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CursorIterable.java
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222 lines (201 loc) · 5.89 KB
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/*
* Copyright © 2016-2025 The LmdbJava Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.lmdbjava;
import static org.lmdbjava.CursorIterable.State.RELEASED;
import static org.lmdbjava.CursorIterable.State.REQUIRES_INITIAL_OP;
import static org.lmdbjava.CursorIterable.State.REQUIRES_ITERATOR_OP;
import static org.lmdbjava.CursorIterable.State.REQUIRES_NEXT_OP;
import static org.lmdbjava.CursorIterable.State.TERMINATED;
import static org.lmdbjava.GetOp.MDB_SET_RANGE;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.lmdbjava.KeyRangeType.CursorOp;
import org.lmdbjava.KeyRangeType.IteratorOp;
/**
* {@link Iterable} that creates a single {@link Iterator} that will iterate over a {@link Cursor}
* as specified by a {@link KeyRange}.
*
* <p>An instance will create and close its own cursor.
*
* @param <T> buffer type
*/
public final class CursorIterable<T> implements Iterable<CursorIterable.KeyVal<T>>, AutoCloseable {
private final Comparator<T> comparator;
private final Cursor<T> cursor;
private final KeyVal<T> entry;
private boolean iteratorReturned;
private final KeyRange<T> range;
private State state = REQUIRES_INITIAL_OP;
CursorIterable(
final Txn<T> txn, final Dbi<T> dbi, final KeyRange<T> range, final Comparator<T> comparator) {
this.cursor = dbi.openCursor(txn);
this.range = range;
this.comparator = comparator;
this.entry = new KeyVal<>();
}
@Override
public void close() {
cursor.close();
}
/**
* Obtain an iterator.
*
* <p>As iteration of the returned iterator will cause movement of the underlying LMDB cursor, an
* {@link IllegalStateException} is thrown if an attempt is made to obtain the iterator more than
* once. For advanced cursor control (such as being able to iterate over the same data multiple
* times etc) please instead refer to {@link Dbi#openCursor(org.lmdbjava.Txn)}.
*
* @return an iterator
*/
@Override
public Iterator<KeyVal<T>> iterator() {
if (iteratorReturned) {
throw new IllegalStateException("Iterator can only be returned once");
}
iteratorReturned = true;
return new Iterator<KeyVal<T>>() {
@Override
public boolean hasNext() {
while (state != RELEASED && state != TERMINATED) {
update();
}
return state == RELEASED;
}
@Override
public KeyVal<T> next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
state = REQUIRES_NEXT_OP;
return entry;
}
@Override
public void remove() {
cursor.delete();
}
};
}
private void executeCursorOp(final CursorOp op) {
final boolean found;
switch (op) {
case FIRST:
found = cursor.first();
break;
case LAST:
found = cursor.last();
break;
case NEXT:
found = cursor.next();
break;
case PREV:
found = cursor.prev();
break;
case GET_START_KEY:
found = cursor.get(range.getStart(), MDB_SET_RANGE);
break;
case GET_START_KEY_BACKWARD:
found = cursor.get(range.getStart(), MDB_SET_RANGE) || cursor.last();
break;
default:
throw new IllegalStateException("Unknown cursor operation");
}
entry.setK(found ? cursor.key() : null);
entry.setV(found ? cursor.val() : null);
}
private void executeIteratorOp() {
final IteratorOp op =
range.getType().iteratorOp(range.getStart(), range.getStop(), entry.key(), comparator);
switch (op) {
case CALL_NEXT_OP:
executeCursorOp(range.getType().nextOp());
state = REQUIRES_ITERATOR_OP;
break;
case TERMINATE:
state = TERMINATED;
break;
case RELEASE:
state = RELEASED;
break;
default:
throw new IllegalStateException("Unknown operation");
}
}
private void update() {
switch (state) {
case REQUIRES_INITIAL_OP:
executeCursorOp(range.getType().initialOp());
state = REQUIRES_ITERATOR_OP;
break;
case REQUIRES_NEXT_OP:
executeCursorOp(range.getType().nextOp());
state = REQUIRES_ITERATOR_OP;
break;
case REQUIRES_ITERATOR_OP:
executeIteratorOp();
break;
case TERMINATED:
break;
default:
throw new IllegalStateException("Unknown state");
}
}
/**
* Holder for a key and value pair.
*
* <p>The same holder instance will always be returned for a given iterator. The returned keys and
* values may change or point to different memory locations following changes in the iterator,
* cursor or transaction.
*
* @param <T> buffer type
*/
public static final class KeyVal<T> {
private T k;
private T v;
/** Explicitly-defined default constructor to avoid warnings. */
public KeyVal() {}
/**
* The key.
*
* @return key
*/
public T key() {
return k;
}
/**
* The value.
*
* @return value
*/
public T val() {
return v;
}
void setK(final T key) {
this.k = key;
}
void setV(final T val) {
this.v = val;
}
}
/** Represents the internal {@link CursorIterable} state. */
enum State {
REQUIRES_INITIAL_OP,
REQUIRES_NEXT_OP,
REQUIRES_ITERATOR_OP,
RELEASED,
TERMINATED
}
}