Class 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 Detail

      • SMACK

        public SMACK()
    • Method Detail

      • getName

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