org.jgroups
Class Channel

java.lang.Object
  extended by org.jgroups.Channel
All Implemented Interfaces:
Transport
Direct Known Subclasses:
JChannel

public abstract class Channel
extends java.lang.Object
implements Transport

A channel represents a group communication endpoint (like BSD datagram sockets). A client joins a group by connecting the channel to a group address and leaves it by disconnecting. Messages sent over the channel are received by all group members that are connected to the same group (that is, all members that have the same group address).

The FSM for a channel is roughly as follows: a channel is created (unconnected). The channel is connected to a group (connected). Messages can now be sent and received. The channel is disconnected from the group (unconnected). The channel could now be connected to a different group again. The channel is closed (closed).

Only a single sender is allowed to be connected to a channel at a time, but there can be more than one channel in an application.

Messages can be sent to the group members using the send method and messages can be received using receive (pull approach).

A channel instance is created using either a ChannelFactory or the public constructor. Each implementation of a channel must provide a subclass of Channel and an implementation of ChannelFactory.

Various degrees of sophistication in message exchange can be achieved using building blocks on top of channels; e.g., light-weight groups, synchronous message invocation, or remote method calls. Channels are on the same abstraction level as sockets, and should really be simple to use. Higher-level abstractions are all built on top of channels.

Author:
Bela Ban
See Also:
DatagramPacket, MulticastSocket

Field Summary
static int AUTO_GETSTATE
          Deprecated. 
static int AUTO_RECONNECT
          Deprecated. 
static int BLOCK
          Deprecated. 
protected  java.util.Set<ChannelListener> channel_listeners
           
static int GET_STATE_EVENTS
          Deprecated. 
static int LOCAL
           
protected  Receiver receiver
           
protected  SocketFactory socket_factory
           
static int SUSPECT
          Deprecated. 
protected  UpHandler up_handler
           
static int VIEW
          Deprecated. 
 
Constructor Summary
Channel()
           
 
Method Summary
 void addChannelListener(ChannelListener listener)
          Allows to be notified when a channel event such as connect, disconnect or close occurs.
abstract  void blockOk()
          Called to acknowledge a block() (callback in MembershipListener or BlockEvent received from call to Receive).
 void clearChannelListeners()
           
abstract  void close()
          Destroys the channel and its associated resources (e.g., the protocol stack).
abstract  void connect(java.lang.String cluster_name)
          Connects the channel to a group.
abstract  void connect(java.lang.String cluster_name, Address target, java.lang.String state_id, long timeout)
          Connects the channel to a group and fetches the state
abstract  void disconnect()
          Disconnects the channel from the current group (if connected), leaving the group.
 void down(Event evt)
          Access to event mechanism of channels.
 java.lang.Object downcall(Event evt)
          Can be used instead of down() when a return value is expected.
 java.lang.String dumpQueue()
           
abstract  java.util.Map<java.lang.String,java.lang.Object> dumpStats()
          Returns a map of statistics of the various protocols and of the channel itself.
abstract  boolean flushSupported()
           
abstract  Address getAddress()
          Returns the channel's own address.
abstract  boolean getAllStates(java.util.Vector targets, long timeout)
          Deprecated. Not really needed - we always want to get the state from a single member
abstract  java.lang.String getChannelName()
          Deprecated. Use getClusterName() instead
abstract  java.lang.String getClusterName()
          Returns the cluster name of the group of which the channel is a member.
abstract  java.util.Map<java.lang.String,java.lang.Object> getInfo()
           
abstract  Address getLocalAddress()
          Deprecated. Use getAddress() instead
protected abstract  Log getLog()
           
abstract  java.lang.String getName()
          Returns the logical name of this channel if set.
abstract  java.lang.String getName(Address member)
          Returns the logical name of a given member.
 int getNumMessages()
          Returns the number of messages that are waiting.
abstract  java.lang.Object getOpt(int option)
          Gets an option.
 java.lang.String getProperties()
           
abstract  ProtocolStack getProtocolStack()
           
 Receiver getReceiver()
           
 SocketFactory getSocketFactory()
           
abstract  boolean getState(Address target, long timeout)
          Retrieve the state of the group.
abstract  boolean getState(Address target, java.lang.String state_id, long timeout)
          Fetches a partial state identified by state_id.
 UpHandler getUpHandler()
           
abstract  View getView()
          Gets the current view.
abstract  boolean isConnected()
          Determines whether the channel is connected to a group.
abstract  boolean isOpen()
          Determines whether the channel is open; i.e., the protocol stack has been created (may not be connected though).
protected  void notifyChannelClosed(Channel c)
           
protected  void notifyChannelConnected(Channel c)
           
protected  void notifyChannelDisconnected(Channel c)
           
 void open()
          Re-opens a closed channel.
static java.lang.String option2String(int option)
           
abstract  java.lang.Object peek(long timeout)
          Deprecated. Use a Receiver instead, this method will not be available in JGroups 3.0
abstract  java.lang.Object receive(long timeout)
          Deprecated. Use a Receiver instead
 void removeChannelListener(ChannelListener listener)
           
abstract  void returnState(byte[] state)
          Called by the application is response to receiving a getState() object when calling receive().
abstract  void returnState(byte[] state, java.lang.String state_id)
          Returns a given substate (state_id of null means return entire state)
abstract  void send(Address dst, Address src, byte[] buf)
           
abstract  void send(Address dst, Address src, byte[] buf, int offset, int length)
           
abstract  void send(Address dst, Address src, java.io.Serializable obj)
          Helper method.
abstract  void send(Message msg)
          Sends a message to a (unicast) destination.
 void setChannelListener(ChannelListener channel_listener)
          Deprecated. Use addChannelListener() instead
abstract  void setInfo(java.lang.String key, java.lang.Object value)
           
abstract  void setName(java.lang.String name)
          Sets the logical name for the channel.
abstract  void setOpt(int option, java.lang.Object value)
          Sets an option.
 void setReceiver(Receiver r)
          Sets the receiver, which will handle all messages, view changes etc
 void setSocketFactory(SocketFactory factory)
           
 void setUpHandler(UpHandler up_handler)
          When up_handler is set, all events will be passed to it directly.
abstract  void shutdown()
          Deprecated. 
abstract  boolean startFlush(boolean automatic_resume)
           
abstract  boolean startFlush(java.util.List<Address> flushParticipants, boolean automatic_resume)
           
abstract  boolean startFlush(long timeout, boolean automatic_resume)
           
abstract  void stopFlush()
           
abstract  void stopFlush(java.util.List<Address> flushParticipants)
           
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

BLOCK

@Deprecated
public static final int BLOCK
Deprecated. 
See Also:
Constant Field Values

VIEW

@Deprecated
public static final int VIEW
Deprecated. 
See Also:
Constant Field Values

SUSPECT

@Deprecated
public static final int SUSPECT
Deprecated. 
See Also:
Constant Field Values

LOCAL

public static final int LOCAL
See Also:
Constant Field Values

GET_STATE_EVENTS

@Deprecated
public static final int GET_STATE_EVENTS
Deprecated. 
See Also:
Constant Field Values

AUTO_RECONNECT

@Deprecated
public static final int AUTO_RECONNECT
Deprecated. 
See Also:
Constant Field Values

AUTO_GETSTATE

@Deprecated
public static final int AUTO_GETSTATE
Deprecated. 
See Also:
Constant Field Values

up_handler

protected UpHandler up_handler

channel_listeners

protected java.util.Set<ChannelListener> channel_listeners

receiver

protected Receiver receiver

socket_factory

protected SocketFactory socket_factory
Constructor Detail

Channel

public Channel()
Method Detail

getLog

protected abstract Log getLog()

getProtocolStack

public abstract ProtocolStack getProtocolStack()

getSocketFactory

public SocketFactory getSocketFactory()

setSocketFactory

public void setSocketFactory(SocketFactory factory)

connect

public abstract void connect(java.lang.String cluster_name)
                      throws ChannelException
Connects the channel to a group. The client is now able to receive group messages, views and block events (depending on the options set) and to send messages to (all or single) group members. This is a null operation if already connected.

All channels with the same name form a group, that means all messages sent to the group will be received by all channels connected to the same channel name.

Parameters:
cluster_name - The name of the chanel to connect to.
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.
See Also:
disconnect()

connect

public abstract void connect(java.lang.String cluster_name,
                             Address target,
                             java.lang.String state_id,
                             long timeout)
                      throws ChannelException
Connects the channel to a group and fetches the state

Parameters:
cluster_name - The name of the cluster to connect to.
target - The address of the member from which the state is to be retrieved. If it is null, the state is retrieved from coordinator is contacted.
state_id - The ID of a substate. If the full state is to be fetched, set this parameter to null
timeout - Milliseconds to wait for the state response (0 = wait indefinitely).
Throws:
ChannelException - thrown if connecting to cluster was not successful
StateTransferException - thrown if state transfer was not successful

disconnect

public abstract void disconnect()
Disconnects the channel from the current group (if connected), leaving the group. It is a null operation if not connected. It is a null operation if the channel is closed.

See Also:
connect(String)

close

public abstract void close()
Destroys the channel and its associated resources (e.g., the protocol stack). After a channel has been closed, invoking methods on it throws the ChannelClosed exception (or results in a null operation). It is a null operation if the channel is already closed.

If the channel is connected to a group, disconnec()t will be called first.


shutdown

@Deprecated
public abstract void shutdown()
Deprecated. 

Shuts down the channel without disconnecting if connected, stops all the threads


open

public void open()
          throws ChannelException
Re-opens a closed channel. Throws an exception if the channel is already open. After this method returns, connect() may be called to join a group. The address of this member will be different from the previous incarnation.

Throws:
ChannelException

isOpen

public abstract boolean isOpen()
Determines whether the channel is open; i.e., the protocol stack has been created (may not be connected though).


isConnected

public abstract boolean isConnected()
Determines whether the channel is connected to a group. This implies it is open. If true is returned, then the channel can be used to send and receive messages.


getNumMessages

public int getNumMessages()
Returns the number of messages that are waiting. Those messages can be removed by receive(long). Note that this number could change after calling this method and before calling receive() (e.g. the latter method might be called by a different thread).

Returns:
The number of messages on the queue, or -1 if the queue/channel is closed/disconnected.

dumpQueue

public java.lang.String dumpQueue()

dumpStats

public abstract java.util.Map<java.lang.String,java.lang.Object> 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.

send

public abstract void send(Message msg)
                   throws ChannelNotConnectedException,
                          ChannelClosedException
Sends a message to a (unicast) destination. The message contains
  1. a destination address (Address). A null address sends the message to all group members.
  2. a source address. Can be left empty. Will be filled in by the protocol stack.
  3. a byte buffer. The message contents.
  4. several additional fields. They can be used by application programs (or patterns). E.g. a message ID, a oneway field which determines whether a response is expected etc.

Specified by:
send in interface Transport
Parameters:
msg - The message to be sent. Destination and buffer should be set. A null destination means to send to all group members.
Throws:
ChannelNotConnectedException - The channel must be connected to send messages.
ChannelClosedException - The channel is closed and therefore cannot be used any longer. A new channel has to be created first.

send

public abstract void send(Address dst,
                          Address src,
                          java.io.Serializable obj)
                   throws ChannelNotConnectedException,
                          ChannelClosedException
Helper method. Will create a Message(dst, src, obj) and use send(Message).

Parameters:
dst - Destination address for message. If null, message will be sent to all current group members
src - Source (sender's) address. If null, it will be set by the protocol's transport layer before being put on the wire. Can usually be set to null.
obj - Serializable object. Will be serialized into the byte buffer of the Message. If it is not serializable, the byte buffer will be null.
Throws:
ChannelNotConnectedException
ChannelClosedException

send

public abstract void send(Address dst,
                          Address src,
                          byte[] buf)
                   throws ChannelNotConnectedException,
                          ChannelClosedException
Throws:
ChannelNotConnectedException
ChannelClosedException

send

public abstract void send(Address dst,
                          Address src,
                          byte[] buf,
                          int offset,
                          int length)
                   throws ChannelNotConnectedException,
                          ChannelClosedException
Throws:
ChannelNotConnectedException
ChannelClosedException

down

public void down(Event evt)
Access to event mechanism of channels. Enables to send and receive events, used by building blocks to communicate with (building block) specific protocol layers. Currently useful only with JChannel.


downcall

public java.lang.Object downcall(Event evt)
Can be used instead of down() when a return value is expected. This will be removed in 3.0 when we change the signature of down() to return Object rather than void

Parameters:
evt -
Returns:

receive

public abstract java.lang.Object receive(long timeout)
                                  throws ChannelNotConnectedException,
                                         ChannelClosedException,
                                         TimeoutException
Deprecated. Use a Receiver instead

Receives a message, a view change or a block event. By using setOpt, the type of objects to be received can be determined (e.g., not views and blocks, just messages). The possible types returned can be:
  1. Message. Normal message
  2. Event. All other events (used by JChannel)
  3. View. A view change.
  4. BlockEvent. A block event indicating that a flush protocol has been started, and we should not send any more messages. This event should be ack'ed by calling blockOk() . Any messages sent after blockOk() returns might get blocked until the flush protocol has completed.
  5. UnblockEvent. An unblock event indicating that the flush protocol has completed and we can resume sending messages
  6. SuspectEvent. A notification of a suspected member.
  7. GetStateEvent. The current state of the application should be returned using ReturnState.
  8. SetStateEvent. The state of a single/all members as requested previously by having called Channel.getState(s).
  9. ExitEvent. Signals that this member was forced to leave the group (e.g., caused by the member being suspected.) The member can rejoin the group by calling open(). If the AUTO_RECONNECT is set (see setOpt()), the reconnect will be done automatically.
The instanceof operator can be used to discriminate between different types returned.

Specified by:
receive in interface Transport
Parameters:
timeout - Value in milliseconds. Value <= 0 means wait forever
Returns:
A Message, View, BlockEvent, SuspectEvent, GetStateEvent, SetStateEvent or ExitEvent, depending on what is on top of the internal queue.
Throws:
ChannelNotConnectedException - The channel must be connected to receive messages.
ChannelClosedException - 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.

peek

public abstract java.lang.Object peek(long timeout)
                               throws ChannelNotConnectedException,
                                      ChannelClosedException,
                                      TimeoutException
Deprecated. Use a Receiver instead, this method will not be available in JGroups 3.0

Returns the next message, view, block, suspect or other event without removing it from the queue.

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:
ChannelNotConnectedException - The channel must be connected to receive messages.
ChannelClosedException - 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(long)

getView

public abstract View getView()
Gets the current view. This does not retrieve a new view, use receive() to do so. The view may only be available after a successful connect(). The result of calling this method on an unconnected channel is implementation defined (may return null). Calling it on a channel that is not enabled to receive view events (via setOpt) returns null. Calling this method on a closed channel returns a null view.

Returns:
The current view.

getLocalAddress

public abstract Address getLocalAddress()
Deprecated. Use getAddress() instead

Returns the channel's own address. The result of calling this method on an unconnected channel is implementation defined (may return null). Calling this method on a closed channel returns null. Addresses can be used as destination in the send() operation.

Returns:
The channel's address (opaque)

getAddress

public abstract Address getAddress()
Returns the channel's own address. The result of calling this method on an unconnected channel is implementation defined (may return null). Calling this method on a closed channel returns null. Successor to getAddress(). Addresses can be used as destination in the send() operation.

Returns:
The channel's address (opaque)

getName

public abstract java.lang.String getName()
Returns the logical name of this channel if set.

Returns:
The logical name or null (if not set)

getName

public abstract java.lang.String getName(Address member)
Returns the logical name of a given member. The lookup is from the local cache of logical address / logical name mappings and no remote communication is performed.

Parameters:
member -
Returns:

setName

public abstract void setName(java.lang.String name)
Sets the logical name for the channel. The name will stay associated with this channel for the channel's lifetime (until close() is called). This method should be called before calling connect().

Parameters:
name -

getChannelName

public abstract java.lang.String getChannelName()
Deprecated. Use getClusterName() instead

Returns the group address of the group of which the channel is a member. This is the object that was the argument to connect(). Calling this method on a closed channel returns null.

Returns:
The group address

getClusterName

public abstract java.lang.String getClusterName()
Returns the cluster name of the group of which the channel is a member. This is the object that was the argument to connect(). Calling this method on a closed channel returns null.

Returns:
The cluster name

getProperties

public java.lang.String getProperties()

setUpHandler

public void setUpHandler(UpHandler up_handler)
When up_handler is set, all events will be passed to it directly. These will not be received by the channel (except connect/disconnect, state retrieval and the like). This can be used by building blocks on top of a channel; thus the channel is used as a pass-through medium, and the building blocks take over some of the channel's tasks. However, tasks such as connection management and state transfer is still handled by the channel.


getUpHandler

public UpHandler getUpHandler()

setChannelListener

public void setChannelListener(ChannelListener channel_listener)
Deprecated. Use addChannelListener() instead

Allows to be notified when a channel event such as connect, disconnect or close occurs. E.g. a PullPushAdapter may choose to stop when the channel is closed, or to start when it is opened.


addChannelListener

public void addChannelListener(ChannelListener listener)
Allows to be notified when a channel event such as connect, disconnect or close occurs. E.g. a PullPushAdapter may choose to stop when the channel is closed, or to start when it is opened.


removeChannelListener

public void removeChannelListener(ChannelListener listener)

clearChannelListeners

public void clearChannelListeners()

setReceiver

public void setReceiver(Receiver r)
Sets the receiver, which will handle all messages, view changes etc


getReceiver

public Receiver getReceiver()

setOpt

public abstract void setOpt(int option,
                            java.lang.Object value)
Sets an option. The following options are currently recognized:
  1. BLOCK. Turn the reception of BLOCK events on/off (value is Boolean). Default is off
  2. LOCAL. Receive its own broadcast messages to the group (value is Boolean). Default is on.
  3. AUTO_RECONNECT. Turn auto-reconnection on/off. If on, when a member if forced out of a group (EXIT event), then we will reconnect.
  4. AUTO_GETSTATE. Turn automatic fetching of state after an auto-reconnect on/off. This also sets AUTO_RECONNECT to true (if not yet set).
This method can be called on an unconnected channel. Calling this method on a closed channel has no effect.


getOpt

public abstract java.lang.Object getOpt(int option)
Gets an option. This method can be called on an unconnected channel. Calling this method on a closed channel returns null.

Parameters:
option - The option to be returned.
Returns:
The object associated with an option.

flushSupported

public abstract boolean flushSupported()

startFlush

public abstract boolean startFlush(java.util.List<Address> flushParticipants,
                                   boolean automatic_resume)

startFlush

public abstract boolean startFlush(boolean automatic_resume)

startFlush

public abstract boolean startFlush(long timeout,
                                   boolean automatic_resume)

stopFlush

public abstract void stopFlush()

stopFlush

public abstract void stopFlush(java.util.List<Address> flushParticipants)

blockOk

public abstract 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.


getState

public abstract boolean getState(Address target,
                                 long timeout)
                          throws ChannelNotConnectedException,
                                 ChannelClosedException
Retrieve the state of the group. Will usually contact the oldest group member to get the state. When the method returns true, a SetStateEvent will have been added to the channel's queue, causing receive() to return the state in one of the next invocations. If false, no state will be retrieved by receive().

Parameters:
target - The address of the member from which the state is to be retrieved. If it is null, the coordinator is contacted.
timeout - Milliseconds to wait for the response (0 = wait indefinitely).
Returns:
boolean True if the state was retrieved successfully, otherwise false.
Throws:
ChannelNotConnectedException - The channel must be connected to receive messages.
ChannelClosedException - The channel is closed and therefore cannot be used any longer. A new channel has to be created first.

getState

public abstract boolean getState(Address target,
                                 java.lang.String state_id,
                                 long timeout)
                          throws ChannelNotConnectedException,
                                 ChannelClosedException
Fetches a partial state identified by state_id.

Parameters:
target -
state_id -
timeout -
Returns:
Throws:
ChannelNotConnectedException
ChannelClosedException

getAllStates

public abstract boolean getAllStates(java.util.Vector targets,
                                     long timeout)
                              throws ChannelNotConnectedException,
                                     ChannelClosedException
Deprecated. Not really needed - we always want to get the state from a single member

Retrieve all states of the group members. Will contact all group members to get the states. When the method returns true, a SetStateEvent will have been added to the channel's queue, causing Receive to return the states in one of the next invocations. If false, no states will be retrieved by Receive.

Parameters:
targets - A list of members which are contacted for states. If the list is null, all the current members of the group will be contacted.
timeout - Milliseconds to wait for the response (0 = wait indefinitely).
Returns:
boolean True if the state was retrieved successfully, otherwise false.
Throws:
ChannelNotConnectedException - The channel must be connected to receive messages.
ChannelClosedException - The channel is closed and therefore cannot be used any longer. A new channel has to be created first.

returnState

public abstract void returnState(byte[] state)
Called by the application is response to receiving a getState() object when calling receive().

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

returnState

public abstract void returnState(byte[] state,
                                 java.lang.String state_id)
Returns a given substate (state_id of null means return entire state)


getInfo

public abstract java.util.Map<java.lang.String,java.lang.Object> getInfo()

setInfo

public abstract void setInfo(java.lang.String key,
                             java.lang.Object value)

option2String

public static java.lang.String option2String(int option)

notifyChannelConnected

protected void notifyChannelConnected(Channel c)

notifyChannelDisconnected

protected void notifyChannelDisconnected(Channel c)

notifyChannelClosed

protected void notifyChannelClosed(Channel c)


Copyright © 1998-2009 Bela Ban / Red Hat. All Rights Reserved.