Transparent Mobility of Distributed Objects using .NET

Transparent Mobility of Distributed Objects using .NET

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  4th International Conferencein Central Europe on .NET Technologies Transparent Mobility of Distributed Objects using .NET Cristóbal Costa, Nour Ali, Carlos Millan, Jose A. Carsí
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  Contents > Background & Motivation > Search Agents case study > OOAttachments approach > Conclusions 2 30/05/200 .NET Technologies 2006
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  Background > Previous workin Component-Based Aspect-Oriented Software Architectures > A characteristic is that the components neglect distributed nor local references of their partners > Transparent entities called Attachments are responsible of:  Interconnecting components  Providing transparent mobility and communication Node1 Node2 Component1 Component2 Attachments 3 30/05/200 .NET Technologies 2006
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  Motivation > To transferprevious experience in attachments to connect objects, instead of aspect-oriented components > To provide a library to support the development of transparent mobility of distributed objects > These features must be provided:  A non intrusive and transparent way of programming  Code should not be precompiled nor preprocessed  Efficiency 4 30/05/200 .NET Technologies 2006
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  Motivation > For example,it can be used by Client & Server architectures to manage both location changes in a transparent way > Why the client object has to worry about its server? Server Client 5 30/05/200 .NET Technologies 2006
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  State of theart > This problem has been dealt in Mobile Agent Systems Most of them are built on Java:  Aglets, Nomads, MobJeX, Voyager, JADE, ProActive, … > There are few approaches on .NET but still in development  MAPNET, Nomad, EtherYatri.NET > Common characteristics of these approaches:  Agents are defined by means of inheritance.  In most of them, the agent has to define all its functionality in one method (usually “Run”) with a specific signature  Events are captured by overriding inherited methods  Communication among agents is realized: by using generic proxies (like “AgentProxy”), by passing messages, or by implementing specific services 6 30/05/200 .NET Technologies 2006
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  Strong vs WeakMobility Strong Mobility Weak Mobility Agent processes are interrupted in The programmer must take care a transparent way of their processes In order to implement strong mobility It is the programmer who saves the ability of thread serialization is processes information before moving required. and restores it after moving. Two main alternatives: As no customization is needed, the By extending the Framework solution is more portable (e.g. JavaThreads [Bouchenak03]) → New releases of the Framework would make it useless By preprocessing the source or binary code (e.g. Brakes [Truyen00]) → Less eficiency 7 30/05/200 .NET Technologies 2006
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  Contents > Background & Motivation > Search Agents case study > OOAttachments approach > Conclusions 8 30/05/200 .NET Technologies 2006
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  SearchAgents case study >There are a lot of resources over the Internet from which we want to collect distributed information > The search grows as a tree, so we need to be able to explore the resources dynamically in a distributed way A B E C D > Our solution: to send only a few agents capable of establishing transparent mobile communications  Network resources are not overloaded, as there only are a few agents travelling through the network  Agents can exchange new subsearches without realizing where the others are  They are completely autonomous: they only come back with the results, so the sender could have been disconnected during the process (e.g. mobile clients) 9 30/05/200 .NET Technologies 2006
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  SearchAgent implementation > The inheritance is not limited: we do not have to inherit from a specific class to benefit from mobility > By this way, an object is made remotely accessible to others > A specific interface can be specified to restrict offered services > An object obtains a reference of a remote object by specifying its ID and current location > The remote reference is a transparent proxy that provides all the remote methods > By this way, an object moves itself to another host > There are no need to use specific methods and signatures for being called when object mobility finishes > Parameters can also be provided (e.g. for providing initialization information) 10 30/05/200 .NET Technologies 2006
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  Contents > Background & Motivation > Search Agents case study > The OOAttachments approach > Conclusions 11 30/05/200 .NET Technologies 2006
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  The OOAttachments approach >Features:  Objects can move autonomously among computers without having to take into account how distributed communications with other objects are performed  Since a connection is established, location-awareness is provided  No need for a centralized infrastructure to manage mobility and object registration services  Dynamic code generation and reflection is combined in order to be able of calling code dynamically, so code precompilation is not needed > Constraints:  Weak mobility is provided, so objects must take care of their threads before moving  In order to establish the first connection, a client object needs to know where the server object is located  Each mobile object must be marked as Serializable  The middleware must be running in each computer 12 30/05/200 .NET Technologies 2006
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  The OOAttachments approach > Objects are connected through entities called Attachments Host A Host B [Serializable] [Serializabl e] Attachment «generated-code» AttachmentServ er Serv er-AttClient objectName: string IDeserializationCallback 1 «NonSerialized» objRef: object Search Search [Serializable] objType: T ype AttachmentClient attClientsURLs: string [0..*] (ArrayList) methodInformation: MethodInfo [1..*] serverIsMovi ng: bool parentType: stri ng serverURL: string AttachmentServer(objRef, objectName, objType) Agent 1 Agent 2 serviceIsConsum ing: bool[] BeginServerMobility() : void EndServerMobility(objectReference) : void Process(methodID, args) : object BeginClientMobility() : void EndClientMobili ty() : void [NonSerialized] 1 StopProcessingServices() : void MarshalByRefObject AttachmentServ erMediator [NonSerialized] 1 methodsList: Delegate[] MarshalByRefObject AttachmentClientMediator RegisterClient(attClientURL) : MethodInfo[1..*] ServerM obilityBegan() : void UnRegisterClient(attClientURL) : void ServerM obilityEnded(newURL) : void RedirectService(methodID, args) : object Client behaviour: Server behaviour: It invokes “NotifyNewLocation” Object layer It offers the “NotifyNewLocation” service Client behaviour: Server behaviour: provided by the AttachmentClient Attachments layer provided by the AttachmentServer .NET Remoting layer > Attachments are created through the AttachmentsManager class 13 30/05/200 .NET Technologies 2006
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  How it works:Communication Host A Host B Attachment Search Search Agent 1 Agent 2 > Server-behaviour is defined by > Server-behaviour is defined by AttachmentServ er [Serializable] the AttachmentServer object the AttachmentServer object objectName: string «NonSerialized» objRef: object objType: Type  Incoming request services are forwarded Incoming request services are forwarded attClientsURLs: string [0..*] (ArrayList) serverIsMoving: bool towards the server object towards the server object AttachmentServer(objRef, objectName, objType)  It notifies about mobility to its connected It notifies about mobility to its connected BeginServerMobility() : void EndServerMobility(objectReference) : void objects objects  One entity is serializable (Marshal By One entity is serializable (Marshal By [NonSerialized]1 MarshalByRefObject Value), so its state can be migrated, and Value), so its state can be migrated, and AttachmentServ erMediator the other is accessible remotely (Marshal the other is accessible remotely (Marshal methodsList: Delegate[] By Reference) By Reference) RegisterClient(attClientURL) : MethodInfo[1..*] UnRegisterClient(attClientURL) : void RedirectService(methodID, args) : object 14 30/05/200 .NET Technologies 2006
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  How it works:Communication Host A Host B Attachment Search Search Agent 1 Agent 2 [Serializable] «generated-code» Serv er-AttClient > Client-behaviour is defined by the > Client-behaviour is defined by the IDeserializationCallback 1 [Serializable] AttachmentClient object AttachmentClient object AttachmentClient methodInformation: MethodInfo [1..*] > Composed by: > Composed by: parentType: string serverURL: string  A runtime generated proxy (MSIL) of the A runtime generated proxy (MSIL) of the serviceIsConsuming: bool[] remote object remote object Process(methodID, args) : object BeginClientMobility() : void  A remote accessible object which allows A remote accessible object which allows EndClientMobility() : void StopProcessingServices() : void to be notified about server mobility to be notified about server mobility [NonSerialized]  A serializable object that A serializable object that 1 MarshalByRefObject manages the attachmentClient state, manages the attachmentClient state, AttachmentClientMediator forwards services to the attachmentServer forwards services to the attachmentServer ServerMobilityBegan() : void ServerMobilityEnded(newURL) : void 15 30/05/200 .NET Technologies 2006
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  How it works:Communication > Inter-object communication is a very frequent operation: it must be as faster as possible > Communication is established dynamically on demand, so dynamic code invocation must be used  Its performance is: Reflection < Delegates << Direct Calls (code generation) > We dynamically generate code on establishing a connection in order to reduce these costs > Total introduced communication costs:  3 direct calls + 1 dynamic invocation (through delegates) ≈ +11% 16 30/05/200 .NET Technologies 2006
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  How it works:Mobility > The MoveObject service performs several steps:  The object to be moved and its communication processes (attachments) are packaged in a MobilityPackage object  This is serialized and transferred to the target host  Before unpacking, it is checked whether the required assemblies are available. If not, they are downloaded from the source host  The information is unpacked and, when communication processes are restored, the transferred object runs by invoking its specified method  If anything fails, all information is restored properly > Simultaneous mobility is also supported  An object can move to another host while other objects, that are connected to it, are being moved at the same time > The mobility process depends on the role of the object to be moved 17 30/05/200 .NET Technologies 2006
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  How it works:Mobility > Client behaviour:  If it has service requests being processed, the mobility process waits until they finish properly (weak mobility)  When mobility finishes, object state is restored, including its connections with remote objects > Server behaviour:  Before moving, pending requests from client objects must finish first  New requests from client objects are blocked (at the attachment level) until mobility finishes.  When mobility finishes, all communication processes are restored and client requests are processed 18 30/05/200 .NET Technologies 2006
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  Contents > Background & Motivation > Search Agents case study > The OOAttachments approach > Conclusions 19 30/05/200 .NET Technologies 2006
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  Conclusions & Futurework > An application can be easily adapted to benefit from these features:  Objects do not have to take into account what communication technology is used  Objects benefit from transparent (weak) mobility and distributed communications in a non-intrusive way  After establishing a connection, location-awareness of connected objects is provided > Further work:  Adaptability to Service-Oriented infrastructures, such as WCF  To provide security features to validate incoming code, such as by signing assemblies and by establishing trusted relations > OpenSource project home page: http://workspaces.gotdotnet.com/OOAttachments 20 30/05/200 .NET Technologies 2006
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  Questions 21 30/05/200 .NET Technologies 2006