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/*
* 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 net.sf.ehcache.util.concurrent;
import net.sf.ehcache.Element;
import net.sf.ehcache.pool.PoolAccessor;
import net.sf.ehcache.pool.PoolParticipant;
import net.sf.ehcache.pool.impl.UnboundedPool;
import java.util.ArrayList;
import java.util.List;
import java.util.Arrays;
import java.util.Map;
import java.util.Set;
import java.util.Collection;
import java.util.AbstractMap;
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.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.io.Serializable;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicReferenceArray;
/**
* A hash table supporting full concurrency of retrievals and
* high expected concurrency for updates. This class is based on the
* same functional standard 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. (More formally, an update operation for a given key bears a
* happens-before relation with any (non-null) retrieval for
* that key reporting the updated value.) 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 or estimation purposes, but not
* for program control.
*
*
The table is dynamically expanded when there are too many
* collisions (i.e., keys that have distinct hash codes but fall into
* the same slot modulo the table size), with the expected average
* effect of maintaining roughly two bins per mapping (corresponding
* to a 0.75 load factor threshold for resizing). There may be much
* variance around this average as mappings are added and removed, but
* overall, this maintains a commonly accepted time/space tradeoff for
* hash tables. However, resizing this or any other kind of hash
* table may be a relatively slow operation. When possible, it is a
* good idea to provide a size estimate as an optional {@code
* initialCapacity} constructor argument. An additional optional
* {@code loadFactor} constructor argument provides a further means of
* customizing initial table capacity by specifying the table density
* to be used in calculating the amount of space to allocate for the
* given number of elements. Also, for compatibility with previous
* versions of this class, constructors may optionally specify an
* expected {@code concurrencyLevel} as an additional hint for
* internal sizing. Note that using many keys with exactly the same
* {@code hashCode()} is a sure way to slow down performance of any
* hash table.
*
*
A {@link Set} projection of a ConcurrentHashMap may be created
* (using {@link #newKeySet()} or {@link #newKeySet(int)}), or viewed
* (using {@link #keySet(Object)} when only keys are of interest, and the
* mapped values are (perhaps transiently) not used or all take the
* same mapping value.
*
*
A ConcurrentHashMap can be used as scalable frequency map (a
* form of histogram or multiset) by using {@link LongAdder} values
* and initializing via {@link #computeIfAbsent}. For example, to add
* a count to a {@code ConcurrentHashMap freqs}, you
* can use {@code freqs.computeIfAbsent(k -> new
* LongAdder()).increment();}
*
* 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.
*
*
ConcurrentHashMaps support parallel operations using the {@link
* ForkJoinPool#commonPool}. (Tasks that may be used in other contexts
* are available in class {@link ForkJoinTasks}). These operations are
* designed to be safely, and often sensibly, applied even with maps
* that are being concurrently updated by other threads; for example,
* when computing a snapshot summary of the values in a shared
* registry. There are three kinds of operation, each with four
* forms, accepting functions with Keys, Values, Entries, and (Key,
* Value) arguments and/or return values. (The first three forms are
* also available via the {@link #keySet()}, {@link #values()} and
* {@link #entrySet()} views). Because the elements of a
* ConcurrentHashMap are not ordered in any particular way, and may be
* processed in different orders in different parallel executions, the
* correctness of supplied functions should not depend on any
* ordering, or on any other objects or values that may transiently
* change while computation is in progress; and except for forEach
* actions, should ideally be side-effect-free.
*
*
* - forEach: Perform a given action on each element.
* A variant form applies a given transformation on each element
* before performing the action.
*
* - search: Return the first available non-null result of
* applying a given function on each element; skipping further
* search when a result is found.
*
* - reduce: Accumulate each element. The supplied reduction
* function cannot rely on ordering (more formally, it should be
* both associative and commutative). There are five variants:
*
*
*
* - Plain reductions. (There is not a form of this method for
* (key, value) function arguments since there is no corresponding
* return type.)
*
* - Mapped reductions that accumulate the results of a given
* function applied to each element.
*
* - Reductions to scalar doubles, longs, and ints, using a
* given basis value.
*
*
*
*
*
* The concurrency properties of bulk operations follow
* from those of ConcurrentHashMap: Any non-null result returned
* from {@code get(key)} and related access methods bears a
* happens-before relation with the associated insertion or
* update. The result of any bulk operation reflects the
* composition of these per-element relations (but is not
* necessarily atomic with respect to the map as a whole unless it
* is somehow known to be quiescent). Conversely, because keys
* and values in the map are never null, null serves as a reliable
* atomic indicator of the current lack of any result. To
* maintain this property, null serves as an implicit basis for
* all non-scalar reduction operations. For the double, long, and
* int versions, the basis should be one that, when combined with
* any other value, returns that other value (more formally, it
* should be the identity element for the reduction). Most common
* reductions have these properties; for example, computing a sum
* with basis 0 or a minimum with basis MAX_VALUE.
*
*
Search and transformation functions provided as arguments
* should similarly return null to indicate the lack of any result
* (in which case it is not used). In the case of mapped
* reductions, this also enables transformations to serve as
* filters, returning null (or, in the case of primitive
* specializations, the identity basis) if the element should not
* be combined. You can create compound transformations and
* filterings by composing them yourself under this "null means
* there is nothing there now" rule before using them in search or
* reduce operations.
*
*
Methods accepting and/or returning Entry arguments maintain
* key-value associations. They may be useful for example when
* finding the key for the greatest value. Note that "plain" Entry
* arguments can be supplied using {@code new
* AbstractMap.SimpleEntry(k,v)}.
*
*
Bulk operations may complete abruptly, throwing an
* exception encountered in the application of a supplied
* function. Bear in mind when handling such exceptions that other
* concurrently executing functions could also have thrown
* exceptions, or would have done so if the first exception had
* not occurred.
*
*
Parallel speedups for bulk operations compared to sequential
* processing are common but not guaranteed. Operations involving
* brief functions on small maps may execute more slowly than
* sequential loops if the underlying work to parallelize the
* computation is more expensive than the computation itself.
* Similarly, parallelization may not lead to much actual parallelism
* if all processors are busy performing unrelated tasks.
*
*
All arguments to all task methods must be non-null.
*
*
jsr166e note: During transition, this class
* uses nested functional interfaces with different names but the
* same forms as those expected for JDK8.
*
*
This class is a member of the
*
* Java Collections Framework.
*
* @since 1.5
* @author Doug Lea
* @param the type of keys maintained by this map
* @param the type of mapped values
*/
@SuppressWarnings("restriction")
public class ConcurrentHashMap
implements ConcurrentMap {
private static final long serialVersionUID = 7249069246763182397L;
protected static final ConcurrentHashMap.Node FAKE_NODE = new Node(0, null, null, null, 0);
protected static final ConcurrentHashMap.Node FAKE_TREE_NODE = new TreeNode(0, null, null, null, 0, null);
/**
* A partitionable iterator. A Spliterator can be traversed
* directly, but can also be partitioned (before traversal) by
* creating another Spliterator that covers a non-overlapping
* portion of the elements, and so may be amenable to parallel
* execution.
*
* This interface exports a subset of expected JDK8
* functionality.
*
*
Sample usage: Here is one (of the several) ways to compute
* the sum of the values held in a map using the ForkJoin
* framework. As illustrated here, Spliterators are well suited to
* designs in which a task repeatedly splits off half its work
* into forked subtasks until small enough to process directly,
* and then joins these subtasks. Variants of this style can also
* be used in completion-based designs.
*
*
* {@code ConcurrentHashMap m = ...
* // split as if have 8 * parallelism, for load balance
* int n = m.size();
* int p = aForkJoinPool.getParallelism() * 8;
* int split = (n < p)? n : p;
* long sum = aForkJoinPool.invoke(new SumValues(m.valueSpliterator(), split, null));
* // ...
* static class SumValues extends RecursiveTask {
* final Spliterator s;
* final int split; // split while > 1
* final SumValues nextJoin; // records forked subtasks to join
* SumValues(Spliterator s, int depth, SumValues nextJoin) {
* this.s = s; this.depth = depth; this.nextJoin = nextJoin;
* }
* public Long compute() {
* long sum = 0;
* SumValues subtasks = null; // fork subtasks
* for (int s = split >>> 1; s > 0; s >>>= 1)
* (subtasks = new SumValues(s.split(), s, subtasks)).fork();
* while (s.hasNext()) // directly process remaining elements
* sum += s.next();
* for (SumValues t = subtasks; t != null; t = t.nextJoin)
* sum += t.join(); // collect subtask results
* return sum;
* }
* }
* }
*/
public static interface Spliterator extends Iterator {
/**
* Returns a Spliterator covering approximately half of the
* elements, guaranteed not to overlap with those subsequently
* returned by this Spliterator. After invoking this method,
* the current Spliterator will not produce any of
* the elements of the returned Spliterator, but the two
* Spliterators together will produce all of the elements that
* would have been produced by this Spliterator had this
* method not been called. The exact number of elements
* produced by the returned Spliterator is not guaranteed, and
* may be zero (i.e., with {@code hasNext()} reporting {@code
* false}) if this Spliterator cannot be further split.
*
* @return a Spliterator covering approximately half of the
* elements
* @throws IllegalStateException if this Spliterator has
* already commenced traversing elements
*/
Spliterator split();
}
/*
* 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. Secondary goals are to keep space consumption about
* the same or better than java.util.HashMap, and to support high
* initial insertion rates on an empty table by many threads.
*
* 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. This also allows
* many of the public methods to be factored into a smaller number
* of internal methods (although sadly not so for the five
* variants of put-related operations). The validation-based
* approach explained below leads to a lot of code sprawl because
* retry-control precludes factoring into smaller methods.
*
* The table is lazily initialized to a power-of-two size upon the
* first insertion. Each bin in the table normally contains a
* list of Nodes (most often, the list has only 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.
*
* We use the top two bits of Node hash fields for control
* purposes -- they are available anyway because of addressing
* constraints. As explained further below, these top bits are
* used as follows:
* 00 - Normal
* 01 - Locked
* 11 - Locked and may have a thread waiting for lock
* 10 - Node is a forwarding node
*
* The lower 30 bits of each Node's hash field contain a
* transformation of the key's hash code, except for forwarding
* nodes, for which the lower bits are zero (and so always have
* hash field == MOVED).
*
* Insertion (via put or its variants) of the first node in an
* empty bin is performed by just CASing it to the bin. This is
* by far the most common case for put operations under most
* key/hash distributions. 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. Blocking support for these locks relies on the builtin
* "synchronized" monitors. However, we also need a tryLock
* construction, so we overlay these by using bits of the Node
* hash field for lock control (see above), and so normally use
* builtin monitors only for blocking and signalling using
* wait/notifyAll constructions. See Node.tryAwaitLock.
*
* 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 after locking it, 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 (upon resizing). However,
* operations that only conditionally update may 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 per-bin locks is that other 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, under
* random hash codes, this is not a common problem. Ideally, the
* frequency of nodes in bins follows a Poisson distribution
* (http://en.wikipedia.org/wiki/Poisson_distribution) with a
* parameter of about 0.5 on average, given the resizing threshold
* of 0.75, although with a large variance because of resizing
* granularity. Ignoring variance, the expected occurrences of
* list size k are (exp(-0.5) * pow(0.5, k) / factorial(k)). The
* first values are:
*
* 0: 0.60653066
* 1: 0.30326533
* 2: 0.07581633
* 3: 0.01263606
* 4: 0.00157952
* 5: 0.00015795
* 6: 0.00001316
* 7: 0.00000094
* 8: 0.00000006
* more: less than 1 in ten million
*
* Lock contention probability for two threads accessing distinct
* elements is roughly 1 / (8 * #elements) under random hashes.
*
* Actual hash code distributions encountered in practice
* sometimes deviate significantly from uniform randomness. This
* includes the case when N > (1<<30), so some keys MUST collide.
* Similarly for dumb or hostile usages in which multiple keys are
* designed to have identical hash codes. Also, although we guard
* against the worst effects of this (see method spread), sets of
* hashes may differ only in bits that do not impact their bin
* index for a given power-of-two mask. So we use a secondary
* strategy that applies when the number of nodes in a bin exceeds
* a threshold, and at least one of the keys implements
* Comparable. These TreeBins use a balanced tree to hold nodes
* (a specialized form of red-black trees), bounding search time
* to O(log N). Each search step in a TreeBin is around twice as
* slow as in a regular list, but given that N cannot exceed
* (1<<64) (before running out of addresses) this bounds search
* steps, lock hold times, etc, to reasonable constants (roughly
* 100 nodes inspected per operation worst case) so long as keys
* are Comparable (which is very common -- String, Long, etc).
* TreeBin nodes (TreeNodes) also maintain the same "next"
* traversal pointers as regular nodes, so can be traversed in
* iterators in the same way.
*
* The table is resized when occupancy exceeds a percentage
* threshold (nominally, 0.75, but see below). Only a single
* thread performs the resize (using field "sizeCtl", 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. 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. On
* average, 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. Upon
* transfer, the old table bin contains only a special forwarding
* node (with hash field "MOVED") that contains the next table as
* its key. On encountering a forwarding node, access and update
* operations restart, using the new table.
*
* Each bin transfer requires its bin lock. However, unlike other
* cases, a transfer can skip a bin if it fails to acquire its
* lock, and revisit it later (unless it is a TreeBin). Method
* rebuild maintains a buffer of TRANSFER_BUFFER_SIZE bins that
* have been skipped because of failure to acquire a lock, and
* blocks only if none are available (i.e., only very rarely).
* The transfer operation must also ensure that all accessible
* bins in both the old and new table are usable by any traversal.
* When there are no lock acquisition failures, this is arranged
* simply by proceeding from the last bin (table.length - 1) up
* towards the first. Upon seeing a forwarding node, traversals
* (see class Iter) arrange to move to the new table
* without revisiting nodes. However, when any node is skipped
* during a transfer, all earlier table bins may have become
* visible, so are initialized with a reverse-forwarding node back
* to the old table until the new ones are established. (This
* sometimes requires transiently locking a forwarding node, which
* is possible under the above encoding.) These more expensive
* mechanics trigger only when necessary.
*
* The traversal scheme also applies to partial traversals of
* ranges of bins (via an alternate Traverser constructor)
* to support 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.
*
* 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 initial capacity settings,
* but harmlessly fail to take effect in cases of races.
*
* 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 attempted either when a bin lock is
* contended, or upon adding to a bin already holding two or more
* nodes (checked before adding in the xIfAbsent methods, after
* adding in others). Under 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. The bulk putAll operation further reduces
* contention by only committing count updates upon these size
* checks.
*
* 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 accept a loadFactor constructor argument,
* but apply it only to initial table capacity (which is the only
* time that we can guarantee to honor it.) We also declare an
* unused "Segment" class that is instantiated in minimal form
* only when serializing.
*/
/* ---------------- Constants -------------- */
/**
* The largest possible table capacity. This value must be
* exactly 1<<30 to stay within Java array allocation and indexing
* bounds for power of two table sizes, and is further required
* because the top two bits of 32bit hash fields are used for
* control purposes.
*/
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 largest possible (non-power of two) array size.
* Needed by toArray and related methods.
*/
static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
* 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 load factor for this table. Overrides of this value in
* constructors affect only the initial table capacity. The
* actual floating point value isn't normally used -- it is
* simpler to use expressions such as {@code n - (n >>> 2)} for
* the associated resizing threshold.
*/
private static final float LOAD_FACTOR = 0.75f;
/**
* The buffer size for skipped bins during transfers. The
* value is arbitrary but should be large enough to avoid
* most locking stalls during resizes.
*/
private static final int TRANSFER_BUFFER_SIZE = 32;
/**
* The bin count threshold for using a tree rather than list for a
* bin. The value reflects the approximate break-even point for
* using tree-based operations.
*/
private static final int TREE_THRESHOLD = 8;
/*
* Encodings for special uses of Node hash fields. See above for
* explanation.
*/
static final int MOVED = 0x80000000; // hash field for forwarding nodes
static final int LOCKED = 0x40000000; // set/tested only as a bit
static final int WAITING = 0xc0000000; // both bits set/tested together
static final int HASH_BITS = 0x3fffffff; // usable bits of normal node hash
/* ---------------- Fields -------------- */
/**
* The array of bins. Lazily initialized upon first insertion.
* Size is always a power of two. Accessed directly by iterators.
*/
transient volatile AtomicReferenceArray table;
private volatile PoolAccessor poolAccessor;
/**
* The counter maintaining number of elements.
*/
private transient final LongAdder counter;
/**
* Table initialization and resizing control. When negative, the
* table is being initialized or resized. Otherwise, when table is
* null, holds the initial table size to use upon creation, or 0
* for default. After initialization, holds the next element count
* value upon which to resize the table.
*/
private transient volatile int sizeCtl;
// views
private transient KeySetView keySet;
private transient ValuesView values;
private transient EntrySetView 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(AtomicReferenceArray tab, int i) { // used by Iter
return tab.get(i);
}
private static final boolean casTabAt(AtomicReferenceArray tab, int i, Node c, Node v) {
return tab.compareAndSet(i, c, v);
}
private static final void setTabAt(AtomicReferenceArray tab, int i, Node v) {
tab.set(i, v);
}
/* ---------------- Nodes -------------- */
/**
* Key-value entry. Note that this is never exported out as a
* user-visible Map.Entry (see MapEntry below). Nodes with a hash
* field of MOVED 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 to be
* non-null.
*/
protected static class Node {
volatile int hash;
final Object key;
volatile Object val;
volatile Node next;
volatile int size;
public Node(int hash, Object key, Object val, Node next) {
this(hash, key, val, next, 0);
}
public Node(int hash, Object key, Object val, Node next, int size) {
HASH_UPDATER.set(this, hash);
this.key = key;
this.val = val;
this.next = next;
this.size = size;
}
/** CompareAndSet the hash field */
final boolean casHash(int cmp, int val) {
return HASH_UPDATER.compareAndSet(this, cmp, val);
}
/** The number of spins before blocking for a lock */
static final int MAX_SPINS =
Runtime.getRuntime().availableProcessors() > 1 ? 64 : 1;
/**
* Spins a while if LOCKED bit set and this node is the first
* of its bin, and then sets WAITING bits on hash field and
* blocks (once) if they are still set. It is OK for this
* method to return even if lock is not available upon exit,
* which enables these simple single-wait mechanics.
*
* The corresponding signalling operation is performed within
* callers: Upon detecting that WAITING has been set when
* unlocking lock (via a failed CAS from non-waiting LOCKED
* state), unlockers acquire the sync lock and perform a
* notifyAll.
*
* The initial sanity check on tab and bounds is not currently
* necessary in the only usages of this method, but enables
* use in other future contexts.
*/
final void tryAwaitLock(AtomicReferenceArray tab, int i) {
if (tab != null && i >= 0 && i < tab.length()) { // sanity check
int r = ThreadLocalRandom.current().nextInt(); // randomize spins
int spins = MAX_SPINS, h;
while (tabAt(tab, i) == this && ((h = hash) & LOCKED) != 0) {
if (spins >= 0) {
r ^= r << 1; r ^= r >>> 3; r ^= r << 10; // xorshift
if (r >= 0 && --spins == 0)
Thread.yield(); // yield before block
}
else if (casHash(h, h | WAITING)) {
synchronized (this) {
if (tabAt(tab, i) == this &&
(hash & WAITING) == WAITING) {
try {
wait();
} catch (InterruptedException ie) {
try {
Thread.currentThread().interrupt();
} catch (SecurityException ignore) {
}
}
}
else
notifyAll(); // possibly won race vs signaller
}
break;
}
}
}
}
static final AtomicIntegerFieldUpdater HASH_UPDATER = AtomicIntegerFieldUpdater.newUpdater(Node.class, "hash");
}
/* ---------------- TreeBins -------------- */
/**
* Nodes for use in TreeBins
*/
protected static final class TreeNode extends Node {
TreeNode parent; // red-black tree links
TreeNode left;
TreeNode right;
TreeNode prev; // needed to unlink next upon deletion
boolean red;
public TreeNode(int hash, Object key, Object val, Node next, int size, TreeNode parent) {
super(hash, key, val, next, size);
this.parent = parent;
}
}
/**
* A specialized form of red-black tree for use in bins
* whose size exceeds a threshold.
*
* TreeBins use a special form of comparison for search and
* related operations (which is the main reason we cannot use
* existing collections such as TreeMaps). TreeBins contain
* Comparable elements, but may contain others, as well as
* elements that are Comparable but not necessarily Comparable
* for the same T, so we cannot invoke compareTo among them. To
* handle this, the tree is ordered primarily by hash value, then
* by getClass().getName() order, and then by Comparator order
* among elements of the same class. On lookup at a node, if
* elements are not comparable or compare as 0, both left and
* right children may need to be searched in the case of tied hash
* values. (This corresponds to the full list search that would be
* necessary if all elements were non-Comparable and had tied
* hashes.) The red-black balancing code is updated from
* pre-jdk-collections
* (http://gee.cs.oswego.edu/dl/classes/collections/RBCell.java)
* based in turn on Cormen, Leiserson, and Rivest "Introduction to
* Algorithms" (CLR).
*
* TreeBins also maintain a separate locking discipline than
* regular bins. Because they are forwarded via special MOVED
* nodes at bin heads (which can never change once established),
* we cannot use those nodes as locks. Instead, TreeBin
* extends AbstractQueuedSynchronizer to support a simple form of
* read-write lock. For update operations and table validation,
* the exclusive form of lock behaves in the same way as bin-head
* locks. However, lookups use shared read-lock mechanics to allow
* multiple readers in the absence of writers. Additionally,
* these lookups do not ever block: While the lock is not
* available, they proceed along the slow traversal path (via
* next-pointers) until the lock becomes available or the list is
* exhausted, whichever comes first. (These cases are not fast,
* but maximize aggregate expected throughput.) The AQS mechanics
* for doing this are straightforward. The lock state is held as
* AQS getState(). Read counts are negative; the write count (1)
* is positive. There are no signalling preferences among readers
* and writers. Since we don't need to export full Lock API, we
* just override the minimal AQS methods and use them directly.
*/
static final class TreeBin extends AbstractQueuedSynchronizer {
private static final long serialVersionUID = 2249069246763182397L;
transient TreeNode root; // root of tree
transient TreeNode first; // head of next-pointer list
/* AQS overrides */
public final boolean isHeldExclusively() { return getState() > 0; }
public final boolean tryAcquire(int ignore) {
if (compareAndSetState(0, 1)) {
setExclusiveOwnerThread(Thread.currentThread());
return true;
}
return false;
}
public final boolean tryRelease(int ignore) {
setExclusiveOwnerThread(null);
setState(0);
return true;
}
public final int tryAcquireShared(int ignore) {
for (int c;;) {
if ((c = getState()) > 0)
return -1;
if (compareAndSetState(c, c -1))
return 1;
}
}
public final boolean tryReleaseShared(int ignore) {
int c;
do {} while (!compareAndSetState(c = getState(), c + 1));
return c == -1;
}
/** From CLR */
private void rotateLeft(TreeNode p) {
if (p != null) {
TreeNode r = p.right, pp, rl;
if ((rl = p.right = r.left) != null)
rl.parent = p;
if ((pp = r.parent = p.parent) == null)
root = r;
else if (pp.left == p)
pp.left = r;
else
pp.right = r;
r.left = p;
p.parent = r;
}
}
/** From CLR */
private void rotateRight(TreeNode p) {
if (p != null) {
TreeNode l = p.left, pp, lr;
if ((lr = p.left = l.right) != null)
lr.parent = p;
if ((pp = l.parent = p.parent) == null)
root = l;
else if (pp.right == p)
pp.right = l;
else
pp.left = l;
l.right = p;
p.parent = l;
}
}
/**
* Returns the TreeNode (or null if not found) for the given key
* starting at given root.
*/
@SuppressWarnings("unchecked") final TreeNode getTreeNode
(int h, Object k, TreeNode p) {
Class c = k.getClass();
while (p != null) {
int dir, ph; Object pk; Class pc;
if ((ph = p.hash) == h) {
if ((pk = p.key) == k || k.equals(pk))
return p;
if (c != (pc = pk.getClass()) ||
!(k instanceof Comparable) ||
(dir = ((Comparable)k).compareTo((Comparable)pk)) == 0) {
if ((dir = (c == pc) ? 0 :
c.getName().compareTo(pc.getName())) == 0) {
TreeNode r = null, pl, pr; // check both sides
if ((pr = p.right) != null &&
(r = getTreeNode(h, k, pr)) != null)
return r;
else
dir = -1;
}
}
}
else
dir = (h < ph) ? -1 : 1;
p = (dir > 0) ? p.right : p.left;
}
return null;
}
/**
* Wrapper for getTreeNode used by CHM.get. Tries to obtain
* read-lock to call getTreeNode, but during failure to get
* lock, searches along next links.
*/
final Object getValue(int h, Object k) {
Node r = null;
int c = getState(); // Must read lock state first
for (Node e = first; e != null; e = e.next) {
if (c <= 0 && compareAndSetState(c, c - 1)) {
try {
r = getTreeNode(h, k, root);
} finally {
releaseShared(0);
}
break;
}
else if ((e.hash & HASH_BITS) == h && k.equals(e.key)) {
r = e;
break;
}
else
c = getState();
}
return r == null ? null : r.val;
}
/**
* Finds or adds a node.
* @return null if added
*/
@SuppressWarnings("unchecked") final TreeNode putTreeNode
(int h, Object k, Object v) {
return putTreeNode(h, k, v, 0);
}
@SuppressWarnings("unchecked") final TreeNode putTreeNode
(int h, Object k, Object v, int size) {
Class c = k.getClass();
TreeNode pp = root, p = null;
int dir = 0;
while (pp != null) { // find existing node or leaf to insert at
int ph; Object pk; Class pc;
p = pp;
if ((ph = p.hash) == h) {
if ((pk = p.key) == k || k.equals(pk))
return p;
if (c != (pc = pk.getClass()) ||
!(k instanceof Comparable) ||
(dir = ((Comparable)k).compareTo((Comparable)pk)) == 0) {
TreeNode s = null, r = null, pr;
if ((dir = (c == pc) ? 0 :
c.getName().compareTo(pc.getName())) == 0) {
if ((pr = p.right) != null &&
(r = getTreeNode(h, k, pr)) != null)
return r;
else // continue left
dir = -1;
}
else if ((pr = p.right) != null && h >= pr.hash)
s = pr;
if (s != null && (r = getTreeNode(h, k, s)) != null)
return r;
}
}
else
dir = (h < ph) ? -1 : 1;
pp = (dir > 0) ? p.right : p.left;
}
TreeNode f = first;
TreeNode x = first = new TreeNode(h, k, v, f, size, p);
if (p == null)
root = x;
else { // attach and rebalance; adapted from CLR
TreeNode xp, xpp;
if (f != null)
f.prev = x;
if (dir <= 0)
p.left = x;
else
p.right = x;
x.red = true;
while (x != null && (xp = x.parent) != null && xp.red &&
(xpp = xp.parent) != null) {
TreeNode xppl = xpp.left;
if (xp == xppl) {
TreeNode y = xpp.right;
if (y != null && y.red) {
y.red = false;
xp.red = false;
xpp.red = true;
x = xpp;
}
else {
if (x == xp.right) {
rotateLeft(x = xp);
xpp = (xp = x.parent) == null ? null : xp.parent;
}
if (xp != null) {
xp.red = false;
if (xpp != null) {
xpp.red = true;
rotateRight(xpp);
}
}
}
}
else {
TreeNode y = xppl;
if (y != null && y.red) {
y.red = false;
xp.red = false;
xpp.red = true;
x = xpp;
}
else {
if (x == xp.left) {
rotateRight(x = xp);
xpp = (xp = x.parent) == null ? null : xp.parent;
}
if (xp != null) {
xp.red = false;
if (xpp != null) {
xpp.red = true;
rotateLeft(xpp);
}
}
}
}
}
TreeNode r = root;
if (r != null && r.red)
r.red = false;
}
return null;
}
/**
* Removes the given node, that must be present before this
* call. This is messier than typical red-black deletion code
* because we cannot swap the contents of an interior node
* with a leaf successor that is pinned by "next" pointers
* that are accessible independently of lock. So instead we
* swap the tree linkages.
*/
final void deleteTreeNode(TreeNode p) {
TreeNode next = (TreeNode)p.next; // unlink traversal pointers
TreeNode pred = p.prev;
if (pred == null)
first = next;
else
pred.next = next;
if (next != null)
next.prev = pred;
TreeNode replacement;
TreeNode pl = p.left;
TreeNode pr = p.right;
if (pl != null && pr != null) {
TreeNode s = pr, sl;
while ((sl = s.left) != null) // find successor
s = sl;
boolean c = s.red; s.red = p.red; p.red = c; // swap colors
TreeNode sr = s.right;
TreeNode pp = p.parent;
if (s == pr) { // p was s's direct parent
p.parent = s;
s.right = p;
}
else {
TreeNode sp = s.parent;
if ((p.parent = sp) != null) {
if (s == sp.left)
sp.left = p;
else
sp.right = p;
}
if ((s.right = pr) != null)
pr.parent = s;
}
p.left = null;
if ((p.right = sr) != null)
sr.parent = p;
if ((s.left = pl) != null)
pl.parent = s;
if ((s.parent = pp) == null)
root = s;
else if (p == pp.left)
pp.left = s;
else
pp.right = s;
replacement = sr;
}
else
replacement = (pl != null) ? pl : pr;
TreeNode pp = p.parent;
if (replacement == null) {
if (pp == null) {
root = null;
return;
}
replacement = p;
}
else {
replacement.parent = pp;
if (pp == null)
root = replacement;
else if (p == pp.left)
pp.left = replacement;
else
pp.right = replacement;
p.left = p.right = p.parent = null;
}
if (!p.red) { // rebalance, from CLR
TreeNode x = replacement;
while (x != null) {
TreeNode xp, xpl;
if (x.red || (xp = x.parent) == null) {
x.red = false;
break;
}
if (x == (xpl = xp.left)) {
TreeNode sib = xp.right;
if (sib != null && sib.red) {
sib.red = false;
xp.red = true;
rotateLeft(xp);
sib = (xp = x.parent) == null ? null : xp.right;
}
if (sib == null)
x = xp;
else {
TreeNode sl = sib.left, sr = sib.right;
if ((sr == null || !sr.red) &&
(sl == null || !sl.red)) {
sib.red = true;
x = xp;
}
else {
if (sr == null || !sr.red) {
if (sl != null)
sl.red = false;
sib.red = true;
rotateRight(sib);
sib = (xp = x.parent) == null ? null : xp.right;
}
if (sib != null) {
sib.red = (xp == null) ? false : xp.red;
if ((sr = sib.right) != null)
sr.red = false;
}
if (xp != null) {
xp.red = false;
rotateLeft(xp);
}
x = root;
}
}
}
else { // symmetric
TreeNode sib = xpl;
if (sib != null && sib.red) {
sib.red = false;
xp.red = true;
rotateRight(xp);
sib = (xp = x.parent) == null ? null : xp.left;
}
if (sib == null)
x = xp;
else {
TreeNode sl = sib.left, sr = sib.right;
if ((sl == null || !sl.red) &&
(sr == null || !sr.red)) {
sib.red = true;
x = xp;
}
else {
if (sl == null || !sl.red) {
if (sr != null)
sr.red = false;
sib.red = true;
rotateLeft(sib);
sib = (xp = x.parent) == null ? null : xp.left;
}
if (sib != null) {
sib.red = (xp == null) ? false : xp.red;
if ((sl = sib.left) != null)
sl.red = false;
}
if (xp != null) {
xp.red = false;
rotateRight(xp);
}
x = root;
}
}
}
}
}
if (p == replacement && (pp = p.parent) != null) {
if (p == pp.left) // detach pointers
pp.left = null;
else if (p == pp.right)
pp.right = null;
p.parent = null;
}
}
}
/* ---------------- Collision reduction methods -------------- */
/**
* Spreads higher bits to lower, and also forces top 2 bits to 0.
* Because the table uses power-of-two masking, sets of hashes
* that vary only in bits above the current mask will always
* collide. (Among known examples are sets of Float keys holding
* consecutive whole numbers in small tables.) To counter this,
* we apply a transform that spreads the impact of higher bits
* downward. There is a tradeoff between speed, utility, and
* quality of bit-spreading. Because many common sets of hashes
* are already reasonably distributed across bits (so don't benefit
* from spreading), and because we use trees to handle large sets
* of collisions in bins, we don't need excessively high quality.
*/
private static final int spread(int h) {
h ^= (h >>> 18) ^ (h >>> 12);
return (h ^ (h >>> 10)) & HASH_BITS;
}
/**
* Replaces a list bin with a tree bin. Call only when locked.
* Fails to replace if the given key is non-comparable or table
* is, or needs, resizing.
*/
private final void replaceWithTreeBin(AtomicReferenceArray tab, int index, Object key) {
if ((key instanceof Comparable) &&
(tab.length() >= MAXIMUM_CAPACITY || counter.sum() < (long)sizeCtl)) {
TreeBin t = new TreeBin();
for (Node e = tabAt(tab, index); e != null; e = e.next) {
t.putTreeNode(e.hash & HASH_BITS, e.key, e.val, e.size);
e.val = null;
e.size = -1;
}
setTabAt(tab, index, new Node(MOVED, t, null, null));
}
}
/* ---------------- Internal access and update methods -------------- */
/** Implementation for get and containsKey */
private final Object internalGet(Object k) {
int h = spread(k.hashCode());
retry: for (AtomicReferenceArray tab = table; tab != null;) {
Node e, p; 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) == MOVED) {
if ((ek = e.key) instanceof TreeBin) // search TreeBin
return ((TreeBin)ek).getValue(h, k);
else { // restart with new table
tab = (AtomicReferenceArray)ek;
continue retry;
}
}
else if ((eh & HASH_BITS) == h && (ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek)))
return ev;
}
break;
}
return null;
}
/**
* 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) {
return internalReplace(k, v, cv, null);
}
private final Object internalReplace(Object k, Object v, Object cv, RemovalCallback hook) {
RuntimeException runtimeException = null;
int h = spread(k.hashCode());
Object oldVal = null;
final int newSize;
if (v != null) {
newSize = (int)poolAccessor.add(k, v, FAKE_TREE_NODE, true);
} else {
newSize = 0;
}
for (AtomicReferenceArray tab = table;;) {
Node f; int i, fh; Object fk;
if (tab == null ||
(f = tabAt(tab, i = (tab.length() - 1) & h)) == null)
break;
else if ((fh = f.hash) == MOVED) {
if ((fk = f.key) instanceof TreeBin) {
TreeBin t = (TreeBin)fk;
boolean validated = false;
boolean deleted = false;
t.acquire(0);
try {
if (tabAt(tab, i) == f) {
validated = true;
TreeNode p = t.getTreeNode(h, k, t.root);
if (p != null) {
Object pv = p.val;
if (cv == null || cv == pv || (!(cv instanceof Element) && cv.equals(pv))) {
oldVal = pv;
if ((p.val = v) == null) {
deleted = true;
t.deleteTreeNode(p);
}
poolAccessor.delete(p.size);
p.size = deleted ? -1 : newSize;
}
}
}
if (deleted && hook != null) {
try {
hook.removed(k, oldVal);
} catch (Throwable e) {
runtimeException = e instanceof RuntimeException ? (RuntimeException) e : new RuntimeException(e);
}
}
} finally {
t.release(0);
}
if (validated) {
if (deleted)
counter.add(-1L);
break;
}
}
else
tab = (AtomicReferenceArray)fk;
}
else if ((fh & HASH_BITS) != h && f.next == null) // precheck
break; // rules out possible existence
else if ((fh & LOCKED) != 0) {
checkForResize(); // try resizing if can't get lock
f.tryAwaitLock(tab, i);
}
else if (f.casHash(fh, fh | LOCKED)) {
boolean validated = false;
boolean deleted = false;
try {
if (tabAt(tab, i) == f) {
validated = true;
for (Node e = f, pred = null;;) {
Object ek, ev;
if ((e.hash & HASH_BITS) == h &&
((ev = e.val) != null) &&
((ek = e.key) == k || k.equals(ek))) {
if (cv == null || cv == ev || (!(cv instanceof Element) && 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);
}
poolAccessor.delete(e.size);
e.size = deleted ? -1 : newSize;
}
break;
}
pred = e;
if ((e = e.next) == null)
break;
}
}
if (deleted && hook != null) {
try {
hook.removed(k, oldVal);
} catch (Throwable e) {
runtimeException = e instanceof RuntimeException ? (RuntimeException) e : new RuntimeException(e);
}
}
} finally {
if (!f.casHash(fh | LOCKED, fh)) {
Node.HASH_UPDATER.set(f, fh);
synchronized (f) { f.notifyAll(); };
}
}
if (validated) {
if (deleted)
counter.add(-1L);
break;
}
}
}
if(newSize > 0 && oldVal == null) {
poolAccessor.delete(newSize);
}
if (runtimeException != null) {
throw runtimeException;
}
return oldVal;
}
/*
* Internal versions of the six insertion methods, each a
* little more complicated than the last. All have
* the same basic structure as the first (internalPut):
* 1. If table uninitialized, create
* 2. If bin empty, try to CAS new node
* 3. If bin stale, use new table
* 4. if bin converted to TreeBin, validate and relay to TreeBin methods
* 5. Lock and validate; if valid, scan and add or update
*
* The others interweave other checks and/or alternative actions:
* * Plain put checks for and performs resize after insertion.
* * putIfAbsent prescans for mapping without lock (and fails to add
* if present), which also makes pre-emptive resize checks worthwhile.
* * computeIfAbsent extends form used in putIfAbsent with additional
* mechanics to deal with, calls, potential exceptions and null
* returns from function call.
* * compute uses the same function-call mechanics, but without
* the prescans
* * merge acts as putIfAbsent in the absent case, but invokes the
* update function if present
* * putAll attempts to pre-allocate enough table space
* and more lazily performs count updates and checks.
*
* Someday when details settle down a bit more, it might be worth
* some factoring to reduce sprawl.
*/
/** Implementation for put */
private final Object internalPut(Object k, Object v) {
int h = spread(k.hashCode());
int count = 0;
for (AtomicReferenceArray tab = table;;) {
int i; Node f; int fh; Object fk;
if (tab == null)
tab = initTable();
else if ((f = 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 ((fh = f.hash) == MOVED) {
if ((fk = f.key) instanceof TreeBin) {
TreeBin t = (TreeBin)fk;
Object oldVal = null;
t.acquire(0);
try {
if (tabAt(tab, i) == f) {
count = 2;
TreeNode p = t.putTreeNode(h, k, v);
if (p != null) {
oldVal = p.val;
p.val = v;
}
}
} finally {
t.release(0);
}
if (count != 0) {
if (oldVal != null)
return oldVal;
break;
}
}
else
tab = (AtomicReferenceArray)fk;
}
else if ((fh & LOCKED) != 0) {
checkForResize();
f.tryAwaitLock(tab, i);
}
else if (f.casHash(fh, fh | LOCKED)) {
Object oldVal = null;
try { // needed in case equals() throws
if (tabAt(tab, i) == f) {
count = 1;
for (Node e = f;; ++count) {
Object ek, ev;
if ((e.hash & HASH_BITS) == h &&
(ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek))) {
oldVal = ev;
e.val = v;
break;
}
Node last = e;
if ((e = e.next) == null) {
last.next = new Node(h, k, v, null);
if (count >= TREE_THRESHOLD)
replaceWithTreeBin(tab, i, k);
break;
}
}
}
} finally { // unlock and signal if needed
if (!f.casHash(fh | LOCKED, fh)) {
Node.HASH_UPDATER.set(f, fh);
synchronized (f) { f.notifyAll(); };
}
}
if (count != 0) {
if (oldVal != null)
return oldVal;
if (tab.length() <= 64)
count = 2;
break;
}
}
}
counter.add(1L);
if (count > 1)
checkForResize();
return null;
}
private final Object internalPutIfAbsent(Object k, Object v) {
return internalPutIfAbsent(k, v, 0);
}
/** Implementation for putIfAbsent */
protected final Object internalPutIfAbsent(Object k, Object v, final int size) {
int h = spread(k.hashCode());
int count = 0;
for (AtomicReferenceArray tab = table;;) {
int i; Node f; int fh; Object fk, fv;
if (tab == null)
tab = initTable();
else if ((f = tabAt(tab, i = (tab.length() - 1) & h)) == null) {
if (casTabAt(tab, i, null, new Node(h, k, v, null, size)))
break;
}
else if ((fh = f.hash) == MOVED) {
if ((fk = f.key) instanceof TreeBin) {
TreeBin t = (TreeBin)fk;
Object oldVal = null;
t.acquire(0);
try {
if (tabAt(tab, i) == f) {
count = 2;
TreeNode p = t.putTreeNode(h, k, v, size);
if (p != null)
oldVal = p.val;
}
} finally {
t.release(0);
}
if (count != 0) {
if (oldVal != null)
return oldVal;
break;
}
}
else
tab = (AtomicReferenceArray)fk;
}
else if ((fh & HASH_BITS) == h && (fv = f.val) != null &&
((fk = f.key) == k || k.equals(fk)))
return fv;
else {
Node g = f.next;
if (g != null) { // at least 2 nodes -- search and maybe resize
for (Node e = g;;) {
Object ek, ev;
if ((e.hash & HASH_BITS) == h && (ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek)))
return ev;
if ((e = e.next) == null) {
checkForResize();
break;
}
}
}
if (((fh = f.hash) & LOCKED) != 0) {
checkForResize();
f.tryAwaitLock(tab, i);
}
else if (tabAt(tab, i) == f && f.casHash(fh, fh | LOCKED)) {
Object oldVal = null;
try {
if (tabAt(tab, i) == f) {
count = 1;
for (Node e = f;; ++count) {
Object ek, ev;
if ((e.hash & HASH_BITS) == h &&
(ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek))) {
oldVal = ev;
break;
}
Node last = e;
if ((e = e.next) == null) {
last.next = new Node(h, k, v, null, size);
if (count >= TREE_THRESHOLD)
replaceWithTreeBin(tab, i, k);
break;
}
}
}
} finally {
if (!f.casHash(fh | LOCKED, fh)) {
Node.HASH_UPDATER.set(f, fh);
synchronized (f) { f.notifyAll(); };
}
}
if (count != 0) {
if (oldVal != null)
return oldVal;
if (tab.length() <= 64)
count = 2;
break;
}
}
}
}
counter.add(1L);
if (count > 1)
checkForResize();
return null;
}
/** Implementation for putAll */
private final void internalPutAll(Map m) {
tryPresize(m.size());
long delta = 0L; // number of uncommitted additions
boolean npe = false; // to throw exception on exit for nulls
try { // to clean up counts on other exceptions
for (Map.Entry entry : m.entrySet()) {
Object k, v;
if (entry == null || (k = entry.getKey()) == null ||
(v = entry.getValue()) == null) {
npe = true;
break;
}
int h = spread(k.hashCode());
for (AtomicReferenceArray tab = table;;) {
int i; Node f; int fh; Object fk;
if (tab == null)
tab = initTable();
else if ((f = tabAt(tab, i = (tab.length() - 1) & h)) == null){
if (casTabAt(tab, i, null, new Node(h, k, v, null))) {
++delta;
break;
}
}
else if ((fh = f.hash) == MOVED) {
if ((fk = f.key) instanceof TreeBin) {
TreeBin t = (TreeBin)fk;
boolean validated = false;
t.acquire(0);
try {
if (tabAt(tab, i) == f) {
validated = true;
TreeNode p = t.getTreeNode(h, k, t.root);
if (p != null)
p.val = v;
else {
t.putTreeNode(h, k, v);
++delta;
}
}
} finally {
t.release(0);
}
if (validated)
break;
}
else
tab = (AtomicReferenceArray)fk;
}
else if ((fh & LOCKED) != 0) {
counter.add(delta);
delta = 0L;
checkForResize();
f.tryAwaitLock(tab, i);
}
else if (f.casHash(fh, fh | LOCKED)) {
int count = 0;
try {
if (tabAt(tab, i) == f) {
count = 1;
for (Node e = f;; ++count) {
Object ek, ev;
if ((e.hash & HASH_BITS) == h &&
(ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek))) {
e.val = v;
break;
}
Node last = e;
if ((e = e.next) == null) {
++delta;
last.next = new Node(h, k, v, null);
if (count >= TREE_THRESHOLD)
replaceWithTreeBin(tab, i, k);
break;
}
}
}
} finally {
if (!f.casHash(fh | LOCKED, fh)) {
Node.HASH_UPDATER.set(f, fh);
synchronized (f) { f.notifyAll(); };
}
}
if (count != 0) {
if (count > 1) {
counter.add(delta);
delta = 0L;
checkForResize();
}
break;
}
}
}
}
} finally {
if (delta != 0)
counter.add(delta);
}
if (npe)
throw new NullPointerException();
}
/* ---------------- Table Initialization and Resizing -------------- */
/**
* Returns a power of two table size for the given desired capacity.
* See Hackers Delight, sec 3.2
*/
private static final int tableSizeFor(int c) {
int n = c - 1;
n |= n >>> 1;
n |= n >>> 2;
n |= n >>> 4;
n |= n >>> 8;
n |= n >>> 16;
return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
}
/**
* Initializes table, using the size recorded in sizeCtl.
*/
private final AtomicReferenceArray initTable() {
AtomicReferenceArray tab; int sc;
while ((tab = table) == null) {
if ((sc = sizeCtl) < 0)
Thread.yield(); // lost initialization race; just spin
else if (SIZECTL_UPDATER.compareAndSet(this, sc, -1)) {
try {
if ((tab = table) == null) {
int n = (sc > 0) ? sc : DEFAULT_CAPACITY;
tab = table = new AtomicReferenceArray(n);
sc = n - (n >>> 2);
}
} finally {
SIZECTL_UPDATER.set(this, sc);
}
break;
}
}
return tab;
}
/**
* If table is too small and not already resizing, creates next
* table and transfers bins. Rechecks occupancy after a transfer
* to see if another resize is already needed because resizings
* are lagging additions.
*/
private final void checkForResize() {
AtomicReferenceArray tab; int n, sc;
while ((tab = table) != null &&
(n = tab.length()) < MAXIMUM_CAPACITY &&
(sc = sizeCtl) >= 0 && counter.sum() >= (long)sc &&
SIZECTL_UPDATER.compareAndSet(this, sc, -1)) {
try {
if (tab == table) {
table = rebuild(tab);
sc = (n << 1) - (n >>> 1);
}
} finally {
SIZECTL_UPDATER.set(this, sc);
}
}
}
/**
* Tries to presize table to accommodate the given number of elements.
*
* @param size number of elements (doesn't need to be perfectly accurate)
*/
private final void tryPresize(int size) {
int c = (size >= (MAXIMUM_CAPACITY >>> 1)) ? MAXIMUM_CAPACITY :
tableSizeFor(size + (size >>> 1) + 1);
int sc;
while ((sc = sizeCtl) >= 0) {
AtomicReferenceArray tab = table; int n;
if (tab == null || (n = tab.length()) == 0) {
n = (sc > c) ? sc : c;
if (SIZECTL_UPDATER.compareAndSet(this, sc, -1)) {
try {
if (table == tab) {
table = new AtomicReferenceArray(n);
sc = n - (n >>> 2);
}
} finally {
SIZECTL_UPDATER.set(this, sc);
}
}
}
else if (c <= sc || n >= MAXIMUM_CAPACITY)
break;
else if (SIZECTL_UPDATER.compareAndSet(this, sc, -1)) {
try {
if (table == tab) {
table = rebuild(tab);
sc = (n << 1) - (n >>> 1);
}
} finally {
SIZECTL_UPDATER.set(this, sc);
}
}
}
}
/*
* Moves and/or copies the nodes in each bin to new table. See
* above for explanation.
*
* @return the new table
*/
private static final AtomicReferenceArray rebuild(AtomicReferenceArray tab) {
int n = tab.length();
AtomicReferenceArray nextTab = new AtomicReferenceArray(n << 1);
Node fwd = new Node(MOVED, nextTab, null, null);
int[] buffer = null; // holds bins to revisit; null until needed
Node rev = null; // reverse forwarder; null until needed
int nbuffered = 0; // the number of bins in buffer list
int bufferIndex = 0; // buffer index of current buffered bin
int bin = n - 1; // current non-buffered bin or -1 if none
for (int i = bin;;) { // start upwards sweep
int fh; Node f;
if ((f = tabAt(tab, i)) == null) {
if (bin >= 0) { // Unbuffered; no lock needed (or available)
if (!casTabAt(tab, i, f, fwd))
continue;
}
else { // transiently use a locked forwarding node
Node g = new Node(MOVED|LOCKED, nextTab, null, null);
if (!casTabAt(tab, i, f, g))
continue;
setTabAt(nextTab, i, null);
setTabAt(nextTab, i + n, null);
setTabAt(tab, i, fwd);
if (!g.casHash(MOVED|LOCKED, MOVED)) {
Node.HASH_UPDATER.set(g, MOVED);
synchronized (g) { g.notifyAll(); }
}
}
}
else if ((fh = f.hash) == MOVED) {
Object fk = f.key;
if (fk instanceof TreeBin) {
TreeBin t = (TreeBin)fk;
boolean validated = false;
t.acquire(0);
try {
if (tabAt(tab, i) == f) {
validated = true;
splitTreeBin(nextTab, i, t);
setTabAt(tab, i, fwd);
}
} finally {
t.release(0);
}
if (!validated)
continue;
}
}
else if ((fh & LOCKED) == 0 && f.casHash(fh, fh|LOCKED)) {
boolean validated = false;
try { // split to lo and hi lists; copying as needed
if (tabAt(tab, i) == f) {
validated = true;
splitBin(nextTab, i, f);
setTabAt(tab, i, fwd);
}
} finally {
if (!f.casHash(fh | LOCKED, fh)) {
Node.HASH_UPDATER.set(f, fh);
synchronized (f) { f.notifyAll(); };
}
}
if (!validated)
continue;
}
else {
if (buffer == null) // initialize buffer for revisits
buffer = new int[TRANSFER_BUFFER_SIZE];
if (bin < 0 && bufferIndex > 0) {
int j = buffer[--bufferIndex];
buffer[bufferIndex] = i;
i = j; // swap with another bin
continue;
}
if (bin < 0 || nbuffered >= TRANSFER_BUFFER_SIZE) {
f.tryAwaitLock(tab, i);
continue; // no other options -- block
}
if (rev == null) // initialize reverse-forwarder
rev = new Node(MOVED, tab, null, null);
if (tabAt(tab, i) != f || (f.hash & LOCKED) == 0)
continue; // recheck before adding to list
buffer[nbuffered++] = i;
setTabAt(nextTab, i, rev); // install place-holders
setTabAt(nextTab, i + n, rev);
}
if (bin > 0)
i = --bin;
else if (buffer != null && nbuffered > 0) {
bin = -1;
i = buffer[bufferIndex = --nbuffered];
}
else
return nextTab;
}
}
/**
* Splits a normal bin with list headed by e into lo and hi parts;
* installs in given table.
*/
private static void splitBin(AtomicReferenceArray nextTab, int i, Node e) {
int bit = nextTab.length() >>> 1; // bit to split on
int runBit = e.hash & bit;
Node lastRun = e, lo = null, hi = null;
for (Node p = e.next; p != null; p = p.next) {
int b = p.hash & bit;
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 & HASH_BITS;
Object pk = p.key, pv = p.val;
int ps = p.size;
if ((ph & bit) == 0)
lo = new Node(ph, pk, pv, lo, ps);
else
hi = new Node(ph, pk, pv, hi, ps);
}
setTabAt(nextTab, i, lo);
setTabAt(nextTab, i + bit, hi);
}
/**
* Splits a tree bin into lo and hi parts; installs in given table.
*/
private static void splitTreeBin(AtomicReferenceArray nextTab, int i, TreeBin t) {
int bit = nextTab.length() >>> 1;
TreeBin lt = new TreeBin();
TreeBin ht = new TreeBin();
int lc = 0, hc = 0;
for (Node e = t.first; e != null; e = e.next) {
int h = e.hash & HASH_BITS;
Object k = e.key, v = e.val;
if ((h & bit) == 0) {
++lc;
lt.putTreeNode(h, k, v, e.size);
}
else {
++hc;
ht.putTreeNode(h, k, v, e.size);
}
e.val = null;
e.size = -1;
}
Node ln, hn; // throw away trees if too small
if (lc <= (TREE_THRESHOLD >>> 1)) {
ln = null;
for (Node p = lt.first; p != null; p = p.next)
ln = new Node(p.hash, p.key, p.val, ln, p.size);
}
else
ln = new Node(MOVED, lt, null, null);
setTabAt(nextTab, i, ln);
if (hc <= (TREE_THRESHOLD >>> 1)) {
hn = null;
for (Node p = ht.first; p != null; p = p.next)
hn = new Node(p.hash, p.key, p.val, hn, p.size);
}
else
hn = new Node(MOVED, ht, null, null);
setTabAt(nextTab, i + bit, hn);
}
/**
* Implementation for clear. Steps through each bin, removing all
* nodes.
*/
private final void internalClear() {
long delta = 0L; // negative number of deletions
int i = 0;
AtomicReferenceArray tab = table;
while (tab != null && i < tab.length()) {
int fh; Object fk;
Node f = tabAt(tab, i);
if (f == null)
++i;
else if ((fh = f.hash) == MOVED) {
if ((fk = f.key) instanceof TreeBin) {
TreeBin t = (TreeBin)fk;
t.acquire(0);
try {
if (tabAt(tab, i) == f) {
for (Node p = t.first; p != null; p = p.next) {
if (p.val != null) { // (currently always true)
p.val = null;
--delta;
}
}
t.first = null;
t.root = null;
++i;
}
} finally {
t.release(0);
}
}
else
tab = (AtomicReferenceArray)fk;
}
else if ((fh & LOCKED) != 0) {
counter.add(delta); // opportunistically update count
delta = 0L;
f.tryAwaitLock(tab, i);
}
else if (f.casHash(fh, fh | LOCKED)) {
try {
if (tabAt(tab, i) == f) {
for (Node e = f; e != null; e = e.next) {
if (e.val != null) { // (currently always true)
e.val = null;
--delta;
}
}
setTabAt(tab, i, null);
++i;
}
} finally {
if (!f.casHash(fh | LOCKED, fh)) {
Node.HASH_UPDATER.set(f, fh);
synchronized (f) { f.notifyAll(); };
}
}
}
}
if (delta != 0)
counter.add(delta);
poolAccessor.clear();
}
/* ----------------Table Traversal -------------- */
/**
* Encapsulates traversal for methods such as containsValue; also
* serves as a base class for other iterators and bulk tasks.
*
* 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 non-null 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. To support iterator.remove, the nextKey field is not
* updated (nulled out) when the iterator cannot advance.
*
* Internal traversals directly access these fields, as in:
* {@code while (it.advance() != null) { process(it.nextKey); }}
*
* Exported iterators must track whether the iterator has advanced
* (in hasNext vs next) (by setting/checking/nulling field
* nextVal), and then extract key, value, or key-value pairs as
* return values of next().
*
* The iterator visits once each still-valid node that was
* reachable upon iterator construction. 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.
*
* This class extends CountedCompleter to streamline parallel
* iteration in bulk operations. This adds only a few fields of
* space overhead, which is small enough in cases where it is not
* needed to not worry about it. Because CountedCompleter is
* Serializable, but iterators need not be, we need to add warning
* suppressions.
*/
@SuppressWarnings("serial") static class Traverser {
final ConcurrentHashMap map;
Node next; // the next entry to use
Object nextKey; // cached key field of next
Object nextVal; // cached val field of next
AtomicReferenceArray tab; // current table; updated if resized
int index; // index of bin to use next
int baseIndex; // current index of initial table
int baseLimit; // index bound for initial table
int baseSize; // initial table size
int batch; // split control
/** Creates iterator for all entries in the table. */
Traverser(ConcurrentHashMap map) {
this.map = map;
}
/** Creates iterator for split() methods and task constructors */
Traverser(ConcurrentHashMap map, Traverser it, int batch) {
this.batch = batch;
if ((this.map = map) != null && it != null) { // split parent
AtomicReferenceArray t;
if ((t = it.tab) == null &&
(t = it.tab = map.table) != null)
it.baseLimit = it.baseSize = t.length();
this.tab = t;
this.baseSize = it.baseSize;
int hi = this.baseLimit = it.baseLimit;
it.baseLimit = this.index = this.baseIndex =
(hi + it.baseIndex + 1) >>> 1;
}
}
/**
* Advances next; returns nextVal or null if terminated.
* See above for explanation.
*/
final Object advance() {
Node e = next;
Object ev = null;
outer: do {
if (e != null) // advance past used/skipped node
e = e.next;
while (e == null) { // get to next non-null bin
ConcurrentHashMap m;
AtomicReferenceArray t; int b, i, n; Object ek; // checks must use locals
if ((t = tab) != null)
n = t.length();
else if ((m = map) != null && (t = tab = m.table) != null)
n = baseLimit = baseSize = t.length();
else
break outer;
if ((b = baseIndex) >= baseLimit ||
(i = index) < 0 || i >= n)
break outer;
if ((e = tabAt(t, i)) != null && e.hash == MOVED) {
if ((ek = e.key) instanceof TreeBin)
e = ((TreeBin)ek).first;
else {
tab = (AtomicReferenceArray)ek;
continue; // restarts due to null val
}
} // visit upper slots if present
index = (i += baseSize) < n ? i : (baseIndex = b + 1);
}
nextKey = e.key;
} while ((ev = e.val) == null); // skip deleted or special nodes
next = e;
return nextVal = ev;
}
public final void remove() {
Object k = nextKey;
if (k == null && (advance() == null || (k = nextKey) == null))
throw new IllegalStateException();
map.internalReplace(k, null, null);
}
public final boolean hasNext() {
return nextVal != null || advance() != null;
}
public final boolean hasMoreElements() { return hasNext(); }
public void compute() { } // default no-op CountedCompleter body
}
/* ---------------- Public operations -------------- */
/**
* Creates a new, empty map with the default initial table size (16).
*/
public ConcurrentHashMap() {
this.counter = new LongAdder();
this.poolAccessor = UnboundedPool.UNBOUNDED_ACCESSOR;
}
/**
* Creates a new, empty map with an initial table size
* accommodating the specified number of elements without the need
* to dynamically resize.
*
* @param initialCapacity The implementation performs internal
* sizing to accommodate this many elements.
* @throws IllegalArgumentException if the initial capacity of
* elements is negative
*/
public ConcurrentHashMap(int initialCapacity) {
if (initialCapacity < 0)
throw new IllegalArgumentException();
int cap = ((initialCapacity >= (MAXIMUM_CAPACITY >>> 1)) ?
MAXIMUM_CAPACITY :
tableSizeFor(initialCapacity + (initialCapacity >>> 1) + 1));
this.counter = new LongAdder();
SIZECTL_UPDATER.set(this, cap);
this.poolAccessor = UnboundedPool.UNBOUNDED_ACCESSOR;
}
/**
* Creates a new map with the same mappings as the given map.
*
* @param m the map
*/
public ConcurrentHashMap(Map m) {
this.counter = new LongAdder();
SIZECTL_UPDATER.set(this, DEFAULT_CAPACITY);
this.poolAccessor = UnboundedPool.UNBOUNDED_ACCESSOR;
internalPutAll(m);
}
/**
* Creates a new, empty map with an initial table size based on
* the given number of elements ({@code initialCapacity}) and
* initial table density ({@code loadFactor}).
*
* @param initialCapacity the initial capacity. The implementation
* performs internal sizing to accommodate this many elements,
* given the specified load factor.
* @param loadFactor the load factor (table density) for
* establishing the initial table size
* @throws IllegalArgumentException if the initial capacity of
* elements is negative or the load factor is nonpositive
*
* @since 1.6
*/
public ConcurrentHashMap(int initialCapacity, float loadFactor) {
this(initialCapacity, loadFactor, 1);
}
/**
* Creates a new, empty map with an initial table size based on
* the given number of elements ({@code initialCapacity}), table
* density ({@code loadFactor}), and number of concurrently
* updating threads ({@code concurrencyLevel}).
*
* @param initialCapacity the initial capacity. The implementation
* performs internal sizing to accommodate this many elements,
* given the specified load factor.
* @param loadFactor the load factor (table density) for
* establishing the initial table size
* @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 ConcurrentHashMap(int initialCapacity,
float loadFactor, int concurrencyLevel) {
if (!(loadFactor > 0.0f) || initialCapacity < 0 || concurrencyLevel <= 0)
throw new IllegalArgumentException();
if (initialCapacity < concurrencyLevel) // Use at least as many bins
initialCapacity = concurrencyLevel; // as estimated threads
long size = (long)(1.0 + (long)initialCapacity / loadFactor);
int cap = (size >= (long)MAXIMUM_CAPACITY) ?
MAXIMUM_CAPACITY : tableSizeFor((int)size);
this.counter = new LongAdder();
SIZECTL_UPDATER.set(this, cap);
this.poolAccessor = UnboundedPool.UNBOUNDED_ACCESSOR;
}
protected void setPoolAccessor(final PoolAccessor poolAccessor) {
this.poolAccessor = poolAccessor;
}
/**
* Creates a new {@link Set} backed by a ConcurrentHashMap
* from the given type to {@code Boolean.TRUE}.
*
* @return the new set
*/
public static KeySetView newKeySet() {
return new KeySetView(new ConcurrentHashMap(),
Boolean.TRUE);
}
/**
* Creates a new {@link Set} backed by a ConcurrentHashMap
* from the given type to {@code Boolean.TRUE}.
*
* @param initialCapacity The implementation performs internal
* sizing to accommodate this many elements.
* @throws IllegalArgumentException if the initial capacity of
* elements is negative
* @return the new set
*/
public static KeySetView newKeySet(int initialCapacity) {
return new KeySetView(new ConcurrentHashMap(initialCapacity),
Boolean.TRUE);
}
/**
* {@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 number of mappings. This method should be used
* instead of {@link #size} because a ConcurrentHashMap may
* contain more mappings than can be represented as an int. The
* value returned is an estimate; the actual count may differ if
* there are concurrent insertions or removals.
*
* @return the number of mappings
*/
public long mappingCount() {
long n = counter.sum();
return (n < 0L) ? 0L : n; // ignore transient negative values
}
/**
* 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);
}
@Deprecated
public void recalculateSize(final K k) {
Object val = null;
int previousSize = 0;
int newSize = 0;
long delta = Long.MIN_VALUE;
boolean calculating = true;
int h = spread(k.hashCode());
while(calculating) {
for (AtomicReferenceArray tab = table;;) {
Node f; int i, fh; Object fk;
if (tab == null ||
(f = tabAt(tab, i = (tab.length() - 1) & h)) == null) {
calculating = false;
break;
} else if ((fh = f.hash) == MOVED) {
if ((fk = f.key) instanceof TreeBin) {
TreeBin t = (TreeBin)fk;
t.acquire(0);
try {
if (tabAt(tab, i) == f) {
TreeNode p = t.getTreeNode(h, k, t.root);
if (p != null) {
if (val == null) {
val = p.val;
previousSize = p.size;
} else if(p.size == previousSize && p.val == val) {
p.size += delta;
newSize = p.size;
calculating = false;
} else {
calculating = false;
}
} else {
calculating = false;
}
break;
}
} finally {
t.release(0);
}
} else {
tab = (AtomicReferenceArray)fk;
}
}
else if ((fh & HASH_BITS) != h && f.next == null) { // precheck
calculating = false;
break; // rules out possible existence
} else if ((fh & LOCKED) != 0) {
checkForResize(); // try resizing if can't get lock
f.tryAwaitLock(tab, i);
}
else if (f.casHash(fh, fh | LOCKED)) {
boolean validated = false;
try {
if (tabAt(tab, i) == f) {
validated = true;
for (Node e = f;;) {
Object ek;
if ((e.hash & HASH_BITS) == h &&
((ek = e.key) == k || k.equals(ek))) {
if (val == null) {
val = e.val;
previousSize = e.size;
} else if(e.size == previousSize && e.val == val) {
e.size += delta;
newSize = e.size;
calculating = false;
} else {
calculating = false;
}
break;
}
if ((e = e.next) == null)
break;
}
}
} finally {
if (!f.casHash(fh | LOCKED, fh)) {
Node.HASH_UPDATER.set(f, fh);
synchronized (f) { f.notifyAll(); };
}
}
if (validated) {
break;
}
}
}
if(val != null) { // Found a value
if (delta == Long.MIN_VALUE) { // Didn't resize it
delta = poolAccessor.replace(previousSize, k, val, FAKE_TREE_NODE, true);
} else if (newSize == 0) { // Resized it, but couldn't save it (entry removed or modified: val or sizing info)
poolAccessor.delete(delta);
calculating = false;
} else {
calculating = false;
}
} else { // Didn't find an entry for this key
calculating = false;
}
}
}
public List getRandomValues(int amount) {
ArrayList sampled = new ArrayList(amount * 2);
// pick a random starting point in the table
int randomHash = ThreadLocalRandom.current().nextInt();
AtomicReferenceArray tab = table;
if(tab == null) {
return sampled;
}
final int tableStart = randomHash & (tab.length() - 1);
int tableIndex = tableStart;
outer:
do {
Node e;
Object ek;
for (e = tabAt(tab, tableIndex); e != null; e = e.next) {
if (e.hash == MOVED) {
if ((ek = e.key) instanceof TreeBin) {
e = ((TreeBin)ek).first;
if(e == null)
break;
sampled.add((V)e.val);
if (sampled.size() == amount) {
break outer;
}
} else {
tab = (AtomicReferenceArray)ek;
break;
}
} else {
sampled.add((V)e.val);
if (sampled.size() == amount) {
break outer;
}
}
}
tableIndex = (tableIndex + 1) & (tab.length() - 1);
} while (tableIndex != tableStart);
return sampled;
}
/**
* Returns the value to which the specified key is mapped,
* or the given defaultValue if this map contains no mapping for the key.
*
* @param key the key
* @param defaultValue the value to return if this map contains
* no mapping for the given key
* @return the mapping for the key, if present; else the defaultValue
* @throws NullPointerException if the specified key is null
*/
@SuppressWarnings("unchecked") public V getValueOrDefault(Object key, V defaultValue) {
if (key == null)
throw new NullPointerException();
V v = (V) internalGet(key);
return v == null ? defaultValue : v;
}
/**
* 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;
Traverser it = new Traverser(this);
while ((v = it.advance()) != null) {
if (v == value || value.equals(v))
return true;
}
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
* 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);
}
/**
* {@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)internalPutIfAbsent(key, value);
}
/**
* 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 m) {
internalPutAll(m);
}
/**
* 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;
}
protected boolean remove(Object key, Object value, RemovalCallback hook) {
if (key == null)
throw new NullPointerException();
if (value == null)
return false;
return internalReplace(key, null, value, hook) != null;
}
protected V removeAndNotify(Object key, RemovalCallback hook) {
return (V)internalReplace(key, null, null, hook);
}
protected V removeAndNotify(Object key, Object value, RemovalCallback hook) {
return (V)internalReplace(key, null, value, hook);
}
/**
* {@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.
*
* @return the set view
*/
public KeySetView keySet() {
KeySetView ks = keySet;
return (ks != null) ? ks : (keySet = new KeySetView(this, null));
}
/**
* Returns a {@link Set} view of the keys in this map, using the
* given common mapped value for any additions (i.e., {@link
* Collection#add} and {@link Collection#addAll}). This is of
* course only appropriate if it is acceptable to use the same
* value for all additions from this view.
*
* @param mappedValue the mapped value to use for any
* additions.
* @return the set view
* @throws NullPointerException if the mappedValue is null
*/
public KeySetView keySet(V mappedValue) {
if (mappedValue == null)
throw new NullPointerException();
return new KeySetView(this, mappedValue);
}
/**
* 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.
*/
public ValuesView values() {
ValuesView vs = values;
return (vs != null) ? vs : (values = new ValuesView(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() {
EntrySetView es = entrySet;
return (es != null) ? es : (entrySet = new EntrySetView(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 a partitionable iterator of the keys in this map.
*
* @return a partitionable iterator of the keys in this map
*/
public Spliterator keySpliterator() {
return new KeyIterator(this);
}
/**
* Returns a partitionable iterator of the values in this map.
*
* @return a partitionable iterator of the values in this map
*/
public Spliterator valueSpliterator() {
return new ValueIterator(this);
}
/**
* Returns a partitionable iterator of the entries in this map.
*
* @return a partitionable iterator of the entries in this map
*/
public Spliterator> entrySpliterator() {
return new EntryIterator(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;
Traverser it = new Traverser(this);
Object v;
while ((v = it.advance()) != null) {
h += it.nextKey.hashCode() ^ v.hashCode();
}
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() {
Traverser it = new Traverser(this);
StringBuilder sb = new StringBuilder();
sb.append('{');
Object v;
if ((v = it.advance()) != null) {
for (;;) {
Object k = it.nextKey;
sb.append(k == this ? "(this Map)" : k);
sb.append('=');
sb.append(v == this ? "(this Map)" : v);
if ((v = it.advance()) == 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;
Traverser it = new Traverser(this);
Object val;
while ((val = it.advance()) != null) {
Object v = m.get(it.nextKey);
if (v == null || (v != val && !v.equals(val)))
return false;
}
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 -------------- */
@SuppressWarnings("serial") static final class KeyIterator extends Traverser
implements Spliterator, Enumeration {
KeyIterator(ConcurrentHashMap map) { super(map); }
KeyIterator(ConcurrentHashMap map, Traverser it) {
super(map, it, -1);
}
public KeyIterator split() {
if (nextKey != null)
throw new IllegalStateException();
return new KeyIterator(map, this);
}
@SuppressWarnings("unchecked") public final K next() {
if (nextVal == null && advance() == null)
throw new NoSuchElementException();
Object k = nextKey;
nextVal = null;
return (K) k;
}
public final K nextElement() { return next(); }
}
@SuppressWarnings("serial") static final class ValueIterator extends Traverser
implements Spliterator, Enumeration {
ValueIterator(ConcurrentHashMap map) { super(map); }
ValueIterator(ConcurrentHashMap map, Traverser it) {
super(map, it, -1);
}
public ValueIterator split() {
if (nextKey != null)
throw new IllegalStateException();
return new ValueIterator(map, this);
}
@SuppressWarnings("unchecked") public final V next() {
Object v;
if ((v = nextVal) == null && (v = advance()) == null)
throw new NoSuchElementException();
nextVal = null;
return (V) v;
}
public final V nextElement() { return next(); }
}
@SuppressWarnings("serial") static final class EntryIterator extends Traverser
implements Spliterator> {
EntryIterator(ConcurrentHashMap map) { super(map); }
EntryIterator(ConcurrentHashMap map, Traverser it) {
super(map, it, -1);
}
public EntryIterator split() {
if (nextKey != null)
throw new IllegalStateException();
return new EntryIterator(map, this);
}
@SuppressWarnings("unchecked") public final Map.Entry next() {
Object v;
if ((v = nextVal) == null && (v = advance()) == null)
throw new NoSuchElementException();
Object k = nextKey;
nextVal = null;
return new MapEntry((K)k, (V)v, map);
}
}
/**
* Exported Entry for iterators
*/
static final class MapEntry implements Map.Entry {
final K key; // non-null
V val; // non-null
final ConcurrentHashMap map;
MapEntry(K key, V val, ConcurrentHashMap map) {
this.key = key;
this.val = val;
this.map = map;
}
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 we do 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;
}
}
/**
* Returns exportable snapshot entry for the given key and value
* when write-through can't or shouldn't be used.
*/
static AbstractMap.SimpleEntry entryFor(K k, V v) {
return new AbstractMap.SimpleEntry(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; }
}
/* ----------------Views -------------- */
/**
* Base class for views.
*/
static abstract class CHMView {
final ConcurrentHashMap map;
CHMView(ConcurrentHashMap map) { this.map = map; }
/**
* Returns the map backing this view.
*
* @return the map backing this view
*/
public ConcurrentHashMap getMap() { return map; }
public final int size() { return map.size(); }
public final boolean isEmpty() { return map.isEmpty(); }
public final void clear() { map.clear(); }
// implementations below rely on concrete classes supplying these
abstract public Iterator iterator();
abstract public boolean contains(Object o);
abstract public boolean remove(Object o);
private static final String oomeMsg = "Required array size too large";
public final Object[] toArray() {
long sz = map.mappingCount();
if (sz > (long)(MAX_ARRAY_SIZE))
throw new OutOfMemoryError(oomeMsg);
int n = (int)sz;
Object[] r = new Object[n];
int i = 0;
Iterator it = iterator();
while (it.hasNext()) {
if (i == n) {
if (n >= MAX_ARRAY_SIZE)
throw new OutOfMemoryError(oomeMsg);
if (n >= MAX_ARRAY_SIZE - (MAX_ARRAY_SIZE >>> 1) - 1)
n = MAX_ARRAY_SIZE;
else
n += (n >>> 1) + 1;
r = Arrays.copyOf(r, n);
}
r[i++] = it.next();
}
return (i == n) ? r : Arrays.copyOf(r, i);
}
@SuppressWarnings("unchecked") public final T[] toArray(T[] a) {
long sz = map.mappingCount();
if (sz > (long)(MAX_ARRAY_SIZE))
throw new OutOfMemoryError(oomeMsg);
int m = (int)sz;
T[] r = (a.length >= m) ? a :
(T[])java.lang.reflect.Array
.newInstance(a.getClass().getComponentType(), m);
int n = r.length;
int i = 0;
Iterator it = iterator();
while (it.hasNext()) {
if (i == n) {
if (n >= MAX_ARRAY_SIZE)
throw new OutOfMemoryError(oomeMsg);
if (n >= MAX_ARRAY_SIZE - (MAX_ARRAY_SIZE >>> 1) - 1)
n = MAX_ARRAY_SIZE;
else
n += (n >>> 1) + 1;
r = Arrays.copyOf(r, n);
}
r[i++] = (T)it.next();
}
if (a == r && i < n) {
r[i] = null; // null-terminate
return r;
}
return (i == n) ? r : Arrays.copyOf(r, i);
}
public final int hashCode() {
int h = 0;
for (Iterator it = iterator(); it.hasNext();)
h += it.next().hashCode();
return h;
}
public final String toString() {
StringBuilder sb = new StringBuilder();
sb.append('[');
Iterator it = iterator();
if (it.hasNext()) {
for (;;) {
Object e = it.next();
sb.append(e == this ? "(this Collection)" : e);
if (!it.hasNext())
break;
sb.append(',').append(' ');
}
}
return sb.append(']').toString();
}
public final boolean containsAll(Collection c) {
if (c != this) {
for (Iterator it = c.iterator(); it.hasNext();) {
Object e = it.next();
if (e == null || !contains(e))
return false;
}
}
return true;
}
public final boolean removeAll(Collection c) {
boolean modified = false;
for (Iterator it = iterator(); it.hasNext();) {
if (c.contains(it.next())) {
it.remove();
modified = true;
}
}
return modified;
}
public final boolean retainAll(Collection c) {
boolean modified = false;
for (Iterator it = iterator(); it.hasNext();) {
if (!c.contains(it.next())) {
it.remove();
modified = true;
}
}
return modified;
}
}
/**
* A view of a ConcurrentHashMap as a {@link Set} of keys, in
* which additions may optionally be enabled by mapping to a
* common value. This class cannot be directly instantiated. See
* {@link #keySet}, {@link #keySet(Object)}, {@link #newKeySet()},
* {@link #newKeySet(int)}.
*/
public static class KeySetView extends CHMView implements Set, java.io.Serializable {
private static final long serialVersionUID = 7249069246763182397L;
private final V value;
KeySetView(ConcurrentHashMap map, V value) { // non-public
super(map);
this.value = value;
}
/**
* Returns the default mapped value for additions,
* or {@code null} if additions are not supported.
*
* @return the default mapped value for additions, or {@code null}
* if not supported.
*/
public V getMappedValue() { return value; }
// implement Set API
public boolean contains(Object o) { return map.containsKey(o); }
public boolean remove(Object o) { return map.remove(o) != null; }
/**
* Returns 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.
*
* @return an iterator over the keys of this map
*/
public Iterator iterator() { return new KeyIterator(map); }
public boolean add(K e) {
V v;
if ((v = value) == null)
throw new UnsupportedOperationException();
if (e == null)
throw new NullPointerException();
return map.internalPutIfAbsent(e, v) == null;
}
public boolean addAll(Collection c) {
boolean added = false;
V v;
if ((v = value) == null)
throw new UnsupportedOperationException();
for (K e : c) {
if (e == null)
throw new NullPointerException();
if (map.internalPutIfAbsent(e, v) == null)
added = true;
}
return added;
}
public boolean equals(Object o) {
Set c;
return ((o instanceof Set) &&
((c = (Set)o) == this ||
(containsAll(c) && c.containsAll(this))));
}
}
/**
* A view of a ConcurrentHashMap as a {@link Collection} of
* values, in which additions are disabled. This class cannot be
* directly instantiated. See {@link #values},
*
* 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 static final class ValuesView extends CHMView
implements Collection {
ValuesView(ConcurrentHashMap map) { super(map); }
public final boolean contains(Object o) { return map.containsValue(o); }
public final boolean remove(Object o) {
if (o != null) {
Iterator it = new ValueIterator(map);
while (it.hasNext()) {
if (o.equals(it.next())) {
it.remove();
return true;
}
}
}
return false;
}
/**
* Returns 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.
*
* @return an iterator over the values of this map
*/
public final Iterator iterator() {
return new ValueIterator(map);
}
public final boolean add(V e) {
throw new UnsupportedOperationException();
}
public final boolean addAll(Collection c) {
throw new UnsupportedOperationException();
}
}
/**
* A view of a ConcurrentHashMap as a {@link Set} of (key, value)
* entries. This class cannot be directly instantiated. See
* {@link #entrySet}.
*/
public static final class EntrySetView extends CHMView
implements Set> {
EntrySetView(ConcurrentHashMap map) { super(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));
}
/**
* Returns 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.
*
* @return an iterator over the entries of this map
*/
public final Iterator> iterator() {
return new EntryIterator(map);
}
public final boolean add(Entry e) {
K key = e.getKey();
V value = e.getValue();
if (key == null || value == null)
throw new NullPointerException();
return map.internalPut(key, value) == null;
}
public final boolean addAll(Collection> c) {
boolean added = false;
for (Entry e : c) {
if (add(e))
added = true;
}
return added;
}
public boolean equals(Object o) {
Set c;
return ((o instanceof Set) &&
((c = (Set)o) == this ||
(containsAll(c) && c.containsAll(this))));
}
}
private static final AtomicIntegerFieldUpdater SIZECTL_UPDATER = AtomicIntegerFieldUpdater.newUpdater(ConcurrentHashMap.class, "sizeCtl");
protected static interface RemovalCallback {
void removed(Object key, Object value);
}
}