Class NakReceiverWindow


  • public class NakReceiverWindow
    extends java.lang.Object
    Keeps track of messages according to their sequence numbers. Allows messages to be added out of order, and with gaps between sequence numbers. Method remove() removes the first message with a sequence number that is 1 higher than next_to_remove (this variable is then incremented), or it returns null if no message is present, or if no message's sequence number is 1 higher.

    When there is a gap upon adding a message, its seqno will be added to the Retransmitter, which (using a timer) requests retransmissions of missing messages and keeps on trying until the message has been received, or the member who sent the message is suspected. There are 3 variables which keep track of messages:

    • low: lowest seqno, modified on stable(). On stable(), we purge msgs [low digest.highest_delivered]
    • highest_delivered: the highest delivered seqno, updated on remove(). The next message to be removed is highest_delivered + 1
    • highest_received: the highest received message, updated on add (if a new message is added, not updated e.g. if a missing msg was received)

    Note that the first seqno expected is 1. This design is described in doc/design.NAKACK.txt

    Example: 1,2,3,5,6,8: low=1, highest_delivered=2 (or 3, depending on whether remove() was called !), highest_received=8

    Version:
    $Id: NakReceiverWindow.java,v 1.52.2.2 2008/06/09 09:23:08 belaban Exp $
    Author:
    Bela Ban May 27 1999, May 2004, Jan 2007, John Georgiadis May 8 2001
    • Field Detail

      • NULL_MSG

        public static final Message NULL_MSG
        dummy for null values: ConcurrentHashMap doesn't allow null values
      • log

        protected static final org.apache.commons.logging.Log log
    • Constructor Detail

      • NakReceiverWindow

        public NakReceiverWindow​(Address sender,
                                 Retransmitter.RetransmitCommand cmd,
                                 long highest_delivered_seqno,
                                 long lowest_seqno,
                                 TimeScheduler sched)
        Creates a new instance with the given retransmit command
        Parameters:
        sender - The sender associated with this instance
        cmd - The command used to retransmit a missing message, will be invoked by the table. If null, the retransmit thread will not be started
        highest_delivered_seqno - The next seqno to remove is highest_delivered_seqno +1
        lowest_seqno - The low seqno purged
        sched - the external scheduler to use for retransmission requests of missing msgs. If it's not provided or is null, an internal
      • NakReceiverWindow

        public NakReceiverWindow​(Address sender,
                                 Retransmitter.RetransmitCommand cmd,
                                 long highest_delivered_seqno,
                                 TimeScheduler sched)
        Creates a new instance with the given retransmit command
        Parameters:
        sender - The sender associated with this instance
        cmd - The command used to retransmit a missing message, will be invoked by the table. If null, the retransmit thread will not be started
        highest_delivered_seqno - The next seqno to remove is highest_delivered_seqno +1
        sched - the external scheduler to use for retransmission requests of missing msgs. If it's not provided or is null, an internal
      • NakReceiverWindow

        public NakReceiverWindow​(Address sender,
                                 Retransmitter.RetransmitCommand cmd,
                                 long highest_delivered_seqno)
        Creates a new instance with the given retransmit command
        Parameters:
        sender - The sender associated with this instance
        cmd - The command used to retransmit a missing message, will be invoked by the table. If null, the retransmit thread will not be started
        highest_delivered_seqno - The next seqno to remove is highest_delivered_seqno +1
    • Method Detail

      • getLock

        public java.util.concurrent.locks.ReentrantLock getLock()
      • setRetransmitTimeouts

        public void setRetransmitTimeouts​(Interval timeouts)
      • setDiscardDeliveredMessages

        public void setDiscardDeliveredMessages​(boolean flag)
      • getMaxXmitBufSize

        public int getMaxXmitBufSize()
      • setMaxXmitBufSize

        public void setMaxXmitBufSize​(int max_xmit_buf_size)
      • getPendingXmits

        public int getPendingXmits()
      • getLossRate

        public double getLossRate()
        Returns the loss rate, which is defined as the number of pending retransmission requests / the total number of messages in xmit_table
        Returns:
        The loss rate
      • getSmoothedLossRate

        public double getSmoothedLossRate()
      • add

        public boolean add​(long seqno,
                           Message msg)
        Adds a message according to its seqno (sequence number).

        There are 4 cases where messages are added:

        1. seqno is the next to be expected seqno: added to map
        2. seqno is <= highest_delivered: discard as we've already delivered it
        3. seqno is smaller than the next expected seqno: missing message, add it
        4. seqno is greater than the next expected seqno: add it to map and fill the gaps with null messages for retransmission. Add the seqno to the retransmitter too
        Returns:
        True if the message was added successfully, false otherwise (e.g. duplicate message)
      • removeOOBMessage

        public Message removeOOBMessage()
      • hasMessagesToRemove

        public boolean hasMessagesToRemove()
      • stable

        public void stable​(long seqno)
        Delete all messages <= seqno (they are stable, that is, have been received at all members). Stop when a number > seqno is encountered (all messages are ordered on seqnos).
      • reset

        public void reset()
        Reset the retransmitter and the nak window
      • destroy

        public void destroy()
        Stop the retransmitter and reset the nak window
      • getLowestSeen

        public long getLowestSeen()
        Returns:
        the lowest sequence number of a message that has been delivered or is a candidate for delivery (by the next call to remove())
      • getHighestDelivered

        public long getHighestDelivered()
        Returns the highest sequence number of a message consumed by the application (by remove()). Note that this is different from the highest deliverable seqno. E.g. in 23,24,26,27,29, the highest delivered message may be 22, whereas the highest deliverable message may be 24 !
        Returns:
        the highest sequence number of a message consumed by the application (by remove())
      • getHighestReceived

        public long getHighestReceived()
        Returns the highest sequence number received so far (which may be higher than the highest seqno delivered so far; e.g., for 1,2,3,5,6 it would be 6.
        See Also:
        getHighestDelivered()
      • get

        public Message get​(long seqno)
        Returns the message from xmit_table
        Parameters:
        seqno -
        Returns:
        Message from xmit_table
      • size

        public int size()
      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object
      • printLossRate

        public java.lang.String printLossRate()