// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// http://code.google.com/p/protobuf/
//
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// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
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// distribution.
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// contributors may be used to endorse or promote products derived from
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//
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package com.google.protobuf;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.TreeMap;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.SortedMap;
/**
* A custom map implementation from FieldDescriptor to Object optimized to
* minimize the number of memory allocations for instances with a small number
* of mappings. The implementation stores the first {@code k} mappings in an
* array for a configurable value of {@code k}, allowing direct access to the
* corresponding {@code Entry}s without the need to create an Iterator. The
* remaining entries are stored in an overflow map. Iteration over the entries
* in the map should be done as follows:
*
* <pre> {@code
* for (int i = 0; i < fieldMap.getNumArrayEntries(); i++) {
* process(fieldMap.getArrayEntryAt(i));
* }
* for (Map.Entry<K, V> entry : fieldMap.getOverflowEntries()) {
* process(entry);
* }
* }</pre>
*
* The resulting iteration is in order of ascending field tag number. The
* object returned by {@link #entrySet()} adheres to the same contract but is
* less efficient as it necessarily involves creating an object for iteration.
* <p>
* The tradeoff for this memory efficiency is that the worst case running time
* of the {@code put()} operation is {@code O(k + lg n)}, which happens when
* entries are added in descending order. {@code k} should be chosen such that
* it covers enough common cases without adversely affecting larger maps. In
* practice, the worst case scenario does not happen for extensions because
* extension fields are serialized and deserialized in order of ascending tag
* number, but the worst case scenario can happen for DynamicMessages.
* <p>
* The running time for all other operations is similar to that of
* {@code TreeMap}.
* <p>
* Instances are not thread-safe until {@link #makeImmutable()} is called,
* after which any modifying operation will result in an
* {@link UnsupportedOperationException}.
*
* @author darick@google.com Darick Tong
*/
// This class is final for all intents and purposes because the constructor is
// private. However, the FieldDescriptor-specific logic is encapsulated in
// a subclass to aid testability of the core logic.
class SmallSortedMap<K extends Comparable<K>, V> extends AbstractMap<K, V> {
/**
* Creates a new instance for mapping FieldDescriptors to their values.
* The {@link #makeImmutable()} implementation will convert the List values
* of any repeated fields to unmodifiable lists.
*
* @param arraySize The size of the entry array containing the
* lexicographically smallest mappings.
*/
static <FieldDescriptorType extends
FieldSet.FieldDescriptorLite<FieldDescriptorType>>
SmallSortedMap<FieldDescriptorType, Object> newFieldMap(int arraySize) {
return new SmallSortedMap<FieldDescriptorType, Object>(arraySize) {
@Override
@SuppressWarnings("unchecked")
public void makeImmutable() {
if (!isImmutable()) {
for (int i = 0; i < getNumArrayEntries(); i++) {
final Map.Entry<FieldDescriptorType, Object> entry =
getArrayEntryAt(i);
if (entry.getKey().isRepeated()) {
final List value = (List) entry.getValue();
entry.setValue(Collections.unmodifiableList(value));
}
}
for (Map.Entry<FieldDescriptorType, Object> entry :
getOverflowEntries()) {
if (entry.getKey().isRepeated()) {
final List value = (List) entry.getValue();
entry.setValue(Collections.unmodifiableList(value));
}
}
}
super.makeImmutable();
}
};
}
/**
* Creates a new instance for testing.
*
* @param arraySize The size of the entry array containing the
* lexicographically smallest mappings.
*/
static <K extends Comparable<K>, V> SmallSortedMap<K, V> newInstanceForTest(
int arraySize) {
return new SmallSortedMap<K, V>(arraySize);
}
private final int maxArraySize;
// The "entry array" is actually a List because generic arrays are not
// allowed. ArrayList also nicely handles the entry shifting on inserts and
// removes.
private List<Entry> entryList;
private Map<K, V> overflowEntries;
private boolean isImmutable;
// The EntrySet is a stateless view of the Map. It's initialized the first
// time it is requested and reused henceforth.
private volatile EntrySet lazyEntrySet;
/**
* @code arraySize Size of the array in which the lexicographically smallest
* mappings are stored. (i.e. the {@code k} referred to in the class
* documentation).
*/
private SmallSortedMap(int arraySize) {
this.maxArraySize = arraySize;
this.entryList = Collections.emptyList();
this.overflowEntries = Collections.emptyMap();
}
/** Make this map immutable from this point forward. */
public void makeImmutable() {
if (!isImmutable) {
// Note: There's no need to wrap the entryList in an unmodifiableList
// because none of the list's accessors are exposed. The iterator() of
// overflowEntries, on the other hand, is exposed so it must be made
// unmodifiable.
overflowEntries = overflowEntries.isEmpty() ?
Collections.<K, V>emptyMap() :
Collections.unmodifiableMap(overflowEntries);
isImmutable = true;
}
}
/** @return Whether {@link #makeImmutable()} has been called. */
public boolean isImmutable() {
return isImmutable;
}
/** @return The number of entries in the entry array. */
public int getNumArrayEntries() {
return entryList.size();
}
/** @return The array entry at the given {@code index}. */
public Map.Entry<K, V> getArrayEntryAt(int index) {
return entryList.get(index);
}
/** @return There number of overflow entries. */
public int getNumOverflowEntries() {
return overflowEntries.size();
}
/** @return An iterable over the overflow entries. */
public Iterable<Map.Entry<K, V>> getOverflowEntries() {
return overflowEntries.isEmpty() ?
EmptySet.<Map.Entry<K, V>>iterable() :
overflowEntries.entrySet();
}
@Override
public int size() {
return entryList.size() + overflowEntries.size();
}
/**
* The implementation throws a {@code ClassCastException} if o is not an
* object of type {@code K}.
*
* {@inheritDoc}
*/
@Override
public boolean containsKey(Object o) {
@SuppressWarnings("unchecked")
final K key = (K) o;
return binarySearchInArray(key) >= 0 || overflowEntries.containsKey(key);
}
/**
* The implementation throws a {@code ClassCastException} if o is not an
* object of type {@code K}.
*
* {@inheritDoc}
*/
@Override
public V get(Object o) {
@SuppressWarnings("unchecked")
final K key = (K) o;
final int index = binarySearchInArray(key);
if (index >= 0) {
return entryList.get(index).getValue();
}
return overflowEntries.get(key);
}
@Override
public V put(K key, V value) {
checkMutable();
final int index = binarySearchInArray(key);
if (index >= 0) {
// Replace existing array entry.
return entryList.get(index).setValue(value);
}
ensureEntryArrayMutable();
final int insertionPoint = -(index + 1);
if (insertionPoint >= maxArraySize) {
// Put directly in overflow.
return getOverflowEntriesMutable().put(key, value);
}
// Insert new Entry in array.
if (entryList.size() == maxArraySize) {
// Shift the last array entry into overflow.
final Entry lastEntryInArray = entryList.remove(maxArraySize - 1);
getOverflowEntriesMutable().put(lastEntryInArray.getKey(),
lastEntryInArray.getValue());
}
entryList.add(insertionPoint, new Entry(key, value));
return null;
}
@Override
public void clear() {
checkMutable();
if (!entryList.isEmpty()) {
entryList.clear();
}
if (!overflowEntries.isEmpty()) {
overflowEntries.clear();
}
}
/**
* The implementation throws a {@code ClassCastException} if o is not an
* object of type {@code K}.
*
* {@inheritDoc}
*/
@Override
public V remove(Object o) {
checkMutable();
@SuppressWarnings("unchecked")
final K key = (K) o;
final int index = binarySearchInArray(key);
if (index >= 0) {
return removeArrayEntryAt(index);
}
// overflowEntries might be Collections.unmodifiableMap(), so only
// call remove() if it is non-empty.
if (overflowEntries.isEmpty()) {
return null;
} else {
return overflowEntries.remove(key);
}
}
private V removeArrayEntryAt(int index) {
checkMutable();
final V removed = entryList.remove(index).getValue();
if (!overflowEntries.isEmpty()) {
// Shift the first entry in the overflow to be the last entry in the
// array.
final Iterator<Map.Entry<K, V>> iterator =
getOverflowEntriesMutable().entrySet().iterator();
entryList.add(new Entry(iterator.next()));
iterator.remove();
}
return removed;
}
/**
* @param key The key to find in the entry array.
* @return The returned integer position follows the same semantics as the
* value returned by {@link java.util.Arrays#binarySearch()}.
*/
private int binarySearchInArray(K key) {
int left = 0;
int right = entryList.size() - 1;
// Optimization: For the common case in which entries are added in
// ascending tag order, check the largest element in the array before
// doing a full binary search.
if (right >= 0) {
int cmp = key.compareTo(entryList.get(right).getKey());
if (cmp > 0) {
return -(right + 2); // Insert point is after "right".
} else if (cmp == 0) {
return right;
}
}
while (left <= right) {
int mid = (left + right) / 2;
int cmp = key.compareTo(entryList.get(mid).getKey());
if (cmp < 0) {
right = mid - 1;
} else if (cmp > 0) {
left = mid + 1;
} else {
return mid;
}
}
return -(left + 1);
}
/**
* Similar to the AbstractMap implementation of {@code keySet()} and
* {@code values()}, the entry set is created the first time this method is
* called, and returned in response to all subsequent calls.
*
* {@inheritDoc}
*/
@Override
public Set<Map.Entry<K, V>> entrySet() {
if (lazyEntrySet == null) {
lazyEntrySet = new EntrySet();
}
return lazyEntrySet;
}
/**
* @throws UnsupportedOperationException if {@link #makeImmutable()} has
* has been called.
*/
private void checkMutable() {
if (isImmutable) {
throw new UnsupportedOperationException();
}
}
/**
* @return a {@link SortedMap} to which overflow entries mappings can be
* added or removed.
* @throws UnsupportedOperationException if {@link #makeImmutable()} has been
* called.
*/
@SuppressWarnings("unchecked")
private SortedMap<K, V> getOverflowEntriesMutable() {
checkMutable();
if (overflowEntries.isEmpty() && !(overflowEntries instanceof TreeMap)) {
overflowEntries = new TreeMap<K, V>();
}
return (SortedMap<K, V>) overflowEntries;
}
/**
* Lazily creates the entry list. Any code that adds to the list must first
* call this method.
*/
private void ensureEntryArrayMutable() {
checkMutable();
if (entryList.isEmpty() && !(entryList instanceof ArrayList)) {
entryList = new ArrayList<Entry>(maxArraySize);
}
}
/**
* Entry implementation that implements Comparable in order to support
* binary search within the entry array. Also checks mutability in
* {@link #setValue()}.
*/
private class Entry implements Map.Entry<K, V>, Comparable<Entry> {
private final K key;
private V value;
Entry(Map.Entry<K, V> copy) {
this(copy.getKey(), copy.getValue());
}
Entry(K key, V value) {
this.key = key;
this.value = value;
}
//@Override (Java 1.6 override semantics, but we must support 1.5)
public K getKey() {
return key;
}
//@Override (Java 1.6 override semantics, but we must support 1.5)
public V getValue() {
return value;
}
//@Override (Java 1.6 override semantics, but we must support 1.5)
public int compareTo(Entry other) {
return getKey().compareTo(other.getKey());
}
//@Override (Java 1.6 override semantics, but we must support 1.5)
public V setValue(V newValue) {
checkMutable();
final V oldValue = this.value;
this.value = newValue;
return oldValue;
}
@Override
public boolean equals(Object o) {
if (o == this) {
return true;
}
if (!(o instanceof Map.Entry)) {
return false;
}
@SuppressWarnings("unchecked")
Map.Entry<?, ?> other = (Map.Entry<?, ?>) o;
return equals(key, other.getKey()) && equals(value, other.getValue());
}
@Override
public int hashCode() {
return (key == null ? 0 : key.hashCode()) ^
(value == null ? 0 : value.hashCode());
}
@Override
public String toString() {
return key + "=" + value;
}
/** equals() that handles null values. */
private boolean equals(Object o1, Object o2) {
return o1 == null ? o2 == null : o1.equals(o2);
}
}
/**
* Stateless view of the entries in the field map.
*/
private class EntrySet extends AbstractSet<Map.Entry<K, V>> {
@Override
public Iterator<Map.Entry<K, V>> iterator() {
return new EntryIterator();
}
@Override
public int size() {
return SmallSortedMap.this.size();
}
/**
* Throws a {@link ClassCastException} if o is not of the expected type.
*
* {@inheritDoc}
*/
@Override
public boolean contains(Object o) {
@SuppressWarnings("unchecked")
final Map.Entry<K, V> entry = (Map.Entry<K, V>) o;
final V existing = get(entry.getKey());
final V value = entry.getValue();
return existing == value ||
(existing != null && existing.equals(value));
}
@Override
public boolean add(Map.Entry<K, V> entry) {
if (!contains(entry)) {
put(entry.getKey(), entry.getValue());
return true;
}
return false;
}
/**
* Throws a {@link ClassCastException} if o is not of the expected type.
*
* {@inheritDoc}
*/
@Override
public boolean remove(Object o) {
@SuppressWarnings("unchecked")
final Map.Entry<K, V> entry = (Map.Entry<K, V>) o;
if (contains(entry)) {
SmallSortedMap.this.remove(entry.getKey());
return true;
}
return false;
}
@Override
public void clear() {
SmallSortedMap.this.clear();
}
}
/**
* Iterator implementation that switches from the entry array to the overflow
* entries appropriately.
*/
private class EntryIterator implements Iterator<Map.Entry<K, V>> {
private int pos = -1;
private boolean nextCalledBeforeRemove;
private Iterator<Map.Entry<K, V>> lazyOverflowIterator;
//@Override (Java 1.6 override semantics, but we must support 1.5)
public boolean hasNext() {
return (pos + 1) < entryList.size() ||
getOverflowIterator().hasNext();
}
//@Override (Java 1.6 override semantics, but we must support 1.5)
public Map.Entry<K, V> next() {
nextCalledBeforeRemove = true;
// Always increment pos so that we know whether the last returned value
// was from the array or from overflow.
if (++pos < entryList.size()) {
return entryList.get(pos);
}
return getOverflowIterator().next();
}
//@Override (Java 1.6 override semantics, but we must support 1.5)
public void remove() {
if (!nextCalledBeforeRemove) {
throw new IllegalStateException("remove() was called before next()");
}
nextCalledBeforeRemove = false;
checkMutable();
if (pos < entryList.size()) {
removeArrayEntryAt(pos--);
} else {
getOverflowIterator().remove();
}
}
/**
* It is important to create the overflow iterator only after the array
* entries have been iterated over because the overflow entry set changes
* when the client calls remove() on the array entries, which invalidates
* any existing iterators.
*/
private Iterator<Map.Entry<K, V>> getOverflowIterator() {
if (lazyOverflowIterator == null) {
lazyOverflowIterator = overflowEntries.entrySet().iterator();
}
return lazyOverflowIterator;
}
}
/**
* Helper class that holds immutable instances of an Iterable/Iterator that
* we return when the overflow entries is empty. This eliminates the creation
* of an Iterator object when there is nothing to iterate over.
*/
private static class EmptySet {
private static final Iterator<Object> ITERATOR = new Iterator<Object>() {
//@Override (Java 1.6 override semantics, but we must support 1.5)
public boolean hasNext() {
return false;
}
//@Override (Java 1.6 override semantics, but we must support 1.5)
public Object next() {
throw new NoSuchElementException();
}
//@Override (Java 1.6 override semantics, but we must support 1.5)
public void remove() {
throw new UnsupportedOperationException();
}
};
private static final Iterable<Object> ITERABLE = new Iterable<Object>() {
//@Override (Java 1.6 override semantics, but we must support 1.5)
public Iterator<Object> iterator() {
return ITERATOR;
}
};
@SuppressWarnings("unchecked")
static <T> Iterable<T> iterable() {
return (Iterable<T>) ITERABLE;
}
}
}