Class UNICAST

java.lang.Object
org.jgroups.stack.Protocol
org.jgroups.protocols.UNICAST
All Implemented Interfaces:
AckSenderWindow.RetransmitCommand, AgeOutCache.Handler<Address>

public class UNICAST extends Protocol implements AckSenderWindow.RetransmitCommand, AgeOutCache.Handler<Address>
Reliable unicast layer. Uses acknowledgement scheme similar to TCP to provide lossless transmission of unicast messages (for reliable multicast see NAKACK layer). When a message is sent to a peer for the first time, we add the pair invalid input: '<'peer_addr, Entry> to the hashtable (peer address is the key). All messages sent to that peer will be added to hashtable.peer_addr.sent_msgs. When we receive a message from a peer for the first time, another entry will be created and added to the hashtable (unless already existing). Msgs will then be added to hashtable.peer_addr.received_msgs.

This layer is used to reliably transmit point-to-point messages, that is, either messages sent to a single receiver (vs. messages multicast to a group) or for example replies to a multicast message. The sender uses an AckSenderWindow which retransmits messages for which it hasn't received an ACK, the receiver uses AckReceiverWindow which keeps track of the lowest seqno received so far, and keeps messages in order.

Messages in both AckSenderWindows and AckReceiverWindows will be removed. A message will be removed from AckSenderWindow when an ACK has been received for it and messages will be removed from AckReceiverWindow whenever a message is received: the new message is added and then we try to remove as many messages as possible (until we stop at a gap, or there are no more messages).
UNICAST was enhanced in April 2009, the new design is described in doc/design/UNICAST.new.txt

Version:
$Id: UNICAST.java,v 1.91.2.14.2.7 2009/04/29 14:34:00 belaban Exp $
Author:
Bela Ban
  • Constructor Details

    • UNICAST

      public UNICAST()
  • Method Details

    • getName

      public String getName()
      All protocol names have to be unique !
      Specified by:
      getName in class Protocol
    • getLocalAddress

      public String getLocalAddress()
    • getMembers

      public String getMembers()
    • printConnections

      public String printConnections()
    • getNumMessagesSent

      public long getNumMessagesSent()
    • getNumMessagesReceived

      public long getNumMessagesReceived()
    • getNumBytesSent

      public long getNumBytesSent()
    • getNumBytesReceived

      public long getNumBytesReceived()
    • getNumAcksSent

      public long getNumAcksSent()
    • getNumAcksReceived

      public long getNumAcksReceived()
    • getNumberOfRetransmitRequestsReceived

      public long getNumberOfRetransmitRequestsReceived()
    • getMaxRetransmitTime

      public long getMaxRetransmitTime()
    • setMaxRetransmitTime

      public void setMaxRetransmitTime(long max_retransmit_time)
    • getAgeOutCacheSize

      public int getAgeOutCacheSize()
    • printAgeOutCache

      public String printAgeOutCache()
    • getAgeOutCache

      public AgeOutCache getAgeOutCache()
    • getNumberOfUnackedMessages

      public int getNumberOfUnackedMessages()
      The number of messages in all Entry.sent_msgs tables (haven't received an ACK yet)
    • getUnackedMessages

      public String getUnackedMessages()
    • getNumberOfMessagesInReceiveWindows

      public int getNumberOfMessagesInReceiveWindows()
    • resetStats

      public void resetStats()
      Overrides:
      resetStats in class Protocol
    • dumpStats

      public Map<String,Object> dumpStats()
      Overrides:
      dumpStats 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
    • start

      public void start() throws 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:
      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
    • 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
    • removeConnection

      public boolean removeConnection(Address mbr)
      Removes and resets from connection table (which is already locked). Returns true if member was found, otherwise false. This method is public only so it can be invoked by unit testing, but should not otherwise be used !
    • removeAllConnections

      public void removeAllConnections()
      This method is public only so it can be invoked by unit testing, but should not otherwise be used !
    • retransmit

      public void retransmit(long seqno, Message msg)
      Called by AckSenderWindow to resend messages for which no ACK has been received yet
      Specified by:
      retransmit in interface AckSenderWindow.RetransmitCommand
    • expired

      public void expired(Address key)
      Called by AgeOutCache, to removed expired connections
      Specified by:
      expired in interface AgeOutCache.Handler<Address>
      Parameters:
      key -