/*
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Created on Jun 9, 2008
*/
package com.bigdata.btree;
import java.util.NoSuchElementException;
import org.apache.log4j.Logger;
import com.bigdata.btree.Leaf.ILeafListener;
import com.bigdata.btree.isolation.IsolatedFusedView;
import com.bigdata.btree.view.FusedView;
import com.bigdata.io.DataOutputBuffer;
import com.bigdata.mdi.LocalPartitionMetadata;
import com.bigdata.util.BytesUtil;
/**
* Class supporting random access to tuples and sequential tuple-based cursor
* movement for an {@link AbstractBTree}.
* <p>
* The tuple position is defined in terms of the current key on which the tuple
* "rests". If there is no tuple associated with that key in the index then you
* will not be able to read the value or optional metadata (delete markers or
* version timestamps) for the key. If the key is associated with a deleted
* tuple then you can not read the value associated with the key, but you can
* read the (optional) delete marker and version metadata if the cursor was
* provisioned to visit deleted tuples.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
*/
abstract public class AbstractBTreeTupleCursor<I extends AbstractBTree, L extends Leaf, E>
implements ITupleCursor2<E> {
protected static final Logger log = Logger
.getLogger(AbstractBTreeTupleCursor.class);
protected static final boolean INFO = log.isInfoEnabled();
protected static final boolean DEBUG = log.isDebugEnabled();
/*
* Some frequently used log messages.
*/
private static transient final String LOG_NO_CURSOR_POSITION = "No cursor position";
private static transient final String LOG_NO_SUCCESSOR = "No successor";
private static transient final String LOG_NO_PREDECESSOR = "No predecessor";
private static transient final String LOG_CURSOR_POSITION_NOT_VISITABLE = "Cursor position is not visitable";
/** From the ctor. */
protected final I btree;
/** From the ctor. */
protected final Tuple<E> tuple;
/** from the ctor. */
protected final byte[] fromKey;
/** from the ctor. */
protected final byte[] toKey;
/** true iff the cursor was provisioned to visit deleted tuples. */
final protected boolean visitDeleted;
@Override
final public I getIndex() {
return btree;
}
/** {@inheritDoc}<p>From the ctor. */
@Override
final public byte[] getFromKey() {
return fromKey;
}
/** {@inheritDoc}<p>From the ctor. */
@Override
final public byte[] getToKey() {
return toKey;
}
@Override
final public boolean isDeletedTupleVisitor() {
return visitDeleted;
}
/**
* The current cursor position (initially <code>null</code>).
*/
protected AbstractCursorPosition<L,E> currentPosition;
// /**
// * A temporary cursor position used by {@link #hasNext()} and
// * {@link #hasPrior()}.
// */
// private AbstractCursorPosition<L,E> tempPosition;
@Override
final public boolean isCursorPositionDefined() {
return currentPosition != null;
}
/**
* The cursor position is undefined until {@link #first(boolean)},
* {@link #last(boolean)}, or {@link #seek(byte[])} is used to position the
* cursor.
*
* @throws IllegalStateException
* if the cursor position is not defined.
*/
final protected void assertCursorPositionDefined() {
if (!isCursorPositionDefined())
throw new IllegalStateException();
}
/**
* Create a new cursor.
*
* @param btree
* The B+Tree whose tuples are visited by this cursor.
* @param tuple
* The tuple into which the data will be copied.
* {@link IRangeQuery#KEYS} MUST be specified for that
* {@link Tuple}. The keys of the index will always be copied
* into the {@link Tuple}, but the <i>flags</i> on the
* {@link Tuple} will determine whether the values paired to the
* key will be copied and whether or not deleted tuples will be
* visited.
* @param fromKey
* The optional inclusive lower bound.
* @param toKey
* The optional exclusive upper bound.
*
* @throws IllegalArgumentException
* if the <i>btree</i> is <code>null</code>.
* @throws IllegalArgumentException
* if the <i>tuple</i> is <code>null</code>.
* @throws IllegalArgumentException
* if the <i>tuple</i> is not associated with that <i>btree</i>.
* @throws IllegalArgumentException
* if the <i>fromKey</i> is GTE the <i>toKey</i>.
*/
public AbstractBTreeTupleCursor(final I btree, final Tuple<E> tuple,
final byte[] fromKey, final byte[] toKey) {
if (btree == null)
throw new IllegalArgumentException();
if (tuple == null)
throw new IllegalArgumentException();
// if (tuple.getBTree() != btree)
// throw new IllegalArgumentException();
if (fromKey != null) {
assert btree.rangeCheck(fromKey, false/* allowUpperBound */);
}
if (toKey != null) {
assert btree.rangeCheck(toKey, true/* allowUpperBound */);
}
if (fromKey != null && toKey != null) {
if (BytesUtil.compareBytes(fromKey, toKey) > 0) {
throw new IllegalArgumentException(
"toKey LT fromKey: fromKey="
+ BytesUtil.toString(fromKey) + ", toKey="
+ BytesUtil.toString(toKey));
}
}
this.btree = btree;
this.tuple = tuple;
this.fromKey = fromKey;
this.toKey = toKey;
this.visitDeleted = ((tuple.flags() & IRangeQuery.DELETED) != 0);
// Note: the cursor position is NOT defined!
currentPosition = null;
// nextPosition = priorPosition = null;
// /*
// * Note: This is used to minimize the costs associated with testing for
// * a prior/next visitable tuple. It is initially set to the first
// * position, but this is an arbitrary choice. It's state is updated from
// * the [currentPosition] each time before it is used.
// */
// tempPosition = firstPosition();
}
@Override
public String toString() {
return "Cursor{fromKey=" + BytesUtil.toString(fromKey) + ", toKey="
+ BytesUtil.toString(toKey) + ", currentKey="
+ BytesUtil.toString(currentKey()) + ", visitDeleted="
+ visitDeleted + "}";
}
/**
* Return <code>true</code> if the <i>key</i> lies inside of the optional
* half-open range constraint.
*
* @return <code>true</code> unless the <i>key</i> is LT [fromKey] or GTE
* [toKey].
*/
final protected boolean rangeCheck(final byte[] key) {
return BytesUtil.rangeCheck(key, fromKey, toKey);
// if (fromKey == null && toKey == null) {
//
// // no range constraint.
// return true;
//
// }
//
// if (fromKey != null) {
//
// if (BytesUtil.compareBytes(key, fromKey) < 0) {
//
// if (DEBUG) {
//
// log.debug("key=" + BytesUtil.toString(key) + " LT fromKey"
// + BytesUtil.toString(fromKey));
//
// }
//
// // key is LT then the optional inclusive lower bound.
// return false;
//
// }
//
// }
//
// if (toKey != null) {
//
// if (BytesUtil.compareBytes(key, toKey) >= 0) {
//
// if (DEBUG) {
//
// log.debug("key=" + BytesUtil.toString(key) + " GTE toKey"
// + BytesUtil.toString(toKey));
//
// }
//
// // key is GTE the optional exclusive upper bound
// return false;
//
// }
//
// }
//
// return true;
}
/**
* The optional inclusive lower bound. If the <i>fromKey</i> constraint was
* specified when the {@link ITupleCursor} was created, then that value is
* returned. Otherwise, if the index is an index partition then the
* {@link LocalPartitionMetadata#getLeftSeparatorKey()} is returned.
* Finally, <code>null</code> is returned if there is no inclusive lower
* bound.
*/
final protected byte[] getInclusiveLowerBound() {
final byte[] fromKey;
if (this.fromKey != null) {
fromKey = this.fromKey;
} else {
IndexMetadata md = getIndex().getIndexMetadata();
LocalPartitionMetadata pmd = md.getPartitionMetadata();
if (pmd != null) {
fromKey = pmd.getLeftSeparatorKey();
} else {
fromKey = null;
}
}
return fromKey;
}
/**
* The optional exclusive upper bound. If the <i>toKey</i> constraint was
* specified when the {@link ITupleCursor} was created, then that value is
* returned. Otherwise, if the index is an index partition then the
* {@link LocalPartitionMetadata#getRightSeparatorKey()} is returned.
* Finally, <code>null</code> is returned if there is no exclusive upper
* bound.
*/
final protected byte[] getExclusiveUpperBound() {
final byte[] toKey;
if(this.toKey!=null) {
toKey = this.toKey;
} else {
IndexMetadata md = getIndex().getIndexMetadata();
LocalPartitionMetadata pmd = md.getPartitionMetadata();
if (pmd != null) {
toKey = pmd.getRightSeparatorKey();
} else {
/*
* Note: unlike the inclusive lower bound, the exclusive upper
* bound can not be defined in the absence of explicit
* constraints since we allow variable length keys.
*/
toKey = null;
}
}
return toKey;
}
/**
* Return a new {@link ICursorPosition} from the <i>leafCursor</i>, tuple
* <i>index</i>, and <i>key</i>
*
* @param leafCursor
* The {@link ILeafCursor} (already positioned on the desired
* leaf).
* @param index
* The index of the tuple corresponding to the <i>key</i> within
* the current leaf of the <i>leafCursor</i> -or- a negative
* integer representing the insertion point for the <i>key</i>
* if the <i>key</i> is spanned by that leaf but there is no
* tuple for that <i>key</i> in the <i>leaf</i>.
* @param key
* The key.
*
* @return The new {@link ICursorPosition}.
*
* @throws IllegalArgumentException
* if <i>leafCursor</i> is <code>null</code>.
* @throws IllegalArgumentException
* if <i>key</i> is <code>null</code>.
*/
abstract protected AbstractCursorPosition<L, E> newPosition(ILeafCursor<L> leafCursor,
int index, byte[] key);
/**
* Return a clone of the given {@link ICursorPosition} designed for use by
* {@link #hasNext()} and {@link #hasPrior()} (temporary test without
* side-effects).
*
* @param p
* The cursor position.
*
* @return A clone of that cursor position.
*
* @deprecated This is never used.
*/
abstract protected AbstractCursorPosition<L, E> newTemporaryPosition(ICursorPosition<L, E> p);
/**
* Return a new {@link ICursorPosition} that is initially positioned on the
* inclusive lower bound and on <code>new byte[]{}</code> if there is no
* inclusive lower bound.
*/
@SuppressWarnings("unchecked")
final protected AbstractCursorPosition<L,E> firstPosition() {
byte[] key = getInclusiveLowerBound();
if (key == null) {
key = BytesUtil.EMPTY;
}
final ILeafCursor<L> leafCursor = btree.newLeafCursor(key);
final int index = leafCursor.leaf().getKeys().search(key);
return newPosition(leafCursor, index, key);
}
/**
* Return a new {@link ICursorPosition} that is initially positioned on the
* given <i>key</i>.
*
* @param leaf
* A leaf (required).
* @param key
* A key that is spanned by that leaf (required, but there is no
* requirement that a tuple corresponding to that key is present
* in the leaf).
*
* @return The new {@link ICursorPosition}.
*
* @throws IllegalArgumentException
* if the key is <code>null</code>.
* @throws KeyOutOfRangeException
* if the key lies outside of the optional constrain on the
* {@link ITupleCursor}.
*/
@SuppressWarnings("unchecked")
final protected AbstractCursorPosition<L,E> newPosition(final byte[] key) {
if (key == null)
throw new IllegalArgumentException();
if (!rangeCheck(key))
throw new KeyOutOfRangeException("key=" + BytesUtil.toString(key)
+ ", fromKey=" + BytesUtil.toString(fromKey) + ", toKey="
+ BytesUtil.toString(toKey));
final ILeafCursor<L> leafCursor = btree.newLeafCursor(key);
final int index = leafCursor.leaf().getKeys().search(key);
return newPosition(leafCursor, index, key);
}
/**
* Return a new {@link ICursorPosition} that is initially positioned on the
* last tuple in the key-range (does not skip over deleted tuples).
* <p>
* Note: If there is no exclusive upper bound and there are no tuples in the
* index then the position is set to <code>new byte[]{}</code> (the same
* behavior as first for an empty index).
*
* @return The leaf spanning {@link #getExclusiveUpperBound()}.
*/
@SuppressWarnings("unchecked")
final protected AbstractCursorPosition<L,E> lastPosition() {
byte[] key = getExclusiveUpperBound();
final ILeafCursor<L> leafCursor;
int index;
if (key == null) {
/*
* Since there is no exclusive upper bound, use the last leaf in the
* B+Tree.
*/
leafCursor = btree.newLeafCursor(SeekEnum.Last);
final L leaf = leafCursor.leaf();
/*
* Use the last key in the leaf.
*/
index = leaf.getKeyCount() - 1;
if (index < 0) {
/*
* This is an insertion point which means that the leaf was
* empty. This case only occurs for an empty root leaf.
*/
key = BytesUtil.EMPTY;
} else {
/*
* Lookup the key in the leaf at that index.
*/
key = leaf.getKeys().get(index);
}
} else {
/*
* Since there is an exclusive upper bound, lookup the leaf spanning
* that key.
*/
leafCursor = btree.newLeafCursor(key);
L leaf = leafCursor.leaf();
/*
* Find the position (or the insertion point) of the key in the
* leaf.
*/
index = leaf.getKeys().search(key);
if (index == 0 || index == -1) {
/*
* Either the key exists in at index ZERO (0) in the leaf -or-
* the insertion point is -1, which means that the key would
* be inserted at index ZERO (0) in
* the leaf. Either way, we want to start the cursor at the
* last tuple in the previous leaf.
*/
// Note: Will be null if there is no prior leaf.
leaf = leafCursor.prior();
// Start at the last tuple in the prior leaf.
index = leaf == null ? 0 : leaf.getKeyCount() - 1;
} else {
if (index > 0) {
/*
* The key exists in the leaf at some position GT the first
* index in the leaf. Since the toKey is an exclusive upper
* bound, we subtract one to start the cursor at the prior
* tuple in the leaf.
*
* Note: The case where index == 0 was handled above.
*/
index--;
} else {
/*
* Since index is an insertion point, it is one index beyond
* the last tuple that we should visit. Therefore we add one
* to the insertion point, which has the effect of shifting
* the index position down by one in the leaf.
*
* Note: The case where index == -1 was handled above.
* Therefore index++ can not turn the insertion point into a
* valid index.
*/
index++;
}
}
}
return newPosition(leafCursor, index, key);
}
@Override
public byte[] currentKey() {
if(!isCursorPositionDefined()) {
if (DEBUG)
log.debug(LOG_NO_CURSOR_POSITION);
// the cursor position is not defined.
return null;
}
return currentPosition.getKey();
}
@Override
public ITuple<E> tuple() {
if(!isCursorPositionDefined()) {
if (DEBUG)
log.debug(LOG_NO_CURSOR_POSITION);
// the cursor position is not defined.
return null;
}
/*
* Copy out the state of the current tuple if the cursor position is on
* a tuple and if that tuple is visitable.
*/
return currentPosition.get(tuple);
}
@Override
public ITuple<E> first() {
// // clear references since no longer valid.
// nextPosition = priorPosition = null;
// new position on the inclusive lower bound.
currentPosition = firstPosition();
// Scan until we reach the first visitable tuple.
if (!currentPosition.forwardScan(false/*skipCurrent*/,false/*testOnly*/)) {
// discard the current position since we have scanned beyond the end of the index / key range.
currentPosition = null;
if (DEBUG)
log.debug(LOG_NO_CURSOR_POSITION);
// Nothing visitable.
return null;
}
// Copy the data into [tuple] and return [tuple].
return currentPosition.get(tuple);
}
@Override
public ITuple<E> last() {
// // clear references since no longer valid.
// nextPosition = priorPosition = null;
// new position after all defined keys.
currentPosition = lastPosition();
// Scan backwards until we reach the first visitable tuple.
if(!currentPosition.reverseScan(false/*skipCurrent*/,false/*testOnly*/)) {
// discard the current position since we have scanned beyond the start of the index / key range.
currentPosition = null;
if (DEBUG)
log.debug(LOG_NO_CURSOR_POSITION);
// Nothing visitable.
return null;
}
// Copy the data into [tuple] and return [tuple].
return currentPosition.get(tuple);
}
@Override
final public ITuple<E> seek(Object key) {
if (key == null)
throw new IllegalArgumentException();
return seek(getIndex().getIndexMetadata().getTupleSerializer()
.serializeKey(key));
}
@Override
public ITuple<E> seek(final byte[] key) {
if (key == null)
throw new IllegalArgumentException();
if (DEBUG)
log.debug("key="+BytesUtil.toString(key));
// // clear references since no longer valid.
// nextPosition = priorPosition = null;
// new position is that key.
currentPosition = newPosition(key);
// Copy the data into [tuple].
return currentPosition.get(tuple);
}
// /**
// * Scan to the next cursor position having a visitable tuple.
// *
// * @param pos
// * A cursor position (required).
// * @param skipCurrent
// * true if the tuple at the current cursor position should be
// * skipped over.
// *
// * @return The next cursor position -or- <code>null</code> if there is no
// * next cursor position having a visitable tuple.
// */
// protected AbstractCursorPosition<L, E> nextPosition(
// AbstractCursorPosition<L, E> pos, boolean skipCurrent) {
//
// assert pos != null;
//
// if (!pos.forwardScan(skipCurrent)) {
//
// // no visitable predecessor.
// if (DEBUG)
// log.debug(LOG_NO_PREDECESSOR);
//
// return null;
//
// }
//
// return pos;
//
// }
//
// /**
// * Scan to the prior cursor position having a visitable tuple.
// *
// * @param pos
// * A cursor position (required).
// * @param skipCurrent
// * true if the tuple at the current cursor position should be
// * skipped over.
// *
// * @return The prior cursor position -or- <code>null</code> if there is no
// * prior cursor position having a visitable tuple.
// */
// protected AbstractCursorPosition<L, E> priorPosition(
// AbstractCursorPosition<L, E> pos, boolean skipCurrent) {
//
// assert pos != null;
//
// if (!pos.reverseScan(skipCurrent)) {
//
// // no visitable predecessor.
// if (DEBUG)
// log.debug(LOG_NO_PREDECESSOR);
//
// return null;
//
// }
//
// return pos;
//
// }
/**
* {@inheritDoc}
* <p>
* Note: This is lighter weight than {@link #hasNext()} and {@link #next()}
* since it does not need to scan to verify that the next position exists
* before visiting that tuple.
*/
@Override
public ITuple<E> nextTuple() {
if(!isCursorPositionDefined()) {
// Cursor position is not defined.
if(DEBUG)
log.debug(LOG_NO_CURSOR_POSITION);
return null;
}
if(!currentPosition.forwardScan(true/*skipCurrent*/,false/*testOnly*/)) {
// // no visitable successor.
// currentPosition = null;
if (DEBUG)
log.debug(LOG_NO_SUCCESSOR);
return null;
}
return currentPosition.get(tuple);
}
@Override
public ITuple<E> next() {
final ITuple<E> t;
if (!isCursorPositionDefined()) {
t = first();
} else {
t = nextTuple();
}
if( t == null) {
throw new NoSuchElementException();
}
return t;
// if (!hasNext())
// throw new NoSuchElementException();
//
// // update the current position.
// currentPosition = nextPosition;
//
// // clear references since no longer valid.
// nextPosition = priorPosition = null;
//
// // Copy the data into [tuple] and return [tuple].
// return currentPosition.get(tuple);
}
@Override
public boolean hasNext() {
// // the next position is already known.
// if (nextPosition != null) return true;
final boolean skipCurrent;
final AbstractCursorPosition<L,E> pos;
if (!isCursorPositionDefined()) {
/*
* Note: In order to have the standard iterator semantics we
* start a new scan if the cursor position is undefined.
*/
pos = firstPosition();
/*
* Don't skip the first position if it is visitable.
*/
skipCurrent = false;
} else {
/*
* The cursor position was already defined we will skip the current
* tuple when scanning forward to the next visitable tuple.
*/
skipCurrent = true;
// if (tempPosition == null) {
//
// pos = tempPosition = newTemporaryPosition(currentPosition);
//
// } else {
//
// pos = tempPosition;
//
// pos.seek(currentPosition);
//
// }
// pos = newTemporaryPosition(currentPosition);
pos = currentPosition;
}
if (!pos.forwardScan(skipCurrent,true/*testOnly*/)) {
if (DEBUG)
log.debug(LOG_NO_SUCCESSOR);
// nothing visitable.
return false;
}
if (DEBUG)
log.debug(pos.toString());
// found something visitable.
return true;
}
/**
* {@inheritDoc}
* <p>
* Note: This is lighter weight than {@link #hasNext()} and {@link #next()}
* since it does not need to scan to verify that the prior position exists
* before visiting that tuple.
*/
@Override
public ITuple<E> priorTuple() {
if(!isCursorPositionDefined()) {
// Cursor position is not defined.
if(DEBUG)
log.debug(LOG_NO_CURSOR_POSITION);
return null;
}
if(!currentPosition.reverseScan(true/*skipCurrent*/,false/*testOnly*/)) {
if (DEBUG)
log.debug(LOG_NO_PREDECESSOR);
return null;
}
return currentPosition.get(tuple);
}
@Override
public ITuple<E> prior() {
final ITuple<E> t;
if (!isCursorPositionDefined()) {
t = last();
} else {
t = priorTuple();
}
if (t == null) {
throw new NoSuchElementException();
}
return t;
// if(!hasPrior()) throw new NoSuchElementException();
//
// // update the current position.
// currentPosition = priorPosition;
//
// // clear references since no longer valid.
// nextPosition = priorPosition = null;
//
// // Copy the data into [tuple] and return [tuple].
// return currentPosition.get(tuple);
}
@Override
public boolean hasPrior() {
// // the prior position is already known.
// if (priorPosition != null) return true;
final boolean skipCurrent;
final AbstractCursorPosition<L,E> pos;
if (!isCursorPositionDefined()) {
/*
* Note: This makes hasPrior() and prior() have semantics exactly
* parallel to those of the standard iterator. See hasNext() for
* details.
*/
pos = lastPosition();
/*
* Don't skip the last position if it is a visitable tuple.
*/
skipCurrent = false;
} else {
/*
* The cursor position was already defined so scan backward
* (skipping the current tuple) to the previous visitable tuple.
*/
skipCurrent = true;
// if (tempPosition == null) {
//
// pos = tempPosition = newTemporaryPosition(currentPosition);
//
// } else {
//
// pos = tempPosition;
//
// pos.seek(currentPosition);
//
// }
// pos = newTemporaryPosition(currentPosition);
pos = currentPosition;
}
if (!pos.reverseScan(skipCurrent,true/*testOnly*/)) {
if (DEBUG)
log.debug(LOG_NO_PREDECESSOR);
// nothing visitable.
return false;
}
if (DEBUG)
log.debug(pos.toString());
// found something visitable.
return true;
}
/**
* FIXME This needs to be overridden for the {@link IsolatedFusedView} in
* order to correctly propagate the version timestamp onto the tuple. See
* the insert() and remove() methods on that class. This will probably be
* done inside of an implementation that extends the {@link FusedView}
* cursor implementation, at which point this notice can be removed.
*/
@Override
public void remove() {
if (btree.isReadOnly())
throw new UnsupportedOperationException();
if (!isCursorPositionDefined()) {
throw new IllegalStateException(LOG_NO_CURSOR_POSITION);
}
if (!currentPosition.isVisitableTuple()) {
/*
* The cursor position is defined, e.g., by seek(), but it is not on
* a visitable tuple.
*/
throw new IllegalStateException(LOG_CURSOR_POSITION_NOT_VISITABLE);
}
// the key for the last visited tuple.
final byte[] key = currentKey();
if (DEBUG)
log.debug("key="+BytesUtil.toString(key));
/*
* Remove the last visited tuple.
*
* Note: this will cause the tuples in the current leaf to have a gap
* (at least logically) and the remaining tuples will be moved down to
* cover that gap. This means that the [index] for the cursor position
* needs to be corrected. That is handled when the cursor position's
* listener notices the mutation event.
*
* Note: This uses the [tuple] on the iterator. This is an optimization
* for REMOVEALL. The [tuple] on the iterator will not have the KEYS or
* VALUES flags set when REMOVEALL is specified for the iterator. That
* means that we will not materialize those keys or values. This reduces
* heap churn and also prevents disk hits when the value is a raw
* record.
*/
if (btree.getIndexMetadata().getDeleteMarkers()) {
// set the delete marker.
btree.insert(key, null/* val */, true/* delete */, false/*putIfAbstent*/,
btree.getRevisionTimestamp(), tuple);
} else {
// remove the tuple.
btree.remove(key, tuple);
}
}
/**
* A cursor position for an {@link ITupleCursor}.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
* @param <L>
* The generic type for the leaves of the B+Tree.
* @param <E>
* The generic type for objects de-serialized from the values in
* the index.
*/
static interface ICursorPosition<L extends Leaf,E> {
/**
* The cursor that owns this cursor position.
*/
public ITupleCursor<E> getCursor();
/**
* The cursor used to navigate the leaves of the B+Tree.
*/
public ILeafCursor<L> getLeafCursor();
/**
* The index of the current tuple in the current leaf.
*/
public int getIndex();
/**
* Return the key corresponding to the cursor position.
*
* @return The key.
*/
public byte[] getKey();
/**
* Copy the data from the tuple at the {@link ICursorPosition} into the
* caller's buffer.
* <p>
* Note: If the {@link ICursorPosition} is not on a visitable tuple then
* this method will return <code>null</code> rather than the caller's
* tuple. This situation can arise if the index is empty (e.g., a root
* leaf with nothing in it) or if current cursor position does not
* correspond to a visitable tuple in the index.
*
* @param tuple
* The caller's buffer.
*
* @return The caller's buffer -or- <code>null</code> if the
* {@link ICursorPosition} is not on a visitable tuple.
*/
public Tuple<E> get(Tuple<E> tuple);
/**
* Return <code>true</code> iff the tuple corresponding to the cursor
* position is visitable. A cursor position for which there is no
* corresponding tuple in the index is not a visitable tuple. A cursor
* position for which the corresponding tuple in the index is deleted is
* visitable iff the {@link ITupleCursor} was provisioned to visit
* deleted tuples.
*
* @return <code>true</code> iff the cursor position corresponds to a
* visitable tuple.
*/
public boolean isVisitableTuple();
/**
* Scan forward to the next visitable tuple from the current position.
*
* @param skipCurrent
* If the current tuple should be skipped over. when
* <code>false</code> position will not be advanced if the
* current tuple is "visitable".
* @param testOnly
* When <code>true</code> the method will report whether or
* not a visitable successor of the cursor position exists
* but must not change the cursor position.
*
* @return <code>true</code> if a visitable tuple was found.
*/
public boolean forwardScan(boolean skipCurrent,boolean testOnly);
/**
* Scan backward to the previous visitable tuple from the current
* position.
*
* @param skipCurrent
* If the current tuple should be skipped over. when
* <code>false</code> position will not be advanced if the
* current tuple is "visitable".
* @param testOnly
* When <code>true</code> the method will report whether or
* not a visitable predecessor of the cursor position exists
* but must not change the cursor position.
*
* @return <code>true</code> if a visitable tuple was found.
*/
public boolean reverseScan(boolean skipCurrent,boolean testOnly);
}
/**
* Abstract base class.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
* @param <E>
*/
abstract static class AbstractCursorPosition<L extends Leaf,E> implements ICursorPosition<L,E> {
/** The owning {@link ITupleCursor2}. */
final protected ITupleCursor2<E> cursor;
/** Used for sequential and random access to the leaves of the B+Tree. */
final protected ILeafCursor<L> leafCursor;
/** The index of the tuple within that leaf. */
protected int index;
/**
* The key corresponding to the current cursor position. This is update
* each time we settle on a new tuple or when the cursor position is
* directed to an explicit key using seek(). Having this state allows us
* to unambiguously position the cursor in response to a seek() and also
* allows us to unambiguously re-position the cursor if the current leaf
* has been invalidated.
*/
private final DataOutputBuffer kbuf;
/**
* When true the methods on this class will re-locate the leaf using the
* key associated with the current tuple before doing anything else
* (this flag is cleared as a side-effect once the leaf has been
* re-located).
* <p>
* Note: This is used to support {@link ILeafListener}s by some derived
* classes
*/
protected boolean leafValid;
// /**
// * Return <code>true</code> iff the tuple position is the same as the
// * given tuple position.
// */
// public boolean isSamePosition(AbstractCursorPosition<Leaf, E> pos) {
//
// if(index != pos.index) return false;
//
// if(leafCursor.leaf()!=pos.leafCursor.leaf()) return false;
//
// return true;
//
// }
public ITupleCursor<E> getCursor() {
return cursor;
}
public ILeafCursor<L> getLeafCursor() {
relocateLeaf();
return leafCursor;
}
public int getIndex() {
relocateLeaf();
return index;
}
/**
* <code>true</code> iff the class registers as an
* {@link ILeafListener} and can therefore handle events that invalidate
* the position by re-locating the appropriate leaf within the B+Tree.
*/
public boolean isLeafListener() {
return false;
}
/**
* Create position on the specified tuple.
*
* @param cursor
* The {@link ITupleCursor}.
* @param leaf
* The leaf cursor (already positioned on the desired leaf).
* @param index
* The index of the tuple in the <i>leaf</i> -or- the
* insertion point for the <i>key</i> if there is no tuple
* for that key in the leaf.
* @param key
* The key (required).
*/
protected AbstractCursorPosition(final ITupleCursor2<E> cursor,
final ILeafCursor<L> leafCursor, final int index,
final byte[] key) {
if (cursor == null)
throw new IllegalArgumentException();
if (leafCursor == null)
throw new IllegalArgumentException();
if (key == null)
throw new IllegalArgumentException();
// /*
// * Note: The <i>index</i> MAY be equal to the #of keys in the leaf,
// * in which case the {@link CursorPosition} MUST be understood to
// * lie in the next leaf (if it exists). The scanForward() method
// * handles this case automatically.
// */
// if(index < 0 || index > leaf.getKeyCount()) {
//
// throw new IllegalArgumentException("index="+index+", nkeys="+leaf.getKeyCount());
//
// }
// @todo the valid range on [index] also includes the insertion points (negative integers).
this.leafValid = true;
this.cursor = cursor;
this.leafCursor = leafCursor;
this.index = index;
this.kbuf = new DataOutputBuffer(key.length);
this.kbuf.put( key );
}
/**
* Copy constructor.
*
* @param p
*/
public AbstractCursorPosition(final AbstractCursorPosition<L,E> p) {
if (p == null)
throw new IllegalArgumentException();
// make sure that source position is valid.
p.relocateLeaf();
this.leafValid = true;
this.cursor = p.cursor;
this.index = p.index;
this.kbuf = new DataOutputBuffer(p.kbuf.capacity());
this.kbuf.copyAll(p.kbuf);
this.leafCursor = p.leafCursor.clone();
}
public String toString() {
return "CursorPosition{" + cursor + ", leafCursor=" + leafCursor + ", index="
+ index + ", leafValid=" + leafValid + ", key="
+ BytesUtil.toString(kbuf.toByteArray()) + "}";
}
/**
* Seek to the given position.
*/
public void seek(final AbstractCursorPosition<L, E> src) {
if (src == null)
throw new IllegalArgumentException();
if (cursor != src.cursor)
throw new IllegalArgumentException();
// make sure the source position is valid.
src.relocateLeaf();
leafValid = true;
index = src.index;
leafCursor.seek(src.leafCursor);
kbuf.reset().copyAll(src.kbuf);
}
final public byte[] getKey() {
return kbuf.toByteArray();
}
/**
* <code>true</code> if the cursor position corresponds to a tuple in
* the index.
* <p>
* Note: A cursor position can be initially constructed with
* [index==nkeys], in which case the cursor is not "on" a tuple.
* Normally the caller will scan forward / backward until they reached a
* visitable tuple so as to avoid that fence post.
* <p>
* Note: The other cause the cursor position not being "on" a tuple is
* an empty root leaf
*/
protected boolean isOnTuple() {
if (index >= 0 && index < leafCursor.leaf().getKeyCount()) {
return true;
}
return false;
}
public boolean isVisitableTuple() {
relocateLeaf();
if(!isOnTuple()) {
/*
* Note: This happens when [index] is an insertion point
* (negative) because there was no tuple in the index for the
* current key.
*/
return false;
}
/*
* Either delete markers are not supported or we are visiting
* deleted tuples or the tuple is not deleted.
*/
final Leaf leaf = leafCursor.leaf();
return !leaf.hasDeleteMarkers() || cursor.isDeletedTupleVisitor()
|| !leaf.getDeleteMarker(index);
}
public Tuple<E> get(final Tuple<E> tuple) {
relocateLeaf();
if(!isVisitableTuple()) {
if (DEBUG)
log.debug(LOG_CURSOR_POSITION_NOT_VISITABLE);
return null;
}
// Note: increments [tuple.nvisited] !!!
tuple.copy(index, leafCursor.leaf());
if(DEBUG) {
log.debug(tuple.toString());
}
return tuple;
}
/**
* The contract for this method is to re-locate the {@link #leaf} and
* then re-locate the {@link #index} of current tuple within that leaf
* using the key reported by {@link #getKey()}. This method is
* triggered when an {@link ILeafListener} is registered against a
* mutable {@link BTree}).
* <p>
* The default implementation does nothing if {@link #leafValid} is
* <code>true</code> (and it will always be true if the B+Tree is
* read-only).
*
* @return true unless if the leaf was re-located but the current tuple
* is no longer present in the leaf (e.g., it was deleted from
* the index). Note that the return is always <code>true</code>
* if delete markers are in effect since a remove() is actually
* an update in that case.
*
* @throws UnsupportedOperationException
* if {@link #leafValid} is <code>false</code>
*
* @todo the return value is never used so this could be declared to
* return <code>void</code>
*/
protected boolean relocateLeaf() {
if(leafValid) return true;
throw new UnsupportedOperationException();
}
/**
* Materialize the next leaf in the natural order of the index.
* <p>
* Note: This method is NOT required to validate that the next leaf lies
* within the optional key-range constraint on the owning
* {@link ITupleCursor}.
*
* @return <code>true</code> if there is successor of the current
* leaf.
*/
protected boolean nextLeaf(final ILeafCursor<L> leafCursor) {
if (leafCursor.next() == null) {
log.info("No right sibling.");
return false;
}
return true;
}
/**
* Materialize the prior leaf in the natural order of the index.
* <p>
* Note: This method is NOT required to validate that the prior leaf
* lies within the optional key-range constraint on the owning
* {@link ITupleCursor}.
*
* @return <code>true</code> if there is a predecessor of the current
* leaf.
*/
protected boolean priorLeaf(ILeafCursor<L> leafCursor) {
if (leafCursor.prior() == null) {
log.info("No left sibling.");
return false;
}
return true;
}
/**
* Return <code>true</code> if the key at the current {@link #index} in
* the current {@link #leaf} lies inside of the optional half-open range
* constraint.
*
* @param leaf
* The current leaf.
* @param index
* The index of the current tuple in that leaf.
* @param forward
* <code>true</code> iff the cursor is moving in the forward
* direction (increasing key order) and <code>false</code>
* iff the cursor is moving in the reverse direction
* (decreasing key order). We only check the
* <code>fromKey</code> when moving in reverse order and the
* <code>toKey</code> when moving in forward order.
*
* @return <code>true</code> unless the current key is LT [fromKey] or
* GTE [toKey].
*
* @todo could only rangeCheck in the direction of the traversal, but
* this causes cursor test failures for some reason.
*
* @todo for a read-only view, we could compute the leaf addr and the
* tuple index of the fromKey and/or to key and then just compare
* those with the given leaf and index to decide if we were within
* the necessary bounds.
*/
private boolean rangeCheck(final L leaf, final int index) {//, boolean forward) {
// optional inclusive lower bound (may be null).
final byte[] fromKey = cursor.getFromKey();
// final byte[] fromKey = forward ? null : cursor.getFromKey();
// optional exclusive upper bound (may be null).
final byte[] toKey = cursor.getToKey();
// final byte[] toKey = forward ? cursor.getToKey() : null;
if (fromKey == null && toKey == null) {
// no range constraint.
return true;
}
/*
* The key for the cursor position.
*/
if (true) {
final byte[] key = leaf.getKeys().get(index);
if (fromKey != null && BytesUtil.compareBytes(key, fromKey) < 0) {
// key is LT then the optional inclusive lower bound.
return false;
}
if (toKey != null && BytesUtil.compareBytes(key, toKey) >= 0) {
// key is GTE the optional exclusive upper bound
return false;
}
} else {
/*
* FIXME This performance optimizes out the allocation of a copy
* of the key using an inline comparison. However, there is
* something wrong as this causes
* AbstractBTreeCursorTestCase#test_baseCase() to fail.
*/
if (tbuf == null) {
tbuf = new DataOutputBuffer(0);
}
leafCursor.leaf().getKeys().copy(index, tbuf);
final int tlen = tbuf.limit();
final byte[] a = tbuf.array();
if (fromKey != null) {
if (BytesUtil.compareBytesWithLenAndOffset(0, tlen, a, 0,
fromKey.length, fromKey) < 0) {
if (DEBUG) {
log.debug("key=" + BytesUtil.toString(a, 0, tlen)
+ " LT fromKey" + BytesUtil.toString(fromKey));
}
// key is LT then the optional inclusive lower bound.
return false;
}
}
if (toKey != null) {
if (BytesUtil.compareBytesWithLenAndOffset(0, tlen, a, 0,
toKey.length, toKey) >= 0) {
if (DEBUG) {
log.debug("key=" + BytesUtil.toString(a, 0, tlen)
+ " GTE toKey" + BytesUtil.toString(toKey));
}
// key is GTE the optional exclusive upper bound
return false;
}
}
}
return true;
}
/**
* Buffer used to range check the current key before it is copied into
* #kbuf.
*/
private DataOutputBuffer tbuf;
// private AbstractCursorPosition<L,E> priorPosition;
// private AbstractCursorPosition<L,E> nextPosition;
/**
* Used to update the position once a visitable tuple has been found.
* Both {@link #forwardScan(boolean, boolean)} and
* {@link #reverseScan(boolean, boolean)} are written to have NO SIDE
* EFFECT on the position unless this method is invoked.
*/
private void updatePosition(final ILeafCursor<L> leafCursor,
final int index) {
// the tuple index.
this.index = index;
/*
* The leaf cursor
*
* Note: The way the forward and reverse scan methods are written we
* use the live leaf cursor unless [testOnly == true] so when it
* comes to update the position this should always be the live leaf
* cursor!
*/
assert this.leafCursor == leafCursor;
// if (this.leafCursor != leafCursor) {
//
// this.leafCursor.seek(leafCursor);
//
// }
// copy the current key.
kbuf.reset();
leafCursor.leaf().getKeys().copy(index, kbuf);
}
final public boolean forwardScan(final boolean skipCurrent,
final boolean testOnly) {
relocateLeaf();
/*
* Note: The use of local variables for [index] and [leafCursor]
* avoids side-effects until we find a visitable successor of the
* current position.
*
* Note: [index] is cloned immediately while [leafCursor] is cloned
* lazily (iff we move onto another leaf and [testOnly == true]).
*/
int index = this.index;
ILeafCursor<L> leafCursor = this.leafCursor;
if (index < 0) {
// if it is an insert position then convert it to an index first.
index = -index - 1;
} else if (skipCurrent) {
/*
* Note: don't skip the current tuple if we had an insertion
* point (and hence we were not actually on a tuple).
*/
index++;
}
/*
* Scan until we find a visitable tuple.
*
* Note: If [index >= nkeys] then the scan will immediately skip to
* the next leaf (if any) in the index.
*/
// set true iff the scan exceeds the optional exclusive upper bound.
boolean done = false;
while (!done) {
final L leaf = leafCursor.leaf();
final int nkeys = leaf.getKeyCount();
/*
* Scan tuples in the current leaf until we find a visitable
* tuple.
*/
for (; index < nkeys; index++) {
if (!rangeCheck(leaf, index)) {//, true/* forward */)) {
// tuple is LT [fromKey] or GTE [toKey].
done = true;
break;
}
if (!leaf.hasDeleteMarkers()
|| cursor.isDeletedTupleVisitor()
|| !leaf.getDeleteMarker(index)) {
// found visitable tuple.
if (!testOnly) {
updatePosition(leafCursor, index);
}
return true;
}
}
if(testOnly) {
// Clone the cursor to avoid side-effects.
leafCursor = leafCursor.clone();
}
if(!nextLeaf(leafCursor)) {
// no more leaves.
break;
}
// always start at index ZERO(0) after the first leaf.
index = 0;
}
if (INFO)
log.info(LOG_NO_SUCCESSOR);
// no visitable tuple.
return false;
}
final public boolean reverseScan(final boolean skipCurrent,final boolean testOnly) {
relocateLeaf();
// Note: updated if we change to a prior leaf!
int nkeys = leafCursor.leaf().getKeyCount();
if (nkeys == 0) {
/*
* This happens when there is an empty root leaf. We have to
* test for this case explicitly since the for() loop below
* allows index == 0.
*/
return false;
}
/*
* Note: The use of local variables for [index] and [leafCursor]
* avoids side-effects until we find a visitable predecessor of the
* current position.
*
* Note: [index] is cloned immediately while [leafCursor] is cloned
* lazily (iff we move onto another leaf and [testOnly == true]).
*/
int index = this.index;
ILeafCursor<L> leafCursor = this.leafCursor;
if (index < 0) {
// if it is an insert position then convert it to an index first.
index = -index - 1;
}
if (skipCurrent) {
index--;
}
/*
* Scan leafs until we find a visitable tuple.
*
* Note: If [index < 0] then the scan will immediately skip to the
* prior leaf (if any) in the index.
*/
// set true iff the scan reaches or exceeds the optional inclusive lower bound.
boolean done = false;
while (!done) {
/*
* Scan tuples in the current leaf until we find a visitable
* tuple.
*/
final L leaf = leafCursor.leaf();
for (; index >= 0; index--) {
if (index == nkeys) continue;
if (!rangeCheck(leaf, index)) {//, false/* forward */)) {
// tuple is LT [fromKey] or GTE [toKey].
done = true;
break;
}
if (!leaf.hasDeleteMarkers()
|| cursor.isDeletedTupleVisitor()
|| !leaf.getDeleteMarker(index)) {
// found visitable tuple.
if(!testOnly) {
updatePosition(leafCursor, index);
}
return true;
}
}
if(testOnly) {
// Clone the cursor to avoid side-effects.
leafCursor = leafCursor.clone();
}
if(!priorLeaf(leafCursor)) {
// no more leaves.
break;
}
// set to the #of keys in the prior leaf.
nkeys = leafCursor.leaf().getKeyCount();
// always reset the index to [nkeys-1] when moving to a prior leaf.
index = nkeys - 1;
}
if (INFO)
log.info(LOG_NO_PREDECESSOR);
// no visitable tuple.
return false;
}
}
/**
* {@link ICursorPosition} for a read-only {@link BTree} (does not establish
* listeners).
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
* @param <E>
*/
static private class ReadOnlyCursorPosition<E> extends
AbstractCursorPosition<Leaf, E> {
/**
* @param cursor
* @param leafCursor
* @param index
* @param key
*/
public ReadOnlyCursorPosition(ITupleCursor2<E> cursor,
ILeafCursor<Leaf> leafCursor, int index, byte[] key) {
super(cursor, leafCursor, index, key);
}
/**
* Copy constructor.
*
* @param p
*/
public ReadOnlyCursorPosition(ReadOnlyCursorPosition<E> p) {
super( p );
}
}
/**
* {@link ICursorPosition} for a mutable {@link BTree} (establishes
* listeners to determine when the current leaf and/or tuple index has been
* invalidated).
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
* @param <E>
*/
static private class MutableCursorPosition<E> extends
ReadOnlyCursorPosition<E> implements ILeafListener {
/**
* @param cursor
* @param leafCursor
* @param index
*/
protected MutableCursorPosition(ITupleCursor2<E> cursor,
ILeafCursor<Leaf> leafCursor, int index, byte[] key) {
super(cursor, leafCursor, index, key);
leafCursor.leaf().addLeafListener(this);
}
/**
* Copy constructor.
*
* @param p
*/
public MutableCursorPosition(MutableCursorPosition<E> p) {
super( p );
leafCursor.leaf().addLeafListener(this);
}
/**
* Note: rather than immediately re-locate the leaf this just notes that
* the leaf is invalid and it will be re-located the next time we need
* to do anything with the leaf.
*/
public void invalidateLeaf() {
leafValid = false;
}
// /**
// * Note: This does NOT establish an {@link ILeafListener} because it is
// * only used for the temporary position (vs the current position).
// */
// @Override
// public void seek(AbstractCursorPosition<Leaf, E> src) {
//
// super.seek(src);
//
// }
@Override
final public boolean isLeafListener() {
return true;
}
/**
* Extended to register ourselves as a listener to the new leaf.
*/
protected boolean priorLeaf(ILeafCursor<Leaf> leafCursor) {
if(super.priorLeaf(leafCursor)) {
leafCursor.leaf().addLeafListener(this);
return true;
}
return false;
}
/**
* Extended to register ourselves as a listener to the new leaf.
*/
protected boolean nextLeaf(ILeafCursor<Leaf>leafCursor) {
if(super.nextLeaf(leafCursor)) {
leafCursor.leaf().addLeafListener(this);
return true;
}
return false;
}
protected boolean relocateLeaf() {
if(leafValid) return true;
// the key corresponding to the cursor position.
final byte[] key = getKey();
if (INFO)
log.info("Relocating leaf: key=" + BytesUtil.toString(key));
/*
* Re-locate the leaf and re-egister the cursor position as a
* listener for the new leaf.
*/
leafCursor.seek(key).addLeafListener(this);
// Re-locate the tuple index for the key in that leaf.
index = leafCursor.leaf().getKeys().search(key);
final boolean tupleDeleted;
if (index < 0) {
tupleDeleted = true;
} else {
tupleDeleted = false;
}
leafValid = true;
return tupleDeleted;
}
}
/**
* An {@link ITuple} that directly supports forward and reverse cursor
* operations on a local {@link BTree}.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
* @param <E>
*/
public static class ReadOnlyBTreeTupleCursor<E> extends
AbstractBTreeTupleCursor<BTree, Leaf, E> {
public ReadOnlyBTreeTupleCursor(final BTree btree,
final Tuple<E> tuple, final byte[] fromKey, final byte[] toKey) {
super(btree, tuple, fromKey, toKey);
}
@Override
protected ReadOnlyCursorPosition<E> newPosition(
final ILeafCursor<Leaf> leafCursor, final int index,
final byte[] key) {
return new ReadOnlyCursorPosition<E>(this, leafCursor, index, key);
}
@Override
protected ReadOnlyCursorPosition<E> newTemporaryPosition(
final ICursorPosition<Leaf, E> p) {
return new ReadOnlyCursorPosition<E>( (ReadOnlyCursorPosition<E>) p );
}
}
/**
* An {@link ITuple} that directly supports forward and reverse cursor
* operations on a local mutable {@link BTree}.
* <p>
* This implementation supports concurrent modification of the {@link BTree}
* but is NOT thread-safe. This means that you can interleave cursor-based
* tuple operations with insert, update, or delete of tuples using the
* {@link BTree}. However, the {@link BTree} itself is NOT thread-safe for
* mutation and this class does not relax that limitation.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
* @param <E>
*/
public static class MutableBTreeTupleCursor<E> extends
ReadOnlyBTreeTupleCursor<E> {
public MutableBTreeTupleCursor(BTree btree, Tuple<E> tuple,
byte[] fromKey, byte[] toKey) {
super(btree, tuple, fromKey, toKey);
}
@Override
protected MutableCursorPosition<E> newPosition(
ILeafCursor<Leaf> leafCursor, int index, byte[] key) {
return new MutableCursorPosition<E>(this, leafCursor, index, key);
}
/**
* Note: This is only used by {@link #hasNext()} and {@link #hasPrior()}
* for a temporary test without side-effects on the state of the
* {@link ITupleCursor} and therefore we do NOTNOT register an
* {@link ILeafListener} since that is just more overhead and it will
* not be used.
*/
@Override
protected ReadOnlyCursorPosition<E> newTemporaryPosition(ICursorPosition<Leaf, E> p) {
return new ReadOnlyCursorPosition<E>( (ReadOnlyCursorPosition<E>) p );
}
}
}