From 271c41d7322c2f62a42a839730641b255f91aadf Mon Sep 17 00:00:00 2001 From: Trustin Lee Date: Wed, 3 Dec 2008 00:39:33 +0000 Subject: [PATCH] Resolved issue: NETTY-93 (ChannelLocal (as a counterpart of ThreadLocal)) * Added ChannelLocal * Added ConcurrentWeakHashMap --- .../org/jboss/netty/channel/ChannelLocal.java | 64 + .../netty/util/ConcurrentWeakHashMap.java | 1567 +++++++++++++++++ 2 files changed, 1631 insertions(+) create mode 100644 src/main/java/org/jboss/netty/channel/ChannelLocal.java create mode 100644 src/main/java/org/jboss/netty/util/ConcurrentWeakHashMap.java diff --git a/src/main/java/org/jboss/netty/channel/ChannelLocal.java b/src/main/java/org/jboss/netty/channel/ChannelLocal.java new file mode 100644 index 0000000000..7bcb997fe5 --- /dev/null +++ b/src/main/java/org/jboss/netty/channel/ChannelLocal.java @@ -0,0 +1,64 @@ +/* + * JBoss, Home of Professional Open Source + * + * Copyright 2008, Red Hat Middleware LLC, and individual contributors + * by the @author tags. See the COPYRIGHT.txt in the distribution for a + * full listing of individual contributors. + * + * This is free software; you can redistribute it and/or modify it + * under the terms of the GNU Lesser General Public License as + * published by the Free Software Foundation; either version 2.1 of + * the License, or (at your option) any later version. + * + * This software 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 + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this software; if not, write to the Free + * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA + * 02110-1301 USA, or see the FSF site: http://www.fsf.org. + */ +package org.jboss.netty.channel; + +import java.util.concurrent.ConcurrentMap; + +import org.jboss.netty.util.ConcurrentWeakHashMap; + +/** + * @author The Netty Project (netty-dev@lists.jboss.org) + * @author Trustin Lee (tlee@redhat.com) + * @version $Rev$, $Date$ + */ +public class ChannelLocal { + private final ConcurrentMap map = new ConcurrentWeakHashMap(); + + protected T initialValue(@SuppressWarnings("unused") Channel channel) { + return null; + } + + public T get(Channel channel) { + T value = map.get(channel); + if (value == null) { + value = initialValue(channel); + T oldValue = setIfAbsent(channel, value); + if (oldValue != null) { + value = oldValue; + } + } + return value; + } + + public T set(Channel channel, T newValue) { + return map.put(channel, newValue); + } + + public T setIfAbsent(Channel channel, T value) { + return map.putIfAbsent(channel, value); + } + + public T remove(Channel channel) { + return map.remove(channel); + } +} diff --git a/src/main/java/org/jboss/netty/util/ConcurrentWeakHashMap.java b/src/main/java/org/jboss/netty/util/ConcurrentWeakHashMap.java new file mode 100644 index 0000000000..afde78e813 --- /dev/null +++ b/src/main/java/org/jboss/netty/util/ConcurrentWeakHashMap.java @@ -0,0 +1,1567 @@ +/* + * JBoss, Home of Professional Open Source + * + * Copyright 2008, Red Hat Middleware LLC, and individual contributors + * by the @author tags. See the COPYRIGHT.txt in the distribution for a + * full listing of individual contributors. + * + * This is free software; you can redistribute it and/or modify it + * under the terms of the GNU Lesser General Public License as + * published by the Free Software Foundation; either version 2.1 of + * the License, or (at your option) any later version. + * + * This software 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 + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this software; if not, write to the Free + * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA + * 02110-1301 USA, or see the FSF site: http://www.fsf.org. + */ +/* + * 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/licenses/publicdomain + */ +package org.jboss.netty.util; + +import java.io.IOException; +import java.io.ObjectInputStream; +import java.io.ObjectOutputStream; +import java.io.Serializable; +import java.lang.ref.Reference; +import java.lang.ref.ReferenceQueue; +import java.lang.ref.WeakReference; +import java.util.AbstractCollection; +import java.util.AbstractMap; +import java.util.AbstractSet; +import java.util.Collection; +import java.util.ConcurrentModificationException; +import java.util.Enumeration; +import java.util.Hashtable; +import java.util.Iterator; +import java.util.Map; +import java.util.NoSuchElementException; +import java.util.Set; +import java.util.concurrent.ConcurrentMap; +import java.util.concurrent.locks.ReentrantLock; + +import org.jboss.netty.util.ConcurrentReferenceHashMap.KeyReference; + +/** + * A {@link ConcurrentMap} with weak keys which is written based on + * {@link ConcurrentReferenceHashMap}. + * + * @author The Netty Project (netty-dev@lists.jboss.org) + * @author Doug Lea + * @author Jason T. Greene + * @author Trustin Lee (tlee@redhat.com) + * @version $Rev$, $Date$ + * + * @param the type of keys maintained by this map + * @param the type of mapped values + */ +public class ConcurrentWeakHashMap extends AbstractMap + implements ConcurrentMap, Serializable { + + private static final long serialVersionUID = 1332231209347394089L; + + /* + * The basic strategy is to subdivide the table among Segments, + * each of which itself is a concurrently readable hash table. + */ + + /** + * 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 integers. + */ + static final int MAXIMUM_CAPACITY = 1 << 30; + + /** + * The maximum number of segments to allow; used to bound constructor + * arguments. + */ + 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 -------------- */ + + /** + * 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[] segments; + + transient Set keySet; + transient Set> entrySet; + transient Collection values; + + /* ---------------- Small Utilities -------------- */ + + /** + * Applies a supplemental hash function to a given hashCode, which defends + * against poor quality hash functions. This is critical because + * ConcurrentReferenceHashMap uses power-of-two length hash tables, that + * otherwise encounter collisions for hashCodes that do not differ in lower + * or upper bits. + */ + private static int hash(int h) { + // 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; + } + + /** + * Returns the segment that should be used for key with given hash. + * + * @param hash the hash code for the key + * @return the segment + */ + final Segment segmentFor(int hash) { + return segments[hash >>> segmentShift & segmentMask]; + } + + private int hashOf(Object key) { + return hash(key.hashCode()); + } + + /* ---------------- Inner Classes -------------- */ + + /** + * A weak-key reference which stores the key hash needed for reclamation. + */ + static final class WeakKeyReference extends WeakReference { + + final int hash; + + WeakKeyReference(K key, int hash, ReferenceQueue refQueue) { + super(key, refQueue); + this.hash = hash; + } + + public final int keyHash() { + return hash; + } + + public final Object keyRef() { + return this; + } + } + + /** + * ConcurrentReferenceHashMap list entry. Note that this is never exported + * out as a user-visible Map.Entry. + * + * Because the value field is volatile, not final, it is legal wrt + * the Java Memory Model for an unsynchronized reader to see null + * instead of initial value when read via a data race. Although a + * reordering leading to this is not likely to ever actually + * occur, the Segment.readValueUnderLock method is used as a + * backup in case a null (pre-initialized) value is ever seen in + * an unsynchronized access method. + */ + static final class HashEntry { + final Object keyRef; + final int hash; + volatile Object valueRef; + final HashEntry next; + + HashEntry( + K key, int hash, HashEntry next, V value, + ReferenceQueue refQueue) { + this.hash = hash; + this.next = next; + this.keyRef = new WeakKeyReference(key, hash, refQueue); + this.valueRef = value; + } + + @SuppressWarnings("unchecked") + final K key() { + return ((WeakReference) keyRef).get(); + } + + final V value() { + return dereferenceValue(valueRef); + } + + @SuppressWarnings("unchecked") + final V dereferenceValue(Object value) { + if (value instanceof KeyReference) { + return ((Reference) value).get(); + } + + return (V) value; + } + + final void setValue(V value) { + this.valueRef = value; + } + + @SuppressWarnings("unchecked") + static final HashEntry[] newArray(int i) { + return new HashEntry[i]; + } + } + + /** + * 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 extends ReentrantLock { + /* + * Segments maintain a table of entry lists that are ALWAYS kept in a + * consistent state, so can be read without locking. Next fields of + * nodes are immutable (final). All list additions are performed at the + * front of each bin. This makes it easy to check changes, and also fast + * to traverse. When nodes would otherwise be changed, new nodes are + * created to replace them. This works well for hash tables since the + * bin lists tend to be short. (The average length is less than two for + * the default load factor threshold.) + * + * Read operations can thus proceed without locking, but rely on + * selected uses of volatiles to ensure that completed write operations + * performed by other threads are noticed. For most purposes, the + * "count" field, tracking the number of elements, serves as that + * volatile variable ensuring visibility. This is convenient because + * this field needs to be read in many read operations anyway: + * + * - All (unsynchronized) read operations must first read the + * "count" field, and should not look at table entries if + * it is 0. + * + * - All (synchronized) write operations should write to + * the "count" field after structurally changing any bin. + * The operations must not take any action that could even + * momentarily cause a concurrent read operation to see + * inconsistent data. This is made easier by the nature of + * the read operations in Map. For example, no operation + * can reveal that the table has grown but the threshold + * has not yet been updated, so there are no atomicity + * requirements for this with respect to reads. + * + * As a guide, all critical volatile reads and writes to the count field + * are marked in code comments. + */ + + private static final long serialVersionUID = -5443833583955251591L; + + /** + * The number of elements in this segment's region. + */ + transient volatile int count; + + /** + * Number of updates that alter the size of the table. This is used + * during bulk-read methods to make sure they see a consistent snapshot: + * If modCounts change during a traversal of segments computing size or + * checking containsValue, then we might have an inconsistent view of + * state so (usually) must retry. + */ + transient int modCount; + + /** + * The table is rehashed when its size exceeds this threshold. + * (The value of this field is always (capacity * loadFactor).) + */ + transient int threshold; + + /** + * The per-segment table. + */ + transient volatile HashEntry[] table; + + /** + * 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; + + /** + * The collected weak-key reference queue for this segment. This should + * be (re)initialized whenever table is assigned, + */ + transient volatile ReferenceQueue refQueue; + + Segment(int initialCapacity, float lf) { + loadFactor = lf; + setTable(HashEntry. newArray(initialCapacity)); + } + + @SuppressWarnings("unchecked") + static final Segment[] newArray(int i) { + return new Segment[i]; + } + + private boolean keyEq(Object src, Object dest) { + return src.equals(dest); + } + + /** + * Sets table to new HashEntry array. Call only while holding lock or in + * constructor. + */ + void setTable(HashEntry[] newTable) { + threshold = (int) (newTable.length * loadFactor); + table = newTable; + refQueue = new ReferenceQueue(); + } + + /** + * Returns properly casted first entry of bin for given hash. + */ + HashEntry getFirst(int hash) { + HashEntry[] tab = table; + return tab[hash & tab.length - 1]; + } + + HashEntry newHashEntry( + K key, int hash, HashEntry next, V value) { + return new HashEntry( + key, hash, next, value, refQueue); + } + + /** + * Reads value field of an entry under lock. Called if value field ever + * appears to be null. This is possible only if a compiler happens to + * reorder a HashEntry initialization with its table assignment, which + * is legal under memory model but is not known to ever occur. + */ + V readValueUnderLock(HashEntry e) { + lock(); + try { + removeStale(); + return e.value(); + } finally { + unlock(); + } + } + + /* Specialized implementations of map methods */ + + V get(Object key, int hash) { + if (count != 0) { // read-volatile + HashEntry e = getFirst(hash); + while (e != null) { + if (e.hash == hash && keyEq(key, e.key())) { + Object opaque = e.valueRef; + if (opaque != null) { + return e.dereferenceValue(opaque); + } + + return readValueUnderLock(e); // recheck + } + e = e.next; + } + } + return null; + } + + boolean containsKey(Object key, int hash) { + if (count != 0) { // read-volatile + HashEntry e = getFirst(hash); + while (e != null) { + if (e.hash == hash && keyEq(key, e.key())) { + return true; + } + e = e.next; + } + } + return false; + } + + boolean containsValue(Object value) { + if (count != 0) { // read-volatile + HashEntry[] tab = table; + int len = tab.length; + for (int i = 0; i < len; i ++) { + for (HashEntry e = tab[i]; e != null; e = e.next) { + Object opaque = e.valueRef; + V v; + + if (opaque == null) { + v = readValueUnderLock(e); // recheck + } else { + v = e.dereferenceValue(opaque); + } + + if (value.equals(v)) { + return true; + } + } + } + } + return false; + } + + boolean replace(K key, int hash, V oldValue, V newValue) { + lock(); + try { + removeStale(); + HashEntry e = getFirst(hash); + while (e != null && (e.hash != hash || !keyEq(key, e.key()))) { + e = e.next; + } + + boolean replaced = false; + if (e != null && oldValue.equals(e.value())) { + replaced = true; + e.setValue(newValue); + } + return replaced; + } finally { + unlock(); + } + } + + V replace(K key, int hash, V newValue) { + lock(); + try { + removeStale(); + HashEntry e = getFirst(hash); + while (e != null && (e.hash != hash || !keyEq(key, e.key()))) { + e = e.next; + } + + V oldValue = null; + if (e != null) { + oldValue = e.value(); + e.setValue(newValue); + } + return oldValue; + } finally { + unlock(); + } + } + + V put(K key, int hash, V value, boolean onlyIfAbsent) { + lock(); + try { + removeStale(); + int c = count; + if (c ++ > threshold) { // ensure capacity + int reduced = rehash(); + if (reduced > 0) { + count = (c -= reduced) - 1; // write-volatile + } + } + + HashEntry[] tab = table; + int index = hash & tab.length - 1; + HashEntry first = tab[index]; + HashEntry e = first; + while (e != null && (e.hash != hash || !keyEq(key, e.key()))) { + e = e.next; + } + + V oldValue; + if (e != null) { + oldValue = e.value(); + if (!onlyIfAbsent) { + e.setValue(value); + } + } else { + oldValue = null; + ++ modCount; + tab[index] = newHashEntry(key, hash, first, value); + count = c; // write-volatile + } + return oldValue; + } finally { + unlock(); + } + } + + int rehash() { + HashEntry[] oldTable = table; + int oldCapacity = oldTable.length; + if (oldCapacity >= MAXIMUM_CAPACITY) { + return 0; + } + + /* + * Reclassify nodes in each list to new Map. 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 + * traversing table right now. + */ + + HashEntry[] newTable = HashEntry.newArray(oldCapacity << 1); + threshold = (int) (newTable.length * loadFactor); + int sizeMask = newTable.length - 1; + int reduce = 0; + for (int i = 0; i < oldCapacity; i ++) { + // We need to guarantee that any existing reads of old Map can + // proceed. So we cannot yet null out each bin. + HashEntry e = oldTable[i]; + + if (e != null) { + HashEntry next = e.next; + int idx = e.hash & sizeMask; + + // Single node on list + if (next == null) { + newTable[idx] = e; + } else { + // Reuse trailing consecutive sequence at same slot + HashEntry lastRun = e; + int lastIdx = idx; + for (HashEntry last = next; last != null; last = last.next) { + int k = last.hash & sizeMask; + if (k != lastIdx) { + lastIdx = k; + lastRun = last; + } + } + newTable[lastIdx] = lastRun; + // Clone all remaining nodes + for (HashEntry p = e; p != lastRun; p = p.next) { + // Skip GC'd weak references + K key = p.key(); + if (key == null) { + reduce ++; + continue; + } + int k = p.hash & sizeMask; + HashEntry n = newTable[k]; + newTable[k] = newHashEntry(key, p.hash, n, p.value()); + } + } + } + } + table = newTable; + return reduce; + } + + /** + * Remove; match on key only if value null, else match both. + */ + V remove(Object key, int hash, Object value, boolean refRemove) { + lock(); + try { + if (!refRemove) { + removeStale(); + } + int c = count - 1; + HashEntry[] tab = table; + int index = hash & tab.length - 1; + HashEntry first = tab[index]; + HashEntry e = first; + // a reference remove operation compares the Reference instance + while (e != null && key != e.keyRef && + (refRemove || hash != e.hash || !keyEq(key, e.key()))) { + e = e.next; + } + + V oldValue = null; + if (e != null) { + V v = e.value(); + if (value == null || value.equals(v)) { + oldValue = v; + // All entries following removed node can stay in list, + // but all preceding ones need to be cloned. + ++ modCount; + HashEntry newFirst = e.next; + for (HashEntry p = first; p != e; p = p.next) { + K pKey = p.key(); + if (pKey == null) { // Skip GC'd keys + c --; + continue; + } + + newFirst = newHashEntry( + pKey, p.hash, newFirst, p.value()); + } + tab[index] = newFirst; + count = c; // write-volatile + } + } + return oldValue; + } finally { + unlock(); + } + } + + final void removeStale() { + KeyReference ref; + while ((ref = (KeyReference) refQueue.poll()) != null) { + remove(ref.keyRef(), ref.keyHash(), null, true); + } + } + + void clear() { + if (count != 0) { + lock(); + try { + HashEntry[] tab = table; + for (int i = 0; i < tab.length; i ++) { + tab[i] = null; + } + ++ modCount; + // replace the reference queue to avoid unnecessary stale + // cleanups + refQueue = new ReferenceQueue(); + 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 ConcurrentWeakHashMap( + 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(cap, loadFactor); + } + } + + /** + * Creates a new, empty map with the specified initial capacity and load + * factor and with the default reference types (weak keys, strong values), + * and 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 + */ + public ConcurrentWeakHashMap(int initialCapacity, float loadFactor) { + this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL); + } + + /** + * Creates a new, empty map with the specified initial capacity, and with + * default reference types (weak keys, strong values), 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 ConcurrentWeakHashMap(int initialCapacity) { + this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); + } + + /** + * Creates a new, empty map with a default initial capacity (16), reference + * types (weak keys, strong values), default load factor (0.75) and + * concurrencyLevel (16). + */ + public ConcurrentWeakHashMap() { + 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 ConcurrentWeakHashMap(Map m) { + this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, + DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR, + DEFAULT_CONCURRENCY_LEVEL); + putAll(m); + } + + /** + * Returns true if this map contains no key-value mappings. + * + * @return true if this map contains no key-value mappings + */ + @Override + public boolean isEmpty() { + final Segment[] 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 Integer.MAX_VALUE elements, returns + * Integer.MAX_VALUE. + * + * @return the number of key-value mappings in this map + */ + @Override + public int size() { + final Segment[] 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. + * + *

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 + */ + @Override + public V get(Object key) { + int hash = hashOf(key); + return segmentFor(hash).get(key, hash); + } + + /** + * Tests if the specified object is a key in this table. + * + * @param key possible key + * @return true if and only if the specified object is a key in + * this table, as determined by the equals method; + * false otherwise. + * @throws NullPointerException if the specified key is null + */ + @Override + public boolean containsKey(Object key) { + int hash = hashOf(key); + return segmentFor(hash).containsKey(key, hash); + } + + /** + * Returns true 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 containsKey. + * + * @param value value whose presence in this map is to be tested + * @return true if this map maps one or more keys to the specified + * value + * @throws NullPointerException if the specified value is null + */ + + @Override + public boolean containsValue(Object value) { + if (value == null) { + throw new NullPointerException(); + } + + // See explanation of modCount use above + + final Segment[] 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 mcsum = 0; + for (int i = 0; i < segments.length; ++ i) { + 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) { + 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 Hashtable}, which supported this method prior to + * introduction of the Java Collections framework. + * + * @param value a value to search for + * @return true if and only if some key maps to the value + * argument in this table as determined by the equals + * method; false 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. + * + *

The value can be retrieved by calling the get 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 key, or null + * if there was no mapping for key + * @throws NullPointerException if the specified key or value is null + */ + @Override + public V put(K key, V value) { + if (value == null) { + throw new NullPointerException(); + } + int hash = hashOf(key); + return segmentFor(hash).put(key, hash, value, false); + } + + /** + * {@inheritDoc} + * + * @return the previous value associated with the specified key, or + * null 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 = hashOf(key); + 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 + */ + @Override + public void putAll(Map m) { + for (Map.Entry 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 key, or null + * if there was no mapping for key + * @throws NullPointerException if the specified key is null + */ + @Override + public V remove(Object key) { + int hash = hashOf(key); + return segmentFor(hash).remove(key, hash, null, false); + } + + /** + * {@inheritDoc} + * + * @throws NullPointerException if the specified key is null + */ + public boolean remove(Object key, Object value) { + int hash = hashOf(key); + if (value == null) { + return false; + } + return segmentFor(hash).remove(key, hash, value, false) != 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 = hashOf(key); + return segmentFor(hash).replace(key, hash, oldValue, newValue); + } + + /** + * {@inheritDoc} + * + * @return the previous value associated with the specified key, or + * null 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 = hashOf(key); + return segmentFor(hash).replace(key, hash, value); + } + + /** + * Removes all of the mappings from this map. + */ + @Override + public void clear() { + for (int i = 0; i < segments.length; ++ i) { + segments[i].clear(); + } + } + + /** + * Removes any stale entries whose keys have been finalized. Use of this + * method is normally not necessary since stale entries are automatically + * removed lazily, when blocking operations are required. However, there are + * some cases where this operation should be performed eagerly, such as + * cleaning up old references to a ClassLoader in a multi-classloader + * environment. + * + * Note: this method will acquire locks, one at a time, across all segments + * of this table, so if it is to be used, it should be used sparingly. + */ + public void purgeStaleEntries() { + for (int i = 0; i < segments.length; ++ i) { + segments[i].removeStale(); + } + } + + /** + * 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 Iterator.remove, + * Set.remove, removeAll, retainAll, and + * clear operations. It does not support the add or + * addAll operations. + * + *

The view's iterator 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. + */ + @Override + public Set keySet() { + Set 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 + * Iterator.remove, Collection.remove, removeAll, + * retainAll, and clear operations. It does not support + * the add or addAll operations. + * + *

The view's iterator 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. + */ + @Override + public Collection values() { + Collection 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 Iterator.remove, + * Set.remove, removeAll, retainAll, and + * clear operations. It does not support the add or + * addAll operations. + * + *

The view's iterator 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. + */ + @Override + public Set> entrySet() { + Set> 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 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 elements() { + return new ValueIterator(); + } + + /* ---------------- Iterator Support -------------- */ + + abstract class HashIterator { + int nextSegmentIndex; + int nextTableIndex; + HashEntry[] currentTable; + HashEntry nextEntry; + HashEntry lastReturned; + K currentKey; // Strong reference to weak key (prevents gc) + + 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 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() { + while (nextEntry != null) { + if (nextEntry.key() != null) { + return true; + } + advance(); + } + + return false; + } + + HashEntry nextEntry() { + do { + if (nextEntry == null) { + throw new NoSuchElementException(); + } + + lastReturned = nextEntry; + currentKey = lastReturned.key(); + advance(); + } while (currentKey == null); // Skip GC'd keys + + return lastReturned; + } + + public void remove() { + if (lastReturned == null) { + throw new IllegalStateException(); + } + ConcurrentWeakHashMap.this.remove(currentKey); + lastReturned = null; + } + } + + final class KeyIterator + extends HashIterator implements Iterator, Enumeration { + + public K next() { + return super.nextEntry().key(); + } + + public K nextElement() { + return super.nextEntry().key(); + } + } + + final class ValueIterator + extends HashIterator implements Iterator, Enumeration { + + public V next() { + return super.nextEntry().value(); + } + + public V nextElement() { + return super.nextEntry().value(); + } + } + + /* + * This class is needed for JDK5 compatibility. + */ + static class SimpleEntry implements Entry, Serializable { + private static final long serialVersionUID = -8499721149061103585L; + + private final K key; + + private V value; + + public SimpleEntry(K key, V value) { + this.key = key; + this.value = value; + + } + + public SimpleEntry(Entry entry) { + this.key = entry.getKey(); + this.value = entry.getValue(); + + } + + public K getKey() { + return key; + } + + public V getValue() { + return value; + } + + public V setValue(V value) { + V oldValue = this.value; + this.value = value; + return oldValue; + } + + @Override + public boolean equals(Object o) { + if (!(o instanceof Map.Entry)) { + return false; + } + @SuppressWarnings("unchecked") + Map.Entry e = (Map.Entry) o; + return eq(key, e.getKey()) && eq(value, e.getValue()); + } + + @Override + public int hashCode() { + return (key == null? 0 : key.hashCode()) ^ (value == null? 0 : value.hashCode()); + } + + @Override + public String toString() { + return key + "=" + value; + } + + private static boolean eq(Object o1, Object o2) { + return o1 == null? o2 == null : o1.equals(o2); + } + } + + /** + * Custom Entry class used by EntryIterator.next(), that relays setValue + * changes to the underlying map. + */ + final class WriteThroughEntry extends SimpleEntry { + private static final long serialVersionUID = -7900634345345313646L; + + 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 can + * not guarantee more. + */ + @Override + public V setValue(V value) { + + if (value == null) { + throw new NullPointerException(); + } + V v = super.setValue(value); + ConcurrentWeakHashMap.this.put(getKey(), value); + return v; + } + + } + + final class EntryIterator extends HashIterator implements + Iterator> { + public Map.Entry next() { + HashEntry e = super.nextEntry(); + return new WriteThroughEntry(e.key(), e.value()); + } + } + + final class KeySet extends AbstractSet { + @Override + public Iterator iterator() { + + return new KeyIterator(); + } + + @Override + public int size() { + return ConcurrentWeakHashMap.this.size(); + } + + @Override + public boolean isEmpty() { + return ConcurrentWeakHashMap.this.isEmpty(); + } + + @Override + public boolean contains(Object o) { + return ConcurrentWeakHashMap.this.containsKey(o); + } + + @Override + public boolean remove(Object o) { + return ConcurrentWeakHashMap.this.remove(o) != null; + + } + + @Override + public void clear() { + ConcurrentWeakHashMap.this.clear(); + } + } + + final class Values extends AbstractCollection { + @Override + public Iterator iterator() { + return new ValueIterator(); + } + + @Override + public int size() { + return ConcurrentWeakHashMap.this.size(); + } + + @Override + public boolean isEmpty() { + return ConcurrentWeakHashMap.this.isEmpty(); + } + + @Override + public boolean contains(Object o) { + return ConcurrentWeakHashMap.this.containsValue(o); + } + + @Override + public void clear() { + ConcurrentWeakHashMap.this.clear(); + } + } + + final class EntrySet extends AbstractSet> { + @Override + public Iterator> iterator() { + return new EntryIterator(); + } + + @Override + public boolean contains(Object o) { + if (!(o instanceof Map.Entry)) { + return false; + } + Map.Entry e = (Map.Entry) o; + V v = ConcurrentWeakHashMap.this.get(e.getKey()); + return v != null && v.equals(e.getValue()); + } + + @Override + public boolean remove(Object o) { + if (!(o instanceof Map.Entry)) { + return false; + } + Map.Entry e = (Map.Entry) o; + return ConcurrentWeakHashMap.this.remove(e.getKey(), e.getValue()); + } + + @Override + public int size() { + return ConcurrentWeakHashMap.this.size(); + } + + @Override + public boolean isEmpty() { + return ConcurrentWeakHashMap.this.isEmpty(); + } + + @Override + public void clear() { + ConcurrentWeakHashMap.this.clear(); + } + } + + /* ---------------- Serialization Support -------------- */ + + /** + * Save the state of the ConcurrentReferenceHashMap 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(ObjectOutputStream s) throws IOException { + s.defaultWriteObject(); + + for (int k = 0; k < segments.length; ++ k) { + Segment seg = segments[k]; + seg.lock(); + try { + HashEntry[] tab = seg.table; + for (int i = 0; i < tab.length; ++ i) { + for (HashEntry e = tab[i]; e != null; e = e.next) { + K key = e.key(); + if (key == null) { + continue; + } + + s.writeObject(key); + s.writeObject(e.value()); + } + } + } finally { + seg.unlock(); + } + } + s.writeObject(null); + s.writeObject(null); + } + + /** + * Reconstitute the ConcurrentReferenceHashMap instance from a + * stream (i.e. deserialize it). + * + * @param s the stream + */ + @SuppressWarnings("unchecked") + private void readObject(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); + } + } +}