/** {@inheritDoc} */
@Override
public final Set<Entry> retrieveEntries(ID id) throws CommunicationException {
// Possible, but rare situation: a new node has joined which now is
// responsible for the id!
if (this.references.getPredecessor() != null
&& !id.isInInterval(this.references.getPredecessor().getNodeID(), this.nodeID)) {
this.logger.fatal(
"The rare situation has occured at time "
+ System.currentTimeMillis()
+ ", id to look up="
+ id
+ ", id of local node="
+ this.nodeID
+ ", id of predecessor="
+ this.references.getPredecessor().getNodeID());
return this.references.getPredecessor().retrieveEntries(id);
}
// return entries from local repository
// for this purpose create a copy of the Set in order to allow the
// thread retrieving the entries to modify the Set without modifying the
// internal Set of entries. sven
return this.entries.getEntries(id);
}
/**
* Determines the closest preceding node for the given ID based on finger table, successor list,
* and predecessor, but without testing the node's liveliness.
*
* @param key ID to find closest preceding node for.
* @throws NullPointerException If ID is <code>null</code>.
* @return Reference on closest preceding node.
*/
final synchronized Node getClosestPrecedingNode(ID key) {
if (key == null) {
NullPointerException e = new NullPointerException("ID may not be null!");
this.logger.error("Null pointer", e);
throw e;
}
Map<ID, Node> foundNodes = new HashMap<ID, Node>();
// determine closest preceding reference of finger table
Node closestNodeFT = this.fingerTable.getClosestPrecedingNode(key);
if (closestNodeFT != null) {
foundNodes.put(closestNodeFT.getNodeID(), closestNodeFT);
}
// determine closest preceding reference of successor list
Node closestNodeSL = this.successorList.getClosestPrecedingNode(key);
if (closestNodeSL != null) {
foundNodes.put(closestNodeSL.getNodeID(), closestNodeSL);
}
// predecessor is appropriate only if it precedes the given id
Node predecessorIfAppropriate = null;
if (this.predecessor != null && key.isInInterval(this.predecessor.getNodeID(), this.localID)) {
predecessorIfAppropriate = this.predecessor;
foundNodes.put(this.predecessor.getNodeID(), predecessor);
}
// with three references which may be null, there are eight (8) cases we
// have to enumerate...
Node closestNode = null;
List<ID> orderedIDList = new ArrayList<ID>(foundNodes.keySet());
orderedIDList.add(key);
int sizeOfList = orderedIDList.size();
// size of list must be greater than one to not only contain the key.
// if (sizeOfList > 1) {
/*
* Sort list in ascending order
*/
Collections.sort(orderedIDList);
/*
* The list item with one index lower than that of the key must be the
* id of the closest predecessor or the key.
*/
int keyIndex = orderedIDList.indexOf(key);
/*
* As all ids are located on a ring if the key is the first item in the
* list we have to select the last item as predecessor with help of this
* calculation.
*/
int index = (sizeOfList + (keyIndex - 1)) % sizeOfList;
/*
* Get the references to the node from the map of collected nodes.
*/
ID idOfclosestNode = orderedIDList.get(index);
closestNode = foundNodes.get(idOfclosestNode);
if (closestNode == null) {
throw new NullPointerException("closestNode must not be null!");
}
/*
* Following code is too complicated.
*/
// if (closestNodeFT == null) {
// if (closestNodeSL == null) {
// if (predecessorIfAppropriate == null) {
// // no reference is appropriate
// closestNode = null;
// } else {
// // only predecessor is appropriate (case should not occur,
// // but anyway...
// closestNode = predecessorIfAppropriate;
// }
// } else {
// if (predecessorIfAppropriate == null) {
// // only reference of successor list is appropriate
// closestNode = closestNodeSL;
// } else {
// // either predecessor or reference of successor list is
// // appropriate; determine one of both
// if (predecessorIfAppropriate.nodeID.isInInterval(
// closestNodeSL.nodeID, key)) {
// closestNode = predecessorIfAppropriate;
// } else {
// closestNode = closestNodeSL;
// }
// }
// }
// } else {
// if (closestNodeSL == null) {
// if (predecessorIfAppropriate == null) {
// // only reference of finger table is appropriate
// closestNode = closestNodeFT;
// } else {
// // either predecessor or reference of finger table is
// // appropriate; determine one of both
// if (predecessorIfAppropriate.nodeID.isInInterval(
// closestNodeFT.nodeID, key)) {
// closestNode = predecessorIfAppropriate;
// } else {
// closestNode = closestNodeFT;
// }
// }
// } else {
// if (predecessorIfAppropriate == null) {
// // either reference of successor list or reference of finger
// // table is appropriate; determine one of both
// if (closestNodeSL.nodeID.isInInterval(closestNodeFT.nodeID,
// key)) {
// closestNode = closestNodeSL;
// } else {
// closestNode = closestNodeFT;
// }
// } else {
// // either of the three reference is appropriate; determine
// // first one of the references of successor list and finger
// // table is more appropriate and afterwards compare with
// // predecessor
// if (closestNodeSL.nodeID.isInInterval(closestNodeFT.nodeID,
// key)) {
// if (predecessorIfAppropriate.nodeID.isInInterval(
// closestNodeSL.nodeID, key)) {
// closestNode = predecessorIfAppropriate;
// } else {
// closestNode = closestNodeSL;
// }
// } else {
// if (predecessorIfAppropriate.nodeID.isInInterval(
// closestNodeFT.nodeID, key)) {
// closestNode = predecessorIfAppropriate;
// } else {
// closestNode = closestNodeFT;
// }
// }
// }
// }
// }
if (this.logger.isEnabledFor(DEBUG)) {
this.logger.debug(
"Closest preceding node of ID "
+ key
+ " at node "
+ this.localID.toString()
+ " is "
+ closestNode.getNodeID()
+ " with closestNodeFT="
+ (closestNodeFT == null ? "null" : "" + closestNodeFT.getNodeID())
+ " and closestNodeSL="
+ (closestNodeSL == null ? "null" : "" + closestNodeSL.getNodeID())
+ " and predecessor (only if it precedes given ID)="
+ (predecessorIfAppropriate == null
? "null"
: "" + predecessorIfAppropriate.getNodeID()));
}
return closestNode;
}