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Diffstat (limited to 'external/jsr166/java/util/concurrent/ConcurrentHashMap.java')
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diff --git a/external/jsr166/java/util/concurrent/ConcurrentHashMap.java b/external/jsr166/java/util/concurrent/ConcurrentHashMap.java new file mode 100644 index 000000000..7f6d4493c --- /dev/null +++ b/external/jsr166/java/util/concurrent/ConcurrentHashMap.java @@ -0,0 +1,1277 @@ +/* + * 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.util.concurrent.locks.*; +import java.util.*; +import java.io.Serializable; +import java.io.IOException; +import java.io.ObjectInputStream; +import java.io.ObjectOutputStream; + +/** + * 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 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 bits. + */ + private static int hash(int h) { + // This function ensures that hashCodes that differ only by + // constant multiples at each bit position have a bounded + // number of collisions (approximately 8 at default load factor). + h ^= (h >>> 20) ^ (h >>> 12); + return h ^ (h >>> 7) ^ (h >>> 4); + } + + /** + * 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 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 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 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); + } + } +} |