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## org.jgroups.protocols
Class UNICAST2

    java.lang.Object
      org.jgroups.stack.Protocol
          org.jgroups.protocols.UNICAST2

All Implemented Interfaces:
  Retransmitter.RetransmitCommand, AgeOutCache.Handler<Address>

    public class UNICAST2

extends Protocol
implements Retransmitter.RetransmitCommand, AgeOutCache.Handler<Address>

Reliable unicast layer. Implemented with negative acks. Every sender keeps its messages in an AckSenderWindow. A receiver stores incoming messages in a NakReceiverWindow, and asks the sender for retransmission if a gap is detected. Every now and then (stable_interval), a timer task sends a STABLE message to all senders, including the highest received and delivered seqnos. A sender purges messages lower than highest delivered and asks the STABLE sender for messages it might have missed (smaller than highest received). A STABLE message can also be sent when a receiver has received more than max_bytes from a given sender.

The advantage of this protocol over `UNICAST` is that it doesn't send acks for every message. Instead, it sends 'acks' after receiving max_bytes and/ or periodically (stable_interval).

Author:
  Bela Ban

Nested Class Summary
`static class` | `UNICAST2.Unicast2Header` The following types and fields are serialized:

Field Summary
`static long` | `DEFAULT_FIRST_SEQNO`
`protected long` | `max_bytes`
`protected long` | `max_retransmit_time`
`protected int` | `max_stable_msgs`
`protected long` | `stable_interval`

Fields inherited from class org.jgroups.stack.Protocol
`down_prot, ergonomics, id, log, name, stack, stats, up_prot`

Constructor Summary
`UNICAST2()`

Method Summary
`void` | `compact()`
`java.lang.Object` | `down(Event evt)` An event is to be sent down the stack.
`java.util.Map<java.lang.String,java.lang.Object>` | `dumpStats()`
`void` | `expired(Address key)` Called by AgeOutCache, to removed expired connections
`AgeOutCache<Address>` | `getAgeOutCache()`
`int` | `getAgeOutCacheSize()`
`java.lang.String` | `getLocalAddress()`
`long` | `getMaxRetransmitTime()`
`java.lang.String` | `getMembers()`
`int` | `getNumberOfMessagesInReceiveWindows()`
`long` | `getNumberOfRetransmissions()`
`long` | `getNumBytesReceived()`
`long` | `getNumBytesSent()`
`long` | `getNumMessagesReceived()`
`long` | `getNumMessagesSent()`
`long[]` | `getTimeout()`
`TimeScheduler` | `getTimer()`
`void` | `init()` Called after instance has been created (null constructor) and before protocol is started.
`java.lang.String` | `printAgeOutCache()`
`java.lang.String` | `printConnections()`
`java.lang.String` | `printRetransmitTableSizes()`
`void` | `purgeAndCompact()`
`void` | `removeAllConnections()` This method is public only so it can be invoked by unit testing, but should not otherwise be used !
`void` | `removeConnection(Address mbr)` Removes and resets from connection table (which is already locked).
`void` | `resetStats()`
`void` | `retransmit(long first_seqno, long last_seqno, Address sender)` Get the missing messages between sequence numbers `first_seqno` and `last_seqno`.
`protected void` | `sendStableMessage(Address dest, long low, long high)`
`void` | `sendStableMessages()`
`void` | `setMaxMessageBatchSize(int size)`
`void` | `setMaxRetransmitTime(long max_retransmit_time)`
`void` | `setTimeout(long[] val)`
`void` | `setTimer(TimeScheduler timer)` Only used for unit tests, don't use !
`protected void` | `stable(Address sender, long highest_delivered, long highest_seen)` Purge all messages in window for local_addr, which are <= low.
`void` | `start()` This method is called on a `Channel.connect(String)`.
`void` | `stop()` This method is called on a `Channel.disconnect()`.
`java.lang.Object` | `up(Event evt)` An event was received from the layer below.

Methods inherited from class org.jgroups.stack.Protocol
`destroy, downThreadEnabled, enableStats, getConfigurableObjects, getDownProtocol, getId, getLevel, getName, getProperties, getProtocolStack, getSocketFactory, getThreadFactory, getTransport, getUpProtocol, getValue, isErgonomics, printStats, providedDownServices, providedUpServices, requiredDownServices, requiredUpServices, setDownProtocol, setErgonomics, setId, setLevel, setProperties, setPropertiesInternal, setProperty, setProtocolStack, setSocketFactory, setUpProtocol, setValue, setValues, statsEnabled, upThreadEnabled`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### DEFAULT_FIRST_SEQNO

    public static final long DEFAULT_FIRST_SEQNO

See Also:
  Constant Field Values

### max_bytes

    protected long max_bytes

### stable_interval

    protected long stable_interval

### max_stable_msgs

    protected int max_stable_msgs

### max_retransmit_time

    protected long max_retransmit_time

Constructor Detail

### UNICAST2

    public UNICAST2()

Method Detail

### getTimeout

    public long[] getTimeout()

### setTimeout

    public void setTimeout(long[] val)

### setMaxMessageBatchSize

    public void setMaxMessageBatchSize(int size)

### getLocalAddress

    public java.lang.String getLocalAddress()

### getMembers

    public java.lang.String getMembers()

### printConnections

    public java.lang.String printConnections()

### getNumMessagesSent

    public long getNumMessagesSent()

### getNumMessagesReceived

    public long getNumMessagesReceived()

### getNumBytesSent

    public long getNumBytesSent()

### getNumBytesReceived

    public long getNumBytesReceived()

### getNumberOfRetransmissions

    public long getNumberOfRetransmissions()

### getMaxRetransmitTime

    public long getMaxRetransmitTime()

### setMaxRetransmitTime

    public void setMaxRetransmitTime(long max_retransmit_time)

### getAgeOutCacheSize

    public int getAgeOutCacheSize()

### printAgeOutCache

    public java.lang.String printAgeOutCache()

### getAgeOutCache

    public AgeOutCache<Address> getAgeOutCache()

### getNumberOfMessagesInReceiveWindows

    public int getNumberOfMessagesInReceiveWindows()

### printRetransmitTableSizes

    public java.lang.String printRetransmitTableSizes()

### compact

    public void compact()

### purgeAndCompact

    public void purgeAndCompact()

### resetStats

    public void resetStats()

  Overrides:
    `resetStats` in class `Protocol`

### dumpStats

    public java.util.Map<java.lang.String,java.lang.Object> dumpStats()

  Overrides:
    `dumpStats` in class `Protocol`

### getTimer

    public TimeScheduler getTimer()

### setTimer

    public void setTimer(TimeScheduler timer)

  Only used for unit tests, don't use !

  Parameters:
    `timer` -

### init

    public void init()
              throws java.lang.Exception

  Description copied from class: `Protocol`
  Called after instance has been created (null constructor) and before protocol is started. Properties are already set. Other protocols are not yet connected and events cannot yet be sent.

  Overrides:
    `init` in class `Protocol`
  Throws:
    `java.lang.Exception` - Thrown if protocol cannot be initialized successfully. This will cause the ProtocolStack to fail, so the channel constructor will throw an exception

### start

    public void start()
               throws java.lang.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:
    `java.lang.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 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`

### stable

    protected void stable(Address sender,
                          long highest_delivered,
                          long highest_seen)

  Purge all messages in window for local_addr, which are <= low. Check if the window's highest received message is > high: if true, retransmit all messages from high - win.high to sender

  Parameters:
    `sender` -
    `highest_delivered` -
    `highest_seen` -

### sendStableMessages

    public void sendStableMessages()

### sendStableMessage

    protected void sendStableMessage(Address dest,
                                     long low,
                                     long high)

### removeConnection

    public void 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 first_seqno,
                           long last_seqno,
                           Address sender)

  Description copied from interface: `Retransmitter.RetransmitCommand`
  Get the missing messages between sequence numbers `first_seqno` and `last_seqno`. This can either be done by sending a retransmit message to destination `sender` (nak-based scheme), or by retransmitting the missing message(s) to `sender` (ack-based scheme).

  Specified by:
    `retransmit` in interface `Retransmitter.RetransmitCommand`
  Parameters:
    `first_seqno` - The sequence number of the first missing message
    `last_seqno` - The sequence number of the last missing message
    `sender` - The destination of the member to which the retransmit request will be sent (nak-based scheme), or to which the message will be retransmitted (ack-based scheme).

### expired

    public void expired(Address key)

  Called by AgeOutCache, to removed expired connections

  Specified by:
    `expired` in interface `AgeOutCache.Handler<Address>`
  Parameters:
    `key` -

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Copyright © 1998-2009 Bela Ban / Red Hat. All Rights Reserved.