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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain. Use, modify, and |
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* redistribute this code in any way without acknowledgement. |
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*/ |
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|
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package java.util.concurrent; |
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import java.util.concurrent.locks.*; |
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import java.util.*; |
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import java.io.Serializable; |
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import java.io.IOException; |
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import java.io.ObjectInputStream; |
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import java.io.ObjectOutputStream; |
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|
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/** |
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* A hash table supporting full concurrency of retrievals and |
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* adjustable expected concurrency for updates. This class obeys the |
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* same functional specification as |
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* <tt>java.util.Hashtable</tt>. However, even though all operations |
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* are thread-safe, retrieval operations do <em>not</em> entail |
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* locking, and there is <em>not</em> any support for locking the |
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* entire table in a way that prevents all access. This class is |
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* fully interoperable with Hashtable in programs that rely on its |
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* thread safety but not on its synchronization details. |
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* |
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* <p> Retrieval operations (including <tt>get</tt>) ordinarily |
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* overlap with update operations (including <tt>put</tt> and |
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* <tt>remove</tt>). Retrievals reflect the results of the most |
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* recently <em>completed</em> update operations holding upon their |
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* onset. For aggregate operations such as <tt>putAll</tt> and |
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* <tt>clear</tt>, concurrent retrievals may reflect insertion or |
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* removal of only some entries. Similarly, Iterators and |
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* Enumerations return elements reflecting the state of the hash table |
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* at some point at or since the creation of the iterator/enumeration. |
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* They do <em>not</em> throw ConcurrentModificationException. |
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* However, Iterators are designed to be used by only one thread at a |
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* time. |
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* |
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* <p> The allowed concurrency among update operations is controlled |
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* by the optional <tt>segments</tt> constructor argument (default |
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* 16). The table is divided into this many independent parts, each of |
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* which can be updated concurrently. Because placement in hash tables |
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* is essentially random, the actual concurrency will vary. As a rough |
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* rule of thumb, you should choose at least as many segments as you |
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* expect concurrent threads. However, using more segments than you |
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* need can waste space and time. Using a value of 1 for |
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* <tt>segments</tt> results in a table that is concurrently readable |
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* but can only be updated by one thread at a time. |
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* |
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* <p> Like Hashtable but unlike java.util.HashMap, this class does |
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* NOT allow <tt>null</tt> to be used as a key or value. |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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*/ |
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public class ConcurrentHashMap<K, V> extends AbstractMap<K, V> |
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implements ConcurrentMap<K, V>, Cloneable, Serializable { |
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|
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/* |
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* The basic strategy is to subdivide the table among Segments, |
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* each of which itself is a concurrently readable hash table. |
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*/ |
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|
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/* ---------------- Constants -------------- */ |
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|
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/** |
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* The default initial number of table slots for this table (32). |
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* Used when not otherwise specified in constructor. |
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*/ |
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private static int DEFAULT_INITIAL_CAPACITY = 16; |
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|
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/** |
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* The maximum capacity, used if a higher value is implicitly |
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* specified by either of the constructors with arguments. MUST |
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* be a power of two <= 1<<30. |
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*/ |
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static final int MAXIMUM_CAPACITY = 1 << 30; |
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|
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/** |
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* The default load factor for this table. Used when not |
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* otherwise specified in constructor. |
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*/ |
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static final float DEFAULT_LOAD_FACTOR = 0.75f; |
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|
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/** |
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* The default number of concurrency control segments. |
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**/ |
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private static final int DEFAULT_SEGMENTS = 16; |
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|
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/* ---------------- Fields -------------- */ |
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|
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/** |
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* Mask value for indexing into segments. The upper bits of a |
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* key's hash code are used to choose the segment. |
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**/ |
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private final int segmentMask; |
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|
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/** |
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* Shift value for indexing within segments. |
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**/ |
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private final int segmentShift; |
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|
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/** |
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* The segments, each of which is a specialized hash table |
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*/ |
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private final Segment[] segments; |
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|
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private transient Set<K> keySet; |
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private transient Set<Map.Entry<K,V>> entrySet; |
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private transient Collection<V> values; |
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|
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/* ---------------- Small Utilities -------------- */ |
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|
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/** |
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* Return a hash code for non-null Object x. |
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* Uses the same hash code spreader as most other j.u hash tables. |
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* @param x the object serving as a key |
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* @return the hash code |
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*/ |
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private static int hash(Object x) { |
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int h = x.hashCode(); |
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h += ~(h << 9); |
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h ^= (h >>> 14); |
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h += (h << 4); |
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h ^= (h >>> 10); |
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return h; |
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} |
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|
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/** |
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* Return the segment that should be used for key with given hash |
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*/ |
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private Segment<K,V> segmentFor(int hash) { |
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return (Segment<K,V>) segments[(hash >>> segmentShift) & segmentMask]; |
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} |
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|
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/* ---------------- Inner Classes -------------- */ |
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|
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/** |
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* Segments are specialized versions of hash tables. This |
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* subclasses from ReentrantLock opportunistically, just to |
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* simplify some locking and avoid separate construction. |
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**/ |
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private static final class Segment<K,V> extends ReentrantLock implements Serializable { |
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/* |
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* Segments maintain a table of entry lists that are ALWAYS |
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* kept in a consistent state, so can be read without locking. |
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* Next fields of nodes are immutable (final). All list |
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* additions are performed at the front of each bin. This |
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* makes it easy to check changes, and also fast to traverse. |
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* When nodes would otherwise be changed, new nodes are |
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* created to replace them. This works well for hash tables |
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* since the bin lists tend to be short. (The average length |
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* is less than two for the default load factor threshold.) |
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* |
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* Read operations can thus proceed without locking, but rely |
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* on a memory barrier to ensure that completed write |
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* operations performed by other threads are |
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* noticed. Conveniently, the "count" field, tracking the |
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* number of elements, can also serve as the volatile variable |
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* providing proper read/write barriers. This is convenient |
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* because this field needs to be read in many read operations |
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* anyway. The use of volatiles for this purpose is only |
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* guaranteed to work in accord with reuirements in |
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* multithreaded environments when run on JVMs conforming to |
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* the clarified JSR133 memory model specification. This true |
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* for hotspot as of release 1.4. |
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* |
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* Implementors note. The basic rules for all this are: |
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* |
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* - All unsynchronized read operations must first read the |
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* "count" field, and should not look at table entries if |
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* it is 0. |
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* |
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* - All synchronized write operations should write to |
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* the "count" field after updating. The operations must not |
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* take any action that could even momentarily cause |
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* a concurrent read operation to see inconsistent |
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* data. This is made easier by the nature of the read |
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* operations in Map. For example, no operation |
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* can reveal that the table has grown but the threshold |
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* has not yet been updated, so there are no atomicity |
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* requirements for this with respect to reads. |
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* |
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* As a guide, all critical volatile reads and writes are marked |
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* in code comments. |
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*/ |
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|
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/** |
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* The number of elements in this segment's region. |
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**/ |
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transient volatile int count; |
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|
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/** |
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* The table is rehashed when its size exceeds this threshold. |
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* (The value of this field is always (int)(capacity * |
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* loadFactor).) |
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*/ |
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private transient int threshold; |
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|
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/** |
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* The per-segment table |
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*/ |
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transient HashEntry[] table; |
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|
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/** |
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* The load factor for the hash table. Even though this value |
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* is same for all segments, it is replicated to avoid needing |
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* links to outer object. |
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* @serial |
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*/ |
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private final float loadFactor; |
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|
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Segment(int initialCapacity, float lf) { |
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loadFactor = lf; |
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setTable(new HashEntry[initialCapacity]); |
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} |
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|
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/** |
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* Set table to new HashEntry array. |
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* Call only while holding lock or in constructor. |
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**/ |
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private void setTable(HashEntry[] newTable) { |
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table = newTable; |
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threshold = (int)(newTable.length * loadFactor); |
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count = count; // write-volatile |
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} |
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|
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/* Specialized implementations of map methods */ |
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|
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V get(K key, int hash) { |
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if (count != 0) { // read-volatile |
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HashEntry[] tab = table; |
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int index = hash & (tab.length - 1); |
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HashEntry<K,V> e = (HashEntry<K,V>) tab[index]; |
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while (e != null) { |
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if (e.hash == hash && key.equals(e.key)) |
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return e.value; |
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e = e.next; |
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} |
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} |
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return null; |
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} |
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|
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boolean containsKey(Object key, int hash) { |
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if (count != 0) { // read-volatile |
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HashEntry[] tab = table; |
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int index = hash & (tab.length - 1); |
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HashEntry<K,V> e = (HashEntry<K,V>) tab[index]; |
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while (e != null) { |
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if (e.hash == hash && key.equals(e.key)) |
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return true; |
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e = e.next; |
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} |
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} |
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return false; |
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} |
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|
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boolean containsValue(Object value) { |
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if (count != 0) { // read-volatile |
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HashEntry[] tab = table; |
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int len = tab.length; |
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for (int i = 0 ; i < len; i++) |
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for (HashEntry<K,V> e = (HashEntry<K,V>)tab[i] ; e != null ; e = e.next) |
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if (value.equals(e.value)) |
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return true; |
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} |
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return false; |
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} |
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|
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V put(K key, int hash, V value, boolean onlyIfAbsent) { |
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lock(); |
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try { |
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int c = count; |
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HashEntry[] tab = table; |
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int index = hash & (tab.length - 1); |
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HashEntry<K,V> first = (HashEntry<K,V>) tab[index]; |
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|
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for (HashEntry<K,V> e = first; e != null; e = (HashEntry<K,V>) e.next) { |
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if (e.hash == hash && key.equals(e.key)) { |
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V oldValue = e.value; |
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if (!onlyIfAbsent) |
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e.value = value; |
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count = c; // write-volatile |
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return oldValue; |
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} |
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} |
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|
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tab[index] = new HashEntry<K,V>(hash, key, value, first); |
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++c; |
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count = c; // write-volatile |
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if (c > threshold) |
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setTable(rehash(tab)); |
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return null; |
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} finally { |
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unlock(); |
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} |
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} |
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|
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private HashEntry[] rehash(HashEntry[] oldTable) { |
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int oldCapacity = oldTable.length; |
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if (oldCapacity >= MAXIMUM_CAPACITY) |
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return oldTable; |
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|
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/* |
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* Reclassify nodes in each list to new Map. Because we are |
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* using power-of-two expansion, the elements from each bin |
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* must either stay at same index, or move with a power of two |
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* offset. We eliminate unnecessary node creation by catching |
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* cases where old nodes can be reused because their next |
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* fields won't change. Statistically, at the default |
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* threshhold, only about one-sixth of them need cloning when |
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* a table doubles. The nodes they replace will be garbage |
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* collectable as soon as they are no longer referenced by any |
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* reader thread that may be in the midst of traversing table |
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* right now. |
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*/ |
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|
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HashEntry[] newTable = new HashEntry[oldCapacity << 1]; |
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int sizeMask = newTable.length - 1; |
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for (int i = 0; i < oldCapacity ; i++) { |
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// We need to guarantee that any existing reads of old Map can |
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// proceed. So we cannot yet null out each bin. |
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HashEntry<K,V> e = (HashEntry<K,V>)oldTable[i]; |
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|
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if (e != null) { |
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HashEntry<K,V> next = e.next; |
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int idx = e.hash & sizeMask; |
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|
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// Single node on list |
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if (next == null) |
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newTable[idx] = e; |
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|
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else { |
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// Reuse trailing consecutive sequence at same slot |
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HashEntry<K,V> lastRun = e; |
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int lastIdx = idx; |
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for (HashEntry<K,V> last = next; |
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last != null; |
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last = last.next) { |
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int k = last.hash & sizeMask; |
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if (k != lastIdx) { |
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lastIdx = k; |
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lastRun = last; |
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} |
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} |
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newTable[lastIdx] = lastRun; |
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|
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// Clone all remaining nodes |
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for (HashEntry<K,V> p = e; p != lastRun; p = p.next) { |
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int k = p.hash & sizeMask; |
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newTable[k] = new HashEntry<K,V>(p.hash, |
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p.key, |
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p.value, |
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(HashEntry<K,V>) newTable[k]); |
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} |
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} |
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} |
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} |
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return newTable; |
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} |
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|
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/** |
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* Remove; match on key only if value null, else match both. |
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*/ |
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V remove(Object key, int hash, Object value) { |
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lock(); |
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try { |
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int c = count; |
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HashEntry[] tab = table; |
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int index = hash & (tab.length - 1); |
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HashEntry<K,V> first = (HashEntry<K,V>)tab[index]; |
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|
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HashEntry<K,V> e = first; |
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for (;;) { |
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if (e == null) |
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return null; |
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if (e.hash == hash && key.equals(e.key)) |
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break; |
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e = e.next; |
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} |
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|
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V oldValue = e.value; |
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if (value != null && !value.equals(oldValue)) |
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return null; |
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|
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// All entries following removed node can stay in list, but |
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// all preceeding ones need to be cloned. |
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HashEntry<K,V> newFirst = e.next; |
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for (HashEntry<K,V> p = first; p != e; p = p.next) |
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newFirst = new HashEntry<K,V>(p.hash, p.key, |
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p.value, newFirst); |
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tab[index] = newFirst; |
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count = c-1; // write-volatile |
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return oldValue; |
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} finally { |
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unlock(); |
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} |
398 |
} |
399 |
|
400 |
void clear() { |
401 |
lock(); |
402 |
try { |
403 |
HashEntry[] tab = table; |
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for (int i = 0; i < tab.length ; i++) |
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tab[i] = null; |
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count = 0; // write-volatile |
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} finally { |
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unlock(); |
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} |
410 |
} |
411 |
} |
412 |
|
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/** |
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* ConcurrentReaderHashMap list entry. |
415 |
*/ |
416 |
private static class HashEntry<K,V> implements Entry<K,V> { |
417 |
private final K key; |
418 |
private V value; |
419 |
private final int hash; |
420 |
private final HashEntry<K,V> next; |
421 |
|
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HashEntry(int hash, K key, V value, HashEntry<K,V> next) { |
423 |
this.value = value; |
424 |
this.hash = hash; |
425 |
this.key = key; |
426 |
this.next = next; |
427 |
} |
428 |
|
429 |
public K getKey() { |
430 |
return key; |
431 |
} |
432 |
|
433 |
public V getValue() { |
434 |
return value; |
435 |
} |
436 |
|
437 |
public V setValue(V newValue) { |
438 |
// We aren't required to, and don't provide any |
439 |
// visibility barriers for setting value. |
440 |
if (newValue == null) |
441 |
throw new NullPointerException(); |
442 |
V oldValue = this.value; |
443 |
this.value = newValue; |
444 |
return oldValue; |
445 |
} |
446 |
|
447 |
public boolean equals(Object o) { |
448 |
if (!(o instanceof Entry)) |
449 |
return false; |
450 |
Entry<K,V> e = (Entry<K,V>)o; |
451 |
return (key.equals(e.getKey()) && value.equals(e.getValue())); |
452 |
} |
453 |
|
454 |
public int hashCode() { |
455 |
return key.hashCode() ^ value.hashCode(); |
456 |
} |
457 |
|
458 |
public String toString() { |
459 |
return key + "=" + value; |
460 |
} |
461 |
} |
462 |
|
463 |
|
464 |
/* ---------------- Public operations -------------- */ |
465 |
|
466 |
/** |
467 |
* Constructs a new, empty map with the specified initial |
468 |
* capacity and the specified load factor. |
469 |
* |
470 |
* @param initialCapacity the initial capacity. The actual |
471 |
* initial capacity is rounded up to the nearest power of two. |
472 |
* @param loadFactor the load factor threshold, used to control resizing. |
473 |
* @param segments the number of concurrently accessible segments. the |
474 |
* actual number of segments is rounded to the next power of two. |
475 |
* @throws IllegalArgumentException if the initial capacity is |
476 |
* negative or the load factor or number of segments are |
477 |
* nonpositive. |
478 |
*/ |
479 |
public ConcurrentHashMap(int initialCapacity, |
480 |
float loadFactor, int segments) { |
481 |
if (!(loadFactor > 0) || initialCapacity < 0 || segments <= 0) |
482 |
throw new IllegalArgumentException(); |
483 |
|
484 |
// Find power-of-two sizes best matching arguments |
485 |
int sshift = 0; |
486 |
int ssize = 1; |
487 |
while (ssize < segments) { |
488 |
++sshift; |
489 |
ssize <<= 1; |
490 |
} |
491 |
segmentShift = 32 - sshift; |
492 |
segmentMask = ssize - 1; |
493 |
this.segments = new Segment[ssize]; |
494 |
|
495 |
if (initialCapacity > MAXIMUM_CAPACITY) |
496 |
initialCapacity = MAXIMUM_CAPACITY; |
497 |
int c = initialCapacity / ssize; |
498 |
if (c * ssize < initialCapacity) |
499 |
++c; |
500 |
int cap = 1; |
501 |
while (cap < c) |
502 |
cap <<= 1; |
503 |
|
504 |
for (int i = 0; i < this.segments.length; ++i) |
505 |
this.segments[i] = new Segment<K,V>(cap, loadFactor); |
506 |
} |
507 |
|
508 |
/** |
509 |
* Constructs a new, empty map with the specified initial |
510 |
* capacity, and with default load factor and segments. |
511 |
* |
512 |
* @param initialCapacity the initial capacity of the |
513 |
* ConcurrentHashMap. |
514 |
* @throws IllegalArgumentException if the initial capacity of |
515 |
* elements is negative. |
516 |
*/ |
517 |
public ConcurrentHashMap(int initialCapacity) { |
518 |
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS); |
519 |
} |
520 |
|
521 |
/** |
522 |
* Constructs a new, empty map with a default initial capacity, |
523 |
* load factor, and number of segments. |
524 |
*/ |
525 |
public ConcurrentHashMap() { |
526 |
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS); |
527 |
} |
528 |
|
529 |
/** |
530 |
* Constructs a new map with the same mappings as the given map. The |
531 |
* map is created with a capacity of twice the number of mappings in |
532 |
* the given map or 11 (whichever is greater), and a default load factor. |
533 |
*/ |
534 |
public <A extends K, B extends V> ConcurrentHashMap(Map<A,B> t) { |
535 |
this(Math.max((int) (t.size() / DEFAULT_LOAD_FACTOR) + 1, |
536 |
11), |
537 |
DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS); |
538 |
putAll(t); |
539 |
} |
540 |
|
541 |
// inherit Map javadoc |
542 |
public int size() { |
543 |
int c = 0; |
544 |
for (int i = 0; i < segments.length; ++i) |
545 |
c += segments[i].count; |
546 |
return c; |
547 |
} |
548 |
|
549 |
// inherit Map javadoc |
550 |
public boolean isEmpty() { |
551 |
for (int i = 0; i < segments.length; ++i) |
552 |
if (segments[i].count != 0) |
553 |
return false; |
554 |
return true; |
555 |
} |
556 |
|
557 |
/** |
558 |
* Returns the value to which the specified key is mapped in this table. |
559 |
* |
560 |
* @param key a key in the table. |
561 |
* @return the value to which the key is mapped in this table; |
562 |
* <code>null</code> if the key is not mapped to any value in |
563 |
* this table. |
564 |
* @throws NullPointerException if the key is |
565 |
* <code>null</code>. |
566 |
* @see #put(Object, Object) |
567 |
*/ |
568 |
public V get(Object key) { |
569 |
int hash = hash(key); // throws NullPointerException if key null |
570 |
return segmentFor(hash).get((K) key, hash); |
571 |
} |
572 |
|
573 |
/** |
574 |
* Tests if the specified object is a key in this table. |
575 |
* |
576 |
* @param key possible key. |
577 |
* @return <code>true</code> if and only if the specified object |
578 |
* is a key in this table, as determined by the |
579 |
* <tt>equals</tt> method; <code>false</code> otherwise. |
580 |
* @throws NullPointerException if the key is |
581 |
* <code>null</code>. |
582 |
* @see #contains(Object) |
583 |
*/ |
584 |
public boolean containsKey(Object key) { |
585 |
int hash = hash(key); // throws NullPointerException if key null |
586 |
return segmentFor(hash).containsKey(key, hash); |
587 |
} |
588 |
|
589 |
/** |
590 |
* Returns <tt>true</tt> if this map maps one or more keys to the |
591 |
* specified value. Note: This method requires a full internal |
592 |
* traversal of the hash table, and so is much slower than |
593 |
* method <tt>containsKey</tt>. |
594 |
* |
595 |
* @param value value whose presence in this map is to be tested. |
596 |
* @return <tt>true</tt> if this map maps one or more keys to the |
597 |
* specified value. |
598 |
* @throws NullPointerException if the value is <code>null</code>. |
599 |
*/ |
600 |
public boolean containsValue(Object value) { |
601 |
if (value == null) |
602 |
throw new NullPointerException(); |
603 |
|
604 |
for (int i = 0; i < segments.length; ++i) { |
605 |
if (segments[i].containsValue(value)) |
606 |
return true; |
607 |
} |
608 |
return false; |
609 |
} |
610 |
/** |
611 |
* Tests if some key maps into the specified value in this table. |
612 |
* This operation is more expensive than the <code>containsKey</code> |
613 |
* method.<p> |
614 |
* |
615 |
* Note that this method is identical in functionality to containsValue, |
616 |
* (which is part of the Map interface in the collections framework). |
617 |
* |
618 |
* @param value a value to search for. |
619 |
* @return <code>true</code> if and only if some key maps to the |
620 |
* <code>value</code> argument in this table as |
621 |
* determined by the <tt>equals</tt> method; |
622 |
* <code>false</code> otherwise. |
623 |
* @throws NullPointerException if the value is <code>null</code>. |
624 |
* @see #containsKey(Object) |
625 |
* @see #containsValue(Object) |
626 |
* @see Map |
627 |
*/ |
628 |
public boolean contains(Object value) { |
629 |
return containsValue(value); |
630 |
} |
631 |
|
632 |
/** |
633 |
* Maps the specified <code>key</code> to the specified |
634 |
* <code>value</code> in this table. Neither the key nor the |
635 |
* value can be <code>null</code>. <p> |
636 |
* |
637 |
* The value can be retrieved by calling the <code>get</code> method |
638 |
* with a key that is equal to the original key. |
639 |
* |
640 |
* @param key the table key. |
641 |
* @param value the value. |
642 |
* @return the previous value of the specified key in this table, |
643 |
* or <code>null</code> if it did not have one. |
644 |
* @throws NullPointerException if the key or value is |
645 |
* <code>null</code>. |
646 |
* @see Object#equals(Object) |
647 |
* @see #get(Object) |
648 |
*/ |
649 |
public V put(K key, V value) { |
650 |
if (value == null) |
651 |
throw new NullPointerException(); |
652 |
int hash = hash(key); |
653 |
return segmentFor(hash).put(key, hash, value, false); |
654 |
} |
655 |
|
656 |
/** |
657 |
* If the specified key is not already associated |
658 |
* with a value, associate it with the given value. |
659 |
* This is equivalent to |
660 |
* <pre> |
661 |
* if (!map.containsKey(key)) map.put(key, value); |
662 |
* return get(key); |
663 |
* </pre> |
664 |
* Except that the action is performed atomically. |
665 |
* @param key key with which the specified value is to be associated. |
666 |
* @param value value to be associated with the specified key. |
667 |
* @return previous value associated with specified key, or <tt>null</tt> |
668 |
* if there was no mapping for key. A <tt>null</tt> return can |
669 |
* also indicate that the map previously associated <tt>null</tt> |
670 |
* with the specified key, if the implementation supports |
671 |
* <tt>null</tt> values. |
672 |
* |
673 |
* @throws NullPointerException this map does not permit <tt>null</tt> |
674 |
* keys or values, and the specified key or value is |
675 |
* <tt>null</tt>. |
676 |
* |
677 |
**/ |
678 |
public V putIfAbsent(K key, V value) { |
679 |
if (value == null) |
680 |
throw new NullPointerException(); |
681 |
int hash = hash(key); |
682 |
return segmentFor(hash).put(key, hash, value, true); |
683 |
} |
684 |
|
685 |
|
686 |
/** |
687 |
* Copies all of the mappings from the specified map to this one. |
688 |
* |
689 |
* These mappings replace any mappings that this map had for any of the |
690 |
* keys currently in the specified Map. |
691 |
* |
692 |
* @param t Mappings to be stored in this map. |
693 |
*/ |
694 |
public void putAll(Map<? extends K, ? extends V> t) { |
695 |
Iterator<Map.Entry<? extends K, ? extends V>> it = t.entrySet().iterator(); |
696 |
while (it.hasNext()) { |
697 |
Entry<? extends K, ? extends V> e = it.next(); |
698 |
put(e.getKey(), e.getValue()); |
699 |
} |
700 |
} |
701 |
|
702 |
/** |
703 |
* Removes the key (and its corresponding value) from this |
704 |
* table. This method does nothing if the key is not in the table. |
705 |
* |
706 |
* @param key the key that needs to be removed. |
707 |
* @return the value to which the key had been mapped in this table, |
708 |
* or <code>null</code> if the key did not have a mapping. |
709 |
* @throws NullPointerException if the key is |
710 |
* <code>null</code>. |
711 |
*/ |
712 |
public V remove(Object key) { |
713 |
int hash = hash(key); |
714 |
return segmentFor(hash).remove(key, hash, null); |
715 |
} |
716 |
|
717 |
/** |
718 |
* Removes the (key, value) pair from this |
719 |
* table. This method does nothing if the key is not in the table, |
720 |
* or if the key is associated with a different value. |
721 |
* |
722 |
* @param key the key that needs to be removed. |
723 |
* @param value the associated value. If the value is null, |
724 |
* it means "any value". |
725 |
* @return the value to which the key had been mapped in this table, |
726 |
* or <code>null</code> if the key did not have a mapping. |
727 |
* @throws NullPointerException if the key is |
728 |
* <code>null</code>. |
729 |
*/ |
730 |
public boolean remove(Object key, Object value) { |
731 |
int hash = hash(key); |
732 |
return segmentFor(hash).remove(key, hash, value) != null; |
733 |
} |
734 |
|
735 |
/** |
736 |
* Removes all mappings from this map. |
737 |
*/ |
738 |
public void clear() { |
739 |
for (int i = 0; i < segments.length; ++i) |
740 |
segments[i].clear(); |
741 |
} |
742 |
|
743 |
|
744 |
/** |
745 |
* Returns a shallow copy of this |
746 |
* <tt>ConcurrentHashMap</tt> instance: the keys and |
747 |
* values themselves are not cloned. |
748 |
* |
749 |
* @return a shallow copy of this map. |
750 |
*/ |
751 |
public Object clone() { |
752 |
// We cannot call super.clone, since it would share final |
753 |
// segments array, and there's no way to reassign finals. |
754 |
|
755 |
float lf = segments[0].loadFactor; |
756 |
int segs = segments.length; |
757 |
int cap = (int)(size() / lf); |
758 |
if (cap < segs) cap = segs; |
759 |
ConcurrentHashMap<K,V> t = new ConcurrentHashMap<K,V>(cap, lf, segs); |
760 |
t.putAll(this); |
761 |
return t; |
762 |
} |
763 |
|
764 |
/** |
765 |
* Returns a set view of the keys contained in this map. The set is |
766 |
* backed by the map, so changes to the map are reflected in the set, and |
767 |
* vice-versa. The set supports element removal, which removes the |
768 |
* corresponding mapping from this map, via the <tt>Iterator.remove</tt>, |
769 |
* <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and |
770 |
* <tt>clear</tt> operations. It does not support the <tt>add</tt> or |
771 |
* <tt>addAll</tt> operations. |
772 |
* The returned <tt>iterator</tt> is a "weakly consistent" iterator that |
773 |
* will never throw {@link java.util.ConcurrentModificationException}, |
774 |
* and guarantees to traverse elements as they existed upon |
775 |
* construction of the iterator, and may (but is not guaranteed to) |
776 |
* reflect any modifications subsequent to construction. |
777 |
* |
778 |
* @return a set view of the keys contained in this map. |
779 |
*/ |
780 |
public Set<K> keySet() { |
781 |
Set<K> ks = keySet; |
782 |
return (ks != null) ? ks : (keySet = new KeySet()); |
783 |
} |
784 |
|
785 |
|
786 |
/** |
787 |
* Returns a collection view of the values contained in this map. The |
788 |
* collection is backed by the map, so changes to the map are reflected in |
789 |
* the collection, and vice-versa. The collection supports element |
790 |
* removal, which removes the corresponding mapping from this map, via the |
791 |
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, |
792 |
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations. |
793 |
* It does not support the <tt>add</tt> or <tt>addAll</tt> operations. |
794 |
* The returned <tt>iterator</tt> is a "weakly consistent" iterator that |
795 |
* will never throw {@link java.util.ConcurrentModificationException}, |
796 |
* and guarantees to traverse elements as they existed upon |
797 |
* construction of the iterator, and may (but is not guaranteed to) |
798 |
* reflect any modifications subsequent to construction. |
799 |
* |
800 |
* @return a collection view of the values contained in this map. |
801 |
*/ |
802 |
public Collection<V> values() { |
803 |
Collection<V> vs = values; |
804 |
return (vs != null) ? vs : (values = new Values()); |
805 |
} |
806 |
|
807 |
|
808 |
/** |
809 |
* Returns a collection view of the mappings contained in this map. Each |
810 |
* element in the returned collection is a <tt>Map.Entry</tt>. The |
811 |
* collection is backed by the map, so changes to the map are reflected in |
812 |
* the collection, and vice-versa. The collection supports element |
813 |
* removal, which removes the corresponding mapping from the map, via the |
814 |
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, |
815 |
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations. |
816 |
* It does not support the <tt>add</tt> or <tt>addAll</tt> operations. |
817 |
* The returned <tt>iterator</tt> is a "weakly consistent" iterator that |
818 |
* will never throw {@link java.util.ConcurrentModificationException}, |
819 |
* and guarantees to traverse elements as they existed upon |
820 |
* construction of the iterator, and may (but is not guaranteed to) |
821 |
* reflect any modifications subsequent to construction. |
822 |
* |
823 |
* @return a collection view of the mappings contained in this map. |
824 |
*/ |
825 |
public Set<Map.Entry<K,V>> entrySet() { |
826 |
Set<Map.Entry<K,V>> es = entrySet; |
827 |
return (es != null) ? es : (entrySet = new EntrySet()); |
828 |
} |
829 |
|
830 |
|
831 |
/** |
832 |
* Returns an enumeration of the keys in this table. |
833 |
* |
834 |
* @return an enumeration of the keys in this table. |
835 |
* @see Enumeration |
836 |
* @see #elements() |
837 |
* @see #keySet() |
838 |
* @see Map |
839 |
*/ |
840 |
public Enumeration<K> keys() { |
841 |
return new KeyIterator(); |
842 |
} |
843 |
|
844 |
/** |
845 |
* Returns an enumeration of the values in this table. |
846 |
* Use the Enumeration methods on the returned object to fetch the elements |
847 |
* sequentially. |
848 |
* |
849 |
* @return an enumeration of the values in this table. |
850 |
* @see java.util.Enumeration |
851 |
* @see #keys() |
852 |
* @see #values() |
853 |
* @see Map |
854 |
*/ |
855 |
public Enumeration<V> elements() { |
856 |
return new ValueIterator(); |
857 |
} |
858 |
|
859 |
/* ---------------- Iterator Support -------------- */ |
860 |
|
861 |
private abstract class HashIterator { |
862 |
private int nextSegmentIndex; |
863 |
private int nextTableIndex; |
864 |
private HashEntry[] currentTable; |
865 |
private HashEntry<K, V> nextEntry; |
866 |
private HashEntry<K, V> lastReturned; |
867 |
|
868 |
private HashIterator() { |
869 |
nextSegmentIndex = segments.length - 1; |
870 |
nextTableIndex = -1; |
871 |
advance(); |
872 |
} |
873 |
|
874 |
public boolean hasMoreElements() { return hasNext(); } |
875 |
|
876 |
private void advance() { |
877 |
if (nextEntry != null && (nextEntry = nextEntry.next) != null) |
878 |
return; |
879 |
|
880 |
while (nextTableIndex >= 0) { |
881 |
if ( (nextEntry = (HashEntry<K,V>)currentTable[nextTableIndex--]) != null) |
882 |
return; |
883 |
} |
884 |
|
885 |
while (nextSegmentIndex >= 0) { |
886 |
Segment<K,V> seg = (Segment<K,V>)segments[nextSegmentIndex--]; |
887 |
if (seg.count != 0) { |
888 |
currentTable = seg.table; |
889 |
for (int j = currentTable.length - 1; j >= 0; --j) { |
890 |
if ( (nextEntry = (HashEntry<K,V>)currentTable[j]) != null) { |
891 |
nextTableIndex = j - 1; |
892 |
return; |
893 |
} |
894 |
} |
895 |
} |
896 |
} |
897 |
} |
898 |
|
899 |
public boolean hasNext() { return nextEntry != null; } |
900 |
|
901 |
HashEntry<K,V> nextEntry() { |
902 |
if (nextEntry == null) |
903 |
throw new NoSuchElementException(); |
904 |
lastReturned = nextEntry; |
905 |
advance(); |
906 |
return lastReturned; |
907 |
} |
908 |
|
909 |
public void remove() { |
910 |
if (lastReturned == null) |
911 |
throw new IllegalStateException(); |
912 |
ConcurrentHashMap.this.remove(lastReturned.key); |
913 |
lastReturned = null; |
914 |
} |
915 |
} |
916 |
|
917 |
private class KeyIterator extends HashIterator implements Iterator<K>, Enumeration<K> { |
918 |
public K next() { return super.nextEntry().key; } |
919 |
public K nextElement() { return super.nextEntry().key; } |
920 |
} |
921 |
|
922 |
private class ValueIterator extends HashIterator implements Iterator<V>, Enumeration<V> { |
923 |
public V next() { return super.nextEntry().value; } |
924 |
public V nextElement() { return super.nextEntry().value; } |
925 |
} |
926 |
|
927 |
private class EntryIterator extends HashIterator implements Iterator<Entry<K,V>> { |
928 |
public Map.Entry<K,V> next() { return super.nextEntry(); } |
929 |
} |
930 |
|
931 |
private class KeySet extends AbstractSet<K> { |
932 |
public Iterator<K> iterator() { |
933 |
return new KeyIterator(); |
934 |
} |
935 |
public int size() { |
936 |
return ConcurrentHashMap.this.size(); |
937 |
} |
938 |
public boolean contains(Object o) { |
939 |
return ConcurrentHashMap.this.containsKey(o); |
940 |
} |
941 |
public boolean remove(Object o) { |
942 |
return ConcurrentHashMap.this.remove(o) != null; |
943 |
} |
944 |
public void clear() { |
945 |
ConcurrentHashMap.this.clear(); |
946 |
} |
947 |
} |
948 |
|
949 |
private class Values extends AbstractCollection<V> { |
950 |
public Iterator<V> iterator() { |
951 |
return new ValueIterator(); |
952 |
} |
953 |
public int size() { |
954 |
return ConcurrentHashMap.this.size(); |
955 |
} |
956 |
public boolean contains(Object o) { |
957 |
return ConcurrentHashMap.this.containsValue(o); |
958 |
} |
959 |
public void clear() { |
960 |
ConcurrentHashMap.this.clear(); |
961 |
} |
962 |
} |
963 |
|
964 |
private class EntrySet extends AbstractSet<Map.Entry<K,V>> { |
965 |
public Iterator<Map.Entry<K,V>> iterator() { |
966 |
return new EntryIterator(); |
967 |
} |
968 |
public boolean contains(Object o) { |
969 |
if (!(o instanceof Map.Entry)) |
970 |
return false; |
971 |
Map.Entry<K,V> e = (Map.Entry<K,V>)o; |
972 |
V v = ConcurrentHashMap.this.get(e.getKey()); |
973 |
return v != null && v.equals(e.getValue()); |
974 |
} |
975 |
public boolean remove(Object o) { |
976 |
if (!(o instanceof Map.Entry)) |
977 |
return false; |
978 |
Map.Entry<K,V> e = (Map.Entry<K,V>)o; |
979 |
return ConcurrentHashMap.this.remove(e.getKey(), e.getValue()); |
980 |
} |
981 |
public int size() { |
982 |
return ConcurrentHashMap.this.size(); |
983 |
} |
984 |
public void clear() { |
985 |
ConcurrentHashMap.this.clear(); |
986 |
} |
987 |
} |
988 |
|
989 |
/* ---------------- Serialization Support -------------- */ |
990 |
|
991 |
/** |
992 |
* Save the state of the <tt>ConcurrentHashMap</tt> |
993 |
* instance to a stream (i.e., |
994 |
* serialize it). |
995 |
* @param s the stream |
996 |
* @serialData |
997 |
* the key (Object) and value (Object) |
998 |
* for each key-value mapping, followed by a null pair. |
999 |
* The key-value mappings are emitted in no particular order. |
1000 |
*/ |
1001 |
private void writeObject(java.io.ObjectOutputStream s) throws IOException { |
1002 |
s.defaultWriteObject(); |
1003 |
|
1004 |
for (int k = 0; k < segments.length; ++k) { |
1005 |
Segment<K,V> seg = (Segment<K,V>)segments[k]; |
1006 |
seg.lock(); |
1007 |
try { |
1008 |
HashEntry[] tab = seg.table; |
1009 |
for (int i = 0; i < tab.length; ++i) { |
1010 |
for (HashEntry<K,V> e = (HashEntry<K,V>)tab[i]; e != null; e = e.next) { |
1011 |
s.writeObject(e.key); |
1012 |
s.writeObject(e.value); |
1013 |
} |
1014 |
} |
1015 |
} finally { |
1016 |
seg.unlock(); |
1017 |
} |
1018 |
} |
1019 |
s.writeObject(null); |
1020 |
s.writeObject(null); |
1021 |
} |
1022 |
|
1023 |
/** |
1024 |
* Reconstitute the <tt>ConcurrentHashMap</tt> |
1025 |
* instance from a stream (i.e., |
1026 |
* deserialize it). |
1027 |
* @param s the stream |
1028 |
*/ |
1029 |
private void readObject(java.io.ObjectInputStream s) |
1030 |
throws IOException, ClassNotFoundException { |
1031 |
s.defaultReadObject(); |
1032 |
|
1033 |
// Initialize each segment to be minimally sized, and let grow. |
1034 |
for (int i = 0; i < segments.length; ++i) { |
1035 |
segments[i].setTable(new HashEntry[1]); |
1036 |
} |
1037 |
|
1038 |
// Read the keys and values, and put the mappings in the table |
1039 |
for (;;) { |
1040 |
K key = (K) s.readObject(); |
1041 |
V value = (V) s.readObject(); |
1042 |
if (key == null) |
1043 |
break; |
1044 |
put(key, value); |
1045 |
} |
1046 |
} |
1047 |
} |
1048 |
|