Package org.jgroups.stack

Class NakReceiverWindow

java.lang.Object
org.jgroups.stack.NakReceiverWindow
public class NakReceiverWindow extends 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

Author:
Bela Ban

  • Field Details

    • log

      protected static final Log log

  • Constructor Details

    • 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, long lowest_seqno, TimeScheduler sched, boolean use_range_based_retransmitter)

    • NakReceiverWindow

      public NakReceiverWindow(Address sender, Retransmitter.RetransmitCommand cmd, long highest_delivered_seqno, long lowest_seqno, TimeScheduler sched, boolean use_range_based_retransmitter, int num_rows, int msgs_per_row, double resize_factor, long max_compaction_time, boolean automatic_purging)

    • 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

  • Method Details

    • getProcessing

      public AtomicBoolean getProcessing()

    • setRetransmitTimeouts

      public void setRetransmitTimeouts(Interval timeouts)

    • setDiscardDeliveredMessages

      @Deprecated public void setDiscardDeliveredMessages(boolean flag)
      Deprecated.

    • getMaxXmitBufSize

      @Deprecated public int getMaxXmitBufSize()
      Deprecated.

    • setMaxXmitBufSize

      @Deprecated public void setMaxXmitBufSize(int max_xmit_buf_size)
      Deprecated.

    • setListener

      public void setListener(NakReceiverWindow.Listener l)

    • 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()

    • getRetransmiTableSize

      public int getRetransmiTableSize()

    • getRetransmitTableCapacity

      public int getRetransmitTableCapacity()

    • getRetransmitTableFillFactor

      public double getRetransmitTableFillFactor()

    • compact

      public void compact()

    • 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 invalid input: '<'= 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)

    • remove

      public Message remove()

    • remove

      public Message remove(boolean acquire_lock, boolean remove_msg)

    • removeMany

      public List<Message> removeMany(AtomicBoolean processing)
      Removes as many messages as possible
      Returns:
      List A list of messages, or null if no available messages were found

    • removeMany

      public List<Message> removeMany(AtomicBoolean processing, boolean remove_msgs, int max_results)
      Removes as many messages as possible
      Parameters:
      remove_msgs - Removes messages from xmit_table
      max_results - Max number of messages to remove in one batch
      Returns:
      List A list of messages, or null if no available messages were found

    • stable

      public void stable(long seqno)
      Delete all messages invalid input: '<'= 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).

    • destroy

      public void destroy()
      Destroys the NakReceiverWindow. After this method returns, no new messages can be added and a new NakReceiverWindow should be used instead. Note that messages can still be removed though.

    • getDigest

      public long[] getDigest()
      Returns the lowest, highest delivered and highest received seqnos

    • 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())

    • setHighestDelivered

      public long setHighestDelivered(long new_val)

    • 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:

    • get

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

    • get

      public List<Message> get(long from, long to)
      Returns a list of messages in the range [from .. to], including from and to
      Parameters:
      from -
      to -
      Returns:
      A list of messages, or null if none in range [from .. to] was found

    • size

      public int size()

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • printMessages

      protected String printMessages()
      Prints xmit_table. Requires read lock to be present
      Returns:
      String

    • printLossRate

      public String printLossRate()

    • printRetransmitStats

      public String printRetransmitStats()