org.jgroups.protocols

Class FD

java.lang.Object

org.jgroups.stack.Protocol

org.jgroups.protocols.FD

Direct Known Subclasses:

FD_ICMP, FD_PING

public class FD
extends Protocol

Failure detection based on simple heartbeat protocol. Regularly polls members for liveness. Multicasts SUSPECT messages when a member is not reachable. The simple algorithms works as follows: the membership is known and ordered. Each HB protocol periodically sends an 'are-you-alive' message to its *neighbor*. A neighbor is the next in rank in the membership list, which is recomputed upon a view change. When a response hasn't been received for n milliseconds and m tries, the corresponding member is suspected (and eventually excluded if faulty).

FD starts when it detects (in a view change notification) that there are at least 2 members in the group. It stops running when the membership drops below 2.

When a message is received from the monitored neighbor member, it causes the pinger thread to 'skip' sending the next are-you-alive message. Thus, traffic is reduced.

Author:

Bela Ban

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected class	FD.Broadcaster Task that periodically broadcasts a list of suspected members to the group.
protected class	FD.BroadcastTask
static class	FD.FdHeader
protected class	FD.Monitor

Field Summary

Fields

Modifier and Type	Field and Description
protected FD.Broadcaster	bcast_task Transmits SUSPECT message until view change or UNSUSPECT is received
protected Address	local_addr
protected Lock	lock
protected List<Address>	members
protected int	num_heartbeats
protected int	num_suspect_events
protected int	num_tries
protected Address	ping_dest
protected List<Address>	pingable_mbrs Members from which we select ping_dest.
protected BoundedList<Address>	suspect_history

Fields inherited from class org.jgroups.stack.Protocol

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

Constructor Summary

Constructors

Constructor and Description
FD()

Method Summary

Methods

Modifier and Type	Method and Description
protected FD.Monitor	createMonitor()
Object	down(Event evt) An event is to be sent down the stack.
int	getCurrentNumTries()
String	getLocalAddress()
int	getMaxTries()
String	getMembers()
int	getNumberOfHeartbeatsSent()
int	getNumSuspectEventsGenerated()
String	getPingableMembers()
String	getPingDest()
long	getTimeout()
void	init() Called after instance has been created (null constructor) and before protocol is started.
boolean	isMonitorRunning()
String	printSuspectHistory()
void	resetStats()
void	setMaxTries(int max_tries)
void	setTimeout(long timeout)
void	startFailureDetection()
void	stop() This method is called on a Channel.disconnect().
void	stopFailureDetection()
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, requiredDownServices, requiredUpServices, resetStatistics, setDownProtocol, setErgonomics, setId, setLevel, setProtocolStack, setSocketFactory, setUpProtocol, setValue, setValues, start, statsEnabled

Methods inherited from class java.lang.Object

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

Field Detail

num_heartbeats

protected int num_heartbeats

num_suspect_events

protected int num_suspect_events

suspect_history

protected final BoundedList<Address> suspect_history

local_addr

protected Address local_addr

num_tries

protected int num_tries

lock

protected final Lock lock

ping_dest

protected Address ping_dest

members

protected final List<Address> members

pingable_mbrs

protected final List<Address> pingable_mbrs

Members from which we select ping_dest. may be subset of members

bcast_task

protected final FD.Broadcaster bcast_task

Transmits SUSPECT message until view change or UNSUSPECT is received

Constructor Detail

FD

public FD()

Method Detail

getLocalAddress

public String getLocalAddress()

getMembers

public String getMembers()

getPingableMembers

public String getPingableMembers()

getPingDest

public String getPingDest()

getNumberOfHeartbeatsSent

public int getNumberOfHeartbeatsSent()

getNumSuspectEventsGenerated

public int getNumSuspectEventsGenerated()

getTimeout

public long getTimeout()

setTimeout

public void setTimeout(long timeout)

getMaxTries

public int getMaxTries()

setMaxTries

public void setMaxTries(int max_tries)

getCurrentNumTries

public int getCurrentNumTries()

printSuspectHistory

public String printSuspectHistory()

resetStats

public void resetStats()

Overrides:

resetStats in class Protocol

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

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

createMonitor

protected FD.Monitor createMonitor()

stopFailureDetection

public void stopFailureDetection()

startFailureDetection

public void startFailureDetection()

isMonitorRunning

public boolean isMonitorRunning()

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