JavaGroups
Class EnsChannel

java.lang.Object
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  +--JavaGroups.Channel
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        +--JavaGroups.EnsChannel

public class EnsChannel

extends Channel

implements Hot_Callbacks

EnsChannel is an implementation of Channel based on Ensemble. It maps a process group to a channel. Requirements are the presence of an executable called outboard (which is Ensemble) and gossip running.

Fields inherited from class JavaGroups.Channel

BLOCK, GET_STATE_EVENTS, LOCAL, SUSPECT, VIEW

Constructor Summary

EnsChannel()

EnsChannel(java.lang.Object props)
Creates a new EnsChannel, which spawns an outboard process and connects to it.

EnsChannel(java.lang.Object props, java.lang.String transport_props, int outboard_port)
Creates a new EnsChannel.

Method Summary

void	AcceptedView(Hot_GroupContext gctx, java.lang.Object env, Hot_ViewState viewState) Called to update you with the new view
void	Block(Hot_GroupContext gctx, java.lang.Object env) Called to let you know Ensemble is blocking
void	BlockOk() Called to acknowledge a Block (callback in MembershipListener or BlockEvent received from call to Receive).
void	Close() Destroys the channel and its associated resources (e.g.
void	Connect(java.lang.Object address) Connects the channel to a group.
void	Disconnect() Disconnects the channel from the current group (if connected), leaving the group.
void	Exit(Hot_GroupContext gctx, java.lang.Object env) Called upon an Exit
void	finalize()
boolean	GetAllStates(java.util.Vector targets, long timeout) Retrieve all states of the group members.
java.lang.Object	GetGroupAddress() Returns the group address of the group of which the channel is a member.
java.lang.Object	GetLocalAddress() Returns the channel's own address.
java.lang.Object	GetOpt(int option) Gets an option.
boolean	GetState(java.lang.Object target, long timeout) Retrieve the state of the group.
View	GetView() Gets the current view.
void	Heartbeat(Hot_GroupContext gctx, java.lang.Object env, int rate) Called to issue you a heartbeat
java.lang.Object	Peek(long timeout) Returns the next message, view, block, suspect or other event without removing it from the queue.
java.lang.Object	Receive(long timeout) Receives a message, a view change or a block event.
void	ReceiveCast(Hot_GroupContext gctx, java.lang.Object env, Hot_Endpoint origin, Hot_Message msg) Called when Ensemble receives a Cast from your group
void	ReceiveSend(Hot_GroupContext gctx, java.lang.Object env, Hot_Endpoint origin, Hot_Message msg) Called when Ensemble receives a point-to-point message for you
void	ReturnState(java.lang.Object state) Called by the application is response to receiving a GetState object when calling Receive.
void	Send(Message msg) Sends a message to a destination.
void	SetOpt(int option, java.lang.Object value) Sets an option.

Methods inherited from class JavaGroups.Channel

Down, SetChannelListener, SetUpHandler

Methods inherited from class java.lang.Object

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

Constructor Detail

EnsChannel

public EnsChannel()
           throws ChannelException

EnsChannel

public EnsChannel(java.lang.Object props)
           throws ChannelException

Creates a new EnsChannel, which spawns an outboard process and connects to it.

Parameters:

name - Channel name. All channels with the same name form a group.

properties - Ensemble properties (cf. Ensemble reference manual). A value of null uses the default properties.

EnsChannel

public EnsChannel(java.lang.Object props,
                  java.lang.String transport_props,
                  int outboard_port)
           throws ChannelException

Creates a new EnsChannel. Instead of spawning a new outboard process, it connects to an already running outboard process (on the same machine) using outboard_port. This allows multiple EnsChannels to share a copy of outboard. If the port is 0, outboard will be spawned. Parameter transport_props defines the type of transport to be used (UDP, ATM, IP MCAST etc).

Parameters:

properties - Ensemble properties (cf. Ensemble reference manual). A value of null uses the default properties.

transport_props - Transport parameters. Null means use default (UDP). Example: "UDP:DEERING" uses IP multicast (gossip is not needed in this case).

outboard_port - Port on which the local outboard process is listening. The outboard process has to be started before. Value of 0 means spawn outboard nevertheless.

Method Detail

Connect

public void Connect(java.lang.Object address)
             throws ChannelClosed

Description copied from class: Channel

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 group address form a group, that means all messages sent to the group will be received by all channels connected to the same group address.

The group address is opaque, and can only be interpreted by a channel implementation, i.e. the implementation decides what to do with the object.

Overrides:

Connect in class Channel

Tags copied from class: Channel

Throws:

ChannelClosed - The channel is closed and therefore cannot be used any longer. A new channel has to be created first.

See Also:

Channel.Disconnect

Disconnect

public void Disconnect()

Description copied from class: Channel

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.

Overrides:

Disconnect in class Channel

Tags copied from class: Channel

See Also:

Channel.Connect

Close

public void Close()

Description copied from class: Channel

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, Disconnect will be called first.

Overrides:

Close in class Channel

finalize

public void finalize()

Send

public void Send(Message msg)
          throws ChannelNotConnected,
                 ChannelClosed

Description copied from class: Channel

Sends a message to a destination. The message contains

1. a destination address (Object). 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.

Overrides:

Send in class Channel

Tags copied from class: Channel

Parameters:

msg - The message to be sent. Destination and buffer should be set. A null destination means to send to all group members.

Throws:

ChannelNotConnected - The channel must be connected to send messages.

ChannelClosed - The channel is closed and therefore cannot be used any longer. A new channel has to be created first.

Receive

public java.lang.Object Receive(long timeout)
                         throws ChannelNotConnected,
                                ChannelClosed,
                                Timeout

Description copied from class: Channel

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 an impending view change.
5. SuspectEvent. A notification of a suspected member.
6. GetStateEvent. The current state of the application should be returned using ReturnState.
7. SetStateEvent. The state of a single/all members as requested previously by having called Channel.GetState(s).

The instanceof operator can be used to discriminate between different types returned.

Overrides:

Receive in class Channel

Tags copied from class: Channel

Parameters:

timeout - Value in milliseconds. Value <= 0 means wait forever

Returns:

A Message, View, BlockEvent,SuspectEvent, GetStateEvent object or SetStateEvent, 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.

Timeout - Thrown when a timeout has occurred.

Peek

public java.lang.Object Peek(long timeout)
                      throws ChannelNotConnected,
                             ChannelClosed,
                             Timeout

Description copied from class: Channel

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

Overrides:

Peek in class Channel

Tags copied from class: 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.

Timeout - Thrown when a timeout has occurred.

See Also:

Receive

GetView

public View GetView()

Description copied from class: Channel

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.

Overrides:

GetView in class Channel

Tags copied from class: Channel

Returns:

The current view.

GetLocalAddress

public java.lang.Object GetLocalAddress()

Description copied from class: Channel

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.

Overrides:

GetLocalAddress in class Channel

Tags copied from class: Channel

Returns:

The channel's address. Generated by the underlying transport, and opaque. Addresses can be used as destination in the Send operation.

GetGroupAddress

public java.lang.Object GetGroupAddress()

Description copied from class: Channel

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.

Overrides:

GetGroupAddress in class Channel

Tags copied from class: Channel

Returns:

The group address

SetOpt

public void SetOpt(int option,
                   java.lang.Object value)

Description copied from class: Channel

Sets an option. The following options are currently recognized:

1. BLOCK (0). Turn the reception of BLOCK events on/off (value is Boolean). Default is off. If set to on, receiving VIEW events will be set to on, too.
2. VIEW (1). Turn the reception of VIEW events on/off (value is Boolean). Default is on.
3. SUSPECT (2). Turn the reception of SUSPECT events on/off (value is Boolean). Default is on.
4. LOCAL (3). Receive its own broadcast messages to the group (value is Boolean). Default is on.
5. GET_STATE_EVENTS (4). Turn the reception of GetState events on/off (value is Boolean). Default is off, which means that no other members can ask this member for its state (null will be returned).

This method can be called on an unconnected channel. Calling this method on a closed channel has no effect.

Overrides:

SetOpt in class Channel

GetOpt

public java.lang.Object GetOpt(int option)

Description copied from class: Channel

Gets an option. This method can be called on an unconnected channel. Calling this method on a closed channel returns null.

Overrides:

GetOpt in class Channel

Tags copied from class: Channel

Parameters:

option - The option to be returned.

Returns:

The object associated with an option.

BlockOk

public void BlockOk()

Description copied from class: Channel

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(java.lang.Object target,
                        long timeout)

Description copied from class: Channel

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.

Overrides:

GetState in class Channel

Tags copied from class: Channel

Parameters:

target - The address of the member from which the state is to be retrieved. If it is null, the oldest member is contacted.

timeout - Milliseconds to wait for the response (0 = wait indefinitely).

Returns:

boolean True if the state was retrieved successfully, otherwise false.

GetAllStates

public boolean GetAllStates(java.util.Vector targets,
                            long timeout)

Description copied from class: Channel

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.

Overrides:

GetAllStates in class Channel

Tags copied from class: Channel

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.

ReturnState

public void ReturnState(java.lang.Object state)

Description copied from class: Channel

Called by the application is response to receiving a GetState object when calling Receive.

Overrides:

ReturnState in class Channel

Tags copied from class: Channel

Parameters:

state - The state of the application as a Serializable or Externaizable (to send over the network).

ReceiveCast

public void ReceiveCast(Hot_GroupContext gctx,
                        java.lang.Object env,
                        Hot_Endpoint origin,
                        Hot_Message msg)

Description copied from interface: Hot_Callbacks

Called when Ensemble receives a Cast from your group

Specified by:

ReceiveCast in interface Hot_Callbacks

ReceiveSend

public void ReceiveSend(Hot_GroupContext gctx,
                        java.lang.Object env,
                        Hot_Endpoint origin,
                        Hot_Message msg)

Description copied from interface: Hot_Callbacks

Called when Ensemble receives a point-to-point message for you

Specified by:

ReceiveSend in interface Hot_Callbacks

AcceptedView

public void AcceptedView(Hot_GroupContext gctx,
                         java.lang.Object env,
                         Hot_ViewState viewState)

Description copied from interface: Hot_Callbacks

Called to update you with the new view

Specified by:

AcceptedView in interface Hot_Callbacks

Heartbeat

public void Heartbeat(Hot_GroupContext gctx,
                      java.lang.Object env,
                      int rate)

Description copied from interface: Hot_Callbacks

Called to issue you a heartbeat

Specified by:

Heartbeat in interface Hot_Callbacks

Block

public void Block(Hot_GroupContext gctx,
                  java.lang.Object env)

Description copied from interface: Hot_Callbacks

Called to let you know Ensemble is blocking

Specified by:

Block in interface Hot_Callbacks

Exit

public void Exit(Hot_GroupContext gctx,
                 java.lang.Object env)

Description copied from interface: Hot_Callbacks

Called upon an Exit

Specified by:

Exit in interface Hot_Callbacks