org.jgroups.fork

Class ForkChannel

java.lang.Object

org.jgroups.Channel

org.jgroups.JChannel

org.jgroups.fork.ForkChannel

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable, ChannelListener

public class ForkChannel
extends JChannel
implements ChannelListener

Implementation of a ForkChannel, which is a light-weight channel. Not all methods are supported, UnsupportedOperationExceptions will be thrown if an unsupported operation is called. See doc/design/FORK.txt for details

Since:

3.4

Author:

Bela Ban

Nested Class Summary

Nested classes/interfaces inherited from class org.jgroups.Channel

Channel.State

Field Summary

Fields

Modifier and Type	Field and Description
protected static java.lang.reflect.Field[]	copied_fields
protected java.lang.String	fork_channel_id
protected Channel	main_channel

Fields inherited from class org.jgroups.JChannel

address_generators, cluster_name, config, DEFAULT_PROTOCOL_STACK, flush_supported, local_addr, my_view, name, probe_handler, prot_stack, received_bytes, received_msgs, sent_bytes, sent_msgs, state_promise, state_transfer_supported, stats

Fields inherited from class org.jgroups.Channel

channel_listeners, discard_own_messages, log, receiver, socket_factory, state, up_handler

Constructor Summary

Constructors

Constructor and Description
ForkChannel(Channel main_channel, java.lang.String fork_stack_id, java.lang.String fork_channel_id, boolean create_fork_if_absent, int position, java.lang.Class<? extends Protocol> neighbor, Protocol... protocols) Creates a new fork-channel from a main-channel.
ForkChannel(Channel main_channel, java.lang.String fork_stack_id, java.lang.String fork_channel_id, Protocol... protocols) Creates a new fork-channel from a main-channel.

Method Summary

Modifier and Type	Method and Description
void	addAddressGenerator(AddressGenerator address_generator) Sets the new AddressGenerator.
void	channelClosed(Channel channel) Channel has been closed notification callback
void	channelConnected(Channel channel) Channel has been connected notification callback
void	channelDisconnected(Channel channel) Channel has been disconnected notification callback
void	close() Closes the fork-channel, essentially setting its state to CLOSED.
void	connect(java.lang.String cluster_name) Connects the fork-channel, which will be operational after this.
void	connect(java.lang.String cluster_name, Address target, long timeout) Connects this channel to a group and gets a state from a specified state provider.
protected void	copyFields() Copies state from main-channel to this fork-channel
void	disconnect() Removes the fork-channel from the fork-stack's hashmap and resets its state.
java.lang.Object	down(Event evt) Sends an event down the protocol stack.
protected static FORK	getFORK(Channel ch, int position, java.lang.Class<? extends Protocol> neighbor, boolean create_fork_if_absent) Creates a new FORK protocol, or returns the existing one, or throws an exception.
void	getState(Address target, long timeout) Retrieves the full state from the target member.
JChannel	name(java.lang.String name) Names a channel, same as Channel.setName(String)
protected void	nullFields()
void	send(Message msg) Sends a message.
protected void	setHeader(Message msg)
protected void	setLocalAddress(Address local_addr)
void	setName(java.lang.String name) Sets the logical name for the channel.
void	startFlush(boolean automatic_resume) Performs the flush of the cluster, ie.
void	startFlush(java.util.List<Address> flushParticipants, boolean automatic_resume) Performs the flush of the cluster but only for the specified flush participants.
void	stopFlush() Stops the current flush of the cluster.
void	stopFlush(java.util.List<Address> flushParticipants) Stops the current flush of the cluster for the specified flush participants.

Methods inherited from class org.jgroups.JChannel

_close, _connect, _preConnect, checkClosed, checkClosedOrNotConnected, connect, connect, dumpChannelStats, dumpStats, dumpStats, dumpStats, dumpTimerQueue, enableStats, flushSupported, generateAddress, getAddress, getAddressAsString, getAddressAsUUID, getAddressGenerator, getClusterName, getName, getName, getNumberOfTasksInTimer, getProperties, getProtocolStack, getReceivedBytes, getReceivedMessages, getSentBytes, getSentMessages, getState, getState, getTimer, getTimerThreads, getVersion, getView, getViewAsString, init, init, init, invokeCallback, printProtocolSpec, receiver, removeAddressGenerator, resetStats, send, send, send, setAddress, setAddressGenerator, setProtocolStack, startStack, statsEnabled, stopStack, toString, up, up

Methods inherited from class org.jgroups.Channel

addChannelListener, clearChannelListeners, getDiscardOwnMessages, getReceiver, getSocketFactory, getState, getUpHandler, isClosed, isConnected, isConnecting, isOpen, notifyChannelClosed, notifyChannelConnected, notifyChannelDisconnected, removeChannelListener, setDiscardOwnMessages, setReceiver, setSocketFactory, setUpHandler

Methods inherited from class java.lang.Object

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

Field Detail

main_channel

protected final Channel main_channel

fork_channel_id

protected final java.lang.String fork_channel_id

copied_fields

protected static final java.lang.reflect.Field[] copied_fields

Constructor Detail

ForkChannel

public ForkChannel(Channel main_channel,
                   java.lang.String fork_stack_id,
                   java.lang.String fork_channel_id,
                   boolean create_fork_if_absent,
                   int position,
                   java.lang.Class<? extends Protocol> neighbor,
                   Protocol... protocols)
            throws java.lang.Exception

Creates a new fork-channel from a main-channel. The channel is unconnected and connect(String) needs to be called to send and receive messages.

Parameters:

main_channel - The main-channel. The lifetime of the newly created channel will be less than or equal to the main-channel

fork_stack_id - The ID to associate the fork-stack with in FORK

fork_channel_id - The ID used to map fork-channel IDs to ForkChannels in the fork-channels protocol stack

create_fork_if_absent - If true, and FORK doesn't exist, a new FORK protocol will be created and inserted into the main-stack at the given position. If false, and FORK doesn't exist, an exception will be thrown

position - The position at which the newly created FORK will be inserted. ProtocolStack.ABOVE or ProtocolStack.BELOW are accepted. Ignored if create_fork_if_absent is false.

neighbor - The class of the neighbor protocol below or above which the newly created FORK protocol will be inserted. Ignored if create_fork_if_absent is false.

protocols - A list of protocols (from bottom to top !) to insert as the fork_stack in FORK under the given fork_stack_id. If the fork-stack with fork_stack_id already exists, an exception will be thrown. Can be null if no protocols should be added. This may be the case when an app only wants to use a ForkChannel to mux/demux messages, but doesn't need a different protocol stack.

Throws:

java.lang.Exception

ForkChannel

public ForkChannel(Channel main_channel,
                   java.lang.String fork_stack_id,
                   java.lang.String fork_channel_id,
                   Protocol... protocols)
            throws java.lang.Exception

Creates a new fork-channel from a main-channel. The channel is unconnected and connect(String) needs to be called to send and receive messages. If FORK is not found in the stack, an exception will be thrown.

Parameters:

main_channel - The main-channel. The lifetime of the newly created channel will be less than or equal to the main-channel

fork_stack_id - The ID to associate the fork-stack with in FORK

fork_channel_id - The ID used to map fork-channel IDs to ForkChannels in the fork-channels protocol stack

protocols - A list of protocols (from bottom to top !) to insert as the fork_stack in FORK under the given fork_stack_id. If the fork-stack with fork_stack_id already exists, an exception will be thrown. Can be null if no protocols should be added. This may be the case when an app only wants to use a ForkChannel to mux/demux messages, but doesn't need a different protocol stack.

Throws:

java.lang.Exception

Method Detail

setName

public void setName(java.lang.String name)

Description copied from class: Channel

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().

Overrides:

setName in class JChannel

name

public JChannel name(java.lang.String name)

Description copied from class: Channel

Names a channel, same as Channel.setName(String)

Overrides:

name in class JChannel

channelConnected

public void channelConnected(Channel channel)

Description copied from interface: ChannelListener

Channel has been connected notification callback

Specified by:

channelConnected in interface ChannelListener

Parameters:

channel - the channel that has been connected

channelDisconnected

public void channelDisconnected(Channel channel)

Description copied from interface: ChannelListener

Channel has been disconnected notification callback

Specified by:

channelDisconnected in interface ChannelListener

Parameters:

channel - the disconnected channel

channelClosed

public void channelClosed(Channel channel)

Description copied from interface: ChannelListener

Channel has been closed notification callback

Specified by:

channelClosed in interface ChannelListener

Parameters:

channel - the closed channel

connect

public void connect(java.lang.String cluster_name)
             throws java.lang.Exception

Connects the fork-channel, which will be operational after this. Note that the fork-channel will have the same state as the main-channel, ie. if the main-channel is disconnected, so will the fork-channel be, even if connect() was called. This connect() method essentially adds the fork-channel to the fork-stack's hashmap, ready to send/receive messages as soon as the main-channel has been connected.

This method does not affect the main-channel.

Overrides:

connect in class JChannel

Parameters:

cluster_name - Ignored, will be the same as the main-channel's cluster name

Throws:

java.lang.Exception

java.lang.IllegalStateException - The channel is closed

connect

public void connect(java.lang.String cluster_name,
                    Address target,
                    long timeout)
             throws java.lang.Exception

Description copied from class: Channel

Connects this channel to a group and gets a state from a specified state provider.

This method essentially invokes connect and getState methods successively. If FLUSH protocol is in channel's stack definition only one flush is executed for both connecting and fetching state rather than two flushes if we invoke connect and getState in succession. If the channel is closed an exception will be thrown.

Overrides:

connect in class JChannel

Parameters:

cluster_name - the cluster name to connect to. Cannot be null.

target - the state provider. If null state will be fetched from coordinator, unless this channel is coordinator.

timeout - the timeout for state transfer.

Throws:

java.lang.Exception - Connecting to the cluster or state transfer was not successful

java.lang.IllegalStateException - The channel is closed and therefore cannot be used

disconnect

public void disconnect()

Removes the fork-channel from the fork-stack's hashmap and resets its state. Does not affect the main-channel

Overrides:

disconnect in class JChannel

See Also:

Channel.connect(String)

close

public void close()

Closes the fork-channel, essentially setting its state to CLOSED. Note that - contrary to a regular channel - a closed fork-channel can be connected again: this means re-attaching the fork-channel to the main-channel

Specified by:

close in interface java.io.Closeable

Specified by:

close in interface java.lang.AutoCloseable

Overrides:

close in class JChannel

down

public java.lang.Object down(Event evt)

Description copied from class: JChannel

Sends an event down the protocol stack. Note that - contrary to JChannel.send(Message), if the event is a message, no checks are performed whether the channel is closed or disconnected.

Overrides:

down in class JChannel

Parameters:

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

Returns:

a response from a particular protocol layer targeted by Event parameter

send

public void send(Message msg)
          throws java.lang.Exception

Description copied from class: Channel

Sends a message. 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 as it will be assigned automatically
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, flags etc

Overrides:

send in class JChannel

Parameters:

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

Throws:

java.lang.IllegalStateException - thrown if the channel is disconnected or closed

java.lang.Exception

startFlush

public void startFlush(java.util.List<Address> flushParticipants,
                       boolean automatic_resume)
                throws java.lang.Exception

Description copied from class: Channel

Performs the flush of the cluster but only for the specified flush participants.

All pending messages are flushed out but only for the flush participants. The remaining members in the cluster are not included in the flush. The list of flush participants should be a proper subset of the current view.

If this flush is not automatically resumed it is an obligation of the application to invoke the matching Channel.stopFlush(List) method with the same list of members used in Channel.startFlush(List, boolean).

Overrides:

startFlush in class JChannel

automatic_resume - if true call Channel.stopFlush() after the flush

Throws:

java.lang.Exception

See Also:

Channel.startFlush(boolean), Util.startFlush(Channel, List, int, long, long)

startFlush

public void startFlush(boolean automatic_resume)
                throws java.lang.Exception

Description copied from class: Channel

Performs the flush of the cluster, ie. all pending application messages are flushed out of the cluster and all members ack their reception. After this call returns, no member will be allowed to send any messages until Channel.stopFlush() is called.

In the case of flush collisions (another member attempts flush at roughly the same time) start flush will fail by throwing an Exception. Applications can re-attempt flushing after certain back-off period.

JGroups provides a helper random sleep time backoff algorithm for flush using Util class.

Overrides:

startFlush in class JChannel

Parameters:

automatic_resume - if true call Channel.stopFlush() after the flush

Throws:

java.lang.Exception

See Also:

Util.startFlush(Channel, List, int, long, long)

stopFlush

public void stopFlush()

Description copied from class: Channel

Stops the current flush of the cluster. Cluster members are unblocked and allowed to send new and pending messages.

Overrides:

stopFlush in class JChannel

See Also:

Channel.startFlush(boolean), Channel.startFlush(List, boolean)

stopFlush

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

Description copied from class: Channel

Stops the current flush of the cluster for the specified flush participants. Flush participants are unblocked and allowed to send new and pending messages.

It is an obligation of the application to invoke the matching Channel.startFlush(List, boolean) method with the same list of members prior to invocation of this method.

Overrides:

stopFlush in class JChannel

Parameters:

flushParticipants - the flush participants

getState

public void getState(Address target,
                     long timeout)
              throws java.lang.Exception

Description copied from class: Channel

Retrieves the full state from the target member.

State transfer is initiated by invoking getState on this channel. The state provider in turn invokes MessageListener.getState(java.io.OutputStream) callback and sends a state to this node, the state receiver. After the state arrives to the state receiver MessageListener.setState(java.io.InputStream) callback is invoked to install the state.

Overrides:

getState in class JChannel

Parameters:

target - The state provider. If null the coordinator is used by default

timeout - The number of milliseconds to wait for the operation to complete successfully. 0 waits until the state has been received

Throws:

java.lang.IllegalStateException - The channel was closed or disconnected, or the flush (if present) failed

StateTransferException - raised if there was a problem during the state transfer

java.lang.Exception

See Also:

MessageListener.getState(java.io.OutputStream), MessageListener.setState(java.io.InputStream)

addAddressGenerator

public void addAddressGenerator(AddressGenerator address_generator)

Description copied from class: JChannel

Sets the new AddressGenerator. New addresses will be generated using the new generator. This should not be done while a channel is connected, but before connecting.

Overrides:

addAddressGenerator in class JChannel

setLocalAddress

protected void setLocalAddress(Address local_addr)

getFORK

protected static FORK getFORK(Channel ch,
                              int position,
                              java.lang.Class<? extends Protocol> neighbor,
                              boolean create_fork_if_absent)
                       throws java.lang.Exception

Creates a new FORK protocol, or returns the existing one, or throws an exception. Never returns null.

Throws:

java.lang.Exception

setHeader

protected void setHeader(Message msg)

copyFields

protected void copyFields()

Copies state from main-channel to this fork-channel

nullFields

protected void nullFields()