org.jgroups.stack

Class Protocol

java.lang.Object

org.jgroups.stack.Protocol

Direct Known Subclasses:

ABP, AUTH, BARRIER, COMPRESS, COUNTER, DAISYCHAIN, DELAY, DELIVERY_TIME, DISCARD, DISCARD_PAYLOAD, Discovery, DUPL, ENCRYPT, EncryptBase, EXAMPLE, Executing, FC, FD, FD_ALL, FD_ALL2, FD_HOST, FD_SOCK, FlowControl, FLUSH, FORK, ForkProtocol, FORWARD_TO_COORD, FRAG, FRAG2, GMS, HDRS, KeyExchange, Locking, MAKE_BATCH, MERGE2, MERGE3, NAKACK, NAKACK2, PDC, PERF, PRIO, ProtocolStack, RATE_LIMITER, RELAY, RELAY2, RSVP, SASL, SCOPE, SEQUENCER, SEQUENCER2, SHUFFLE, SIZE, STABLE, STATE_TRANSFER, STATS, STOMP, StreamingStateTransfer, SUPERVISOR, TOA, TP, TP.ProtocolAdapter, TRACE, UNICAST, UNICAST2, UNICAST3, VERIFY_SUSPECT

public abstract class Protocol
extends java.lang.Object

The Protocol class provides a set of common services for protocol layers. Each layer has to be a subclass of Protocol and override a number of methods (typically just up(), down() and getName(). Layers are stacked in a certain order to form a protocol stack. Events are passed from lower layers to upper ones and vice versa. E.g. a Message received by the UDP layer at the bottom will be passed to its higher layer as an Event. That layer will in turn pass the Event to its layer and so on, until a layer handles the Message and sends a response or discards it, the former resulting in another Event being passed down the stack.

The important thing to bear in mind is that Events have to passed on between layers in FIFO order which is guaranteed by the Protocol implementation and must be guranteed by subclasses implementing their on Event queuing.

Note that each class implementing interface Protocol MUST provide an empty, public constructor !

Author:

Bela Ban

Field Summary

Fields

Modifier and Type	Field and Description
protected java.lang.String	after_creation_hook
protected Protocol	down_prot
protected boolean	ergonomics
protected short	id
protected Log	log
protected java.lang.String	name The name of the protocol.
protected ProtocolStack	stack
protected boolean	stats
protected Protocol	up_prot

Constructor Summary

Constructors

Constructor and Description
Protocol()

Method Summary

Modifier and Type	Method and Description
protected boolean	accept(Message msg) Called by the default implementation of up(org.jgroups.util.MessageBatch) for each message to determine if the message should be removed from the message batch (and handled by the current protocol) or not.
java.lang.String	afterCreationHook()
void	destroy() This method is called on a Channel.close().
java.lang.Object	down(Event evt) An event is to be sent down the stack.
java.util.Map<java.lang.String,java.lang.Object>	dumpStats()
void	enableStats(boolean flag)
protected java.util.List<java.lang.Object>	getConfigurableObjects() After configuring the protocol itself from the properties defined in the XML config, a protocol might have additional objects which need to be configured.
Protocol	getDownProtocol()
java.util.List<java.lang.Integer>	getDownServices() Returns all services provided by protocols below the current protocol
short	getId()
short[]	getIdsAbove() Returns the protocol IDs of all protocols above this one (excluding the current protocol)
java.lang.String	getLevel()
Log	getLog()
java.lang.String	getName()
ProtocolStack	getProtocolStack()
SocketFactory	getSocketFactory() Returns the SocketFactory associated with this protocol, if overridden in a subclass, or passes the call down
ThreadFactory	getThreadFactory() Supposed to be overwritten by subclasses.
protected TP	getTransport()
Protocol	getUpProtocol()
java.util.List<java.lang.Integer>	getUpServices() Returns all services provided by the protocols above the current protocol
java.lang.Object	getValue(java.lang.String name)
void	init() Called after instance has been created (null constructor) and before protocol is started.
boolean	isErgonomics()
Protocol	level(java.lang.String level)
void	parse(org.w3c.dom.Node node) Called by the XML parser when subelements are found in the configuration of a protocol.
java.lang.String	printStats()
java.util.List<java.lang.Integer>	providedDownServices() List of events that are provided to layers below (they will be handled when sent down below)
java.util.List<java.lang.Integer>	providedUpServices() List of events that are provided to layers above (they will be handled when sent down from above)
java.util.List<java.lang.Integer>	requiredDownServices() List of events that are required to be answered by some layer below
java.util.List<java.lang.Integer>	requiredUpServices() List of events that are required to be answered by some layer above
void	resetStatistics()
void	resetStats()
Protocol	setDownProtocol(Protocol prot)
Protocol	setErgonomics(boolean ergonomics)
Protocol	setId(short id)
Protocol	setLevel(java.lang.String level) Sets the level of a logger.
Protocol	setProtocolStack(ProtocolStack s)
void	setSocketFactory(SocketFactory factory) Sets a SocketFactory.
Protocol	setUpProtocol(Protocol prot)
Protocol	setValue(java.lang.String name, java.lang.Object value)
Protocol	setValues(java.util.Map<java.lang.String,java.lang.Object> values)
void	start() This method is called on a Channel.connect(String).
boolean	statsEnabled()
void	stop() This method is called on a Channel.disconnect().
java.lang.Object	up(Event evt) An event was received from the layer below.
void	up(MessageBatch batch) Sends up a multiple messages in a MessageBatch.

Methods inherited from class java.lang.Object

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

Field Detail

up_prot

protected Protocol up_prot

down_prot

protected Protocol down_prot

stack

protected ProtocolStack stack

stats

protected boolean stats

ergonomics

protected boolean ergonomics

name

protected java.lang.String name

The name of the protocol. Is by default set to the protocol's classname. This property should rarely need to be set, e.g. only in cases where we want to create more than 1 protocol of the same class in the same stack

after_creation_hook

protected java.lang.String after_creation_hook

id

protected short id

log

protected final Log log

Constructor Detail

Protocol

public Protocol()

Method Detail

setLevel

public Protocol setLevel(java.lang.String level)

Sets the level of a logger. This method is used to dynamically change the logging level of a running system, e.g. via JMX. The appender of a level needs to exist.

Parameters:

level - The new level. Valid values are "fatal", "error", "warn", "info", "debug", "trace" (capitalization not relevant)

getLevel

public java.lang.String getLevel()

level

public Protocol level(java.lang.String level)

getLog

public Log getLog()

isErgonomics

public boolean isErgonomics()

setErgonomics

public Protocol setErgonomics(boolean ergonomics)

getProtocolStack

public ProtocolStack getProtocolStack()

statsEnabled

public boolean statsEnabled()

enableStats

public void enableStats(boolean flag)

getName

public java.lang.String getName()

getId

public short getId()

setId

public Protocol setId(short id)

getUpProtocol

public Protocol getUpProtocol()

getDownProtocol

public Protocol getDownProtocol()

setUpProtocol

public Protocol setUpProtocol(Protocol prot)

setDownProtocol

public Protocol setDownProtocol(Protocol prot)

setProtocolStack

public Protocol setProtocolStack(ProtocolStack s)

afterCreationHook

public java.lang.String afterCreationHook()

getValue

public java.lang.Object getValue(java.lang.String name)

setValues

public Protocol setValues(java.util.Map<java.lang.String,java.lang.Object> values)

setValue

public Protocol setValue(java.lang.String name,
                         java.lang.Object value)

getConfigurableObjects

protected java.util.List<java.lang.Object> getConfigurableObjects()

After configuring the protocol itself from the properties defined in the XML config, a protocol might have additional objects which need to be configured. This callback allows a protocol developer to configure those other objects. This call is guaranteed to be invoked after the protocol itself has been configured. See AUTH for an example.

Returns:

parse

public void parse(org.w3c.dom.Node node)
           throws java.lang.Exception

Called by the XML parser when subelements are found in the configuration of a protocol. This allows a protocol to define protocol-specific information and to parse it

Throws:

java.lang.Exception

getIdsAbove

public short[] getIdsAbove()

Returns the protocol IDs of all protocols above this one (excluding the current protocol)

getTransport

protected TP getTransport()

getThreadFactory

public ThreadFactory getThreadFactory()

Supposed to be overwritten by subclasses. Usually the transport returns a valid non-null thread factory, but thread factories can also be created by individual protocols

Returns:

getSocketFactory

public SocketFactory getSocketFactory()

Returns the SocketFactory associated with this protocol, if overridden in a subclass, or passes the call down

Returns:

SocketFactory

setSocketFactory

public void setSocketFactory(SocketFactory factory)

Sets a SocketFactory. Socket factories are typically provided by the transport (TP) or TP.ProtocolAdapter

Parameters:

factory -

resetStatistics

public void resetStatistics()

resetStats

public void resetStats()

printStats

public java.lang.String printStats()

dumpStats

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

init

public void init()
          throws java.lang.Exception

Called after instance has been created (null constructor) and before protocol is started. Properties are already set. Other protocols are not yet connected and events cannot yet be sent.

Throws:

java.lang.Exception - Thrown if protocol cannot be initialized successfully. This will cause the ProtocolStack to fail, so the channel constructor will throw an exception

start

public void start()
           throws java.lang.Exception

This method is called on a Channel.connect(String). Starts work. Protocols are connected and queues are ready to receive events. Will be called from bottom to top. This call will replace the START and START_OK events.

Throws:

java.lang.Exception - Thrown if protocol cannot be started successfully. This will cause the ProtocolStack to fail, so Channel.connect(String) will throw an exception

stop

public void stop()

This method is called on a Channel.disconnect(). Stops work (e.g. by closing multicast socket). Will be called from top to bottom. This means that at the time of the method invocation the neighbor protocol below is still working. This method will replace the STOP, STOP_OK, CLEANUP and CLEANUP_OK events. The ProtocolStack guarantees that when this method is called all messages in the down queue will have been flushed

destroy

public void destroy()

This method is called on a Channel.close(). Does some cleanup; after the call the VM will terminate

requiredUpServices

public java.util.List<java.lang.Integer> requiredUpServices()

List of events that are required to be answered by some layer above

requiredDownServices

public java.util.List<java.lang.Integer> requiredDownServices()

List of events that are required to be answered by some layer below

providedUpServices

public java.util.List<java.lang.Integer> providedUpServices()

List of events that are provided to layers above (they will be handled when sent down from above)

providedDownServices

public java.util.List<java.lang.Integer> providedDownServices()

List of events that are provided to layers below (they will be handled when sent down below)

getDownServices

public final java.util.List<java.lang.Integer> getDownServices()

Returns all services provided by protocols below the current protocol

getUpServices

public final java.util.List<java.lang.Integer> getUpServices()

Returns all services provided by the protocols above the current protocol

up

public java.lang.Object up(Event evt)

An event was received from the layer below. Usually the current layer will want to examine the event type and - depending on its type - perform some computation (e.g. removing headers from a MSG event type, or updating the internal membership list when receiving a VIEW_CHANGE event). Finally the event is either a) discarded, or b) an event is sent down the stack using down_prot.down() or c) the event (or another event) is sent up the stack using up_prot.up().

accept

protected boolean accept(Message msg)

Called by the default implementation of up(org.jgroups.util.MessageBatch) for each message to determine if the message should be removed from the message batch (and handled by the current protocol) or not.

Parameters:

msg - The message. Guaranteed to be non-null

Returns:

True if the message should be handled by this protocol (will be removed from the batch), false if the message should remain in the batch and be passed up.

The default implementation tries to find a header matching the current protocol's ID and returns true if there is a match, or false otherwise

up

public void up(MessageBatch batch)

Sends up a multiple messages in a MessageBatch. The sender of the batch is always the same, and so is the destination (null == multicast messages). Messages in a batch can be OOB messages, regular messages, or mixed messages, although the transport itself will create initial MessageBatches that contain only either OOB or regular messages.

The default processing below sends messages up the stack individually, based on a matching criteria (calling accept(org.jgroups.Message)), and - if true - calls up(org.jgroups.Event) for that message and removes the message. If the batch is not empty, it is passed up, or else it is dropped.

Subclasses should check if there are any messages destined for them (e.g. using MessageBatch.getMatchingMessages(short,boolean)), then possibly remove and process them and finally pass the batch up to the next protocol. Protocols can also modify messages in place, e.g. ENCRYPT could decrypt all encrypted messages in the batch, not remove them, and pass the batch up when done.

Parameters:

batch - The message batch

down

public java.lang.Object down(Event evt)

An event is to be sent down the stack. The layer may want to examine its type and perform some action on it, depending on the event's type. If the event is a message MSG, then the layer may need to add a header to it (or do nothing at all) before sending it down the stack using down_prot.down(). In case of a GET_ADDRESS event (which tries to retrieve the stack's address from one of the bottom layers), the layer may need to send a new response event back up the stack using up_prot.up().