org.jcsp.net.cns
Class CNSService

java.lang.Object
  org.jcsp.net.cns.CNSService

All Implemented Interfaces:

CNSUser, Service

public class CNSService
extends Object
implements Service, CNSUser

This class is the Channel Name Server's main client process class.

One instance of this class needs to be instantiated at each Node wishing to interact with a Channel Name Server.

At present only one instance of this service class should be installed at each Node, however, it is envisaged that it may be desirable to be able to use multiple Channel Name servers. This functionality has been partially implemented and eventually multiple instances of this service will be able to be installed. Each instance would be given a separate name.

A default instance of this class can be held. Interaction with this default instance is facilitated through the static methods of the CNS class.

Once constructed, an instance of the object can be installed into the Node's service manager in the same way as any other Service (see ServiceManager). Alternatively, the one of the static install methods may be used (see install(NodeKey, NodeAddressID), install(NodeKey, NodeAddressID, String)).

Author:

Quickstone Technologies Limited

See Also:

CNS

Field Summary

static String	CNS_DEFAULT_SERVICE_NAME Constant specifying the default name of this service.
static String	CNS_SETTING_NAME_ADDRESS Constant specifying the setting name for CNS address.
static String	CNS_SETTING_NAME_ADMIN_CHANNEL_LABEL Constant specifying the setting name for server's admin channel.
static String	CNS_SETTING_NAME_SERVICE_NAME Constant specifying the setting name for setting the service name.

Constructor Summary

CNSService()
Default constructor that does not supply any of the necessary settings for initializing the CNS.

CNSService(NodeAddressID cnsAddress)
Constructor which takes an address of the Node hosting the Channel Name Server.

CNSService(NodeAddressID cnsAddress, boolean start)
Constructor which takes an address of the Node hosting the Channel Name Server as well as a boolean indicating whether or not the service should be started.

CNSService(NodeAddressID cnsAddress, String adminChannelLabel)
Constructor which takes an address of the Node hosting the Channel Name Server as well as the label of the Channel Name Server's admin channel.

CNSService(NodeAddressID cnsAddress, String adminChannelLabel, boolean start)
Constructor which takes an address of the Node hosting the Channel Name Server, the label of the Channel Name Server's admin channel and a boolean indicating whether the service should be started.

Method Summary

boolean	deregisterChannelName(String name, NameAccessLevel accessLevel, ChannelNameKey channelKey) This deregisters a Channel name from the Channel Name Server.
ServiceUserObject	getUserObject() This returns a ServiceUserObject which implements the Resolver interface.
boolean	init(ServiceSettings settings) Initializes the this instance of the CNSService.
static CNSService	install(NodeKey key, NodeAddressID cnsAddress) Installs and starts a Channel Name Server client service on the local Node.
static CNSService	install(NodeKey key, NodeAddressID cnsAddress, String serviceName) Installs and starts a Channel Name Server client service on the local Node.
boolean	isRunning() This returns whether the service is running.
ChannelNameKey	leaseChannelName(String name, NameAccessLevel accessLevel, ChannelNameKey channelKey) Leases the channel name within the specified name space from the Channel Name Server.
ChannelNameKey	register(NetChannelLocation ownerLocation, String name, NameAccessLevel accessLevel, ChannelNameKey key) This method allows a channel's location to be registered against a name in the Channel Name Server.
ChannelNameKey	register(Networked owner, String name) This method allows a channel (or any instance of a class implementing Networked) to be registered with the Channel Name Server.
ChannelNameKey	register(Networked owner, String name, ChannelNameKey key) This method allows a channel (or any instance of a class implementing Networked) that has previously been registered with the to be reregistered with the Channel Name Server.
ChannelNameKey	register(Networked owner, String name, NameAccessLevel accessLevel) This method allows a channel (or any instance of a class implementing Networked) to be registered with the Channel Name Server.
ChannelNameKey	register(Networked owner, String name, NameAccessLevel accessLevel, ChannelNameKey key) This method allows a channel (or any instance of a class implementing Networked) that has previously been registered to be reregistered with the Channel Name Server.
NetChannelLocation	resolve(String name) This method resolves a channel name into a NetChannelLocation object.
NetChannelLocation	resolve(String name, NameAccessLevel accessLevel) This method resolves a channel name into a NetChannelLocation object.
boolean	start() This checks to see if the service is already running, if it is not then it starts it.
boolean	stop() This checks to see if the service is running, if it is then it stops it.

Methods inherited from class java.lang.Object

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

Field Detail

CNS_SETTING_NAME_ADDRESS

public static final String CNS_SETTING_NAME_ADDRESS

Constant specifying the setting name for CNS address.

See Also:

Constant Field Values

CNS_SETTING_NAME_SERVICE_NAME

public static final String CNS_SETTING_NAME_SERVICE_NAME

Constant specifying the setting name for setting the service name.

See Also:

Constant Field Values

CNS_SETTING_NAME_ADMIN_CHANNEL_LABEL

public static final String CNS_SETTING_NAME_ADMIN_CHANNEL_LABEL

Constant specifying the setting name for server's admin channel.

See Also:

Constant Field Values

CNS_DEFAULT_SERVICE_NAME

public static final String CNS_DEFAULT_SERVICE_NAME

Constant specifying the default name of this service.

See Also:

Constant Field Values

Constructor Detail

CNSService

public CNSService()

Default constructor that does not supply any of the necessary settings for initializing the CNS. The init(ServiceSettings) method must be called if this constructor is used.

CNSService

public CNSService(NodeAddressID cnsAddress)

Constructor which takes an address of the Node hosting the Channel Name Server.

In order to connect to the Channel Name Server, this service must know the label of the server's admin channel. By default this is given the value of the CNS.CNS_CHANNEL_LABEL constant. This constructor assumes that this label has been used. It is equivalent to calling the constructor which takes (NodeAddressID, String) parameters.

Parameters:

cnsAddress - the address of channel name server to use.

See Also:

CNSService(NodeAddressID,String)

CNSService

public CNSService(NodeAddressID cnsAddress,
                  boolean start)

Constructor which takes an address of the Node hosting the Channel Name Server as well as a boolean indicating whether or not the service should be started.

In order to connect to the Channel Name Server, this service must know the label of the server's admin channel. By default this is given the value of the CNS.CNS_CHANNEL_LABEL constant. This constructor assumes that this label has been used. It is equivalent to calling the constructor which takes (NodeAddressID, String,boolean) parameters.

Parameters:

cnsAddress - the address of channel name server to use.

start - indicates whether the service should be started. Should be true to start service.

See Also:

CNSService(NodeAddressID,String,boolean)

CNSService

public CNSService(NodeAddressID cnsAddress,
                  String adminChannelLabel)

Constructor which takes an address of the Node hosting the Channel Name Server as well as the label of the Channel Name Server's admin channel.

This is equivalent to using the construtor with (NodeAddressID, String, boolean) parameters with the boolean equal to false.

Parameters:

cnsAddress - the address of channel name server to use.

adminChannelLabel - the label of server's admin channel.

See Also:

CNSService(NodeAddressID,String,boolean)

CNSService

public CNSService(NodeAddressID cnsAddress,
                  String adminChannelLabel,
                  boolean start)

Constructor which takes an address of the Node hosting the Channel Name Server, the label of the Channel Name Server's admin channel and a boolean indicating whether the service should be started.

If the service is started, there is no need to initialize and start the service separately.

Parameters:

cnsAddress - the address of channel name server to use.

adminChannelLabel - the label of server's admin channel.

start - indicates whether the service should be started. Should be true to start service.

See Also:

NodeAddressID

Method Detail

init

public boolean init(ServiceSettings settings)

Initializes the this instance of the CNSService.

If the default constructor was used to construct the instance of this class, then a name of the instance must be supplied along with at least one address of a channel name server. The admin channel label of the server may also be supplied. The keys to use in the ServiceSettings are held as constants in this class (CNS_SETTING_NAME_ADDRESS, CNS_SETTING_NAME_SERVICE_NAME, CNS_SETTING_NAME_ADMIN_CHANNEL_LABEL).

This need only be called if the no-arg constructor is used.

Specified by:

init in interface Service

Parameters:

settings - A ServiceSettings object that holds the settings for this service.

Returns:

true if this request to initialize the service succeeds.

start

public boolean start()

This checks to see if the service is already running, if it is not then it starts it.

Specified by:

start in interface Service

Returns:

true iff the service is running once this method has returned.

stop

public boolean stop()

This checks to see if the service is running, if it is then it stops it.

Specified by:

stop in interface Service

Returns:

true if the service is NOT running.

isRunning

public boolean isRunning()

This returns whether the service is running. If the service is currently starting or stopping, this method will block until the state change is complete.

Specified by:

isRunning in interface Service

Returns:

true iff the service is running.

getUserObject

public ServiceUserObject getUserObject()
                                throws SecurityException

This returns a ServiceUserObject which implements the Resolver interface. This allows processes to obtain a reference to an installed CNS Service without having admin privileges. A SecurityException may be thrown if the calling process does not have permission to obtain the ServiceUserObject.

Specified by:

getUserObject in interface Service

Returns:

a Resolver which can be used to resolve names using this CNSService.

Throws:

SecurityException - if the calling process does not have permission to obtain the ServiceUserObject.

See Also:

CNSUser

install

public static CNSService install(NodeKey key,
                                 NodeAddressID cnsAddress)

Installs and starts a Channel Name Server client service on the local Node. The service is installed with the default service name as specified by CNSService.CNS_DEFAULT_SERVICE_NAME. This method needs to be supplied with the local Node's NodeKey. This is required in order to obtain access to the Node's service manager.

Parameters:

key - the local Node's NodeKey.

cnsAddress - the address of the Channel Name Server to use.

Returns:

the CNS object installed.

Throws:

ServiceInstallationException - if installation fails.

install

public static CNSService install(NodeKey key,
                                 NodeAddressID cnsAddress,
                                 String serviceName)

Installs and starts a Channel Name Server client service on the local Node. The service is installed with the specified service name. This method needs to be supplied with the local Node's NodeKey. This is required in order to obtain access to the Node's service manager.

Parameters:

key - the local Node's NodeKey.

cnsAddress - the address of the Channel Name Server to use.

name - the name to give the service.

Returns:

the CNS object installed.

Throws:

ServiceInstallationException - if installation fails.

See Also:

NodeAddressID

resolve

public NetChannelLocation resolve(String name)

This method resolves a channel name into a NetChannelLocation object. The name is assumed to be in the global name space (see NameAccessLevel.GLOBAL_ACCESS_LEVEL).

This method is safe to be called by concurrent processes.

Specified by:

resolve in interface CNSUser

Parameters:

name - the name of channel to resolve.

Returns:

the location to which the name resolved.

resolve

public NetChannelLocation resolve(String name,
                                  NameAccessLevel accessLevel)

This method resolves a channel name into a NetChannelLocation object. The name must exist in the specified name space.

The name space is specified by passing in a NameAccessLevel object. A name space includes itself and any name space higher up in the hierarchy. The global name space is the highest level of name space.

This method is safe to be called by concurrent processes.

Specified by:

resolve in interface CNSUser

Parameters:

name - the name of channel to resolve.

accessLevel - the name space in which to resolve the channel name.

Returns:

the location to which the name resolved.

register

public ChannelNameKey register(Networked owner,
                               String name)

This method allows a channel (or any instance of a class implementing Networked) to be registered with the Channel Name Server. The name will be registered in the global name space.

A name will stay registered with the Channel Name Server until it has been leased, deregistered or the Node that registered the name has shut down.

This method is safe to be called by concurrent processes.

Specified by:

register in interface CNSUser

Parameters:

owner - the Networked object whose location should be registered.

name - the name against which to register the channel.

Returns:

the ChannelNameKey needed for managing the name registration or null if registration failed.

register

public ChannelNameKey register(Networked owner,
                               String name,
                               NameAccessLevel accessLevel)

This method allows a channel (or any instance of a class implementing Networked) to be registered with the Channel Name Server.

The name will be registered in the specified name space. This is specified by passing in a NameAccessLevel object.

A name will stay registered with the Channel Name Server until it has been leased, deregistered or the Node that registered the name has shut down.

This method is safe to be called by concurrent processes.

Specified by:

register in interface CNSUser

Parameters:

owner - the Networked object whose location should be registered.

name - the name against which to register the channel.

accessLevel - the name space in which to register the channel name.

Returns:

the ChannelNameKey needed for managing the name registration or null if registration failed.

See Also:

NameAccessLevel

register

public ChannelNameKey register(Networked owner,
                               String name,
                               ChannelNameKey key)

This method allows a channel (or any instance of a class implementing Networked) that has previously been registered with the to be reregistered with the Channel Name Server. The name should have been leased (see leaseChannelName(String, NameAccessLevel, ChannelNameKey) ). It is necessaray to supply the key that was obtained when the name was leased. If the channel name has not previously been registered, then the key can be specified as null.

The name will be registered in the in the global name space.

A name will stay registered with the Channel Name Server until it has been leased, deregistered or the Node that registered the name has shut down.

This method is safe to be called by concurrent processes.

Specified by:

register in interface CNSUser

Parameters:

owner - the Networked object whose location should be registered.

name - the name against which to register the channel.

accessLevel - the name space in which to register the channel name.

Returns:

the ChannelNameKey needed for managing the name registration or null if registration failed.

register

public ChannelNameKey register(Networked owner,
                               String name,
                               NameAccessLevel accessLevel,
                               ChannelNameKey key)

This method allows a channel (or any instance of a class implementing Networked) that has previously been registered to be reregistered with the Channel Name Server. The name should have been leased (see leaseChannelName(String, NameAccessLevel, ChannelNameKey) ). It is necessaray to supply the key that was obtained when the name was leased. If the channel name has not previously been registered, then the key can be specified as null.

The name will be registered in the specified name space. This is specified by passing in a NameAccessLevel object.

A name will stay registered with the Channel Name Server until it has been leased, deregistered or the Node that registered the name has shut down.

This method is safe to be called by concurrent processes.

Specified by:

register in interface CNSUser

Parameters:

owner - the Networked object whose location should be registered.

name - the name against which to register the channel.

accessLevel - the name space in which to register the channel name.

key - the ChannelNameKey returned when the name was leased.

Returns:

the ChannelNameKey needed for managing the name registration or null if registration failed.

See Also:

NameAccessLevel

register

public ChannelNameKey register(NetChannelLocation ownerLocation,
                               String name,
                               NameAccessLevel accessLevel,
                               ChannelNameKey key)

This method allows a channel's location to be registered against a name in the Channel Name Server. It differs from the other register methods in that it takes a NetChannelLocation object instead of a Networked object. This can be obtained from a Networked object by invoking its #getChannelLocation() method (see Networked.getChannelLocation()).

The name will be registered in the specified name space. This is specified by passing in a NameAccessLevel object.

This method also allows a leased channel name to be registered against an actual location (see register(Networked, String, NameAccessLevel, ChannelNameKey) ).

A name will stay registered with the Channel Name Server until it has been leased, deregistered or the Node that registered the name has shut down.

This method is safe to be called by concurrent processes.

Specified by:

register in interface CNSUser

Parameters:

ownerLocation - the location of a channel to be registered against the name.

name - the name against which to register the channel.

accessLevel - the name space in which to register the channel name.

key - the ChannelNameKey returned when the name was leased.

Returns:

the ChannelNameKey needed for managing the name registration or null if registration failed.

See Also:

register(Networked, String, NameAccessLevel, ChannelNameKey), NameAccessLevel

leaseChannelName

public ChannelNameKey leaseChannelName(String name,
                                       NameAccessLevel accessLevel,
                                       ChannelNameKey channelKey)
                                throws ChannelNameException,
                                       NameAccessLevelException

Leases the channel name within the specified name space from the Channel Name Server. Once a name has been leased, a channel cannot be registered with that name without supplying the key returned by the call to this method.

Currently, leases are infinite; they never expire. This is likely to change in the future so that leases have to be renewed. Leases can be given up by deregistering the name. Leases will remain even after the obtaining Node has shut down. This allows a channel to move its registered location to another channel on a different Node. There is no danger of another party managing to obtain the name as transfering a registered name into a lease is an atomic action. Although leases are currently infinite, there is no reason why a program cannot renew the lease by recalling this method.

A name may be leased without first registering a channel against it.

This method is safe to be called by concurrent processes.

Specified by:

leaseChannelName in interface CNSUser

Parameters:

name - the name to lease.

accessLevel - the name space in which to lease the name.

channelKey - the key to use if the name is currently registered or leased.

Returns:

a new ChannelNameKey needed for managing the lease or null if leasing failed.

Throws:

ChannelNameException - if the channel name is invalid.

NameAccessLevelException - if the specifed name space is invalid.

deregisterChannelName

public boolean deregisterChannelName(String name,
                                     NameAccessLevel accessLevel,
                                     ChannelNameKey channelKey)

This deregisters a Channel name from the Channel Name Server. If the CNS Service is not running, this method will block until it is running. A boolean is returned to indicate whether deregistration was successful. This is also returned if the link to the CNS is lost.

This method is safe to be called by concurrent processes.

Specified by:

deregisterChannelName in interface CNSUser

Parameters:

name - the name of the channel as a String.

nameAccessLevel - the nameAccessLevel of the channel.

channelKey - the ChannelNameKey to use to deregister the Channel name.

Returns:

a boolean indicating success.