/*
* 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
* compatibility 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 {@code 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. And similarly, so do the internal
* methods of auxiliary iterator and view classes. All public
* generic typed methods relay in/out of these internal methods,
* supplying null-checks and 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 list of
* Nodes (most often, zero or one Node). 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 value before checking key equality. (All valid
* hash codes are nonnegative. Negative values are reserved for
* special forwarding nodes; see below.)
*
* Insertion (via put or putIfAbsent) of the first node in an
* empty bin is performed by just CASing it to the bin. This is
* on average by far the most common case for put operations.
* Other update operations (insert, delete, and replace) require
* locks. 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 plain "synchronized"
* locks. These save space and we can live with 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, operations
* that only conditionally update can and sometimes do inspect
* nodes until the point of update. This is a converse of sorts to
* the lazy locking technique described by Herlihy & Shavit.
*
* The main disadvantage of this approach is that most update
* operations on other nodes in a bin list protected by the same
* lock can stall, for example when user equals() or mapping
* functions take a long time. However, statistically, this is
* not a common enough problem to outweigh the time/space overhead
* of alternatives: Under random hash codes, the frequency of
* nodes in bins follows a Poisson distribution
* (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. Lock contention probability for two threads
* accessing distinct elements is roughly 1 / (8 * #elements).
* Function "spread" performs hashCode randomization that improves
* the likelihood that these assumptions hold unless users define
* exactly the same value for too many hashCodes.
*
* 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
* 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 field) 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. Upon seeing a
* forwarding node, traversals (see class InternalIterator)
* 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 of access and iteration schemes that
* could admit out-of-order or concurrent bin transfers.
*
* This traversal scheme also applies to partial traversals of
* ranges of bins (via an alternate InternalIterator constructor)
* to support partitioned aggregate operations (that are not
* otherwise implemented yet). 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.
*
* Lazy table initialization minimizes footprint until first use,
* and also avoids resizings when the first operation is from a
* putAll, constructor with map argument, or deserialization.
* These cases attempt to override the targetCapacity used in
* growTable (which may harmlessly fail to take effect in cases of
* races with other ongoing resizings).
*
* The element count is maintained using a LongAdder, which avoids
* contention on updates but can encounter cache thrashing if read
* too frequently during concurrent access. To avoid reading so
* often, resizing is normally attempted only upon adding to a bin
* already holding two or more nodes. Under the default load
* factor 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 probability 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 default
* is rarely overridden, and in any case is close enough to other
* plausible values not to waste dynamic probability computation
* for the sake of more precision.
*
* Maintaining API and serialization compatibility with previous
* versions of this class introduces several oddities. Mainly: We
* leave untouched but unused constructor arguments refering to
* concurrencyLevel. We also declare an unused "Segment" class
* that is instantiated in minimal form only when serializing.
*/
/* ---------------- Constants -------------- */
/**
* The largest allowed table capacity. Must be a power of 2, at
* most 1<<30 to stay within Java array size limits.
*/
private static final int MAXIMUM_CAPACITY = 1 << 30;
/**
* The default initial table capacity. Must be a power of 2
* (i.e., at least 1) and at most MAXIMUM_CAPACITY.
*/
private static final int DEFAULT_CAPACITY = 16;
/**
* The default load factor for this table, used when not otherwise
* specified in a constructor.
*/
private 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.
*/
private static final int DEFAULT_CONCURRENCY_LEVEL = 16;
/**
* The count value to offset thresholds to compensate for checking
* for the need to resize only when inserting into bins with two
* or more elements. See above for explanation.
*/
private static final int THRESHOLD_OFFSET = 8;
/* ---------------- Nodes -------------- */
/**
* Key-value entry. Note that this is never exported out as a
* user-visible Map.Entry. Nodes with a negative hash field are
* special, and do not contain user keys or values. Otherwise,
* keys are never null, and null val fields indicate that a node
* is in the process of being deleted or created. For purposes of
* read-only, access, a key may be read before a val, but can only
* be used after checking val. (For an update operation, when a
* lock is held on a node, order doesn't matter.)
*/
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;
}
}
/**
* Sign bit of node hash value indicating to use table in node.key.
*/
private static final int SIGN_BIT = 0x80000000;
/* ---------------- Fields -------------- */
/**
* The array of bins. Lazily initialized upon first insertion.
* Size is always a power of two. Accessed directly by iterators.
*/
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 next element count value upon which to resize the table. */
private transient int threshold;
/** The target capacity; volatile to cover initialization races. */
private transient volatile int targetCapacity;
/** The target load factor for the table */
private transient final float loadFactor;
// views
private transient KeySet keySet;
private transient Values values;
private transient EntrySet entrySet;
/** For serialization compatibility. Null unless serialized; see below */
private Segment[] segments;
/* ---------------- Table element access -------------- */
/*
* Volatile access methods are used for table elements as well as
* elements of in-progress next table while resizing. Uses 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. Note that, to be correct
* wrt arbitrary concurrency errors by users, bounds checks must
* operate on local variables, which accounts for some odd-looking
* inline assignments below.
*/
static final Node tabAt(Node[] tab, int i) { // used by InternalIterator
return (Node)UNSAFE.getObjectVolatile(tab, ((long)i<>> 1;
n |= n >>> 2;
n |= n >>> 4;
n |= n >>> 8;
n |= n >>> 16;
return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
}
/**
* If not already resizing, initializes or creates next table and
* transfers bins. Initial table size uses the capacity recorded
* in targetCapacity. Rechecks occupancy after a transfer to see
* if another resize is already needed because resizings are
* lagging additions.
*
* @return current table
*/
private final Node[] growTable() {
if (resizing == 0 &&
UNSAFE.compareAndSwapInt(this, resizingOffset, 0, 1)) {
try {
for (;;) {
Node[] tab = table;
int n, c;
if (tab == null)
n = (c = targetCapacity) > 0 ? c : DEFAULT_CAPACITY;
else if ((n = tab.length) < MAXIMUM_CAPACITY &&
counter.sum() >= threshold)
n <<= 1;
else
break;
Node[] nextTab = new Node[n];
threshold = (int)(n * loadFactor) - THRESHOLD_OFFSET;
if (tab != null)
transfer(tab, nextTab,
new Node(SIGN_BIT, nextTab, null, null));
table = nextTab;
if (tab == null)
break;
}
} finally {
resizing = 0;
}
}
else if (table == null)
Thread.yield(); // lost initialization race; just spin
return table;
}
/*
* 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 loadFactor, 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, Node fwd) {
int n = tab.length;
Node ignore = nextTab[n + n - 1]; // force bounds check
for (int i = n - 1; i >= 0; --i) {
for (Node e;;) {
if ((e = tabAt(tab, i)) != null) {
boolean validated = false;
synchronized (e) {
if (tabAt(tab, i) == e) {
validated = true;
Node lo = null, hi = null, lastRun = e;
int runBit = e.hash & n;
for (Node p = e.next; p != null; p = p.next) {
int b = p.hash & n;
if (b != runBit) {
runBit = b;
lastRun = p;
}
}
if (runBit == 0)
lo = lastRun;
else
hi = lastRun;
for (Node p = e; p != lastRun; p = p.next) {
int ph = p.hash;
Object pk = p.key, pv = p.val;
if ((ph & n) == 0)
lo = new Node(ph, pk, pv, lo);
else
hi = new Node(ph, pk, pv, hi);
}
setTabAt(nextTab, i, lo);
setTabAt(nextTab, i + n, hi);
setTabAt(tab, i, fwd);
}
}
if (validated)
break;
}
else if (casTabAt(tab, i, e, fwd))
break;
}
}
}
/* ---------------- Internal access and update methods -------------- */
/**
* 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
}
/** Implementation for get and containsKey */
private final Object internalGet(Object k) {
int h = spread(k.hashCode());
retry: for (Node[] tab = table; tab != null;) {
Node e; Object ek, ev; int eh; // locals to read fields once
for (e = tabAt(tab, (tab.length - 1) & h); e != null; e = e.next) {
if ((eh = e.hash) == h) {
if ((ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek)))
return ev;
}
else if (eh < 0) { // sign bit set
tab = (Node[])e.key; // bin was moved during resize
continue retry;
}
}
break;
}
return null;
}
/** Implementation for put and putIfAbsent */
private final Object internalPut(Object k, Object v, boolean replace) {
int h = spread(k.hashCode());
Object oldVal = null; // previous value or null if none
for (Node[] tab = table;;) {
Node e; int i; Object ek, ev;
if (tab == null)
tab = growTable();
else if ((e = tabAt(tab, i = (tab.length - 1) & h)) == null) {
if (casTabAt(tab, i, null, new Node(h, k, v, null)))
break; // no lock when adding to empty bin
}
else if (e.hash < 0) // resized -- restart with new table
tab = (Node[])e.key;
else if (!replace && e.hash == h && (ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek))) {
if (tabAt(tab, i) == e) { // inspect and validate 1st node
oldVal = ev; // without lock for putIfAbsent
break;
}
}
else {
boolean validated = false;
boolean checkSize = false;
synchronized (e) { // lock the 1st node of bin list
if (tabAt(tab, i) == e) {
validated = true; // retry if 1st already deleted
for (Node first = e;;) {
if (e.hash == h &&
((ek = e.key) == k || k.equals(ek)) &&
(ev = e.val) != null) {
oldVal = ev;
if (replace)
e.val = v;
break;
}
Node last = e;
if ((e = e.next) == null) {
last.next = new Node(h, k, v, null);
if (last != first || tab.length <= 64)
checkSize = true;
break;
}
}
}
}
if (validated) {
if (checkSize && tab.length < MAXIMUM_CAPACITY &&
resizing == 0 && counter.sum() >= threshold)
growTable();
break;
}
}
}
if (oldVal == null)
counter.increment(); // update counter outside of locks
return oldVal;
}
/**
* Implementation for 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());
for (Node[] tab = table;;) {
Node e; int i;
if (tab == null ||
(e = tabAt(tab, i = (tab.length - 1) & h)) == null)
return null;
else if (e.hash < 0)
tab = (Node[])e.key;
else {
Object oldVal = null;
boolean validated = false;
boolean deleted = false;
synchronized (e) {
if (tabAt(tab, i) == e) {
validated = true;
Node pred = null;
do {
Object ek, ev;
if (e.hash == h &&
((ek = e.key) == k || k.equals(ek)) &&
((ev = e.val) != null)) {
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;
}
} while ((e = (pred = e).next) != null);
}
}
if (validated) {
if (deleted)
counter.decrement();
return oldVal;
}
}
}
}
/** Implementation for computeIfAbsent and compute. Like put, but messier. */
@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;
Node[] tab = table;
outer:for (;;) {
Node e; int i; Object ek, ev;
if (tab == null)
tab = growTable();
else if ((e = tabAt(tab, i = (tab.length - 1) & h)) == null) {
Node node = new Node(h, k, null, null);
boolean validated = false;
synchronized (node) { // must lock while computing value
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);
}
}
}
if (validated)
break;
}
else if (e.hash < 0)
tab = (Node[])e.key;
else if (!replace && e.hash == h && (ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek))) {
if (tabAt(tab, i) == e) {
val = (V)ev;
break;
}
}
else if (Thread.holdsLock(e))
throw new IllegalStateException("Recursive map computation");
else {
boolean validated = false;
boolean checkSize = false;
synchronized (e) {
if (tabAt(tab, i) == e) {
validated = true;
for (Node first = e;;) {
if (e.hash == h &&
((ek = e.key) == k || k.equals(ek)) &&
((ev = e.val) != null)) {
Object fv;
if (replace && (fv = f.map(k)) != null)
ev = e.val = fv;
val = (V)ev;
break;
}
Node last = e;
if ((e = e.next) == null) {
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 (validated) {
if (checkSize && tab.length < MAXIMUM_CAPACITY &&
resizing == 0 && counter.sum() >= threshold)
growTable();
break;
}
}
}
if (added)
counter.increment();
return val;
}
/**
* Implementation for clear. Steps through each bin, removing all nodes.
*/
private final void internalClear() {
long delta = 0L; // negative number of deletions
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;
Node en;
do {
en = e.next;
if (e.val != null) { // currently always true
e.val = null;
--delta;
}
} while ((e = en) != null);
setTabAt(tab, i, null);
}
}
if (validated)
++i;
}
}
counter.add(delta);
}
/* ----------------Table Traversal -------------- */
/**
* Encapsulates traversal for methods such as containsValue; also
* serves as a base class for other iterators.
*
* At each step, the iterator snapshots the key ("nextKey") and
* value ("nextVal") of a valid node (i.e., one that, at point of
* snapshot, has a nonnull user value). Because val fields can
* change (including to null, indicating deletion), field nextVal
* might not be accurate at point of use, but still maintains the
* weak consistency property of holding a value that was once
* valid.
*
* Internal traversals directly access these fields, as in:
* {@code while (it.next != null) { process(nextKey); it.advance(); }}
*
* Exported iterators (subclasses of ViewIterator) extract key,
* value, or key-value pairs as return values of Iterator.next(),
* and encapulate the it.next check as hasNext();
*
* The iterator visits each valid node that was reachable upon
* iterator construction once. It might miss some that were added
* to a bin after the bin was visited, which is OK wrt consistency
* guarantees. Maintaining this property in the face of possible
* ongoing resizes requires a fair amount of bookkeeping state
* that is difficult to optimize away amidst volatile accesses.
* Even so, traversal maintains reasonable throughput.
*
* 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 sharing by users of iterators
* across threads, iteration terminates if a bounds checks fails
* for a table read.
*
* The range-based constructor enables creation of parallel
* range-splitting traversals. (Not yet implemented.)
*/
static class InternalIterator {
Node next; // the next entry to use
Node last; // the last entry used
Object nextKey; // cached key field of next
Object nextVal; // cached val field of next
Node[] tab; // current table; updated if resized
int index; // index of bin to use next
int baseIndex; // current index of initial table
final int baseLimit; // index bound for initial table
final int baseSize; // initial table size
/** Creates iterator for all entries in the table. */
InternalIterator(Node[] tab) {
this.tab = tab;
baseLimit = baseSize = (tab == null) ? 0 : tab.length;
index = baseIndex = 0;
next = null;
advance();
}
/** Creates iterator for the given range of the table */
InternalIterator(Node[] tab, int lo, int hi) {
this.tab = tab;
baseSize = (tab == null) ? 0 : tab.length;
baseLimit = (hi <= baseSize) ? hi : baseSize;
index = baseIndex = lo;
next = null;
advance();
}
/** Advances next. See above for explanation. */
final void advance() {
Node e = last = next;
outer: do {
if (e != null) // pass used or skipped node
e = e.next;
while (e == null) { // get to next non-null bin
Node[] t; int b, i, n; // checks must use locals
if ((b = baseIndex) >= baseLimit || (i = index) < 0 ||
(t = tab) == null || i >= (n = t.length))
break outer;
else if ((e = tabAt(t, i)) != null && e.hash < 0)
tab = (Node[])e.key; // restarts due to null val
else // visit upper slots if present
index = (i += baseSize) < n ? i : (baseIndex = b + 1);
}
nextKey = e.key;
} while ((nextVal = e.val) == null); // skip deleted or special nodes
next = e;
}
}
/* ---------------- 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 > 0.0f) || initialCapacity < 0 || concurrencyLevel <= 0)
throw new IllegalArgumentException();
int cap = tableSizeFor(initialCapacity);
this.counter = new LongAdder();
this.loadFactor = loadFactor;
this.targetCapacity = cap;
}
/**
* 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);
putAll(m);
}
/**
* {@inheritDoc}
*/
public boolean isEmpty() {
return counter.sum() <= 0L; // ignore transient negative values
}
/**
* {@inheritDoc}
*/
public int size() {
long n = counter.sum();
return ((n < 0L) ? 0 :
(n > (long)Integer.MAX_VALUE) ? Integer.MAX_VALUE :
(int)n);
}
/**
* 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 may require a full traversal
* of the map, and 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();
Object v;
InternalIterator it = new InternalIterator(table);
while (it.next != null) {
if ((v = it.nextVal) == value || value.equals(v))
return true;
it.advance();
}
return false;
}
/**
* 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();
/*
* If uninitialized, try to adjust targetCapacity to
* accommodate the given number of elements.
*/
if (table == null) {
int size = m.size();
int cap = (size >= (MAXIMUM_CAPACITY >>> 1)) ? MAXIMUM_CAPACITY :
tableSizeFor(size + (size >>> 1));
if (cap > targetCapacity)
targetCapacity = cap;
}
for (Map.Entry extends K, ? extends V> e : m.entrySet())
put(e.getKey(), e.getValue());
}
/**
* 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
*
{@code
* 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
* {@code
* 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() {
KeySet ks = keySet;
return (ks != null) ? ks : (keySet = new KeySet(this));
}
/**
* 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() {
Values vs = values;
return (vs != null) ? vs : (values = new Values(this));
}
/**
* 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() {
EntrySet es = entrySet;
return (es != null) ? es : (entrySet = new EntrySet(this));
}
/**
* 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(this);
}
/**
* 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(this);
}
/**
* 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() {
int h = 0;
InternalIterator it = new InternalIterator(table);
while (it.next != null) {
h += it.nextKey.hashCode() ^ it.nextVal.hashCode();
it.advance();
}
return h;
}
/**
* 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() {
InternalIterator it = new InternalIterator(table);
StringBuilder sb = new StringBuilder();
sb.append('{');
if (it.next != null) {
for (;;) {
Object k = it.nextKey, v = it.nextVal;
sb.append(k == this ? "(this Map)" : k);
sb.append('=');
sb.append(v == this ? "(this Map)" : v);
it.advance();
if (it.next == null)
break;
sb.append(',').append(' ');
}
}
return sb.append('}').toString();
}
/**
* 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) {
if (!(o instanceof Map))
return false;
Map,?> m = (Map,?>) o;
InternalIterator it = new InternalIterator(table);
while (it.next != null) {
Object val = it.nextVal;
Object v = m.get(it.nextKey);
if (v == null || (v != val && !v.equals(val)))
return false;
it.advance();
}
for (Map.Entry,?> e : m.entrySet()) {
Object mk, mv, v;
if ((mk = e.getKey()) == null ||
(mv = e.getValue()) == null ||
(v = internalGet(mk)) == null ||
(mv != v && !mv.equals(v)))
return false;
}
}
return true;
}
/* ----------------Iterators -------------- */
/**
* Base class for key, value, and entry iterators. Adds a map
* reference to InternalIterator to support Iterator.remove.
*/
static abstract class ViewIterator extends InternalIterator {
final ConcurrentHashMapV8 map;
ViewIterator(ConcurrentHashMapV8 map) {
super(map.table);
this.map = map;
}
public final void remove() {
if (last == null)
throw new IllegalStateException();
map.remove(last.key);
last = null;
}
public final boolean hasNext() { return next != null; }
public final boolean hasMoreElements() { return next != null; }
}
static final class KeyIterator extends ViewIterator
implements Iterator, Enumeration {
KeyIterator(ConcurrentHashMapV8 map) { super(map); }
@SuppressWarnings("unchecked")
public final K next() {
if (next == null)
throw new NoSuchElementException();
Object k = nextKey;
advance();
return (K)k;
}
public final K nextElement() { return next(); }
}
static final class ValueIterator extends ViewIterator
implements Iterator, Enumeration {
ValueIterator(ConcurrentHashMapV8 map) { super(map); }
@SuppressWarnings("unchecked")
public final V next() {
if (next == null)
throw new NoSuchElementException();
Object v = nextVal;
advance();
return (V)v;
}
public final V nextElement() { return next(); }
}
static final class EntryIterator extends ViewIterator
implements Iterator> {
EntryIterator(ConcurrentHashMapV8 map) { super(map); }
@SuppressWarnings("unchecked")
public final Map.Entry next() {
if (next == null)
throw new NoSuchElementException();
Object k = nextKey;
Object v = nextVal;
advance();
return new WriteThroughEntry(map, (K)k, (V)v);
}
}
/**
* Custom Entry class used by EntryIterator.next(), that relays
* setValue changes to the underlying map.
*/
static final class WriteThroughEntry implements Map.Entry {
final ConcurrentHashMapV8 map;
final K key; // non-null
V val; // non-null
WriteThroughEntry(ConcurrentHashMapV8 map, K key, V val) {
this.map = map; this.key = key; this.val = val;
}
public final K getKey() { return key; }
public final V getValue() { return val; }
public final int hashCode() { return key.hashCode() ^ val.hashCode(); }
public final String toString(){ return key + "=" + val; }
public final boolean equals(Object o) {
Object k, v; Map.Entry,?> e;
return ((o instanceof Map.Entry) &&
(k = (e = (Map.Entry,?>)o).getKey()) != null &&
(v = e.getValue()) != null &&
(k == key || k.equals(key)) &&
(v == val || v.equals(val)));
}
/**
* 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 final V setValue(V value) {
if (value == null) throw new NullPointerException();
V v = val;
val = value;
map.put(key, value);
return v;
}
}
/* ----------------Views -------------- */
/*
* These currently just extend java.util.AbstractX classes, but
* may need a new custom base to support partitioned traversal.
*/
static final class KeySet extends AbstractSet {
final ConcurrentHashMapV8 map;
KeySet(ConcurrentHashMapV8 map) { this.map = map; }
public final int size() { return map.size(); }
public final boolean isEmpty() { return map.isEmpty(); }
public final void clear() { map.clear(); }
public final boolean contains(Object o) { return map.containsKey(o); }
public final boolean remove(Object o) { return map.remove(o) != null; }
public final Iterator iterator() {
return new KeyIterator(map);
}
}
static final class Values extends AbstractCollection {
final ConcurrentHashMapV8 map;
Values(ConcurrentHashMapV8 map) { this.map = map; }
public final int size() { return map.size(); }
public final boolean isEmpty() { return map.isEmpty(); }
public final void clear() { map.clear(); }
public final boolean contains(Object o) { return map.containsValue(o); }
public final Iterator iterator() {
return new ValueIterator(map);
}
}
static final class EntrySet extends AbstractSet> {
final ConcurrentHashMapV8 map;
EntrySet(ConcurrentHashMapV8 map) { this.map = map; }
public final int size() { return map.size(); }
public final boolean isEmpty() { return map.isEmpty(); }
public final void clear() { map.clear(); }
public final Iterator> iterator() {
return new EntryIterator(map);
}
public final boolean contains(Object o) {
Object k, v, r; Map.Entry,?> e;
return ((o instanceof Map.Entry) &&
(k = (e = (Map.Entry,?>)o).getKey()) != null &&
(r = map.get(k)) != null &&
(v = e.getValue()) != null &&
(v == r || v.equals(r)));
}
public final boolean remove(Object o) {
Object k, v; Map.Entry,?> e;
return ((o instanceof Map.Entry) &&
(k = (e = (Map.Entry,?>)o).getKey()) != null &&
(v = e.getValue()) != null &&
map.remove(k, v));
}
}
/* ---------------- Serialization Support -------------- */
/**
* Stripped-down version of helper class used in previous version,
* declared for the sake of serialization compatibility
*/
static class Segment 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(DEFAULT_LOAD_FACTOR);
}
s.defaultWriteObject();
InternalIterator it = new InternalIterator(table);
while (it.next != null) {
s.writeObject(it.nextKey);
s.writeObject(it.nextVal);
it.advance();
}
s.writeObject(null);
s.writeObject(null);
segments = null; // throw away
}
/**
* Reconstitutes the instance from a stream (that is, deserializes it).
* @param s the stream
*/
@SuppressWarnings("unchecked")
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
this.segments = null; // unneeded
// initalize transient final fields
UNSAFE.putObjectVolatile(this, counterOffset, new LongAdder());
UNSAFE.putFloatVolatile(this, loadFactorOffset, DEFAULT_LOAD_FACTOR);
this.targetCapacity = DEFAULT_CAPACITY;
// Create all nodes, then place in table once size is known
long size = 0L;
Node p = null;
for (;;) {
K k = (K) s.readObject();
V v = (V) s.readObject();
if (k != null && v != null) {
p = new Node(spread(k.hashCode()), k, v, p);
++size;
}
else
break;
}
if (p != null) {
boolean init = false;
if (resizing == 0 &&
UNSAFE.compareAndSwapInt(this, resizingOffset, 0, 1)) {
try {
if (table == null) {
init = true;
int n;
if (size >= (long)(MAXIMUM_CAPACITY >>> 1))
n = MAXIMUM_CAPACITY;
else {
int sz = (int)size;
n = tableSizeFor(sz + (sz >>> 1));
}
threshold = (n - (n >>> 2)) - THRESHOLD_OFFSET;
Node[] tab = new Node[n];
int mask = n - 1;
while (p != null) {
int j = p.hash & mask;
Node next = p.next;
p.next = tabAt(tab, j);
setTabAt(tab, j, p);
p = next;
}
table = tab;
counter.add(size);
}
} finally {
resizing = 0;
}
}
if (!init) { // Can only happen if unsafely published.
while (p != null) {
internalPut(p.key, p.val, true);
p = p.next;
}
}
}
}
// Unsafe mechanics
private static final sun.misc.Unsafe UNSAFE;
private static final long counterOffset;
private static final long loadFactorOffset;
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"));
loadFactorOffset = UNSAFE.objectFieldOffset
(k.getDeclaredField("loadFactor"));
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());
}
}
}
}