchastheSockets,SSL,TLI,andsharedmemory,that
helptoconfiguretheACEAcceptor-Connectorframeworkforspecificplatformsand
applications.
• Last but not least, the ACE frameworks don’t exist in isolation. You can therefore
combinetheminnovelwaystocreatenetworkedapplicationsandentirelynewtypes
of middleware. For example, you can integrate the Reactor framework with the
Acceptor-Connector framework to separate connection establishment from service
processing functionality in event-driven applications. You can likewise introduce
variousformsofconcurrencyintoyourapplicationsusingtheACETaskframework.
As a result of advising and leading many software projects over the years, I’ve found
that ACE greatly simplifies the task of employing reusable middleware that can be cus-
tomized readily to meet the needs of networked applications. Not all networked applica-
tionsneedheavyweightmiddleware,suchasapplicationservers,webservices,andcomplex
componentmodels. Yetmostnetworkedapplicationscanbenefitfromportableandefficient
hostinfrastructuremiddlewarelikeACE.ThisflexibilityisthecoreofACE’ssuccesssince
you needn’t commit to an entire middleware suite if you don’t use all of it. Instead, you
can combine just the essential ACE middleware classes you need to compose applications
thataresmall,butaspowerfulasnecessary. Forthisreason,IpredictthatACEwillstillbe
widelyusedlongaftertheinfluenceoftoday’sheavyweightmiddlewarehaswaned.
ACE’s tremendous flexibility also needn’t lead to a sea of incompatible middleware
implementations. For example, if you build an embedded system that speaks the CORBA
Internetinter-ORBprotocol(IIOP)totheoutsideworld,youcanuseTheACEORB(TAO),
which is a CORBA-compliant, open-source, real-time object request broker (ORB) built
usingtheACEwrapperfacadesandframeworks. IfCORBAisoverkillforyourapplication
needs,however,youcanbuildcustom,yetinteroperable,middlewareusingtheappropriate
ACE classes. Both solutions can be based on the same core structures and protocols, such
as the ACE Common Data Representation (CDR) classes and its TCP/IP Socket wrapper
facades. They can therefore communicate seamlessly with one another, just as you can
take a train from Paris to Istanbul—the famous Orient Express—and travel through many
Europeancountrieswithouthavingtochangetrainsduetoincompatiblerailroadnetworks.
As Steve Vinoski and I have pointed out, there are many similarities between high-
qualitymasstransitsystemsandhigh-qualitynetworkingmiddleware. Tomeandthousands
of other C++ developers around the world, ACE is the toolkit for building the latter! Af-
ter saying so many good things about ACE, however, let’s return to the main intent of this
foreword: introducing the second volume (C++NPv2) of the C++ Network Programming
series. As with all software technologies and middleware, the more you understand your
tools, the better you’ll be able to apply them. It turns out that using ACE in your appli-
cations is just one aspect of improving your networked software. To benefit significantly