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/*
 * Copyright (C) 2012 The Guava Authors
 *
 * 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 com.google.common.collect;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.j2objc.annotations.WeakOuter;
import java.util.Arrays;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;
import java.util.Spliterator;
import java.util.Spliterators;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * CompactLinkedHashMap is an implementation of a Map with insertion or LRU iteration order,
 * maintained with a doubly linked list through the entries. All optional operations (put and
 * remove) are supported. Null keys and values are supported.
 *
 * 

{@code containsKey(k)}, {@code put(k, v)} and {@code remove(k)} are all (expected and * amortized) constant time operations. Expected in the hashtable sense (depends on the hash * function doing a good job of distributing the elements to the buckets to a distribution not far * from uniform), and amortized since some operations can trigger a hash table resize. * *

As compared with {@link java.util.LinkedHashMap}, this structure places significantly reduced * load on the garbage collector by only using a constant number of internal objects. * *

This class should not be assumed to be universally superior to {@code * java.util.LinkedHashMap}. Generally speaking, this class reduces object allocation and memory * consumption at the price of moderately increased constant factors of CPU. Only use this class * when there is a specific reason to prioritize memory over CPU. * * @author Louis Wasserman */ @GwtIncompatible // not worth using in GWT for now class CompactLinkedHashMap extends CompactHashMap { // TODO(lowasser): implement removeEldestEntry so this can be used as a drop-in replacement /** Creates an empty {@code CompactLinkedHashMap} instance. */ public static CompactLinkedHashMap create() { return new CompactLinkedHashMap<>(); } /** * Creates a {@code CompactLinkedHashMap} instance, with a high enough "initial capacity" that it * should hold {@code expectedSize} elements without rebuilding internal data structures. * * @param expectedSize the number of elements you expect to add to the returned set * @return a new, empty {@code CompactLinkedHashMap} with enough capacity to hold {@code * expectedSize} elements without resizing * @throws IllegalArgumentException if {@code expectedSize} is negative */ public static CompactLinkedHashMap createWithExpectedSize(int expectedSize) { return new CompactLinkedHashMap<>(expectedSize); } private static final int ENDPOINT = -2; /** * Contains the link pointers corresponding with the entries, in the range of [0, size()). The * high 32 bits of each long is the "prev" pointer, whereas the low 32 bits is the "succ" pointer * (pointing to the next entry in the linked list). The pointers in [size(), entries.length) are * all "null" (UNSET). * *

A node with "prev" pointer equal to {@code ENDPOINT} is the first node in the linked list, * and a node with "next" pointer equal to {@code ENDPOINT} is the last node. */ @VisibleForTesting transient long @Nullable [] links; /** Pointer to the first node in the linked list, or {@code ENDPOINT} if there are no entries. */ private transient int firstEntry; /** Pointer to the last node in the linked list, or {@code ENDPOINT} if there are no entries. */ private transient int lastEntry; private final boolean accessOrder; CompactLinkedHashMap() { this(CompactHashing.DEFAULT_SIZE); } CompactLinkedHashMap(int expectedSize) { this(expectedSize, false); } CompactLinkedHashMap(int expectedSize, boolean accessOrder) { super(expectedSize); this.accessOrder = accessOrder; } @Override void init(int expectedSize) { super.init(expectedSize); this.firstEntry = ENDPOINT; this.lastEntry = ENDPOINT; } @Override int allocArrays() { int expectedSize = super.allocArrays(); this.links = new long[expectedSize]; return expectedSize; } @Override Map createHashFloodingResistantDelegate(int tableSize) { return new LinkedHashMap(tableSize, 1.0f, accessOrder); } @Override @CanIgnoreReturnValue Map convertToHashFloodingResistantImplementation() { Map result = super.convertToHashFloodingResistantImplementation(); links = null; return result; } private int getPredecessor(int entry) { return ((int) (links[entry] >>> 32)) - 1; } @Override int getSuccessor(int entry) { return ((int) links[entry]) - 1; } private void setSuccessor(int entry, int succ) { long succMask = (~0L) >>> 32; links[entry] = (links[entry] & ~succMask) | ((succ + 1) & succMask); } private void setPredecessor(int entry, int pred) { long predMask = ~0L << 32; links[entry] = (links[entry] & ~predMask) | ((long) (pred + 1) << 32); } private void setSucceeds(int pred, int succ) { if (pred == ENDPOINT) { firstEntry = succ; } else { setSuccessor(pred, succ); } if (succ == ENDPOINT) { lastEntry = pred; } else { setPredecessor(succ, pred); } } @Override void insertEntry(int entryIndex, @Nullable K key, @Nullable V value, int hash, int mask) { super.insertEntry(entryIndex, key, value, hash, mask); setSucceeds(lastEntry, entryIndex); setSucceeds(entryIndex, ENDPOINT); } @Override void accessEntry(int index) { if (accessOrder) { // delete from previous position... setSucceeds(getPredecessor(index), getSuccessor(index)); // ...and insert at the end. setSucceeds(lastEntry, index); setSucceeds(index, ENDPOINT); incrementModCount(); } } @Override void moveLastEntry(int dstIndex, int mask) { int srcIndex = size() - 1; super.moveLastEntry(dstIndex, mask); setSucceeds(getPredecessor(dstIndex), getSuccessor(dstIndex)); if (dstIndex < srcIndex) { setSucceeds(getPredecessor(srcIndex), dstIndex); setSucceeds(dstIndex, getSuccessor(srcIndex)); } links[srcIndex] = 0; } @Override void resizeEntries(int newCapacity) { super.resizeEntries(newCapacity); links = Arrays.copyOf(links, newCapacity); } @Override int firstEntryIndex() { return firstEntry; } @Override int adjustAfterRemove(int indexBeforeRemove, int indexRemoved) { return (indexBeforeRemove >= size()) ? indexRemoved : indexBeforeRemove; } @Override Set> createEntrySet() { @WeakOuter class EntrySetImpl extends EntrySetView { @Override public Spliterator> spliterator() { return Spliterators.spliterator(this, Spliterator.ORDERED | Spliterator.DISTINCT); } } return new EntrySetImpl(); } @Override Set createKeySet() { @WeakOuter class KeySetImpl extends KeySetView { @Override public Object[] toArray() { return ObjectArrays.toArrayImpl(this); } @Override public T[] toArray(T[] a) { return ObjectArrays.toArrayImpl(this, a); } @Override public Spliterator spliterator() { return Spliterators.spliterator(this, Spliterator.ORDERED | Spliterator.DISTINCT); } } return new KeySetImpl(); } @Override Collection createValues() { @WeakOuter class ValuesImpl extends ValuesView { @Override public Object[] toArray() { return ObjectArrays.toArrayImpl(this); } @Override public T[] toArray(T[] a) { return ObjectArrays.toArrayImpl(this, a); } @Override public Spliterator spliterator() { return Spliterators.spliterator(this, Spliterator.ORDERED); } } return new ValuesImpl(); } @Override public void clear() { if (needsAllocArrays()) { return; } this.firstEntry = ENDPOINT; this.lastEntry = ENDPOINT; if (links != null) { Arrays.fill(links, 0, size(), 0); } super.clear(); } }





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