Microsoft COM and 'NET Framework

1
Microsoft COM and .NET Framework

• Srini Ganapathy
• Developer Support Engineer
• Developer Support Distributed Services
• Microsoft Corporation

2
Agenda

• Brief introduction to Microsoft COM
• Microsoft .NET and CLR
• COM services accessed through managed code
• Contexts transactions
• Security
• Loosely-coupled events
• Queued components
• Object pooling just-in-time activation
• Remoting and COM
• Registration of COM components
• Miscellanea
• Questions

3
Brief Introduction to COM

• COM is about providing services
• Services provided by COM contexts
• Automatic transactions
• Object pooling
• Just-in-time activation (JITA)
• Loosely-coupled events
• Etc.
• COM provides these services at the operating
  system level

4
.NET CLR and COM

• CLR introduces a newer and easier programming
  model for COM
• The COM services are still available only at the
  operating system/unmanaged world
• Transitions between managed/unmanaged layers are
  taken care of by System.EnterpriseServices
  namespace
• Services are made available to components using
  attributes

5
.NET and ServicedComponent

• COM class derives from ServicedComponent
• Example
• ComVisible(true)
• ObjectPooling(MinPoolSize2, MaxPoolSize5)
• Guid("57F01F20-9C0C-4e63-9588-720D5D537E66")
• Transaction(TransactionOption.Required)
• public class SVCCompClass ServicedComponent
• In COM 1.0, the list of services are not changed
• In COM 1.5 (Microsoft Windows XP Professional
  and .NET server), newer services are available to
  leverage CLR features

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Contexts

• Contexts are the primary service providers
• System.EnterpriseServices.ContextUtil class
  provides access to contexts as did
  CoGetObjectContext
• Rich set of static and member functions exposed
  by System.EnterpriseServices.ContextUtil

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ContextUtil Class

• Methods exposed by the ContextUtil class are
• SetComplete
• SetAbort
• EnableCommit
• DisableCommit
• IsCallerInRole
• GetNamedProperty

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ContextUtil Class (2)

• Some useful static members of ContextUtil class
• ActivityId
• IsSecurityEnabled
• TransactionId
• DeactivateOnReturn
• MyTransactionVote

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ContextUtil Class Transaction Control

• public bool TestTransMethod()
• //Setting the doneness bit to true
• ContextUtil.DeactivateOnReturn true
• //Setting the initial transaction voting to
  abort
• ContextUtil.MyTransactionVote
  TransactionVote.Abort
• //Do Some Transaction work
• //if success, commit the work
• ContextUtil.MyTransactionVote
  TransactionVote.Commit
• return true

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ContextUtil Class Transaction Control (2)

• public void TestTransMethod2()
• try
• //Do Some Transaction work
• ContextUtil.SetComplete()
• catch (Exception ex)
• ContextUtil.SetAbort()
• //Handle the exception

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ContextUtil Class Transaction Control (3)

• AutoComplete()
• public void TestTransMethod2()
• //Do Some Transaction work
• AutoComplete attribute calls SetComplete/SetAbort
  appropriately

12
Security

• Access, authentication, and impersonation levels
  specified using attributes at the assembly level
• assemblyApplicationAccessControl(
• AccessChecksLevel
• AccessChecksLevelOption.ApplicationComponent,
• AuthenticationAuthenticationOption.Default,
• ImpersonationLevelImpersonationLevelOption.Imper
  sonate)
• These attributes act on the COM application as a
  whole

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Security Component Level

• Component-level security enabled using the
  ComponentAccessControl attribute
• ComponentAccessControl
• Role-based security enabled by attribute
• SecurityRole(AllUserGroup",true)

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Security SecurityCallContext class

• Describes the chain of callers until the current
  method call
• CurrentCall property returns SecurityCallContext
  for a component
• SecurityCallers collection maintains the
  security call chain

15
Security SecurityCallContext Class

• SecurityIdentity contains information regarding
  an identity in a COM call chain
• Other important methods IsSecurityEnabled,
  IsCallerInRole, IsUserInRole, etc.

16
Loosely-Coupled Events Programming

• Attributes come in handy!!
• EventClass attribute declares an EventClass
• FireInParallel, AllowInprocSubscribers, and
  PublisherFilter properties can be specified in
  EventClass attribute constructor

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Queued Component Programming

• Enabling an application to be queued
• assembly ApplicationQueuing(Enabled
  true,QueueListenerEnabledtrue)
• Enabling interface-level queuing applied on a
  component class
• InterfaceQueuing(Interface IQueuedInterface"
  
• Exception class specified through
  ExceptionClass attribute on a component class

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Object Pooling

• Any .NET ServicedComponent could be pooled
• Pooling is made available through the
  ObjectPooling attribute
• ObjectPooling(MinPoolSize2, MaxPoolSize5)
• public class SVCCompClass ServicedComponent

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Object Pooling (2)

• The values should NOT be overridden using
  Component Services Explorer
• Override CanBePooled method to return a vote on
  pooling
• protected override bool CanBePooled()
• return true

20
Object Pooling JITA

• Both OP JITA could be combined for a simpler
  and a scalable component architecture
• Enabling JITA on a pooled component returns it
  to the pool on each method return
• From the client side, use Dispose() to return the
  object to the pool if JIT is not enabled

21
Remoting and COM

• Remoting communication protocol between
  entities in CLR
• Remoting could be used to access managed COM
  components
• IIS as a remoting host
• Custom host used to invoke COM component

22
Hosting a COM Component Using IISServer-Side
Configuration

• Create a virtual directory out of the component
  directory. Assembly present in \bin subdirectory.
• Expose end points and protocol using the
  Web.config file for the IIS VRoot.

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Hosting a COM Component Using IIS Web.Config
File

• ltconfigurationgt
• ltsystem.runtime.remotinggt
• ltapplicationgt
• ltservicegt
• ltwellknown mode"SingleCall"type"SVCCompSoap.SVC
  CompSoapCls,SVCCompSoap objectUri"SVCCompSoap.so
  ap"/gt
• lt/servicegt
• lt/applicationgt
• lt/system.runtime.remotinggt
• lt/configurationgt

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Hosting a COM Component Using IISClient Side

• Sample client code
• RemotingConfiguration.Configure("SVCCompSoapClnt.c
  onfig")
• SVCCompSoapCls obj new SVCCompSoap.SVCCompSoapCl
  s()
• string str obj.Method1()
• Console.WriteLine(str.ToString())
• Console.ReadLine()
• obj.Dispose()

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Hosting a COM component using IIS Client
Configuration File

• ltconfigurationgt
• ltsystem.runtime.remotinggt
• ltapplicationgt
• ltclient url"http//localhost/SVCCompSoa
  p/"gt
• ltwellknown
• type"SVCCompSoap.SVCCompSoa
  pCls, SVCCompSoap"
• url"http//localhost/SVCCom
  pSoap/SVCCompSoap.soap"/gt
• lt/clientgt
• lt/applicationgt
• lt/system.runtime.remotinggt
• lt/configurationgt

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COM Component as a Web Service

• New feature with COM 1.5
• An easy check box creates the VRoot
• This approach uses .NET remoting

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Remoting Using a Custom Host

• This needs a listener process to expose the
  endpoints for the COM component

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Remoting Using a Custom Host Listener Process

• The listener process can be configured to use a
  Config file containing protocol and port info
• Code snippet of a listener process
• static void Main(string args)
• // TODO Add code to start application here
• RemotingConfiguration.Configure("SVCCompTCPListen
  er.config")
• Console.WriteLine("Listening on Port 8888")
• Console.ReadLine()

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Using a Custom Host Listener Processs Config
File

• Config file for the listener process
• ltconfigurationgt
• ltsystem.runtime.remotinggt
• ltapplication name"SVCCompTCP"gt
• ltservicegt
• ltwellknown mode"SingleCall"
  type"SVCCompTCP.SVCCompTCPCls, SVCCompTCP"
  objectUri"SVC.rem" /gt
• lt/servicegt
• ltchannelsgt
• ltchannel ref"tcp" port8888" /gt
• lt/channelsgt
• lt/applicationgt
• lt/system.runtime.remotinggt
• lt/configurationgt

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Deployment of COM Applications

• Attributes to specify a library/server
  application
• assemblyApplicationActivation(ActivationOption.S
  erver)
• Provide a strong name to the assembly
• assembly AssemblyKeyFile("..\\..\\SVCComp.snk")
  

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Deployment of COM Applications (2)

• Add the assembly to the global assembly cache
• C\Documents and Settingsgt gacutil /I SVCComp.dll
• Register the assembly with the COM
  infrastructure
• C\Documents and Settingsgt regsvcs SVCComp.dll
• Components could be registered only by members of
  the administrators group

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Deployment of Client Proxies

• Usual methodology of exporting works
• Ensure compatibility is checked between COM
  versions (1.5 vs. 1.0)
• After installation, set a reference in the client
  application

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Miscellanea

• Avoiding multiple installations of components in
  a COM package
• Use a GUID to decorate a COM component class
• OR
• Explicitly set all parts of the AssemblyVersion
• assembly AssemblyVersion("1.0.")
• Static methods execute in callers context

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Good Sources of Information

• Platform SDK
• COM Web Services
• A good article on enterprise services and COM
• A good article on COM 1.5

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