org.jgroups.protocols.pbcast

Class FLUSH

java.lang.Object

org.jgroups.stack.Protocol

org.jgroups.protocols.pbcast.FLUSH

public class FLUSH
extends Protocol

Flush, as it name implies, forces group members to flush their pending messages while blocking them to send any additional messages. The process of flushing acquiesces the group so that state transfer or a join can be done. It is also called stop-the-world model as nobody will be able to send messages while a flush is in process.

Flush is needed for:

(1) State transfer. When a member requests state transfer, the coordinator tells everyone to stop sending messages and waits for everyone's ack. Then it asks the application for its state and ships it back to the requester. After the requester has received and set the state successfully, the coordinator tells everyone to resume sending messages.

(2) View changes (e.g.a join). Before installing a new view V2, flushing would ensure that all messages *sent* in the current view V1 are indeed *delivered* in V1, rather than in V2 (in all non-faulty members). This is essentially Virtual Synchrony.

Since:

2.4

Author:

Vladimir Blagojevic

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	FLUSH.FlushHeader

Field Summary

Fields

Modifier and Type	Field and Description
protected boolean	bypass
protected static short	DIGEST_PRESENT
protected static short	PARTICIPANTS_PRESENT

Fields inherited from class org.jgroups.stack.Protocol

after_creation_hook, down_prot, ergonomics, id, log, name, stack, stats, up_prot

Constructor Summary

Constructors

Constructor and Description
FLUSH()

Method Summary

Modifier and Type	Method and Description
java.lang.Object	down(Event evt) An event is to be sent down the stack.
double	getAverageFlushDuration()
int	getNumberOfFlushes()
long	getRetryTimeout()
long	getStartFlushTimeout()
long	getTotalTimeInFlush()
protected static Buffer	marshal(java.util.Collection<? extends Address> participants, Digest digest)
protected static Digest	maxSeqnos(View view, java.util.List<Digest> digests) Returns a digest which contains, for all members of view, the highest delivered and received seqno of all digests
java.util.List<java.lang.Integer>	providedDownServices() List of events that are provided to layers below (they will be handled when sent down below)
protected Tuple<java.util.Collection<? extends Address>,Digest>	readParticipantsAndDigest(byte[] buffer, int offset, int length)
protected static boolean	same(java.util.List<Digest> digests)
boolean	setBypass(boolean flag)
void	setRetryTimeout(long retry_timeout)
void	setStartFlushTimeout(long start_flush_timeout)
void	start() This method is called on a Channel.connect(String).
void	startFlush()
void	stop() This method is called on a Channel.disconnect().
void	stopFlush()
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 org.jgroups.stack.Protocol

accept, afterCreationHook, destroy, dumpStats, enableStats, getConfigurableObjects, getDownProtocol, getDownServices, getId, getIdsAbove, getLevel, getLog, getName, getProtocolStack, getSocketFactory, getThreadFactory, getTransport, getUpProtocol, getUpServices, getValue, init, isErgonomics, level, parse, printStats, providedUpServices, requiredDownServices, requiredUpServices, resetStatistics, resetStats, setDownProtocol, setErgonomics, setId, setLevel, setProtocolStack, setSocketFactory, setUpProtocol, setValue, setValues, statsEnabled

Methods inherited from class java.lang.Object

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

Field Detail

DIGEST_PRESENT

protected static final short DIGEST_PRESENT

See Also:

Constant Field Values

PARTICIPANTS_PRESENT

protected static final short PARTICIPANTS_PRESENT

See Also:

Constant Field Values

bypass

protected boolean bypass

Constructor Detail

FLUSH

public FLUSH()

Method Detail

getStartFlushTimeout

public long getStartFlushTimeout()

setStartFlushTimeout

public void setStartFlushTimeout(long start_flush_timeout)

getRetryTimeout

public long getRetryTimeout()

setRetryTimeout

public void setRetryTimeout(long retry_timeout)

start

public void start()
           throws java.lang.Exception

Description copied from class: Protocol

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.

Overrides:

start in class Protocol

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()

Description copied from class: Protocol

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

Overrides:

stop in class Protocol

getAverageFlushDuration

public double getAverageFlushDuration()

getTotalTimeInFlush

public long getTotalTimeInFlush()

getNumberOfFlushes

public int getNumberOfFlushes()

setBypass

public boolean setBypass(boolean flag)

startFlush

public void startFlush()

stopFlush

public void stopFlush()

down

public java.lang.Object down(Event evt)

Description copied from class: Protocol

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().

Overrides:

down in class Protocol

up

public java.lang.Object up(Event evt)

Description copied from class: Protocol

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().

Overrides:

up in class Protocol

up

public void up(MessageBatch batch)

Description copied from class: Protocol

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 Protocol.accept(org.jgroups.Message)), and - if true - calls Protocol.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.

Overrides:

up in class Protocol

Parameters:

batch - The message batch

providedDownServices

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

Description copied from class: Protocol

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

Overrides:

providedDownServices in class Protocol

same

protected static boolean same(java.util.List<Digest> digests)

maxSeqnos

protected static Digest maxSeqnos(View view,
                                  java.util.List<Digest> digests)

Returns a digest which contains, for all members of view, the highest delivered and received seqno of all digests

marshal

protected static Buffer marshal(java.util.Collection<? extends Address> participants,
                                Digest digest)

readParticipantsAndDigest

protected Tuple<java.util.Collection<? extends Address>,Digest> readParticipantsAndDigest(byte[] buffer,
                                                                                          int offset,
                                                                                          int length)