kafka BaseHashTable 源码
kafka BaseHashTable 代码
文件路径:/metadata/src/main/java/org/apache/kafka/timeline/BaseHashTable.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.apache.kafka.timeline;
import java.util.ArrayList;
import java.util.List;
/**
* A hash table which uses separate chaining.
*
* In order to optimize memory consumption a bit, the common case where there is
* one element per slot is handled by simply placing the element in the slot,
* and the case where there are multiple elements is handled by creating an
* array and putting that in the slot. Java is storing type info in memory
* about every object whether we want it or not, so let's get some benefit
* out of it.
*
* Arrays and null values cannot be inserted.
*/
@SuppressWarnings("unchecked")
class BaseHashTable<T> {
/**
* The maximum load factor we will allow the hash table to climb to before expanding.
*/
private final static double MAX_LOAD_FACTOR = 0.75f;
/**
* The minimum number of slots we can have in the hash table.
*/
final static int MIN_CAPACITY = 2;
/**
* The maximum number of slots we can have in the hash table.
*/
final static int MAX_CAPACITY = 1 << 30;
private Object[] elements;
private int size = 0;
BaseHashTable(int expectedSize) {
this.elements = new Object[expectedSizeToCapacity(expectedSize)];
}
/**
* Calculate the capacity we should provision, given the expected size.
*
* Our capacity must always be a power of 2, and never less than 2 or more
* than MAX_CAPACITY. We use 64-bit numbers here to avoid overflow
* concerns.
*/
static int expectedSizeToCapacity(int expectedSize) {
long minCapacity = (long) Math.ceil((float) expectedSize / MAX_LOAD_FACTOR);
return Math.max(MIN_CAPACITY,
(int) Math.min(MAX_CAPACITY, roundUpToPowerOfTwo(minCapacity)));
}
private static long roundUpToPowerOfTwo(long i) {
if (i <= 0) {
return 0;
} else if (i > (1L << 62)) {
throw new ArithmeticException("There are no 63-bit powers of 2 higher than " +
"or equal to " + i);
} else {
return 1L << -Long.numberOfLeadingZeros(i - 1);
}
}
final int baseSize() {
return size;
}
final Object[] baseElements() {
return elements;
}
final T baseGet(Object key) {
int slot = findSlot(key, elements.length);
Object value = elements[slot];
if (value == null) {
return null;
} else if (value instanceof Object[]) {
T[] array = (T[]) value;
for (T object : array) {
if (object.equals(key)) {
return object;
}
}
return null;
} else if (value.equals(key)) {
return (T) value;
} else {
return null;
}
}
final T baseAddOrReplace(T newObject) {
if (((size + 1) * MAX_LOAD_FACTOR > elements.length) &&
(elements.length < MAX_CAPACITY)) {
int newSize = elements.length * 2;
rehash(newSize);
}
int slot = findSlot(newObject, elements.length);
Object cur = elements[slot];
if (cur == null) {
size++;
elements[slot] = newObject;
return null;
} else if (cur instanceof Object[]) {
T[] curArray = (T[]) cur;
for (int i = 0; i < curArray.length; i++) {
T value = curArray[i];
if (value.equals(newObject)) {
curArray[i] = newObject;
return value;
}
}
size++;
T[] newArray = (T[]) new Object[curArray.length + 1];
System.arraycopy(curArray, 0, newArray, 0, curArray.length);
newArray[curArray.length] = newObject;
elements[slot] = newArray;
return null;
} else if (cur.equals(newObject)) {
elements[slot] = newObject;
return (T) cur;
} else {
size++;
elements[slot] = new Object[] {cur, newObject};
return null;
}
}
final T baseRemove(Object key) {
int slot = findSlot(key, elements.length);
Object object = elements[slot];
if (object == null) {
return null;
} else if (object instanceof Object[]) {
Object[] curArray = (Object[]) object;
for (int i = 0; i < curArray.length; i++) {
if (curArray[i].equals(key)) {
size--;
if (curArray.length <= 2) {
int j = i == 0 ? 1 : 0;
elements[slot] = curArray[j];
} else {
Object[] newArray = new Object[curArray.length - 1];
System.arraycopy(curArray, 0, newArray, 0, i);
System.arraycopy(curArray, i + 1, newArray, i, curArray.length - 1 - i);
elements[slot] = newArray;
}
return (T) curArray[i];
}
}
return null;
} else if (object.equals(key)) {
size--;
elements[slot] = null;
return (T) object;
} else {
return null;
}
}
/**
* Expand the hash table to a new size. Existing elements will be copied to new slots.
*/
final private void rehash(int newSize) {
Object[] prevElements = elements;
elements = new Object[newSize];
List<Object> ready = new ArrayList<>();
for (int slot = 0; slot < prevElements.length; slot++) {
unpackSlot(ready, prevElements, slot);
for (Object object : ready) {
int newSlot = findSlot(object, elements.length);
Object cur = elements[newSlot];
if (cur == null) {
elements[newSlot] = object;
} else if (cur instanceof Object[]) {
Object[] curArray = (Object[]) cur;
Object[] newArray = new Object[curArray.length + 1];
System.arraycopy(curArray, 0, newArray, 0, curArray.length);
newArray[curArray.length] = object;
elements[newSlot] = newArray;
} else {
elements[newSlot] = new Object[]{cur, object};
}
}
ready.clear();
}
}
/**
* Find the slot in the array that an element should go into.
*/
static int findSlot(Object object, int numElements) {
// This performs a secondary hash using Knuth's multiplicative Fibonacci
// hashing. Then, we choose some of the highest bits. The number of bits
// we choose is based on the table size. If the size is 2, we need 1 bit;
// if the size is 4, we need 2 bits, etc.
int objectHashCode = object.hashCode();
int log2size = 32 - Integer.numberOfLeadingZeros(numElements);
int shift = 65 - log2size;
return (int) ((objectHashCode * -7046029254386353131L) >>> shift);
}
/**
* Copy any elements in the given slot into the output list.
*/
static <T> void unpackSlot(List<T> out, Object[] elements, int slot) {
Object value = elements[slot];
if (value == null) {
return;
} else if (value instanceof Object[]) {
Object[] array = (Object[]) value;
for (Object object : array) {
out.add((T) object);
}
} else {
out.add((T) value);
}
}
String baseToDebugString() {
StringBuilder bld = new StringBuilder();
bld.append("BaseHashTable{");
for (int i = 0; i < elements.length; i++) {
Object slotObject = elements[i];
bld.append(String.format("%n%d: ", i));
if (slotObject == null) {
bld.append("null");
} else if (slotObject instanceof Object[]) {
Object[] array = (Object[]) slotObject;
String prefix = "";
for (Object object : array) {
bld.append(prefix);
prefix = ", ";
bld.append(object);
}
} else {
bld.append(slotObject);
}
}
bld.append(String.format("%n}"));
return bld.toString();
}
}
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