org.javagroups.protocols.pbcast
Class GMS

java.lang.Object
  |
  +--org.javagroups.stack.Protocol
        |
        +--org.javagroups.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
           
 
Field Summary
 long digest_timeout
           
 java.lang.String group_addr
           
 java.lang.Object impl_mutex
           
 long join_retry_timeout
           
 long join_timeout
           
 java.util.Vector joining
           
 long leave_timeout
           
 Address local_addr
           
 long ltime
           
 Membership members
           
 long merge_timeout
           
 java.util.Properties props
           
 Membership tmp_members
           
 ViewId view_id
           
 
Fields inherited from class org.javagroups.stack.Protocol
down_handler, down_prot, down_queue, down_thread, down_thread_prio, observer, stack, up_handler, up_prot, up_queue, up_thread, up_thread_prio
 
Constructor Summary
GMS()
           
 
Method Summary
 void becomeClient()
           
 void becomeCoordinator()
           
 void becomeParticipant()
           
 View 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)
           
 void castViewChange(View new_view, Digest digest)
           
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.
 Digest getDigest()
          Sends down a GET_DIGEST event and waits for the GET_DIGEST_OK response, or timeout, whichever occurs first
 GmsImpl getImpl()
           
 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.
 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.
 View makeView(java.util.Vector mbrs)
           
 View makeView(java.util.Vector mbrs, ViewId vid)
           
 void mergeDigest(Digest d)
          Send down a MERGE_DIGEST event
 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 PBCAST layer.
 java.util.Vector requiredDownServices()
          List of events that are required to be answered by some layer below.
 void setDigest(Digest d)
          Send down a SET_DIGEST event
 void setImpl(GmsImpl new_impl)
           
 boolean setProperties(java.util.Properties props)
          Setup the Protocol instance according to the configuration string
 void start()
          This method is called on a Channel.connect(String).
 void stop()
          This method is called on a Channel.disconnect().
 void up(Event evt)
          An event was received from the layer below.
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.javagroups.stack.Protocol
destroy, getDownProtocol, getDownQueue, getProperties, getUpProtocol, getUpQueue, passDown, passUp, providedDownServices, providedUpServices, receiveDownEvent, requiredUpServices, setDownProtocol, setObserver, setPropertiesInternal, setProtocolStack, setUpProtocol, startDownHandler, startUpHandler, stopInternal
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

props

public java.util.Properties props

local_addr

public Address local_addr

group_addr

public java.lang.String group_addr

members

public Membership members

tmp_members

public Membership tmp_members

joining

public java.util.Vector joining

view_id

public ViewId view_id

ltime

public long ltime

join_timeout

public long join_timeout

join_retry_timeout

public long join_retry_timeout

leave_timeout

public long leave_timeout

digest_timeout

public long digest_timeout

merge_timeout

public long merge_timeout

impl_mutex

public java.lang.Object impl_mutex
Constructor Detail

GMS

public GMS()
Method Detail

getName

public java.lang.String getName()
Specified by:
getName 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 View 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).

Returns:
View The new view

castViewChange

public void castViewChange(View new_view)

castViewChange

public void castViewChange(View new_view,
                           Digest digest)

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 PBCAST layer. It therefore sends down a GET_DIGEST event, to which the PBCAST 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


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