A message digest, which is used e.g. 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.
add
public void add(Address sender,
long low_seqno,
long high_seqno)
add
public void add(Address sender,
long low_seqno,
long high_seqno,
long high_seqno_seen)
contains
public boolean contains(Address sender)
getIndex
public int getIndex(Address sender)
highSeqnoAt
public long highSeqnoAt(int index)
highSeqnoAt
public long highSeqnoAt(Address sender)
highSeqnoSeenAt
public long highSeqnoSeenAt(int index)
highSeqnoSeenAt
public long highSeqnoSeenAt(Address sender)
incrementHighSeqno
public void incrementHighSeqno(Address sender)
Increment the sender's high_seqno by 1
lowSeqnoAt
public long lowSeqnoAt(int index)
merge
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)
merge
public void merge(Digest d)
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.
printHighSeqnos
public String printHighSeqnos()
printHighSeqnosSeen
public String printHighSeqnosSeen()
readExternal
public void readExternal(ObjectInput in)
throws IOException,
ClassNotFoundException
reset
public void reset(int size)
resetAt
public void resetAt(int index)
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.
sameSenders
public boolean sameSenders(Digest other)
Compares two digests and returns true if the senders are the same, otherwise false
senderAt
public Address senderAt(int index)
setHighSeqnoAt
public void setHighSeqnoAt(int index,
long high_seqno)
setHighSeqnoAt
public void setHighSeqnoAt(Address sender,
long high_seqno)
setHighSeqnoSeenAt
public void setHighSeqnoSeenAt(int index,
long high_seqno_seen)
setHighSeqnoSeenAt
public void setHighSeqnoSeenAt(Address sender,
long high_seqno_seen)
setLowSeqnoAt
public void setLowSeqnoAt(int index,
long low_seqno)
toString
public String toString()
writeExternal
public void writeExternal(ObjectOutput out)
throws IOException