mirror of git://gcc.gnu.org/git/gcc.git
1278 lines
46 KiB
Java
1278 lines
46 KiB
Java
/*
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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/licenses/publicdomain
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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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* 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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* The basic strategy is to subdivide the table among Segments,
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* each of which itself is a concurrently readable hash table.
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*/
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/* ---------------- Constants -------------- */
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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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* 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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* 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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* 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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* The maximum number of segments to allow; used to bound
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* constructor arguments.
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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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* 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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/* ---------------- Fields -------------- */
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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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* 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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* 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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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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/* ---------------- Small Utilities -------------- */
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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 bits.
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*/
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private static int hash(int h) {
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// This function ensures that hashCodes that differ only by
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// constant multiples at each bit position have a bounded
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// number of collisions (approximately 8 at default load factor).
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h ^= (h >>> 20) ^ (h >>> 12);
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return h ^ (h >>> 7) ^ (h >>> 4);
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}
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/**
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* Returns the segment that should be used for key with given hash
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* @param hash the hash code for the key
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* @return the segment
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*/
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final Segment<K,V> segmentFor(int hash) {
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return segments[(hash >>> segmentShift) & segmentMask];
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}
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/* ---------------- Inner Classes -------------- */
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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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*
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* Because the value field is volatile, not final, it is legal wrt
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* the Java Memory Model for an unsynchronized reader to see null
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* instead of initial value when read via a data race. Although a
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* reordering leading to this is not likely to ever actually
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* occur, the Segment.readValueUnderLock method is used as a
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* backup in case a null (pre-initialized) value is ever seen in
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* an unsynchronized access method.
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*/
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static final class HashEntry<K,V> {
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final K key;
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final int hash;
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volatile V value;
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final HashEntry<K,V> next;
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HashEntry(K key, int hash, HashEntry<K,V> next, V value) {
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this.key = key;
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this.hash = hash;
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this.next = next;
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this.value = value;
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}
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@SuppressWarnings("unchecked")
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static final <K,V> HashEntry<K,V>[] newArray(int i) {
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return new HashEntry[i];
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}
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}
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/**
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* Segments are specialized versions of hash tables. This
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* subclasses from ReentrantLock opportunistically, just to
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* simplify some locking and avoid separate construction.
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*/
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static final class Segment<K,V> extends ReentrantLock implements Serializable {
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/*
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* Segments maintain a table of entry lists that are ALWAYS
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* kept in a consistent state, so can be read without locking.
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* Next fields of nodes are immutable (final). All list
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* additions are performed at the front of each bin. This
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* makes it easy to check changes, and also fast to traverse.
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* When nodes would otherwise be changed, new nodes are
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* created to replace them. This works well for hash tables
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* since the bin lists tend to be short. (The average length
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* is less than two for the default load factor threshold.)
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*
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* Read operations can thus proceed without locking, but rely
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* on selected uses of volatiles to ensure that completed
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* write operations performed by other threads are
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* noticed. For most purposes, the "count" field, tracking the
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* number of elements, serves as that volatile variable
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* ensuring visibility. This is convenient because this field
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* needs to be read in many read operations anyway:
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*
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* - All (unsynchronized) read operations must first read the
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* "count" field, and should not look at table entries if
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* it is 0.
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*
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* - All (synchronized) write operations should write to
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* the "count" field after structurally changing any bin.
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* The operations must not take any action that could even
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* momentarily cause a concurrent read operation to see
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* inconsistent data. This is made easier by the nature of
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* the read operations in Map. For example, no operation
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* can reveal that the table has grown but the threshold
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* has not yet been updated, so there are no atomicity
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* requirements for this with respect to reads.
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*
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* As a guide, all critical volatile reads and writes to the
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* count field are marked in code comments.
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*/
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private static final long serialVersionUID = 2249069246763182397L;
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/**
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* The number of elements in this segment's region.
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*/
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transient volatile int count;
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/**
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* Number of updates that alter the size of the table. This is
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* used during bulk-read methods to make sure they see a
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* consistent snapshot: If modCounts change during a traversal
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* of segments computing size or checking containsValue, then
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* we might have an inconsistent view of state so (usually)
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* must retry.
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*/
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transient int modCount;
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/**
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* The table is rehashed when its size exceeds this threshold.
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* (The value of this field is always <tt>(int)(capacity *
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* loadFactor)</tt>.)
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*/
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transient int threshold;
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/**
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* The per-segment table.
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*/
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transient volatile HashEntry<K,V>[] table;
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/**
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* The load factor for the hash table. Even though this value
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* is same for all segments, it is replicated to avoid needing
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* links to outer object.
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* @serial
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*/
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final float loadFactor;
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Segment(int initialCapacity, float lf) {
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loadFactor = lf;
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setTable(HashEntry.<K,V>newArray(initialCapacity));
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}
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@SuppressWarnings("unchecked")
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static final <K,V> Segment<K,V>[] newArray(int i) {
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return new Segment[i];
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}
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/**
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* Sets table to new HashEntry array.
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* Call only while holding lock or in constructor.
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*/
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void setTable(HashEntry<K,V>[] newTable) {
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threshold = (int)(newTable.length * loadFactor);
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table = newTable;
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}
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/**
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* Returns properly casted first entry of bin for given hash.
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*/
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HashEntry<K,V> getFirst(int hash) {
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HashEntry<K,V>[] tab = table;
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return tab[hash & (tab.length - 1)];
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}
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/**
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* Reads value field of an entry under lock. Called if value
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* field ever appears to be null. This is possible only if a
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* compiler happens to reorder a HashEntry initialization with
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* its table assignment, which is legal under memory model
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* but is not known to ever occur.
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*/
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V readValueUnderLock(HashEntry<K,V> e) {
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lock();
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try {
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return e.value;
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} finally {
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unlock();
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}
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}
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/* Specialized implementations of map methods */
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V get(Object key, int hash) {
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if (count != 0) { // read-volatile
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HashEntry<K,V> e = getFirst(hash);
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while (e != null) {
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if (e.hash == hash && key.equals(e.key)) {
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V v = e.value;
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if (v != null)
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return v;
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return readValueUnderLock(e); // recheck
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}
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e = e.next;
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}
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}
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return null;
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}
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boolean containsKey(Object key, int hash) {
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if (count != 0) { // read-volatile
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HashEntry<K,V> e = getFirst(hash);
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while (e != null) {
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if (e.hash == hash && key.equals(e.key))
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return true;
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e = e.next;
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}
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}
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return false;
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}
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boolean containsValue(Object value) {
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if (count != 0) { // read-volatile
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HashEntry<K,V>[] tab = table;
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int len = tab.length;
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for (int i = 0 ; i < len; i++) {
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for (HashEntry<K,V> e = tab[i]; e != null; e = e.next) {
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V v = e.value;
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if (v == null) // recheck
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v = readValueUnderLock(e);
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if (value.equals(v))
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return true;
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}
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}
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}
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return false;
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}
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boolean replace(K key, int hash, V oldValue, V newValue) {
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lock();
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try {
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HashEntry<K,V> e = getFirst(hash);
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while (e != null && (e.hash != hash || !key.equals(e.key)))
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e = e.next;
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boolean replaced = false;
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if (e != null && oldValue.equals(e.value)) {
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replaced = true;
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e.value = newValue;
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}
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return replaced;
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} finally {
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unlock();
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}
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}
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V replace(K key, int hash, V newValue) {
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lock();
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try {
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HashEntry<K,V> e = getFirst(hash);
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while (e != null && (e.hash != hash || !key.equals(e.key)))
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e = e.next;
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V oldValue = null;
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if (e != null) {
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oldValue = e.value;
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e.value = newValue;
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}
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return oldValue;
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} finally {
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unlock();
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}
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}
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V put(K key, int hash, V value, boolean onlyIfAbsent) {
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lock();
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try {
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int c = count;
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if (c++ > threshold) // ensure capacity
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rehash();
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HashEntry<K,V>[] tab = table;
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int index = hash & (tab.length - 1);
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HashEntry<K,V> first = tab[index];
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HashEntry<K,V> e = first;
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while (e != null && (e.hash != hash || !key.equals(e.key)))
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e = e.next;
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V oldValue;
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if (e != null) {
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oldValue = e.value;
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if (!onlyIfAbsent)
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e.value = value;
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}
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else {
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oldValue = null;
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++modCount;
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tab[index] = new HashEntry<K,V>(key, hash, first, value);
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count = c; // write-volatile
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}
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return oldValue;
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} finally {
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unlock();
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}
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}
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void rehash() {
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HashEntry<K,V>[] oldTable = table;
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int oldCapacity = oldTable.length;
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if (oldCapacity >= MAXIMUM_CAPACITY)
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return;
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/*
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* Reclassify nodes in each list to new Map. Because we are
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* using power-of-two expansion, the elements from each bin
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* must either stay at same index, or move with a power of two
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* offset. We eliminate unnecessary node creation by catching
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* cases where old nodes can be reused because their next
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* fields won't change. Statistically, at the default
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* threshold, only about one-sixth of them need cloning when
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* a table doubles. The nodes they replace will be garbage
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* collectable as soon as they are no longer referenced by any
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* reader thread that may be in the midst of traversing table
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* right now.
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*/
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HashEntry<K,V>[] newTable = HashEntry.newArray(oldCapacity<<1);
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threshold = (int)(newTable.length * loadFactor);
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int sizeMask = newTable.length - 1;
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for (int i = 0; i < oldCapacity ; i++) {
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// We need to guarantee that any existing reads of old Map can
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// proceed. So we cannot yet null out each bin.
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HashEntry<K,V> e = oldTable[i];
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if (e != null) {
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HashEntry<K,V> next = e.next;
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int idx = e.hash & sizeMask;
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// Single node on list
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if (next == null)
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newTable[idx] = e;
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else {
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// Reuse trailing consecutive sequence at same slot
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HashEntry<K,V> lastRun = e;
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int lastIdx = idx;
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for (HashEntry<K,V> last = next;
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last != null;
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last = last.next) {
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int k = last.hash & sizeMask;
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if (k != lastIdx) {
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lastIdx = k;
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lastRun = last;
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}
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}
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newTable[lastIdx] = lastRun;
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// Clone all remaining nodes
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for (HashEntry<K,V> p = e; p != lastRun; p = p.next) {
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int k = p.hash & sizeMask;
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HashEntry<K,V> n = newTable[k];
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newTable[k] = new HashEntry<K,V>(p.key, p.hash,
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n, p.value);
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}
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}
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}
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}
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table = newTable;
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}
|
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|
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/**
|
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* Remove; match on key only if value null, else match both.
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|
*/
|
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V remove(Object key, int hash, Object value) {
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lock();
|
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try {
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int c = count - 1;
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HashEntry<K,V>[] tab = table;
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int index = hash & (tab.length - 1);
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HashEntry<K,V> first = tab[index];
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HashEntry<K,V> e = first;
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while (e != null && (e.hash != hash || !key.equals(e.key)))
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e = e.next;
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V oldValue = null;
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if (e != null) {
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V v = e.value;
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if (value == null || value.equals(v)) {
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oldValue = v;
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// All entries following removed node can stay
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// in list, but all preceding ones need to be
|
|
// cloned.
|
|
++modCount;
|
|
HashEntry<K,V> newFirst = e.next;
|
|
for (HashEntry<K,V> p = first; p != e; p = p.next)
|
|
newFirst = new HashEntry<K,V>(p.key, p.hash,
|
|
newFirst, p.value);
|
|
tab[index] = newFirst;
|
|
count = c; // write-volatile
|
|
}
|
|
}
|
|
return oldValue;
|
|
} finally {
|
|
unlock();
|
|
}
|
|
}
|
|
|
|
void clear() {
|
|
if (count != 0) {
|
|
lock();
|
|
try {
|
|
HashEntry<K,V>[] tab = table;
|
|
for (int i = 0; i < tab.length ; i++)
|
|
tab[i] = null;
|
|
++modCount;
|
|
count = 0; // write-volatile
|
|
} finally {
|
|
unlock();
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
|
|
/* ---------------- Public operations -------------- */
|
|
|
|
/**
|
|
* Creates a new, empty map with the specified initial
|
|
* capacity, load factor and concurrency level.
|
|
*
|
|
* @param initialCapacity the initial capacity. The implementation
|
|
* performs internal sizing to accommodate this many elements.
|
|
* @param loadFactor the load factor threshold, used to control resizing.
|
|
* Resizing may be performed when the average number of elements per
|
|
* bin exceeds this threshold.
|
|
* @param concurrencyLevel the estimated number of concurrently
|
|
* updating threads. The implementation performs internal sizing
|
|
* to try to accommodate this many threads.
|
|
* @throws IllegalArgumentException if the initial capacity is
|
|
* negative or the load factor or concurrencyLevel are
|
|
* nonpositive.
|
|
*/
|
|
public ConcurrentHashMap(int initialCapacity,
|
|
float loadFactor, int concurrencyLevel) {
|
|
if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0)
|
|
throw new IllegalArgumentException();
|
|
|
|
if (concurrencyLevel > MAX_SEGMENTS)
|
|
concurrencyLevel = MAX_SEGMENTS;
|
|
|
|
// Find power-of-two sizes best matching arguments
|
|
int sshift = 0;
|
|
int ssize = 1;
|
|
while (ssize < concurrencyLevel) {
|
|
++sshift;
|
|
ssize <<= 1;
|
|
}
|
|
segmentShift = 32 - sshift;
|
|
segmentMask = ssize - 1;
|
|
this.segments = Segment.newArray(ssize);
|
|
|
|
if (initialCapacity > MAXIMUM_CAPACITY)
|
|
initialCapacity = MAXIMUM_CAPACITY;
|
|
int c = initialCapacity / ssize;
|
|
if (c * ssize < initialCapacity)
|
|
++c;
|
|
int cap = 1;
|
|
while (cap < c)
|
|
cap <<= 1;
|
|
|
|
for (int i = 0; i < this.segments.length; ++i)
|
|
this.segments[i] = new Segment<K,V>(cap, loadFactor);
|
|
}
|
|
|
|
/**
|
|
* Creates a new, empty map with the specified initial capacity
|
|
* and load factor and with the default concurrencyLevel (16).
|
|
*
|
|
* @param initialCapacity The implementation performs internal
|
|
* sizing to accommodate this many elements.
|
|
* @param loadFactor the load factor threshold, used to control resizing.
|
|
* Resizing may be performed when the average number of elements per
|
|
* bin exceeds this threshold.
|
|
* @throws IllegalArgumentException if the initial capacity of
|
|
* elements is negative or the load factor is nonpositive
|
|
*
|
|
* @since 1.6
|
|
*/
|
|
public ConcurrentHashMap(int initialCapacity, float loadFactor) {
|
|
this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);
|
|
}
|
|
|
|
/**
|
|
* Creates a new, empty map with the specified initial capacity,
|
|
* and with default load factor (0.75) and concurrencyLevel (16).
|
|
*
|
|
* @param initialCapacity the initial capacity. The implementation
|
|
* performs internal sizing to accommodate this many elements.
|
|
* @throws IllegalArgumentException if the initial capacity of
|
|
* elements is negative.
|
|
*/
|
|
public ConcurrentHashMap(int initialCapacity) {
|
|
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
|
|
}
|
|
|
|
/**
|
|
* Creates a new, empty map with a default initial capacity (16),
|
|
* load factor (0.75) and concurrencyLevel (16).
|
|
*/
|
|
public ConcurrentHashMap() {
|
|
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
|
|
}
|
|
|
|
/**
|
|
* Creates a new map with the same mappings as the given map.
|
|
* The map is created with a capacity of 1.5 times the number
|
|
* of mappings in the given map or 16 (whichever is greater),
|
|
* and a default load factor (0.75) and concurrencyLevel (16).
|
|
*
|
|
* @param m the map
|
|
*/
|
|
public ConcurrentHashMap(Map<? extends K, ? extends V> m) {
|
|
this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
|
|
DEFAULT_INITIAL_CAPACITY),
|
|
DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
|
|
putAll(m);
|
|
}
|
|
|
|
/**
|
|
* Returns <tt>true</tt> if this map contains no key-value mappings.
|
|
*
|
|
* @return <tt>true</tt> if this map contains no key-value mappings
|
|
*/
|
|
public boolean isEmpty() {
|
|
final Segment<K,V>[] segments = this.segments;
|
|
/*
|
|
* We keep track of per-segment modCounts to avoid ABA
|
|
* problems in which an element in one segment was added and
|
|
* in another removed during traversal, in which case the
|
|
* table was never actually empty at any point. Note the
|
|
* similar use of modCounts in the size() and containsValue()
|
|
* methods, which are the only other methods also susceptible
|
|
* to ABA problems.
|
|
*/
|
|
int[] mc = new int[segments.length];
|
|
int mcsum = 0;
|
|
for (int i = 0; i < segments.length; ++i) {
|
|
if (segments[i].count != 0)
|
|
return false;
|
|
else
|
|
mcsum += mc[i] = segments[i].modCount;
|
|
}
|
|
// If mcsum happens to be zero, then we know we got a snapshot
|
|
// before any modifications at all were made. This is
|
|
// probably common enough to bother tracking.
|
|
if (mcsum != 0) {
|
|
for (int i = 0; i < segments.length; ++i) {
|
|
if (segments[i].count != 0 ||
|
|
mc[i] != segments[i].modCount)
|
|
return false;
|
|
}
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/**
|
|
* Returns the number of key-value mappings in this map. If the
|
|
* map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
|
|
* <tt>Integer.MAX_VALUE</tt>.
|
|
*
|
|
* @return the number of key-value mappings in this map
|
|
*/
|
|
public int size() {
|
|
final Segment<K,V>[] segments = this.segments;
|
|
long sum = 0;
|
|
long check = 0;
|
|
int[] mc = new int[segments.length];
|
|
// Try a few times to get accurate count. On failure due to
|
|
// continuous async changes in table, resort to locking.
|
|
for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
|
|
check = 0;
|
|
sum = 0;
|
|
int mcsum = 0;
|
|
for (int i = 0; i < segments.length; ++i) {
|
|
sum += segments[i].count;
|
|
mcsum += mc[i] = segments[i].modCount;
|
|
}
|
|
if (mcsum != 0) {
|
|
for (int i = 0; i < segments.length; ++i) {
|
|
check += segments[i].count;
|
|
if (mc[i] != segments[i].modCount) {
|
|
check = -1; // force retry
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
if (check == sum)
|
|
break;
|
|
}
|
|
if (check != sum) { // Resort to locking all segments
|
|
sum = 0;
|
|
for (int i = 0; i < segments.length; ++i)
|
|
segments[i].lock();
|
|
for (int i = 0; i < segments.length; ++i)
|
|
sum += segments[i].count;
|
|
for (int i = 0; i < segments.length; ++i)
|
|
segments[i].unlock();
|
|
}
|
|
if (sum > Integer.MAX_VALUE)
|
|
return Integer.MAX_VALUE;
|
|
else
|
|
return (int)sum;
|
|
}
|
|
|
|
/**
|
|
* Returns the value to which the specified key is mapped,
|
|
* or {@code null} if this map contains no mapping for the key.
|
|
*
|
|
* <p>More formally, if this map contains a mapping from a key
|
|
* {@code k} to a value {@code v} such that {@code key.equals(k)},
|
|
* then this method returns {@code v}; otherwise it returns
|
|
* {@code null}. (There can be at most one such mapping.)
|
|
*
|
|
* @throws NullPointerException if the specified key is null
|
|
*/
|
|
public V get(Object key) {
|
|
int hash = hash(key.hashCode());
|
|
return segmentFor(hash).get(key, hash);
|
|
}
|
|
|
|
/**
|
|
* Tests if the specified object is a key in this table.
|
|
*
|
|
* @param key possible key
|
|
* @return <tt>true</tt> if and only if the specified object
|
|
* is a key in this table, as determined by the
|
|
* <tt>equals</tt> method; <tt>false</tt> otherwise.
|
|
* @throws NullPointerException if the specified key is null
|
|
*/
|
|
public boolean containsKey(Object key) {
|
|
int hash = hash(key.hashCode());
|
|
return segmentFor(hash).containsKey(key, hash);
|
|
}
|
|
|
|
/**
|
|
* Returns <tt>true</tt> if this map maps one or more keys to the
|
|
* specified value. Note: This method requires a full internal
|
|
* traversal of the hash table, and so is much slower than
|
|
* method <tt>containsKey</tt>.
|
|
*
|
|
* @param value value whose presence in this map is to be tested
|
|
* @return <tt>true</tt> if this map maps one or more keys to the
|
|
* specified value
|
|
* @throws NullPointerException if the specified value is null
|
|
*/
|
|
public boolean containsValue(Object value) {
|
|
if (value == null)
|
|
throw new NullPointerException();
|
|
|
|
// See explanation of modCount use above
|
|
|
|
final Segment<K,V>[] segments = this.segments;
|
|
int[] mc = new int[segments.length];
|
|
|
|
// Try a few times without locking
|
|
for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
|
|
int sum = 0;
|
|
int mcsum = 0;
|
|
for (int i = 0; i < segments.length; ++i) {
|
|
int c = segments[i].count;
|
|
mcsum += mc[i] = segments[i].modCount;
|
|
if (segments[i].containsValue(value))
|
|
return true;
|
|
}
|
|
boolean cleanSweep = true;
|
|
if (mcsum != 0) {
|
|
for (int i = 0; i < segments.length; ++i) {
|
|
int c = segments[i].count;
|
|
if (mc[i] != segments[i].modCount) {
|
|
cleanSweep = false;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
if (cleanSweep)
|
|
return false;
|
|
}
|
|
// Resort to locking all segments
|
|
for (int i = 0; i < segments.length; ++i)
|
|
segments[i].lock();
|
|
boolean found = false;
|
|
try {
|
|
for (int i = 0; i < segments.length; ++i) {
|
|
if (segments[i].containsValue(value)) {
|
|
found = true;
|
|
break;
|
|
}
|
|
}
|
|
} finally {
|
|
for (int i = 0; i < segments.length; ++i)
|
|
segments[i].unlock();
|
|
}
|
|
return found;
|
|
}
|
|
|
|
/**
|
|
* Legacy method testing if some key maps into the specified value
|
|
* in this table. This method is identical in functionality to
|
|
* {@link #containsValue}, and exists solely to ensure
|
|
* full compatibility with class {@link java.util.Hashtable},
|
|
* which supported this method prior to introduction of the
|
|
* Java Collections framework.
|
|
|
|
* @param value a value to search for
|
|
* @return <tt>true</tt> if and only if some key maps to the
|
|
* <tt>value</tt> argument in this table as
|
|
* determined by the <tt>equals</tt> method;
|
|
* <tt>false</tt> otherwise
|
|
* @throws NullPointerException if the specified value is null
|
|
*/
|
|
public boolean contains(Object value) {
|
|
return containsValue(value);
|
|
}
|
|
|
|
/**
|
|
* Maps the specified key to the specified value in this table.
|
|
* Neither the key nor the value can be null.
|
|
*
|
|
* <p> The value can be retrieved by calling the <tt>get</tt> method
|
|
* with a key that is equal to the original key.
|
|
*
|
|
* @param key key with which the specified value is to be associated
|
|
* @param value value to be associated with the specified key
|
|
* @return the previous value associated with <tt>key</tt>, or
|
|
* <tt>null</tt> if there was no mapping for <tt>key</tt>
|
|
* @throws NullPointerException if the specified key or value is null
|
|
*/
|
|
public V put(K key, V value) {
|
|
if (value == null)
|
|
throw new NullPointerException();
|
|
int hash = hash(key.hashCode());
|
|
return segmentFor(hash).put(key, hash, value, false);
|
|
}
|
|
|
|
/**
|
|
* {@inheritDoc}
|
|
*
|
|
* @return the previous value associated with the specified key,
|
|
* or <tt>null</tt> if there was no mapping for the key
|
|
* @throws NullPointerException if the specified key or value is null
|
|
*/
|
|
public V putIfAbsent(K key, V value) {
|
|
if (value == null)
|
|
throw new NullPointerException();
|
|
int hash = hash(key.hashCode());
|
|
return segmentFor(hash).put(key, hash, value, true);
|
|
}
|
|
|
|
/**
|
|
* Copies all of the mappings from the specified map to this one.
|
|
* These mappings replace any mappings that this map had for any of the
|
|
* keys currently in the specified map.
|
|
*
|
|
* @param m mappings to be stored in this map
|
|
*/
|
|
public void putAll(Map<? extends K, ? extends V> m) {
|
|
for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
|
|
put(e.getKey(), e.getValue());
|
|
}
|
|
|
|
/**
|
|
* Removes the key (and its corresponding value) from this map.
|
|
* This method does nothing if the key is not in the map.
|
|
*
|
|
* @param key the key that needs to be removed
|
|
* @return the previous value associated with <tt>key</tt>, or
|
|
* <tt>null</tt> if there was no mapping for <tt>key</tt>
|
|
* @throws NullPointerException if the specified key is null
|
|
*/
|
|
public V remove(Object key) {
|
|
int hash = hash(key.hashCode());
|
|
return segmentFor(hash).remove(key, hash, null);
|
|
}
|
|
|
|
/**
|
|
* {@inheritDoc}
|
|
*
|
|
* @throws NullPointerException if the specified key is null
|
|
*/
|
|
public boolean remove(Object key, Object value) {
|
|
int hash = hash(key.hashCode());
|
|
if (value == null)
|
|
return false;
|
|
return segmentFor(hash).remove(key, hash, value) != null;
|
|
}
|
|
|
|
/**
|
|
* {@inheritDoc}
|
|
*
|
|
* @throws NullPointerException if any of the arguments are null
|
|
*/
|
|
public boolean replace(K key, V oldValue, V newValue) {
|
|
if (oldValue == null || newValue == null)
|
|
throw new NullPointerException();
|
|
int hash = hash(key.hashCode());
|
|
return segmentFor(hash).replace(key, hash, oldValue, newValue);
|
|
}
|
|
|
|
/**
|
|
* {@inheritDoc}
|
|
*
|
|
* @return the previous value associated with the specified key,
|
|
* or <tt>null</tt> if there was no mapping for the key
|
|
* @throws NullPointerException if the specified key or value is null
|
|
*/
|
|
public V replace(K key, V value) {
|
|
if (value == null)
|
|
throw new NullPointerException();
|
|
int hash = hash(key.hashCode());
|
|
return segmentFor(hash).replace(key, hash, value);
|
|
}
|
|
|
|
/**
|
|
* Removes all of the mappings from this map.
|
|
*/
|
|
public void clear() {
|
|
for (int i = 0; i < segments.length; ++i)
|
|
segments[i].clear();
|
|
}
|
|
|
|
/**
|
|
* Returns a {@link Set} view of the keys contained in this map.
|
|
* The set is backed by the map, so changes to the map are
|
|
* reflected in the set, and vice-versa. The set supports element
|
|
* removal, which removes the corresponding mapping from this map,
|
|
* via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
|
|
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
|
|
* operations. It does not support the <tt>add</tt> or
|
|
* <tt>addAll</tt> operations.
|
|
*
|
|
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
|
|
* that will never throw {@link ConcurrentModificationException},
|
|
* and guarantees to traverse elements as they existed upon
|
|
* construction of the iterator, and may (but is not guaranteed to)
|
|
* reflect any modifications subsequent to construction.
|
|
*/
|
|
public Set<K> keySet() {
|
|
Set<K> ks = keySet;
|
|
return (ks != null) ? ks : (keySet = new KeySet());
|
|
}
|
|
|
|
/**
|
|
* Returns a {@link Collection} view of the values contained in this map.
|
|
* The collection is backed by the map, so changes to the map are
|
|
* reflected in the collection, and vice-versa. The collection
|
|
* supports element removal, which removes the corresponding
|
|
* mapping from this map, via the <tt>Iterator.remove</tt>,
|
|
* <tt>Collection.remove</tt>, <tt>removeAll</tt>,
|
|
* <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not
|
|
* support the <tt>add</tt> or <tt>addAll</tt> operations.
|
|
*
|
|
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
|
|
* that will never throw {@link ConcurrentModificationException},
|
|
* and guarantees to traverse elements as they existed upon
|
|
* construction of the iterator, and may (but is not guaranteed to)
|
|
* reflect any modifications subsequent to construction.
|
|
*/
|
|
public Collection<V> values() {
|
|
Collection<V> vs = values;
|
|
return (vs != null) ? vs : (values = new Values());
|
|
}
|
|
|
|
/**
|
|
* Returns a {@link Set} view of the mappings contained in this map.
|
|
* The set is backed by the map, so changes to the map are
|
|
* reflected in the set, and vice-versa. The set supports element
|
|
* removal, which removes the corresponding mapping from the map,
|
|
* via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
|
|
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
|
|
* operations. It does not support the <tt>add</tt> or
|
|
* <tt>addAll</tt> operations.
|
|
*
|
|
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
|
|
* that will never throw {@link ConcurrentModificationException},
|
|
* and guarantees to traverse elements as they existed upon
|
|
* construction of the iterator, and may (but is not guaranteed to)
|
|
* reflect any modifications subsequent to construction.
|
|
*/
|
|
public Set<Map.Entry<K,V>> entrySet() {
|
|
Set<Map.Entry<K,V>> es = entrySet;
|
|
return (es != null) ? es : (entrySet = new EntrySet());
|
|
}
|
|
|
|
/**
|
|
* Returns an enumeration of the keys in this table.
|
|
*
|
|
* @return an enumeration of the keys in this table
|
|
* @see #keySet
|
|
*/
|
|
public Enumeration<K> keys() {
|
|
return new KeyIterator();
|
|
}
|
|
|
|
/**
|
|
* Returns an enumeration of the values in this table.
|
|
*
|
|
* @return an enumeration of the values in this table
|
|
* @see #values
|
|
*/
|
|
public Enumeration<V> elements() {
|
|
return new ValueIterator();
|
|
}
|
|
|
|
/* ---------------- Iterator Support -------------- */
|
|
|
|
abstract class HashIterator {
|
|
int nextSegmentIndex;
|
|
int nextTableIndex;
|
|
HashEntry<K,V>[] currentTable;
|
|
HashEntry<K, V> nextEntry;
|
|
HashEntry<K, V> lastReturned;
|
|
|
|
HashIterator() {
|
|
nextSegmentIndex = segments.length - 1;
|
|
nextTableIndex = -1;
|
|
advance();
|
|
}
|
|
|
|
public boolean hasMoreElements() { return hasNext(); }
|
|
|
|
final void advance() {
|
|
if (nextEntry != null && (nextEntry = nextEntry.next) != null)
|
|
return;
|
|
|
|
while (nextTableIndex >= 0) {
|
|
if ( (nextEntry = currentTable[nextTableIndex--]) != null)
|
|
return;
|
|
}
|
|
|
|
while (nextSegmentIndex >= 0) {
|
|
Segment<K,V> seg = segments[nextSegmentIndex--];
|
|
if (seg.count != 0) {
|
|
currentTable = seg.table;
|
|
for (int j = currentTable.length - 1; j >= 0; --j) {
|
|
if ( (nextEntry = currentTable[j]) != null) {
|
|
nextTableIndex = j - 1;
|
|
return;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
public boolean hasNext() { return nextEntry != null; }
|
|
|
|
HashEntry<K,V> nextEntry() {
|
|
if (nextEntry == null)
|
|
throw new NoSuchElementException();
|
|
lastReturned = nextEntry;
|
|
advance();
|
|
return lastReturned;
|
|
}
|
|
|
|
public void remove() {
|
|
if (lastReturned == null)
|
|
throw new IllegalStateException();
|
|
ConcurrentHashMap.this.remove(lastReturned.key);
|
|
lastReturned = null;
|
|
}
|
|
}
|
|
|
|
final class KeyIterator
|
|
extends HashIterator
|
|
implements Iterator<K>, Enumeration<K>
|
|
{
|
|
public K next() { return super.nextEntry().key; }
|
|
public K nextElement() { return super.nextEntry().key; }
|
|
}
|
|
|
|
final class ValueIterator
|
|
extends HashIterator
|
|
implements Iterator<V>, Enumeration<V>
|
|
{
|
|
public V next() { return super.nextEntry().value; }
|
|
public V nextElement() { return super.nextEntry().value; }
|
|
}
|
|
|
|
/**
|
|
* Custom Entry class used by EntryIterator.next(), that relays
|
|
* setValue changes to the underlying map.
|
|
*/
|
|
final class WriteThroughEntry
|
|
extends AbstractMap.SimpleEntry<K,V>
|
|
{
|
|
WriteThroughEntry(K k, V v) {
|
|
super(k,v);
|
|
}
|
|
|
|
/**
|
|
* Set our entry's value and write through to the map. The
|
|
* value to return is somewhat arbitrary here. Since a
|
|
* WriteThroughEntry does not necessarily track asynchronous
|
|
* changes, the most recent "previous" value could be
|
|
* different from what we return (or could even have been
|
|
* removed in which case the put will re-establish). We do not
|
|
* and cannot guarantee more.
|
|
*/
|
|
public V setValue(V value) {
|
|
if (value == null) throw new NullPointerException();
|
|
V v = super.setValue(value);
|
|
ConcurrentHashMap.this.put(getKey(), value);
|
|
return v;
|
|
}
|
|
}
|
|
|
|
final class EntryIterator
|
|
extends HashIterator
|
|
implements Iterator<Entry<K,V>>
|
|
{
|
|
public Map.Entry<K,V> next() {
|
|
HashEntry<K,V> e = super.nextEntry();
|
|
return new WriteThroughEntry(e.key, e.value);
|
|
}
|
|
}
|
|
|
|
final class KeySet extends AbstractSet<K> {
|
|
public Iterator<K> iterator() {
|
|
return new KeyIterator();
|
|
}
|
|
public int size() {
|
|
return ConcurrentHashMap.this.size();
|
|
}
|
|
public boolean contains(Object o) {
|
|
return ConcurrentHashMap.this.containsKey(o);
|
|
}
|
|
public boolean remove(Object o) {
|
|
return ConcurrentHashMap.this.remove(o) != null;
|
|
}
|
|
public void clear() {
|
|
ConcurrentHashMap.this.clear();
|
|
}
|
|
}
|
|
|
|
final class Values extends AbstractCollection<V> {
|
|
public Iterator<V> iterator() {
|
|
return new ValueIterator();
|
|
}
|
|
public int size() {
|
|
return ConcurrentHashMap.this.size();
|
|
}
|
|
public boolean contains(Object o) {
|
|
return ConcurrentHashMap.this.containsValue(o);
|
|
}
|
|
public void clear() {
|
|
ConcurrentHashMap.this.clear();
|
|
}
|
|
}
|
|
|
|
final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
|
|
public Iterator<Map.Entry<K,V>> iterator() {
|
|
return new EntryIterator();
|
|
}
|
|
public boolean contains(Object o) {
|
|
if (!(o instanceof Map.Entry))
|
|
return false;
|
|
Map.Entry<?,?> e = (Map.Entry<?,?>)o;
|
|
V v = ConcurrentHashMap.this.get(e.getKey());
|
|
return v != null && v.equals(e.getValue());
|
|
}
|
|
public boolean remove(Object o) {
|
|
if (!(o instanceof Map.Entry))
|
|
return false;
|
|
Map.Entry<?,?> e = (Map.Entry<?,?>)o;
|
|
return ConcurrentHashMap.this.remove(e.getKey(), e.getValue());
|
|
}
|
|
public int size() {
|
|
return ConcurrentHashMap.this.size();
|
|
}
|
|
public void clear() {
|
|
ConcurrentHashMap.this.clear();
|
|
}
|
|
}
|
|
|
|
/* ---------------- Serialization Support -------------- */
|
|
|
|
/**
|
|
* Save the state of the <tt>ConcurrentHashMap</tt> instance to a
|
|
* stream (i.e., serialize it).
|
|
* @param s the stream
|
|
* @serialData
|
|
* the key (Object) and value (Object)
|
|
* for each key-value mapping, followed by a null pair.
|
|
* The key-value mappings are emitted in no particular order.
|
|
*/
|
|
private void writeObject(java.io.ObjectOutputStream s) throws IOException {
|
|
s.defaultWriteObject();
|
|
|
|
for (int k = 0; k < segments.length; ++k) {
|
|
Segment<K,V> seg = segments[k];
|
|
seg.lock();
|
|
try {
|
|
HashEntry<K,V>[] tab = seg.table;
|
|
for (int i = 0; i < tab.length; ++i) {
|
|
for (HashEntry<K,V> e = tab[i]; e != null; e = e.next) {
|
|
s.writeObject(e.key);
|
|
s.writeObject(e.value);
|
|
}
|
|
}
|
|
} finally {
|
|
seg.unlock();
|
|
}
|
|
}
|
|
s.writeObject(null);
|
|
s.writeObject(null);
|
|
}
|
|
|
|
/**
|
|
* Reconstitute the <tt>ConcurrentHashMap</tt> instance from a
|
|
* stream (i.e., deserialize it).
|
|
* @param s the stream
|
|
*/
|
|
private void readObject(java.io.ObjectInputStream s)
|
|
throws IOException, ClassNotFoundException {
|
|
s.defaultReadObject();
|
|
|
|
// Initialize each segment to be minimally sized, and let grow.
|
|
for (int i = 0; i < segments.length; ++i) {
|
|
segments[i].setTable(new HashEntry[1]);
|
|
}
|
|
|
|
// Read the keys and values, and put the mappings in the table
|
|
for (;;) {
|
|
K key = (K) s.readObject();
|
|
V value = (V) s.readObject();
|
|
if (key == null)
|
|
break;
|
|
put(key, value);
|
|
}
|
|
}
|
|
}
|