AgentOS Kernel

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AgentOS Kernel

• Jieping Lu

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Topics
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1.AgentOS Kernel Overview
AgentOS Kernel Overview
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1.1. AgentOS Kernel Functionality
AgentOS kernel Overview

• Provides access to system services
• directory service, registry, etc ( to be
  discussed in service model).
• Enables network-wide communication between agents
• allows syn/asyn message sending, active/passive
  message receiving, etc (to be discussed in event
  model).
• Monitors network connection
• accepts agents from other nodes over the AgentOS
  network (to be discussed in Kernel class).

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1.2. Kernel Structure
AgentOS kernel Overview
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1.3. Kernel Components
AgentOS kernel Overview

• Classes required to run the AgentOS kernel
• AgentOS Class
• to start the AgentOS kernels functionality ( to
  be discussed in the demonstration).
• Kernel Class
• responsible for providing access to system
  services and the system-wide event exchange.
• ServiceEnum Class
• responsible for managing the list of available
  services, and creates instances of service
  providers as agents request them.
• Eventpool Class
• Provides a communication mechanism between agents
  within the same node.

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Topics
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2. Kernel Class

• Loaded by the AgentOS class to start the AgentOS
  kernel services.
• Functions
• starts the event pool to allow message exchange
  between agents.
• loads the service agents.
• accepts agents migrating from other nodes.

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2.1. Kernel Class Definition
Kernel Class

• Member Variables
• protected AgentOSConfig m_theConfig
• The instance of an AgentOSConfig class used in
  AgentOS
• protected ServiceEnum m_theServEnum
• The global ServiceEnum object
• protected ServerSocket m_sockListener
• The server socket used to listen to clients
• protected ThreadGroup m_tgSysContext
• Thread group of all system contexts
• protected ThreadGroup m_tgAgentContext
• Thread group of all normal contexts
• protected EventPool eventPool
• The instance of the event pool.

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2.1. Kernel Class Definition
Kernel Class

• Member Functions
• public Kernel()
• Setup the event pool.
• boolean initOS (AgentOSConfig Config)
• Setup ListernerSocket to allow incomming
  connections.
• void run()
• continuously waits for agents migrating from
  other nodes.
• public void startAgent(URL agentURL) throws
  Exception
• Starts an incoming agent.
• boolean setupListenerSocket()
• Creates a ServerSocket instance used to listen
  to clients (agents).

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2.2. Kernel Class Implementation
Kernel Class

• The constructor of the Kernel class will start
  the EventPool to handling message exchange among
  agents
• public Kernel()
• super("kernel thread")
• //start the event pool here
• eventPool new EventPool()

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2.2. Kernel Class Implementation
Kernel Class

• Initialize the kernel by loading the services and
  setting up the socket listener
• public boolean initOS(AgentOSConfig config)
• m_theConfig config
• m_theServEnum m_theConfig.m_seServices
• // set up the socket to listen to
  clients
• setupListenerSocket()
• // load the standard services into
  their agent contexts
• loadServices()
• return true

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2.2. Kernel Class Implementation
Kernel Class

• Run the Kernel thread
• public void run()
• while (true)
• // waiting for agents migrating from other
  nodes
• Socket sockClient m_sockListener.accept()
• //create the agent on this node
• ContextLoader cl new ContextLoader(this,
  null, sockClient)
• //start the agent on this node
• cl.start()

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2.2. Kernel Class Implementation
Kernel Class

• Other Functions
• public void startAgent(URL agentURL) throws
  Exception
• //create context using the agent class
• AgentContext context new AgentContext(this,ag
  entURL)
• context.initAgent()
• context.start()
• public int getPort()
• return m_theConfig.m_nPort

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2.2. Kernel Class Implementation
Kernel Class

• Other Functions
• protected boolean loadServices()
• return true // Currently not handling services
• protected boolean setupListenerSocket()
• m_sockListener new
  ServerSocket(m_theConfig.m_nPort)

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Topics
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3. Service Model

• Defines the way that agents can request services
• Three components
• ServiceEnum Class
• manages the services available on the node
• service implementers (under construction)
• special agents that provide services to other
  agents
• must register to the ServiceEnum to be accessed
  by other agents
• service providers (under construction)
• interfaces between serving agents and requesting
  agents
• Each service implementer class exposes its
  services through one service provider interface.

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3.1. ServiceEnum Class
Services Model

• Manages the list of services available on the
  system.
• standard services basic services provided by the
  kernel, such as directory service, registry
  service.
• Extended services other services.
• Keeps track of the service implementers that have
  been instantiated.
• Creates an instance of the corresponding service
  provider when an agent requests the service of a
  service implementer.

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3.1.1. ServiceEnum Class Definition
Services Model

• Member Variables
• protected final String strDefExtServiceCount
  "0"
• protected final String strDefStdServiceRoot
  "stdservices"
• protected final String strDefExtServiceRoot
  "extservices"
• default values for the number of services, root
  directory to find standard and extended services.
• protected int m_nExtServiceCount
• protected int m_nStdServiceCount
• number of extended and standard services.
• protected String m_strExtServiceRoot
• protected String m_strStdServiceRoot
• the root directory to find extended and standard
  services.
• protected String m_strStdServices
  "Directory", "Registry", "RunningList",
• 
  "HistoryList", "NodeNeighbor",
• the name of standard services.
• int m_nTotalServiceCount 0
• The count of all registered services standard
  and extended.
• protected Vector m_vecServices null
• The list of ServiceInfo objects one for each
  registered service.

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3.1.1. ServiceEnum Class Definition
Services Model

• Member Functions
• public boolean loadServiceList(Properties p)
• Loads in the service list from the configuration
  info.
• p is a Properties object containing the set up
  information specified in the configuration file.
• protected boolean addExtService(String strInfo,
  int nIndex)
• Adds an extended service with given the
  information and index.
• strInfo contains information on the service as
  specified in the configuration file.
• nIndex the index at which the service is to be
  stored.

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3.1.2. ServiceEnum Class Implementation
Services Model

• Add a service to the kernel
• protected boolean addExtService(String strInfo,
  int nIndex)
• //get the name of the service
• int nIndexSep strInfo.indexOf(',')
• String strName strInfo.substring(0,
  nIndexSep)
• //determine if the service should be loaded when
  kernel start
• String strRequired strInfo.substring(nInde
  xSep1, nIndexSep2)
• int fRequired Integer.parseInt(strRequired
  )
• //store the information in a data structure
• ServiceInfo s new ServiceInfo(strName,
  fRequired, ServiceInfo.SERVICEEXT)
• //add this service to the service list
• m_vecServices.insertElementAt(s, nIndex
  m_nStdServiceCount)
• return true

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ServiceInfo Class
Services Model

• Stores the information related to each service
• Member Variables
• public final static int SERVICESTD 0
• public final static int SERVICEEXT 1
• protected String m_strName
• Name assigned to the service - used in
  determining package file name
• protected boolean m_fRequired
• If required the service is loaded at AgentOS
  startup otherwise loaded on a need basis.
• protected int m_nServiceType
• The type of service - standard or extended
• public int m_nInstanceID
• public AgentOSInstance m_instance
• The creation instance for the service implementor
  agent.

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3.2. Service Implementer
Services Model

• Implemented as an agent.
• Implements the actual services in its member
  functions .
• Provides its functionality by responding to
  events received from service providers.
• Loaded from local file system only, not through
  network transfer.
• Has a relaxed security model
• allowed more access to the file system (write,
  delete, etc.).
• Not mobile
• does not migrate from one node to another.
• Has both a human readable name and an unique
  AgentOSID (to be discussed ).

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3.3. Service Provider
Services Model

• An interface for agents to access services of the
  service implementers.
• A corresponding service provider accompanies each
  service implementer.
• Transform agent requests into events
  understandable by their respective implementers.
• Agents can not access the service implementer
  directly.
• potential benefits.

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3.3.1. Service Provider Interfaces
Services Model

• Each service implementer must implement at least
  the services defined in the following two
  interfaces
• Interface 1 services to be accessed by ordinary
  agents.
• public interface IServiceProvider
• // get information on the service
• public AgentOSID getServiceID()
• public String getServiceName()
• public boolean isExtendedService()

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3.3.2. Service Provider Implementation
Services Model

• Interface 2 services to be accessed by system
  components (such as the ServiceEnum object)
• public interface IServiceProviderSys
• // get the IServiceProvider implementation
• public IServiceProvider getIServiceProvider()
• // set the service implementer id
• public setImplementerInstance(AgentOSInstanceID
  theImplementer)

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3.4. Impementer / Provider Model Benefits
Services Model

• More secure without direct access by agents
• avoid breaches such as block of service (through
  monopolizing by an agents) and corruption of data
  (through illegal service requests).
• Better module isolation
• an agent only needs the service provider, not the
  implementer, at the time of compilation.
• Favors transaction oriented services
• otherwise, a single service implementer has to
  maintain a state for each agent that is using the
  service.

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3.5. Create a Service - Step 1
Services Model

• Create a new service provider by extending the
  IServiceProvider interface.
• Declare the functions that will be implemented.
• Do not implement the functions.
• Example create an IDirectoryServiceProvider
• public interface IDirectoryServiceProvider
  extends IServiceProvider
• // methods specific to the Directory Service.
• Method_A(...)
• Method_B(...)

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3.5. Create a Service - Step 2
Services Model

• Create a new service implementer which implements
  the functions defined in the service provider.
• Implement the functions defined in the service
  provider.
• Example create a DirectoryServiceProvider
• public class DirectoryServiceProvider implements
  IDirectoryServiceProvider,
  IServiceProviderSys
• // implement the methods in IDirectoryServiceProv
  ider
• // and IServiceProviderSys
• Method_A()
• Method_B()
• ...

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3.6. Standard Services(to be constructed)
Services Model

• Services provided by the AgnetOS kernel
• AgentOSID Generator IAgentOSIDGenServiceProvider,
  "AgentOS.AgentOSIDGen"
• Provides agents with the ability to create new
  unique identifiers. This can be used in creating
  new agents by agents themselves.
• Registry IRegistryServiceProvider,
  "AgentOS.Registry"
• The Registry Service provides access to the
  registry, which is a list of categorized agents.
  
• RunningList IRunningListServiceProvider,
  "AgentOS.RunningList"
• The RunningList Service provides a list of agents
  currently active on the node. This enables agents
  to discover other agents to communicate with
  (using events).

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3.6. Standard Services(to be constructed)
Services Model

• History IHistoryServiceProvider,
  "AgentOS.History"
• Provide a listing of agents that have been
  activated on the node, and their source node and
  their destination node, if the agent had migrated
  .
• The History can be used in conjunction with the
  Running List to implement an efficient agent
  search algorithm.
• Directory IDirectoryServiceProvider,
  "AgentOS.Directory"
• The Directory is a list of all active agents
  within the AgentOS network.
• The Directory Service can search the AgentOS
  network for a specified agent.
• Agents can communicate with other agents
  regardless of their location.

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3.6. Standard Services(to be constructed)
Services Model

• Agent Package Factory IAgentPkgFactoryServiceProv
  ider, "AgentOS.AgentPkgFactory"
• Allows agents to create new agent packages from
  Java source code.
• Node Information IAgentOSNodeInfoServiceProvider,
  "AgentOS.NodeInfo"
• Provides means for agents to query their current
  location.
• It allows access to standard system information
  such as the type of operating system , user name,
  and to AgentOS specific information such as the
  list of neighboring nodes etc.

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Topics
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4. Event Model (under construction)

• Allows communication between
• Agents
• Service providers and their respective service
  implementers.
• Communication between agents on the same node
• The event is sent to and fetched from an event
  pool by using event API of the AgentContext.
• Communication between agents on different nodes
• The AgentContext of the source agent send an
  Event agent to the node of the destination agent.
• The Event agent exchanges information with the
  destination agent though event pool.
• The Event agent returns back to the source agent
  and pass the message back to the source agent
  through event pool.

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4.1. Event Sending
Event Model

• Two modes
• Synchronous the event source is suspended until
  the event listener responds to the event
• Asynchronous the event source continues
  execution, while the event is delivered and
  processed by the event listener.
• The Event can be send to a certain agent, or
  broadcast to a set of agents.

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4.2. Event Listening
Event Model

• Two modes
• Active the event listener requests an event of
  specified type, and remains blocked until the
  event arrives.
• Passive the event listener informs the event
  pool of its interest in a certain kind of event,
  and passes a callback function that the event
  pool can invoke when that event happens.

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4.3. Event Model Advantages
Event Model

• Uniform
• allows communication between agents on the same
  node and across nodes using the same API and same
  agent code.
• Scalable
• different modes for different purposes.
• Flexible
• allows agents to define the format of the
  messages used.

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4.4 Eventpool Class
Event Model

• Each AgentOS system contains a single EventPool.
• The EventPool provides both message broadcasting
  and point-to-point communication among agents
  within the same node.
• The EventPool supports multiple forms of
  event-based communication as discussed.
• It relies on the unique identification to
  identify each agent in the network.

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4.4.1. Eventpool Class Description
Event Model

• Member Variables
• private PublicForum publicForum
• the messages here are for all agents
• private Hashtable privateForums
• a list of private forums for two agents to
  exchange messages
• Member Functions
• public EventPool()
• create a public and a hash table to store
  private forums
• public PublicForum getPublicForum()
• return the instance of the public forum
• public PrivateForum createPrivateForum(int
  session)
• create a private forum on request
• public PrivateForum getPrivateForum(int session)
• get the private forum specified by the session
  number

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4.4.2. Eventpool Class Implementation
Event Model

• Eventpool Constructor
• create a public forum
• create a hash table to store private forums
• public EventPool()
• //create a public forum
• publicForum new PublicForum()
• //create a hash table to store the list of
  private forums
• privateForums new Hashtable()

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4.4.2. Eventpool Class Implementation
Event Model

• Create a private forum with a given session
  number for message exchange between two agents.
• public PrivateForum createPrivateForum(int
  session)
• //create a private forum
• PrivateForum pf new PrivateForum(session)
• //put this forum into the hash table
• Integer i new Integer(session)
• privateForums.put(i, pf)
• return pf

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4.4.2. Eventpool Class Implementation
Event Model

• Get the public forum
• public PublicForum getPublicForum()
• return publicForum
• Get the private forum with a certain session
  number
• public PrivateForum getPrivateForum(int session)
  
• Integer i new Integer(session)
• // return the private forum with the given
  session number
• return (PrivateForum)privateForums.get(i)

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Topics
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5. Unique Naming Space
Unique Naming Scheme

• Provide unique identifiers for both static
  objects (such as agent classes) and active
  objects (such as instances of agents) in the
  AgentOS network.
• This uniqueness is achieved using two
  identifiers
• AgentOSID
• a static ID that is assigned to static objects
  when they are created.
• AgentInstanceID
• a dynamic ID that is assigned to dynamic objects
  when they are created.

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5.1. AgentOSID Class
Unique Naming Scheme

• Creates globally unique identifiers --AgentOSID
• The AgentOSID guarantees uniqueness of all static
  objects.
• It is generated using a combination of a hash
  code that is unique to each Java Virtual Machine,
  a network address, a time stamp and a sequential
  counter (represented in hexadecimal number
  format).

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5.2. AgentInstanceID Class
Unique Naming Scheme

• Creates globally unique identifiers
  --AgentInstanceID
• Guarantees the uniqueness of dynamic objects and
  is assigned on a per-instance basis.
• It is based on static AgentOSID, the network
  address of the node where the object was first
  created and the time of creation.
• The AgentInstaceID guarantees the uniqueness of
  dynamic objects
• multiple instances of the same static ID result
  in different instance IDs.