org.jgroups.protocols.pbcast
Class GMS

java.lang.Object
  org.jgroups.stack.Protocol
      org.jgroups.protocols.pbcast.GMS

public class GMS
extends Protocol

Group membership protocol. Handles joins/leaves/crashes (suspicions) and emits new views accordingly. Use VIEW_ENFORCER on top of this layer to make sure new members don't receive any messages until they are members.

Nested Class Summary

static class	GMS.GmsHeader
static class	GMS.Request

Field Summary

protected int	num_prev_mbrs Max number of old members to keep in history
org.jgroups.protocols.pbcast.GMS.ViewHandler	view_handler Class to process JOIN, LEAVE and MERGE requests

Fields inherited from class org.jgroups.stack.Protocol

down_handler, down_prot, down_queue, down_thread, down_thread_prio, log, observer, props, stack, stats, trace, up_handler, up_prot, up_queue, up_thread, up_thread_prio, warn

Constructor Summary

GMS()

Method Summary

void	becomeClient()
void	becomeCoordinator()
void	becomeParticipant()
void	castViewChange(java.util.Vector new_mbrs, java.util.Vector old_mbrs, java.util.Vector suspected_mbrs) Compute a new view, given the current view, the new members and the suspected/left members.
void	castViewChange(View new_view, Digest digest)
void	castViewChangeWithDest(View new_view, Digest digest, java.util.List members) Broadcasts the new view and digest, and waits for acks from all members in the list given as argument.
protected boolean	checkSelfInclusion(java.util.Vector mbrs) Returns true if local_addr is member of mbrs, else false
protected Address	determineCoordinator()
void	down(Event evt) An event is to be sent down the stack.
java.lang.String	dumpViewHandlerHistory()
java.lang.String	dumpViewHandlerQueue()
Digest	getDigest() Sends down a GET_DIGEST event and waits for the GET_DIGEST_OK response, or timeout, whichever occurs first
GmsImpl	getImpl()
long	getJoinRetryTimeout()
long	getJoinTimeout()
java.lang.String	getLocalAddress()
java.lang.String	getMembers()
java.lang.String	getName()
View	getNextView(java.util.Vector new_mbrs, java.util.Vector old_mbrs, java.util.Vector suspected_mbrs) Computes the next view.
int	getNumberOfViews()
int	getNumMembers()
java.lang.String	getView()
void	init() Called after instance has been created (null constructor) and before protocol is started.
void	installView(View new_view) Sets the new view and sends a VIEW_CHANGE event up and down the stack.
void	installView(View new_view, Digest digest) Sets the new view and sends a VIEW_CHANGE event up and down the stack.
boolean	isCoordinator()
boolean	isShun()
boolean	isViewHandlerSuspended()
View	makeView(java.util.Vector mbrs)
View	makeView(java.util.Vector mbrs, ViewId vid)
void	mergeDigest(Digest d) Send down a MERGE_DIGEST event
java.lang.String	printPreviousMembers()
java.lang.String	printPreviousViews()
void	receiveUpEvent(Event evt) This method is overridden to avoid hanging on getDigest(): when a JOIN is received, the coordinator needs to retrieve the digest from the NAKACK layer.
java.util.Vector	requiredDownServices() List of events that are required to be answered by some layer below.
void	resetStats()
void	resumeViewHandler()
void	setDigest(Digest d) Send down a SET_DIGEST event
void	setImpl(GmsImpl new_impl)
void	setJoinRetryTimeout(long t)
void	setJoinTimeout(long t)
boolean	setProperties(java.util.Properties props) Setup the Protocol instance according to the configuration string
void	setShun(boolean s)
void	start() This method is called on a Channel.connect(String).
void	stop() This method is called on a Channel.disconnect().
void	suspendViewHandler()
void	up(Event evt) An event was received from the layer below.
int	viewHandlerSize()
protected boolean	wouldBeNewCoordinator(Address potential_new_coord) Checks whether the potential_new_coord would be the new coordinator (2nd in line)

Methods inherited from class org.jgroups.stack.Protocol

destroy, downThreadEnabled, dumpStats, enableStats, getDownProtocol, getDownQueue, getProperties, getUpProtocol, getUpQueue, handleSpecialDownEvent, isTrace, isWarn, passDown, passUp, printStats, providedDownServices, providedUpServices, receiveDownEvent, requiredUpServices, setDownProtocol, setObserver, setPropertiesInternal, setProtocolStack, setTrace, setUpProtocol, setWarn, startDownHandler, startUpHandler, statsEnabled, stopInternal, upThreadEnabled

Methods inherited from class java.lang.Object

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

Field Detail

num_prev_mbrs

protected int num_prev_mbrs

Max number of old members to keep in history

view_handler

public final org.jgroups.protocols.pbcast.GMS.ViewHandler view_handler

Class to process JOIN, LEAVE and MERGE requests

Constructor Detail

GMS

public GMS()

Method Detail

getName

public java.lang.String getName()

Specified by:

getName in class Protocol

getView

public java.lang.String getView()

getNumberOfViews

public int getNumberOfViews()

getLocalAddress

public java.lang.String getLocalAddress()

getMembers

public java.lang.String getMembers()

getNumMembers

public int getNumMembers()

getJoinTimeout

public long getJoinTimeout()

setJoinTimeout

public void setJoinTimeout(long t)

getJoinRetryTimeout

public long getJoinRetryTimeout()

setJoinRetryTimeout

public void setJoinRetryTimeout(long t)

isShun

public boolean isShun()

setShun

public void setShun(boolean s)

printPreviousMembers

public java.lang.String printPreviousMembers()

viewHandlerSize

public int viewHandlerSize()

isViewHandlerSuspended

public boolean isViewHandlerSuspended()

dumpViewHandlerQueue

public java.lang.String dumpViewHandlerQueue()

dumpViewHandlerHistory

public java.lang.String dumpViewHandlerHistory()

suspendViewHandler

public void suspendViewHandler()

resumeViewHandler

public void resumeViewHandler()

printPreviousViews

public java.lang.String printPreviousViews()

isCoordinator

public boolean isCoordinator()

resetStats

public void resetStats()

Overrides:

resetStats in class Protocol

requiredDownServices

public java.util.Vector 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)

setImpl

public void setImpl(GmsImpl new_impl)

getImpl

public GmsImpl getImpl()

init

public void init()
          throws java.lang.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:

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

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

becomeCoordinator

public void becomeCoordinator()

becomeParticipant

public void becomeParticipant()

becomeClient

public void becomeClient()

getNextView

public View getNextView(java.util.Vector new_mbrs,
                        java.util.Vector old_mbrs,
                        java.util.Vector suspected_mbrs)

Computes the next view. Returns a copy that has old_mbrs and suspected_mbrs removed and new_mbrs added.

castViewChange

public void castViewChange(java.util.Vector new_mbrs,
                           java.util.Vector old_mbrs,
                           java.util.Vector suspected_mbrs)

Compute a new view, given the current view, the new members and the suspected/left members. Then simply mcast the view to all members. This is different to the VS GMS protocol, in which we run a FLUSH protocol which tries to achive consensus on the set of messages mcast in the current view before proceeding to install the next view. The members for the new view are computed as follows:

     existing          leaving        suspected          joining

     1. new_view      y                 n               n                 y
     2. tmp_view      y                 y               n                 y
     (view_dest)
     

1. The new view to be installed includes the existing members plus the joining ones and excludes the leaving and suspected members.
2. A temporary view is sent down the stack as an event. This allows the bottom layer (e.g. UDP or TCP) to determine the members to which to send a multicast message. Compared to the new view, leaving members are included since they have are waiting for a view in which they are not members any longer before they leave. So, if we did not set a temporary view, joining members would not receive the view (signalling that they have been joined successfully). The temporary view is essentially the current view plus the joining members (old members are still part of the current view).

castViewChange

public void castViewChange(View new_view,
                           Digest digest)

castViewChangeWithDest

public void castViewChangeWithDest(View new_view,
                                   Digest digest,
                                   java.util.List members)

Broadcasts the new view and digest, and waits for acks from all members in the list given as argument. If the list is null, we take the members who are part of new_view

Parameters:

new_view -

digest -

members -

installView

public void installView(View new_view,
                        Digest digest)

Sets the new view and sends a VIEW_CHANGE event up and down the stack. If the view is a MergeView (subclass of View), then digest will be non-null and has to be set before installing the view.

installView

public void installView(View new_view)

Sets the new view and sends a VIEW_CHANGE event up and down the stack.

determineCoordinator

protected Address determineCoordinator()

wouldBeNewCoordinator

protected boolean wouldBeNewCoordinator(Address potential_new_coord)

Checks whether the potential_new_coord would be the new coordinator (2nd in line)

checkSelfInclusion

protected boolean checkSelfInclusion(java.util.Vector mbrs)

Returns true if local_addr is member of mbrs, else false

makeView

public View makeView(java.util.Vector mbrs)

makeView

public View makeView(java.util.Vector mbrs,
                     ViewId vid)

setDigest

public void setDigest(Digest d)

Send down a SET_DIGEST event

mergeDigest

public void mergeDigest(Digest d)

Send down a MERGE_DIGEST event

getDigest

public Digest getDigest()

Sends down a GET_DIGEST event and waits for the GET_DIGEST_OK response, or timeout, whichever occurs first

up

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

Overrides:

up in class Protocol

receiveUpEvent

public void receiveUpEvent(Event evt)

This method is overridden to avoid hanging on getDigest(): when a JOIN is received, the coordinator needs to retrieve the digest from the NAKACK layer. It therefore sends down a GET_DIGEST event, to which the NAKACK layer responds with a GET_DIGEST_OK event.

However, the GET_DIGEST_OK event will not be processed because the thread handling the JOIN request won't process the GET_DIGEST_OK event until the JOIN event returns. The receiveUpEvent() method is executed by the up-handler thread of the lower protocol and therefore can handle the event. All we do here is unblock the mutex on which JOIN is waiting, allowing JOIN to return with a valid digest. The GET_DIGEST_OK event is then discarded, because it won't be processed twice.

Overrides:

receiveUpEvent in class Protocol

down

public void 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 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().

Overrides:

down in class Protocol

setProperties

public boolean setProperties(java.util.Properties props)

Setup the Protocol instance according to the configuration string

Overrides:

setProperties in class Protocol