| /* |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| /* |
| * This file is available under and governed by the GNU General Public |
| * License version 2 only, as published by the Free Software Foundation. |
| * However, the following notice accompanied the original version of this |
| * file: |
| * |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent; |
| import java.util.concurrent.locks.*; |
| import java.util.*; |
| import java.io.Serializable; |
| import java.io.IOException; |
| import java.io.ObjectInputStream; |
| import java.io.ObjectOutputStream; |
| import java.io.ObjectStreamField; |
| |
| /** |
| * A hash table supporting full concurrency of retrievals and |
| * adjustable expected concurrency for updates. This class obeys the |
| * same functional specification as {@link java.util.Hashtable}, and |
| * includes versions of methods corresponding to each method of |
| * <tt>Hashtable</tt>. However, even though all operations are |
| * thread-safe, retrieval operations do <em>not</em> entail locking, |
| * and there is <em>not</em> any support for locking the entire table |
| * in a way that prevents all access. This class is fully |
| * interoperable with <tt>Hashtable</tt> in programs that rely on its |
| * thread safety but not on its synchronization details. |
| * |
| * <p> Retrieval operations (including <tt>get</tt>) generally do not |
| * block, so may overlap with update operations (including |
| * <tt>put</tt> and <tt>remove</tt>). Retrievals reflect the results |
| * of the most recently <em>completed</em> update operations holding |
| * upon their onset. For aggregate operations such as <tt>putAll</tt> |
| * and <tt>clear</tt>, concurrent retrievals may reflect insertion or |
| * removal of only some entries. Similarly, Iterators and |
| * Enumerations return elements reflecting the state of the hash table |
| * at some point at or since the creation of the iterator/enumeration. |
| * They do <em>not</em> throw {@link ConcurrentModificationException}. |
| * However, iterators are designed to be used by only one thread at a time. |
| * |
| * <p> The allowed concurrency among update operations is guided by |
| * the optional <tt>concurrencyLevel</tt> constructor argument |
| * (default <tt>16</tt>), which is used as a hint for internal sizing. The |
| * table is internally partitioned to try to permit the indicated |
| * number of concurrent updates without contention. Because placement |
| * in hash tables is essentially random, the actual concurrency will |
| * vary. Ideally, you should choose a value to accommodate as many |
| * threads as will ever concurrently modify the table. Using a |
| * significantly higher value than you need can waste space and time, |
| * and a significantly lower value can lead to thread contention. But |
| * overestimates and underestimates within an order of magnitude do |
| * not usually have much noticeable impact. A value of one is |
| * appropriate when it is known that only one thread will modify and |
| * all others will only read. Also, resizing this or any other kind of |
| * hash table is a relatively slow operation, so, when possible, it is |
| * a good idea to provide estimates of expected table sizes in |
| * constructors. |
| * |
| * <p>This class and its views and iterators implement all of the |
| * <em>optional</em> methods of the {@link Map} and {@link Iterator} |
| * interfaces. |
| * |
| * <p> Like {@link Hashtable} but unlike {@link HashMap}, this class |
| * does <em>not</em> allow <tt>null</tt> to be used as a key or value. |
| * |
| * <p>This class is a member of the |
| * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| * Java Collections Framework</a>. |
| * |
| * @since 1.5 |
| * @author Doug Lea |
| * @param <K> the type of keys maintained by this map |
| * @param <V> the type of mapped values |
| */ |
| public class ConcurrentHashMap<K, V> extends AbstractMap<K, V> |
| implements ConcurrentMap<K, V>, Serializable { |
| private static final long serialVersionUID = 7249069246763182397L; |
| |
| /* |
| * The basic strategy is to subdivide the table among Segments, |
| * each of which itself is a concurrently readable hash table. To |
| * reduce footprint, all but one segments are constructed only |
| * when first needed (see ensureSegment). To maintain visibility |
| * in the presence of lazy construction, accesses to segments as |
| * well as elements of segment's table must use volatile access, |
| * which is done via Unsafe within methods segmentAt etc |
| * below. These provide the functionality of AtomicReferenceArrays |
| * but reduce the levels of indirection. Additionally, |
| * volatile-writes of table elements and entry "next" fields |
| * within locked operations use the cheaper "lazySet" forms of |
| * writes (via putOrderedObject) because these writes are always |
| * followed by lock releases that maintain sequential consistency |
| * of table updates. |
| * |
| * Historical note: The previous version of this class relied |
| * heavily on "final" fields, which avoided some volatile reads at |
| * the expense of a large initial footprint. Some remnants of |
| * that design (including forced construction of segment 0) exist |
| * to ensure serialization compatibility. |
| */ |
| |
| /* ---------------- Constants -------------- */ |
| |
| /** |
| * The default initial capacity for this table, |
| * used when not otherwise specified in a constructor. |
| */ |
| static final int DEFAULT_INITIAL_CAPACITY = 16; |
| |
| /** |
| * The default load factor for this table, used when not |
| * otherwise specified in a constructor. |
| */ |
| static final float DEFAULT_LOAD_FACTOR = 0.75f; |
| |
| /** |
| * The default concurrency level for this table, used when not |
| * otherwise specified in a constructor. |
| */ |
| static final int DEFAULT_CONCURRENCY_LEVEL = 16; |
| |
| /** |
| * The maximum capacity, used if a higher value is implicitly |
| * specified by either of the constructors with arguments. MUST |
| * be a power of two <= 1<<30 to ensure that entries are indexable |
| * using ints. |
| */ |
| static final int MAXIMUM_CAPACITY = 1 << 30; |
| |
| /** |
| * The minimum capacity for per-segment tables. Must be a power |
| * of two, at least two to avoid immediate resizing on next use |
| * after lazy construction. |
| */ |
| static final int MIN_SEGMENT_TABLE_CAPACITY = 2; |
| |
| /** |
| * The maximum number of segments to allow; used to bound |
| * constructor arguments. Must be power of two less than 1 << 24. |
| */ |
| static final int MAX_SEGMENTS = 1 << 16; // slightly conservative |
| |
| /** |
| * Number of unsynchronized retries in size and containsValue |
| * methods before resorting to locking. This is used to avoid |
| * unbounded retries if tables undergo continuous modification |
| * which would make it impossible to obtain an accurate result. |
| */ |
| static final int RETRIES_BEFORE_LOCK = 2; |
| |
| /* ---------------- Fields -------------- */ |
| |
| /** |
| * holds values which can't be initialized until after VM is booted. |
| */ |
| private static class Holder { |
| |
| /** |
| * Enable alternative hashing of String keys? |
| * |
| * <p>Unlike the other hash map implementations we do not implement a |
| * threshold for regulating whether alternative hashing is used for |
| * String keys. Alternative hashing is either enabled for all instances |
| * or disabled for all instances. |
| */ |
| static final boolean ALTERNATIVE_HASHING; |
| |
| static { |
| // Use the "threshold" system property even though our threshold |
| // behaviour is "ON" or "OFF". |
| String altThreshold = java.security.AccessController.doPrivileged( |
| new sun.security.action.GetPropertyAction( |
| "jdk.map.althashing.threshold")); |
| |
| int threshold; |
| try { |
| threshold = (null != altThreshold) |
| ? Integer.parseInt(altThreshold) |
| : Integer.MAX_VALUE; |
| |
| // disable alternative hashing if -1 |
| if (threshold == -1) { |
| threshold = Integer.MAX_VALUE; |
| } |
| |
| if (threshold < 0) { |
| throw new IllegalArgumentException("value must be positive integer."); |
| } |
| } catch(IllegalArgumentException failed) { |
| throw new Error("Illegal value for 'jdk.map.althashing.threshold'", failed); |
| } |
| ALTERNATIVE_HASHING = threshold <= MAXIMUM_CAPACITY; |
| } |
| } |
| |
| /** |
| * A randomizing value associated with this instance that is applied to |
| * hash code of keys to make hash collisions harder to find. |
| */ |
| private transient final int hashSeed = randomHashSeed(this); |
| |
| private static int randomHashSeed(ConcurrentHashMap instance) { |
| if (sun.misc.VM.isBooted() && Holder.ALTERNATIVE_HASHING) { |
| return sun.misc.Hashing.randomHashSeed(instance); |
| } |
| |
| return 0; |
| } |
| |
| /** |
| * Mask value for indexing into segments. The upper bits of a |
| * key's hash code are used to choose the segment. |
| */ |
| final int segmentMask; |
| |
| /** |
| * Shift value for indexing within segments. |
| */ |
| final int segmentShift; |
| |
| /** |
| * The segments, each of which is a specialized hash table. |
| */ |
| final Segment<K,V>[] segments; |
| |
| transient Set<K> keySet; |
| transient Set<Map.Entry<K,V>> entrySet; |
| transient Collection<V> values; |
| |
| /** |
| * ConcurrentHashMap list entry. Note that this is never exported |
| * out as a user-visible Map.Entry. |
| */ |
| static final class HashEntry<K,V> { |
| final int hash; |
| final K key; |
| volatile V value; |
| volatile HashEntry<K,V> next; |
| |
| HashEntry(int hash, K key, V value, HashEntry<K,V> next) { |
| this.hash = hash; |
| this.key = key; |
| this.value = value; |
| this.next = next; |
| } |
| |
| /** |
| * Sets next field with volatile write semantics. (See above |
| * about use of putOrderedObject.) |
| */ |
| final void setNext(HashEntry<K,V> n) { |
| UNSAFE.putOrderedObject(this, nextOffset, n); |
| } |
| |
| // Unsafe mechanics |
| static final sun.misc.Unsafe UNSAFE; |
| static final long nextOffset; |
| static { |
| try { |
| UNSAFE = sun.misc.Unsafe.getUnsafe(); |
| Class k = HashEntry.class; |
| nextOffset = UNSAFE.objectFieldOffset |
| (k.getDeclaredField("next")); |
| } catch (Exception e) { |
| throw new Error(e); |
| } |
| } |
| } |
| |
| /** |
| * Gets the ith element of given table (if nonnull) with volatile |
| * read semantics. Note: This is manually integrated into a few |
| * performance-sensitive methods to reduce call overhead. |
| */ |
| @SuppressWarnings("unchecked") |
| static final <K,V> HashEntry<K,V> entryAt(HashEntry<K,V>[] tab, int i) { |
| return (tab == null) ? null : |
| (HashEntry<K,V>) UNSAFE.getObjectVolatile |
| (tab, ((long)i << TSHIFT) + TBASE); |
| } |
| |
| /** |
| * Sets the ith element of given table, with volatile write |
| * semantics. (See above about use of putOrderedObject.) |
| */ |
| static final <K,V> void setEntryAt(HashEntry<K,V>[] tab, int i, |
| HashEntry<K,V> e) { |
| UNSAFE.putOrderedObject(tab, ((long)i << TSHIFT) + TBASE, e); |
| } |
| |
| /** |
| * Applies a supplemental hash function to a given hashCode, which |
| * defends against poor quality hash functions. This is critical |
| * because ConcurrentHashMap uses power-of-two length hash tables, |
| * that otherwise encounter collisions for hashCodes that do not |
| * differ in lower or upper bits. |
| */ |
| private int hash(Object k) { |
| int h = hashSeed; |
| |
| if ((0 != h) && (k instanceof String)) { |
| return sun.misc.Hashing.stringHash32((String) k); |
| } |
| |
| h ^= k.hashCode(); |
| |
| // Spread bits to regularize both segment and index locations, |
| // using variant of single-word Wang/Jenkins hash. |
| h += (h << 15) ^ 0xffffcd7d; |
| h ^= (h >>> 10); |
| h += (h << 3); |
| h ^= (h >>> 6); |
| h += (h << 2) + (h << 14); |
| return h ^ (h >>> 16); |
| } |
| |
| /** |
| * Segments are specialized versions of hash tables. This |
| * subclasses from ReentrantLock opportunistically, just to |
| * simplify some locking and avoid separate construction. |
| */ |
| static final class Segment<K,V> extends ReentrantLock implements Serializable { |
| /* |
| * Segments maintain a table of entry lists that are always |
| * kept in a consistent state, so can be read (via volatile |
| * reads of segments and tables) without locking. This |
| * requires replicating nodes when necessary during table |
| * resizing, so the old lists can be traversed by readers |
| * still using old version of table. |
| * |
| * This class defines only mutative methods requiring locking. |
| * Except as noted, the methods of this class perform the |
| * per-segment versions of ConcurrentHashMap methods. (Other |
| * methods are integrated directly into ConcurrentHashMap |
| * methods.) These mutative methods use a form of controlled |
| * spinning on contention via methods scanAndLock and |
| * scanAndLockForPut. These intersperse tryLocks with |
| * traversals to locate nodes. The main benefit is to absorb |
| * cache misses (which are very common for hash tables) while |
| * obtaining locks so that traversal is faster once |
| * acquired. We do not actually use the found nodes since they |
| * must be re-acquired under lock anyway to ensure sequential |
| * consistency of updates (and in any case may be undetectably |
| * stale), but they will normally be much faster to re-locate. |
| * Also, scanAndLockForPut speculatively creates a fresh node |
| * to use in put if no node is found. |
| */ |
| |
| private static final long serialVersionUID = 2249069246763182397L; |
| |
| /** |
| * The maximum number of times to tryLock in a prescan before |
| * possibly blocking on acquire in preparation for a locked |
| * segment operation. On multiprocessors, using a bounded |
| * number of retries maintains cache acquired while locating |
| * nodes. |
| */ |
| static final int MAX_SCAN_RETRIES = |
| Runtime.getRuntime().availableProcessors() > 1 ? 64 : 1; |
| |
| /** |
| * The per-segment table. Elements are accessed via |
| * entryAt/setEntryAt providing volatile semantics. |
| */ |
| transient volatile HashEntry<K,V>[] table; |
| |
| /** |
| * The number of elements. Accessed only either within locks |
| * or among other volatile reads that maintain visibility. |
| */ |
| transient int count; |
| |
| /** |
| * The total number of mutative operations in this segment. |
| * Even though this may overflows 32 bits, it provides |
| * sufficient accuracy for stability checks in CHM isEmpty() |
| * and size() methods. Accessed only either within locks or |
| * among other volatile reads that maintain visibility. |
| */ |
| transient int modCount; |
| |
| /** |
| * The table is rehashed when its size exceeds this threshold. |
| * (The value of this field is always <tt>(int)(capacity * |
| * loadFactor)</tt>.) |
| */ |
| transient int threshold; |
| |
| /** |
| * The load factor for the hash table. Even though this value |
| * is same for all segments, it is replicated to avoid needing |
| * links to outer object. |
| * @serial |
| */ |
| final float loadFactor; |
| |
| Segment(float lf, int threshold, HashEntry<K,V>[] tab) { |
| this.loadFactor = lf; |
| this.threshold = threshold; |
| this.table = tab; |
| } |
| |
| final V put(K key, int hash, V value, boolean onlyIfAbsent) { |
| HashEntry<K,V> node = tryLock() ? null : |
| scanAndLockForPut(key, hash, value); |
| V oldValue; |
| try { |
| HashEntry<K,V>[] tab = table; |
| int index = (tab.length - 1) & hash; |
| HashEntry<K,V> first = entryAt(tab, index); |
| for (HashEntry<K,V> e = first;;) { |
| if (e != null) { |
| K k; |
| if ((k = e.key) == key || |
| (e.hash == hash && key.equals(k))) { |
| oldValue = e.value; |
| if (!onlyIfAbsent) { |
| e.value = value; |
| ++modCount; |
| } |
| break; |
| } |
| e = e.next; |
| } |
| else { |
| if (node != null) |
| node.setNext(first); |
| else |
| node = new HashEntry<K,V>(hash, key, value, first); |
| int c = count + 1; |
| if (c > threshold && tab.length < MAXIMUM_CAPACITY) |
| rehash(node); |
| else |
| setEntryAt(tab, index, node); |
| ++modCount; |
| count = c; |
| oldValue = null; |
| break; |
| } |
| } |
| } finally { |
| unlock(); |
| } |
| return oldValue; |
| } |
| |
| /** |
| * Doubles size of table and repacks entries, also adding the |
| * given node to new table |
| */ |
| @SuppressWarnings("unchecked") |
| private void rehash(HashEntry<K,V> node) { |
| /* |
| * Reclassify nodes in each list to new table. Because we |
| * are using power-of-two expansion, the elements from |
| * each bin must either stay at same index, or move with a |
| * power of two offset. We eliminate unnecessary node |
| * creation by catching cases where old nodes can be |
| * reused because their next fields won't change. |
| * Statistically, at the default threshold, only about |
| * one-sixth of them need cloning when a table |
| * doubles. The nodes they replace will be garbage |
| * collectable as soon as they are no longer referenced by |
| * any reader thread that may be in the midst of |
| * concurrently traversing table. Entry accesses use plain |
| * array indexing because they are followed by volatile |
| * table write. |
| */ |
| HashEntry<K,V>[] oldTable = table; |
| int oldCapacity = oldTable.length; |
| int newCapacity = oldCapacity << 1; |
| threshold = (int)(newCapacity * loadFactor); |
| HashEntry<K,V>[] newTable = |
| (HashEntry<K,V>[]) new HashEntry[newCapacity]; |
| int sizeMask = newCapacity - 1; |
| for (int i = 0; i < oldCapacity ; i++) { |
| HashEntry<K,V> e = oldTable[i]; |
| if (e != null) { |
| HashEntry<K,V> next = e.next; |
| int idx = e.hash & sizeMask; |
| if (next == null) // Single node on list |
| newTable[idx] = e; |
| else { // Reuse consecutive sequence at same slot |
| HashEntry<K,V> lastRun = e; |
| int lastIdx = idx; |
| for (HashEntry<K,V> last = next; |
| last != null; |
| last = last.next) { |
| int k = last.hash & sizeMask; |
| if (k != lastIdx) { |
| lastIdx = k; |
| lastRun = last; |
| } |
| } |
| newTable[lastIdx] = lastRun; |
| // Clone remaining nodes |
| for (HashEntry<K,V> p = e; p != lastRun; p = p.next) { |
| V v = p.value; |
| int h = p.hash; |
| int k = h & sizeMask; |
| HashEntry<K,V> n = newTable[k]; |
| newTable[k] = new HashEntry<K,V>(h, p.key, v, n); |
| } |
| } |
| } |
| } |
| int nodeIndex = node.hash & sizeMask; // add the new node |
| node.setNext(newTable[nodeIndex]); |
| newTable[nodeIndex] = node; |
| table = newTable; |
| } |
| |
| /** |
| * Scans for a node containing given key while trying to |
| * acquire lock, creating and returning one if not found. Upon |
| * return, guarantees that lock is held. UNlike in most |
| * methods, calls to method equals are not screened: Since |
| * traversal speed doesn't matter, we might as well help warm |
| * up the associated code and accesses as well. |
| * |
| * @return a new node if key not found, else null |
| */ |
| private HashEntry<K,V> scanAndLockForPut(K key, int hash, V value) { |
| HashEntry<K,V> first = entryForHash(this, hash); |
| HashEntry<K,V> e = first; |
| HashEntry<K,V> node = null; |
| int retries = -1; // negative while locating node |
| while (!tryLock()) { |
| HashEntry<K,V> f; // to recheck first below |
| if (retries < 0) { |
| if (e == null) { |
| if (node == null) // speculatively create node |
| node = new HashEntry<K,V>(hash, key, value, null); |
| retries = 0; |
| } |
| else if (key.equals(e.key)) |
| retries = 0; |
| else |
| e = e.next; |
| } |
| else if (++retries > MAX_SCAN_RETRIES) { |
| lock(); |
| break; |
| } |
| else if ((retries & 1) == 0 && |
| (f = entryForHash(this, hash)) != first) { |
| e = first = f; // re-traverse if entry changed |
| retries = -1; |
| } |
| } |
| return node; |
| } |
| |
| /** |
| * Scans for a node containing the given key while trying to |
| * acquire lock for a remove or replace operation. Upon |
| * return, guarantees that lock is held. Note that we must |
| * lock even if the key is not found, to ensure sequential |
| * consistency of updates. |
| */ |
| private void scanAndLock(Object key, int hash) { |
| // similar to but simpler than scanAndLockForPut |
| HashEntry<K,V> first = entryForHash(this, hash); |
| HashEntry<K,V> e = first; |
| int retries = -1; |
| while (!tryLock()) { |
| HashEntry<K,V> f; |
| if (retries < 0) { |
| if (e == null || key.equals(e.key)) |
| retries = 0; |
| else |
| e = e.next; |
| } |
| else if (++retries > MAX_SCAN_RETRIES) { |
| lock(); |
| break; |
| } |
| else if ((retries & 1) == 0 && |
| (f = entryForHash(this, hash)) != first) { |
| e = first = f; |
| retries = -1; |
| } |
| } |
| } |
| |
| /** |
| * Remove; match on key only if value null, else match both. |
| */ |
| final V remove(Object key, int hash, Object value) { |
| if (!tryLock()) |
| scanAndLock(key, hash); |
| V oldValue = null; |
| try { |
| HashEntry<K,V>[] tab = table; |
| int index = (tab.length - 1) & hash; |
| HashEntry<K,V> e = entryAt(tab, index); |
| HashEntry<K,V> pred = null; |
| while (e != null) { |
| K k; |
| HashEntry<K,V> next = e.next; |
| if ((k = e.key) == key || |
| (e.hash == hash && key.equals(k))) { |
| V v = e.value; |
| if (value == null || value == v || value.equals(v)) { |
| if (pred == null) |
| setEntryAt(tab, index, next); |
| else |
| pred.setNext(next); |
| ++modCount; |
| --count; |
| oldValue = v; |
| } |
| break; |
| } |
| pred = e; |
| e = next; |
| } |
| } finally { |
| unlock(); |
| } |
| return oldValue; |
| } |
| |
| final boolean replace(K key, int hash, V oldValue, V newValue) { |
| if (!tryLock()) |
| scanAndLock(key, hash); |
| boolean replaced = false; |
| try { |
| HashEntry<K,V> e; |
| for (e = entryForHash(this, hash); e != null; e = e.next) { |
| K k; |
| if ((k = e.key) == key || |
| (e.hash == hash && key.equals(k))) { |
| if (oldValue.equals(e.value)) { |
| e.value = newValue; |
| ++modCount; |
| replaced = true; |
| } |
| break; |
| } |
| } |
| } finally { |
| unlock(); |
| } |
| return replaced; |
| } |
| |
| final V replace(K key, int hash, V value) { |
| if (!tryLock()) |
| scanAndLock(key, hash); |
| V oldValue = null; |
| try { |
| HashEntry<K,V> e; |
| for (e = entryForHash(this, hash); e != null; e = e.next) { |
| K k; |
| if ((k = e.key) == key || |
| (e.hash == hash && key.equals(k))) { |
| oldValue = e.value; |
| e.value = value; |
| ++modCount; |
| break; |
| } |
| } |
| } finally { |
| unlock(); |
| } |
| return oldValue; |
| } |
| |
| final void clear() { |
| lock(); |
| try { |
| HashEntry<K,V>[] tab = table; |
| for (int i = 0; i < tab.length ; i++) |
| setEntryAt(tab, i, null); |
| ++modCount; |
| count = 0; |
| } finally { |
| unlock(); |
| } |
| } |
| } |
| |
| // Accessing segments |
| |
| /** |
| * Gets the jth element of given segment array (if nonnull) with |
| * volatile element access semantics via Unsafe. (The null check |
| * can trigger harmlessly only during deserialization.) Note: |
| * because each element of segments array is set only once (using |
| * fully ordered writes), some performance-sensitive methods rely |
| * on this method only as a recheck upon null reads. |
| */ |
| @SuppressWarnings("unchecked") |
| static final <K,V> Segment<K,V> segmentAt(Segment<K,V>[] ss, int j) { |
| long u = (j << SSHIFT) + SBASE; |
| return ss == null ? null : |
| (Segment<K,V>) UNSAFE.getObjectVolatile(ss, u); |
| } |
| |
| /** |
| * Returns the segment for the given index, creating it and |
| * recording in segment table (via CAS) if not already present. |
| * |
| * @param k the index |
| * @return the segment |
| */ |
| @SuppressWarnings("unchecked") |
| private Segment<K,V> ensureSegment(int k) { |
| final Segment<K,V>[] ss = this.segments; |
| long u = (k << SSHIFT) + SBASE; // raw offset |
| Segment<K,V> seg; |
| if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) == null) { |
| Segment<K,V> proto = ss[0]; // use segment 0 as prototype |
| int cap = proto.table.length; |
| float lf = proto.loadFactor; |
| int threshold = (int)(cap * lf); |
| HashEntry<K,V>[] tab = (HashEntry<K,V>[])new HashEntry[cap]; |
| if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) |
| == null) { // recheck |
| Segment<K,V> s = new Segment<K,V>(lf, threshold, tab); |
| while ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) |
| == null) { |
| if (UNSAFE.compareAndSwapObject(ss, u, null, seg = s)) |
| break; |
| } |
| } |
| } |
| return seg; |
| } |
| |
| // Hash-based segment and entry accesses |
| |
| /** |
| * Get the segment for the given hash |
| */ |
| @SuppressWarnings("unchecked") |
| private Segment<K,V> segmentForHash(int h) { |
| long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE; |
| return (Segment<K,V>) UNSAFE.getObjectVolatile(segments, u); |
| } |
| |
| /** |
| * Gets the table entry for the given segment and hash |
| */ |
| @SuppressWarnings("unchecked") |
| static final <K,V> HashEntry<K,V> entryForHash(Segment<K,V> seg, int h) { |
| HashEntry<K,V>[] tab; |
| return (seg == null || (tab = seg.table) == null) ? null : |
| (HashEntry<K,V>) UNSAFE.getObjectVolatile |
| (tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE); |
| } |
| |
| /* ---------------- 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. |
| */ |
| @SuppressWarnings("unchecked") |
| 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; |
| } |
| this.segmentShift = 32 - sshift; |
| this.segmentMask = ssize - 1; |
| if (initialCapacity > MAXIMUM_CAPACITY) |
| initialCapacity = MAXIMUM_CAPACITY; |
| int c = initialCapacity / ssize; |
| if (c * ssize < initialCapacity) |
| ++c; |
| int cap = MIN_SEGMENT_TABLE_CAPACITY; |
| while (cap < c) |
| cap <<= 1; |
| // create segments and segments[0] |
| Segment<K,V> s0 = |
| new Segment<K,V>(loadFactor, (int)(cap * loadFactor), |
| (HashEntry<K,V>[])new HashEntry[cap]); |
| Segment<K,V>[] ss = (Segment<K,V>[])new Segment[ssize]; |
| UNSAFE.putOrderedObject(ss, SBASE, s0); // ordered write of segments[0] |
| this.segments = ss; |
| } |
| |
| /** |
| * 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() { |
| /* |
| * Sum per-segment modCounts to avoid mis-reporting when |
| * elements are concurrently added and removed in one segment |
| * while checking another, in which case the table was never |
| * actually empty at any point. (The sum ensures accuracy up |
| * through at least 1<<31 per-segment modifications before |
| * recheck.) Methods size() and containsValue() use similar |
| * constructions for stability checks. |
| */ |
| long sum = 0L; |
| final Segment<K,V>[] segments = this.segments; |
| for (int j = 0; j < segments.length; ++j) { |
| Segment<K,V> seg = segmentAt(segments, j); |
| if (seg != null) { |
| if (seg.count != 0) |
| return false; |
| sum += seg.modCount; |
| } |
| } |
| if (sum != 0L) { // recheck unless no modifications |
| for (int j = 0; j < segments.length; ++j) { |
| Segment<K,V> seg = segmentAt(segments, j); |
| if (seg != null) { |
| if (seg.count != 0) |
| return false; |
| sum -= seg.modCount; |
| } |
| } |
| if (sum != 0L) |
| 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() { |
| // Try a few times to get accurate count. On failure due to |
| // continuous async changes in table, resort to locking. |
| final Segment<K,V>[] segments = this.segments; |
| int size; |
| boolean overflow; // true if size overflows 32 bits |
| long sum; // sum of modCounts |
| long last = 0L; // previous sum |
| int retries = -1; // first iteration isn't retry |
| try { |
| for (;;) { |
| if (retries++ == RETRIES_BEFORE_LOCK) { |
| for (int j = 0; j < segments.length; ++j) |
| ensureSegment(j).lock(); // force creation |
| } |
| sum = 0L; |
| size = 0; |
| overflow = false; |
| for (int j = 0; j < segments.length; ++j) { |
| Segment<K,V> seg = segmentAt(segments, j); |
| if (seg != null) { |
| sum += seg.modCount; |
| int c = seg.count; |
| if (c < 0 || (size += c) < 0) |
| overflow = true; |
| } |
| } |
| if (sum == last) |
| break; |
| last = sum; |
| } |
| } finally { |
| if (retries > RETRIES_BEFORE_LOCK) { |
| for (int j = 0; j < segments.length; ++j) |
| segmentAt(segments, j).unlock(); |
| } |
| } |
| return overflow ? Integer.MAX_VALUE : size; |
| } |
| |
| /** |
| * 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) { |
| Segment<K,V> s; // manually integrate access methods to reduce overhead |
| HashEntry<K,V>[] tab; |
| int h = hash(key); |
| long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE; |
| if ((s = (Segment<K,V>)UNSAFE.getObjectVolatile(segments, u)) != null && |
| (tab = s.table) != null) { |
| for (HashEntry<K,V> e = (HashEntry<K,V>) UNSAFE.getObjectVolatile |
| (tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE); |
| e != null; e = e.next) { |
| K k; |
| if ((k = e.key) == key || (e.hash == h && key.equals(k))) |
| return e.value; |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * 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 |
| */ |
| @SuppressWarnings("unchecked") |
| public boolean containsKey(Object key) { |
| Segment<K,V> s; // same as get() except no need for volatile value read |
| HashEntry<K,V>[] tab; |
| int h = hash(key); |
| long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE; |
| if ((s = (Segment<K,V>)UNSAFE.getObjectVolatile(segments, u)) != null && |
| (tab = s.table) != null) { |
| for (HashEntry<K,V> e = (HashEntry<K,V>) UNSAFE.getObjectVolatile |
| (tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE); |
| e != null; e = e.next) { |
| K k; |
| if ((k = e.key) == key || (e.hash == h && key.equals(k))) |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| /** |
| * 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) { |
| // Same idea as size() |
| if (value == null) |
| throw new NullPointerException(); |
| final Segment<K,V>[] segments = this.segments; |
| boolean found = false; |
| long last = 0; |
| int retries = -1; |
| try { |
| outer: for (;;) { |
| if (retries++ == RETRIES_BEFORE_LOCK) { |
| for (int j = 0; j < segments.length; ++j) |
| ensureSegment(j).lock(); // force creation |
| } |
| long hashSum = 0L; |
| int sum = 0; |
| for (int j = 0; j < segments.length; ++j) { |
| HashEntry<K,V>[] tab; |
| Segment<K,V> seg = segmentAt(segments, j); |
| if (seg != null && (tab = seg.table) != null) { |
| for (int i = 0 ; i < tab.length; i++) { |
| HashEntry<K,V> e; |
| for (e = entryAt(tab, i); e != null; e = e.next) { |
| V v = e.value; |
| if (v != null && value.equals(v)) { |
| found = true; |
| break outer; |
| } |
| } |
| } |
| sum += seg.modCount; |
| } |
| } |
| if (retries > 0 && sum == last) |
| break; |
| last = sum; |
| } |
| } finally { |
| if (retries > RETRIES_BEFORE_LOCK) { |
| for (int j = 0; j < segments.length; ++j) |
| segmentAt(segments, j).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 |
| */ |
| @SuppressWarnings("unchecked") |
| public V put(K key, V value) { |
| Segment<K,V> s; |
| if (value == null) |
| throw new NullPointerException(); |
| int hash = hash(key); |
| int j = (hash >>> segmentShift) & segmentMask; |
| if ((s = (Segment<K,V>)UNSAFE.getObject // nonvolatile; recheck |
| (segments, (j << SSHIFT) + SBASE)) == null) // in ensureSegment |
| s = ensureSegment(j); |
| return s.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 |
| */ |
| @SuppressWarnings("unchecked") |
| public V putIfAbsent(K key, V value) { |
| Segment<K,V> s; |
| if (value == null) |
| throw new NullPointerException(); |
| int hash = hash(key); |
| int j = (hash >>> segmentShift) & segmentMask; |
| if ((s = (Segment<K,V>)UNSAFE.getObject |
| (segments, (j << SSHIFT) + SBASE)) == null) |
| s = ensureSegment(j); |
| return s.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); |
| Segment<K,V> s = segmentForHash(hash); |
| return s == null ? null : s.remove(key, hash, null); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * @throws NullPointerException if the specified key is null |
| */ |
| public boolean remove(Object key, Object value) { |
| int hash = hash(key); |
| Segment<K,V> s; |
| return value != null && (s = segmentForHash(hash)) != null && |
| s.remove(key, hash, value) != null; |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * @throws NullPointerException if any of the arguments are null |
| */ |
| public boolean replace(K key, V oldValue, V newValue) { |
| int hash = hash(key); |
| if (oldValue == null || newValue == null) |
| throw new NullPointerException(); |
| Segment<K,V> s = segmentForHash(hash); |
| return s != null && s.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) { |
| int hash = hash(key); |
| if (value == null) |
| throw new NullPointerException(); |
| Segment<K,V> s = segmentForHash(hash); |
| return s == null ? null : s.replace(key, hash, value); |
| } |
| |
| /** |
| * Removes all of the mappings from this map. |
| */ |
| public void clear() { |
| final Segment<K,V>[] segments = this.segments; |
| for (int j = 0; j < segments.length; ++j) { |
| Segment<K,V> s = segmentAt(segments, j); |
| if (s != null) |
| s.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(); |
| } |
| |
| /** |
| * Set nextEntry to first node of next non-empty table |
| * (in backwards order, to simplify checks). |
| */ |
| final void advance() { |
| for (;;) { |
| if (nextTableIndex >= 0) { |
| if ((nextEntry = entryAt(currentTable, |
| nextTableIndex--)) != null) |
| break; |
| } |
| else if (nextSegmentIndex >= 0) { |
| Segment<K,V> seg = segmentAt(segments, nextSegmentIndex--); |
| if (seg != null && (currentTable = seg.table) != null) |
| nextTableIndex = currentTable.length - 1; |
| } |
| else |
| break; |
| } |
| } |
| |
| final HashEntry<K,V> nextEntry() { |
| HashEntry<K,V> e = nextEntry; |
| if (e == null) |
| throw new NoSuchElementException(); |
| lastReturned = e; // cannot assign until after null check |
| if ((nextEntry = e.next) == null) |
| advance(); |
| return e; |
| } |
| |
| public final boolean hasNext() { return nextEntry != null; } |
| public final boolean hasMoreElements() { return nextEntry != null; } |
| |
| public final 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 final K next() { return super.nextEntry().key; } |
| public final K nextElement() { return super.nextEntry().key; } |
| } |
| |
| final class ValueIterator |
| extends HashIterator |
| implements Iterator<V>, Enumeration<V> |
| { |
| public final V next() { return super.nextEntry().value; } |
| public final 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 isEmpty() { |
| return ConcurrentHashMap.this.isEmpty(); |
| } |
| 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 isEmpty() { |
| return ConcurrentHashMap.this.isEmpty(); |
| } |
| 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 boolean isEmpty() { |
| return ConcurrentHashMap.this.isEmpty(); |
| } |
| 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 { |
| // force all segments for serialization compatibility |
| for (int k = 0; k < segments.length; ++k) |
| ensureSegment(k); |
| s.defaultWriteObject(); |
| |
| final Segment<K,V>[] segments = this.segments; |
| for (int k = 0; k < segments.length; ++k) { |
| Segment<K,V> seg = segmentAt(segments, k); |
| seg.lock(); |
| try { |
| HashEntry<K,V>[] tab = seg.table; |
| for (int i = 0; i < tab.length; ++i) { |
| HashEntry<K,V> e; |
| for (e = entryAt(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 |
| */ |
| @SuppressWarnings("unchecked") |
| private void readObject(java.io.ObjectInputStream s) |
| throws IOException, ClassNotFoundException { |
| // Don't call defaultReadObject() |
| ObjectInputStream.GetField oisFields = s.readFields(); |
| final Segment<K,V>[] oisSegments = (Segment<K,V>[])oisFields.get("segments", null); |
| |
| final int ssize = oisSegments.length; |
| if (ssize < 1 || ssize > MAX_SEGMENTS |
| || (ssize & (ssize-1)) != 0 ) // ssize not power of two |
| throw new java.io.InvalidObjectException("Bad number of segments:" |
| + ssize); |
| int sshift = 0, ssizeTmp = ssize; |
| while (ssizeTmp > 1) { |
| ++sshift; |
| ssizeTmp >>>= 1; |
| } |
| UNSAFE.putIntVolatile(this, SEGSHIFT_OFFSET, 32 - sshift); |
| UNSAFE.putIntVolatile(this, SEGMASK_OFFSET, ssize - 1); |
| UNSAFE.putObjectVolatile(this, SEGMENTS_OFFSET, oisSegments); |
| |
| // set hashMask |
| UNSAFE.putIntVolatile(this, HASHSEED_OFFSET, randomHashSeed(this)); |
| |
| // Re-initialize segments to be minimally sized, and let grow. |
| int cap = MIN_SEGMENT_TABLE_CAPACITY; |
| final Segment<K,V>[] segments = this.segments; |
| for (int k = 0; k < segments.length; ++k) { |
| Segment<K,V> seg = segments[k]; |
| if (seg != null) { |
| seg.threshold = (int)(cap * seg.loadFactor); |
| seg.table = (HashEntry<K,V>[]) new HashEntry[cap]; |
| } |
| } |
| |
| // 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); |
| } |
| } |
| |
| // Unsafe mechanics |
| private static final sun.misc.Unsafe UNSAFE; |
| private static final long SBASE; |
| private static final int SSHIFT; |
| private static final long TBASE; |
| private static final int TSHIFT; |
| private static final long HASHSEED_OFFSET; |
| private static final long SEGSHIFT_OFFSET; |
| private static final long SEGMASK_OFFSET; |
| private static final long SEGMENTS_OFFSET; |
| |
| static { |
| int ss, ts; |
| try { |
| UNSAFE = sun.misc.Unsafe.getUnsafe(); |
| Class tc = HashEntry[].class; |
| Class sc = Segment[].class; |
| TBASE = UNSAFE.arrayBaseOffset(tc); |
| SBASE = UNSAFE.arrayBaseOffset(sc); |
| ts = UNSAFE.arrayIndexScale(tc); |
| ss = UNSAFE.arrayIndexScale(sc); |
| HASHSEED_OFFSET = UNSAFE.objectFieldOffset( |
| ConcurrentHashMap.class.getDeclaredField("hashSeed")); |
| SEGSHIFT_OFFSET = UNSAFE.objectFieldOffset( |
| ConcurrentHashMap.class.getDeclaredField("segmentShift")); |
| SEGMASK_OFFSET = UNSAFE.objectFieldOffset( |
| ConcurrentHashMap.class.getDeclaredField("segmentMask")); |
| SEGMENTS_OFFSET = UNSAFE.objectFieldOffset( |
| ConcurrentHashMap.class.getDeclaredField("segments")); |
| } catch (Exception e) { |
| throw new Error(e); |
| } |
| if ((ss & (ss-1)) != 0 || (ts & (ts-1)) != 0) |
| throw new Error("data type scale not a power of two"); |
| SSHIFT = 31 - Integer.numberOfLeadingZeros(ss); |
| TSHIFT = 31 - Integer.numberOfLeadingZeros(ts); |
| } |
| |
| } |