Class Digest

java.lang.Object

org.jgroups.util.Digest

All Implemented Interfaces:

Externalizable, Serializable, Streamable

Direct Known Subclasses:

MutableDigest

public class Digest
extends Object
implements Externalizable, Streamable

A message digest, which is used by the PBCAST layer for gossiping (also used by NAKACK for keeping track of current seqnos for all members). It contains pairs of senders and a range of seqnos (low and high), where each sender is associated with its highest and lowest seqnos seen so far. That is, the lowest seqno which was not yet garbage-collected and the highest that was seen so far and is deliverable (or was already delivered) to the application. A range of [0 - 0] means no messages have been received yet.

April 3 2001 (bela): Added high_seqnos_seen member. It is used to disseminate information about the last (highest) message M received from a sender P. Since we might be using a negative acknowledgment message numbering scheme, we would never know if the last message was lost. Therefore we periodically gossip and include the last message seqno. Members who haven't seen it (e.g. because msg was dropped) will request a retransmission. See DESIGN for details.

Version:

$Id: Digest.java,v 1.8.2.1 2008/01/22 10:01:17 belaban Exp $

Author:

Bela Ban

See Also:

• Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	Digest.Entry	Class keeping track of the lowest and highest sequence numbers delivered, and the highest sequence numbers received, per member.

Field Summary

Fields

Modifier and Type	Field	Description
static final Digest	EMPTY_DIGEST
protected static final org.apache.commons.logging.Log	log
protected final Map<Address, Digest.Entry>	senders	Map<Address, Entry>

Constructor Summary

Constructors

Constructor	Description
Digest()	Used for externalization
Digest(int size)
Digest(Map<Address, Digest.Entry> map)	Creates a new digest from an existing map by copying the keys and values from map
Digest(Address sender, long low, long highest_delivered)
Digest(Address sender, long low, long highest_delivered, long highest_received)
Digest(Digest d)

Method Summary

Modifier and Type	Method	Description
boolean	contains(Address sender)
Digest	copy()
Digest	difference(Digest other)
boolean	equals(Object obj)
Digest.Entry	get(Address sender)	Returns the Entry for the given sender.
Map<Address, Digest.Entry>	getSenders()	Returns an unmodifiable map, so modifications will result in exceptions
long	highestDeliveredSeqnoAt(Address sender)
long	highestReceivedSeqnoAt(Address sender)
Digest	highestSequence(Digest other)
boolean	isGreaterThanOrEqual(Digest other)	Returns true if all senders of the current digest have their seqnos >= the ones from other
long	lowSeqnoAt(Address sender)
String	printHighestDeliveredSeqnos()
String	printHighestReceivedSeqnos()
void	readExternal(ObjectInput in)
void	readFrom(DataInputStream in)	Read the state of the current object (including superclasses) from instream Note that the input stream must not be closed
boolean	sameSenders(Digest other)	Compares two digests and returns true if the senders are the same, otherwise false.
long	serializedSize()
int	size()
String	toString()
void	writeExternal(ObjectOutput out)
void	writeTo(DataOutputStream out)	Write the entire state of the current object (including superclasses) to outstream.

Methods inherited from class Object

clone, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Details

EMPTY_DIGEST

public static final Digest EMPTY_DIGEST

senders

protected final Map<Address, Digest.Entry> senders

Map<Address, Entry>

log

protected static final org.apache.commons.logging.Log log

Constructor Details

Digest

public Digest()

Used for externalization

Digest

public Digest(int size)

Digest

public Digest(Map<Address, Digest.Entry> map)

Creates a new digest from an existing map by copying the keys and values from map

Digest

public Digest(Digest d)

Digest

public Digest(Address sender,
 long low,
 long highest_delivered,
 long highest_received)

Digest

public Digest(Address sender,
 long low,
 long highest_delivered)

Method Details

getSenders

public Map<Address, Digest.Entry> getSenders()

Returns an unmodifiable map, so modifications will result in exceptions

equals

public boolean equals(Object obj)

Overrides:

equals in class Object

contains

public boolean contains(Address sender)

get

public Digest.Entry get(Address sender)

Returns the Entry for the given sender. Note that Entry is immutable

sameSenders

public boolean sameSenders(Digest other)

Compares two digests and returns true if the senders are the same, otherwise false.

Parameters:

other -

Returns:

True if senders are the same, otherwise false.

difference

public Digest difference(Digest other)

highestSequence

public Digest highestSequence(Digest other)

size

public int size()

lowSeqnoAt

public long lowSeqnoAt(Address sender)

highestDeliveredSeqnoAt

public long highestDeliveredSeqnoAt(Address sender)

highestReceivedSeqnoAt

public long highestReceivedSeqnoAt(Address sender)

isGreaterThanOrEqual

public boolean isGreaterThanOrEqual(Digest other)

Returns true if all senders of the current digest have their seqnos >= the ones from other

Parameters:

other -

Returns:

copy

public Digest copy()

toString

public String toString()

Overrides:

toString in class Object

printHighestDeliveredSeqnos

public String printHighestDeliveredSeqnos()

printHighestReceivedSeqnos

public String printHighestReceivedSeqnos()

writeExternal

public void writeExternal(ObjectOutput out)
                   throws IOException

Specified by:

writeExternal in interface Externalizable

Throws:

IOException

readExternal

public void readExternal(ObjectInput in)
                  throws IOException,
ClassNotFoundException

Specified by:

readExternal in interface Externalizable

Throws:

IOException

ClassNotFoundException

writeTo

public void writeTo(DataOutputStream out)
             throws IOException

Description copied from interface: Streamable

Write the entire state of the current object (including superclasses) to outstream. Note that the output stream must not be closed

Specified by:

writeTo in interface Streamable

Throws:

IOException

readFrom

public void readFrom(DataInputStream in)
              throws IOException,
IllegalAccessException,
InstantiationException

Description copied from interface: Streamable

Read the state of the current object (including superclasses) from instream Note that the input stream must not be closed

Specified by:

readFrom in interface Streamable

Throws:

IOException

IllegalAccessException

InstantiationException

serializedSize

public long serializedSize()