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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, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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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>) generally do not |
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* block, so may overlap with update operations (including |
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* <tt>put</tt> and <tt>remove</tt>). Retrievals reflect the results |
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* of the most recently <em>completed</em> update operations holding |
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* upon their onset. For aggregate operations such as <tt>putAll</tt> |
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* and <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 {@link ConcurrentModificationException}. |
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* However, iterators are designed to be used by only one thread at a 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 <tt>16</tt>), 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 modify 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. A value of one is |
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* appropriate when it is known that only one thread will modify and |
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* all others will only read. Also, resizing this or any other kind of |
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* hash table is a relatively slow operation, so, when possible, it is |
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* a good idea to provide estimates of expected table sizes in |
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* constructors. |
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* |
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* <p>This class and its views and iterators implement all of the |
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* <em>optional</em> methods of the {@link Map} and {@link Iterator} |
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* interfaces. |
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* |
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* <p> Like {@link Hashtable} but unlike {@link HashMap}, this class |
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* does <em>not</em> allow <tt>null</tt> to be used as a key or value. |
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* |
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* <p>This class is a member of the |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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* @param <K> the type of keys maintained by this map |
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* @param <V> the type of mapped values |
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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>, 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. To |
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* reduce footprint, all but one segments are constructed only |
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* when first needed (see ensureSegment). To maintain visibility |
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* in the presence of lazy construction, accesses to segments as |
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* well as elements of segment's table must use volatile access, |
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* which is done via Unsafe within methods segmentAt etc |
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* below. These provide the functionality of AtomicReferenceArrays |
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* but reduce the levels of indirection. Additionally, |
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* volatile-writes of table elements and entry "next" fields |
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* within locked operations use the cheaper "lazySet" forms of |
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* writes (via putOrderedObject) because these writes are always |
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* followed by lock releases that maintain sequential consistency |
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* of table updates. |
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* |
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* Historical note: The previous version of this class relied |
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* heavily on "final" fields, which avoided some volatile reads at |
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* the expense of a large initial footprint. Some remnants of |
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* that design (including forced construction of segment 0) exist |
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* to ensure serialization compatibility. |
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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 capacity for this table, |
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* used when not otherwise specified in a constructor. |
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*/ |
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static final int DEFAULT_INITIAL_CAPACITY = 16; |
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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 a constructor. |
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*/ |
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static final float DEFAULT_LOAD_FACTOR = 0.75f; |
113 |
|
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/** |
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* The default concurrency level for this table, used when not |
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* otherwise specified in a constructor. |
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*/ |
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static final int DEFAULT_CONCURRENCY_LEVEL = 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 indexable |
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* using ints. |
125 |
*/ |
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static final int MAXIMUM_CAPACITY = 1 << 30; |
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|
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/** |
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* The minimum capacity for per-segment tables. Must be a power |
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* of two, at least two to avoid immediate resizing on next use |
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* after lazy construction. |
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*/ |
133 |
static final int MIN_SEGMENT_TABLE_CAPACITY = 2; |
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|
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/** |
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* The maximum number of segments to allow; used to bound |
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* constructor arguments. Must be power of two less than 1 << 24. |
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*/ |
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static final int MAX_SEGMENTS = 1 << 16; // slightly conservative |
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|
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/** |
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* Number of unsynchronized retries in size and containsValue |
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* methods before resorting to locking. This is used to avoid |
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* unbounded retries if tables undergo continuous modification |
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* which would make it impossible to obtain an accurate result. |
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*/ |
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static final int RETRIES_BEFORE_LOCK = 2; |
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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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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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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. |
164 |
*/ |
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final Segment<K,V>[] segments; |
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|
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transient Set<K> keySet; |
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transient Set<Map.Entry<K,V>> entrySet; |
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transient Collection<V> values; |
170 |
|
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/** |
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* ConcurrentHashMap list entry. Note that this is never exported |
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* out as a user-visible Map.Entry. |
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*/ |
175 |
static final class HashEntry<K,V> { |
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final int hash; |
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final K key; |
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volatile V value; |
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volatile HashEntry<K,V> next; |
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|
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HashEntry(int hash, K key, V value, HashEntry<K,V> next) { |
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this.hash = hash; |
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this.key = key; |
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this.value = value; |
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this.next = next; |
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} |
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|
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/** |
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* Sets next field with volatile write semantics. (See above |
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* about use of putOrderedObject.) |
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*/ |
192 |
final void setNext(HashEntry<K,V> n) { |
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UNSAFE.putOrderedObject(this, nextOffset, n); |
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} |
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|
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// Unsafe mechanics |
197 |
static final sun.misc.Unsafe UNSAFE; |
198 |
static final long nextOffset; |
199 |
static { |
200 |
try { |
201 |
UNSAFE = sun.misc.Unsafe.getUnsafe(); |
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Class k = HashEntry.class; |
203 |
nextOffset = UNSAFE.objectFieldOffset |
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(k.getDeclaredField("next")); |
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} catch (Exception e) { |
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throw new Error(e); |
207 |
} |
208 |
} |
209 |
} |
210 |
|
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/** |
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* Gets the ith element of given table (if nonnull) with volatile |
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* read semantics. Note: This is manually integrated into a few |
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* performance-sensitive methods to reduce call overhead. |
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*/ |
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@SuppressWarnings("unchecked") |
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static final <K,V> HashEntry<K,V> entryAt(HashEntry<K,V>[] tab, int i) { |
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return (tab == null) ? null : |
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(HashEntry<K,V>) UNSAFE.getObjectVolatile |
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(tab, ((long)i << TSHIFT) + TBASE); |
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} |
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|
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/** |
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* Sets the ith element of given table, with volatile write |
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* semantics. (See above about use of putOrderedObject.) |
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*/ |
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static final <K,V> void setEntryAt(HashEntry<K,V>[] tab, int i, |
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HashEntry<K,V> e) { |
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UNSAFE.putOrderedObject(tab, ((long)i << TSHIFT) + TBASE, e); |
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} |
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|
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/** |
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* Applies a supplemental hash function to a given hashCode, which |
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* defends against poor quality hash functions. This is critical |
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* because ConcurrentHashMap uses power-of-two length hash tables, |
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* that otherwise encounter collisions for hashCodes that do not |
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* differ in lower or upper bits. |
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*/ |
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private static int hash(int h) { |
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// Spread bits to regularize both segment and index locations, |
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// using variant of single-word Wang/Jenkins hash. |
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h += (h << 15) ^ 0xffffcd7d; |
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h ^= (h >>> 10); |
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h += (h << 3); |
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h ^= (h >>> 6); |
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h += (h << 2) + (h << 14); |
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return h ^ (h >>> 16); |
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} |
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|
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/** |
251 |
* Segments are specialized versions of hash tables. This |
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* subclasses from ReentrantLock opportunistically, just to |
253 |
* simplify some locking and avoid separate construction. |
254 |
*/ |
255 |
static final class Segment<K,V> extends ReentrantLock implements Serializable { |
256 |
/* |
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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 (via volatile |
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* reads of segments and tables) without locking. This |
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* requires replicating nodes when necessary during table |
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* resizing, so the old lists can be traversed by readers |
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* still using old version of table. |
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* |
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* This class defines only mutative methods requiring locking. |
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* Except as noted, the methods of this class perform the |
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* per-segment versions of ConcurrentHashMap methods. (Other |
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* methods are integrated directly into ConcurrentHashMap |
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* methods.) These mutative methods use a form of controlled |
269 |
* spinning on contention via methods scanAndLock and |
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* scanAndLockForPut. These intersperse tryLocks with |
271 |
* traversals to locate nodes. The main benefit is to absorb |
272 |
* cache misses (which are very common for hash tables) while |
273 |
* obtaining locks so that traversal is faster once |
274 |
* acquired. We do not actually use the found nodes since they |
275 |
* must be re-acquired under lock anyway to ensure sequential |
276 |
* consistency of updates (and in any case may be undetectably |
277 |
* stale), but they will normally be much faster to re-locate. |
278 |
* Also, scanAndLockForPut speculatively creates a fresh node |
279 |
* to use in put if no node is found. |
280 |
*/ |
281 |
|
282 |
private static final long serialVersionUID = 2249069246763182397L; |
283 |
|
284 |
/** |
285 |
* The maximum number of times to tryLock in a prescan before |
286 |
* possibly blocking on acquire in preparation for a locked |
287 |
* segment operation. On multiprocessors, using a bounded |
288 |
* number of retries maintains cache acquired while locating |
289 |
* nodes. |
290 |
*/ |
291 |
static final int MAX_SCAN_RETRIES = |
292 |
Runtime.getRuntime().availableProcessors() > 1 ? 64 : 1; |
293 |
|
294 |
/** |
295 |
* The per-segment table. Elements are accessed via |
296 |
* entryAt/setEntryAt providing volatile semantics. |
297 |
*/ |
298 |
transient volatile HashEntry<K,V>[] table; |
299 |
|
300 |
/** |
301 |
* The number of elements. Accessed only either within locks |
302 |
* or among other volatile reads that maintain visibility. |
303 |
*/ |
304 |
transient int count; |
305 |
|
306 |
/** |
307 |
* The total number of mutative operations in this segment. |
308 |
* Even though this may overflows 32 bits, it provides |
309 |
* sufficient accuracy for stability checks in CHM isEmpty() |
310 |
* and size() methods. Accessed only either within locks or |
311 |
* among other volatile reads that maintain visibility. |
312 |
*/ |
313 |
transient int modCount; |
314 |
|
315 |
/** |
316 |
* The table is rehashed when its size exceeds this threshold. |
317 |
* (The value of this field is always <tt>(int)(capacity * |
318 |
* loadFactor)</tt>.) |
319 |
*/ |
320 |
transient int threshold; |
321 |
|
322 |
/** |
323 |
* The load factor for the hash table. Even though this value |
324 |
* is same for all segments, it is replicated to avoid needing |
325 |
* links to outer object. |
326 |
* @serial |
327 |
*/ |
328 |
final float loadFactor; |
329 |
|
330 |
Segment(float lf, int threshold, HashEntry<K,V>[] tab) { |
331 |
this.loadFactor = lf; |
332 |
this.threshold = threshold; |
333 |
this.table = tab; |
334 |
} |
335 |
|
336 |
final V put(K key, int hash, V value, boolean onlyIfAbsent) { |
337 |
HashEntry<K,V> node = tryLock() ? null : |
338 |
scanAndLockForPut(key, hash, value); |
339 |
V oldValue; |
340 |
try { |
341 |
HashEntry<K,V>[] tab = table; |
342 |
int index = (tab.length - 1) & hash; |
343 |
HashEntry<K,V> first = entryAt(tab, index); |
344 |
for (HashEntry<K,V> e = first;;) { |
345 |
if (e != null) { |
346 |
K k; |
347 |
if ((k = e.key) == key || |
348 |
(e.hash == hash && key.equals(k))) { |
349 |
oldValue = e.value; |
350 |
if (!onlyIfAbsent) { |
351 |
e.value = value; |
352 |
++modCount; |
353 |
} |
354 |
break; |
355 |
} |
356 |
e = e.next; |
357 |
} |
358 |
else { |
359 |
if (node != null) |
360 |
node.setNext(first); |
361 |
else |
362 |
node = new HashEntry<K,V>(hash, key, value, first); |
363 |
int c = count + 1; |
364 |
if (c > threshold && tab.length < MAXIMUM_CAPACITY) |
365 |
rehash(node); |
366 |
else |
367 |
setEntryAt(tab, index, node); |
368 |
++modCount; |
369 |
count = c; |
370 |
oldValue = null; |
371 |
break; |
372 |
} |
373 |
} |
374 |
} finally { |
375 |
unlock(); |
376 |
} |
377 |
return oldValue; |
378 |
} |
379 |
|
380 |
/** |
381 |
* Doubles size of table and repacks entries, also adding the |
382 |
* given node to new table |
383 |
*/ |
384 |
@SuppressWarnings("unchecked") |
385 |
private void rehash(HashEntry<K,V> node) { |
386 |
/* |
387 |
* Reclassify nodes in each list to new table. Because we |
388 |
* are using power-of-two expansion, the elements from |
389 |
* each bin must either stay at same index, or move with a |
390 |
* power of two offset. We eliminate unnecessary node |
391 |
* creation by catching cases where old nodes can be |
392 |
* reused because their next fields won't change. |
393 |
* Statistically, at the default threshold, only about |
394 |
* one-sixth of them need cloning when a table |
395 |
* doubles. The nodes they replace will be garbage |
396 |
* collectable as soon as they are no longer referenced by |
397 |
* any reader thread that may be in the midst of |
398 |
* concurrently traversing table. Entry accesses use plain |
399 |
* array indexing because they are followed by volatile |
400 |
* table write. |
401 |
*/ |
402 |
HashEntry<K,V>[] oldTable = table; |
403 |
int oldCapacity = oldTable.length; |
404 |
int newCapacity = oldCapacity << 1; |
405 |
threshold = (int)(newCapacity * loadFactor); |
406 |
HashEntry<K,V>[] newTable = |
407 |
(HashEntry<K,V>[]) new HashEntry[newCapacity]; |
408 |
int sizeMask = newCapacity - 1; |
409 |
for (int i = 0; i < oldCapacity ; i++) { |
410 |
HashEntry<K,V> e = oldTable[i]; |
411 |
if (e != null) { |
412 |
HashEntry<K,V> next = e.next; |
413 |
int idx = e.hash & sizeMask; |
414 |
if (next == null) // Single node on list |
415 |
newTable[idx] = e; |
416 |
else { // Reuse consecutive sequence at same slot |
417 |
HashEntry<K,V> lastRun = e; |
418 |
int lastIdx = idx; |
419 |
for (HashEntry<K,V> last = next; |
420 |
last != null; |
421 |
last = last.next) { |
422 |
int k = last.hash & sizeMask; |
423 |
if (k != lastIdx) { |
424 |
lastIdx = k; |
425 |
lastRun = last; |
426 |
} |
427 |
} |
428 |
newTable[lastIdx] = lastRun; |
429 |
// Clone remaining nodes |
430 |
for (HashEntry<K,V> p = e; p != lastRun; p = p.next) { |
431 |
V v = p.value; |
432 |
int h = p.hash; |
433 |
int k = h & sizeMask; |
434 |
HashEntry<K,V> n = newTable[k]; |
435 |
newTable[k] = new HashEntry<K,V>(h, p.key, v, n); |
436 |
} |
437 |
} |
438 |
} |
439 |
} |
440 |
int nodeIndex = node.hash & sizeMask; // add the new node |
441 |
node.setNext(newTable[nodeIndex]); |
442 |
newTable[nodeIndex] = node; |
443 |
table = newTable; |
444 |
} |
445 |
|
446 |
/** |
447 |
* Scans for a node containing given key while trying to |
448 |
* acquire lock, creating and returning one if not found. Upon |
449 |
* return, guarantees that lock is held. Unlike in most |
450 |
* methods, calls to method equals are not screened: Since |
451 |
* traversal speed doesn't matter, we might as well help warm |
452 |
* up the associated code and accesses as well. |
453 |
* |
454 |
* @return a new node if key not found, else null |
455 |
*/ |
456 |
private HashEntry<K,V> scanAndLockForPut(K key, int hash, V value) { |
457 |
HashEntry<K,V> first = entryForHash(this, hash); |
458 |
HashEntry<K,V> e = first; |
459 |
HashEntry<K,V> node = null; |
460 |
int retries = -1; // negative while locating node |
461 |
while (!tryLock()) { |
462 |
HashEntry<K,V> f; // to recheck first below |
463 |
if (retries < 0) { |
464 |
if (e == null) { |
465 |
if (node == null) // speculatively create node |
466 |
node = new HashEntry<K,V>(hash, key, value, null); |
467 |
retries = 0; |
468 |
} |
469 |
else if (key.equals(e.key)) |
470 |
retries = 0; |
471 |
else |
472 |
e = e.next; |
473 |
} |
474 |
else if (++retries > MAX_SCAN_RETRIES) { |
475 |
lock(); |
476 |
break; |
477 |
} |
478 |
else if ((retries & 1) == 0 && |
479 |
(f = entryForHash(this, hash)) != first) { |
480 |
e = first = f; // re-traverse if entry changed |
481 |
retries = -1; |
482 |
} |
483 |
} |
484 |
return node; |
485 |
} |
486 |
|
487 |
/** |
488 |
* Scans for a node containing the given key while trying to |
489 |
* acquire lock for a remove or replace operation. Upon |
490 |
* return, guarantees that lock is held. Note that we must |
491 |
* lock even if the key is not found, to ensure sequential |
492 |
* consistency of updates. |
493 |
*/ |
494 |
private void scanAndLock(Object key, int hash) { |
495 |
// similar to but simpler than scanAndLockForPut |
496 |
HashEntry<K,V> first = entryForHash(this, hash); |
497 |
HashEntry<K,V> e = first; |
498 |
int retries = -1; |
499 |
while (!tryLock()) { |
500 |
HashEntry<K,V> f; |
501 |
if (retries < 0) { |
502 |
if (e == null || key.equals(e.key)) |
503 |
retries = 0; |
504 |
else |
505 |
e = e.next; |
506 |
} |
507 |
else if (++retries > MAX_SCAN_RETRIES) { |
508 |
lock(); |
509 |
break; |
510 |
} |
511 |
else if ((retries & 1) == 0 && |
512 |
(f = entryForHash(this, hash)) != first) { |
513 |
e = first = f; |
514 |
retries = -1; |
515 |
} |
516 |
} |
517 |
} |
518 |
|
519 |
/** |
520 |
* Remove; match on key only if value null, else match both. |
521 |
*/ |
522 |
final V remove(Object key, int hash, Object value) { |
523 |
if (!tryLock()) |
524 |
scanAndLock(key, hash); |
525 |
V oldValue = null; |
526 |
try { |
527 |
HashEntry<K,V>[] tab = table; |
528 |
int index = (tab.length - 1) & hash; |
529 |
HashEntry<K,V> e = entryAt(tab, index); |
530 |
HashEntry<K,V> pred = null; |
531 |
while (e != null) { |
532 |
K k; |
533 |
HashEntry<K,V> next = e.next; |
534 |
if ((k = e.key) == key || |
535 |
(e.hash == hash && key.equals(k))) { |
536 |
V v = e.value; |
537 |
if (value == null || value == v || value.equals(v)) { |
538 |
if (pred == null) |
539 |
setEntryAt(tab, index, next); |
540 |
else |
541 |
pred.setNext(next); |
542 |
++modCount; |
543 |
--count; |
544 |
oldValue = v; |
545 |
} |
546 |
break; |
547 |
} |
548 |
pred = e; |
549 |
e = next; |
550 |
} |
551 |
} finally { |
552 |
unlock(); |
553 |
} |
554 |
return oldValue; |
555 |
} |
556 |
|
557 |
final boolean replace(K key, int hash, V oldValue, V newValue) { |
558 |
if (!tryLock()) |
559 |
scanAndLock(key, hash); |
560 |
boolean replaced = false; |
561 |
try { |
562 |
HashEntry<K,V> e; |
563 |
for (e = entryForHash(this, hash); e != null; e = e.next) { |
564 |
K k; |
565 |
if ((k = e.key) == key || |
566 |
(e.hash == hash && key.equals(k))) { |
567 |
if (oldValue.equals(e.value)) { |
568 |
e.value = newValue; |
569 |
++modCount; |
570 |
replaced = true; |
571 |
} |
572 |
break; |
573 |
} |
574 |
} |
575 |
} finally { |
576 |
unlock(); |
577 |
} |
578 |
return replaced; |
579 |
} |
580 |
|
581 |
final V replace(K key, int hash, V value) { |
582 |
if (!tryLock()) |
583 |
scanAndLock(key, hash); |
584 |
V oldValue = null; |
585 |
try { |
586 |
HashEntry<K,V> e; |
587 |
for (e = entryForHash(this, hash); e != null; e = e.next) { |
588 |
K k; |
589 |
if ((k = e.key) == key || |
590 |
(e.hash == hash && key.equals(k))) { |
591 |
oldValue = e.value; |
592 |
e.value = value; |
593 |
++modCount; |
594 |
break; |
595 |
} |
596 |
} |
597 |
} finally { |
598 |
unlock(); |
599 |
} |
600 |
return oldValue; |
601 |
} |
602 |
|
603 |
final void clear() { |
604 |
lock(); |
605 |
try { |
606 |
HashEntry<K,V>[] tab = table; |
607 |
for (int i = 0; i < tab.length ; i++) |
608 |
setEntryAt(tab, i, null); |
609 |
++modCount; |
610 |
count = 0; |
611 |
} finally { |
612 |
unlock(); |
613 |
} |
614 |
} |
615 |
} |
616 |
|
617 |
// Accessing segments |
618 |
|
619 |
/** |
620 |
* Gets the jth element of given segment array (if nonnull) with |
621 |
* volatile element access semantics via Unsafe. (The null check |
622 |
* can trigger harmlessly only during deserialization.) Note: |
623 |
* because each element of segments array is set only once (using |
624 |
* fully ordered writes), some performance-sensitive methods rely |
625 |
* on this method only as a recheck upon null reads. |
626 |
*/ |
627 |
@SuppressWarnings("unchecked") |
628 |
static final <K,V> Segment<K,V> segmentAt(Segment<K,V>[] ss, int j) { |
629 |
long u = (j << SSHIFT) + SBASE; |
630 |
return ss == null ? null : |
631 |
(Segment<K,V>) UNSAFE.getObjectVolatile(ss, u); |
632 |
} |
633 |
|
634 |
/** |
635 |
* Returns the segment for the given index, creating it and |
636 |
* recording in segment table (via CAS) if not already present. |
637 |
* |
638 |
* @param k the index |
639 |
* @return the segment |
640 |
*/ |
641 |
@SuppressWarnings("unchecked") |
642 |
private Segment<K,V> ensureSegment(int k) { |
643 |
final Segment<K,V>[] ss = this.segments; |
644 |
long u = (k << SSHIFT) + SBASE; // raw offset |
645 |
Segment<K,V> seg; |
646 |
if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) == null) { |
647 |
Segment<K,V> proto = ss[0]; // use segment 0 as prototype |
648 |
int cap = proto.table.length; |
649 |
float lf = proto.loadFactor; |
650 |
int threshold = (int)(cap * lf); |
651 |
HashEntry<K,V>[] tab = (HashEntry<K,V>[])new HashEntry[cap]; |
652 |
if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) |
653 |
== null) { // recheck |
654 |
Segment<K,V> s = new Segment<K,V>(lf, threshold, tab); |
655 |
while ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) |
656 |
== null) { |
657 |
if (UNSAFE.compareAndSwapObject(ss, u, null, seg = s)) |
658 |
break; |
659 |
} |
660 |
} |
661 |
} |
662 |
return seg; |
663 |
} |
664 |
|
665 |
// Hash-based segment and entry accesses |
666 |
|
667 |
/** |
668 |
* Get the segment for the given hash |
669 |
*/ |
670 |
@SuppressWarnings("unchecked") |
671 |
private Segment<K,V> segmentForHash(int h) { |
672 |
long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE; |
673 |
return (Segment<K,V>) UNSAFE.getObjectVolatile(segments, u); |
674 |
} |
675 |
|
676 |
/** |
677 |
* Gets the table entry for the given segment and hash |
678 |
*/ |
679 |
@SuppressWarnings("unchecked") |
680 |
static final <K,V> HashEntry<K,V> entryForHash(Segment<K,V> seg, int h) { |
681 |
HashEntry<K,V>[] tab; |
682 |
return (seg == null || (tab = seg.table) == null) ? null : |
683 |
(HashEntry<K,V>) UNSAFE.getObjectVolatile |
684 |
(tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE); |
685 |
} |
686 |
|
687 |
/* ---------------- Public operations -------------- */ |
688 |
|
689 |
/** |
690 |
* Creates a new, empty map with the specified initial |
691 |
* capacity, load factor and concurrency level. |
692 |
* |
693 |
* @param initialCapacity the initial capacity. The implementation |
694 |
* performs internal sizing to accommodate this many elements. |
695 |
* @param loadFactor the load factor threshold, used to control resizing. |
696 |
* Resizing may be performed when the average number of elements per |
697 |
* bin exceeds this threshold. |
698 |
* @param concurrencyLevel the estimated number of concurrently |
699 |
* updating threads. The implementation performs internal sizing |
700 |
* to try to accommodate this many threads. |
701 |
* @throws IllegalArgumentException if the initial capacity is |
702 |
* negative or the load factor or concurrencyLevel are |
703 |
* nonpositive. |
704 |
*/ |
705 |
@SuppressWarnings("unchecked") |
706 |
public ConcurrentHashMap(int initialCapacity, |
707 |
float loadFactor, int concurrencyLevel) { |
708 |
if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0) |
709 |
throw new IllegalArgumentException(); |
710 |
if (concurrencyLevel > MAX_SEGMENTS) |
711 |
concurrencyLevel = MAX_SEGMENTS; |
712 |
// Find power-of-two sizes best matching arguments |
713 |
int sshift = 0; |
714 |
int ssize = 1; |
715 |
while (ssize < concurrencyLevel) { |
716 |
++sshift; |
717 |
ssize <<= 1; |
718 |
} |
719 |
this.segmentShift = 32 - sshift; |
720 |
this.segmentMask = ssize - 1; |
721 |
if (initialCapacity > MAXIMUM_CAPACITY) |
722 |
initialCapacity = MAXIMUM_CAPACITY; |
723 |
int c = initialCapacity / ssize; |
724 |
if (c * ssize < initialCapacity) |
725 |
++c; |
726 |
int cap = MIN_SEGMENT_TABLE_CAPACITY; |
727 |
while (cap < c) |
728 |
cap <<= 1; |
729 |
// create segments and segments[0] |
730 |
Segment<K,V> s0 = |
731 |
new Segment<K,V>(loadFactor, (int)(cap * loadFactor), |
732 |
(HashEntry<K,V>[])new HashEntry[cap]); |
733 |
Segment<K,V>[] ss = (Segment<K,V>[])new Segment[ssize]; |
734 |
UNSAFE.putOrderedObject(ss, SBASE, s0); // ordered write of segments[0] |
735 |
this.segments = ss; |
736 |
} |
737 |
|
738 |
/** |
739 |
* Creates a new, empty map with the specified initial capacity |
740 |
* and load factor and with the default concurrencyLevel (16). |
741 |
* |
742 |
* @param initialCapacity The implementation performs internal |
743 |
* sizing to accommodate this many elements. |
744 |
* @param loadFactor the load factor threshold, used to control resizing. |
745 |
* Resizing may be performed when the average number of elements per |
746 |
* bin exceeds this threshold. |
747 |
* @throws IllegalArgumentException if the initial capacity of |
748 |
* elements is negative or the load factor is nonpositive |
749 |
* |
750 |
* @since 1.6 |
751 |
*/ |
752 |
public ConcurrentHashMap(int initialCapacity, float loadFactor) { |
753 |
this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL); |
754 |
} |
755 |
|
756 |
/** |
757 |
* Creates a new, empty map with the specified initial capacity, |
758 |
* and with default load factor (0.75) and concurrencyLevel (16). |
759 |
* |
760 |
* @param initialCapacity the initial capacity. The implementation |
761 |
* performs internal sizing to accommodate this many elements. |
762 |
* @throws IllegalArgumentException if the initial capacity of |
763 |
* elements is negative. |
764 |
*/ |
765 |
public ConcurrentHashMap(int initialCapacity) { |
766 |
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
767 |
} |
768 |
|
769 |
/** |
770 |
* Creates a new, empty map with a default initial capacity (16), |
771 |
* load factor (0.75) and concurrencyLevel (16). |
772 |
*/ |
773 |
public ConcurrentHashMap() { |
774 |
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
775 |
} |
776 |
|
777 |
/** |
778 |
* Creates a new map with the same mappings as the given map. |
779 |
* The map is created with a capacity of 1.5 times the number |
780 |
* of mappings in the given map or 16 (whichever is greater), |
781 |
* and a default load factor (0.75) and concurrencyLevel (16). |
782 |
* |
783 |
* @param m the map |
784 |
*/ |
785 |
public ConcurrentHashMap(Map<? extends K, ? extends V> m) { |
786 |
this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, |
787 |
DEFAULT_INITIAL_CAPACITY), |
788 |
DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
789 |
putAll(m); |
790 |
} |
791 |
|
792 |
/** |
793 |
* Returns <tt>true</tt> if this map contains no key-value mappings. |
794 |
* |
795 |
* @return <tt>true</tt> if this map contains no key-value mappings |
796 |
*/ |
797 |
public boolean isEmpty() { |
798 |
/* |
799 |
* Sum per-segment modCounts to avoid mis-reporting when |
800 |
* elements are concurrently added and removed in one segment |
801 |
* while checking another, in which case the table was never |
802 |
* actually empty at any point. (The sum ensures accuracy up |
803 |
* through at least 1<<31 per-segment modifications before |
804 |
* recheck.) Methods size() and containsValue() use similar |
805 |
* constructions for stability checks. |
806 |
*/ |
807 |
long sum = 0L; |
808 |
final Segment<K,V>[] segments = this.segments; |
809 |
for (int j = 0; j < segments.length; ++j) { |
810 |
Segment<K,V> seg = segmentAt(segments, j); |
811 |
if (seg != null) { |
812 |
if (seg.count != 0) |
813 |
return false; |
814 |
sum += seg.modCount; |
815 |
} |
816 |
} |
817 |
if (sum != 0L) { // recheck unless no modifications |
818 |
for (int j = 0; j < segments.length; ++j) { |
819 |
Segment<K,V> seg = segmentAt(segments, j); |
820 |
if (seg != null) { |
821 |
if (seg.count != 0) |
822 |
return false; |
823 |
sum -= seg.modCount; |
824 |
} |
825 |
} |
826 |
if (sum != 0L) |
827 |
return false; |
828 |
} |
829 |
return true; |
830 |
} |
831 |
|
832 |
/** |
833 |
* Returns the number of key-value mappings in this map. If the |
834 |
* map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns |
835 |
* <tt>Integer.MAX_VALUE</tt>. |
836 |
* |
837 |
* @return the number of key-value mappings in this map |
838 |
*/ |
839 |
public int size() { |
840 |
// Try a few times to get accurate count. On failure due to |
841 |
// continuous async changes in table, resort to locking. |
842 |
final Segment<K,V>[] segments = this.segments; |
843 |
int size; |
844 |
boolean overflow; // true if size overflows 32 bits |
845 |
long sum; // sum of modCounts |
846 |
long last = 0L; // previous sum |
847 |
int retries = -1; // first iteration isn't retry |
848 |
try { |
849 |
for (;;) { |
850 |
if (retries++ == RETRIES_BEFORE_LOCK) { |
851 |
for (int j = 0; j < segments.length; ++j) |
852 |
ensureSegment(j).lock(); // force creation |
853 |
} |
854 |
sum = 0L; |
855 |
size = 0; |
856 |
overflow = false; |
857 |
for (int j = 0; j < segments.length; ++j) { |
858 |
Segment<K,V> seg = segmentAt(segments, j); |
859 |
if (seg != null) { |
860 |
sum += seg.modCount; |
861 |
int c = seg.count; |
862 |
if (c < 0 || (size += c) < 0) |
863 |
overflow = true; |
864 |
} |
865 |
} |
866 |
if (sum == last) |
867 |
break; |
868 |
last = sum; |
869 |
} |
870 |
} finally { |
871 |
if (retries > RETRIES_BEFORE_LOCK) { |
872 |
for (int j = 0; j < segments.length; ++j) |
873 |
segmentAt(segments, j).unlock(); |
874 |
} |
875 |
} |
876 |
return overflow ? Integer.MAX_VALUE : size; |
877 |
} |
878 |
|
879 |
/** |
880 |
* Returns the value to which the specified key is mapped, |
881 |
* or {@code null} if this map contains no mapping for the key. |
882 |
* |
883 |
* <p>More formally, if this map contains a mapping from a key |
884 |
* {@code k} to a value {@code v} such that {@code key.equals(k)}, |
885 |
* then this method returns {@code v}; otherwise it returns |
886 |
* {@code null}. (There can be at most one such mapping.) |
887 |
* |
888 |
* @throws NullPointerException if the specified key is null |
889 |
*/ |
890 |
public V get(Object key) { |
891 |
Segment<K,V> s; // manually integrate access methods to reduce overhead |
892 |
HashEntry<K,V>[] tab; |
893 |
int h = hash(key.hashCode()); |
894 |
long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE; |
895 |
if ((s = (Segment<K,V>)UNSAFE.getObjectVolatile(segments, u)) != null && |
896 |
(tab = s.table) != null) { |
897 |
for (HashEntry<K,V> e = (HashEntry<K,V>) UNSAFE.getObjectVolatile |
898 |
(tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE); |
899 |
e != null; e = e.next) { |
900 |
K k; |
901 |
if ((k = e.key) == key || (e.hash == h && key.equals(k))) |
902 |
return e.value; |
903 |
} |
904 |
} |
905 |
return null; |
906 |
} |
907 |
|
908 |
/** |
909 |
* Tests if the specified object is a key in this table. |
910 |
* |
911 |
* @param key possible key |
912 |
* @return <tt>true</tt> if and only if the specified object |
913 |
* is a key in this table, as determined by the |
914 |
* <tt>equals</tt> method; <tt>false</tt> otherwise. |
915 |
* @throws NullPointerException if the specified key is null |
916 |
*/ |
917 |
@SuppressWarnings("unchecked") |
918 |
public boolean containsKey(Object key) { |
919 |
Segment<K,V> s; // same as get() except no need for volatile value read |
920 |
HashEntry<K,V>[] tab; |
921 |
int h = hash(key.hashCode()); |
922 |
long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE; |
923 |
if ((s = (Segment<K,V>)UNSAFE.getObjectVolatile(segments, u)) != null && |
924 |
(tab = s.table) != null) { |
925 |
for (HashEntry<K,V> e = (HashEntry<K,V>) UNSAFE.getObjectVolatile |
926 |
(tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE); |
927 |
e != null; e = e.next) { |
928 |
K k; |
929 |
if ((k = e.key) == key || (e.hash == h && key.equals(k))) |
930 |
return true; |
931 |
} |
932 |
} |
933 |
return false; |
934 |
} |
935 |
|
936 |
/** |
937 |
* Returns <tt>true</tt> if this map maps one or more keys to the |
938 |
* specified value. Note: This method requires a full internal |
939 |
* traversal of the hash table, and so is much slower than |
940 |
* method <tt>containsKey</tt>. |
941 |
* |
942 |
* @param value value whose presence in this map is to be tested |
943 |
* @return <tt>true</tt> if this map maps one or more keys to the |
944 |
* specified value |
945 |
* @throws NullPointerException if the specified value is null |
946 |
*/ |
947 |
public boolean containsValue(Object value) { |
948 |
// Same idea as size() |
949 |
if (value == null) |
950 |
throw new NullPointerException(); |
951 |
final Segment<K,V>[] segments = this.segments; |
952 |
boolean found = false; |
953 |
long last = 0L; // previous sum |
954 |
int retries = -1; |
955 |
try { |
956 |
outer: for (;;) { |
957 |
if (retries++ == RETRIES_BEFORE_LOCK) { |
958 |
for (int j = 0; j < segments.length; ++j) |
959 |
ensureSegment(j).lock(); // force creation |
960 |
} |
961 |
long sum = 0L; |
962 |
for (int j = 0; j < segments.length; ++j) { |
963 |
HashEntry<K,V>[] tab; |
964 |
Segment<K,V> seg = segmentAt(segments, j); |
965 |
if (seg != null && (tab = seg.table) != null) { |
966 |
for (int i = 0 ; i < tab.length; i++) { |
967 |
HashEntry<K,V> e; |
968 |
for (e = entryAt(tab, i); e != null; e = e.next) { |
969 |
V v = e.value; |
970 |
if (v != null && value.equals(v)) { |
971 |
found = true; |
972 |
break outer; |
973 |
} |
974 |
} |
975 |
} |
976 |
sum += seg.modCount; |
977 |
} |
978 |
} |
979 |
if (retries > 0 && sum == last) |
980 |
break; |
981 |
last = sum; |
982 |
} |
983 |
} finally { |
984 |
if (retries > RETRIES_BEFORE_LOCK) { |
985 |
for (int j = 0; j < segments.length; ++j) |
986 |
segmentAt(segments, j).unlock(); |
987 |
} |
988 |
} |
989 |
return found; |
990 |
} |
991 |
|
992 |
/** |
993 |
* Legacy method testing if some key maps into the specified value |
994 |
* in this table. This method is identical in functionality to |
995 |
* {@link #containsValue}, and exists solely to ensure |
996 |
* full compatibility with class {@link java.util.Hashtable}, |
997 |
* which supported this method prior to introduction of the |
998 |
* Java Collections framework. |
999 |
|
1000 |
* @param value a value to search for |
1001 |
* @return <tt>true</tt> if and only if some key maps to the |
1002 |
* <tt>value</tt> argument in this table as |
1003 |
* determined by the <tt>equals</tt> method; |
1004 |
* <tt>false</tt> otherwise |
1005 |
* @throws NullPointerException if the specified value is null |
1006 |
*/ |
1007 |
public boolean contains(Object value) { |
1008 |
return containsValue(value); |
1009 |
} |
1010 |
|
1011 |
/** |
1012 |
* Maps the specified key to the specified value in this table. |
1013 |
* Neither the key nor the value can be null. |
1014 |
* |
1015 |
* <p> The value can be retrieved by calling the <tt>get</tt> method |
1016 |
* with a key that is equal to the original key. |
1017 |
* |
1018 |
* @param key key with which the specified value is to be associated |
1019 |
* @param value value to be associated with the specified key |
1020 |
* @return the previous value associated with <tt>key</tt>, or |
1021 |
* <tt>null</tt> if there was no mapping for <tt>key</tt> |
1022 |
* @throws NullPointerException if the specified key or value is null |
1023 |
*/ |
1024 |
@SuppressWarnings("unchecked") |
1025 |
public V put(K key, V value) { |
1026 |
Segment<K,V> s; |
1027 |
if (value == null) |
1028 |
throw new NullPointerException(); |
1029 |
int hash = hash(key.hashCode()); |
1030 |
int j = (hash >>> segmentShift) & segmentMask; |
1031 |
if ((s = (Segment<K,V>)UNSAFE.getObject // nonvolatile; recheck |
1032 |
(segments, (j << SSHIFT) + SBASE)) == null) // in ensureSegment |
1033 |
s = ensureSegment(j); |
1034 |
return s.put(key, hash, value, false); |
1035 |
} |
1036 |
|
1037 |
/** |
1038 |
* {@inheritDoc} |
1039 |
* |
1040 |
* @return the previous value associated with the specified key, |
1041 |
* or <tt>null</tt> if there was no mapping for the key |
1042 |
* @throws NullPointerException if the specified key or value is null |
1043 |
*/ |
1044 |
@SuppressWarnings("unchecked") |
1045 |
public V putIfAbsent(K key, V value) { |
1046 |
Segment<K,V> s; |
1047 |
if (value == null) |
1048 |
throw new NullPointerException(); |
1049 |
int hash = hash(key.hashCode()); |
1050 |
int j = (hash >>> segmentShift) & segmentMask; |
1051 |
if ((s = (Segment<K,V>)UNSAFE.getObject |
1052 |
(segments, (j << SSHIFT) + SBASE)) == null) |
1053 |
s = ensureSegment(j); |
1054 |
return s.put(key, hash, value, true); |
1055 |
} |
1056 |
|
1057 |
/** |
1058 |
* Copies all of the mappings from the specified map to this one. |
1059 |
* These mappings replace any mappings that this map had for any of the |
1060 |
* keys currently in the specified map. |
1061 |
* |
1062 |
* @param m mappings to be stored in this map |
1063 |
*/ |
1064 |
public void putAll(Map<? extends K, ? extends V> m) { |
1065 |
for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) |
1066 |
put(e.getKey(), e.getValue()); |
1067 |
} |
1068 |
|
1069 |
/** |
1070 |
* Removes the key (and its corresponding value) from this map. |
1071 |
* This method does nothing if the key is not in the map. |
1072 |
* |
1073 |
* @param key the key that needs to be removed |
1074 |
* @return the previous value associated with <tt>key</tt>, or |
1075 |
* <tt>null</tt> if there was no mapping for <tt>key</tt> |
1076 |
* @throws NullPointerException if the specified key is null |
1077 |
*/ |
1078 |
public V remove(Object key) { |
1079 |
int hash = hash(key.hashCode()); |
1080 |
Segment<K,V> s = segmentForHash(hash); |
1081 |
return s == null ? null : s.remove(key, hash, null); |
1082 |
} |
1083 |
|
1084 |
/** |
1085 |
* {@inheritDoc} |
1086 |
* |
1087 |
* @throws NullPointerException if the specified key is null |
1088 |
*/ |
1089 |
public boolean remove(Object key, Object value) { |
1090 |
int hash = hash(key.hashCode()); |
1091 |
Segment<K,V> s; |
1092 |
return value != null && (s = segmentForHash(hash)) != null && |
1093 |
s.remove(key, hash, value) != null; |
1094 |
} |
1095 |
|
1096 |
/** |
1097 |
* {@inheritDoc} |
1098 |
* |
1099 |
* @throws NullPointerException if any of the arguments are null |
1100 |
*/ |
1101 |
public boolean replace(K key, V oldValue, V newValue) { |
1102 |
int hash = hash(key.hashCode()); |
1103 |
if (oldValue == null || newValue == null) |
1104 |
throw new NullPointerException(); |
1105 |
Segment<K,V> s = segmentForHash(hash); |
1106 |
return s != null && s.replace(key, hash, oldValue, newValue); |
1107 |
} |
1108 |
|
1109 |
/** |
1110 |
* {@inheritDoc} |
1111 |
* |
1112 |
* @return the previous value associated with the specified key, |
1113 |
* or <tt>null</tt> if there was no mapping for the key |
1114 |
* @throws NullPointerException if the specified key or value is null |
1115 |
*/ |
1116 |
public V replace(K key, V value) { |
1117 |
int hash = hash(key.hashCode()); |
1118 |
if (value == null) |
1119 |
throw new NullPointerException(); |
1120 |
Segment<K,V> s = segmentForHash(hash); |
1121 |
return s == null ? null : s.replace(key, hash, value); |
1122 |
} |
1123 |
|
1124 |
/** |
1125 |
* Removes all of the mappings from this map. |
1126 |
*/ |
1127 |
public void clear() { |
1128 |
final Segment<K,V>[] segments = this.segments; |
1129 |
for (int j = 0; j < segments.length; ++j) { |
1130 |
Segment<K,V> s = segmentAt(segments, j); |
1131 |
if (s != null) |
1132 |
s.clear(); |
1133 |
} |
1134 |
} |
1135 |
|
1136 |
/** |
1137 |
* Returns a {@link Set} view of the keys contained in this map. |
1138 |
* The set is backed by the map, so changes to the map are |
1139 |
* reflected in the set, and vice-versa. The set supports element |
1140 |
* removal, which removes the corresponding mapping from this map, |
1141 |
* via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, |
1142 |
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> |
1143 |
* operations. It does not support the <tt>add</tt> or |
1144 |
* <tt>addAll</tt> operations. |
1145 |
* |
1146 |
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator |
1147 |
* that will never throw {@link ConcurrentModificationException}, |
1148 |
* and guarantees to traverse elements as they existed upon |
1149 |
* construction of the iterator, and may (but is not guaranteed to) |
1150 |
* reflect any modifications subsequent to construction. |
1151 |
*/ |
1152 |
public Set<K> keySet() { |
1153 |
Set<K> ks = keySet; |
1154 |
return (ks != null) ? ks : (keySet = new KeySet()); |
1155 |
} |
1156 |
|
1157 |
/** |
1158 |
* Returns a {@link Collection} view of the values contained in this map. |
1159 |
* The collection is backed by the map, so changes to the map are |
1160 |
* reflected in the collection, and vice-versa. The collection |
1161 |
* supports element removal, which removes the corresponding |
1162 |
* mapping from this map, via the <tt>Iterator.remove</tt>, |
1163 |
* <tt>Collection.remove</tt>, <tt>removeAll</tt>, |
1164 |
* <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not |
1165 |
* support the <tt>add</tt> or <tt>addAll</tt> operations. |
1166 |
* |
1167 |
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator |
1168 |
* that will never throw {@link ConcurrentModificationException}, |
1169 |
* and guarantees to traverse elements as they existed upon |
1170 |
* construction of the iterator, and may (but is not guaranteed to) |
1171 |
* reflect any modifications subsequent to construction. |
1172 |
*/ |
1173 |
public Collection<V> values() { |
1174 |
Collection<V> vs = values; |
1175 |
return (vs != null) ? vs : (values = new Values()); |
1176 |
} |
1177 |
|
1178 |
/** |
1179 |
* Returns a {@link Set} view of the mappings contained in this map. |
1180 |
* The set is backed by the map, so changes to the map are |
1181 |
* reflected in the set, and vice-versa. The set supports element |
1182 |
* removal, which removes the corresponding mapping from the map, |
1183 |
* via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, |
1184 |
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> |
1185 |
* operations. It does not support the <tt>add</tt> or |
1186 |
* <tt>addAll</tt> operations. |
1187 |
* |
1188 |
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator |
1189 |
* that will never throw {@link ConcurrentModificationException}, |
1190 |
* and guarantees to traverse elements as they existed upon |
1191 |
* construction of the iterator, and may (but is not guaranteed to) |
1192 |
* reflect any modifications subsequent to construction. |
1193 |
*/ |
1194 |
public Set<Map.Entry<K,V>> entrySet() { |
1195 |
Set<Map.Entry<K,V>> es = entrySet; |
1196 |
return (es != null) ? es : (entrySet = new EntrySet()); |
1197 |
} |
1198 |
|
1199 |
/** |
1200 |
* Returns an enumeration of the keys in this table. |
1201 |
* |
1202 |
* @return an enumeration of the keys in this table |
1203 |
* @see #keySet() |
1204 |
*/ |
1205 |
public Enumeration<K> keys() { |
1206 |
return new KeyIterator(); |
1207 |
} |
1208 |
|
1209 |
/** |
1210 |
* Returns an enumeration of the values in this table. |
1211 |
* |
1212 |
* @return an enumeration of the values in this table |
1213 |
* @see #values() |
1214 |
*/ |
1215 |
public Enumeration<V> elements() { |
1216 |
return new ValueIterator(); |
1217 |
} |
1218 |
|
1219 |
/* ---------------- Iterator Support -------------- */ |
1220 |
|
1221 |
abstract class HashIterator { |
1222 |
int nextSegmentIndex; |
1223 |
int nextTableIndex; |
1224 |
HashEntry<K,V>[] currentTable; |
1225 |
HashEntry<K, V> nextEntry; |
1226 |
HashEntry<K, V> lastReturned; |
1227 |
|
1228 |
HashIterator() { |
1229 |
nextSegmentIndex = segments.length - 1; |
1230 |
nextTableIndex = -1; |
1231 |
advance(); |
1232 |
} |
1233 |
|
1234 |
/** |
1235 |
* Set nextEntry to first node of next non-empty table |
1236 |
* (in backwards order, to simplify checks). |
1237 |
*/ |
1238 |
final void advance() { |
1239 |
for (;;) { |
1240 |
if (nextTableIndex >= 0) { |
1241 |
if ((nextEntry = entryAt(currentTable, |
1242 |
nextTableIndex--)) != null) |
1243 |
break; |
1244 |
} |
1245 |
else if (nextSegmentIndex >= 0) { |
1246 |
Segment<K,V> seg = segmentAt(segments, nextSegmentIndex--); |
1247 |
if (seg != null && (currentTable = seg.table) != null) |
1248 |
nextTableIndex = currentTable.length - 1; |
1249 |
} |
1250 |
else |
1251 |
break; |
1252 |
} |
1253 |
} |
1254 |
|
1255 |
final HashEntry<K,V> nextEntry() { |
1256 |
HashEntry<K,V> e = nextEntry; |
1257 |
if (e == null) |
1258 |
throw new NoSuchElementException(); |
1259 |
lastReturned = e; // cannot assign until after null check |
1260 |
if ((nextEntry = e.next) == null) |
1261 |
advance(); |
1262 |
return e; |
1263 |
} |
1264 |
|
1265 |
public final boolean hasNext() { return nextEntry != null; } |
1266 |
public final boolean hasMoreElements() { return nextEntry != null; } |
1267 |
|
1268 |
public final void remove() { |
1269 |
if (lastReturned == null) |
1270 |
throw new IllegalStateException(); |
1271 |
ConcurrentHashMap.this.remove(lastReturned.key); |
1272 |
lastReturned = null; |
1273 |
} |
1274 |
} |
1275 |
|
1276 |
final class KeyIterator |
1277 |
extends HashIterator |
1278 |
implements Iterator<K>, Enumeration<K> |
1279 |
{ |
1280 |
public final K next() { return super.nextEntry().key; } |
1281 |
public final K nextElement() { return super.nextEntry().key; } |
1282 |
} |
1283 |
|
1284 |
final class ValueIterator |
1285 |
extends HashIterator |
1286 |
implements Iterator<V>, Enumeration<V> |
1287 |
{ |
1288 |
public final V next() { return super.nextEntry().value; } |
1289 |
public final V nextElement() { return super.nextEntry().value; } |
1290 |
} |
1291 |
|
1292 |
/** |
1293 |
* Custom Entry class used by EntryIterator.next(), that relays |
1294 |
* setValue changes to the underlying map. |
1295 |
*/ |
1296 |
final class WriteThroughEntry |
1297 |
extends AbstractMap.SimpleEntry<K,V> |
1298 |
{ |
1299 |
WriteThroughEntry(K k, V v) { |
1300 |
super(k,v); |
1301 |
} |
1302 |
|
1303 |
/** |
1304 |
* Set our entry's value and write through to the map. The |
1305 |
* value to return is somewhat arbitrary here. Since a |
1306 |
* WriteThroughEntry does not necessarily track asynchronous |
1307 |
* changes, the most recent "previous" value could be |
1308 |
* different from what we return (or could even have been |
1309 |
* removed in which case the put will re-establish). We do not |
1310 |
* and cannot guarantee more. |
1311 |
*/ |
1312 |
public V setValue(V value) { |
1313 |
if (value == null) throw new NullPointerException(); |
1314 |
V v = super.setValue(value); |
1315 |
ConcurrentHashMap.this.put(getKey(), value); |
1316 |
return v; |
1317 |
} |
1318 |
} |
1319 |
|
1320 |
final class EntryIterator |
1321 |
extends HashIterator |
1322 |
implements Iterator<Entry<K,V>> |
1323 |
{ |
1324 |
public Map.Entry<K,V> next() { |
1325 |
HashEntry<K,V> e = super.nextEntry(); |
1326 |
return new WriteThroughEntry(e.key, e.value); |
1327 |
} |
1328 |
} |
1329 |
|
1330 |
final class KeySet extends AbstractSet<K> { |
1331 |
public Iterator<K> iterator() { |
1332 |
return new KeyIterator(); |
1333 |
} |
1334 |
public int size() { |
1335 |
return ConcurrentHashMap.this.size(); |
1336 |
} |
1337 |
public boolean isEmpty() { |
1338 |
return ConcurrentHashMap.this.isEmpty(); |
1339 |
} |
1340 |
public boolean contains(Object o) { |
1341 |
return ConcurrentHashMap.this.containsKey(o); |
1342 |
} |
1343 |
public boolean remove(Object o) { |
1344 |
return ConcurrentHashMap.this.remove(o) != null; |
1345 |
} |
1346 |
public void clear() { |
1347 |
ConcurrentHashMap.this.clear(); |
1348 |
} |
1349 |
} |
1350 |
|
1351 |
final class Values extends AbstractCollection<V> { |
1352 |
public Iterator<V> iterator() { |
1353 |
return new ValueIterator(); |
1354 |
} |
1355 |
public int size() { |
1356 |
return ConcurrentHashMap.this.size(); |
1357 |
} |
1358 |
public boolean isEmpty() { |
1359 |
return ConcurrentHashMap.this.isEmpty(); |
1360 |
} |
1361 |
public boolean contains(Object o) { |
1362 |
return ConcurrentHashMap.this.containsValue(o); |
1363 |
} |
1364 |
public void clear() { |
1365 |
ConcurrentHashMap.this.clear(); |
1366 |
} |
1367 |
} |
1368 |
|
1369 |
final class EntrySet extends AbstractSet<Map.Entry<K,V>> { |
1370 |
public Iterator<Map.Entry<K,V>> iterator() { |
1371 |
return new EntryIterator(); |
1372 |
} |
1373 |
public boolean contains(Object o) { |
1374 |
if (!(o instanceof Map.Entry)) |
1375 |
return false; |
1376 |
Map.Entry<?,?> e = (Map.Entry<?,?>)o; |
1377 |
V v = ConcurrentHashMap.this.get(e.getKey()); |
1378 |
return v != null && v.equals(e.getValue()); |
1379 |
} |
1380 |
public boolean remove(Object o) { |
1381 |
if (!(o instanceof Map.Entry)) |
1382 |
return false; |
1383 |
Map.Entry<?,?> e = (Map.Entry<?,?>)o; |
1384 |
return ConcurrentHashMap.this.remove(e.getKey(), e.getValue()); |
1385 |
} |
1386 |
public int size() { |
1387 |
return ConcurrentHashMap.this.size(); |
1388 |
} |
1389 |
public boolean isEmpty() { |
1390 |
return ConcurrentHashMap.this.isEmpty(); |
1391 |
} |
1392 |
public void clear() { |
1393 |
ConcurrentHashMap.this.clear(); |
1394 |
} |
1395 |
} |
1396 |
|
1397 |
/* ---------------- Serialization Support -------------- */ |
1398 |
|
1399 |
/** |
1400 |
* Save the state of the <tt>ConcurrentHashMap</tt> instance to a |
1401 |
* stream (i.e., serialize it). |
1402 |
* @param s the stream |
1403 |
* @serialData |
1404 |
* the key (Object) and value (Object) |
1405 |
* for each key-value mapping, followed by a null pair. |
1406 |
* The key-value mappings are emitted in no particular order. |
1407 |
*/ |
1408 |
private void writeObject(java.io.ObjectOutputStream s) throws IOException { |
1409 |
// force all segments for serialization compatibility |
1410 |
for (int k = 0; k < segments.length; ++k) |
1411 |
ensureSegment(k); |
1412 |
s.defaultWriteObject(); |
1413 |
|
1414 |
final Segment<K,V>[] segments = this.segments; |
1415 |
for (int k = 0; k < segments.length; ++k) { |
1416 |
Segment<K,V> seg = segmentAt(segments, k); |
1417 |
seg.lock(); |
1418 |
try { |
1419 |
HashEntry<K,V>[] tab = seg.table; |
1420 |
for (int i = 0; i < tab.length; ++i) { |
1421 |
HashEntry<K,V> e; |
1422 |
for (e = entryAt(tab, i); e != null; e = e.next) { |
1423 |
s.writeObject(e.key); |
1424 |
s.writeObject(e.value); |
1425 |
} |
1426 |
} |
1427 |
} finally { |
1428 |
seg.unlock(); |
1429 |
} |
1430 |
} |
1431 |
s.writeObject(null); |
1432 |
s.writeObject(null); |
1433 |
} |
1434 |
|
1435 |
/** |
1436 |
* Reconstitute the <tt>ConcurrentHashMap</tt> instance from a |
1437 |
* stream (i.e., deserialize it). |
1438 |
* @param s the stream |
1439 |
*/ |
1440 |
@SuppressWarnings("unchecked") |
1441 |
private void readObject(java.io.ObjectInputStream s) |
1442 |
throws IOException, ClassNotFoundException { |
1443 |
s.defaultReadObject(); |
1444 |
|
1445 |
// Re-initialize segments to be minimally sized, and let grow. |
1446 |
int cap = MIN_SEGMENT_TABLE_CAPACITY; |
1447 |
final Segment<K,V>[] segments = this.segments; |
1448 |
for (int k = 0; k < segments.length; ++k) { |
1449 |
Segment<K,V> seg = segments[k]; |
1450 |
if (seg != null) { |
1451 |
seg.threshold = (int)(cap * seg.loadFactor); |
1452 |
seg.table = (HashEntry<K,V>[]) new HashEntry[cap]; |
1453 |
} |
1454 |
} |
1455 |
|
1456 |
// Read the keys and values, and put the mappings in the table |
1457 |
for (;;) { |
1458 |
K key = (K) s.readObject(); |
1459 |
V value = (V) s.readObject(); |
1460 |
if (key == null) |
1461 |
break; |
1462 |
put(key, value); |
1463 |
} |
1464 |
} |
1465 |
|
1466 |
// Unsafe mechanics |
1467 |
private static final sun.misc.Unsafe UNSAFE; |
1468 |
private static final long SBASE; |
1469 |
private static final int SSHIFT; |
1470 |
private static final long TBASE; |
1471 |
private static final int TSHIFT; |
1472 |
|
1473 |
static { |
1474 |
int ss, ts; |
1475 |
try { |
1476 |
UNSAFE = sun.misc.Unsafe.getUnsafe(); |
1477 |
Class tc = HashEntry[].class; |
1478 |
Class sc = Segment[].class; |
1479 |
TBASE = UNSAFE.arrayBaseOffset(tc); |
1480 |
SBASE = UNSAFE.arrayBaseOffset(sc); |
1481 |
ts = UNSAFE.arrayIndexScale(tc); |
1482 |
ss = UNSAFE.arrayIndexScale(sc); |
1483 |
} catch (Exception e) { |
1484 |
throw new Error(e); |
1485 |
} |
1486 |
if ((ss & (ss-1)) != 0 || (ts & (ts-1)) != 0) |
1487 |
throw new Error("data type scale not a power of two"); |
1488 |
SSHIFT = 31 - Integer.numberOfLeadingZeros(ss); |
1489 |
TSHIFT = 31 - Integer.numberOfLeadingZeros(ts); |
1490 |
} |
1491 |
|
1492 |
} |