org.javagroups
Class JChannel

java.lang.Object
  |
  +--org.javagroups.Channel
        |
        +--org.javagroups.JChannel
All Implemented Interfaces:
Transport

public class JChannel
extends Channel

JChannel is a pure Java implementation of Channel When a JChannel object is instantiated it automatically sets up the protocol stack

Version:
$Revision: 1.17 $
Author:
Bela Ban, Filip Hanik

Fields inherited from class org.javagroups.Channel
AUTO_GETSTATE, AUTO_RECONNECT, BLOCK, channel_listener, GET_STATE_EVENTS, LOCAL, SUSPECT, up_handler, VIEW
 
Constructor Summary
  JChannel()
          initializes the JChannel with its default settings and default protocol stack
protected JChannel(boolean dummy)
          initializes the JChannel with its default settings and default protocol stack
  JChannel(java.lang.Object properties)
          creates a new JChannel with the protocol stack as defined in the properties parameter.
 
Method Summary
 void blockOk()
          Called to acknowledge a block() (callback in MembershipListener or BlockEvent received from call to receive()).
 void close()
          Destroys the channel.
After this method has been called, the channel us unusable.
This operation will disconnect the channel and close the channel receive queue immediately
 void connect(java.lang.String channel_name)
          Connects the channel to a group.
If the channel is already connected, an error message will be printed to the error log
If the channel is closed a ChannelClosed exception will be thrown
This method starts the protocol stack by calling ProtocolStack.start
then it sends an Event.CONNECT event down the stack and waits to receive a CONNECT_OK event
Once the CONNECT_OK event arrives from the protocol stack, any channel listeners are notified
and the channel is considered connected
 void disconnect()
          disconnects the channel if it is connected.
if the channel is closed, this operation is ignored
Otherwise the following actions happen in the listed order
1.
 void down(Event evt)
          Sends a message through the protocol stack if the stack is available
 boolean getAllStates(java.util.Vector targets, long timeout)
          Retrieves the current group state.
 java.lang.String getChannelName()
          returns the name of the channel if the channel is not connected or if it is closed it will return null
 Address getLocalAddress()
          returns the local address of the channel returns null if the channel is closed
 java.lang.Object getOpt(int option)
          returns the value of an option.
 java.lang.String getProperties()
          returns the protocol stack configuration in string format.
 ProtocolStack getProtocolStack()
          Returns the protocol stack.
 boolean getState(Address target, long timeout)
          Retrieves the current group state.
 View getView()
          returns the current view.
if the channel is not connected or if it is closed it will return null
 boolean isConnected()
          returns true if the Connect operation has been called successfully
 boolean isOpen()
          returns true if the Open operation has been called successfully
 void open()
          Opens the channel.
this does the following actions
1.
 java.lang.Object peek(long timeout)
          Just peeks at the next message, view or block.
 java.lang.String printProtocolSpec(boolean include_properties)
          Returns a pretty-printed form of all the protocols.
 java.lang.Object receive(long timeout)
          Blocking receive method.
 void returnState(java.lang.Object state)
          Called by the application is response to receiving a getState() object when calling receive().
When the application receives a getState() message on the receive() method, it should call returnState() to reply with the state of the application
 void send(Address dst, Address src, java.io.Serializable obj)
          creates a new message with the destination address, and the source address and the object as the message value
 void send(Message msg)
          implementation of the Transport interface.
Sends a message through the protocol stack
 void setOpt(int option, java.lang.Object value)
          sets a channel option the options can be either
 void up(Event evt)
          Callback method
Called by the ProtocolStack when a message is received.
 
Methods inherited from class org.javagroups.Channel
option2String, setChannelListener, setUpHandler
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

JChannel

protected JChannel(boolean dummy)
            throws ChannelException
initializes the JChannel with its default settings and default protocol stack

JChannel

public JChannel()
         throws ChannelException
initializes the JChannel with its default settings and default protocol stack

JChannel

public JChannel(java.lang.Object properties)
         throws ChannelException
creates a new JChannel with the protocol stack as defined in the properties parameter. an example of this parameter is
"UDP:PING:FD:STABLE:NAKACK:UNICAST:FRAG:FLUSH:GMS:VIEW_ENFORCER:STATE_TRANSFER:QUEUE"
Another example is http://www.filip.net/javagroups/javagroups-protocol.xml
Parameters:
properties - the protocol stack setup, if null, the default protocol stack will be used
properties - the properties can also be a java.net.URL object or a string that is a URL spec. The JChannel will validate any URL object and String object to see if they are a URL. In case of the parameter being a url, the JChannel will try to load the xml from there.
Method Detail

getProtocolStack

public ProtocolStack getProtocolStack()
Returns the protocol stack. Currently used by Debugger. Specific to JChannel, therefore not visible in Channel

getProperties

public java.lang.String getProperties()
returns the protocol stack configuration in string format. an example of this property is
"UDP:PING:FD:STABLE:NAKACK:UNICAST:FRAG:FLUSH:GMS:VIEW_ENFORCER:STATE_TRANSFER:QUEUE"

printProtocolSpec

public java.lang.String printProtocolSpec(boolean include_properties)
Returns a pretty-printed form of all the protocols. If include_properties is set, the properties for each protocol will also be printed.

connect

public void connect(java.lang.String channel_name)
             throws ChannelClosedException
Connects the channel to a group.
If the channel is already connected, an error message will be printed to the error log
If the channel is closed a ChannelClosed exception will be thrown
This method starts the protocol stack by calling ProtocolStack.start
then it sends an Event.CONNECT event down the stack and waits to receive a CONNECT_OK event
Once the CONNECT_OK event arrives from the protocol stack, any channel listeners are notified
and the channel is considered connected
Overrides:
connect in class Channel
Parameters:
channel_name - A String denoting the group name. Cannot be null.
Throws:
throws - a ChannelClosed exception if the close() method has been called

disconnect

public void disconnect()
disconnects the channel if it is connected.
if the channel is closed, this operation is ignored
Otherwise the following actions happen in the listed order
1. The JChannel sends a DISCONNECT event down the protocol stack
2. Blocks until the channel to receives a DISCONNECT_OK event
3. Sends a STOP_QUEING event down the stack
4. Sends a CLEANUP event down the stack
5. Blocks until the channel receives a CLEANUP_OK event
6. Stops the protocol stack by calling ProtocolStack.stop()
7. Notifies the listener, if the listener is available
Overrides:
disconnect in class Channel
Following copied from class: org.javagroups.Channel
See Also:
Channel.connect

close

public void close()
Destroys the channel.
After this method has been called, the channel us unusable.
This operation will disconnect the channel and close the channel receive queue immediately
Overrides:
close in class Channel

open

public void open()
          throws ChannelException
Opens the channel.
this does the following actions
1. Resets the receiver queue by calling Queue.reset
2. Sets up the protocol stack by calling ProtocolStack.setup
3. Sets the closed flag to false.
Overrides:
open in class Channel

isOpen

public boolean isOpen()
returns true if the Open operation has been called successfully
Overrides:
isOpen in class Channel

isConnected

public boolean isConnected()
returns true if the Connect operation has been called successfully
Overrides:
isConnected in class Channel

send

public void send(Message msg)
          throws ChannelNotConnectedException,
                 ChannelClosedException
implementation of the Transport interface.
Sends a message through the protocol stack
Overrides:
send in class Channel
Parameters:
msg - the message to be sent through the protocol stack, the destination of the message is specified inside the message itself
Throws:
ChannelNotConnected -  
ChannelClosed -  

send

public void send(Address dst,
                 Address src,
                 java.io.Serializable obj)
          throws ChannelNotConnectedException,
                 ChannelClosedException
creates a new message with the destination address, and the source address and the object as the message value
Overrides:
send in class Channel
Parameters:
dst - - the destination address of the message, null for all members
src - - the source address of the message
obj - - the value of the message
Throws:
ChannelNotConnected -  
ChannelClosed -  
See Also:
send(org.javagroups.Message)

receive

public java.lang.Object receive(long timeout)
                         throws ChannelNotConnectedException,
                                ChannelClosedException,
                                TimeoutException
Blocking receive method. This method returns the object that was first received by this JChannel and that has not been received before. After the object is received, it is removed from the receive queue.
If you only want to inspect the object received without removing it from the queue call JChannel.peek
If no messages are in the receive queue, this method blocks until a message is added or the operation times out
By specifying a timeout of 0, the operation blocks forever, or until a message has been received.
Overrides:
receive in class Channel
Parameters:
timeout, - the number of milliseconds to wait if the receive queue is empty. 0 means wait forever
Throws:
TimeoutException - if a timeout occured prior to a new message was received
ChannelNotConnected -  
ChannelClosed - * @see JChannel#peek

peek

public java.lang.Object peek(long timeout)
                      throws ChannelNotConnectedException,
                             ChannelClosedException,
                             TimeoutException
Just peeks at the next message, view or block. Does not install new view if view is received
Does the same thing as JChannel.receive but doesn't remove the object from the receiver queue
Overrides:
peek in class Channel
Following copied from class: org.javagroups.Channel
Parameters:
timeout - Value in milliseconds. Value <= 0 means wait forever
Returns:
A Message, View, BlockEvent, SuspectEvent, GetStateEvent or SetStateEvent object, depending on what is on top of the internal queue.
Throws:
ChannelNotConnected - The channel must be connected to receive messages.
ChannelClosed - The channel is closed and therefore cannot be used any longer. A new channel has to be created first.
TimeoutException - Thrown when a timeout has occurred.
See Also:
Receive

getView

public View getView()
returns the current view.
if the channel is not connected or if it is closed it will return null
Overrides:
getView in class Channel
Returns:
returns the current group view, or null if the channel is closed or disconnected

getLocalAddress

public Address getLocalAddress()
returns the local address of the channel returns null if the channel is closed
Overrides:
getLocalAddress in class Channel
Following copied from class: org.javagroups.Channel
Returns:
The channel's address. Generated by the underlying transport, and opaque. Addresses can be used as destination in the Send operation.

getChannelName

public java.lang.String getChannelName()
returns the name of the channel if the channel is not connected or if it is closed it will return null
Overrides:
getChannelName in class Channel
Following copied from class: org.javagroups.Channel
Returns:
The group address

setOpt

public void setOpt(int option,
                   java.lang.Object value)
sets a channel option the options can be either
     Channel.BLOCK
     Channel.VIEW
     Channel.SUSPECT
     Channel.LOCAL
     Channel.GET_STATE_EVENTS
     Channel.AUTO_RECONNECT
     Channel.AUTO_GETSTATE
 
There are certain dependencies between the options that you can set, I will try to describe them here
Option: Channel.VIEW option
Value: java.lang.Boolean
Result: set to true the JChannel will receive VIEW change events

Option: Channel.SUSPECT
Value: java.lang.Boolean
Result: set to true the JChannel will receive SUSPECT events

Option: Channel.BLOCK
Value: java.lang.Boolean
Result: set to true will set setOpt(VIEW, true) and the JChannel will receive BLOCKS and VIEW events

Option: GET_STATE_EVENTS
Value: java.lang.Boolean
Result: set to true the JChannel will receive state events

Option: LOCAL
Value: java.lang.Boolean
Result: set to true the JChannel will receive messages that it self sent out.

Option: AUTO_RECONNECT
Value: java.lang.Boolean
Result: set to true and the JChannel will try to reconnect when it is being closed

Option: AUTO_GETSTATE
Value: java.lang.Boolean
Result: set to true, the AUTO_RECONNECT will be set to true and the JChannel will try to get the state after a close and reconnect happens

Overrides:
setOpt in class Channel
Parameters:
option - the parameter option Channel.VIEW, Channel.SUSPECT, etc
value - the value to set for this option

getOpt

public java.lang.Object getOpt(int option)
returns the value of an option.
Overrides:
getOpt in class Channel
Parameters:
option - the option you want to see the value for
Returns:
the object value, in most cases java.lang.Boolean
See Also:
setOpt(int, java.lang.Object)

blockOk

public void blockOk()
Called to acknowledge a block() (callback in MembershipListener or BlockEvent received from call to receive()). After sending blockOk(), no messages should be sent until a new view has been received. Calling this method on a closed channel has no effect.
Overrides:
blockOk in class Channel

getState

public boolean getState(Address target,
                        long timeout)
Retrieves the current group state. Sends GET_STATE event down to STATE_TRANSFER layer. Blocks until STATE_TRANSFER sends up a GET_STATE_OK event or until timeout milliseconds have elapsed. The argument of GET_STATE_OK should be a single object.
Overrides:
getState in class Channel
Parameters:
target - - the target member to receive the state from. if null, state is retrieved from coordinator
timeout - - the number of milliseconds to wait for the operation to complete successfully
Returns:
true of the state was received, false if the operation timed out

getAllStates

public boolean getAllStates(java.util.Vector targets,
                            long timeout)
Retrieves the current group state. Sends GET_STATE event down to STATE_TRANSFER layer. Blocks until STATE_TRANSFER sends up a GET_STATE_OK event or until timeout milliseconds have elapsed. The argument of GET_STATE_OK should be a vector of objects.
Overrides:
getAllStates in class Channel
Parameters:
target - - the target members to receive the state from ( an Address list )
timeout - - the number of milliseconds to wait for the operation to complete successfully
Returns:
true of the state was received, false if the operation timed out

returnState

public void returnState(java.lang.Object state)
Called by the application is response to receiving a getState() object when calling receive().
When the application receives a getState() message on the receive() method, it should call returnState() to reply with the state of the application
Overrides:
returnState in class Channel
Parameters:
state - The state of the application as a Serializable or Externalizable (to send over the network).

up

public void up(Event evt)
Callback method
Called by the ProtocolStack when a message is received. It will be added to the message queue from which subsequent Receives will dequeue it.
Parameters:
evt - the event carrying the message from the protocol stack

down

public void down(Event evt)
Sends a message through the protocol stack if the stack is available
Overrides:
down in class Channel
Parameters:
evt - the message to send down, encapsulated in an event


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