org.jgroups.protocols.pbcast
Class Digest
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.
Author: Bela Ban
Nested Class Summary |
static class | Digest.Entry
Class keeping track of the lowest and highest sequence numbers delivered, and the highest
sequence numbers received, per member |
Method Summary |
void | add(Address sender, long low_seqno, long high_seqno) |
void | add(Address sender, long low_seqno, long high_seqno, long high_seqno_seen) |
void | add(Digest d) |
void | clear() |
boolean | contains(Address sender) |
Digest | copy() |
boolean | equals(Object obj) |
Digest.Entry | get(Address sender) |
long | highSeqnoAt(Address sender) |
long | highSeqnoSeenAt(Address sender) |
void | incrementHighSeqno(Address sender)
Increments the sender's high_seqno by 1. |
long | lowSeqnoAt(Address sender) |
void | merge(Digest d)
Adds a digest to this digest. |
void | merge(Address sender, long low_seqno, long high_seqno, long high_seqno_seen)
Similar to add(), but if the sender already exists, its seqnos will be modified (no new entry) as follows:
- this.low_seqno=min(this.low_seqno, low_seqno)
- this.high_seqno=max(this.high_seqno, high_seqno)
- this.high_seqno_seen=max(this.high_seqno_seen, high_seqno_seen)
If the sender doesn not exist, a new entry will be added (provided there is enough space) |
String | printHighSeqnos() |
String | printHighSeqnosSeen() |
void | readExternal(ObjectInput in) |
void | readFrom(DataInputStream in) |
void | replace(Digest d) |
void | resetAt(Address sender)
Resets the seqnos for the sender at 'index' to 0. |
boolean | sameSenders(Digest other)
Compares two digests and returns true if the senders are the same, otherwise false. |
long | serializedSize() |
boolean | set(Address sender, long low_seqno, long high_seqno, long high_seqno_seen) |
void | setHighestDeliveredAndSeenSeqnos(Address sender, long high_seqno, long high_seqno_seen) |
void | setHighSeqnoAt(Address sender, long high_seqno) |
void | setHighSeqnoSeenAt(Address sender, long high_seqno_seen) |
int | size() |
String | toString() |
void | writeExternal(ObjectOutput out) |
void | writeTo(DataOutputStream out) |
protected static final Log log
public Digest()
public Digest(int size)
public void add(
Address sender, long low_seqno, long high_seqno)
public void add(
Address sender, long low_seqno, long high_seqno, long high_seqno_seen)
public void clear()
public boolean contains(
Address sender)
public boolean equals(Object obj)
public long highSeqnoAt(
Address sender)
public long highSeqnoSeenAt(
Address sender)
public void incrementHighSeqno(
Address sender)
Increments the sender's high_seqno by 1.
public long lowSeqnoAt(
Address sender)
Adds a digest to this digest. This digest must have enough space to add the other digest; otherwise an error
message will be written. For each sender in the other digest, the merge() method will be called.
public void merge(
Address sender, long low_seqno, long high_seqno, long high_seqno_seen)
Similar to add(), but if the sender already exists, its seqnos will be modified (no new entry) as follows:
- this.low_seqno=min(this.low_seqno, low_seqno)
- this.high_seqno=max(this.high_seqno, high_seqno)
- this.high_seqno_seen=max(this.high_seqno_seen, high_seqno_seen)
If the sender doesn not exist, a new entry will be added (provided there is enough space)
public String printHighSeqnos()
public String printHighSeqnosSeen()
public void readExternal(ObjectInput in)
public void readFrom(DataInputStream in)
public void resetAt(
Address sender)
Resets the seqnos for the sender at 'index' to 0. This happens when a member has left the group,
but it is still in the digest. Resetting its seqnos ensures that no-one will request a message
retransmission from the dead member.
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.
public long serializedSize()
public boolean set(
Address sender, long low_seqno, long high_seqno, long high_seqno_seen)
public void setHighestDeliveredAndSeenSeqnos(
Address sender, long high_seqno, long high_seqno_seen)
public void setHighSeqnoAt(
Address sender, long high_seqno)
public void setHighSeqnoSeenAt(
Address sender, long high_seqno_seen)
public int size()
public String toString()
public void writeExternal(ObjectOutput out)
public void writeTo(DataOutputStream out)
Copyright ? 1998-2005 Bela Ban. All Rights Reserved.