| /* |
| * 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 |
| */ |
| |
| package java.util.concurrent; |
| |
| import java.io.IOException; |
| import java.io.Serializable; |
| import java.util.AbstractCollection; |
| import java.util.AbstractMap; |
| import java.util.AbstractSet; |
| import java.util.Collection; |
| import java.util.ConcurrentModificationException; |
| import java.util.Enumeration; |
| import java.util.HashMap; |
| import java.util.Hashtable; |
| import java.util.Iterator; |
| import java.util.Map; |
| import java.util.NoSuchElementException; |
| import java.util.Set; |
| import java.util.concurrent.locks.ReentrantLock; |
| |
| // BEGIN android-note |
| // removed link to collections framework docs |
| // END android-note |
| |
| /** |
| * 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. |
| * |
| * @since 1.5 |
| * @author Doug Lea |
| * @param <K> the type of keys maintained by this map |
| * @param <V> the type of mapped values |
| */ |
| public class ConcurrentHashMap<K, 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<K,V>[] segments; |
| |
| transient Set<K> keySet; |
| transient Set<Map.Entry<K,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 |
| */ |
| final Segment<K,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 final class HashEntry<K,V> { |
| final K key; |
| final int hash; |
| volatile V value; |
| final HashEntry<K,V> next; |
| |
| HashEntry(K key, int hash, HashEntry<K,V> next, V value) { |
| this.key = key; |
| this.hash = hash; |
| this.next = next; |
| this.value = value; |
| } |
| |
| @SuppressWarnings("unchecked") |
| static final <K,V> HashEntry<K,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 final class Segment<K,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<K,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.<K,V>newArray(initialCapacity)); |
| } |
| |
| @SuppressWarnings("unchecked") |
| static final <K,V> Segment<K,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<K,V>[] newTable) { |
| threshold = (int)(newTable.length * loadFactor); |
| table = newTable; |
| } |
| |
| /** |
| * Returns properly casted first entry of bin for given hash. |
| */ |
| HashEntry<K,V> getFirst(int hash) { |
| HashEntry<K,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<K,V> e) { |
| lock(); |
| try { |
| return e.value; |
| } finally { |
| unlock(); |
| } |
| } |
| |
| /* Specialized implementations of map methods */ |
| |
| V get(Object key, int hash) { |
| if (count != 0) { // read-volatile |
| HashEntry<K,V> e = getFirst(hash); |
| while (e != null) { |
| if (e.hash == hash && key.equals(e.key)) { |
| V v = e.value; |
| if (v != null) |
| return v; |
| return readValueUnderLock(e); // recheck |
| } |
| e = e.next; |
| } |
| } |
| return null; |
| } |
| |
| boolean containsKey(Object key, int hash) { |
| if (count != 0) { // read-volatile |
| HashEntry<K,V> e = getFirst(hash); |
| while (e != null) { |
| if (e.hash == hash && key.equals(e.key)) |
| return true; |
| e = e.next; |
| } |
| } |
| return false; |
| } |
| |
| boolean containsValue(Object value) { |
| if (count != 0) { // read-volatile |
| HashEntry<K,V>[] tab = table; |
| int len = tab.length; |
| for (int i = 0 ; i < len; i++) { |
| for (HashEntry<K,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(K key, int hash, V oldValue, V newValue) { |
| lock(); |
| try { |
| HashEntry<K,V> e = getFirst(hash); |
| while (e != null && (e.hash != hash || !key.equals(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(K key, int hash, V newValue) { |
| lock(); |
| try { |
| HashEntry<K,V> e = getFirst(hash); |
| while (e != null && (e.hash != hash || !key.equals(e.key))) |
| e = e.next; |
| |
| V oldValue = null; |
| if (e != null) { |
| oldValue = e.value; |
| e.value = newValue; |
| } |
| return oldValue; |
| } finally { |
| unlock(); |
| } |
| } |
| |
| |
| V put(K key, int hash, V value, boolean onlyIfAbsent) { |
| lock(); |
| try { |
| int c = count; |
| if (c++ > threshold) // ensure capacity |
| rehash(); |
| HashEntry<K,V>[] tab = table; |
| int index = hash & (tab.length - 1); |
| HashEntry<K,V> first = tab[index]; |
| HashEntry<K,V> e = first; |
| while (e != null && (e.hash != hash || !key.equals(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<K,V>(key, hash, first, value); |
| count = c; // write-volatile |
| } |
| return oldValue; |
| } finally { |
| unlock(); |
| } |
| } |
| |
| void rehash() { |
| HashEntry<K,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<K,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<K,V> e = oldTable[i]; |
| |
| if (e != null) { |
| HashEntry<K,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<K,V> lastRun = e; |
| int lastIdx = idx; |
| for (HashEntry<K,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<K,V> p = e; p != lastRun; p = p.next) { |
| int k = p.hash & sizeMask; |
| HashEntry<K,V> n = newTable[k]; |
| newTable[k] = new HashEntry<K,V>(p.key, p.hash, |
| n, p.value); |
| } |
| } |
| } |
| } |
| table = newTable; |
| } |
| |
| /** |
| * Remove; match on key only if value null, else match both. |
| */ |
| V remove(Object key, int hash, Object value) { |
| lock(); |
| try { |
| int c = count - 1; |
| HashEntry<K,V>[] tab = table; |
| int index = hash & (tab.length - 1); |
| HashEntry<K,V> first = tab[index]; |
| HashEntry<K,V> e = first; |
| while (e != null && (e.hash != hash || !key.equals(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<K,V> newFirst = e.next; |
| for (HashEntry<K,V> p = first; p != e; p = p.next) |
| newFirst = new HashEntry<K,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<K,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 ConcurrentHashMap(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<K,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 1.6 |
| */ |
| public ConcurrentHashMap(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 ConcurrentHashMap(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 ConcurrentHashMap() { |
| this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
| } |
| |
| /** |
| * Creates a new map with the same mappings as the given map. |
| * The map is created with a capacity of 1.5 times the number |
| * of mappings in the given map or 16 (whichever is greater), |
| * and a default load factor (0.75) and concurrencyLevel (16). |
| * |
| * @param m the map |
| */ |
| public ConcurrentHashMap(Map<? extends K, ? extends V> m) { |
| this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, |
| DEFAULT_INITIAL_CAPACITY), |
| DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
| putAll(m); |
| } |
| |
| /** |
| * 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<K,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<K,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(Object key) { |
| int hash = hash(key.hashCode()); |
| 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(Object key) { |
| int hash = hash(key.hashCode()); |
| 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<K,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(K key, V value) { |
| if (value == null) |
| throw new NullPointerException(); |
| int hash = hash(key.hashCode()); |
| return segmentFor(hash).put(key, hash, value, false); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * @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(K key, V value) { |
| if (value == null) |
| throw new NullPointerException(); |
| int hash = hash(key.hashCode()); |
| return segmentFor(hash).put(key, hash, value, true); |
| } |
| |
| /** |
| * Copies all of the mappings from the specified map to this one. |
| * These mappings replace any mappings that this map had for any of the |
| * keys currently in the specified map. |
| * |
| * @param m mappings to be stored in this map |
| */ |
| public void putAll(Map<? extends K, ? extends V> m) { |
| for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) |
| put(e.getKey(), e.getValue()); |
| } |
| |
| /** |
| * 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(Object key) { |
| int hash = hash(key.hashCode()); |
| return segmentFor(hash).remove(key, hash, null); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * @throws NullPointerException if the specified key is null |
| */ |
| public boolean remove(Object key, Object value) { |
| int hash = hash(key.hashCode()); |
| if (value == null) |
| return false; |
| return segmentFor(hash).remove(key, hash, value) != null; |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * @throws NullPointerException if any of the arguments are null |
| */ |
| public boolean replace(K key, V oldValue, V newValue) { |
| if (oldValue == null || newValue == null) |
| throw new NullPointerException(); |
| int hash = hash(key.hashCode()); |
| return segmentFor(hash).replace(key, hash, oldValue, newValue); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * @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(K key, V value) { |
| if (value == null) |
| throw new NullPointerException(); |
| int hash = hash(key.hashCode()); |
| 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(); |
| } |
| |
| /** |
| * Returns a {@link Set} view of the keys contained in this map. |
| * The set is backed by the map, so changes to the map are |
| * reflected in the set, and vice-versa. The set supports element |
| * removal, which removes the corresponding mapping from this map, |
| * via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, |
| * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> |
| * operations. It does not support the <tt>add</tt> or |
| * <tt>addAll</tt> operations. |
| * |
| * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator |
| * that will never throw {@link ConcurrentModificationException}, |
| * and guarantees to traverse elements as they existed upon |
| * construction of the iterator, and may (but is not guaranteed to) |
| * reflect any modifications subsequent to construction. |
| */ |
| public Set<K> keySet() { |
| Set<K> ks = keySet; |
| return (ks != null) ? ks : (keySet = new KeySet()); |
| } |
| |
| /** |
| * Returns a {@link Collection} view of the values contained in this map. |
| * The collection is backed by the map, so changes to the map are |
| * reflected in the collection, and vice-versa. The collection |
| * supports element removal, which removes the corresponding |
| * mapping from this map, via the <tt>Iterator.remove</tt>, |
| * <tt>Collection.remove</tt>, <tt>removeAll</tt>, |
| * <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not |
| * support the <tt>add</tt> or <tt>addAll</tt> operations. |
| * |
| * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator |
| * that will never throw {@link ConcurrentModificationException}, |
| * and guarantees to traverse elements as they existed upon |
| * construction of the iterator, and may (but is not guaranteed to) |
| * reflect any modifications subsequent to construction. |
| */ |
| public Collection<V> values() { |
| Collection<V> vs = values; |
| return (vs != null) ? vs : (values = new Values()); |
| } |
| |
| /** |
| * Returns a {@link Set} view of the mappings contained in this map. |
| * The set is backed by the map, so changes to the map are |
| * reflected in the set, and vice-versa. The set supports element |
| * removal, which removes the corresponding mapping from the map, |
| * via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, |
| * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> |
| * operations. It does not support the <tt>add</tt> or |
| * <tt>addAll</tt> operations. |
| * |
| * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator |
| * that will never throw {@link ConcurrentModificationException}, |
| * and guarantees to traverse elements as they existed upon |
| * construction of the iterator, and may (but is not guaranteed to) |
| * reflect any modifications subsequent to construction. |
| */ |
| public Set<Map.Entry<K,V>> entrySet() { |
| Set<Map.Entry<K,V>> es = entrySet; |
| return (es != null) ? es : (entrySet = new EntrySet()); |
| } |
| |
| /** |
| * Returns an enumeration of the keys in this table. |
| * |
| * @return an enumeration of the keys in this table |
| * @see #keySet() |
| */ |
| public Enumeration<K> keys() { |
| return new KeyIterator(); |
| } |
| |
| /** |
| * Returns an enumeration of the values in this table. |
| * |
| * @return an enumeration of the values in this table |
| * @see #values() |
| */ |
| public Enumeration<V> elements() { |
| return new ValueIterator(); |
| } |
| |
| /* ---------------- Iterator Support -------------- */ |
| |
| abstract class HashIterator { |
| int nextSegmentIndex; |
| int nextTableIndex; |
| HashEntry<K,V>[] currentTable; |
| HashEntry<K, V> nextEntry; |
| HashEntry<K, V> lastReturned; |
| |
| HashIterator() { |
| nextSegmentIndex = segments.length - 1; |
| nextTableIndex = -1; |
| advance(); |
| } |
| |
| public boolean hasMoreElements() { return hasNext(); } |
| |
| final void advance() { |
| if (nextEntry != null && (nextEntry = nextEntry.next) != null) |
| return; |
| |
| while (nextTableIndex >= 0) { |
| if ( (nextEntry = currentTable[nextTableIndex--]) != null) |
| return; |
| } |
| |
| while (nextSegmentIndex >= 0) { |
| Segment<K,V> seg = segments[nextSegmentIndex--]; |
| if (seg.count != 0) { |
| currentTable = seg.table; |
| for (int j = currentTable.length - 1; j >= 0; --j) { |
| if ( (nextEntry = currentTable[j]) != null) { |
| nextTableIndex = j - 1; |
| return; |
| } |
| } |
| } |
| } |
| } |
| |
| public boolean hasNext() { return nextEntry != null; } |
| |
| HashEntry<K,V> nextEntry() { |
| if (nextEntry == null) |
| throw new NoSuchElementException(); |
| lastReturned = nextEntry; |
| advance(); |
| return lastReturned; |
| } |
| |
| public void remove() { |
| if (lastReturned == null) |
| throw new IllegalStateException(); |
| ConcurrentHashMap.this.remove(lastReturned.key); |
| lastReturned = null; |
| } |
| } |
| |
| final class KeyIterator |
| extends HashIterator |
| implements Iterator<K>, Enumeration<K> |
| { |
| public K next() { return super.nextEntry().key; } |
| public K nextElement() { return super.nextEntry().key; } |
| } |
| |
| final class ValueIterator |
| extends HashIterator |
| implements Iterator<V>, Enumeration<V> |
| { |
| public V next() { return super.nextEntry().value; } |
| public V nextElement() { return super.nextEntry().value; } |
| } |
| |
| /** |
| * Custom Entry class used by EntryIterator.next(), that relays |
| * setValue changes to the underlying map. |
| */ |
| final class WriteThroughEntry |
| extends AbstractMap.SimpleEntry<K,V> |
| { |
| WriteThroughEntry(K k, V v) { |
| super(k,v); |
| } |
| |
| /** |
| * Set our entry's value and write through to the map. The |
| * value to return is somewhat arbitrary here. Since a |
| * WriteThroughEntry does not necessarily track asynchronous |
| * changes, the most recent "previous" value could be |
| * different from what we return (or could even have been |
| * removed in which case the put will re-establish). We do not |
| * and cannot guarantee more. |
| */ |
| public V setValue(V value) { |
| if (value == null) throw new NullPointerException(); |
| V v = super.setValue(value); |
| ConcurrentHashMap.this.put(getKey(), value); |
| return v; |
| } |
| } |
| |
| final class EntryIterator |
| extends HashIterator |
| implements Iterator<Entry<K,V>> |
| { |
| public Map.Entry<K,V> next() { |
| HashEntry<K,V> e = super.nextEntry(); |
| return new WriteThroughEntry(e.key, e.value); |
| } |
| } |
| |
| final class KeySet extends AbstractSet<K> { |
| public Iterator<K> iterator() { |
| return new KeyIterator(); |
| } |
| public int size() { |
| return ConcurrentHashMap.this.size(); |
| } |
| public boolean isEmpty() { |
| return ConcurrentHashMap.this.isEmpty(); |
| } |
| public boolean contains(Object o) { |
| return ConcurrentHashMap.this.containsKey(o); |
| } |
| public boolean remove(Object o) { |
| return ConcurrentHashMap.this.remove(o) != null; |
| } |
| public void clear() { |
| ConcurrentHashMap.this.clear(); |
| } |
| } |
| |
| final class Values extends AbstractCollection<V> { |
| public Iterator<V> iterator() { |
| return new ValueIterator(); |
| } |
| public int size() { |
| return ConcurrentHashMap.this.size(); |
| } |
| public boolean isEmpty() { |
| return ConcurrentHashMap.this.isEmpty(); |
| } |
| public boolean contains(Object o) { |
| return ConcurrentHashMap.this.containsValue(o); |
| } |
| public void clear() { |
| ConcurrentHashMap.this.clear(); |
| } |
| } |
| |
| final class EntrySet extends AbstractSet<Map.Entry<K,V>> { |
| public Iterator<Map.Entry<K,V>> iterator() { |
| return new EntryIterator(); |
| } |
| public boolean contains(Object o) { |
| if (!(o instanceof Map.Entry)) |
| return false; |
| Map.Entry<?,?> e = (Map.Entry<?,?>)o; |
| V v = ConcurrentHashMap.this.get(e.getKey()); |
| return v != null && v.equals(e.getValue()); |
| } |
| public boolean remove(Object o) { |
| if (!(o instanceof Map.Entry)) |
| return false; |
| Map.Entry<?,?> e = (Map.Entry<?,?>)o; |
| return ConcurrentHashMap.this.remove(e.getKey(), e.getValue()); |
| } |
| public int size() { |
| return ConcurrentHashMap.this.size(); |
| } |
| public boolean isEmpty() { |
| return ConcurrentHashMap.this.isEmpty(); |
| } |
| public void clear() { |
| ConcurrentHashMap.this.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<K,V> seg = segments[k]; |
| seg.lock(); |
| try { |
| HashEntry<K,V>[] tab = seg.table; |
| for (int i = 0; i < tab.length; ++i) { |
| for (HashEntry<K,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 |
| */ |
| 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 (;;) { |
| K key = (K) s.readObject(); |
| V value = (V) s.readObject(); |
| if (key == null) |
| break; |
| put(key, value); |
| } |
| } |
| } |