org.javagroups.protocols
Class FD_PID

java.lang.Object
  |
  +--org.javagroups.stack.Protocol
        |
        +--org.javagroups.protocols.FD_PID

public class FD_PID
extends Protocol

Process-ID based FD protocol. The existence of a process will be tested via the process ID instead of message based pinging. In order to probe a process' existence, the application (or some other protocol layer) has to send down a SET_PID event for the member. The addresses of all members will be associated with their respective PIDs. The PID will be used to probe for the existence of that process.

A cache of Addresses and PIDs is maintained in each member, which is adjusted upon reception of view changes. The population of the addr:pid cache is as follows:
When a new member joins, it requests the PID cache from the coordinator. Then it broadcasts its own addr:pid association, so all members can update their cache. When a member P is to be pinged by Q, and Q doesn't have P'd PID, Q will broadcast a WHO_HAS_PID message, to which all members who have that entry will respond. The latter case should actually never happen because all members should always have consistent caches. However, it is left in the code as a second line of defense.

Note that 1. The SET_PID has to be sent down after connecting to a channel !

2. Note that if a process is shunned and subsequently reconnects, the SET_PID event has to be resent !

3. This protocol only works for groups whose members are on the same host . 'Host' actually means the same IP address (e.g. for multi-homed systems).


Inner Class Summary
static class FD_PID.FdHeader
           
 
Fields inherited from class org.javagroups.stack.Protocol
down_handler, down_prot, down_queue, down_thread, observer, props, stack, up_handler, up_prot, up_queue, up_thread
 
Constructor Summary
FD_PID()
           
 
Method Summary
 void down(Event evt)
          An event is to be sent down the stack.
 java.lang.String getName()
           
 boolean setProperties(java.util.Properties props)
          Configures the protocol initially.
 void up(Event evt)
          An event was received from the layer below.
 
Methods inherited from class org.javagroups.stack.Protocol
getDownProtocol, getDownQueue, getProperties, getUpProtocol, getUpQueue, init, passDown, passUp, providedDownServices, providedUpServices, receiveDownEvent, receiveUpEvent, requiredDownServices, 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
 

Constructor Detail

FD_PID

public FD_PID()
Method Detail

getName

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

setProperties

public boolean setProperties(java.util.Properties props)
Description copied from class: Protocol
Configures the protocol initially. A configuration string consists of name=value items, separated by a ';' (semicolon), e.g.:
 "loopback=false;unicast_inport=4444"
 
Overrides:
setProperties in class Protocol

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

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


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