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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; |
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|
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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. |
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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 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. |
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*/ |
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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; |
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|
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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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*/ |
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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 |
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static final sun.misc.Unsafe UNSAFE; |
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static final long nextOffset; |
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static { |
200 |
try { |
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UNSAFE = sun.misc.Unsafe.getUnsafe(); |
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Class k = HashEntry.class; |
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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. |
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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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/** |
250 |
* 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. |
253 |
*/ |
254 |
static final class Segment<K,V> extends ReentrantLock implements Serializable { |
255 |
/* |
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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 |
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* spinning on contention via methods scanAndLock and |
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* scanAndLockForPut. These intersperse tryLocks with |
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* traversals to locate nodes. The main benefit is to absorb |
271 |
* cache misses (which are very common for hash tables) while |
272 |
* obtaining locks so that traversal is faster once |
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* acquired. We do not actually use the found nodes since they |
274 |
* must be re-acquired under lock anyway to ensure sequential |
275 |
* consistency of updates (and in any case may be undetectably |
276 |
* stale), but they will normally be much faster to re-locate. |
277 |
* Also, scanAndLockForPut speculatively creates a fresh node |
278 |
* to use in put if no node is found. |
279 |
*/ |
280 |
|
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private static final long serialVersionUID = 2249069246763182397L; |
282 |
|
283 |
/** |
284 |
* The maximum number of times to tryLock in a prescan before |
285 |
* possibly blocking on acquire in preparation for a locked |
286 |
* segment operation. On multiprocessors, using a bounded |
287 |
* number of retries maintains cache acquired while locating |
288 |
* nodes. |
289 |
*/ |
290 |
static final int MAX_SCAN_RETRIES = |
291 |
Runtime.getRuntime().availableProcessors() > 1 ? 64 : 1; |
292 |
|
293 |
/** |
294 |
* The per-segment table. Elements are accessed via |
295 |
* entryAt/setEntryAt providing volatile semantics. |
296 |
*/ |
297 |
transient volatile HashEntry<K,V>[] table; |
298 |
|
299 |
/** |
300 |
* The number of elements. Accessed only either within locks |
301 |
* or among other volatile reads that maintain visibility. |
302 |
*/ |
303 |
transient int count; |
304 |
|
305 |
/** |
306 |
* The total number of insertions and removals in this |
307 |
* segment. Even though this may overflows 32 bits, it |
308 |
* provides sufficient accuracy for stability checks in CHM |
309 |
* isEmpty() and size() methods. Accessed only either within |
310 |
* locks or among other volatile reads that maintain |
311 |
* 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 |
|
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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 |
break; |
353 |
} |
354 |
e = e.next; |
355 |
} |
356 |
else { |
357 |
if (node != null) |
358 |
node.setNext(first); |
359 |
else |
360 |
node = new HashEntry<K,V>(hash, key, value, first); |
361 |
int c = count + 1; |
362 |
if (c > threshold && first != null && |
363 |
tab.length < MAXIMUM_CAPACITY) |
364 |
rehash(node); |
365 |
else |
366 |
setEntryAt(tab, index, node); |
367 |
++modCount; |
368 |
count = c; |
369 |
oldValue = null; |
370 |
break; |
371 |
} |
372 |
} |
373 |
} finally { |
374 |
unlock(); |
375 |
} |
376 |
return oldValue; |
377 |
} |
378 |
|
379 |
/** |
380 |
* Doubles size of table and repacks entries, also adding the |
381 |
* given node to new table |
382 |
*/ |
383 |
@SuppressWarnings("unchecked") |
384 |
private void rehash(HashEntry<K,V> node) { |
385 |
/* |
386 |
* Reclassify nodes in each list to new table. Because we |
387 |
* are using power-of-two expansion, the elements from |
388 |
* each bin must either stay at same index, or move with a |
389 |
* power of two offset. We eliminate unnecessary node |
390 |
* creation by catching cases where old nodes can be |
391 |
* reused because their next fields won't change. |
392 |
* Statistically, at the default threshold, only about |
393 |
* one-sixth of them need cloning when a table |
394 |
* doubles. The nodes they replace will be garbage |
395 |
* collectable as soon as they are no longer referenced by |
396 |
* any reader thread that may be in the midst of |
397 |
* concurrently traversing table. Entry accesses use plain |
398 |
* array indexing because they are followed by volatile |
399 |
* table write. |
400 |
*/ |
401 |
HashEntry<K,V>[] oldTable = table; |
402 |
int oldCapacity = oldTable.length; |
403 |
int newCapacity = oldCapacity << 1; |
404 |
threshold = (int)(newCapacity * loadFactor); |
405 |
HashEntry<K,V>[] newTable = |
406 |
(HashEntry<K,V>[]) new HashEntry[newCapacity]; |
407 |
int sizeMask = newCapacity - 1; |
408 |
for (int i = 0; i < oldCapacity ; i++) { |
409 |
HashEntry<K,V> e = oldTable[i]; |
410 |
if (e != null) { |
411 |
HashEntry<K,V> next = e.next; |
412 |
int idx = e.hash & sizeMask; |
413 |
if (next == null) // Single node on list |
414 |
newTable[idx] = e; |
415 |
else { // Reuse consecutive sequence at same slot |
416 |
HashEntry<K,V> lastRun = e; |
417 |
int lastIdx = idx; |
418 |
for (HashEntry<K,V> last = next; |
419 |
last != null; |
420 |
last = last.next) { |
421 |
int k = last.hash & sizeMask; |
422 |
if (k != lastIdx) { |
423 |
lastIdx = k; |
424 |
lastRun = last; |
425 |
} |
426 |
} |
427 |
newTable[lastIdx] = lastRun; |
428 |
// Clone remaining nodes |
429 |
for (HashEntry<K,V> p = e; p != lastRun; p = p.next) { |
430 |
V v = p.value; |
431 |
int h = p.hash; |
432 |
int k = h & sizeMask; |
433 |
HashEntry<K,V> n = newTable[k]; |
434 |
newTable[k] = new HashEntry<K,V>(h, p.key, v, n); |
435 |
} |
436 |
} |
437 |
} |
438 |
} |
439 |
int nodeIndex = node.hash & sizeMask; // add the new node |
440 |
node.setNext(newTable[nodeIndex]); |
441 |
newTable[nodeIndex] = node; |
442 |
table = newTable; |
443 |
} |
444 |
|
445 |
/** |
446 |
* Scans for a node containing given key while trying to |
447 |
* acquire lock, creating and returning one if not found. Upon |
448 |
* return, guarantees that lock is held. |
449 |
* |
450 |
* @return a new node if key not found, else null |
451 |
*/ |
452 |
private HashEntry<K,V> scanAndLockForPut(K key, int hash, V value) { |
453 |
HashEntry<K,V> first = entryForHash(this, hash); |
454 |
HashEntry<K,V> e = first; |
455 |
HashEntry<K,V> node = null; |
456 |
int retries = -1; // negative while locating node |
457 |
while (!tryLock()) { |
458 |
HashEntry<K,V> f; // to recheck first below |
459 |
if (retries < 0) { |
460 |
if (e == null) { |
461 |
if (node == null) // speculatively create node |
462 |
node = new HashEntry<K,V>(hash, key, value, null); |
463 |
retries = 0; |
464 |
} |
465 |
else if (key.equals(e.key)) |
466 |
retries = 0; |
467 |
else |
468 |
e = e.next; |
469 |
} |
470 |
else if (++retries > MAX_SCAN_RETRIES) { |
471 |
lock(); |
472 |
break; |
473 |
} |
474 |
else if ((retries & 1) == 0 && |
475 |
(f = entryForHash(this, hash)) != first) { |
476 |
e = first = f; // re-traverse if entry changed |
477 |
retries = -1; |
478 |
} |
479 |
} |
480 |
return node; |
481 |
} |
482 |
|
483 |
/** |
484 |
* Scans for a node containing the given key while trying to |
485 |
* acquire lock for a remove or replace operation. Upon |
486 |
* return, guarantees that lock is held. Note that we must |
487 |
* lock even if the key is not found, to ensure sequential |
488 |
* consistency of updates. |
489 |
*/ |
490 |
private void scanAndLock(Object key, int hash) { |
491 |
// similar to but simpler than scanAndLockForPut |
492 |
HashEntry<K,V> first = entryForHash(this, hash); |
493 |
HashEntry<K,V> e = first; |
494 |
int retries = -1; |
495 |
while (!tryLock()) { |
496 |
HashEntry<K,V> f; |
497 |
if (retries < 0) { |
498 |
if (e == null || key.equals(e.key)) |
499 |
retries = 0; |
500 |
else |
501 |
e = e.next; |
502 |
} |
503 |
else if (++retries > MAX_SCAN_RETRIES) { |
504 |
lock(); |
505 |
break; |
506 |
} |
507 |
else if ((retries & 1) == 0 && |
508 |
(f = entryForHash(this, hash)) != first) { |
509 |
e = first = f; |
510 |
retries = -1; |
511 |
} |
512 |
} |
513 |
} |
514 |
|
515 |
/** |
516 |
* Remove; match on key only if value null, else match both. |
517 |
*/ |
518 |
final V remove(Object key, int hash, Object value) { |
519 |
if (!tryLock()) |
520 |
scanAndLock(key, hash); |
521 |
V oldValue = null; |
522 |
try { |
523 |
HashEntry<K,V>[] tab = table; |
524 |
int index = (tab.length - 1) & hash; |
525 |
HashEntry<K,V> e = entryAt(tab, index); |
526 |
HashEntry<K,V> pred = null; |
527 |
while (e != null) { |
528 |
K k; |
529 |
HashEntry<K,V> next = e.next; |
530 |
if ((k = e.key) == key || |
531 |
(e.hash == hash && key.equals(k))) { |
532 |
V v = e.value; |
533 |
if (value == null || value == v || value.equals(v)) { |
534 |
if (pred == null) |
535 |
setEntryAt(tab, index, next); |
536 |
else |
537 |
pred.setNext(next); |
538 |
++modCount; |
539 |
--count; |
540 |
oldValue = v; |
541 |
} |
542 |
break; |
543 |
} |
544 |
pred = e; |
545 |
e = next; |
546 |
} |
547 |
} finally { |
548 |
unlock(); |
549 |
} |
550 |
return oldValue; |
551 |
} |
552 |
|
553 |
final boolean replace(K key, int hash, V oldValue, V newValue) { |
554 |
if (!tryLock()) |
555 |
scanAndLock(key, hash); |
556 |
boolean replaced = false; |
557 |
try { |
558 |
HashEntry<K,V> e; |
559 |
for (e = entryForHash(this, hash); e != null; e = e.next) { |
560 |
K k; |
561 |
if ((k = e.key) == key || |
562 |
(e.hash == hash && key.equals(k))) { |
563 |
if (oldValue.equals(e.value)) { |
564 |
e.value = newValue; |
565 |
replaced = true; |
566 |
} |
567 |
break; |
568 |
} |
569 |
} |
570 |
} finally { |
571 |
unlock(); |
572 |
} |
573 |
return replaced; |
574 |
} |
575 |
|
576 |
final V replace(K key, int hash, V value) { |
577 |
if (!tryLock()) |
578 |
scanAndLock(key, hash); |
579 |
V oldValue = null; |
580 |
try { |
581 |
HashEntry<K,V> e; |
582 |
for (e = entryForHash(this, hash); e != null; e = e.next) { |
583 |
K k; |
584 |
if ((k = e.key) == key || |
585 |
(e.hash == hash && key.equals(k))) { |
586 |
oldValue = e.value; |
587 |
e.value = value; |
588 |
break; |
589 |
} |
590 |
} |
591 |
} finally { |
592 |
unlock(); |
593 |
} |
594 |
return oldValue; |
595 |
} |
596 |
|
597 |
final void clear() { |
598 |
lock(); |
599 |
try { |
600 |
HashEntry<K,V>[] tab = table; |
601 |
for (int i = 0; i < tab.length ; i++) |
602 |
setEntryAt(tab, i, null); |
603 |
++modCount; |
604 |
count = 0; |
605 |
} finally { |
606 |
unlock(); |
607 |
} |
608 |
} |
609 |
} |
610 |
|
611 |
// Accessing segments |
612 |
|
613 |
/** |
614 |
* Gets the jth element of given segment array (if nonnull) with |
615 |
* volatile element access semantics via Unsafe. |
616 |
*/ |
617 |
@SuppressWarnings("unchecked") |
618 |
static final <K,V> Segment<K,V> segmentAt(Segment<K,V>[] ss, int j) { |
619 |
long u = (j << SSHIFT) + SBASE; |
620 |
return ss == null ? null : |
621 |
(Segment<K,V>) UNSAFE.getObjectVolatile(ss, u); |
622 |
} |
623 |
|
624 |
/** |
625 |
* Returns the segment for the given index, creating it and |
626 |
* recording in segment table (via CAS) if not already present. |
627 |
* |
628 |
* @param k the index |
629 |
* @return the segment |
630 |
*/ |
631 |
@SuppressWarnings("unchecked") |
632 |
private Segment<K,V> ensureSegment(int k) { |
633 |
final Segment<K,V>[] ss = this.segments; |
634 |
long u = (k << SSHIFT) + SBASE; // raw offset |
635 |
Segment<K,V> seg; |
636 |
if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) == null) { |
637 |
Segment<K,V> proto = ss[0]; // use segment 0 as prototype |
638 |
int cap = proto.table.length; |
639 |
float lf = proto.loadFactor; |
640 |
int threshold = (int)(cap * lf); |
641 |
HashEntry<K,V>[] tab = (HashEntry<K,V>[])new HashEntry[cap]; |
642 |
if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) |
643 |
== null) { // recheck |
644 |
Segment<K,V> s = new Segment<K,V>(lf, threshold, tab); |
645 |
while ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) |
646 |
== null) { |
647 |
if (UNSAFE.compareAndSwapObject(ss, u, null, seg = s)) |
648 |
break; |
649 |
} |
650 |
} |
651 |
} |
652 |
return seg; |
653 |
} |
654 |
|
655 |
// Hash-based segment and entry accesses |
656 |
|
657 |
/** |
658 |
* Get the segment for the given hash |
659 |
*/ |
660 |
@SuppressWarnings("unchecked") |
661 |
private Segment<K,V> segmentForHash(int h) { |
662 |
long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE; |
663 |
return (Segment<K,V>) UNSAFE.getObjectVolatile(segments, u); |
664 |
} |
665 |
|
666 |
/** |
667 |
* Gets the table entry for the given segment and hash |
668 |
*/ |
669 |
@SuppressWarnings("unchecked") |
670 |
static final <K,V> HashEntry<K,V> entryForHash(Segment<K,V> seg, int h) { |
671 |
HashEntry<K,V>[] tab; |
672 |
return (seg == null || (tab = seg.table) == null) ? null : |
673 |
(HashEntry<K,V>) UNSAFE.getObjectVolatile |
674 |
(tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE); |
675 |
} |
676 |
|
677 |
/* ---------------- Public operations -------------- */ |
678 |
|
679 |
/** |
680 |
* Creates a new, empty map with the specified initial |
681 |
* capacity, load factor and concurrency level. |
682 |
* |
683 |
* @param initialCapacity the initial capacity. The implementation |
684 |
* performs internal sizing to accommodate this many elements. |
685 |
* @param loadFactor the load factor threshold, used to control resizing. |
686 |
* Resizing may be performed when the average number of elements per |
687 |
* bin exceeds this threshold. |
688 |
* @param concurrencyLevel the estimated number of concurrently |
689 |
* updating threads. The implementation performs internal sizing |
690 |
* to try to accommodate this many threads. |
691 |
* @throws IllegalArgumentException if the initial capacity is |
692 |
* negative or the load factor or concurrencyLevel are |
693 |
* nonpositive. |
694 |
*/ |
695 |
@SuppressWarnings("unchecked") |
696 |
public ConcurrentHashMap(int initialCapacity, |
697 |
float loadFactor, int concurrencyLevel) { |
698 |
if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0) |
699 |
throw new IllegalArgumentException(); |
700 |
if (concurrencyLevel > MAX_SEGMENTS) |
701 |
concurrencyLevel = MAX_SEGMENTS; |
702 |
// Find power-of-two sizes best matching arguments |
703 |
int sshift = 0; |
704 |
int ssize = 1; |
705 |
while (ssize < concurrencyLevel) { |
706 |
++sshift; |
707 |
ssize <<= 1; |
708 |
} |
709 |
this.segmentShift = 32 - sshift; |
710 |
this.segmentMask = ssize - 1; |
711 |
if (initialCapacity > MAXIMUM_CAPACITY) |
712 |
initialCapacity = MAXIMUM_CAPACITY; |
713 |
int c = initialCapacity / ssize; |
714 |
if (c * ssize < initialCapacity) |
715 |
++c; |
716 |
int cap = MIN_SEGMENT_TABLE_CAPACITY; |
717 |
while (cap < c) |
718 |
cap <<= 1; |
719 |
// create segments and segments[0] |
720 |
Segment<K,V> s0 = |
721 |
new Segment<K,V>(loadFactor, (int)(cap * loadFactor), |
722 |
(HashEntry<K,V>[])new HashEntry[cap]); |
723 |
Segment<K,V>[] ss = (Segment<K,V>[])new Segment[ssize]; |
724 |
UNSAFE.putOrderedObject(ss, SBASE, s0); // ordered write of segments[0] |
725 |
this.segments = ss; |
726 |
} |
727 |
|
728 |
/** |
729 |
* Creates a new, empty map with the specified initial capacity |
730 |
* and load factor and with the default concurrencyLevel (16). |
731 |
* |
732 |
* @param initialCapacity The implementation performs internal |
733 |
* sizing to accommodate this many elements. |
734 |
* @param loadFactor the load factor threshold, used to control resizing. |
735 |
* Resizing may be performed when the average number of elements per |
736 |
* bin exceeds this threshold. |
737 |
* @throws IllegalArgumentException if the initial capacity of |
738 |
* elements is negative or the load factor is nonpositive |
739 |
* |
740 |
* @since 1.6 |
741 |
*/ |
742 |
public ConcurrentHashMap(int initialCapacity, float loadFactor) { |
743 |
this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL); |
744 |
} |
745 |
|
746 |
/** |
747 |
* Creates a new, empty map with the specified initial capacity, |
748 |
* and with default load factor (0.75) and concurrencyLevel (16). |
749 |
* |
750 |
* @param initialCapacity the initial capacity. The implementation |
751 |
* performs internal sizing to accommodate this many elements. |
752 |
* @throws IllegalArgumentException if the initial capacity of |
753 |
* elements is negative. |
754 |
*/ |
755 |
public ConcurrentHashMap(int initialCapacity) { |
756 |
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
757 |
} |
758 |
|
759 |
/** |
760 |
* Creates a new, empty map with a default initial capacity (16), |
761 |
* load factor (0.75) and concurrencyLevel (16). |
762 |
*/ |
763 |
public ConcurrentHashMap() { |
764 |
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
765 |
} |
766 |
|
767 |
/** |
768 |
* Creates a new map with the same mappings as the given map. |
769 |
* The map is created with a capacity of 1.5 times the number |
770 |
* of mappings in the given map or 16 (whichever is greater), |
771 |
* and a default load factor (0.75) and concurrencyLevel (16). |
772 |
* |
773 |
* @param m the map |
774 |
*/ |
775 |
public ConcurrentHashMap(Map<? extends K, ? extends V> m) { |
776 |
this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, |
777 |
DEFAULT_INITIAL_CAPACITY), |
778 |
DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
779 |
putAll(m); |
780 |
} |
781 |
|
782 |
/** |
783 |
* Returns <tt>true</tt> if this map contains no key-value mappings. |
784 |
* |
785 |
* @return <tt>true</tt> if this map contains no key-value mappings |
786 |
*/ |
787 |
public boolean isEmpty() { |
788 |
/* |
789 |
* Sum per-segment modCounts to avoid mis-reporting when |
790 |
* elements are concurrently added and removed in one segment |
791 |
* while checking another, in which case the table was never |
792 |
* actually empty at any point. (The sum ensures accuracy up |
793 |
* through at least 1<<31 per-segment modifications before |
794 |
* recheck.) Methods size() and containsValue() use similar |
795 |
* constructions for stability checks. |
796 |
*/ |
797 |
long sum = 0L; |
798 |
final Segment<K,V>[] segments = this.segments; |
799 |
for (int j = 0; j < segments.length; ++j) { |
800 |
Segment<K,V> seg = segmentAt(segments, j); |
801 |
if (seg != null) { |
802 |
if (seg.count != 0) |
803 |
return false; |
804 |
sum += seg.modCount; |
805 |
} |
806 |
} |
807 |
if (sum != 0L) { // recheck unless no modifications |
808 |
for (int j = 0; j < segments.length; ++j) { |
809 |
Segment<K,V> seg = segmentAt(segments, j); |
810 |
if (seg != null) { |
811 |
if (seg.count != 0) |
812 |
return false; |
813 |
sum -= seg.modCount; |
814 |
} |
815 |
} |
816 |
if (sum != 0L) |
817 |
return false; |
818 |
} |
819 |
return true; |
820 |
} |
821 |
|
822 |
/** |
823 |
* Returns the number of key-value mappings in this map. If the |
824 |
* map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns |
825 |
* <tt>Integer.MAX_VALUE</tt>. |
826 |
* |
827 |
* @return the number of key-value mappings in this map |
828 |
*/ |
829 |
public int size() { |
830 |
// Try a few times to get accurate count. On failure due to |
831 |
// continuous async changes in table, resort to locking. |
832 |
final Segment<K,V>[] segments = this.segments; |
833 |
int size; |
834 |
boolean overflow; // true if size overflows 32 bits |
835 |
long sum; // sum of modCounts |
836 |
long last = 0L; // previous sum |
837 |
int retries = -1; // first iteration isn't retry |
838 |
try { |
839 |
for (;;) { |
840 |
if (retries++ == RETRIES_BEFORE_LOCK) { |
841 |
for (int j = 0; j < segments.length; ++j) |
842 |
ensureSegment(j).lock(); // force creation |
843 |
} |
844 |
sum = 0L; |
845 |
size = 0; |
846 |
overflow = false; |
847 |
for (int j = 0; j < segments.length; ++j) { |
848 |
Segment<K,V> seg = segmentAt(segments, j); |
849 |
if (seg != null) { |
850 |
sum += seg.modCount; |
851 |
int c = seg.count; |
852 |
if (c < 0 || (size += c) < 0) |
853 |
overflow = true; |
854 |
} |
855 |
} |
856 |
if (sum == last) |
857 |
break; |
858 |
last = sum; |
859 |
} |
860 |
} finally { |
861 |
if (retries > RETRIES_BEFORE_LOCK) { |
862 |
for (int j = 0; j < segments.length; ++j) |
863 |
segmentAt(segments, j).unlock(); |
864 |
} |
865 |
} |
866 |
return overflow ? Integer.MAX_VALUE : size; |
867 |
} |
868 |
|
869 |
/** |
870 |
* Returns the value to which the specified key is mapped, |
871 |
* or {@code null} if this map contains no mapping for the key. |
872 |
* |
873 |
* <p>More formally, if this map contains a mapping from a key |
874 |
* {@code k} to a value {@code v} such that {@code key.equals(k)}, |
875 |
* then this method returns {@code v}; otherwise it returns |
876 |
* {@code null}. (There can be at most one such mapping.) |
877 |
* |
878 |
* @throws NullPointerException if the specified key is null |
879 |
*/ |
880 |
public V get(Object key) { |
881 |
int hash = hash(key.hashCode()); |
882 |
for (HashEntry<K,V> e = entryForHash(segmentForHash(hash), hash); |
883 |
e != null; e = e.next) { |
884 |
K k; |
885 |
if ((k = e.key) == key || (e.hash == hash && key.equals(k))) |
886 |
return e.value; |
887 |
} |
888 |
return null; |
889 |
} |
890 |
|
891 |
/** |
892 |
* Tests if the specified object is a key in this table. |
893 |
* |
894 |
* @param key possible key |
895 |
* @return <tt>true</tt> if and only if the specified object |
896 |
* is a key in this table, as determined by the |
897 |
* <tt>equals</tt> method; <tt>false</tt> otherwise. |
898 |
* @throws NullPointerException if the specified key is null |
899 |
*/ |
900 |
public boolean containsKey(Object key) { |
901 |
int hash = hash(key.hashCode()); |
902 |
for (HashEntry<K,V> e = entryForHash(segmentForHash(hash), hash); |
903 |
e != null; e = e.next) { |
904 |
K k; |
905 |
if ((k = e.key) == key || (e.hash == hash && key.equals(k))) |
906 |
return true; |
907 |
} |
908 |
return false; |
909 |
} |
910 |
|
911 |
/** |
912 |
* Returns <tt>true</tt> if this map maps one or more keys to the |
913 |
* specified value. Note: This method requires a full internal |
914 |
* traversal of the hash table, and so is much slower than |
915 |
* method <tt>containsKey</tt>. |
916 |
* |
917 |
* @param value value whose presence in this map is to be tested |
918 |
* @return <tt>true</tt> if this map maps one or more keys to the |
919 |
* specified value |
920 |
* @throws NullPointerException if the specified value is null |
921 |
*/ |
922 |
public boolean containsValue(Object value) { |
923 |
// Same idea as size() but using hashes as checksum |
924 |
if (value == null) |
925 |
throw new NullPointerException(); |
926 |
final Segment<K,V>[] segments = this.segments; |
927 |
boolean found = false; |
928 |
long last = 0L; |
929 |
int retries = -1; |
930 |
try { |
931 |
outer: for (;;) { |
932 |
if (retries++ == RETRIES_BEFORE_LOCK) { |
933 |
for (int j = 0; j < segments.length; ++j) |
934 |
ensureSegment(j).lock(); // force creation |
935 |
} |
936 |
long sum = 0L; |
937 |
for (int j = 0; j < segments.length; ++j) { |
938 |
HashEntry<K,V>[] tab; |
939 |
Segment<K,V> seg = segmentAt(segments, j); |
940 |
if (seg != null && (tab = seg.table) != null) { |
941 |
for (int i = 0 ; i < tab.length; i++) { |
942 |
HashEntry<K,V> e; |
943 |
for (e = entryAt(tab, i); e != null; e = e.next) { |
944 |
V v = e.value; |
945 |
if (v != null && value.equals(v)) { |
946 |
found = true; |
947 |
break outer; |
948 |
} |
949 |
sum += e.hash; |
950 |
} |
951 |
} |
952 |
} |
953 |
} |
954 |
if (sum == last) |
955 |
break; |
956 |
last = sum; |
957 |
} |
958 |
} finally { |
959 |
if (retries > RETRIES_BEFORE_LOCK) { |
960 |
for (int j = 0; j < segments.length; ++j) |
961 |
segmentAt(segments, j).unlock(); |
962 |
} |
963 |
} |
964 |
return found; |
965 |
} |
966 |
|
967 |
/** |
968 |
* Legacy method testing if some key maps into the specified value |
969 |
* in this table. This method is identical in functionality to |
970 |
* {@link #containsValue}, and exists solely to ensure |
971 |
* full compatibility with class {@link java.util.Hashtable}, |
972 |
* which supported this method prior to introduction of the |
973 |
* Java Collections framework. |
974 |
|
975 |
* @param value a value to search for |
976 |
* @return <tt>true</tt> if and only if some key maps to the |
977 |
* <tt>value</tt> argument in this table as |
978 |
* determined by the <tt>equals</tt> method; |
979 |
* <tt>false</tt> otherwise |
980 |
* @throws NullPointerException if the specified value is null |
981 |
*/ |
982 |
public boolean contains(Object value) { |
983 |
return containsValue(value); |
984 |
} |
985 |
|
986 |
/** |
987 |
* Maps the specified key to the specified value in this table. |
988 |
* Neither the key nor the value can be null. |
989 |
* |
990 |
* <p> The value can be retrieved by calling the <tt>get</tt> method |
991 |
* with a key that is equal to the original key. |
992 |
* |
993 |
* @param key key with which the specified value is to be associated |
994 |
* @param value value to be associated with the specified key |
995 |
* @return the previous value associated with <tt>key</tt>, or |
996 |
* <tt>null</tt> if there was no mapping for <tt>key</tt> |
997 |
* @throws NullPointerException if the specified key or value is null |
998 |
*/ |
999 |
public V put(K key, V value) { |
1000 |
if (value == null) |
1001 |
throw new NullPointerException(); |
1002 |
int hash = hash(key.hashCode()); |
1003 |
int j = (hash >>> segmentShift) & segmentMask; |
1004 |
Segment<K,V> s = segmentAt(segments, j); |
1005 |
if (s == null) |
1006 |
s = ensureSegment(j); |
1007 |
return s.put(key, hash, value, false); |
1008 |
} |
1009 |
|
1010 |
/** |
1011 |
* {@inheritDoc} |
1012 |
* |
1013 |
* @return the previous value associated with the specified key, |
1014 |
* or <tt>null</tt> if there was no mapping for the key |
1015 |
* @throws NullPointerException if the specified key or value is null |
1016 |
*/ |
1017 |
public V putIfAbsent(K key, V value) { |
1018 |
if (value == null) |
1019 |
throw new NullPointerException(); |
1020 |
int hash = hash(key.hashCode()); |
1021 |
int j = (hash >>> segmentShift) & segmentMask; |
1022 |
Segment<K,V> s = segmentAt(segments, j); |
1023 |
if (s == null) |
1024 |
s = ensureSegment(j); |
1025 |
return s.put(key, hash, value, true); |
1026 |
} |
1027 |
|
1028 |
/** |
1029 |
* Copies all of the mappings from the specified map to this one. |
1030 |
* These mappings replace any mappings that this map had for any of the |
1031 |
* keys currently in the specified map. |
1032 |
* |
1033 |
* @param m mappings to be stored in this map |
1034 |
*/ |
1035 |
public void putAll(Map<? extends K, ? extends V> m) { |
1036 |
for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) |
1037 |
put(e.getKey(), e.getValue()); |
1038 |
} |
1039 |
|
1040 |
/** |
1041 |
* Removes the key (and its corresponding value) from this map. |
1042 |
* This method does nothing if the key is not in the map. |
1043 |
* |
1044 |
* @param key the key that needs to be removed |
1045 |
* @return the previous value associated with <tt>key</tt>, or |
1046 |
* <tt>null</tt> if there was no mapping for <tt>key</tt> |
1047 |
* @throws NullPointerException if the specified key is null |
1048 |
*/ |
1049 |
public V remove(Object key) { |
1050 |
int hash = hash(key.hashCode()); |
1051 |
Segment<K,V> s = segmentForHash(hash); |
1052 |
return s == null ? null : s.remove(key, hash, null); |
1053 |
} |
1054 |
|
1055 |
/** |
1056 |
* {@inheritDoc} |
1057 |
* |
1058 |
* @throws NullPointerException if the specified key is null |
1059 |
*/ |
1060 |
public boolean remove(Object key, Object value) { |
1061 |
int hash = hash(key.hashCode()); |
1062 |
Segment<K,V> s; |
1063 |
return value != null && (s = segmentForHash(hash)) != null && |
1064 |
s.remove(key, hash, value) != null; |
1065 |
} |
1066 |
|
1067 |
/** |
1068 |
* {@inheritDoc} |
1069 |
* |
1070 |
* @throws NullPointerException if any of the arguments are null |
1071 |
*/ |
1072 |
public boolean replace(K key, V oldValue, V newValue) { |
1073 |
int hash = hash(key.hashCode()); |
1074 |
if (oldValue == null || newValue == null) |
1075 |
throw new NullPointerException(); |
1076 |
Segment<K,V> s = segmentForHash(hash); |
1077 |
return s != null && s.replace(key, hash, oldValue, newValue); |
1078 |
} |
1079 |
|
1080 |
/** |
1081 |
* {@inheritDoc} |
1082 |
* |
1083 |
* @return the previous value associated with the specified key, |
1084 |
* or <tt>null</tt> if there was no mapping for the key |
1085 |
* @throws NullPointerException if the specified key or value is null |
1086 |
*/ |
1087 |
public V replace(K key, V value) { |
1088 |
int hash = hash(key.hashCode()); |
1089 |
if (value == null) |
1090 |
throw new NullPointerException(); |
1091 |
Segment<K,V> s = segmentForHash(hash); |
1092 |
return s == null ? null : s.replace(key, hash, value); |
1093 |
} |
1094 |
|
1095 |
/** |
1096 |
* Removes all of the mappings from this map. |
1097 |
*/ |
1098 |
public void clear() { |
1099 |
final Segment<K,V>[] segments = this.segments; |
1100 |
for (int j = 0; j < segments.length; ++j) { |
1101 |
Segment<K,V> s = segmentAt(segments, j); |
1102 |
if (s != null) |
1103 |
s.clear(); |
1104 |
} |
1105 |
} |
1106 |
|
1107 |
/** |
1108 |
* Returns a {@link Set} view of the keys contained in this map. |
1109 |
* The set is backed by the map, so changes to the map are |
1110 |
* reflected in the set, and vice-versa. The set supports element |
1111 |
* removal, which removes the corresponding mapping from this map, |
1112 |
* via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, |
1113 |
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> |
1114 |
* operations. It does not support the <tt>add</tt> or |
1115 |
* <tt>addAll</tt> operations. |
1116 |
* |
1117 |
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator |
1118 |
* that will never throw {@link ConcurrentModificationException}, |
1119 |
* and guarantees to traverse elements as they existed upon |
1120 |
* construction of the iterator, and may (but is not guaranteed to) |
1121 |
* reflect any modifications subsequent to construction. |
1122 |
*/ |
1123 |
public Set<K> keySet() { |
1124 |
Set<K> ks = keySet; |
1125 |
return (ks != null) ? ks : (keySet = new KeySet()); |
1126 |
} |
1127 |
|
1128 |
/** |
1129 |
* Returns a {@link Collection} view of the values contained in this map. |
1130 |
* The collection is backed by the map, so changes to the map are |
1131 |
* reflected in the collection, and vice-versa. The collection |
1132 |
* supports element removal, which removes the corresponding |
1133 |
* mapping from this map, via the <tt>Iterator.remove</tt>, |
1134 |
* <tt>Collection.remove</tt>, <tt>removeAll</tt>, |
1135 |
* <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not |
1136 |
* support the <tt>add</tt> or <tt>addAll</tt> operations. |
1137 |
* |
1138 |
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator |
1139 |
* that will never throw {@link ConcurrentModificationException}, |
1140 |
* and guarantees to traverse elements as they existed upon |
1141 |
* construction of the iterator, and may (but is not guaranteed to) |
1142 |
* reflect any modifications subsequent to construction. |
1143 |
*/ |
1144 |
public Collection<V> values() { |
1145 |
Collection<V> vs = values; |
1146 |
return (vs != null) ? vs : (values = new Values()); |
1147 |
} |
1148 |
|
1149 |
/** |
1150 |
* Returns a {@link Set} view of the mappings contained in this map. |
1151 |
* The set is backed by the map, so changes to the map are |
1152 |
* reflected in the set, and vice-versa. The set supports element |
1153 |
* removal, which removes the corresponding mapping from the map, |
1154 |
* via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, |
1155 |
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> |
1156 |
* operations. It does not support the <tt>add</tt> or |
1157 |
* <tt>addAll</tt> operations. |
1158 |
* |
1159 |
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator |
1160 |
* that will never throw {@link ConcurrentModificationException}, |
1161 |
* and guarantees to traverse elements as they existed upon |
1162 |
* construction of the iterator, and may (but is not guaranteed to) |
1163 |
* reflect any modifications subsequent to construction. |
1164 |
*/ |
1165 |
public Set<Map.Entry<K,V>> entrySet() { |
1166 |
Set<Map.Entry<K,V>> es = entrySet; |
1167 |
return (es != null) ? es : (entrySet = new EntrySet()); |
1168 |
} |
1169 |
|
1170 |
/** |
1171 |
* Returns an enumeration of the keys in this table. |
1172 |
* |
1173 |
* @return an enumeration of the keys in this table |
1174 |
* @see #keySet() |
1175 |
*/ |
1176 |
public Enumeration<K> keys() { |
1177 |
return new KeyIterator(); |
1178 |
} |
1179 |
|
1180 |
/** |
1181 |
* Returns an enumeration of the values in this table. |
1182 |
* |
1183 |
* @return an enumeration of the values in this table |
1184 |
* @see #values() |
1185 |
*/ |
1186 |
public Enumeration<V> elements() { |
1187 |
return new ValueIterator(); |
1188 |
} |
1189 |
|
1190 |
/* ---------------- Iterator Support -------------- */ |
1191 |
|
1192 |
abstract class HashIterator { |
1193 |
int nextSegmentIndex; |
1194 |
int nextTableIndex; |
1195 |
HashEntry<K,V>[] currentTable; |
1196 |
HashEntry<K, V> nextEntry; |
1197 |
HashEntry<K, V> lastReturned; |
1198 |
|
1199 |
HashIterator() { |
1200 |
nextSegmentIndex = segments.length - 1; |
1201 |
nextTableIndex = -1; |
1202 |
advance(); |
1203 |
} |
1204 |
|
1205 |
/** |
1206 |
* Set nextEntry to first node of next non-empty table |
1207 |
* (in backwards order, to simplify checks). |
1208 |
*/ |
1209 |
final void advance() { |
1210 |
for (;;) { |
1211 |
if (nextTableIndex >= 0) { |
1212 |
if ((nextEntry = entryAt(currentTable, |
1213 |
nextTableIndex--)) != null) |
1214 |
break; |
1215 |
} |
1216 |
else if (nextSegmentIndex >= 0) { |
1217 |
Segment<K,V> seg = segmentAt(segments, nextSegmentIndex--); |
1218 |
if (seg != null && (currentTable = seg.table) != null) |
1219 |
nextTableIndex = currentTable.length - 1; |
1220 |
} |
1221 |
else |
1222 |
break; |
1223 |
} |
1224 |
} |
1225 |
|
1226 |
final HashEntry<K,V> nextEntry() { |
1227 |
HashEntry<K,V> e = lastReturned = nextEntry; |
1228 |
if (e == null) |
1229 |
throw new NoSuchElementException(); |
1230 |
if ((nextEntry = e.next) == null) |
1231 |
advance(); |
1232 |
return e; |
1233 |
} |
1234 |
|
1235 |
public final boolean hasNext() { return nextEntry != null; } |
1236 |
public final boolean hasMoreElements() { return nextEntry != null; } |
1237 |
|
1238 |
public final void remove() { |
1239 |
if (lastReturned == null) |
1240 |
throw new IllegalStateException(); |
1241 |
ConcurrentHashMap.this.remove(lastReturned.key); |
1242 |
lastReturned = null; |
1243 |
} |
1244 |
} |
1245 |
|
1246 |
final class KeyIterator |
1247 |
extends HashIterator |
1248 |
implements Iterator<K>, Enumeration<K> |
1249 |
{ |
1250 |
public final K next() { return super.nextEntry().key; } |
1251 |
public final K nextElement() { return super.nextEntry().key; } |
1252 |
} |
1253 |
|
1254 |
final class ValueIterator |
1255 |
extends HashIterator |
1256 |
implements Iterator<V>, Enumeration<V> |
1257 |
{ |
1258 |
public final V next() { return super.nextEntry().value; } |
1259 |
public final V nextElement() { return super.nextEntry().value; } |
1260 |
} |
1261 |
|
1262 |
/** |
1263 |
* Custom Entry class used by EntryIterator.next(), that relays |
1264 |
* setValue changes to the underlying map. |
1265 |
*/ |
1266 |
final class WriteThroughEntry |
1267 |
extends AbstractMap.SimpleEntry<K,V> |
1268 |
{ |
1269 |
WriteThroughEntry(K k, V v) { |
1270 |
super(k,v); |
1271 |
} |
1272 |
|
1273 |
/** |
1274 |
* Set our entry's value and write through to the map. The |
1275 |
* value to return is somewhat arbitrary here. Since a |
1276 |
* WriteThroughEntry does not necessarily track asynchronous |
1277 |
* changes, the most recent "previous" value could be |
1278 |
* different from what we return (or could even have been |
1279 |
* removed in which case the put will re-establish). We do not |
1280 |
* and cannot guarantee more. |
1281 |
*/ |
1282 |
public V setValue(V value) { |
1283 |
if (value == null) throw new NullPointerException(); |
1284 |
V v = super.setValue(value); |
1285 |
ConcurrentHashMap.this.put(getKey(), value); |
1286 |
return v; |
1287 |
} |
1288 |
} |
1289 |
|
1290 |
final class EntryIterator |
1291 |
extends HashIterator |
1292 |
implements Iterator<Entry<K,V>> |
1293 |
{ |
1294 |
public Map.Entry<K,V> next() { |
1295 |
HashEntry<K,V> e = super.nextEntry(); |
1296 |
return new WriteThroughEntry(e.key, e.value); |
1297 |
} |
1298 |
} |
1299 |
|
1300 |
final class KeySet extends AbstractSet<K> { |
1301 |
public Iterator<K> iterator() { |
1302 |
return new KeyIterator(); |
1303 |
} |
1304 |
public int size() { |
1305 |
return ConcurrentHashMap.this.size(); |
1306 |
} |
1307 |
public boolean isEmpty() { |
1308 |
return ConcurrentHashMap.this.isEmpty(); |
1309 |
} |
1310 |
public boolean contains(Object o) { |
1311 |
return ConcurrentHashMap.this.containsKey(o); |
1312 |
} |
1313 |
public boolean remove(Object o) { |
1314 |
return ConcurrentHashMap.this.remove(o) != null; |
1315 |
} |
1316 |
public void clear() { |
1317 |
ConcurrentHashMap.this.clear(); |
1318 |
} |
1319 |
} |
1320 |
|
1321 |
final class Values extends AbstractCollection<V> { |
1322 |
public Iterator<V> iterator() { |
1323 |
return new ValueIterator(); |
1324 |
} |
1325 |
public int size() { |
1326 |
return ConcurrentHashMap.this.size(); |
1327 |
} |
1328 |
public boolean isEmpty() { |
1329 |
return ConcurrentHashMap.this.isEmpty(); |
1330 |
} |
1331 |
public boolean contains(Object o) { |
1332 |
return ConcurrentHashMap.this.containsValue(o); |
1333 |
} |
1334 |
public void clear() { |
1335 |
ConcurrentHashMap.this.clear(); |
1336 |
} |
1337 |
} |
1338 |
|
1339 |
final class EntrySet extends AbstractSet<Map.Entry<K,V>> { |
1340 |
public Iterator<Map.Entry<K,V>> iterator() { |
1341 |
return new EntryIterator(); |
1342 |
} |
1343 |
public boolean contains(Object o) { |
1344 |
if (!(o instanceof Map.Entry)) |
1345 |
return false; |
1346 |
Map.Entry<?,?> e = (Map.Entry<?,?>)o; |
1347 |
V v = ConcurrentHashMap.this.get(e.getKey()); |
1348 |
return v != null && v.equals(e.getValue()); |
1349 |
} |
1350 |
public boolean remove(Object o) { |
1351 |
if (!(o instanceof Map.Entry)) |
1352 |
return false; |
1353 |
Map.Entry<?,?> e = (Map.Entry<?,?>)o; |
1354 |
return ConcurrentHashMap.this.remove(e.getKey(), e.getValue()); |
1355 |
} |
1356 |
public int size() { |
1357 |
return ConcurrentHashMap.this.size(); |
1358 |
} |
1359 |
public boolean isEmpty() { |
1360 |
return ConcurrentHashMap.this.isEmpty(); |
1361 |
} |
1362 |
public void clear() { |
1363 |
ConcurrentHashMap.this.clear(); |
1364 |
} |
1365 |
} |
1366 |
|
1367 |
/* ---------------- Serialization Support -------------- */ |
1368 |
|
1369 |
/** |
1370 |
* Save the state of the <tt>ConcurrentHashMap</tt> instance to a |
1371 |
* stream (i.e., serialize it). |
1372 |
* @param s the stream |
1373 |
* @serialData |
1374 |
* the key (Object) and value (Object) |
1375 |
* for each key-value mapping, followed by a null pair. |
1376 |
* The key-value mappings are emitted in no particular order. |
1377 |
*/ |
1378 |
private void writeObject(java.io.ObjectOutputStream s) throws IOException { |
1379 |
// force all segments for serialization compatibility |
1380 |
for (int k = 0; k < segments.length; ++k) |
1381 |
ensureSegment(k); |
1382 |
s.defaultWriteObject(); |
1383 |
|
1384 |
final Segment<K,V>[] segments = this.segments; |
1385 |
for (int k = 0; k < segments.length; ++k) { |
1386 |
Segment<K,V> seg = segmentAt(segments, k); |
1387 |
seg.lock(); |
1388 |
try { |
1389 |
HashEntry<K,V>[] tab = seg.table; |
1390 |
for (int i = 0; i < tab.length; ++i) { |
1391 |
HashEntry<K,V> e; |
1392 |
for (e = entryAt(tab, i); e != null; e = e.next) { |
1393 |
s.writeObject(e.key); |
1394 |
s.writeObject(e.value); |
1395 |
} |
1396 |
} |
1397 |
} finally { |
1398 |
seg.unlock(); |
1399 |
} |
1400 |
} |
1401 |
s.writeObject(null); |
1402 |
s.writeObject(null); |
1403 |
} |
1404 |
|
1405 |
/** |
1406 |
* Reconstitute the <tt>ConcurrentHashMap</tt> instance from a |
1407 |
* stream (i.e., deserialize it). |
1408 |
* @param s the stream |
1409 |
*/ |
1410 |
@SuppressWarnings("unchecked") |
1411 |
private void readObject(java.io.ObjectInputStream s) |
1412 |
throws IOException, ClassNotFoundException { |
1413 |
s.defaultReadObject(); |
1414 |
|
1415 |
// Re-initialize segments to be minimally sized, and let grow. |
1416 |
int cap = MIN_SEGMENT_TABLE_CAPACITY; |
1417 |
final Segment<K,V>[] segments = this.segments; |
1418 |
for (int k = 0; k < segments.length; ++k) { |
1419 |
Segment<K,V> seg = segments[k]; |
1420 |
if (seg != null) { |
1421 |
seg.threshold = (int)(cap * seg.loadFactor); |
1422 |
seg.table = (HashEntry<K,V>[]) new HashEntry[cap]; |
1423 |
} |
1424 |
} |
1425 |
|
1426 |
// Read the keys and values, and put the mappings in the table |
1427 |
for (;;) { |
1428 |
K key = (K) s.readObject(); |
1429 |
V value = (V) s.readObject(); |
1430 |
if (key == null) |
1431 |
break; |
1432 |
put(key, value); |
1433 |
} |
1434 |
} |
1435 |
|
1436 |
// Unsafe mechanics |
1437 |
private static final sun.misc.Unsafe UNSAFE; |
1438 |
private static final long SBASE; |
1439 |
private static final int SSHIFT; |
1440 |
private static final long TBASE; |
1441 |
private static final int TSHIFT; |
1442 |
|
1443 |
static { |
1444 |
int ss, ts; |
1445 |
try { |
1446 |
UNSAFE = sun.misc.Unsafe.getUnsafe(); |
1447 |
Class tc = HashEntry[].class; |
1448 |
Class sc = Segment[].class; |
1449 |
TBASE = UNSAFE.arrayBaseOffset(tc); |
1450 |
SBASE = UNSAFE.arrayBaseOffset(sc); |
1451 |
ts = UNSAFE.arrayIndexScale(tc); |
1452 |
ss = UNSAFE.arrayIndexScale(sc); |
1453 |
} catch (Exception e) { |
1454 |
throw new Error(e); |
1455 |
} |
1456 |
if ((ss & (ss-1)) != 0 || (ts & (ts-1)) != 0) |
1457 |
throw new Error("data type scale not a power of two"); |
1458 |
SSHIFT = 31 - Integer.numberOfLeadingZeros(ss); |
1459 |
TSHIFT = 31 - Integer.numberOfLeadingZeros(ts); |
1460 |
} |
1461 |
|
1462 |
} |