/*
* 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 jsr166e;
import jsr166e.LongAdder;
import java.util.Map;
import java.util.Set;
import java.util.Collection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.AbstractCollection;
import java.util.Hashtable;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Enumeration;
import java.util.ConcurrentModificationException;
import java.util.NoSuchElementException;
import java.util.concurrent.ConcurrentMap;
import java.io.Serializable;
/**
* A hash table supporting full concurrency of retrievals and
* high 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
* {@code Hashtable}. However, even though all operations are
* thread-safe, retrieval operations do not entail locking,
* and there is not any support for locking the entire table
* in a way that prevents all access. This class is fully
* interoperable with {@code Hashtable} in programs that rely on its
* thread safety but not on its synchronization details.
*
*
Retrieval operations (including {@code get}) generally do not
* block, so may overlap with update operations (including {@code put}
* and {@code remove}). Retrievals reflect the results of the most
* recently completed update operations holding upon their
* onset. For aggregate operations such as {@code putAll} and {@code
* clear}, 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
* not throw {@link ConcurrentModificationException}.
* However, iterators are designed to be used by only one thread at a
* time. Bear in mind that the results of aggregate status methods
* including {@code size}, {@code isEmpty}, and {@code containsValue}
* are typically useful only when a map is not undergoing concurrent
* updates in other threads. Otherwise the results of these methods
* reflect transient states that may be adequate for monitoring
* purposes, but not for program control.
*
*
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. Also, for
* compatability with previous versions of this class, constructors
* may optionally specify an expected {@code concurrencyLevel} as an
* additional hint for internal sizing.
*
*
This class and its views and iterators implement all of the
* optional methods of the {@link Map} and {@link Iterator}
* interfaces.
*
*
Like {@link Hashtable} but unlike {@link HashMap}, this class
* does not allow {@code null} to be used as a key or value.
*
*
This class is a member of the
*
* Java Collections Framework.
*
*
jsr166e note: This class is a candidate replacement for
* java.util.concurrent.ConcurrentHashMap.
*
* @since 1.5
* @author Doug Lea
* @param the type of keys maintained by this map
* @param the type of mapped values
*/
public class ConcurrentHashMapV8
implements ConcurrentMap, Serializable {
private static final long serialVersionUID = 7249069246763182397L;
/**
* A function computing a mapping from the given key to a value,
* or null
if there is no mapping. This is a
* place-holder for an upcoming JDK8 interface.
*/
public static interface MappingFunction {
/**
* Returns a value for the given key, or null if there is no
* mapping. If this function throws an (unchecked) exception,
* the exception is rethrown to its caller, and no mapping is
* recorded. Because this function is invoked within
* atomicity control, the computation should be short and
* simple. The most common usage is to construct a new object
* serving as an initial mapped value.
*
* @param key the (non-null) key
* @return a value, or null if none
*/
V map(K key);
}
/*
* Overview:
*
* The primary design goal of this hash table is to maintain
* concurrent readability (typically method get(), but also
* iterators and related methods) while minimizing update
* contention.
*
* Each key-value mapping is held in a Node. Because Node fields
* can contain special values, they are defined using plain Object
* types. Similarly in turn, all internal methods that use them
* work off Object types. All public generic-typed methods relay
* in/out of these internal methods, supplying casts as needed.
*
* The table is lazily initialized to a power-of-two size upon the
* first insertion. Each bin in the table contains a (typically
* short) list of Nodes. Table accesses require volatile/atomic
* reads, writes, and CASes. Because there is no other way to
* arrange this without adding further indirections, we use
* intrinsics (sun.misc.Unsafe) operations. The lists of nodes
* within bins are always accurately traversable under volatile
* reads, so long as lookups check hash code and non-nullness of
* key and value before checking key equality. (All valid hash
* codes are nonnegative. Negative values are reserved for special
* forwarding nodes; see below.)
*
* A bin may be locked during update (insert, delete, and replace)
* operations. We do not want to waste the space required to
* associate a distinct lock object with each bin, so instead use
* the first node of a bin list itself as a lock, using builtin
* "synchronized" locks. These save space and we can live with
* only plain block-structured lock/unlock operations. Using the
* first node of a list as a lock does not by itself suffice
* though: When a node is locked, any update must first validate
* that it is still the first node, and retry if not. (Because new
* nodes are always appended to lists, once a node is first in a
* bin, it remains first until deleted or the bin becomes
* invalidated.) However, update operations can and usually do
* still traverse the bin until the point of update, which helps
* reduce cache misses on retries. This is a converse of sorts to
* the lazy locking technique described by Herlihy & Shavit. If
* there is no existing node during a put operation, then one can
* be CAS'ed in (without need for lock except in computeIfAbsent);
* the CAS serves as validation. This is on average the most
* common case for put operations -- under random hash codes, the
* distribution of nodes in bins follows a Poisson distribution
* (see http://en.wikipedia.org/wiki/Poisson_distribution) with a
* parameter of 0.5 on average under the default loadFactor of
* 0.75. The expected number of locks covering different elements
* (i.e., bins with 2 or more nodes) is approximately 10% at
* steady state under default settings. Lock contention
* probability for two threads accessing arbitrary distinct
* elements is, roughly, 1 / (8 * #elements).
*
* The table is resized when occupancy exceeds a threshold. Only
* a single thread performs the resize (using field "resizing", to
* arrange exclusion), but the table otherwise remains usable for
* both reads and updates. Resizing proceeds by transferring bins,
* one by one, from the table to the next table. Upon transfer,
* the old table bin contains only a special forwarding node (with
* negative hash code ("MOVED")) that contains the next table as
* its key. On encountering a forwarding node, access and update
* operations restart, using the new table. To ensure concurrent
* readability of traversals, transfers must proceed from the last
* bin (table.length - 1) up towards the first. Any traversal
* starting from the first bin can then arrange to move to the new
* table for the rest of the traversal without revisiting nodes.
* This constrains bin transfers to a particular order, and so can
* block indefinitely waiting for the next lock, and other threads
* cannot help with the transfer. However, expected stalls are
* infrequent enough to not warrant the additional overhead and
* complexity of access and iteration schemes that could admit
* out-of-order or concurrent bin transfers.
*
* A similar traversal scheme (not yet implemented) can apply to
* partial traversals during partitioned aggregate operations.
* Also, read-only operations give up if ever forwarded to a null
* table, which provides support for shutdown-style clearing,
* which is also not currently implemented.
*
* The element count is maintained using a LongAdder, which avoids
* contention on updates but can encounter cache thrashing if read
* too frequently during concurrent updates. To avoid reading so
* often, resizing is normally attempted only upon adding to a bin
* already holding two or more nodes. Under the default threshold
* (0.75), and uniform hash distributions, the probability of this
* occurring at threshold is around 13%, meaning that only about 1
* in 8 puts check threshold (and after resizing, many fewer do
* so). But this approximation has high variance for small table
* sizes, so we check on any collision for sizes <= 64. Further,
* to increase the probablity that a resize occurs soon enough, we
* offset the threshold (see THRESHOLD_OFFSET) by the expected
* number of puts between checks. This is currently set to 8, in
* accord with the default load factor. In practice, this is
* rarely overridden, and in any case is close enough to other
* plausible values not to waste dynamic probablity computation
* for more precision.
*/
/* ---------------- Constants -------------- */
/**
* The smallest allowed table capacity. Must be a power of 2, at
* least 2.
*/
static final int MINIMUM_CAPACITY = 2;
/**
* The largest allowed table capacity. Must be a power of 2, at
* most 1<<30.
*/
static final int MAXIMUM_CAPACITY = 1 << 30;
/**
* The default initial table capacity. Must be a power of 2, at
* least MINIMUM_CAPACITY and at most MAXIMUM_CAPACITY
*/
static final int DEFAULT_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. Unused, but
* defined for compatibility with previous versions of this class.
*/
static final int DEFAULT_CONCURRENCY_LEVEL = 16;
/**
* The count value to offset thesholds to compensate for checking
* for resizing only when inserting into bins with two or more
* elements. See above for explanation.
*/
static final int THRESHOLD_OFFSET = 8;
/**
* Special node hash value indicating to use table in node.key
* Must be negative.
*/
static final int MOVED = -1;
/* ---------------- Fields -------------- */
/**
* The array of bins. Lazily initialized upon first insertion.
* Size is always a power of two. Accessed directly by inner
* classes.
*/
transient volatile Node[] table;
/** The counter maintaining number of elements. */
private transient final LongAdder counter;
/** Nonzero when table is being initialized or resized. Updated via CAS. */
private transient volatile int resizing;
/** The target load factor for the table. */
private transient float loadFactor;
/** The next element count value upon which to resize the table. */
private transient int threshold;
/** The initial capacity of the table. */
private transient int initCap;
// views
transient Set keySet;
transient Set> entrySet;
transient Collection values;
/** For serialization compatability. Null unless serialized; see below */
Segment[] segments;
/**
* Applies a supplemental hash function to a given hashCode, which
* defends against poor quality hash functions. The result must
* be non-negative, and for reasonable performance must have good
* avalanche properties; i.e., that each bit of the argument
* affects each bit (except sign bit) of the result.
*/
private static final int spread(int h) {
// Apply base step of MurmurHash; see http://code.google.com/p/smhasher/
h ^= h >>> 16;
h *= 0x85ebca6b;
h ^= h >>> 13;
h *= 0xc2b2ae35;
return (h >>> 16) ^ (h & 0x7fffffff); // mask out sign bit
}
/**
* Key-value entry. Note that this is never exported out as a
* user-visible Map.Entry.
*/
static final class Node {
final int hash;
final Object key;
volatile Object val;
volatile Node next;
Node(int hash, Object key, Object val, Node next) {
this.hash = hash;
this.key = key;
this.val = val;
this.next = next;
}
}
/*
* Volatile access nethods are used for table elements as well as
* elements of in-progress next table while resizing. Uses in
* access and update methods are null checked by callers, and
* implicitly bounds-checked, relying on the invariants that tab
* arrays have non-zero size, and all indices are masked with
* (tab.length - 1) which is never negative and always less than
* length. The "relaxed" non-volatile forms are used only during
* table initialization. The only other usage is in
* HashIterator.advance, which performs explicit checks.
*/
static final Node tabAt(Node[] tab, int i) { // used in HashIterator
return (Node)UNSAFE.getObjectVolatile(tab, ((long)i<= threshold)
grow(0);
break;
}
}
}
if (oldVal == null)
counter.increment();
return oldVal;
}
/**
* Covers the four public remove/replace methods: Replaces node
* value with v, conditional upon match of cv if non-null. If
* resulting value is null, delete.
*/
private final Object internalReplace(Object k, Object v, Object cv) {
int h = spread(k.hashCode());
Object oldVal = null;
Node e; int i;
Node[] tab = table;
while (tab != null &&
(e = tabAt(tab, i = (tab.length - 1) & h)) != null) {
if (e.hash < 0)
tab = (Node[])e.key;
else {
boolean validated = false;
boolean deleted = false;
synchronized (e) {
Node pred = null;
Node first = e;
for (;;) {
Object ek, ev;
if ((ev = e.val) == null)
break;
if (e.hash == h && (ek = e.key) != null &&
(k == ek || k.equals(ek))) {
if (tabAt(tab, i) == first) {
validated = true;
if (cv == null || cv == ev || cv.equals(ev)) {
oldVal = ev;
if ((e.val = v) == null) {
deleted = true;
Node en = e.next;
if (pred != null)
pred.next = en;
else
setTabAt(tab, i, en);
}
}
}
break;
}
pred = e;
if ((e = e.next) == null) {
if (tabAt(tab, i) == first)
validated = true;
break;
}
}
}
if (validated) {
if (deleted)
counter.decrement();
break;
}
}
}
return oldVal;
}
/** Implementation for computeIfAbsent and compute */
@SuppressWarnings("unchecked")
private final V internalCompute(K k,
MappingFunction super K, ? extends V> f,
boolean replace) {
int h = spread(k.hashCode());
V val = null;
boolean added = false;
boolean validated = false;
Node[] tab = table;
do {
Node e; int i;
if (tab == null)
tab = grow(0);
else if ((e = tabAt(tab, i = (tab.length - 1) & h)) == null) {
Node node = new Node(h, k, null, null);
synchronized (node) {
if (casTabAt(tab, i, null, node)) {
validated = true;
try {
val = f.map(k);
if (val != null) {
node.val = val;
added = true;
}
} finally {
if (!added)
setTabAt(tab, i, null);
}
}
}
}
else if (e.hash < 0)
tab = (Node[])e.key;
else if (Thread.holdsLock(e))
throw new IllegalStateException("Recursive map computation");
else {
boolean checkSize = false;
synchronized (e) {
Node first = e;
for (;;) {
Object ek, ev;
if ((ev = e.val) == null)
break;
if (e.hash == h && (ek = e.key) != null &&
(k == ek || k.equals(ek))) {
if (tabAt(tab, i) == first) {
validated = true;
if (replace && (ev = f.map(k)) != null)
e.val = ev;
val = (V)ev;
}
break;
}
Node last = e;
if ((e = e.next) == null) {
if (tabAt(tab, i) == first) {
validated = true;
if ((val = f.map(k)) != null) {
last.next = new Node(h, k, val, null);
added = true;
if (last != first || tab.length <= 64)
checkSize = true;
}
}
break;
}
}
}
if (checkSize && tab.length < MAXIMUM_CAPACITY &&
resizing == 0 && counter.sum() >= threshold)
grow(0);
}
} while (!validated);
if (added)
counter.increment();
return val;
}
/*
* Reclassifies nodes in each bin 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.
*
* Transfers are done from the bottom up to preserve iterator
* traversability. On each step, the old bin is locked,
* moved/copied, and then replaced with a forwarding node.
*/
private static final void transfer(Node[] tab, Node[] nextTab) {
int n = tab.length;
int mask = nextTab.length - 1;
Node fwd = new Node(MOVED, nextTab, null, null);
for (int i = n - 1; i >= 0; --i) {
for (Node e;;) {
if ((e = tabAt(tab, i)) == null) {
if (casTabAt(tab, i, e, fwd))
break;
}
else {
boolean validated = false;
synchronized (e) {
int idx = e.hash & mask;
Node lastRun = e;
for (Node p = e.next; p != null; p = p.next) {
int j = p.hash & mask;
if (j != idx) {
idx = j;
lastRun = p;
}
}
if (tabAt(tab, i) == e) {
validated = true;
relaxedSetTabAt(nextTab, idx, lastRun);
for (Node p = e; p != lastRun; p = p.next) {
int h = p.hash;
int j = h & mask;
Node r = relaxedTabAt(nextTab, j);
relaxedSetTabAt(nextTab, j,
new Node(h, p.key, p.val, r));
}
setTabAt(tab, i, fwd);
}
}
if (validated)
break;
}
}
}
}
/**
* If not already resizing, initializes or creates next table and
* transfers bins. Rechecks occupancy after a transfer to see if
* another resize is already needed because resizings are lagging
* additions.
*
* @param sizeHint overridden capacity target (nonzero only from putAll)
* @return current table
*/
private final Node[] grow(int sizeHint) {
if (resizing == 0 &&
UNSAFE.compareAndSwapInt(this, resizingOffset, 0, 1)) {
try {
for (;;) {
int cap, n;
Node[] tab = table;
if (tab == null) {
int c = initCap;
if (c < sizeHint)
c = sizeHint;
if (c == DEFAULT_CAPACITY)
cap = c;
else if (c >= MAXIMUM_CAPACITY)
cap = MAXIMUM_CAPACITY;
else {
cap = MINIMUM_CAPACITY;
while (cap < c)
cap <<= 1;
}
}
else if ((n = tab.length) < MAXIMUM_CAPACITY &&
(sizeHint <= 0 || n < sizeHint))
cap = n << 1;
else
break;
threshold = (int)(cap * loadFactor) - THRESHOLD_OFFSET;
Node[] nextTab = new Node[cap];
if (tab != null)
transfer(tab, nextTab);
table = nextTab;
if (tab == null || cap >= MAXIMUM_CAPACITY ||
(sizeHint > 0 && cap >= sizeHint) ||
counter.sum() < threshold)
break;
}
} finally {
resizing = 0;
}
}
else if (table == null)
Thread.yield(); // lost initialization race; just spin
return table;
}
/**
* Implementation for putAll and constructor with Map
* argument. Tries to first override initial capacity or grow
* based on map size to pre-allocate table space.
*/
private final void internalPutAll(Map extends K, ? extends V> m) {
int s = m.size();
grow((s >= (MAXIMUM_CAPACITY >>> 1)) ? s : s + (s >>> 1));
for (Map.Entry extends K, ? extends V> e : m.entrySet()) {
Object k = e.getKey();
Object v = e.getValue();
if (k == null || v == null)
throw new NullPointerException();
internalPut(k, v, true);
}
}
/**
* Implementation for clear. Steps through each bin, removing all nodes.
*/
private final void internalClear() {
long deletions = 0L;
int i = 0;
Node[] tab = table;
while (tab != null && i < tab.length) {
Node e = tabAt(tab, i);
if (e == null)
++i;
else if (e.hash < 0)
tab = (Node[])e.key;
else {
boolean validated = false;
synchronized (e) {
if (tabAt(tab, i) == e) {
validated = true;
do {
if (e.val != null) {
e.val = null;
++deletions;
}
} while ((e = e.next) != null);
setTabAt(tab, i, null);
}
}
if (validated) {
++i;
if (deletions > THRESHOLD_OFFSET) { // bound lag in counts
counter.add(-deletions);
deletions = 0L;
}
}
}
}
if (deletions != 0L)
counter.add(-deletions);
}
/**
* Base class for key, value, and entry iterators, plus internal
* implementations of public traversal-based methods, to avoid
* duplicating traversal code.
*/
class HashIterator {
private Node next; // the next entry to return
private Node[] tab; // current table; updated if resized
private Node lastReturned; // the last entry returned, for remove
private Object nextVal; // cached value of next
private int index; // index of bin to use next
private int baseIndex; // current index of initial table
private final int baseSize; // initial table size
HashIterator() {
Node[] t = tab = table;
if (t == null)
baseSize = 0;
else {
baseSize = t.length;
advance(null);
}
}
public final boolean hasNext() { return next != null; }
public final boolean hasMoreElements() { return next != null; }
/**
* Advances next. Normally, iteration proceeds bin-by-bin
* traversing lists. However, if the table has been resized,
* then all future steps must traverse both the bin at the
* current index as well as at (index + baseSize); and so on
* for further resizings. To paranoically cope with potential
* (improper) sharing of iterators across threads, table reads
* are bounds-checked.
*/
final void advance(Node e) {
for (;;) {
Node[] t; int i; // for bounds checks
if (e != null) {
Object ek = e.key, ev = e.val;
if (ev != null && ek != null) {
nextVal = ev;
next = e;
break;
}
e = e.next;
}
else if (baseIndex < baseSize && (t = tab) != null &&
t.length > (i = index) && i >= 0) {
if ((e = tabAt(t, i)) != null && e.hash < 0) {
tab = (Node[])e.key;
e = null;
}
else if (i + baseSize < t.length)
index += baseSize; // visit forwarded upper slots
else
index = ++baseIndex;
}
else {
next = null;
break;
}
}
}
final Object nextKey() {
Node e = next;
if (e == null)
throw new NoSuchElementException();
Object k = e.key;
advance((lastReturned = e).next);
return k;
}
final Object nextValue() {
Node e = next;
if (e == null)
throw new NoSuchElementException();
Object v = nextVal;
advance((lastReturned = e).next);
return v;
}
final WriteThroughEntry nextEntry() {
Node e = next;
if (e == null)
throw new NoSuchElementException();
WriteThroughEntry entry =
new WriteThroughEntry(e.key, nextVal);
advance((lastReturned = e).next);
return entry;
}
public final void remove() {
if (lastReturned == null)
throw new IllegalStateException();
ConcurrentHashMapV8.this.remove(lastReturned.key);
lastReturned = null;
}
/** Helper for serialization */
final void writeEntries(java.io.ObjectOutputStream s)
throws java.io.IOException {
Node e;
while ((e = next) != null) {
s.writeObject(e.key);
s.writeObject(nextVal);
advance(e.next);
}
}
/** Helper for containsValue */
final boolean containsVal(Object value) {
if (value != null) {
Node e;
while ((e = next) != null) {
Object v = nextVal;
if (value == v || value.equals(v))
return true;
advance(e.next);
}
}
return false;
}
/** Helper for Map.hashCode */
final int mapHashCode() {
int h = 0;
Node e;
while ((e = next) != null) {
h += e.key.hashCode() ^ nextVal.hashCode();
advance(e.next);
}
return h;
}
/** Helper for Map.toString */
final String mapToString() {
Node e = next;
if (e == null)
return "{}";
StringBuilder sb = new StringBuilder();
sb.append('{');
for (;;) {
sb.append(e.key == this ? "(this Map)" : e.key);
sb.append('=');
sb.append(nextVal == this ? "(this Map)" : nextVal);
advance(e.next);
if ((e = next) != null)
sb.append(',').append(' ');
else
return sb.append('}').toString();
}
}
}
/* ---------------- 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 may use this value as
* a sizing hint.
* @throws IllegalArgumentException if the initial capacity is
* negative or the load factor or concurrencyLevel are
* nonpositive.
*/
public ConcurrentHashMapV8(int initialCapacity,
float loadFactor, int concurrencyLevel) {
if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0)
throw new IllegalArgumentException();
this.initCap = initialCapacity;
this.loadFactor = loadFactor;
this.counter = new LongAdder();
}
/**
* 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 ConcurrentHashMapV8(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 ConcurrentHashMapV8(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 ConcurrentHashMapV8() {
this(DEFAULT_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 ConcurrentHashMapV8(Map extends K, ? extends V> m) {
this(DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
if (m == null)
throw new NullPointerException();
internalPutAll(m);
}
/**
* Returns {@code true} if this map contains no key-value mappings.
*
* @return {@code true} if this map contains no key-value mappings
*/
public boolean isEmpty() {
return counter.sum() <= 0L; // ignore transient negative values
}
/**
* Returns the number of key-value mappings in this map. If the
* map contains more than {@code Integer.MAX_VALUE} elements, returns
* {@code Integer.MAX_VALUE}.
*
* @return the number of key-value mappings in this map
*/
public int size() {
long n = counter.sum();
return ((n >>> 31) == 0) ? (int)n : (n < 0L) ? 0 : Integer.MAX_VALUE;
}
/**
* 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
*/
@SuppressWarnings("unchecked")
public V get(Object key) {
if (key == null)
throw new NullPointerException();
return (V)internalGet(key);
}
/**
* Tests if the specified object is a key in this table.
*
* @param key possible key
* @return {@code true} if and only if the specified object
* is a key in this table, as determined by the
* {@code equals} method; {@code false} otherwise.
* @throws NullPointerException if the specified key is null
*/
public boolean containsKey(Object key) {
if (key == null)
throw new NullPointerException();
return internalGet(key) != null;
}
/**
* Returns {@code 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 {@code containsKey}.
*
* @param value value whose presence in this map is to be tested
* @return {@code true} if this map maps one or more keys to the
* specified value
* @throws NullPointerException if the specified value is null
*/
public boolean containsValue(Object value) {
if (value == null)
throw new NullPointerException();
return new HashIterator().containsVal(value);
}
/**
* 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 {@code true} if and only if some key maps to the
* {@code value} argument in this table as
* determined by the {@code equals} method;
* {@code 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 {@code 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 {@code key}, or
* {@code null} if there was no mapping for {@code key}
* @throws NullPointerException if the specified key or value is null
*/
@SuppressWarnings("unchecked")
public V put(K key, V value) {
if (key == null || value == null)
throw new NullPointerException();
return (V)internalPut(key, value, true);
}
/**
* {@inheritDoc}
*
* @return the previous value associated with the specified key,
* or {@code null} 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) {
if (key == null || value == null)
throw new NullPointerException();
return (V)internalPut(key, value, false);
}
/**
* 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) {
if (m == null)
throw new NullPointerException();
internalPutAll(m);
}
/**
* If the specified key is not already associated with a value,
* computes its value using the given mappingFunction, and if
* non-null, enters it into the map. This is equivalent to
*
*
* if (map.containsKey(key))
* return map.get(key);
* value = mappingFunction.map(key);
* if (value != null)
* map.put(key, value);
* return value;
*
*
* except that the action is performed atomically. Some attempted
* update operations on this map by other threads may be blocked
* while computation is in progress, so the computation should be
* short and simple, and must not attempt to update any other
* mappings of this Map. The most appropriate usage is to
* construct a new object serving as an initial mapped value, or
* memoized result, as in:
* {@code
* map.computeIfAbsent(key, new MappingFunction() {
* public V map(K k) { return new Value(f(k)); }};
* }
*
* @param key key with which the specified value is to be associated
* @param mappingFunction the function to compute a value
* @return the current (existing or computed) value associated with
* the specified key, or {@code null} if the computation
* returned {@code null}.
* @throws NullPointerException if the specified key or mappingFunction
* is null,
* @throws IllegalStateException if the computation detectably
* attempts a recursive update to this map that would
* otherwise never complete.
* @throws RuntimeException or Error if the mappingFunction does so,
* in which case the mapping is left unestablished.
*/
public V computeIfAbsent(K key, MappingFunction super K, ? extends V> mappingFunction) {
if (key == null || mappingFunction == null)
throw new NullPointerException();
return internalCompute(key, mappingFunction, false);
}
/**
* Computes the value associated with the given key using the given
* mappingFunction, and if non-null, enters it into the map. This
* is equivalent to
*
*
* value = mappingFunction.map(key);
* if (value != null)
* map.put(key, value);
* else
* value = map.get(key);
* return value;
*
*
* except that the action is performed atomically. Some attempted
* update operations on this map by other threads may be blocked
* while computation is in progress, so the computation should be
* short and simple, and must not attempt to update any other
* mappings of this Map.
*
* @param key key with which the specified value is to be associated
* @param mappingFunction the function to compute a value
* @return the current value associated with
* the specified key, or {@code null} if the computation
* returned {@code null} and the value was not otherwise present.
* @throws NullPointerException if the specified key or mappingFunction
* is null,
* @throws IllegalStateException if the computation detectably
* attempts a recursive update to this map that would
* otherwise never complete.
* @throws RuntimeException or Error if the mappingFunction does so,
* in which case the mapping is unchanged.
*/
public V compute(K key, MappingFunction super K, ? extends V> mappingFunction) {
if (key == null || mappingFunction == null)
throw new NullPointerException();
return internalCompute(key, mappingFunction, true);
}
/**
* 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 {@code key}, or
* {@code null} if there was no mapping for {@code key}
* @throws NullPointerException if the specified key is null
*/
@SuppressWarnings("unchecked")
public V remove(Object key) {
if (key == null)
throw new NullPointerException();
return (V)internalReplace(key, null, null);
}
/**
* {@inheritDoc}
*
* @throws NullPointerException if the specified key is null
*/
public boolean remove(Object key, Object value) {
if (key == null)
throw new NullPointerException();
if (value == null)
return false;
return internalReplace(key, null, value) != null;
}
/**
* {@inheritDoc}
*
* @throws NullPointerException if any of the arguments are null
*/
public boolean replace(K key, V oldValue, V newValue) {
if (key == null || oldValue == null || newValue == null)
throw new NullPointerException();
return internalReplace(key, newValue, oldValue) != null;
}
/**
* {@inheritDoc}
*
* @return the previous value associated with the specified key,
* or {@code null} if there was no mapping for the key
* @throws NullPointerException if the specified key or value is null
*/
@SuppressWarnings("unchecked")
public V replace(K key, V value) {
if (key == null || value == null)
throw new NullPointerException();
return (V)internalReplace(key, value, null);
}
/**
* Removes all of the mappings from this map.
*/
public void clear() {
internalClear();
}
/**
* 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 {@code Iterator.remove}, {@code Set.remove},
* {@code removeAll}, {@code retainAll}, and {@code clear}
* operations. It does not support the {@code add} or
* {@code addAll} operations.
*
* The view's {@code 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.
*/
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 {@code Iterator.remove},
* {@code Collection.remove}, {@code removeAll},
* {@code retainAll}, and {@code clear} operations. It does not
* support the {@code add} or {@code addAll} operations.
*
* The view's {@code 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.
*/
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 {@code Iterator.remove}, {@code Set.remove},
* {@code removeAll}, {@code retainAll}, and {@code clear}
* operations. It does not support the {@code add} or
* {@code addAll} operations.
*
* The view's {@code 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.
*/
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();
}
/**
* Returns the hash code value for this {@link Map}, i.e.,
* the sum of, for each key-value pair in the map,
* {@code key.hashCode() ^ value.hashCode()}.
*
* @return the hash code value for this map
*/
public int hashCode() {
return new HashIterator().mapHashCode();
}
/**
* Returns a string representation of this map. The string
* representation consists of a list of key-value mappings (in no
* particular order) enclosed in braces ("{@code {}}"). Adjacent
* mappings are separated by the characters {@code ", "} (comma
* and space). Each key-value mapping is rendered as the key
* followed by an equals sign ("{@code =}") followed by the
* associated value.
*
* @return a string representation of this map
*/
public String toString() {
return new HashIterator().mapToString();
}
/**
* Compares the specified object with this map for equality.
* Returns {@code true} if the given object is a map with the same
* mappings as this map. This operation may return misleading
* results if either map is concurrently modified during execution
* of this method.
*
* @param o object to be compared for equality with this map
* @return {@code true} if the specified object is equal to this map
*/
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Map))
return false;
Map,?> m = (Map,?>) o;
try {
for (Map.Entry e : this.entrySet())
if (! e.getValue().equals(m.get(e.getKey())))
return false;
for (Map.Entry,?> e : m.entrySet()) {
Object k = e.getKey();
Object v = e.getValue();
if (k == null || v == null || !v.equals(get(k)))
return false;
}
return true;
} catch (ClassCastException unused) {
return false;
} catch (NullPointerException unused) {
return false;
}
}
/**
* Custom Entry class used by EntryIterator.next(), that relays
* setValue changes to the underlying map.
*/
final class WriteThroughEntry extends AbstractMap.SimpleEntry {
@SuppressWarnings("unchecked")
WriteThroughEntry(Object k, Object v) {
super((K)k, (V)v);
}
/**
* Sets our entry's value and writes 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);
ConcurrentHashMapV8.this.put(getKey(), value);
return v;
}
}
final class KeyIterator extends HashIterator
implements Iterator, Enumeration {
@SuppressWarnings("unchecked")
public final K next() { return (K)super.nextKey(); }
@SuppressWarnings("unchecked")
public final K nextElement() { return (K)super.nextKey(); }
}
final class ValueIterator extends HashIterator
implements Iterator, Enumeration {
@SuppressWarnings("unchecked")
public final V next() { return (V)super.nextValue(); }
@SuppressWarnings("unchecked")
public final V nextElement() { return (V)super.nextValue(); }
}
final class EntryIterator extends HashIterator
implements Iterator> {
public final Map.Entry next() { return super.nextEntry(); }
}
final class KeySet extends AbstractSet {
public int size() {
return ConcurrentHashMapV8.this.size();
}
public boolean isEmpty() {
return ConcurrentHashMapV8.this.isEmpty();
}
public void clear() {
ConcurrentHashMapV8.this.clear();
}
public Iterator iterator() {
return new KeyIterator();
}
public boolean contains(Object o) {
return ConcurrentHashMapV8.this.containsKey(o);
}
public boolean remove(Object o) {
return ConcurrentHashMapV8.this.remove(o) != null;
}
}
final class Values extends AbstractCollection {
public int size() {
return ConcurrentHashMapV8.this.size();
}
public boolean isEmpty() {
return ConcurrentHashMapV8.this.isEmpty();
}
public void clear() {
ConcurrentHashMapV8.this.clear();
}
public Iterator iterator() {
return new ValueIterator();
}
public boolean contains(Object o) {
return ConcurrentHashMapV8.this.containsValue(o);
}
}
final class EntrySet extends AbstractSet> {
public int size() {
return ConcurrentHashMapV8.this.size();
}
public boolean isEmpty() {
return ConcurrentHashMapV8.this.isEmpty();
}
public void clear() {
ConcurrentHashMapV8.this.clear();
}
public Iterator> iterator() {
return new EntryIterator();
}
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry,?> e = (Map.Entry,?>)o;
V v = ConcurrentHashMapV8.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 ConcurrentHashMapV8.this.remove(e.getKey(), e.getValue());
}
}
/* ---------------- Serialization Support -------------- */
/**
* Helper class used in previous version, declared for the sake of
* serialization compatibility
*/
static class Segment extends java.util.concurrent.locks.ReentrantLock
implements Serializable {
private static final long serialVersionUID = 2249069246763182397L;
final float loadFactor;
Segment(float lf) { this.loadFactor = lf; }
}
/**
* Saves the state of the {@code ConcurrentHashMapV8} instance to a
* stream (i.e., serializes 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.
*/
@SuppressWarnings("unchecked")
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
if (segments == null) { // for serialization compatibility
segments = (Segment[])
new Segment,?>[DEFAULT_CONCURRENCY_LEVEL];
for (int i = 0; i < segments.length; ++i)
segments[i] = new Segment(loadFactor);
}
s.defaultWriteObject();
new HashIterator().writeEntries(s);
s.writeObject(null);
s.writeObject(null);
segments = null; // throw away
}
/**
* Reconstitutes the instance from a
* stream (i.e., deserializes it).
* @param s the stream
*/
@SuppressWarnings("unchecked")
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
// find load factor in a segment, if one exists
if (segments != null && segments.length != 0)
this.loadFactor = segments[0].loadFactor;
else
this.loadFactor = DEFAULT_LOAD_FACTOR;
this.initCap = DEFAULT_CAPACITY;
LongAdder ct = new LongAdder(); // force final field write
UNSAFE.putObjectVolatile(this, counterOffset, ct);
this.segments = null; // unneeded
// 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 counterOffset;
private static final long resizingOffset;
private static final long ABASE;
private static final int ASHIFT;
static {
int ss;
try {
UNSAFE = getUnsafe();
Class> k = ConcurrentHashMapV8.class;
counterOffset = UNSAFE.objectFieldOffset
(k.getDeclaredField("counter"));
resizingOffset = UNSAFE.objectFieldOffset
(k.getDeclaredField("resizing"));
Class> sc = Node[].class;
ABASE = UNSAFE.arrayBaseOffset(sc);
ss = UNSAFE.arrayIndexScale(sc);
} catch (Exception e) {
throw new Error(e);
}
if ((ss & (ss-1)) != 0)
throw new Error("data type scale not a power of two");
ASHIFT = 31 - Integer.numberOfLeadingZeros(ss);
}
/**
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
* Replace with a simple call to Unsafe.getUnsafe when integrating
* into a jdk.
*
* @return a sun.misc.Unsafe
*/
private static sun.misc.Unsafe getUnsafe() {
try {
return sun.misc.Unsafe.getUnsafe();
} catch (SecurityException se) {
try {
return java.security.AccessController.doPrivileged
(new java.security
.PrivilegedExceptionAction() {
public sun.misc.Unsafe run() throws Exception {
java.lang.reflect.Field f = sun.misc
.Unsafe.class.getDeclaredField("theUnsafe");
f.setAccessible(true);
return (sun.misc.Unsafe) f.get(null);
}});
} catch (java.security.PrivilegedActionException e) {
throw new RuntimeException("Could not initialize intrinsics",
e.getCause());
}
}
}
}