Class SMACK

java.lang.Object
org.jgroups.stack.Protocol
org.jgroups.protocols.SMACK
All Implemented Interfaces:
AckMcastSenderWindow.RetransmitCommand

public class SMACK extends Protocol implements AckMcastSenderWindow.RetransmitCommand
Simple Multicast ACK protocol. A positive acknowledgment-based protocol for reliable delivery of multicast messages, which does not need any group membership service. Basically works as follows:
  • Sender S sends multicast message M
  • When member P receives M, it sends back a unicast ack to S
  • When S receives the ack from P, it checks whether P is in its membership list. If not, P will be added. This is necessary to retransmit the next message sent to P.
  • When S sends a multicast message M, all members are added to a retransmission entry (containing all members to which the message was sent), which is added to a hashmap (keyed by seqno). Whenever an ack is received from receiver X, X will be removed from the retransmission list for the given seqno. When the retransmission list is empty, the seqno will be removed from the hashmap.
  • A retransmitter thread in the sender periodically retransmits (either via unicast, or multicast) messages for which no ack has been received yet
  • When a max number of (unsuccessful) retransmissions have been exceeded, all remaining members for that seqno are removed from the local membership, and the seqno is removed from the hashmap, ceasing all retransmissions
Advantage of this protocol: no group membership necessary, fast.
Version:
$Id: SMACK.java,v 1.26.4.1 2009/04/06 11:47:12 belaban Exp $
Fix membershop bug: start a, b, kill b, restart b: b will be suspected by a.
Author:
Bela Ban Aug 2002
  • Constructor Details

    • SMACK

      public SMACK()
  • Method Details

    • getName

      public String getName()
      Specified by:
      getName in class Protocol
    • setProperties

      public boolean setProperties(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
    • 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 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
    • retransmit

      public void retransmit(long seqno, Message msg, Address dest)
      Description copied from interface: AckMcastSenderWindow.RetransmitCommand
      Retranmit the given msg
      Specified by:
      retransmit in interface AckMcastSenderWindow.RetransmitCommand
      Parameters:
      seqno - the sequence number associated with the message
      msg - the msg to retransmit (it should be a copy!)
      dest - the msg destination