org.jgroups.protocols.pbcast

Class STABLE

java.lang.Object

org.jgroups.stack.Protocol

org.jgroups.protocols.pbcast.STABLE

public class STABLE
extends Protocol

Computes the broadcast messages that are stable; i.e., have been received by all members. Sends STABLE events up the stack when this is the case. This allows NAKACK to garbage collect messages that have been seen by all members.

Works as follows: periodically we mcast our highest seqnos (seen for each member) to the group. A stability vector, which maintains the highest seqno for each member and initially contains no data, is updated when such a message is received. The entry for a member P is computed set to min(entry[P], digest[P]). When messages from all members have been received, a stability message is mcast, which causes all members to send a STABLE event up the stack (triggering garbage collection in the NAKACK layer).

New: when max_bytes is exceeded (unless disabled by setting it to 0), a STABLE task will be started (unless it is already running). Design in docs/design/STABLE.txt

Author:

Bela Ban

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	STABLE.StableHeader

Field Summary

Fields

Modifier and Type	Field and Description
protected double	cap
protected long	max_bytes Total amount of bytes from incoming messages (default = 0 = disabled).
protected long	original_max_bytes
protected boolean	suspended When true, don't take part in garbage collection: neither send STABLE messages nor handle STABILITY messages

Fields inherited from class org.jgroups.stack.Protocol

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

Constructor Summary

Constructors

Constructor and Description
STABLE()

Method Summary

Methods

Modifier and Type	Method and Description
Object	down(Event evt) An event is to be sent down the stack.
void	gc()
long	getBytes()
long	getDesiredAverageGossip()
long	getMaxBytes()
int	getStabilityReceived()
int	getStabilitySent()
int	getStableReceived()
int	getStableSent()
boolean	getStableTaskRunning()
void	init() Called after instance has been created (null constructor) and before protocol is started.
List<Integer>	requiredDownServices() List of events that are required to be answered by some layer below.
void	resetStats()
void	runMessageGarbageCollection()
void	setDesiredAverageGossip(long gossip_interval)
void	setMaxBytes(long max_bytes)
void	start() This method is called on a Channel.connect(String).
void	stop() This method is called on a Channel.disconnect().
Object	up(Event evt) An event was received from the layer below.

Methods inherited from class org.jgroups.stack.Protocol

destroy, dumpStats, enableStats, getConfigurableObjects, getDownProtocol, getId, getLevel, getName, getProtocolStack, getSocketFactory, getThreadFactory, getTransport, getUpProtocol, getValue, isErgonomics, printStats, providedDownServices, providedUpServices, requiredUpServices, resetStatistics, 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

max_bytes

protected long max_bytes

Total amount of bytes from incoming messages (default = 0 = disabled). When exceeded, a STABLE message will be broadcast and num_bytes_received reset to 0 . If this is > 0, then ideally stability_delay should be set to a low number as well

original_max_bytes

protected long original_max_bytes

cap

protected double cap

suspended

protected volatile boolean suspended

When true, don't take part in garbage collection: neither send STABLE messages nor handle STABILITY messages

Constructor Detail

STABLE

public STABLE()

Method Detail

getDesiredAverageGossip

public long getDesiredAverageGossip()

setDesiredAverageGossip

public void setDesiredAverageGossip(long gossip_interval)

getMaxBytes

public long getMaxBytes()

setMaxBytes

public void setMaxBytes(long max_bytes)

getBytes

public long getBytes()

getStableSent

public int getStableSent()

getStableReceived

public int getStableReceived()

getStabilitySent

public int getStabilitySent()

getStabilityReceived

public int getStabilityReceived()

getStableTaskRunning

public boolean getStableTaskRunning()

resetStats

public void resetStats()

Overrides:

resetStats in class Protocol

requiredDownServices

public List<Integer> requiredDownServices()

Description copied from class: Protocol

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

Overrides:

requiredDownServices in class Protocol

Returns:

Vector (of Integers)

init

public void init()
          throws Exception

Description copied from class: Protocol

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.

Overrides:

init in class Protocol

Throws:

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 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:

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

up

public 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

down

public 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

runMessageGarbageCollection

public void runMessageGarbageCollection()

gc

public void gc()