/**
* Add a node to the overlay network topology.
*
* @param data unused for this hash ring; nodes are placed evenly based on current topology
* characteristics. You may safely pass 'null' to this method.
* @return the location of the new node in the hash space.
*/
@Override
public BigInteger addNode(T data) throws HashTopologyException, HashException {
/* Edge case: when there are no entries in the hash ring yet. */
if (entryMap.values().size() == 0) {
BigInteger pos;
if (randomize) {
/* Find a random location to start with */
pos = function.randomHash();
} else {
pos = BigInteger.ZERO;
}
HashRingEntry firstEntry = new HashRingEntry(pos);
entryMap.put(pos, firstEntry);
return pos;
}
/* Edge case: only one entry in the hash ring */
if (entryMap.values().size() == 1) {
HashRingEntry firstEntry = entryMap.values().iterator().next();
BigInteger halfSize = maxHash.divide(BigInteger.valueOf(2));
BigInteger secondPos = firstEntry.position.add(halfSize);
if (secondPos.compareTo(maxHash) > 0) {
secondPos = secondPos.subtract(maxHash);
}
HashRingEntry secondEntry = new HashRingEntry(secondPos, firstEntry);
firstEntry.neighbor = secondEntry;
entryMap.put(secondPos, secondEntry);
return secondPos;
}
/* Find the largest empty span of hash space */
BigInteger largestSpan = BigInteger.ZERO;
HashRingEntry largestEntry = null;
for (HashRingEntry entry : entryMap.values()) {
BigInteger len = lengthBetween(entry, entry.neighbor);
if (len.compareTo(largestSpan) > 0) {
largestSpan = len;
largestEntry = entry;
}
}
if (largestEntry == null) {
return BigInteger.ONE.negate();
}
/* Put the new node in the middle of the largest span */
BigInteger half = half(largestEntry, largestEntry.neighbor);
addRingEntry(half, largestEntry);
return half;
}
/**
* Insert a node into the hash ring internal data structures. Nodes are relinked with the proper
* neighbors.
*
* @param position place in the hash space
* @param predecessor the predecessor node in the hash space.
*/
private void addRingEntry(BigInteger position, HashRingEntry predecessor)
throws HashTopologyException {
if (entryMap.get(position) != null) {
/* Something is already here! */
System.out.println(position);
throw new HashTopologyException("Hash space exhausted!");
}
HashRingEntry newEntry = new HashRingEntry(position, predecessor.neighbor);
predecessor.neighbor = newEntry;
entryMap.put(position, newEntry);
}