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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 {@link java.util.Hashtable}, and |
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* includes versions of methods corresponding to each method of |
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* <tt>Hashtable</tt> . However, even though all operations are |
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* thread-safe, retrieval operations do <em>not</em> entail locking, |
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* and there is <em>not</em> any support for locking the entire table |
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* in a way that prevents all access. This class is fully |
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* interoperable with <tt>Hashtable</tt> 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 <tt>ConcurrentModificationException</tt>. |
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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 guided by |
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* the optional <tt>concurrencyLevel</tt> constructor argument |
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* (default 16), which is used as a hint for internal sizing. The |
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* table is internally partitioned to try to permit the indicated |
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* number of concurrent updates without contention. Because placement |
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* in hash tables is essentially random, the actual concurrency will |
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* vary. Ideally, you should choose a value to accommodate as many |
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* threads as will ever concurrently access the table. Using a |
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* significantly higher value than you need can waste space and time, |
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* and a significantly lower value can lead to thread contention. But |
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* overestimates and underestimates within an order of magnitude do |
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* not usually have much noticeable impact. |
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* |
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* <p> Like {@link java.util.Hashtable} but unlike {@link |
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* java.util.HashMap}, this class does NOT allow <tt>null</tt> to be |
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* 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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private static final long serialVersionUID = 7249069246763182397L; |
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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. |
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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 to ensure that entries are indexible |
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* using ints. |
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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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/** |
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* The maximum number of segments to allow; used to bound ctor arguments. |
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*/ |
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private static final int MAX_SEGMENTS = 1 << 16; // slightly conservative |
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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. |
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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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* Number of updates; used for checking lack of modifications |
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* in bulk-read methods. |
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*/ |
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transient int modCount; |
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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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++modCount; |
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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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++modCount; |
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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; |
395 |
} |
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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; |
400 |
|
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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. |
403 |
HashEntry<K,V> newFirst = e.next; |
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for (HashEntry<K,V> p = first; p != e; p = p.next) |
405 |
newFirst = new HashEntry<K,V>(p.hash, p.key, |
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p.value, newFirst); |
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tab[index] = newFirst; |
408 |
++modCount; |
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count = c-1; // write-volatile |
410 |
return oldValue; |
411 |
} finally { |
412 |
unlock(); |
413 |
} |
414 |
} |
415 |
|
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void clear() { |
417 |
lock(); |
418 |
try { |
419 |
HashEntry[] tab = table; |
420 |
for (int i = 0; i < tab.length ; i++) |
421 |
tab[i] = null; |
422 |
++modCount; |
423 |
count = 0; // write-volatile |
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} finally { |
425 |
unlock(); |
426 |
} |
427 |
} |
428 |
} |
429 |
|
430 |
/** |
431 |
* ConcurrentHashMap list entry. |
432 |
*/ |
433 |
private static class HashEntry<K,V> implements Entry<K,V> { |
434 |
private final K key; |
435 |
private V value; |
436 |
private final int hash; |
437 |
private final HashEntry<K,V> next; |
438 |
|
439 |
HashEntry(int hash, K key, V value, HashEntry<K,V> next) { |
440 |
this.value = value; |
441 |
this.hash = hash; |
442 |
this.key = key; |
443 |
this.next = next; |
444 |
} |
445 |
|
446 |
public K getKey() { |
447 |
return key; |
448 |
} |
449 |
|
450 |
public V getValue() { |
451 |
return value; |
452 |
} |
453 |
|
454 |
public V setValue(V newValue) { |
455 |
// We aren't required to, and don't provide any |
456 |
// visibility barriers for setting value. |
457 |
if (newValue == null) |
458 |
throw new NullPointerException(); |
459 |
V oldValue = this.value; |
460 |
this.value = newValue; |
461 |
return oldValue; |
462 |
} |
463 |
|
464 |
public boolean equals(Object o) { |
465 |
if (!(o instanceof Entry)) |
466 |
return false; |
467 |
Entry<K,V> e = (Entry<K,V>)o; |
468 |
return (key.equals(e.getKey()) && value.equals(e.getValue())); |
469 |
} |
470 |
|
471 |
public int hashCode() { |
472 |
return key.hashCode() ^ value.hashCode(); |
473 |
} |
474 |
|
475 |
public String toString() { |
476 |
return key + "=" + value; |
477 |
} |
478 |
} |
479 |
|
480 |
|
481 |
/* ---------------- Public operations -------------- */ |
482 |
|
483 |
/** |
484 |
* Constructs a new, empty map with the specified initial |
485 |
* capacity and the specified load factor. |
486 |
* |
487 |
* @param initialCapacity the initial capacity. The implementation |
488 |
* performs internal sizing to accommodate this many elements. |
489 |
* @param loadFactor the load factor threshold, used to control resizing. |
490 |
* @param concurrencyLevel the estimated number of concurrently |
491 |
* updating threads. The implementation performs internal sizing |
492 |
* to try to accommodate this many threads. |
493 |
* @throws IllegalArgumentException if the initial capacity is |
494 |
* negative or the load factor or concurrencyLevel are |
495 |
* nonpositive. |
496 |
*/ |
497 |
public ConcurrentHashMap(int initialCapacity, |
498 |
float loadFactor, int concurrencyLevel) { |
499 |
if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0) |
500 |
throw new IllegalArgumentException(); |
501 |
|
502 |
if (concurrencyLevel > MAX_SEGMENTS) |
503 |
concurrencyLevel = MAX_SEGMENTS; |
504 |
|
505 |
// Find power-of-two sizes best matching arguments |
506 |
int sshift = 0; |
507 |
int ssize = 1; |
508 |
while (ssize < concurrencyLevel) { |
509 |
++sshift; |
510 |
ssize <<= 1; |
511 |
} |
512 |
segmentShift = 32 - sshift; |
513 |
segmentMask = ssize - 1; |
514 |
this.segments = new Segment[ssize]; |
515 |
|
516 |
if (initialCapacity > MAXIMUM_CAPACITY) |
517 |
initialCapacity = MAXIMUM_CAPACITY; |
518 |
int c = initialCapacity / ssize; |
519 |
if (c * ssize < initialCapacity) |
520 |
++c; |
521 |
int cap = 1; |
522 |
while (cap < c) |
523 |
cap <<= 1; |
524 |
|
525 |
for (int i = 0; i < this.segments.length; ++i) |
526 |
this.segments[i] = new Segment<K,V>(cap, loadFactor); |
527 |
} |
528 |
|
529 |
/** |
530 |
* Constructs a new, empty map with the specified initial |
531 |
* capacity, and with default load factor and concurrencyLevel. |
532 |
* |
533 |
* @param initialCapacity The implementation performs internal |
534 |
* sizing to accommodate this many elements. |
535 |
* @throws IllegalArgumentException if the initial capacity of |
536 |
* elements is negative. |
537 |
*/ |
538 |
public ConcurrentHashMap(int initialCapacity) { |
539 |
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS); |
540 |
} |
541 |
|
542 |
/** |
543 |
* Constructs a new, empty map with a default initial capacity, |
544 |
* load factor, and number of concurrencyLevel. |
545 |
*/ |
546 |
public ConcurrentHashMap() { |
547 |
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS); |
548 |
} |
549 |
|
550 |
/** |
551 |
* Constructs a new map with the same mappings as the given map. The |
552 |
* map is created with a capacity of twice the number of mappings in |
553 |
* the given map or 11 (whichever is greater), and a default load factor. |
554 |
*/ |
555 |
public <A extends K, B extends V> ConcurrentHashMap(Map<A,B> t) { |
556 |
this(Math.max((int) (t.size() / DEFAULT_LOAD_FACTOR) + 1, |
557 |
11), |
558 |
DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS); |
559 |
putAll(t); |
560 |
} |
561 |
|
562 |
// inherit Map javadoc |
563 |
public boolean isEmpty() { |
564 |
/* |
565 |
* We need to keep track of per-segment modCounts to avoid ABA |
566 |
* problems in which an element in one segment was added and |
567 |
* in another removed during traversal, in which case the |
568 |
* table was never actually empty at any point. Note the |
569 |
* similar use of modCounts in the size() and containsValue() |
570 |
* methods, which are the only other methods also susceptible |
571 |
* to ABA problems. |
572 |
*/ |
573 |
int[] mc = new int[segments.length]; |
574 |
int mcsum = 0; |
575 |
for (int i = 0; i < segments.length; ++i) { |
576 |
if (segments[i].count != 0) |
577 |
return false; |
578 |
else |
579 |
mcsum += mc[i] = segments[i].modCount; |
580 |
} |
581 |
// If mcsum happens to be zero, then we know we got a snapshot |
582 |
// before any modifications at all were made. This is |
583 |
// probably common enough to bother tracking. |
584 |
if (mcsum != 0) { |
585 |
for (int i = 0; i < segments.length; ++i) { |
586 |
if (segments[i].count != 0 || |
587 |
mc[i] != segments[i].modCount) |
588 |
return false; |
589 |
} |
590 |
} |
591 |
return true; |
592 |
} |
593 |
|
594 |
// inherit Map javadoc |
595 |
public int size() { |
596 |
int[] mc = new int[segments.length]; |
597 |
for (;;) { |
598 |
int sum = 0; |
599 |
int mcsum = 0; |
600 |
for (int i = 0; i < segments.length; ++i) { |
601 |
sum += segments[i].count; |
602 |
mcsum += mc[i] = segments[i].modCount; |
603 |
} |
604 |
int check = 0; |
605 |
if (mcsum != 0) { |
606 |
for (int i = 0; i < segments.length; ++i) { |
607 |
check += segments[i].count; |
608 |
if (mc[i] != segments[i].modCount) { |
609 |
check = -1; // force retry |
610 |
break; |
611 |
} |
612 |
} |
613 |
} |
614 |
if (check == sum) |
615 |
return sum; |
616 |
} |
617 |
} |
618 |
|
619 |
|
620 |
/** |
621 |
* Returns the value to which the specified key is mapped in this table. |
622 |
* |
623 |
* @param key a key in the table. |
624 |
* @return the value to which the key is mapped in this table; |
625 |
* <tt>null</tt> if the key is not mapped to any value in |
626 |
* this table. |
627 |
* @throws NullPointerException if the key is |
628 |
* <tt>null</tt>. |
629 |
* @see #put(Object, Object) |
630 |
*/ |
631 |
public V get(Object key) { |
632 |
int hash = hash(key); // throws NullPointerException if key null |
633 |
return segmentFor(hash).get((K) key, hash); |
634 |
} |
635 |
|
636 |
/** |
637 |
* Tests if the specified object is a key in this table. |
638 |
* |
639 |
* @param key possible key. |
640 |
* @return <tt>true</tt> if and only if the specified object |
641 |
* is a key in this table, as determined by the |
642 |
* <tt>equals</tt> method; <tt>false</tt> otherwise. |
643 |
* @throws NullPointerException if the key is |
644 |
* <tt>null</tt>. |
645 |
* @see #contains(Object) |
646 |
*/ |
647 |
public boolean containsKey(Object key) { |
648 |
int hash = hash(key); // throws NullPointerException if key null |
649 |
return segmentFor(hash).containsKey(key, hash); |
650 |
} |
651 |
|
652 |
/** |
653 |
* Returns <tt>true</tt> if this map maps one or more keys to the |
654 |
* specified value. Note: This method requires a full internal |
655 |
* traversal of the hash table, and so is much slower than |
656 |
* method <tt>containsKey</tt>. |
657 |
* |
658 |
* @param value value whose presence in this map is to be tested. |
659 |
* @return <tt>true</tt> if this map maps one or more keys to the |
660 |
* specified value. |
661 |
* @throws NullPointerException if the value is <tt>null</tt>. |
662 |
*/ |
663 |
public boolean containsValue(Object value) { |
664 |
if (value == null) |
665 |
throw new NullPointerException(); |
666 |
|
667 |
int[] mc = new int[segments.length]; |
668 |
for (;;) { |
669 |
int sum = 0; |
670 |
int mcsum = 0; |
671 |
for (int i = 0; i < segments.length; ++i) { |
672 |
int c = segments[i].count; |
673 |
mcsum += mc[i] = segments[i].modCount; |
674 |
if (segments[i].containsValue(value)) |
675 |
return true; |
676 |
} |
677 |
boolean cleanSweep = true; |
678 |
if (mcsum != 0) { |
679 |
for (int i = 0; i < segments.length; ++i) { |
680 |
int c = segments[i].count; |
681 |
if (mc[i] != segments[i].modCount) { |
682 |
cleanSweep = false; |
683 |
break; |
684 |
} |
685 |
} |
686 |
} |
687 |
if (cleanSweep) |
688 |
return false; |
689 |
} |
690 |
} |
691 |
|
692 |
/** |
693 |
* Legacy method testing if some key maps into the specified value |
694 |
* in this table. This operation is more expensive than the |
695 |
* <tt>containsKey</tt> method. |
696 |
* |
697 |
* <p> Note that this method is identical in functionality to |
698 |
* <tt>containsValue</tt>, This method exists solely to ensure |
699 |
* full compatibility with class {@link java.util.Hashtable}, |
700 |
* which supported this method prior to introduction of the |
701 |
* collections framework. |
702 |
|
703 |
* @param value a value to search for. |
704 |
* @return <tt>true</tt> if and only if some key maps to the |
705 |
* <tt>value</tt> argument in this table as |
706 |
* determined by the <tt>equals</tt> method; |
707 |
* <tt>false</tt> otherwise. |
708 |
* @throws NullPointerException if the value is <tt>null</tt>. |
709 |
* @see #containsKey(Object) |
710 |
* @see #containsValue(Object) |
711 |
* @see Map |
712 |
*/ |
713 |
public boolean contains(Object value) { |
714 |
return containsValue(value); |
715 |
} |
716 |
|
717 |
/** |
718 |
* Maps the specified <tt>key</tt> to the specified |
719 |
* <tt>value</tt> in this table. Neither the key nor the |
720 |
* value can be <tt>null</tt>. <p> |
721 |
* |
722 |
* The value can be retrieved by calling the <tt>get</tt> method |
723 |
* with a key that is equal to the original key. |
724 |
* |
725 |
* @param key the table key. |
726 |
* @param value the value. |
727 |
* @return the previous value of the specified key in this table, |
728 |
* or <tt>null</tt> if it did not have one. |
729 |
* @throws NullPointerException if the key or value is |
730 |
* <tt>null</tt>. |
731 |
* @see Object#equals(Object) |
732 |
* @see #get(Object) |
733 |
*/ |
734 |
public V put(K key, V value) { |
735 |
if (value == null) |
736 |
throw new NullPointerException(); |
737 |
int hash = hash(key); |
738 |
return segmentFor(hash).put(key, hash, value, false); |
739 |
} |
740 |
|
741 |
/** |
742 |
* If the specified key is not already associated |
743 |
* with a value, associate it with the given value. |
744 |
* This is equivalent to |
745 |
* <pre> |
746 |
* if (!map.containsKey(key)) |
747 |
* return map.put(key, value); |
748 |
* else |
749 |
* return map.get(key); |
750 |
* </pre> |
751 |
* Except that the action is performed atomically. |
752 |
* @param key key with which the specified value is to be associated. |
753 |
* @param value value to be associated with the specified key. |
754 |
* @return previous value associated with specified key, or <tt>null</tt> |
755 |
* if there was no mapping for key. A <tt>null</tt> return can |
756 |
* also indicate that the map previously associated <tt>null</tt> |
757 |
* with the specified key, if the implementation supports |
758 |
* <tt>null</tt> values. |
759 |
* |
760 |
* @throws UnsupportedOperationException if the <tt>put</tt> operation is |
761 |
* not supported by this map. |
762 |
* @throws ClassCastException if the class of the specified key or value |
763 |
* prevents it from being stored in this map. |
764 |
* @throws NullPointerException if the specified key or value is |
765 |
* <tt>null</tt>. |
766 |
* |
767 |
**/ |
768 |
public V putIfAbsent(K key, V value) { |
769 |
if (value == null) |
770 |
throw new NullPointerException(); |
771 |
int hash = hash(key); |
772 |
return segmentFor(hash).put(key, hash, value, true); |
773 |
} |
774 |
|
775 |
|
776 |
/** |
777 |
* Copies all of the mappings from the specified map to this one. |
778 |
* |
779 |
* These mappings replace any mappings that this map had for any of the |
780 |
* keys currently in the specified Map. |
781 |
* |
782 |
* @param t Mappings to be stored in this map. |
783 |
*/ |
784 |
public void putAll(Map<? extends K, ? extends V> t) { |
785 |
Iterator<Map.Entry<? extends K, ? extends V>> it = t.entrySet().iterator(); |
786 |
while (it.hasNext()) { |
787 |
Entry<? extends K, ? extends V> e = it.next(); |
788 |
put(e.getKey(), e.getValue()); |
789 |
} |
790 |
} |
791 |
|
792 |
/** |
793 |
* Removes the key (and its corresponding value) from this |
794 |
* table. This method does nothing if the key is not in the table. |
795 |
* |
796 |
* @param key the key that needs to be removed. |
797 |
* @return the value to which the key had been mapped in this table, |
798 |
* or <tt>null</tt> if the key did not have a mapping. |
799 |
* @throws NullPointerException if the key is |
800 |
* <tt>null</tt>. |
801 |
*/ |
802 |
public V remove(Object key) { |
803 |
int hash = hash(key); |
804 |
return segmentFor(hash).remove(key, hash, null); |
805 |
} |
806 |
|
807 |
/** |
808 |
* Remove entry for key only if currently mapped to given value. |
809 |
* Acts as |
810 |
* <pre> |
811 |
* if (map.get(key).equals(value)) { |
812 |
* map.remove(key); |
813 |
* return true; |
814 |
* } else return false; |
815 |
* </pre> |
816 |
* except that the action is performed atomically. |
817 |
* @param key key with which the specified value is associated. |
818 |
* @param value value associated with the specified key. |
819 |
* @return true if the value was removed |
820 |
* @throws NullPointerException if the specified key is |
821 |
* <tt>null</tt>. |
822 |
*/ |
823 |
public boolean remove(Object key, Object value) { |
824 |
int hash = hash(key); |
825 |
return segmentFor(hash).remove(key, hash, value) != null; |
826 |
} |
827 |
|
828 |
/** |
829 |
* Removes all mappings from this map. |
830 |
*/ |
831 |
public void clear() { |
832 |
for (int i = 0; i < segments.length; ++i) |
833 |
segments[i].clear(); |
834 |
} |
835 |
|
836 |
|
837 |
/** |
838 |
* Returns a shallow copy of this |
839 |
* <tt>ConcurrentHashMap</tt> instance: the keys and |
840 |
* values themselves are not cloned. |
841 |
* |
842 |
* @return a shallow copy of this map. |
843 |
*/ |
844 |
public Object clone() { |
845 |
// We cannot call super.clone, since it would share final |
846 |
// segments array, and there's no way to reassign finals. |
847 |
|
848 |
float lf = segments[0].loadFactor; |
849 |
int segs = segments.length; |
850 |
int cap = (int)(size() / lf); |
851 |
if (cap < segs) cap = segs; |
852 |
ConcurrentHashMap<K,V> t = new ConcurrentHashMap<K,V>(cap, lf, segs); |
853 |
t.putAll(this); |
854 |
return t; |
855 |
} |
856 |
|
857 |
/** |
858 |
* Returns a set view of the keys contained in this map. The set is |
859 |
* backed by the map, so changes to the map are reflected in the set, and |
860 |
* vice-versa. The set supports element removal, which removes the |
861 |
* corresponding mapping from this map, via the <tt>Iterator.remove</tt>, |
862 |
* <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and |
863 |
* <tt>clear</tt> operations. It does not support the <tt>add</tt> or |
864 |
* <tt>addAll</tt> operations. |
865 |
* The returned <tt>iterator</tt> is a "weakly consistent" iterator that |
866 |
* will never throw {@link java.util.ConcurrentModificationException}, |
867 |
* and guarantees to traverse elements as they existed upon |
868 |
* construction of the iterator, and may (but is not guaranteed to) |
869 |
* reflect any modifications subsequent to construction. |
870 |
* |
871 |
* @return a set view of the keys contained in this map. |
872 |
*/ |
873 |
public Set<K> keySet() { |
874 |
Set<K> ks = keySet; |
875 |
return (ks != null) ? ks : (keySet = new KeySet()); |
876 |
} |
877 |
|
878 |
|
879 |
/** |
880 |
* Returns a collection view of the values contained in this map. The |
881 |
* collection is backed by the map, so changes to the map are reflected in |
882 |
* the collection, and vice-versa. The collection supports element |
883 |
* removal, which removes the corresponding mapping from this map, via the |
884 |
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, |
885 |
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations. |
886 |
* It does not support the <tt>add</tt> or <tt>addAll</tt> operations. |
887 |
* The returned <tt>iterator</tt> is a "weakly consistent" iterator that |
888 |
* will never throw {@link java.util.ConcurrentModificationException}, |
889 |
* and guarantees to traverse elements as they existed upon |
890 |
* construction of the iterator, and may (but is not guaranteed to) |
891 |
* reflect any modifications subsequent to construction. |
892 |
* |
893 |
* @return a collection view of the values contained in this map. |
894 |
*/ |
895 |
public Collection<V> values() { |
896 |
Collection<V> vs = values; |
897 |
return (vs != null) ? vs : (values = new Values()); |
898 |
} |
899 |
|
900 |
|
901 |
/** |
902 |
* Returns a collection view of the mappings contained in this map. Each |
903 |
* element in the returned collection is a <tt>Map.Entry</tt>. The |
904 |
* collection is backed by the map, so changes to the map are reflected in |
905 |
* the collection, and vice-versa. The collection supports element |
906 |
* removal, which removes the corresponding mapping from the map, via the |
907 |
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, |
908 |
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations. |
909 |
* It does not support the <tt>add</tt> or <tt>addAll</tt> operations. |
910 |
* The returned <tt>iterator</tt> is a "weakly consistent" iterator that |
911 |
* will never throw {@link java.util.ConcurrentModificationException}, |
912 |
* and guarantees to traverse elements as they existed upon |
913 |
* construction of the iterator, and may (but is not guaranteed to) |
914 |
* reflect any modifications subsequent to construction. |
915 |
* |
916 |
* @return a collection view of the mappings contained in this map. |
917 |
*/ |
918 |
public Set<Map.Entry<K,V>> entrySet() { |
919 |
Set<Map.Entry<K,V>> es = entrySet; |
920 |
return (es != null) ? es : (entrySet = new EntrySet()); |
921 |
} |
922 |
|
923 |
|
924 |
/** |
925 |
* Returns an enumeration of the keys in this table. |
926 |
* |
927 |
* @return an enumeration of the keys in this table. |
928 |
* @see Enumeration |
929 |
* @see #elements() |
930 |
* @see #keySet() |
931 |
* @see Map |
932 |
*/ |
933 |
public Enumeration<K> keys() { |
934 |
return new KeyIterator(); |
935 |
} |
936 |
|
937 |
/** |
938 |
* Returns an enumeration of the values in this table. |
939 |
* Use the Enumeration methods on the returned object to fetch the elements |
940 |
* sequentially. |
941 |
* |
942 |
* @return an enumeration of the values in this table. |
943 |
* @see java.util.Enumeration |
944 |
* @see #keys() |
945 |
* @see #values() |
946 |
* @see Map |
947 |
*/ |
948 |
public Enumeration<V> elements() { |
949 |
return new ValueIterator(); |
950 |
} |
951 |
|
952 |
/* ---------------- Iterator Support -------------- */ |
953 |
|
954 |
private abstract class HashIterator { |
955 |
private int nextSegmentIndex; |
956 |
private int nextTableIndex; |
957 |
private HashEntry[] currentTable; |
958 |
private HashEntry<K, V> nextEntry; |
959 |
private HashEntry<K, V> lastReturned; |
960 |
|
961 |
private HashIterator() { |
962 |
nextSegmentIndex = segments.length - 1; |
963 |
nextTableIndex = -1; |
964 |
advance(); |
965 |
} |
966 |
|
967 |
public boolean hasMoreElements() { return hasNext(); } |
968 |
|
969 |
private void advance() { |
970 |
if (nextEntry != null && (nextEntry = nextEntry.next) != null) |
971 |
return; |
972 |
|
973 |
while (nextTableIndex >= 0) { |
974 |
if ( (nextEntry = (HashEntry<K,V>)currentTable[nextTableIndex--]) != null) |
975 |
return; |
976 |
} |
977 |
|
978 |
while (nextSegmentIndex >= 0) { |
979 |
Segment<K,V> seg = (Segment<K,V>)segments[nextSegmentIndex--]; |
980 |
if (seg.count != 0) { |
981 |
currentTable = seg.table; |
982 |
for (int j = currentTable.length - 1; j >= 0; --j) { |
983 |
if ( (nextEntry = (HashEntry<K,V>)currentTable[j]) != null) { |
984 |
nextTableIndex = j - 1; |
985 |
return; |
986 |
} |
987 |
} |
988 |
} |
989 |
} |
990 |
} |
991 |
|
992 |
public boolean hasNext() { return nextEntry != null; } |
993 |
|
994 |
HashEntry<K,V> nextEntry() { |
995 |
if (nextEntry == null) |
996 |
throw new NoSuchElementException(); |
997 |
lastReturned = nextEntry; |
998 |
advance(); |
999 |
return lastReturned; |
1000 |
} |
1001 |
|
1002 |
public void remove() { |
1003 |
if (lastReturned == null) |
1004 |
throw new IllegalStateException(); |
1005 |
ConcurrentHashMap.this.remove(lastReturned.key); |
1006 |
lastReturned = null; |
1007 |
} |
1008 |
} |
1009 |
|
1010 |
private class KeyIterator extends HashIterator implements Iterator<K>, Enumeration<K> { |
1011 |
public K next() { return super.nextEntry().key; } |
1012 |
public K nextElement() { return super.nextEntry().key; } |
1013 |
} |
1014 |
|
1015 |
private class ValueIterator extends HashIterator implements Iterator<V>, Enumeration<V> { |
1016 |
public V next() { return super.nextEntry().value; } |
1017 |
public V nextElement() { return super.nextEntry().value; } |
1018 |
} |
1019 |
|
1020 |
private class EntryIterator extends HashIterator implements Iterator<Entry<K,V>> { |
1021 |
public Map.Entry<K,V> next() { return super.nextEntry(); } |
1022 |
} |
1023 |
|
1024 |
private class KeySet extends AbstractSet<K> { |
1025 |
public Iterator<K> iterator() { |
1026 |
return new KeyIterator(); |
1027 |
} |
1028 |
public int size() { |
1029 |
return ConcurrentHashMap.this.size(); |
1030 |
} |
1031 |
public boolean contains(Object o) { |
1032 |
return ConcurrentHashMap.this.containsKey(o); |
1033 |
} |
1034 |
public boolean remove(Object o) { |
1035 |
return ConcurrentHashMap.this.remove(o) != null; |
1036 |
} |
1037 |
public void clear() { |
1038 |
ConcurrentHashMap.this.clear(); |
1039 |
} |
1040 |
} |
1041 |
|
1042 |
private class Values extends AbstractCollection<V> { |
1043 |
public Iterator<V> iterator() { |
1044 |
return new ValueIterator(); |
1045 |
} |
1046 |
public int size() { |
1047 |
return ConcurrentHashMap.this.size(); |
1048 |
} |
1049 |
public boolean contains(Object o) { |
1050 |
return ConcurrentHashMap.this.containsValue(o); |
1051 |
} |
1052 |
public void clear() { |
1053 |
ConcurrentHashMap.this.clear(); |
1054 |
} |
1055 |
} |
1056 |
|
1057 |
private class EntrySet extends AbstractSet<Map.Entry<K,V>> { |
1058 |
public Iterator<Map.Entry<K,V>> iterator() { |
1059 |
return new EntryIterator(); |
1060 |
} |
1061 |
public boolean contains(Object o) { |
1062 |
if (!(o instanceof Map.Entry)) |
1063 |
return false; |
1064 |
Map.Entry<K,V> e = (Map.Entry<K,V>)o; |
1065 |
V v = ConcurrentHashMap.this.get(e.getKey()); |
1066 |
return v != null && v.equals(e.getValue()); |
1067 |
} |
1068 |
public boolean remove(Object o) { |
1069 |
if (!(o instanceof Map.Entry)) |
1070 |
return false; |
1071 |
Map.Entry<K,V> e = (Map.Entry<K,V>)o; |
1072 |
return ConcurrentHashMap.this.remove(e.getKey(), e.getValue()); |
1073 |
} |
1074 |
public int size() { |
1075 |
return ConcurrentHashMap.this.size(); |
1076 |
} |
1077 |
public void clear() { |
1078 |
ConcurrentHashMap.this.clear(); |
1079 |
} |
1080 |
} |
1081 |
|
1082 |
/* ---------------- Serialization Support -------------- */ |
1083 |
|
1084 |
/** |
1085 |
* Save the state of the <tt>ConcurrentHashMap</tt> |
1086 |
* instance to a stream (i.e., |
1087 |
* serialize it). |
1088 |
* @param s the stream |
1089 |
* @serialData |
1090 |
* the key (Object) and value (Object) |
1091 |
* for each key-value mapping, followed by a null pair. |
1092 |
* The key-value mappings are emitted in no particular order. |
1093 |
*/ |
1094 |
private void writeObject(java.io.ObjectOutputStream s) throws IOException { |
1095 |
s.defaultWriteObject(); |
1096 |
|
1097 |
for (int k = 0; k < segments.length; ++k) { |
1098 |
Segment<K,V> seg = (Segment<K,V>)segments[k]; |
1099 |
seg.lock(); |
1100 |
try { |
1101 |
HashEntry[] tab = seg.table; |
1102 |
for (int i = 0; i < tab.length; ++i) { |
1103 |
for (HashEntry<K,V> e = (HashEntry<K,V>)tab[i]; e != null; e = e.next) { |
1104 |
s.writeObject(e.key); |
1105 |
s.writeObject(e.value); |
1106 |
} |
1107 |
} |
1108 |
} finally { |
1109 |
seg.unlock(); |
1110 |
} |
1111 |
} |
1112 |
s.writeObject(null); |
1113 |
s.writeObject(null); |
1114 |
} |
1115 |
|
1116 |
/** |
1117 |
* Reconstitute the <tt>ConcurrentHashMap</tt> |
1118 |
* instance from a stream (i.e., |
1119 |
* deserialize it). |
1120 |
* @param s the stream |
1121 |
*/ |
1122 |
private void readObject(java.io.ObjectInputStream s) |
1123 |
throws IOException, ClassNotFoundException { |
1124 |
s.defaultReadObject(); |
1125 |
|
1126 |
// Initialize each segment to be minimally sized, and let grow. |
1127 |
for (int i = 0; i < segments.length; ++i) { |
1128 |
segments[i].setTable(new HashEntry[1]); |
1129 |
} |
1130 |
|
1131 |
// Read the keys and values, and put the mappings in the table |
1132 |
for (;;) { |
1133 |
K key = (K) s.readObject(); |
1134 |
V value = (V) s.readObject(); |
1135 |
if (key == null) |
1136 |
break; |
1137 |
put(key, value); |
1138 |
} |
1139 |
} |
1140 |
} |
1141 |
|