org.jgroups

Class JChannel

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: 1.22 $

Authors:
Bela Ban
Filip Hanik

Field Summary

static String
DEFAULT_PROTOCOL_STACK
The default protocol stack used by the default constructor.
protected org.jgroups.JChannel.CloserThread
closer
Thread responsible for closing a channel and potentially reconnecting to it (e.g.
protected Log
log
protected boolean
state_received
Indicates whether the state was retrieved correctly (even a null state if we are the first member)

Fields inherited from class org.jgroups.Channel

AUTO_GETSTATE, AUTO_RECONNECT, BLOCK, GET_STATE_EVENTS, LOCAL, SUSPECT, VIEW, channel_listener, up_handler

Constructor Summary

JChannel()
Constructs a JChannel instance with the protocol stack specified by the DEFAULT_PROTOCOL_STACK member.
JChannel(Element properties)
Constructs a JChannel instance with the protocol stack configuration contained by the specified XML element.
JChannel(File properties)
Constructs a JChannel instance with the protocol stack configuration contained by the specified file.
JChannel(Object properties)
Deprecated. Use the constructors with specific parameter types instead.
JChannel(String properties)
Constructs a JChannel instance with the protocol stack configuration based upon the specified properties parameter.
JChannel(URL properties)
Constructs a JChannel instance with the protocol stack configuration indicated by the specified URL.
JChannel(ProtocolStackConfigurator configurator)
Constructs a JChannel instance with the protocol stack configuration contained by the protocol stack configurator 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(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.
void
down(Event evt)
Sends a message through the protocol stack if the stack is available
boolean
getAllStates(Vector targets, long timeout)
Retrieves the current group state.
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
int
getNumMessages()
Object
getOpt(int option)
returns the value of an option.
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.
Object
peek(long timeout)
Just peeks at the next message, view or block.
String
printProtocolSpec(boolean include_properties)
Returns a pretty-printed form of all the protocols.
Object
receive(long timeout)
Blocking receive method.
void
returnState(byte[] 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, 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, 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

String
toString(boolean details)
void
up(Event evt)
Callback method
Called by the ProtocolStack when a message is received.

Methods inherited from class org.jgroups.Channel

blockOk, close, connect, disconnect, down, getAllStates, getChannelName, getLocalAddress, getNumMessages, getOpt, getState, getView, isConnected, isOpen, open, option2String, peek, receive, returnState, send, send, setChannelListener, setOpt, setUpHandler

Field Details

DEFAULT_PROTOCOL_STACK

public static final String DEFAULT_PROTOCOL_STACK
The default protocol stack used by the default constructor.


closer

protected org.jgroups.JChannel.CloserThread closer
Thread responsible for closing a channel and potentially reconnecting to it (e.g. when shunned)


log

protected Log log


state_received

protected boolean state_received
Indicates whether the state was retrieved correctly (even a null state if we are the first member)

Constructor Details

JChannel

public JChannel()
            throws ChannelException
Constructs a JChannel instance with the protocol stack specified by the DEFAULT_PROTOCOL_STACK member.

Throws:
ChannelException - if problems occur during the initialization of the protocol stack.


JChannel

public JChannel(Element properties)
            throws ChannelException
Constructs a JChannel instance with the protocol stack configuration contained by the specified XML element.

Parameters:
properties - a XML element containing a JGroups XML protocol stack configuration.

Throws:
ChannelException - if problems occur during the configuration or initialization of the protocol stack.


JChannel

public JChannel(File properties)
            throws ChannelException
Constructs a JChannel instance with the protocol stack configuration contained by the specified file.

Parameters:
properties - a file containing a JGroups XML protocol stack configuration.

Throws:
ChannelException - if problems occur during the configuration or initialization of the protocol stack.


JChannel

public JChannel(Object properties)
            throws ChannelException

Deprecated. Use the constructors with specific parameter types instead.

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/jgroups/jgroups-protocol.xml

Parameters:
properties - the protocol stack setup, if null, the default protocol stack will be used


JChannel

public JChannel(String properties)
            throws ChannelException
Constructs a JChannel instance with the protocol stack configuration based upon the specified properties parameter.

Parameters:
properties - an old style property string, a string representing a system resource containing a JGroups XML configuration, a string representing a URL pointing to a JGroups XML XML configuration, or a string representing a file name that contains a JGroups XML configuration.

Throws:
ChannelException - if problems occur during the configuration and initialization of the protocol stack.


JChannel

public JChannel(URL properties)
            throws ChannelException
Constructs a JChannel instance with the protocol stack configuration indicated by the specified URL.

Parameters:
properties - a URL pointing to a JGroups XML protocol stack configuration.

Throws:
ChannelException - if problems occur during the configuration or initialization of the protocol stack.


JChannel

protected JChannel(ProtocolStackConfigurator configurator)
            throws ChannelException
Constructs a JChannel instance with the protocol stack configuration contained by the protocol stack configurator parameter.

All of the public constructors of this class eventually delegate to this method.

Parameters:
configurator - a protocol stack configurator containing a JGroups protocol stack configuration.

Throws:
ChannelException - if problems occur during the initialization of the protocol stack.

Method Details

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 interface Channel


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 interface Channel


connect

public void connect(String channel_name)
            throws ChannelException,
                   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 interface Channel

Parameters:
channel_name - A String denoting the group name. Cannot be null.

Throws:
ChannelException - The protocol stack cannot be started
ChannelClosedException - The channel is closed and therefore cannot be used any longer. A new channel has to be created first.


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. Stops the protocol stack by calling ProtocolStack.stop()
  5. Notifies the listener, if the listener is available
Overrides:
disconnect in interface Channel


down

public void down(Event evt)
Sends a message through the protocol stack if the stack is available
Overrides:
down in interface Channel

Parameters:
evt - the message to send down, encapsulated in an event


getAllStates

public boolean getAllStates(Vector targets,
                            long timeout)
            throws ChannelNotConnectedException,
                   ChannelClosedException
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 interface Channel

Parameters:
targets - - 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


getChannelName

public 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 interface Channel


getLocalAddress

public Address getLocalAddress()
returns the local address of the channel returns null if the channel is closed
Overrides:
getLocalAddress in interface Channel


getNumMessages

public int getNumMessages()
Overrides:
getNumMessages in interface Channel


getOpt

public Object getOpt(int option)
returns the value of an option.
Overrides:
getOpt in interface 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,Object)


getProperties

public 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"


getProtocolStack

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


getState

public boolean getState(Address target,
                        long timeout)
            throws ChannelNotConnectedException,
                   ChannelClosedException
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 interface 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


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 interface Channel

Returns:
returns the current group view, or null if the channel is closed or disconnected


isConnected

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


isOpen

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


peek

public 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 interface Channel


printProtocolSpec

public 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.


receive

public 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.
Specified by:
receive in interface Transport
Overrides:
receive in interface 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
ChannelNotConnectedException -
ChannelClosedException -

See Also:
peek(long)


returnState

public void returnState(byte[] 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 interface Channel

Parameters:
state - The state of the application as a byte buffer (to send over the network).


send

public void send(Address dst,
                 Address src,
                 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 interface 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:
ChannelNotConnectedException -
ChannelClosedException -

See Also:
JChannel.send


send

public void send(Message msg)
            throws ChannelNotConnectedException,
                   ChannelClosedException
implementation of the Transport interface.
Sends a message through the protocol stack
Specified by:
send in interface Transport
Overrides:
send in interface Channel

Parameters:
msg - the message to be sent through the protocol stack, the destination of the message is specified inside the message itself

Throws:
ChannelNotConnectedException -
ChannelClosedException -


setOpt

public void setOpt(int option,
                   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 interface Channel

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


toString

public String toString(boolean details)


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


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