org.jgroups

Class JChannel

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.

Properties

Properties are used to configure a channel, and are accepted in several forms; the String form is described here. A property string consists of a number of properties separated by colons. For example:

"<prop1>(arg1=val1):<prop2>(arg1=val1;arg2=val2):<prop3>:<propn>"

Each property relates directly to a protocol layer, which is implemented as a Java class. When a protocol stack is to be created based on the above property string, the first property becomes the bottom-most layer, the second one will be placed on the first, etc.: the stack is created from the bottom to the top, as the string is parsed from left to right. Each property has to be the name of a Java class that resides in the org.jgroups.protocols package.

Note that only the base name has to be given, not the fully specified class name (e.g., UDP instead of org.jgroups.protocols.UDP).

Each layer may have 0 or more arguments, which are specified as a list of name/value pairs in parentheses directly after the property. In the example above, the first protocol layer has 1 argument, the second 2, the third none. When a layer is created, these properties (if there are any) will be set in a layer by invoking the layer's setProperties() method

As an example the property string below instructs JGroups to create a JChannel with protocols UDP, PING, FD and GMS:

"UDP(mcast_addr=228.10.9.8;mcast_port=5678):PING:FD:GMS"

The UDP protocol layer is at the bottom of the stack, and it should use mcast address 228.10.9.8. and port 5678 rather than the default IP multicast address and port. The only other argument instructs FD to output debug information while executing. Property UDP refers to a class UDP, which is subsequently loaded and an instance of which is created as protocol layer. If any of these classes are not found, an exception will be thrown and the construction of the stack will be aborted.

Version: $Revision: 1.45.2.1 $

Author: Bela Ban Filip Hanik

Field Summary
protected JChannel.CloserThreadcloser
Thread responsible for closing a channel and potentially reconnecting to it (e.g., when shunned).
static StringDEFAULT_PROTOCOL_STACK
The default protocol stack used by the default constructor.
protected Loglog
protected longreceived_bytes
protected longreceived_msgs
protected longsent_bytes
protected longsent_msgs
protected booleanstats
Collect statistics
Constructor Summary
JChannel()
Constructs a JChannel instance with the protocol stack specified by the DEFAULT_PROTOCOL_STACK member.
JChannel(File properties)
Constructs a JChannel instance with the protocol stack configuration contained by the specified file.
JChannel(Element properties)
Constructs a JChannel instance with the protocol stack configuration contained by the specified XML element.
JChannel(URL properties)
Constructs a JChannel instance with the protocol stack configuration indicated by the specified URL.
JChannel(String properties)
Constructs a JChannel instance with the protocol stack configuration based upon the specified properties parameter.
protected JChannel(ProtocolStackConfigurator configurator)
Constructs a JChannel instance with the protocol stack configuration contained by the protocol stack configurator parameter.
JChannel(Object properties)
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"
Other examples can be found in the ./conf directory
Method Summary
voidblockOk()
Called to acknowledge a block() (callback in MembershipListener or BlockEvent received from call to receive()).
voidclose()
Destroys the channel.
voidconnect(String channel_name)
Connects the channel to a group.
voiddisconnect()
Disconnects the channel if it is connected.
voiddown(Event evt)
Sends a message through the protocol stack if the stack is available
StringdumpQueue()
MapdumpStats()
Returns a map of statistics of the various protocols and of the channel itself.
StringdumpTimerQueue()
voidenableStats(boolean stats)
booleangetAllStates(Vector targets, long timeout)
Retrieves the current group state.
StringgetChannelName()
returns the name of the channel if the channel is not connected or if it is closed it will return null
AddressgetLocalAddress()
returns the local address of the channel returns null if the channel is closed
protected LoggetLog()
intgetNumberOfTasksInTimer()
intgetNumMessages()
ObjectgetOpt(int option)
returns the value of an option.
StringgetProperties()
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"
ProtocolStackgetProtocolStack()
Returns the protocol stack.
longgetReceivedBytes()
longgetReceivedMessages()
longgetSentBytes()
longgetSentMessages()
booleangetState(Address target, long timeout)
Retrieves the current group state.
ViewgetView()
Returns the current view.
booleanisConnected()
returns true if the Connect operation has been called successfully
booleanisOpen()
returns true if the Open operation has been called successfully
booleanisSuspended()
voidopen()
Opens the channel.
Objectpeek(long timeout)
Just peeks at the next message, view or block.
StringprintProtocolSpec(boolean include_properties)
Returns a pretty-printed form of all the protocols.
Objectreceive(long timeout)
Blocking receive method.
voidresetStats()
voidresume()
Send() unblocks
voidreturnState(byte[] state)
Called by the application is response to receiving a getState() object when calling receive().
voidsend(Message msg)
Sends a message through the protocol stack.
voidsend(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
voidsetOpt(int option, Object value)
Sets a channel option.
voidshutdown()
Shuts down the channel without disconnecting
booleanstatsEnabled()
voidsuspend()
Send() blocks from now on, until resume() is called
StringtoString(boolean details)
voidup(Event evt)
Callback method
Called by the ProtocolStack when a message is received.

Field Detail

closer

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

DEFAULT_PROTOCOL_STACK

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

log

protected final Log log

received_bytes

protected long received_bytes

received_msgs

protected long received_msgs

sent_bytes

protected long sent_bytes

sent_msgs

protected long sent_msgs

stats

protected boolean stats
Collect statistics

Constructor Detail

JChannel

public JChannel()
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(File properties)
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(Element properties)
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(URL properties)
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

public JChannel(String properties)
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

protected JChannel(ProtocolStackConfigurator configurator)
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.

JChannel

public JChannel(Object properties)

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"
Other examples can be found in the ./conf directory

Parameters: properties the protocol stack setup; if null, the default protocol stack will be used. 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. In case properties is a org.w3c.dom.Element, the ConfiguratorFactory will parse the DOM tree with the element as its root element.

Method Detail

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.

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

connect

public 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.

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

down

public void down(Event evt)
Sends a message through the protocol stack if the stack is available

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

dumpQueue

public String dumpQueue()

dumpStats

public Map dumpStats()
Returns a map of statistics of the various protocols and of the channel itself.

Returns: Map. A map where the keys are the protocols ("channel" pseudo key is used for the channel itself") and the values are property maps.

dumpTimerQueue

public String dumpTimerQueue()

enableStats

public void enableStats(boolean stats)

getAllStates

public boolean getAllStates(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.

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

getLocalAddress

public Address getLocalAddress()
returns the local address of the channel returns null if the channel is closed

getLog

protected Log getLog()

getNumberOfTasksInTimer

public int getNumberOfTasksInTimer()

getNumMessages

public int getNumMessages()

getOpt

public Object getOpt(int option)
returns the value of an option.

Parameters: option the option you want to see the value for

Returns: the object value, in most cases java.lang.Boolean

See Also: JChannel

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

getReceivedBytes

public long getReceivedBytes()

getReceivedMessages

public long getReceivedMessages()

getSentBytes

public long getSentBytes()

getSentMessages

public long getSentMessages()

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.

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.

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

isOpen

public boolean isOpen()
returns true if the Open operation has been called successfully

isSuspended

public boolean isSuspended()

open

public void open()
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

peek

public Object peek(long timeout)
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

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)
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.

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: JChannel

resetStats

public void resetStats()

resume

public void resume()
Send() unblocks

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

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

send

public void send(Message msg)
Sends a message through the protocol stack. Implements the Transport interface.

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

send

public 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

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

setOpt

public void setOpt(int option, Object value)
Sets a channel option. The options can be one of the following:

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

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

shutdown

public void shutdown()
Shuts down the channel without disconnecting

statsEnabled

public boolean statsEnabled()

suspend

public void suspend()
Send() blocks from now on, until resume() is called

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

Copyright ? 1998-2005 Bela Ban. All Rights Reserved.