Package org.jcsp.net

Class Link

java.lang.Object
org.jcsp.net.Link
All Implemented Interfaces:
CSProcess
Direct Known Subclasses:
LoopbackLink, TCPIPLink
public abstract class Link extends Object implements CSProcess

This class is an abstract class that all JCSP.NET protocol implementations must implement. Concrete implementations of the Link class must provide the mechanism for sending data to remote Nodes and receiving data back. When a concrete implementation of link is initiated by calling the run() method, it must inititate a handshaking procedure and call certain protected methods in this abstract class.

During handshaking, the runTests(ChannelInput, ChannelOutput, boolean) should be called. See the documentation for this method for a full explanation.

When a Link receives an object from over the network it should deliver the object to its destination by calling the deliverReceivedObject(Object) method.

Link implementations obtain objects to send to the remote Node by reading from the protected txChannel object.

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Class
    Description
    private static class 
    Link.LinkTest
     

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private boolean
    client
    True if this is a client during handshaking, false if it is the server.
    private boolean
    connected
    True if connect() has been called or the underlying connection is already open.
    private static final int
    HS_ERROR
    Handshake result code - a problem occurred
    private static final int
    HS_OK
    Handshake result code - permanant link ok
    private static final int
    HS_TEMPORARY
    Handshake result code - temporary link
    private IndexManager
    im
     
    private boolean
    performedPingTest
     
    private One2OneChannel
    pingReplyChan
     
    private long
    pingTime
     
    private Profile
    profile
     
    private ProtocolID
    protocolID
     
    protected NodeID
    remoteNodeID
    The remote NodeID.
    private SecurityAuthority
    securityAuthority
     
    protected boolean
    sendNodeID
    True if the subclass must pass the ID of this node to the peer node.
    private Specification[]
    specifications
     
    protected FilteredAny2OneChannel
    txChannel
    The channel used for TX over the link.

  • Constructor Summary

    Constructors
    Constructor
    Description
    Link(ProtocolID protocolID, boolean client, boolean connected)
    A constructor that must be called by sub-classes.

  • Method Summary

    Modifier and Type
    Method
    Description
    (package private) void
    addTxFilter(Filter filter, int index)
    Adds a transmission filter.
    protected boolean
    connect()
    Establishes a connection to the peer node.
    protected boolean
    createResources()
    Allocates the resources necessary for the actual connection.
    protected void
    deliverReceivedObject(Object obj)
    A protected method for concrete implementations of this class to call when they received a an object from the remote Node.
    protected void
    destroyResources()
    Deallocates any resources allocated by createResources.
    final boolean
    equals(Object o)
    Compares another object with this object.
    protected boolean
    exchangeNodeIDs()
    Sends the ID of this node to the peer process and receives its ID.
    long
    getPingTime()
    A public accessor for obtaining the ping time between the local Node and this Link's remote Node.
    (package private) Profile
    getProfile()
     
    protected ProtocolID
    getProtocolID()
    A protected accessor for obtaining the identifier of the protocol implementing this Link object.
    protected boolean[]
    getReadSequence(boolean client)
    This is used by concrete Link implementations before calling the runTests method.
    protected NodeID
    getRemoteNodeID()
    Returns the other computer's ID.
    (package private) Specification[]
    getSpecifications()
     
    protected ChannelOutput
    getTxChannel()
    Returns channel to use for transmitting.
    (package private) int
    getTxFilterCount()
    Gets the number of installed transmission filters.
    private int
    handshake()
    Does handshaking.
    final int
    hashCode()
    Returns an int hash code for this Link.
    private int
    lostLink()
    This should be called once to notify users of the link that the link has been dropped.
    final NodeID
    obtainNodeID()
    This returns the NodeID of the remote Node to which this link is connected.
    boolean
    performedPingTest()
    A public accessor for enquiring as to whether this Link object has performed a ping test.
    long
    ping()
    Performs a ping on the link.
    protected boolean
    readLinkDecision()
    Reads a boolean link decision as to whether this node can keep or discard the link.
    protected Object
    readTestObject()
    Reads a test object from the underlying connection.
    private void
    registerFailure()
    Called to inform the local LinkManager that this link has failed.
    private boolean
    registerLink()
    This is called during handshaking in order to register the link with the local LinkManager.
    (package private) void
    removeTxFilter(Filter filter)
    Removes a transmission filter.
    final void
    run()
    Main process for the link, containing generic code that makes calls on the abstract methods that should be implemented by a concrete subclass.
    private void
    runTestProcess(ChannelInput in, ChannelOutput out, boolean client)
    This should be called during the handshaking process.
    protected void
    runTxRxLoop()
    Performs send and receive actions for the link exchanging data with the peer node.
    (package private) void
    setProfile(Profile profile)
     
    (package private) void
    setSpecifications(Specification[] specifications)
     
    protected void
    waitForReplies(int numAcknowledgements)
    Waits for numRepliesOutstanding instances of LinkLost to arrive from the txChannel.
    protected void
    writeLinkDecision(boolean use)
    Writes a boolean link decision as to whether the other node has the option to keep or discard the link.
    protected void
    writeTestObject(Object obj)
    Writes a test object to the underlying connection.

    Methods inherited from class java.lang.Object

    clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

  • Field Details

    • HS_ERROR

      private static final int HS_ERROR
      Handshake result code - a problem occurred
      See Also:

    • HS_TEMPORARY

      private static final int HS_TEMPORARY
      Handshake result code - temporary link
      See Also:

    • HS_OK

      private static final int HS_OK
      Handshake result code - permanant link ok
      See Also:

    • connected

      private boolean connected
      True if connect() has been called or the underlying connection is already open. False otherwise.

    • client

      private boolean client
      True if this is a client during handshaking, false if it is the server.

    • im

      private IndexManager im

    • txChannel

      protected FilteredAny2OneChannel txChannel
      The channel used for TX over the link. In the future, this might be made private. It is recommended that implementations use the getTxChannel() to obtain the channel. Protocol implementations should NOT alter any of the filters on this channel.

    • remoteNodeID

      protected NodeID remoteNodeID
      The remote NodeID. The subclass must set this during exchangeNodeIDs.

    • sendNodeID

      protected boolean sendNodeID
      True if the subclass must pass the ID of this node to the peer node.

    • protocolID

      private ProtocolID protocolID

    • specifications

      private Specification[] specifications

    • performedPingTest

      private boolean performedPingTest

    • pingTime

      private long pingTime

    • profile

      private Profile profile

    • pingReplyChan

      private One2OneChannel pingReplyChan

    • securityAuthority

      private SecurityAuthority securityAuthority

  • Constructor Details

    • Link

      public Link(ProtocolID protocolID, boolean client, boolean connected)

      A constructor that must be called by sub-classes.

      Parameters:
      protocolID - A ProtocolID object for identifying the protocol that is implementing the Link.
      client - Indicates whether this is the client (true) or server (false) end of the connection.
      connected - true if a connection is already established; otherwise connect() will later be called

  • Method Details

    • connect

      protected boolean connect() throws Exception

      Establishes a connection to the peer node. Called when the process is started unless connected was true in the constructor. This is called internally from this class' run method - do not call it.

      Returns:
      true on success, false on failure
      Throws:
      Exception

    • createResources

      protected boolean createResources() throws Exception

      Allocates the resources necessary for the actual connection. Called as the first part of the handshaking process. This is called internally from the class' handshake method - do not call it.

      Returns:
      true on success, false on failure
      Throws:
      Exception

    • destroyResources

      protected void destroyResources() throws Exception

      Deallocates any resources allocated by createResources. Called in the event of an error during handshaking or when the link is dropped. An implementation of this method must cope with being called multiple times without an intervening call to createResources.

      Throws:
      Exception

    • exchangeNodeIDs

      protected boolean exchangeNodeIDs() throws Exception

      Sends the ID of this node to the peer process and receives its ID. It is only necessary to send this node's ID if sendNodeID is true. The remoteNodeID attribute should be set to the ID of the remote node if received. This is called internally during handshaking - do not call it.

      Returns:
      true on success, false on failure.
      Throws:
      Exception

    • runTxRxLoop

      protected void runTxRxLoop() throws Exception
      Performs send and receive actions for the link exchanging data with the peer node. This is called from this class' run method - do not call it directly.
      Throws:
      Exception

    • waitForReplies

      protected void waitForReplies(int numAcknowledgements) throws Exception
      Waits for numRepliesOutstanding instances of LinkLost to arrive from the txChannel. This is called internally from this class' run method - do not call it directly.
      Parameters:
      numRepliesOutstanding - LinkLost instances to wait for.
      Throws:
      Exception

    • writeTestObject

      protected void writeTestObject(Object obj) throws Exception
      Writes a test object to the underlying connection. Called internally during handshaking - do not call it directly. The value written must be delivered by readTestObject at the remote node.
      Parameters:
      obj - object to be written
      Throws:
      Exception

    • readTestObject

      protected Object readTestObject() throws Exception
      Reads a test object from the underlying connection. Called internally during handshaking - do not call it directly. It must deliver the value passed to writeTestObject at the peer node.
      Returns:
      the object received.
      Throws:
      Exception

    • writeLinkDecision

      protected void writeLinkDecision(boolean use) throws Exception
      Writes a boolean link decision as to whether the other node has the option to keep or discard the link. Called internally during handshaking - do not call it directly. The value written must be delivered by readLinkDecision at the peer node.
      Parameters:
      use - decision result
      Throws:
      Exception

    • readLinkDecision

      protected boolean readLinkDecision() throws Exception
      Reads a boolean link decision as to whether this node can keep or discard the link. Called internally during handshaking - do not call it directly. It must return the value passed to writeLinkDecision at the peer node.
      Returns:
      decision result
      Throws:
      Exception

    • addTxFilter

      void addTxFilter(Filter filter, int index)
      Adds a transmission filter. This filter will run in the thread that is trying to send something over this Link.
      Parameters:
      filter - the filter.
      index - the index position of the filter.

    • removeTxFilter

      void removeTxFilter(Filter filter)
      Removes a transmission filter.
      Parameters:
      filter - the filter to remove.

    • getTxFilterCount

      int getTxFilterCount()
      Gets the number of installed transmission filters.
      Returns:
      the number of transmission filters installed.

    • getRemoteNodeID

      protected NodeID getRemoteNodeID()
      Returns the other computer's ID. This method is safe to call while the process is running, however it will return null if the other computer has not yet identified itself.
      Returns:
      ID of connected computer.

    • getProtocolID

      protected ProtocolID getProtocolID()
      A protected accessor for obtaining the identifier of the protocol implementing this Link object.
      Returns:
      the ProtocolID of the protocol implementing this Link.

    • setProfile

      void setProfile(Profile profile)

    • getProfile

      Profile getProfile()

    • getTxChannel

      protected ChannelOutput getTxChannel()
      Returns channel to use for transmitting. This method is safe to call while the process is running. May block for if handshaking is still in progress. When written to, if the object supplied is not Serializable then an IllegalArgumentException Runtime exception.
      Returns:
      Channel you should send data to if you want to transmit on this Connection.

    • deliverReceivedObject

      protected void deliverReceivedObject(Object obj)
      A protected method for concrete implementations of this class to call when they received a an object from the remote Node. This method delivers the message to its destination (a Channel, Connection etc.).
      Parameters:
      obj - the object to deliver.

    • getSpecifications

      Specification[] getSpecifications()

    • setSpecifications

      void setSpecifications(Specification[] specifications)

    • getPingTime

      public long getPingTime()
      A public accessor for obtaining the ping time between the local Node and this Link's remote Node.
      Returns:
      the ping time as a long.

    • ping

      public long ping()
      Performs a ping on the link.
      Returns:
      the ping time in ms.

    • performedPingTest

      public boolean performedPingTest()

      A public accessor for enquiring as to whether this Link object has performed a ping test.

      Returns:
      true iff a ping test has been performed.

    • getReadSequence

      protected boolean[] getReadSequence(boolean client)

      This is used by concrete Link implementations before calling the runTests method. When tests are run, a series of messages are exchanged between both sides of the link. This allows the link to perform its tests using a single thread.

      Parameters:
      client - a boolean indicating whether this Link object is the client side of the link. If this object is the client then the parameter should be true.
      Returns:
      an array of boolean values indicating the sequence of when to read and when to transmit.

    • runTestProcess

      private void runTestProcess(ChannelInput in, ChannelOutput out, boolean client)

      This should be called during the handshaking process. The in parameter should be a ChannelInput that reads from a process that receives object from the remote Node. The out parameter is a ChannelOutput that, when written to, will transmit the object to the remote Node. The client parameter should be true iff the current Link is acting as a client side link (if it establishes the initial connection).

      The method will start a testing process and then return. The concrete implementation of Link that calls this method should call the getReadSequence(boolean) method before calling this method. Once this method has returned, the calling process should loop through the returned array of boolean values. If the value is true, the process should wait to recieve an object from over the network and then send it down the channel supplied as the in parameter. If the value is false, the process should read from the channel supplied as the out parameter and then send the object it receives over the network.

      Once the calling process has finished looping through the array, it should perform a read from the channel supplied as the out channel. This is some example code for what concrete implementations of Link need to do: 

          One2OneChannel fromTestProcess = Channel.one2one();
    One2OneChannel toTestProcess = Channel.one2one();
    boolean[] readSequence = super.getReadSequence(client);
    super.runTests(toTestProcess.in(), fromTestProcess.out(), client);
    try {
        for(int i=0; iinvalid input: '<'readSequence.length; i++) {
            if(readSequence[i] == true) {
                Object obj = rxStream.readObject();
                toTestProcess.out().write(obj);
            }else {
                Object obj = fromTestProcess.in().read();
                txStream.writeObject(obj);
                txStream.flush();
                txStream.reset();
            }
        }
    }catch (Exception e) {
        //Handle Error
    }
    fromTestProcess.read();
      Parameters:
      in - a ChannelInput that the test process can use to receive objects from over the network.
      out - a ChannelOutput that the test process should use to send objects over the network.
      client - a boolean that is true iff this Link object is the object that established the connection to the remote Node.

    • registerLink

      private boolean registerLink()

      This is called during handshaking in order to register the link with the local LinkManager. It returns true if the link is successfully registered.

      Returns:
      true iff the link is successfully registered.

    • registerFailure

      private void registerFailure()

      Called to inform the local LinkManager that this link has failed.

      Currently, this should be called if the link fails once it has been registered but before the handshaking is complete.

    • lostLink

      private int lostLink()

      This should be called once to notify users of the link that the link has been dropped. The method returns the number of channels that are using the link that has been dropped. Implementations should read from txChannel the number of times returned by this method.

      This is an example: 

          int numRepliesOutstanding = super.lostLink();
    while (numRepliesOutstanding > 0) {
        Object obj = txChannel.read();
        if (obj instanceof LinkLost) {
            numRepliesOutstanding--;
        }
    }
      Returns:
      an int indicating the number of channels that are using the link.

    • equals

      public final boolean equals(Object o)

      Compares another object with this object. This implementation returns true iff the supplied object is the same instance object as this object.

      Overrides:
      equals in class Object
      Parameters:
      o - an object to compare with this object.
      Returns:
      true iff the parameter equals this object.

    • hashCode

      public final int hashCode()

      Returns an int hash code for this Link. The current implementation just uses the instance from Object.

      Overrides:
      hashCode in class Object
      Returns:
      an int hash code.

    • run

      public final void run()

      Main process for the link, containing generic code that makes calls on the abstract methods that should be implemented by a concrete subclass. The subclass will be required to connect() if it hasn't done so, perform handshaking, runTxRxLoop() and then waitForReplies() to acknowledge link termination.

      Specified by:
      run in interface CSProcess

    • handshake

      private int handshake()

      Does handshaking. Checks that the other side is a JCSP.net server of the same version, then decides whether or not this link is a duplicate of an existing link. If the versions match and there is no link to the other server, then the link is registered with the LinkManager, true is returned, and the link is ready for real data. Otherwise, the link is closed and false is returned.

      This method contains generic code. Calls are made on abstract methods that a concrete subclass must implement to provide link functionality.

      Returns:
      HS_ERROR if a problem occurs, HS_REMPORARY if the link is to be discarded or HS_OK for a permanent link.

    • obtainNodeID

      public final NodeID obtainNodeID()

      This returns the NodeID of the remote Node to which this link is connected. If a connection has not already been established, this method may connect to the remote Node and request its NodeID and then drop the connection.

      Returns:
      the remote Node's NodeID object.