| /* |
| * 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.geode.internal; |
| |
| import java.io.IOException; |
| import java.io.Serializable; |
| import java.util.ConcurrentModificationException; |
| import java.util.HashMap; |
| import java.util.Hashtable; |
| import java.util.Iterator; |
| import java.util.Map; |
| import java.util.concurrent.locks.ReentrantLock; |
| |
| /** |
| * Written by Doug Lea with assistance from members of JCP JSR-166 Expert Group and released to the |
| * public domain, as explained at http://creativecommons.org/licenses/publicdomain |
| * |
| * <p> |
| * A hash table supporting full concurrency of retrievals and adjustable expected concurrency for |
| * updates. This class obeys the same functional specification as {@link java.util.Hashtable}, and |
| * includes versions of methods corresponding to each method of <tt>Hashtable</tt>. However, even |
| * though all operations are thread-safe, retrieval operations do <em>not</em> entail locking, and |
| * there is <em>not</em> any support for locking the entire table in a way that prevents all access. |
| * This class is fully interoperable with <tt>Hashtable</tt> in programs that rely on its thread |
| * safety but not on its synchronization details. |
| * |
| * <p> |
| * Retrieval operations (including <tt>get</tt>) generally do not block, so may overlap with update |
| * operations (including <tt>put</tt> and <tt>remove</tt>). Retrievals reflect the results of the |
| * most recently <em>completed</em> update operations holding upon their onset. For aggregate |
| * operations such as <tt>putAll</tt> and <tt>clear</tt>, concurrent retrievals may reflect |
| * insertion or removal of only some entries. Similarly, Iterators and Enumerations return elements |
| * reflecting the state of the hash table at some point at or since the creation of the |
| * iterator/enumeration. They do <em>not</em> throw {@link ConcurrentModificationException}. |
| * However, iterators are designed to be used by only one thread at a time. |
| * |
| * <p> |
| * The allowed concurrency among update operations is guided by the optional |
| * <tt>concurrencyLevel</tt> constructor argument (default <tt>16</tt>), which is used as a hint for |
| * internal sizing. The table is internally partitioned to try to permit the indicated number of |
| * concurrent updates without contention. Because placement in hash tables is essentially random, |
| * the actual concurrency will vary. Ideally, you should choose a value to accommodate as many |
| * threads as will ever concurrently modify the table. Using a significantly higher value than you |
| * need can waste space and time, and a significantly lower value can lead to thread contention. But |
| * overestimates and underestimates within an order of magnitude do not usually have much noticeable |
| * impact. A value of one is appropriate when it is known that only one thread will modify and all |
| * others will only read. Also, resizing this or any other kind of hash table is a relatively slow |
| * operation, so, when possible, it is a good idea to provide estimates of expected table sizes in |
| * constructors. |
| * |
| * <p> |
| * This class and its views and iterators implement all of the <em>optional</em> methods of the |
| * {@link Map} and {@link Iterator} interfaces. |
| * |
| * <p> |
| * Like {@link Hashtable} but unlike {@link HashMap}, this class does <em>not</em> allow |
| * <tt>null</tt> to be used as a key or value. |
| * |
| * <p> |
| * This class is a member of the <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| * Java Collections Framework</a>. |
| * |
| * @since GemFire 1.5 |
| * @param <V> the type of mapped values |
| * |
| * Keys on this map are a primitive "int". |
| */ |
| public class ObjIdConcurrentMap<V> /* extends AbstractMap<K, V> */ |
| implements /* ConcurrentMap<K, V>, */ Serializable { |
| private static final long serialVersionUID = 7249069246763182397L; |
| |
| /* |
| * The basic strategy is to subdivide the table among Segments, each of which itself is a |
| * concurrently readable hash table. |
| */ |
| |
| /* ---------------- Constants -------------- */ |
| |
| /** |
| * The default initial capacity for this table, used when not otherwise specified in a |
| * constructor. |
| */ |
| static final int DEFAULT_INITIAL_CAPACITY = 16; |
| |
| /** |
| * The default load factor for this table, used when not otherwise specified in a constructor. |
| */ |
| static final float DEFAULT_LOAD_FACTOR = 0.75f; |
| |
| /** |
| * The default concurrency level for this table, used when not otherwise specified in a |
| * constructor. |
| */ |
| static final int DEFAULT_CONCURRENCY_LEVEL = 16; |
| |
| /** |
| * The maximum capacity, used if a higher value is implicitly specified by either of the |
| * constructors with arguments. MUST be a power of two <= 1<<30 to ensure that entries are |
| * indexable using ints. |
| */ |
| static final int MAXIMUM_CAPACITY = 1 << 30; |
| |
| /** |
| * The maximum number of segments to allow; used to bound constructor arguments. |
| */ |
| static final int MAX_SEGMENTS = 1 << 16; // slightly conservative |
| |
| /** |
| * Number of unsynchronized retries in size and containsValue methods before resorting to locking. |
| * This is used to avoid unbounded retries if tables undergo continuous modification which would |
| * make it impossible to obtain an accurate result. |
| */ |
| static final int RETRIES_BEFORE_LOCK = 2; |
| |
| /* ---------------- Fields -------------- */ |
| |
| /** |
| * Mask value for indexing into segments. The upper bits of a key's hash code are used to choose |
| * the segment. |
| */ |
| final int segmentMask; |
| |
| /** |
| * Shift value for indexing within segments. |
| */ |
| final int segmentShift; |
| |
| /** |
| * The segments, each of which is a specialized hash table |
| */ |
| final Segment<V>[] segments; |
| |
| // transient Set keySet; |
| // transient Set<Entry<V>> entrySet; |
| // transient Collection<V> values; |
| |
| /* ---------------- Small Utilities -------------- */ |
| |
| /** |
| * Applies a supplemental hash function to a given hashCode, which defends against poor quality |
| * hash functions. This is critical because ConcurrentHashMap uses power-of-two length hash |
| * tables, that otherwise encounter collisions for hashCodes that do not differ in lower or upper |
| * bits. |
| */ |
| private static int hash(int h) { |
| // Spread bits to regularize both segment and index locations, |
| // using variant of single-word Wang/Jenkins hash. |
| h += (h << 15) ^ 0xffffcd7d; |
| h ^= (h >>> 10); |
| h += (h << 3); |
| h ^= (h >>> 6); |
| h += (h << 2) + (h << 14); |
| return h ^ (h >>> 16); |
| } |
| |
| /** |
| * Returns the segment that should be used for key with given hash |
| * |
| * @param hash the hash code for the key |
| * @return the segment |
| */ |
| Segment<V> segmentFor(int hash) { |
| return segments[(hash >>> segmentShift) & segmentMask]; |
| } |
| |
| /* ---------------- Inner Classes -------------- */ |
| |
| /** |
| * ConcurrentHashMap list entry. Note that this is never exported out as a user-visible Map.Entry. |
| * |
| * Because the value field is volatile, not final, it is legal wrt the Java Memory Model for an |
| * unsynchronized reader to see null instead of initial value when read via a data race. Although |
| * a reordering leading to this is not likely to ever actually occur, the |
| * Segment.readValueUnderLock method is used as a backup in case a null (pre-initialized) value is |
| * ever seen in an unsynchronized access method. |
| */ |
| static class HashEntry<V> { |
| final int key; |
| final int hash; |
| volatile V value; |
| final HashEntry<V> next; |
| |
| HashEntry(int key, int hash, HashEntry<V> next, V value) { |
| this.key = key; |
| this.hash = hash; |
| this.next = next; |
| this.value = value; |
| } |
| |
| @SuppressWarnings("unchecked") |
| static <V> HashEntry<V>[] newArray(int i) { |
| return new HashEntry[i]; |
| } |
| } |
| |
| /** |
| * Segments are specialized versions of hash tables. This subclasses from ReentrantLock |
| * opportunistically, just to simplify some locking and avoid separate construction. |
| */ |
| static class Segment<V> extends ReentrantLock implements Serializable { |
| /* |
| * Segments maintain a table of entry lists that are ALWAYS kept in a consistent state, so can |
| * be read without locking. Next fields of nodes are immutable (final). All list additions are |
| * performed at the front of each bin. This makes it easy to check changes, and also fast to |
| * traverse. When nodes would otherwise be changed, new nodes are created to replace them. This |
| * works well for hash tables since the bin lists tend to be short. (The average length is less |
| * than two for the default load factor threshold.) |
| * |
| * Read operations can thus proceed without locking, but rely on selected uses of volatiles to |
| * ensure that completed write operations performed by other threads are noticed. For most |
| * purposes, the "count" field, tracking the number of elements, serves as that volatile |
| * variable ensuring visibility. This is convenient because this field needs to be read in many |
| * read operations anyway: |
| * |
| * - All (unsynchronized) read operations must first read the "count" field, and should not look |
| * at table entries if it is 0. |
| * |
| * - All (synchronized) write operations should write to the "count" field after structurally |
| * changing any bin. The operations must not take any action that could even momentarily cause a |
| * concurrent read operation to see inconsistent data. This is made easier by the nature of the |
| * read operations in Map. For example, no operation can reveal that the table has grown but the |
| * threshold has not yet been updated, so there are no atomicity requirements for this with |
| * respect to reads. |
| * |
| * As a guide, all critical volatile reads and writes to the count field are marked in code |
| * comments. |
| */ |
| |
| private static final long serialVersionUID = 2249069246763182397L; |
| |
| /** |
| * The number of elements in this segment's region. |
| */ |
| transient volatile int count; |
| |
| /** |
| * Number of updates that alter the size of the table. This is used during bulk-read methods to |
| * make sure they see a consistent snapshot: If modCounts change during a traversal of segments |
| * computing size or checking containsValue, then we might have an inconsistent view of state so |
| * (usually) must retry. |
| */ |
| transient int modCount; |
| |
| /** |
| * The table is rehashed when its size exceeds this threshold. (The value of this field is |
| * always <tt>(int)(capacity * |
| * loadFactor)</tt>.) |
| */ |
| transient int threshold; |
| |
| /** |
| * The per-segment table. |
| */ |
| transient volatile HashEntry<V>[] table; |
| |
| /** |
| * The load factor for the hash table. Even though this value is same for all segments, it is |
| * replicated to avoid needing links to outer object. |
| * |
| * @serial |
| */ |
| final float loadFactor; |
| |
| Segment(int initialCapacity, float lf) { |
| loadFactor = lf; |
| setTable(HashEntry.<V>newArray(initialCapacity)); |
| } |
| |
| @SuppressWarnings("unchecked") |
| static <K, V> Segment<V>[] newArray(int i) { |
| return new Segment[i]; |
| } |
| |
| /** |
| * Sets table to new HashEntry array. Call only while holding lock or in constructor. |
| */ |
| void setTable(HashEntry<V>[] newTable) { |
| threshold = (int) (newTable.length * loadFactor); |
| table = newTable; |
| } |
| |
| /** |
| * Returns properly casted first entry of bin for given hash. |
| */ |
| HashEntry<V> getFirst(int hash) { |
| HashEntry<V>[] tab = table; |
| return tab[hash & (tab.length - 1)]; |
| } |
| |
| /** |
| * Reads value field of an entry under lock. Called if value field ever appears to be null. This |
| * is possible only if a compiler happens to reorder a HashEntry initialization with its table |
| * assignment, which is legal under memory model but is not known to ever occur. |
| */ |
| V readValueUnderLock(HashEntry<V> e) { |
| lock(); |
| try { |
| return e.value; |
| } finally { |
| unlock(); |
| } |
| } |
| |
| /* Specialized implementations of map methods */ |
| |
| V get(int key, int hash) { |
| if (count != 0) { // read-volatile |
| HashEntry<V> e = getFirst(hash); |
| while (e != null) { |
| if (e.hash == hash && key == e.key) { |
| V v = e.value; |
| if (v != null) |
| return v; |
| return readValueUnderLock(e); // recheck |
| } |
| e = e.next; |
| } |
| } |
| return null; |
| } |
| |
| boolean containsKey(int key, int hash) { |
| if (count != 0) { // read-volatile |
| HashEntry<V> e = getFirst(hash); |
| while (e != null) { |
| if (e.hash == hash && key == e.key) |
| return true; |
| e = e.next; |
| } |
| } |
| return false; |
| } |
| |
| boolean containsValue(Object value) { |
| if (count != 0) { // read-volatile |
| HashEntry<V>[] tab = table; |
| int len = tab.length; |
| for (int i = 0; i < len; i++) { |
| for (HashEntry<V> e = tab[i]; e != null; e = e.next) { |
| V v = e.value; |
| if (v == null) // recheck |
| v = readValueUnderLock(e); |
| if (value.equals(v)) |
| return true; |
| } |
| } |
| } |
| return false; |
| } |
| |
| boolean replace(int key, int hash, V oldValue, V newValue) { |
| lock(); |
| try { |
| HashEntry<V> e = getFirst(hash); |
| while (e != null && (e.hash != hash || key != e.key)) |
| e = e.next; |
| |
| boolean replaced = false; |
| if (e != null && oldValue.equals(e.value)) { |
| replaced = true; |
| e.value = newValue; |
| } |
| return replaced; |
| } finally { |
| unlock(); |
| } |
| } |
| |
| V replace(int key, int hash, V newValue) { |
| lock(); |
| try { |
| HashEntry<V> e = getFirst(hash); |
| while (e != null && (e.hash != hash || key != e.key)) |
| e = e.next; |
| |
| V oldValue = null; |
| if (e != null) { |
| oldValue = e.value; |
| e.value = newValue; |
| } |
| return oldValue; |
| } finally { |
| unlock(); |
| } |
| } |
| |
| |
| V put(int key, int hash, V value, boolean onlyIfAbsent) { |
| lock(); |
| try { |
| int c = count; |
| if (c++ > threshold) // ensure capacity |
| rehash(); |
| HashEntry<V>[] tab = table; |
| int index = hash & (tab.length - 1); |
| HashEntry<V> first = tab[index]; |
| HashEntry<V> e = first; |
| while (e != null && (e.hash != hash || key != e.key)) |
| e = e.next; |
| |
| V oldValue; |
| if (e != null) { |
| oldValue = e.value; |
| if (!onlyIfAbsent) |
| e.value = value; |
| } else { |
| oldValue = null; |
| ++modCount; |
| tab[index] = new HashEntry<V>(key, hash, first, value); |
| count = c; // write-volatile |
| } |
| return oldValue; |
| } finally { |
| unlock(); |
| } |
| } |
| |
| void rehash() { |
| HashEntry<V>[] oldTable = table; |
| int oldCapacity = oldTable.length; |
| if (oldCapacity >= MAXIMUM_CAPACITY) |
| return; |
| |
| /* |
| * Reclassify nodes in each list to new Map. Because we are using power-of-two expansion, the |
| * elements from each bin must either stay at same index, or move with a power of two offset. |
| * We eliminate unnecessary node creation by catching cases where old nodes can be reused |
| * because their next fields won't change. Statistically, at the default threshold, only about |
| * one-sixth of them need cloning when a table doubles. The nodes they replace will be garbage |
| * collectable as soon as they are no longer referenced by any reader thread that may be in |
| * the midst of traversing table right now. |
| */ |
| |
| HashEntry<V>[] newTable = HashEntry.newArray(oldCapacity << 1); |
| threshold = (int) (newTable.length * loadFactor); |
| int sizeMask = newTable.length - 1; |
| for (int i = 0; i < oldCapacity; i++) { |
| // We need to guarantee that any existing reads of old Map can |
| // proceed. So we cannot yet null out each bin. |
| HashEntry<V> e = oldTable[i]; |
| |
| if (e != null) { |
| HashEntry<V> next = e.next; |
| int idx = e.hash & sizeMask; |
| |
| // Single node on list |
| if (next == null) |
| newTable[idx] = e; |
| |
| else { |
| // Reuse trailing consecutive sequence at same slot |
| HashEntry<V> lastRun = e; |
| int lastIdx = idx; |
| for (HashEntry<V> last = next; last != null; last = last.next) { |
| int k = last.hash & sizeMask; |
| if (k != lastIdx) { |
| lastIdx = k; |
| lastRun = last; |
| } |
| } |
| newTable[lastIdx] = lastRun; |
| |
| // Clone all remaining nodes |
| for (HashEntry<V> p = e; p != lastRun; p = p.next) { |
| int k = p.hash & sizeMask; |
| HashEntry<V> n = newTable[k]; |
| newTable[k] = new HashEntry<V>(p.key, p.hash, n, p.value); |
| } |
| } |
| } |
| } |
| table = newTable; |
| } |
| |
| /** |
| * Remove; match on key only if value null, else match both. |
| */ |
| V remove(int key, int hash, Object value) { |
| lock(); |
| try { |
| int c = count - 1; |
| HashEntry<V>[] tab = table; |
| int index = hash & (tab.length - 1); |
| HashEntry<V> first = tab[index]; |
| HashEntry<V> e = first; |
| while (e != null && (e.hash != hash || key != e.key)) |
| e = e.next; |
| |
| V oldValue = null; |
| if (e != null) { |
| V v = e.value; |
| if (value == null || value.equals(v)) { |
| oldValue = v; |
| // All entries following removed node can stay |
| // in list, but all preceding ones need to be |
| // cloned. |
| ++modCount; |
| HashEntry<V> newFirst = e.next; |
| for (HashEntry<V> p = first; p != e; p = p.next) |
| newFirst = new HashEntry<V>(p.key, p.hash, newFirst, p.value); |
| tab[index] = newFirst; |
| count = c; // write-volatile |
| } |
| } |
| return oldValue; |
| } finally { |
| unlock(); |
| } |
| } |
| |
| void clear() { |
| if (count != 0) { |
| lock(); |
| try { |
| HashEntry<V>[] tab = table; |
| for (int i = 0; i < tab.length; i++) |
| tab[i] = null; |
| ++modCount; |
| count = 0; // write-volatile |
| } finally { |
| unlock(); |
| } |
| } |
| } |
| } |
| |
| |
| |
| /* ---------------- Public operations -------------- */ |
| |
| /** |
| * Creates a new, empty map with the specified initial capacity, load factor and concurrency |
| * level. |
| * |
| * @param initialCapacity the initial capacity. The implementation performs internal sizing to |
| * accommodate this many elements. |
| * @param loadFactor the load factor threshold, used to control resizing. Resizing may be |
| * performed when the average number of elements per bin exceeds this threshold. |
| * @param concurrencyLevel the estimated number of concurrently updating threads. The |
| * implementation performs internal sizing to try to accommodate this many threads. |
| * @throws IllegalArgumentException if the initial capacity is negative or the load factor or |
| * concurrencyLevel are nonpositive. |
| */ |
| public ObjIdConcurrentMap(int initialCapacity, float loadFactor, int concurrencyLevel) { |
| if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0) |
| throw new IllegalArgumentException(); |
| |
| if (concurrencyLevel > MAX_SEGMENTS) |
| concurrencyLevel = MAX_SEGMENTS; |
| |
| // Find power-of-two sizes best matching arguments |
| int sshift = 0; |
| int ssize = 1; |
| while (ssize < concurrencyLevel) { |
| ++sshift; |
| ssize <<= 1; |
| } |
| segmentShift = 32 - sshift; |
| segmentMask = ssize - 1; |
| this.segments = Segment.newArray(ssize); |
| |
| if (initialCapacity > MAXIMUM_CAPACITY) |
| initialCapacity = MAXIMUM_CAPACITY; |
| int c = initialCapacity / ssize; |
| if (c * ssize < initialCapacity) |
| ++c; |
| int cap = 1; |
| while (cap < c) |
| cap <<= 1; |
| |
| for (int i = 0; i < this.segments.length; ++i) |
| this.segments[i] = new Segment<V>(cap, loadFactor); |
| } |
| |
| /** |
| * Creates a new, empty map with the specified initial capacity and load factor and with the |
| * default concurrencyLevel (16). |
| * |
| * @param initialCapacity The implementation performs internal sizing to accommodate this many |
| * elements. |
| * @param loadFactor the load factor threshold, used to control resizing. Resizing may be |
| * performed when the average number of elements per bin exceeds this threshold. |
| * @throws IllegalArgumentException if the initial capacity of elements is negative or the load |
| * factor is nonpositive |
| * |
| * @since GemFire 1.6 |
| */ |
| public ObjIdConcurrentMap(int initialCapacity, float loadFactor) { |
| this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL); |
| } |
| |
| /** |
| * Creates a new, empty map with the specified initial capacity, and with default load factor |
| * (0.75) and concurrencyLevel (16). |
| * |
| * @param initialCapacity the initial capacity. The implementation performs internal sizing to |
| * accommodate this many elements. |
| * @throws IllegalArgumentException if the initial capacity of elements is negative. |
| */ |
| public ObjIdConcurrentMap(int initialCapacity) { |
| this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
| } |
| |
| /** |
| * Creates a new, empty map with a default initial capacity (16), load factor (0.75) and |
| * concurrencyLevel (16). |
| */ |
| public ObjIdConcurrentMap() { |
| this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
| } |
| |
| /** |
| * Returns <tt>true</tt> if this map contains no key-value mappings. |
| * |
| * @return <tt>true</tt> if this map contains no key-value mappings |
| */ |
| public boolean isEmpty() { |
| final Segment<V>[] segments = this.segments; |
| /* |
| * We keep track of per-segment modCounts to avoid ABA problems in which an element in one |
| * segment was added and in another removed during traversal, in which case the table was never |
| * actually empty at any point. Note the similar use of modCounts in the size() and |
| * containsValue() methods, which are the only other methods also susceptible to ABA problems. |
| */ |
| int[] mc = new int[segments.length]; |
| int mcsum = 0; |
| for (int i = 0; i < segments.length; ++i) { |
| if (segments[i].count != 0) |
| return false; |
| else |
| mcsum += mc[i] = segments[i].modCount; |
| } |
| // If mcsum happens to be zero, then we know we got a snapshot |
| // before any modifications at all were made. This is |
| // probably common enough to bother tracking. |
| if (mcsum != 0) { |
| for (int i = 0; i < segments.length; ++i) { |
| if (segments[i].count != 0 || mc[i] != segments[i].modCount) |
| return false; |
| } |
| } |
| return true; |
| } |
| |
| /** |
| * Returns the number of key-value mappings in this map. If the map contains more than |
| * <tt>Integer.MAX_VALUE</tt> elements, returns <tt>Integer.MAX_VALUE</tt>. |
| * |
| * @return the number of key-value mappings in this map |
| */ |
| public int size() { |
| final Segment<V>[] segments = this.segments; |
| long sum = 0; |
| long check = 0; |
| int[] mc = new int[segments.length]; |
| // Try a few times to get accurate count. On failure due to |
| // continuous async changes in table, resort to locking. |
| for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) { |
| check = 0; |
| sum = 0; |
| int mcsum = 0; |
| for (int i = 0; i < segments.length; ++i) { |
| sum += segments[i].count; |
| mcsum += mc[i] = segments[i].modCount; |
| } |
| if (mcsum != 0) { |
| for (int i = 0; i < segments.length; ++i) { |
| check += segments[i].count; |
| if (mc[i] != segments[i].modCount) { |
| check = -1; // force retry |
| break; |
| } |
| } |
| } |
| if (check == sum) |
| break; |
| } |
| if (check != sum) { // Resort to locking all segments |
| sum = 0; |
| for (int i = 0; i < segments.length; ++i) |
| segments[i].lock(); |
| for (int i = 0; i < segments.length; ++i) |
| sum += segments[i].count; |
| for (int i = 0; i < segments.length; ++i) |
| segments[i].unlock(); |
| } |
| if (sum > Integer.MAX_VALUE) |
| return Integer.MAX_VALUE; |
| else |
| return (int) sum; |
| } |
| |
| /** |
| * Returns the value to which the specified key is mapped, or {@code null} if this map contains no |
| * mapping for the key. |
| * |
| * <p> |
| * More formally, if this map contains a mapping from a key {@code k} to a value {@code v} such |
| * that {@code key.equals(k)}, then this method returns {@code v}; otherwise it returns |
| * {@code null}. (There can be at most one such mapping.) |
| * |
| * @throws NullPointerException if the specified key is null |
| */ |
| public V get(int key) { |
| int hash = hash(key); |
| return segmentFor(hash).get(key, hash); |
| } |
| |
| /** |
| * Tests if the specified object is a key in this table. |
| * |
| * @param key possible key |
| * @return <tt>true</tt> if and only if the specified object is a key in this table, as determined |
| * by the <tt>equals</tt> method; <tt>false</tt> otherwise. |
| * @throws NullPointerException if the specified key is null |
| */ |
| public boolean containsKey(int key) { |
| int hash = hash(key); |
| return segmentFor(hash).containsKey(key, hash); |
| } |
| |
| /** |
| * Returns <tt>true</tt> if this map maps one or more keys to the specified value. Note: This |
| * method requires a full internal traversal of the hash table, and so is much slower than method |
| * <tt>containsKey</tt>. |
| * |
| * @param value value whose presence in this map is to be tested |
| * @return <tt>true</tt> if this map maps one or more keys to the specified value |
| * @throws NullPointerException if the specified value is null |
| */ |
| public boolean containsValue(Object value) { |
| if (value == null) |
| throw new NullPointerException(); |
| |
| // See explanation of modCount use above |
| |
| final Segment<V>[] segments = this.segments; |
| int[] mc = new int[segments.length]; |
| |
| // Try a few times without locking |
| for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) { |
| // int sum = 0; |
| int mcsum = 0; |
| for (int i = 0; i < segments.length; ++i) { |
| // int c = segments[i].count; |
| mcsum += mc[i] = segments[i].modCount; |
| if (segments[i].containsValue(value)) |
| return true; |
| } |
| boolean cleanSweep = true; |
| if (mcsum != 0) { |
| for (int i = 0; i < segments.length; ++i) { |
| // int c = segments[i].count; |
| if (mc[i] != segments[i].modCount) { |
| cleanSweep = false; |
| break; |
| } |
| } |
| } |
| if (cleanSweep) |
| return false; |
| } |
| // Resort to locking all segments |
| for (int i = 0; i < segments.length; ++i) |
| segments[i].lock(); |
| boolean found = false; |
| try { |
| for (int i = 0; i < segments.length; ++i) { |
| if (segments[i].containsValue(value)) { |
| found = true; |
| break; |
| } |
| } |
| } finally { |
| for (int i = 0; i < segments.length; ++i) |
| segments[i].unlock(); |
| } |
| return found; |
| } |
| |
| /** |
| * Legacy method testing if some key maps into the specified value in this table. This method is |
| * identical in functionality to {@link #containsValue}, and exists solely to ensure full |
| * compatibility with class {@link java.util.Hashtable}, which supported this method prior to |
| * introduction of the Java Collections framework. |
| * |
| * @param value a value to search for |
| * @return <tt>true</tt> if and only if some key maps to the <tt>value</tt> argument in this table |
| * as determined by the <tt>equals</tt> method; <tt>false</tt> otherwise |
| * @throws NullPointerException if the specified value is null |
| */ |
| public boolean contains(Object value) { |
| return containsValue(value); |
| } |
| |
| /** |
| * Maps the specified key to the specified value in this table. Neither the key nor the value can |
| * be null. |
| * |
| * <p> |
| * The value can be retrieved by calling the <tt>get</tt> method with a key that is equal to the |
| * original key. |
| * |
| * @param key key with which the specified value is to be associated |
| * @param value value to be associated with the specified key |
| * @return the previous value associated with <tt>key</tt>, or <tt>null</tt> if there was no |
| * mapping for <tt>key</tt> |
| * @throws NullPointerException if the specified key or value is null |
| */ |
| public V put(int key, V value) { |
| if (value == null) |
| throw new NullPointerException(); |
| int hash = hash(key); |
| return segmentFor(hash).put(key, hash, value, false); |
| } |
| |
| /** |
| * |
| * @return the previous value associated with the specified key, or <tt>null</tt> if there was no |
| * mapping for the key |
| * @throws NullPointerException if the specified key or value is null |
| */ |
| public V putIfAbsent(int key, V value) { |
| if (value == null) |
| throw new NullPointerException(); |
| int hash = hash(key); |
| return segmentFor(hash).put(key, hash, value, true); |
| } |
| |
| /** |
| * Removes the key (and its corresponding value) from this map. This method does nothing if the |
| * key is not in the map. |
| * |
| * @param key the key that needs to be removed |
| * @return the previous value associated with <tt>key</tt>, or <tt>null</tt> if there was no |
| * mapping for <tt>key</tt> |
| * @throws NullPointerException if the specified key is null |
| */ |
| public V remove(int key) { |
| int hash = hash(key); |
| return segmentFor(hash).remove(key, hash, null); |
| } |
| |
| /** |
| * |
| * @throws NullPointerException if the specified key is null |
| */ |
| public boolean remove(int key, Object value) { |
| int hash = hash(key); |
| if (value == null) |
| return false; |
| return segmentFor(hash).remove(key, hash, value) != null; |
| } |
| |
| /** |
| * |
| * @throws NullPointerException if any of the arguments are null |
| */ |
| public boolean replace(int key, V oldValue, V newValue) { |
| if (oldValue == null || newValue == null) |
| throw new NullPointerException(); |
| int hash = hash(key); |
| return segmentFor(hash).replace(key, hash, oldValue, newValue); |
| } |
| |
| /** |
| * |
| * @return the previous value associated with the specified key, or <tt>null</tt> if there was no |
| * mapping for the key |
| * @throws NullPointerException if the specified key or value is null |
| */ |
| public V replace(int key, V value) { |
| if (value == null) |
| throw new NullPointerException(); |
| int hash = hash(key); |
| return segmentFor(hash).replace(key, hash, value); |
| } |
| |
| /** |
| * Removes all of the mappings from this map. |
| */ |
| public void clear() { |
| for (int i = 0; i < segments.length; ++i) |
| segments[i].clear(); |
| } |
| |
| /* ---------------- Serialization Support -------------- */ |
| |
| /** |
| * Save the state of the <tt>ConcurrentHashMap</tt> instance to a stream (i.e., serialize it). |
| * |
| * @param s the stream |
| * @serialData the key (Object) and value (Object) for each key-value mapping, followed by a null |
| * pair. The key-value mappings are emitted in no particular order. |
| */ |
| private void writeObject(java.io.ObjectOutputStream s) throws IOException { |
| s.defaultWriteObject(); |
| |
| for (int k = 0; k < segments.length; ++k) { |
| Segment<V> seg = segments[k]; |
| seg.lock(); |
| try { |
| HashEntry<V>[] tab = seg.table; |
| for (int i = 0; i < tab.length; ++i) { |
| for (HashEntry<V> e = tab[i]; e != null; e = e.next) { |
| s.writeObject(e.key); |
| s.writeObject(e.value); |
| } |
| } |
| } finally { |
| seg.unlock(); |
| } |
| } |
| s.writeObject(null); |
| s.writeObject(null); |
| } |
| |
| /** |
| * Reconstitute the <tt>ConcurrentHashMap</tt> instance from a stream (i.e., deserialize it). |
| * |
| * @param s the stream |
| */ |
| @SuppressWarnings("unchecked") |
| private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException { |
| s.defaultReadObject(); |
| |
| // Initialize each segment to be minimally sized, and let grow. |
| for (int i = 0; i < segments.length; ++i) { |
| segments[i].setTable(new HashEntry[1]); |
| } |
| |
| // Read the keys and values, and put the mappings in the table |
| for (;;) { |
| int key = s.readInt(); |
| V value = (V) s.readObject(); |
| // if (key == null) |
| // break; |
| put(key, value); |
| } |
| } |
| } |