org.jgroups.stack

Class Protocol

Known Direct Subclasses:
AUTOCONF, BSH, CAUSAL, COMPRESS, DELAY, DISCARD, DUMMY, ENCRYPT1_4, EXAMPLE, FC, FD, FD, FD_PID, FD_PROB, FD_SIMPLE, FD_SOCK, FLOWCONTROL, FRAG, FRAG2, GMS, HDRS, JMS, LOOPBACK, LOSS, MessageProtocol, MERGE, MERGE2, MERGEFAST, NAKACK, NAKACK, PARTITIONER, PBCAST, PERF, PERF_TP, PIGGYBACK, PING, ProtocolStack, PRINTMETHODS, PRINTOBJS, QUEUE, SHUFFLE, SIZE, SMACK, STABLE, STATE_TRANSFER, STATE_TRANSFER, TCP, TCPGOSSIP, TCPPING, TOTAL, TOTAL_OLD, TRACE, TUNNEL, UDP, UDP1_4, UNICAST, VERIFY_SUSPECT, VIEW_ENFORCER, WANPING, WANPIPE

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.

Each layer has 2 FIFO queues, one for up Events and one for down Events. When an Event is received by a layer (calling the internal upcall ReceiveUpEvent), it is placed in the up-queue where it will be retrieved by the up-handler thread which will invoke method Up of the layer. The same applies for Events traveling down the stack. Handling of the up-handler and down-handler threads and the 2 FIFO queues is donw by the Protocol class, subclasses will almost never have to override this behavior.

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 !

Field Summary

protected org.jgroups.stack.DownHandler
down_handler
protected Protocol
down_prot
protected Queue
down_queue
protected boolean
down_thread
protected int
down_thread_prio
protected Log
log
protected ProtocolObserver
observer
protected Properties
props
protected ProtocolStack
stack
protected org.jgroups.stack.UpHandler
up_handler
protected Protocol
up_prot
protected Queue
up_queue
protected boolean
up_thread
protected int
up_thread_prio

Method Summary

void
destroy()
This method is called on a Channel.close().
void
down(Event evt)
An event is to be sent down the stack.
Protocol
getDownProtocol()
Queue
getDownQueue()
abstract String
getName()
Properties
getProperties()
Protocol
getUpProtocol()
Queue
getUpQueue()
protected boolean
handleSpecialDownEvent(Event evt)
These are special internal events that should not be handled by protocols
void
init()
Called after instance has been created (null constructor) and before protocol is started.
void
passDown(Event evt)
Causes the event to be forwarded to the next layer down in the hierarchy.Typically called by the implementation of Down (when done).
void
passUp(Event evt)
Causes the event to be forwarded to the next layer up in the hierarchy.
Vector
providedDownServices()
List of events that are provided to layers below (they will be handled when sent down from below).
Vector
providedUpServices()
List of events that are provided to layers above (they will be handled when sent down from above).
protected void
receiveDownEvent(Event evt)
Internal method, should not be called by clients.
protected void
receiveUpEvent(Event evt)
Internal method, should not be called by clients.
Vector
requiredDownServices()
List of events that are required to be answered by some layer below.
Vector
requiredUpServices()
List of events that are required to be answered by some layer above.
void
setDownProtocol(Protocol down_prot)
void
setObserver(ProtocolObserver observer)
boolean
setProperties(Properties props)
Configures the protocol initially.
boolean
setPropertiesInternal(Properties props)
Called by Configurator.
void
setProtocolStack(ProtocolStack stack)
void
setUpProtocol(Protocol up_prot)
void
start()
This method is called on a Channel.connect(String).
void
startDownHandler()
Used internally.
void
startUpHandler()
Used internally.
void
stop()
This method is called on a Channel.disconnect().
void
stopInternal()
Used internally.
void
up(Event evt)
An event was received from the layer below.

Field Details

down_handler

protected org.jgroups.stack.DownHandler down_handler

down_prot

protected Protocol down_prot

down_queue

protected Queue down_queue

down_thread

protected boolean down_thread

down_thread_prio

protected int down_thread_prio

log

protected Log log

observer

protected ProtocolObserver observer

props

protected Properties props

stack

protected ProtocolStack stack

up_handler

protected org.jgroups.stack.UpHandler up_handler

up_prot

protected Protocol up_prot

up_queue

protected Queue up_queue

up_thread

protected boolean up_thread

up_thread_prio

protected int up_thread_prio

Method Details

destroy

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

down

public void 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 passDown(). 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 passUp().

getDownProtocol

public Protocol getDownProtocol()

getDownQueue

public Queue getDownQueue()

getName

public abstract String getName()

getProperties

public Properties getProperties()

getUpProtocol

public Protocol getUpProtocol()

getUpQueue

public Queue getUpQueue()

handleSpecialDownEvent

protected boolean handleSpecialDownEvent(Event evt)
These are special internal events that should not be handled by protocols
Returns:
boolean True: the event should be passed further down the stack. False: the event should be discarded (not passed down the stack)

init

public void init()
            throws 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.

passDown

public void passDown(Event evt)
Causes the event to be forwarded to the next layer down in the hierarchy.Typically called by the implementation of Down (when done).

passUp

public void passUp(Event evt)
Causes the event to be forwarded to the next layer up in the hierarchy. Typically called by the implementation of Up (when done).

providedDownServices

public Vector providedDownServices()
List of events that are provided to layers below (they will be handled when sent down from below).
Returns:
Vector (of Integers)

providedUpServices

public Vector providedUpServices()
List of events that are provided to layers above (they will be handled when sent down from above).
Returns:
Vector (of Integers)

receiveDownEvent

protected void receiveDownEvent(Event evt)
Internal method, should not be called by clients. Used by ProtocolStack. I would have used the 'friends' modifier, but this is available only in C++ ... If the down_handler thread is not available (down_thread == false), then directly call the down() method: we will run on the caller's thread (e.g. the protocol layer above us).

receiveUpEvent

protected void receiveUpEvent(Event evt)
Internal method, should not be called by clients. Used by ProtocolStack. I would have used the 'friends' modifier, but this is available only in C++ ... If the up_handler thread is not available (down_thread == false), then directly call the up() method: we will run on the caller's thread (e.g. the protocol layer below us).

requiredDownServices

public Vector requiredDownServices()
List of events that are required to be answered by some layer below.
Returns:
Vector (of Integers)

requiredUpServices

public Vector requiredUpServices()
List of events that are required to be answered by some layer above.
Returns:
Vector (of Integers)

setDownProtocol

public void setDownProtocol(Protocol down_prot)

setObserver

public void setObserver(ProtocolObserver observer)

setProperties

public boolean setProperties(Properties props)
Configures the protocol initially. A configuration string consists of name=value items, separated by a ';' (semicolon), e.g.:
 "loopback=false;unicast_inport=4444"
 

setPropertiesInternal

public boolean setPropertiesInternal(Properties props)
Called by Configurator. Removes 2 properties which are used by the Protocol directly and then calls setProperties(), which might invoke the setProperties() method of the actual protocol instance.

setProtocolStack

public void setProtocolStack(ProtocolStack stack)

setUpProtocol

public void setUpProtocol(Protocol up_prot)

start

public void start()
            throws 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.

startDownHandler

public void startDownHandler()
Used internally. If overridden, call this method first. Only creates the down_handler thread if down_thread is true

startUpHandler

public void startUpHandler()
Used internally. If overridden, call this method first. Only creates the up_handler thread if down_thread is true

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

stopInternal

public void stopInternal()
Used internally. If overridden, call parent's method first

up

public void 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 passDown() or c) the event (or another event) is sent up the stack using passUp().

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