org.jgroups.protocols
Class PING

java.lang.Object
  extended byorg.jgroups.stack.Protocol
      extended byorg.jgroups.protocols.PING

public class PING
extends Protocol

The PING protocol layer retrieves the initial membership (used by the GMS when started by sending event FIND_INITIAL_MBRS down the stack). We do this by mcasting PING requests to an IP MCAST address (or, if gossiping is enabled, by contacting the GossipServer). The responses should allow us to determine the coordinator whom we have to contact, e.g. in case we want to join the group. When we are a server (after having received the BECOME_SERVER event), we'll respond to PING requests with a PING response.

The FIND_INITIAL_MBRS event will eventually be answered with a FIND_INITIAL_MBRS_OK event up the stack. The following properties are available property: timeout - the timeout (ms) to wait for the initial members, default is 3000=3 secs property: num_initial_members - the minimum number of initial members for a FIND_INITAL_MBRS, default is 2 property: gossip_host - if you are using GOSSIP then this defines the host of the GossipServer, default is null property: gossip_port - if you are using GOSSIP then this defines the port of the GossipServer, default is null


Field Summary
 
Fields inherited from class org.jgroups.stack.Protocol
down_handler, down_prot, down_queue, down_thread, down_thread_prio, observer, props, stack, up_handler, up_prot, up_queue, up_thread, up_thread_prio
 
Constructor Summary
PING()
           
 
Method Summary
 void down(Event evt)
          An event is to be sent down the stack.
 java.lang.String getName()
           
 java.util.Vector providedUpServices()
          List of events that are provided to layers above (they will be handled when sent down from above).
 boolean setProperties(java.util.Properties props)
          sets the properties of the PING protocol.
 void stop()
          This method is called on a Channel.disconnect().
 void up(Event evt)
          An event was received from the layer below.
 
Methods inherited from class org.jgroups.stack.Protocol
destroy, getDownProtocol, getDownQueue, getProperties, getUpProtocol, getUpQueue, init, passDown, passUp, providedDownServices, receiveDownEvent, receiveUpEvent, requiredDownServices, requiredUpServices, setDownProtocol, setObserver, setPropertiesInternal, setProtocolStack, setUpProtocol, start, startDownHandler, startUpHandler, stopInternal
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

PING

public PING()
Method Detail

getName

public java.lang.String getName()
Specified by:
getName in class Protocol

providedUpServices

public java.util.Vector providedUpServices()
Description copied from class: Protocol
List of events that are provided to layers above (they will be handled when sent down from above).

Overrides:
providedUpServices in class Protocol
Returns:
Vector (of Integers)

setProperties

public boolean setProperties(java.util.Properties props)
sets the properties of the PING protocol. The following properties are available property: timeout - the timeout (ms) to wait for the initial members, default is 3000=3 secs property: num_initial_members - the minimum number of initial members for a FIND_INITAL_MBRS, default is 2 property: gossip_host - if you are using GOSSIP then this defines the host of the GossipServer, default is null property: gossip_port - if you are using GOSSIP then this defines the port of the GossipServer, default is null

Overrides:
setProperties in class Protocol
Parameters:
props - - a property set containing only PING properties
Returns:
returns true if all properties were parsed properly returns false if there are unrecnogized properties in the property set

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 void up(Event evt)
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. For the PING protocol, the Up operation does the following things. 1. If the event is a Event.MSG then PING will inspect the message header. If the header is null, PING simply passes up the event If the header is PingHeader.GET_MBRS_REQ then the PING protocol will PassDown a PingRequest message If the header is PingHeader.GET_MBRS_RSP we will add the message to the initial members vector and wake up any waiting threads. 2. If the event is Event.SET_LOCAL_ADDR we will simple set the local address of this protocol 3. For all other messages we simple pass it up to the protocol above

Overrides:
up in class Protocol
Parameters:
evt - - the event that has been sent from the layer below

down

public void down(Event evt)
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. The PING protocol is interested in several different down events, Event.FIND_INITIAL_MBRS - sent by the GMS layer and expecting a GET_MBRS_OK Event.TMP_VIEW and Event.VIEW_CHANGE - a view change event Event.BECOME_SERVER - called after client has joined and is fully working group member Event.CONNECT, Event.DISCONNECT.

Overrides:
down in class Protocol


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