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/*
* Copyright 2016-2022 chronicle.software
*
* https://chronicle.software
*
* 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 net.openhft.chronicle.queue.impl.single;
import net.openhft.chronicle.queue.ExcerptTailer;
import net.openhft.chronicle.queue.RollCycle;
import net.openhft.chronicle.wire.DocumentContext;
import net.openhft.chronicle.wire.Wire;
import org.jetbrains.annotations.NotNull;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NavigableSet;
public enum BinarySearch {
INSTANCE;
/**
* returns the index or -1 if not found or the index if an exact match is found, an approximation in the form of -approximateIndex
* or -1 if there was no searching to be done.
*
* Warning : This implementation is unreliable as index are an encoded 64bits, where we could use all the bits including the
* high bit which is used for the sign. At the moment it will work as its unlikely to reach a point where we store
* enough messages in the chronicle queue to use the high bit, having said this its possible in the future the
* high bit in the index ( used for the sign ) may be used, this implementation is unsafe as it relies on this
* bit not being set ( in other words set to zero ).
*/
public static long search(@NotNull ExcerptTailer tailer,
@NotNull Wire key,
@NotNull Comparator c) {
final long readPosition = key.bytes().readPosition();
try {
final long start = tailer.toStart().index();
final long end = tailer.toEnd().index();
final RollCycle rollCycle = tailer.queue().rollCycle();
final int startCycle = rollCycle.toCycle(start);
final int endCycle = rollCycle.toCycle(end);
if (startCycle == endCycle)
return findWithinCycle(key, c, startCycle, tailer, rollCycle);
final NavigableSet cycles = ((SingleChronicleQueue)tailer.queue()).listCyclesBetween(startCycle, endCycle);
final int cycle = (int) findCycleLinearSearch(cycles, key, c, tailer);
if (cycle == -1)
return -1;
return findWithinCycle(key, c, cycle, tailer, rollCycle);
} finally {
key.bytes().readPosition(readPosition);
}
}
private static long findCycleLinearSearch(@NotNull NavigableSet cycles, Wire key,
@NotNull Comparator c,
@NotNull ExcerptTailer tailer) {
long readPosition = key.bytes().readPosition();
final Iterator iterator = cycles.iterator();
if (!iterator.hasNext())
return -1;
final RollCycle rollCycle = tailer.queue().rollCycle();
long prevIndex = iterator.next();
cycleLoop:
while (iterator.hasNext()) {
final Long current = iterator.next();
final boolean b = tailer.moveToIndex(rollCycle.toIndex((int) (long) current, 0));
if (!b)
return prevIndex;
while (true) {
try (final DocumentContext dc = tailer.readingDocument()) {
if (!dc.isPresent()) {
return prevIndex;
}
if (rollCycle.toCycle(dc.index()) > current) {
continue cycleLoop;
}
try {
final int compare = c.compare(dc.wire(), key);
if (compare == 0)
return current;
else if (compare > 0)
return prevIndex;
prevIndex = current;
break;
} catch (NotComparableException e) {
// Keep scanning forward
} finally {
key.bytes().readPosition(readPosition);
}
}
}
}
return prevIndex;
}
/**
* @return The index if an exact match is found, an approximation in the form of -approximateIndex
* or a negative number (- the approx index) if there was no searching to be done.
*
* Warning : This implementation is unreliable as index are an encoded 64bits, where we could use all the bits including the
* high bit which is used for the sign. At the moment it will work as its unlikely to reach a point where we store
* enough messages in the chronicle queue to use the high bit, having said this its possible in the future the
* high bit in the index ( used for the sign ) may be used, this implementation is unsafe as it relies on this
* bit not being set ( in other words set to zero ).
*/
public static long findWithinCycle(@NotNull Wire key,
@NotNull Comparator c,
int cycle,
@NotNull ExcerptTailer tailer,
@NotNull final RollCycle rollCycle) {
final long readPosition = key.bytes().readPosition();
try {
long lowSeqNum = 0;
long highSeqNum = tailer.excerptsInCycle(cycle) - 1;
// nothing to search
if (highSeqNum < lowSeqNum)
return -1;
long midIndex = 0;
while (lowSeqNum <= highSeqNum) {
long midSeqNumber = (lowSeqNum + highSeqNum) >>> 1L;
midIndex = rollCycle.toIndex(cycle, midSeqNumber);
final boolean b = tailer.moveToIndex(midIndex);
assert b;
while (true) {
try (DocumentContext dc = tailer.readingDocument()) {
if (!dc.isPresent())
return -1;
key.bytes().readPosition(readPosition);
try {
int cmp = c.compare(dc.wire(), key);
if (cmp < 0) {
lowSeqNum = rollCycle.toSequenceNumber(dc.index()) + 1;
break;
}
else if (cmp > 0) {
highSeqNum = midSeqNumber - 1;
break;
}
else
return dc.index(); // key found
} catch (NotComparableException e) {
// We reached the upper bound, eliminate the top half of the range
if (rollCycle.toSequenceNumber(dc.index()) == highSeqNum) {
highSeqNum = midSeqNumber - 1;
break;
}
}
}
}
}
return midIndex == 0 ? -1 : -midIndex; // -approximateIndex
} finally {
key.bytes().readPosition(readPosition);
}
}
}