JDK8의 ConcurrentHashMap 원본 해독
본고는 주로put(),transfer(),addCount()에 대해 분석(replaceNode()원본이put와 비슷하면 더 이상 말하지 않는다)
만약 여러분들이 그에 대해 이의가 있다면, 메시지를 남겨 주십시오.
공동 발전(2018-03-02)
package java.util.concurrent;
import java.io.ObjectStreamField;
import java.io.Serializable;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.AbstractMap;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.Spliterator;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.LockSupport;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.BinaryOperator;
import java.util.function.Consumer;
import java.util.function.DoubleBinaryOperator;
import java.util.function.Function;
import java.util.function.IntBinaryOperator;
import java.util.function.LongBinaryOperator;
import java.util.function.ToDoubleBiFunction;
import java.util.function.ToDoubleFunction;
import java.util.function.ToIntBiFunction;
import java.util.function.ToIntFunction;
import java.util.function.ToLongBiFunction;
import java.util.function.ToLongFunction;
import java.util.stream.Stream;
/**
* A hash table supporting full concurrency of retrievals and
* high expected concurrency for updates. This class obeys the
* same functional specification as {
@link java.util.Hashtable}, and
* includes versions of methods corresponding to each method of
* {
@code Hashtable}. However, even though all operations are
* thread-safe, retrieval operations do not entail locking,
* and there is not any support for locking the entire table
* in a way that prevents all access. This class is fully
* interoperable with {
@code Hashtable} in programs that rely on its
* thread safety but not on its synchronization details.
*
* Retrieval operations (including {
@code get}) generally do not
* block, so may overlap with update operations (including {
@code put}
* and {
@code remove}). Retrievals reflect the results of the most
* recently completed update operations holding upon their
* onset. (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, Spliterators 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
* java.util.ConcurrentModificationException 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. To ameliorate impact, when keys are {
@link Comparable},
* this class may use comparison order among keys to help break ties.
*
* 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
* java.util.concurrent.atomic.LongAdder} values and initializing via
* {
@link #computeIfAbsent computeIfAbsent}. For example, to add a count
* to a {
@code ConcurrentHashMap
* 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.
*
*
*
*
*
* These bulk operations accept a {
@code parallelismThreshold}
* argument. Methods proceed sequentially if the current map size is
* estimated to be less than the given threshold. Using a value of
* {
@code Long.MAX_VALUE} suppresses all parallelism. Using a value
* of {
@code 1} results in maximal parallelism by partitioning into
* enough subtasks to fully utilize the {
@link
* ForkJoinPool#commonPool()} that is used for all parallel
* computations. Normally, you would initially choose one of these
* extreme values, and then measure performance of using in-between
* values that trade off overhead versus throughput.
*
* 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.
*
* Speedups for parallel compared to sequential forms are common
* but not guaranteed. Parallel operations involving brief functions
* on small maps may execute more slowly than sequential forms 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.
*
* This class is a member of the
* {@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework.
*
* @since 1.5
* @author Doug Lea
* @param <K> the type of keys maintained by this map
* @param <V> the type of mapped values
*/
public class ConcurrentHashMap,V> extends AbstractMap,V>
implements ConcurrentMap,V>, Serializable {
private static final long serialVersionUID = 7249069246763182397L;
/*
* 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.
*
* This map usually acts as a binned (bucketed) hash table. Each
* key-value mapping is held in a Node. Most nodes are instances
* of the basic Node class with hash, key, value, and next
* fields. However, various subclasses exist: TreeNodes are
* arranged in balanced trees, not lists. TreeBins hold the roots
* of sets of TreeNodes. ForwardingNodes are placed at the heads
* of bins during resizing. ReservationNodes are used as
* placeholders while establishing values in computeIfAbsent and
* related methods. The types TreeBin, ForwardingNode, and
* ReservationNode do not hold normal user keys, values, or
* hashes, and are readily distinguishable during search etc
* because they have negative hash fields and null key and value
* fields. (These special nodes are either uncommon or transient,
* so the impact of carrying around some unused fields is
* insignificant.)
*
* 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.
*
* We use the top (sign) bit of Node hash fields for control
* purposes -- it is available anyway because of addressing
* constraints. Nodes with negative hash fields are specially
* handled or ignored in map methods.
*
* 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. Locking support for these locks relies on builtin
* "synchronized" monitors.
*
* 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).
*
* 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 or ones that differs only
* in masked-out high bits. So we use a secondary strategy that
* applies when the number of nodes in a bin exceeds a
* threshold. 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 at least 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). Any thread
* noticing an overfull bin may assist in resizing after the
* initiating thread allocates and sets up the replacement array.
* However, rather than stalling, these other threads may proceed
* with insertions etc. The use of TreeBins shields us from the
* worst case effects of overfilling while resizes are in
* progress. Resizing proceeds by transferring bins, one by one,
* from the table to the next table. However, threads claim small
* blocks of indices to transfer (via field transferIndex) before
* doing so, reducing contention. A generation stamp in field
* sizeCtl ensures that resizings do not overlap. 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, which can stall
* waiting for locks while resizing. However, because other
* threads can join in and help resize rather than contend for
* locks, average aggregate waits become shorter as resizing
* progresses. The transfer operation must also ensure that all
* accessible bins in both the old and new table are usable by any
* traversal. This is arranged in part by proceeding from the
* last bin (table.length - 1) up towards the first. Upon seeing
* a forwarding node, traversals (see class Traverser) arrange to
* move to the new table without revisiting nodes. To ensure that
* no intervening nodes are skipped even when moved out of order,
* a stack (see class TableStack) is created on first encounter of
* a forwarding node during a traversal, to maintain its place if
* later processing the current table. The need for these
* save/restore mechanics is relatively rare, but when one
* forwarding node is encountered, typically many more will be.
* So Traversers use a simple caching scheme to avoid creating so
* many new TableStack nodes. (Thanks to Peter Levart for
* suggesting use of a stack here.)
*
* 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 specialization of
* LongAdder. We need to incorporate a specialization rather than
* just use a LongAdder in order to access implicit
* contention-sensing that leads to creation of multiple
* CounterCells. The counter mechanics avoid contention on
* updates but can encounter cache thrashing if read too
* frequently during concurrent access. To avoid reading so often,
* resizing under contention is attempted only upon adding to a
* bin already holding two or more nodes. 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).
*
* 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
* Comparable.compareTo order if applicable. On lookup at a node,
* if elements are not comparable or compare as 0 then 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.) On insertion, to keep a total ordering (or as
* close as is required here) across rebalancings, we compare
* classes and identityHashCodes as tie-breakers. 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 require an additional locking mechanism. While
* list traversal is always possible by readers even during
* updates, tree traversal is not, mainly because of tree-rotations
* that may change the root node and/or its linkages. TreeBins
* include a simple read-write lock mechanism parasitic on the
* main bin-synchronization strategy: Structural adjustments
* associated with an insertion or removal are already bin-locked
* (and so cannot conflict with other writers) but must wait for
* ongoing readers to finish. Since there can be only one such
* waiter, we use a simple scheme using a single "waiter" field to
* block writers. However, readers need never block. If the root
* lock is held, 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.
*
* 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.
*
* Also, solely for compatibility with previous versions of this
* class, it extends AbstractMap, even though all of its methods
* are overridden, so it is just useless baggage.
*
* This file is organized to make things a little easier to follow
* while reading than they might otherwise: First the main static
* declarations and utilities, then fields, then main public
* methods (with a few factorings of multiple public methods into
* internal ones), then sizing methods, trees, traversers, and
* bulk operations.
*/
/* ---------------- 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.
*/
/**
* Concurrency_level ， 1.8
* ， Concurrecy_level
*/
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 bin count threshold for using a tree rather than list for a
* bin. Bins are converted to trees when adding an element to a
* bin with at least this many nodes. The value must be greater
* than 2, and should be at least 8 to mesh with assumptions in
* tree removal about conversion back to plain bins upon
* shrinkage.
*/
static final int TREEIFY_THRESHOLD = 8;
/**
* The bin count threshold for untreeifying a (split) bin during a
* resize operation. Should be less than TREEIFY_THRESHOLD, and at
* most 6 to mesh with shrinkage detection under removal.
*/
static final int UNTREEIFY_THRESHOLD = 6;
/**
* The smallest table capacity for which bins may be treeified.
* (Otherwise the table is resized if too many nodes in a bin.)
* The value should be at least 4 * TREEIFY_THRESHOLD to avoid
* conflicts between resizing and treeification thresholds.
*/
static final int MIN_TREEIFY_CAPACITY = 64;
/**
* Minimum number of rebinnings per transfer step. Ranges are
* subdivided to allow multiple resizer threads. This value
* serves as a lower bound to avoid resizers encountering
* excessive memory contention. The value should be at least
* DEFAULT_CAPACITY.
*/
/**
* ( ) slot （ CPU ）， ，
*
*/
private static final int MIN_TRANSFER_STRIDE = 16;
/**
* The number of bits used for generation stamp in sizeCtl.
* Must be at least 6 for 32bit arrays.
*/
private static int RESIZE_STAMP_BITS = 16;
/**
* The maximum number of threads that can help resize.
* Must fit in 32 - RESIZE_STAMP_BITS bits.
*/
private static final int MAX_RESIZERS = (1 << (32 - RESIZE_STAMP_BITS)) - 1;
/**
* The bit shift for recording size stamp in sizeCtl.
*/
private static final int RESIZE_STAMP_SHIFT = 32 - RESIZE_STAMP_BITS;
/*
* Encodings for Node hash fields. See above for explanation.
*/
/**
* hash -1 ForwardingNode，ForwardingNode MOVED
* ，TREEBIN TreeBin ,RESERVED ReservationNode
*/
static final int MOVED = -1; // hash for forwarding nodes
static final int TREEBIN = -2; // hash for roots of trees
static final int RESERVED = -3; // hash for transient reservations
static final int HASH_BITS = 0x7fffffff; // usable bits of normal node hash
/** Number of CPUS, to place bounds on some sizings */
static final int NCPU = Runtime.getRuntime().availableProcessors();
/** For serialization compatibility. */
private static final ObjectStreamField[] serialPersistentFields = {
new ObjectStreamField("segments", Segment[].class),
new ObjectStreamField("segmentMask", Integer.TYPE),
new ObjectStreamField("segmentShift", Integer.TYPE)
};
/* ---------------- Nodes -------------- */
/**
* Key-value entry. This class is never exported out as a
* user-mutable Map.Entry (i.e., one supporting setValue; see
* MapEntry below), but can be used for read-only traversals used
* in bulk tasks. Subclasses of Node with a negative hash field
* are special, and contain null keys and values (but are never
* exported). Otherwise, keys and vals are never null.
*/
static class Node,V> implements Map.Entry,V> {
final int hash;
final K key;
volatile V val;
volatile Node,V> next;
Node(int hash, K key, V val, Node,V> next) {
this.hash = hash;
this.key = key;
this.val = val;
this.next = next;
}
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 V setValue(V value) {
throw new UnsupportedOperationException();
}
public final boolean equals(Object o) {
Object k, v, u; 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 == (u = val) || v.equals(u)));
}
/**
* Virtualized support for map.get(); overridden in subclasses.
*/
Node,V> find(int h, Object k) {
Node,V> e = this;
if (k != null) {
do {
K ek;
if (e.hash == h &&
((ek = e.key) == k || (ek != null && k.equals(ek))))
return e;
} while ((e = e.next) != null);
}
return null;
}
}
/* ---------------- Static utilities -------------- */
/**
* Spreads (XORs) higher bits of hash to lower and also forces top
* bit 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.) So 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 (so don't benefit from
* spreading), and because we use trees to handle large sets of
* collisions in bins, we just XOR some shifted bits in the
* cheapest possible way to reduce systematic lossage, as well as
* to incorporate impact of the highest bits that would otherwise
* never be used in index calculations because of table bounds.
*/
/**
* hashcode， hashcode 16 hashcode
*/
static final int spread(int h) {
return (h ^ (h >>> 16)) & HASH_BITS;
}
/**
* 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;
}
/**
* Returns x's Class if it is of the form "class C implements
* Comparable,V> Node,V> tabAt(Node,V>[] tab, int i) {
return (Node,V>)U.getObjectVolatile(tab, ((long)i << ASHIFT) + ABASE);
}
static final ,V> boolean casTabAt(Node,V>[] tab, int i,
Node,V> c, Node,V> v) {
return U.compareAndSwapObject(tab, ((long)i << ASHIFT) + ABASE, c, v);
}
static final ,V> void setTabAt(Node,V>[] tab, int i, Node,V> v) {
U.putObjectVolatile(tab, ((long)i << ASHIFT) + ABASE, v);
}
/* ---------------- Fields -------------- */
/**
* The array of bins. Lazily initialized upon first insertion.
* Size is always a power of two. Accessed directly by iterators.
*/
transient volatile Node,V>[] table;
/**
* The next table to use; non-null only while resizing.
*/
private transient volatile Node,V>[] nextTable;
/**
* Base counter value, used mainly when there is no contention,
* but also as a fallback during table initialization
* races. Updated via CAS.
*/
/**
* ， map.size()
* counterCells ， .
* CAS
*/
private transient volatile long baseCount;
/**
* Table initialization and resizing control. When negative, the
* table is being initialized or resized: -1 for initialization,
* else -(1 + the number of active resizing threads). 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.
*/
/**
* 1、-1
* 2、-N N-1
* 3、0 table null。
* 4、 ，
* （ ， ConcurrentHashMap 0.75 ， loadfactor ）
*/
private transient volatile int sizeCtl;
/**
* The next table index (plus one) to split while resizing.
* ， table.length， 0 transferIndex
*/
private transient volatile int transferIndex;
/**
* Spinlock (locked via CAS) used when resizing and/or creating CounterCells.
*/
/**
* ， counterCells
* cellsBusy 0 cells
*/
private transient volatile int cellsBusy;
/**
* Table of counter cells. When non-null, size is a power of 2.
* 2
*/
/**
* base， AtomicLong
* ， hash
* cells ， AtomicLong
* value ， value
* ， ，
* cell value base 。
*/
private transient volatile CounterCell[] counterCells;
// views
private transient KeySetView,V> keySet;
private transient ValuesView,V> values;
private transient EntrySetView,V> entrySet;
/* ---------------- Public operations -------------- */
/**
* Creates a new, empty map with the default initial table size (16).
*/
public ConcurrentHashMap() {
}
/**
* 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.sizeCtl = cap;
}
/**
* Creates a new map with the same mappings as the given map.
*
* @param m the map
*/
public ConcurrentHashMap(Map extends K, ? extends V> m) {
this.sizeCtl = DEFAULT_CAPACITY;
putAll(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.sizeCtl = cap;
}
// Original (since JDK1.2) Map methods
/**
* {
@inheritDoc}
*/
public int size() {
long n = sumCount();
return ((n < 0L) ? 0 :
(n > (long)Integer.MAX_VALUE) ? Integer.MAX_VALUE :
(int)n);
}
/**
* {
@inheritDoc}
*/
public boolean isEmpty() {
return sumCount() <= 0L; // 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
*/
public V get(Object key) {
Node,V>[] tab; Node,V> e, p; int n, eh; K ek;
int h = spread(key.hashCode());
if ((tab = table) != null && (n = tab.length) > 0 &&
(e = tabAt(tab, (n - 1) & h)) != null) {
if ((eh = e.hash) == h) {
if ((ek = e.key) == key || (ek != null && key.equals(ek)))
return e.val;
}
else if (eh < 0)
return (p = e.find(h, key)) != null ? p.val : null;
while ((e = e.next) != null) {
if (e.hash == h &&
((ek = e.key) == key || (ek != null && key.equals(ek))))
return e.val;
}
}
return null;
}
/**
* 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) {
return get(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();
Node,V>[] t;
if ((t = table) != null) {
Traverser,V> it = new Traverser,V>(t, t.length, 0, t.length);
for (Node,V> p; (p = it.advance()) != null; ) {
V v;
if ((v = p.val) == value || (v != null && value.equals(v)))
return true;
}
}
return false;
}
/**
* 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
*/
public V put(K key, V value) {
return putVal(key, value, false);
}
/** Implementation for put and putIfAbsent */
final V putVal(K key, V value, boolean onlyIfAbsent) {
if (key == null || value == null) throw new NullPointerException();
int hash = spread(key.hashCode());
int binCount = 0;
/**
* ： CAS （ ）
* （ ）
*/
for (Node,V>[] tab = table;;) {
Node,V> f; int n, i, fh;
/**
* put ，
*/
if (tab == null || (n = tab.length) == 0)
tab = initTable();
/**
* Null, CAS
*/
else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
if (casTabAt(tab, i, null,
new Node,V>(hash, key, value, null)))
break; // no lock when adding to empty bin
}
/**
* ForwardingNode ，
* 、 ，
*/
else if ((fh = f.hash) == MOVED)
tab = helpTransfer(tab, f);
else {
//
V oldVal = null;
synchronized (f) {
if (tabAt(tab, i) == f) {
if (fh >= 0) {
// ， ， ，
binCount = 1;
for (Node,V> e = f;; ++binCount) {
K ek;
if (e.hash == hash &&
((ek = e.key) == key ||
(ek != null && key.equals(ek)))) {
oldVal = e.val;
if (!onlyIfAbsent)
e.val = value;
break;
}
Node,V> pred = e;
if ((e = e.next) == null) {
pred.next = new Node,V>(hash, key,
value, null);
break;
}
}
}else if (f instanceof TreeBin) {
// ， hashMap(1.8)
Node,V> p;
binCount = 2;
if ((p = ((TreeBin,V>)f).putTreeVal(hash, key,
value)) != null) {
oldVal = p.val;
if (!onlyIfAbsent)
p.val = value;
}
}
}
}
/**
* binCount != 0 ， ， 。
* ：binCount ， ++binCount ，
* ，binCount （ ， ，
* ）
*/
if (binCount != 0) {
if (binCount >= TREEIFY_THRESHOLD)
treeifyBin(tab, i);
// ，
if (oldVal != null)
return oldVal;
break;
}
}
}
addCount(1L, binCount);
return null;
}
/**
* Copies all of the mappings from the specified map to this one.
* These mappings replace any mappings that this map had for any of the
* keys currently in the specified map.
*
* @param m mappings to be stored in this map
*/
public void putAll(Map extends K, ? extends V> m) {
tryPresize(m.size());
for (Map.Entry extends K, ? extends V> e : m.entrySet())
putVal(e.getKey(), e.getValue(), false);
}
/**
* 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
*/
public V remove(Object key) {
return replaceNode(key, null, 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.
*/
/**
* putVal() ， putVal ，
*
*/
final V replaceNode(Object key, V value, Object cv) {
int hash = spread(key.hashCode());
for (Node,V>[] tab = table;;) {
Node,V> f; int n, i, fh;
if (tab == null || (n = tab.length) == 0 ||
(f = tabAt(tab, i = (n - 1) & hash)) == null)
break;
else if ((fh = f.hash) == MOVED)
tab = helpTransfer(tab, f);
else {
V oldVal = null;
boolean validated = false;
synchronized (f) {
if (tabAt(tab, i) == f) {
if (fh >= 0) {
validated = true;
for (Node,V> e = f, pred = null;;) {
K ek;
if (e.hash == hash &&
((ek = e.key) == key ||
(ek != null && key.equals(ek)))) {
V ev = e.val;
if (cv == null || cv == ev ||
(ev != null && cv.equals(ev))) {
oldVal = ev;
if (value != null)
e.val = value;
else if (pred != null)
pred.next = e.next;
else
setTabAt(tab, i, e.next);
}
break;
}
pred = e;
if ((e = e.next) == null)
break;
}
}
else if (f instanceof TreeBin) {
validated = true;
TreeBin,V> t = (TreeBin,V>)f;
TreeNode,V> r, p;
if ((r = t.root) != null &&
(p = r.findTreeNode(hash, key, null)) != null) {
V pv = p.val;
if (cv == null || cv == pv ||
(pv != null && cv.equals(pv))) {
oldVal = pv;
if (value != null)
p.val = value;
else if (t.removeTreeNode(p))
setTabAt(tab, i, untreeify(t.first));
}
}
}
}
}
if (validated) {
if (oldVal != null) {
if (value == null)
addCount(-1L, -1);
return oldVal;
}
break;
}
}
}
return null;
}
/**
* Removes all of the mappings from this map.
*/
public void clear() {
long delta = 0L; // negative number of deletions
int i = 0;
Node,V>[] tab = table;
while (tab != null && i < tab.length) {
int fh;
Node,V> f = tabAt(tab, i);
if (f == null)
++i;
else if ((fh = f.hash) == MOVED) {
tab = helpTransfer(tab, f);
i = 0; // restart
}
else {
synchronized (f) {
if (tabAt(tab, i) == f) {
Node,V> p = (fh >= 0 ? f :
(f instanceof TreeBin) ?
((TreeBin,V>)f).first : null);
while (p != null) {
--delta;
p = p.next;
}
setTabAt(tab, i++, null);
}
}
}
}
if (delta != 0L)
addCount(delta, -1);
}
/**
* Returns a {
@link Set} view of the keys contained in this map.
* The set is backed by the map, so changes to the map are
* reflected in the set, and vice-versa. The set supports element
* removal, which removes the corresponding mapping from this map,
* via the {
@code Iterator.remove}, {
@code Set.remove},
* {
@code removeAll}, {
@code retainAll}, and {
@code clear}
* operations. It does not support the {
@code add} or
* {
@code addAll} operations.
*
* The view's iterators and spliterators are
* weakly consistent.
*
* The view's {
@code spliterator} reports {
@link Spliterator#CONCURRENT},
* {
@link Spliterator#DISTINCT}, and {
@link Spliterator#NONNULL}.
*
* @return the set view
*/
public KeySetView,V> keySet() {
KeySetView,V> ks;
return (ks = keySet) != null ? ks : (keySet = new KeySetView,V>(this, null));
}
/**
* Returns a {
@link Collection} view of the values contained in this map.
* The collection is backed by the map, so changes to the map are
* reflected in the collection, and vice-versa. The collection
* supports element removal, which removes the corresponding
* mapping from this map, via the {
@code Iterator.remove},
* {
@code Collection.remove}, {
@code removeAll},
* {
@code retainAll}, and {
@code clear} operations. It does not
* support the {
@code add} or {
@code addAll} operations.
*
* The view's iterators and spliterators are
* weakly consistent.
*
* The view's {
@code spliterator} reports {
@link Spliterator#CONCURRENT}
* and {
@link Spliterator#NONNULL}.
*
* @return the collection view
*/
public Collection values() {
ValuesView,V> vs;
return (vs = values) != null ? vs : (values = new ValuesView,V>(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.
*
* The view's iterators and spliterators are
* weakly consistent.
*
* The view's {
@code spliterator} reports {
@link Spliterator#CONCURRENT},
* {
@link Spliterator#DISTINCT}, and {
@link Spliterator#NONNULL}.
*
* @return the set view
*/
public Set,V>> entrySet() {
EntrySetView,V> es;
return (es = entrySet) != null ? es : (entrySet = new EntrySetView,V>(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;
Node,V>[] t;
if ((t = table) != null) {
Traverser,V> it = new Traverser,V>(t, t.length, 0, t.length);
for (Node,V> p; (p = it.advance()) != null; )
h += p.key.hashCode() ^ p.val.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() {
Node,V>[] t;
int f = (t = table) == null ? 0 : t.length;
Traverser,V> it = new Traverser,V>(t, f, 0, f);
StringBuilder sb = new StringBuilder();
sb.append('{');
Node,V> p;
if ((p = it.advance()) != null) {
for (;;) {
K k = p.key;
V v = p.val;
sb.append(k == this ? "(this Map)" : k);
sb.append('=');
sb.append(v == this ? "(this Map)" : v);
if ((p = 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;
Node,V>[] t;
int f = (t = table) == null ? 0 : t.length;
Traverser,V> it = new Traverser,V>(t, f, 0, f);
for (Node,V> p; (p = it.advance()) != null; ) {
V val = p.val;
Object v = m.get(p.key);
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 = get(mk)) == null ||
(mv != v && !mv.equals(v)))
return false;
}
}
return true;
}
/**
* Stripped-down version of helper class used in previous version,
* declared for the sake of serialization compatibility
*/
static class Segment,V> extends ReentrantLock implements Serializable {
private static final long serialVersionUID = 2249069246763182397L;
final float loadFactor;
Segment(float lf) { this.loadFactor = lf; }
}
/**
* Saves the state of the {
@code ConcurrentHashMap} instance to a
* stream (i.e., serializes it).
* @param s the stream
* @throws java.io.IOException if an I/O error occurs
* @serialData
* the key (Object) and value (Object)
* for each key-value mapping, followed by a null pair.
* The key-value mappings are emitted in no particular order.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
// For serialization compatibility
// Emulate segment calculation from previous version of this class
int sshift = 0;
int ssize = 1;
while (ssize < DEFAULT_CONCURRENCY_LEVEL) {
++sshift;
ssize <<= 1;
}
int segmentShift = 32 - sshift;
int segmentMask = ssize - 1;
@SuppressWarnings("unchecked")
Segment,V>[] segments = (Segment,V>[])
new Segment,?>[DEFAULT_CONCURRENCY_LEVEL];
for (int i = 0; i < segments.length; ++i)
segments[i] = new Segment,V>(LOAD_FACTOR);
s.putFields().put("segments", segments);
s.putFields().put("segmentShift", segmentShift);
s.putFields().put("segmentMask", segmentMask);
s.writeFields();
Node,V>[] t;
if ((t = table) != null) {
Traverser,V> it = new Traverser,V>(t, t.length, 0, t.length);
for (Node,V> p; (p = it.advance()) != null; ) {
s.writeObject(p.key);
s.writeObject(p.val);
}
}
s.writeObject(null);
s.writeObject(null);
segments = null; // throw away
}
/**
* Reconstitutes the instance from a stream (that is, deserializes it).
* @param s the stream
* @throws ClassNotFoundException if the class of a serialized object
* could not be found
* @throws java.io.IOException if an I/O error occurs
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
/*
* To improve performance in typical cases, we create nodes
* while reading, then place in table once size is known.
* However, we must also validate uniqueness and deal with
* overpopulated bins while doing so, which requires
* specialized versions of putVal mechanics.
*/
sizeCtl = -1; // force exclusion for table construction
s.defaultReadObject();
long size = 0L;
Node,V> p = null;
for (;;) {
@SuppressWarnings("unchecked")
K k = (K) s.readObject();
@SuppressWarnings("unchecked")
V v = (V) s.readObject();
if (k != null && v != null) {
p = new Node,V>(spread(k.hashCode()), k, v, p);
++size;
}
else
break;
}
if (size == 0L)
sizeCtl = 0;
else {
int n;
if (size >= (long)(MAXIMUM_CAPACITY >>> 1))
n = MAXIMUM_CAPACITY;
else {
int sz = (int)size;
n = tableSizeFor(sz + (sz >>> 1) + 1);
}
@SuppressWarnings("unchecked")
Node,V>[] tab = (Node,V>[])new Node,?>[n];
int mask = n - 1;
long added = 0L;
while (p != null) {
boolean insertAtFront;
Node,V> next = p.next, first;
int h = p.hash, j = h & mask;
if ((first = tabAt(tab, j)) == null)
insertAtFront = true;
else {
K k = p.key;
if (first.hash < 0) {
TreeBin,V> t = (TreeBin,V>)first;
if (t.putTreeVal(h, k, p.val) == null)
++added;
insertAtFront = false;
}
else {
int binCount = 0;
insertAtFront = true;
Node,V> q; K qk;
for (q = first; q != null; q = q.next) {
if (q.hash == h &&
((qk = q.key) == k ||
(qk != null && k.equals(qk)))) {
insertAtFront = false;
break;
}
++binCount;
}
if (insertAtFront && binCount >= TREEIFY_THRESHOLD) {
insertAtFront = false;
++added;
p.next = first;
TreeNode,V> hd = null, tl = null;
for (q = p; q != null; q = q.next) {
TreeNode,V> t = new TreeNode,V>
(q.hash, q.key, q.val, null, null);
if ((t.prev = tl) == null)
hd = t;
else
tl.next = t;
tl = t;
}
setTabAt(tab, j, new TreeBin,V>(hd));
}
}
}
if (insertAtFront) {
++added;
p.next = first;
setTabAt(tab, j, p);
}
p = next;
}
table = tab;
sizeCtl = n - (n >>> 2);
baseCount = added;
}
}
// ConcurrentMap methods
/**
* {
@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
*/
public V putIfAbsent(K key, V value) {
return putVal(key, value, true);
}
/**
* {
@inheritDoc}
*
* @throws NullPointerException if the specified key is null
*/
public boolean remove(Object key, Object value) {
if (key == null)
throw new NullPointerException();
return value != null && replaceNode(key, null, value) != null;
}
/**
* {
@inheritDoc}
*
* @throws NullPointerException if any of the arguments are null
*/
public boolean replace(K key, V oldValue, V newValue) {
if (key == null || oldValue == null || newValue == null)
throw new NullPointerException();
return replaceNode(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
*/
public V replace(K key, V value) {
if (key == null || value == null)
throw new NullPointerException();
return replaceNode(key, value, null);
}
// Overrides of JDK8+ Map extension method defaults
/**
* Returns the value to which the specified key is mapped, or the
* given default value if this map contains no mapping for the
* key.
*
* @param key the key whose associated value is to be returned
* @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 default value
* @throws NullPointerException if the specified key is null
*/
public V getOrDefault(Object key, V defaultValue) {
V v;
return (v = get(key)) == null ? defaultValue : v;
}
public void forEach(BiConsumer super K, ? super V> action) {
if (action == null) throw new NullPointerException();
Node,V>[] t;
if ((t = table) != null) {
Traverser,V> it = new Traverser,V>(t, t.length, 0, t.length);
for (Node,V> p; (p = it.advance()) != null; ) {
action.accept(p.key, p.val);
}
}
}
public void replaceAll(BiFunction super K, ? super V, ? extends V> function) {
if (function == null) throw new NullPointerException();
Node,V>[] t;
if ((t = table) != null) {
Traverser,V> it = new Traverser,V>(t, t.length, 0, t.length);
for (Node,V> p; (p = it.advance()) != null; ) {
V oldValue = p.val;
for (K key = p.key;;) {
V newValue = function.apply(key, oldValue);
if (newValue == null)
throw new NullPointerException();
if (replaceNode(key, newValue, oldValue) != null ||
(oldValue = get(key)) == null)
break;
}
}
}
}
/**
* If the specified key is not already associated with a value,
* attempts to compute its value using the given mapping function
* and enters it into this map unless {
@code null}. The entire
* method invocation is performed atomically, so the function is
* applied at most once per key. Some attempted update operations
* on this map by other threads may be blocked while computation
* is in progress, so the computation should be short and simple,
* and must not attempt to update any other mappings of this map.
*
* @param key key with which the specified value is to be associated
* @param mappingFunction the function to compute a value
* @return the current (existing or computed) value associated with
* the specified key, or null if the computed value is null
* @throws NullPointerException if the specified key or mappingFunction
* is null
* @throws IllegalStateException if the computation detectably
* attempts a recursive update to this map that would
* otherwise never complete
* @throws RuntimeException or Error if the mappingFunction does so,
* in which case the mapping is left unestablished
*/
public V computeIfAbsent(K key, Function super K, ? extends V> mappingFunction) {
if (key == null || mappingFunction == null)
throw new NullPointerException();
int h = spread(key.hashCode());
V val = null;
int binCount = 0;
for (Node,V>[] tab = table;;) {
Node,V> f; int n, i, fh;
if (tab == null || (n = tab.length) == 0)
tab = initTable();
else if ((f = tabAt(tab, i = (n - 1) & h)) == null) {
Node,V> r = new ReservationNode,V>();
synchronized (r) {
if (casTabAt(tab, i, null, r)) {
binCount = 1;
Node,V> node = null;
try {
if ((val = mappingFunction.apply(key)) != null)
node = new Node,V>(h, key, val, null);
} finally {
setTabAt(tab, i, node);
}
}
}
if (binCount != 0)
break;
}
else if ((fh = f.hash) == MOVED)
tab = helpTransfer(tab, f);
else {
boolean added = false;
synchronized (f) {
if (tabAt(tab, i) == f) {
if (fh >= 0) {
binCount = 1;
for (Node,V> e = f;; ++binCount) {
K ek; V ev;
if (e.hash == h &&
((ek = e.key) == key ||
(ek != null && key.equals(ek)))) {
val = e.val;
break;
}
Node,V> pred = e;
if ((e = e.next) == null) {
if ((val = mappingFunction.apply(key)) != null) {
added = true;
pred.next = new Node,V>(h, key, val, null);
}
break;
}
}
}
else if (f instanceof TreeBin) {
binCount = 2;
TreeBin,V> t = (TreeBin,V>)f;
TreeNode,V> r, p;
if ((r = t.root) != null &&
(p = r.findTreeNode(h, key, null)) != null)
val = p.val;
else if ((val = mappingFunction.apply(key)) != null) {
added = true;
t.putTreeVal(h, key, val);
}
}
}
}
if (binCount != 0) {
if (binCount >= TREEIFY_THRESHOLD)
treeifyBin(tab, i);
if (!added)
return val;
break;
}
}
}
if (val != null)
addCount(1L, binCount);
return val;
}
/**
* If the value for the specified key is present, attempts to
* compute a new mapping given the key and its current mapped
* value. The entire method invocation is performed atomically.
* Some attempted update operations on this map by other threads
* may be blocked while computation is in progress, so the
* computation should be short and simple, and must not attempt to
* update any other mappings of this map.
*
* @param key key with which a value may be associated
* @param remappingFunction the function to compute a value
* @return the new value associated with the specified key, or null if none
* @throws NullPointerException if the specified key or remappingFunction
* is null
* @throws IllegalStateException if the computation detectably
* attempts a recursive update to this map that would
* otherwise never complete
* @throws RuntimeException or Error if the remappingFunction does so,
* in which case the mapping is unchanged
*/
public V computeIfPresent(K key, BiFunction super K, ? super V, ? extends V> remappingFunction) {
if (key == null || remappingFunction == null)
throw new NullPointerException();
int h = spread(key.hashCode());
V val = null;
int delta = 0;
int binCount = 0;
for (Node,V>[] tab = table;;) {
Node,V> f; int n, i, fh;
if (tab == null || (n = tab.length) == 0)
tab = initTable();
else if ((f = tabAt(tab, i = (n - 1) & h)) == null)
break;
else if ((fh = f.hash) == MOVED)
tab = helpTransfer(tab, f);
else {
synchronized (f) {
if (tabAt(tab, i) == f) {
if (fh >= 0) {
binCount = 1;
for (Node,V> e = f, pred = null;; ++binCount) {
K ek;
if (e.hash == h &&
((ek = e.key) == key ||
(ek != null && key.equals(ek)))) {
val = remappingFunction.apply(key, e.val);
if (val != null)
e.val = val;
else {
delta = -1;
Node,V> en = e.next;
if (pred != null)
pred.next = en;
else
setTabAt(tab, i, en);
}
break;
}
pred = e;
if ((e = e.next) == null)
break;
}
}
else if (f instanceof TreeBin) {
binCount = 2;
TreeBin,V> t = (TreeBin,V>)f;
TreeNode,V> r, p;
if ((r = t.root) != null &&
(p = r.findTreeNode(h, key, null)) != null) {
val = remappingFunction.apply(key, p.val);
if (val != null)
p.val = val;
else {
delta = -1;
if (t.removeTreeNode(p))
setTabAt(tab, i, untreeify(t.first));
}
}
}
}
}
if (binCount != 0)
break;
}
}
if (delta != 0)
addCount((long)delta, binCount);
return val;
}
/**
* Attempts to compute a mapping for the specified key and its
* current mapped value (or {
@code null} if there is no current
* mapping). The entire method invocation is performed atomically.
* Some attempted update operations on this map by other threads
* may be blocked while computation is in progress, so the
* computation should be short and simple, and must not attempt to
* update any other mappings of this Map.
*
* @param key key with which the specified value is to be associated
* @param remappingFunction the function to compute a value
* @return the new value associated with the specified key, or null if none
* @throws NullPointerException if the specified key or remappingFunction
* is null
* @throws IllegalStateException if the computation detectably
* attempts a recursive update to this map that would
* otherwise never complete
* @throws RuntimeException or Error if the remappingFunction does so,
* in which case the mapping is unchanged
*/
public V compute(K key,
BiFunction super K, ? super V, ? extends V> remappingFunction) {
if (key == null || remappingFunction == null)
throw new NullPointerException();
int h = spread(key.hashCode());
V val = null;
int delta = 0;
int binCount = 0;
for (Node,V>[] tab = table;;) {
Node,V> f; int n, i, fh;
if (tab == null || (n = tab.length) == 0)
tab = initTable();
else if ((f = tabAt(tab, i = (n - 1) & h)) == null) {
Node,V> r = new ReservationNode,V>();
synchronized (r) {
if (casTabAt(tab, i, null, r)) {
binCount = 1;
Node,V> node = null;
try {
if ((val = remappingFunction.apply(key, null)) != null) {
delta = 1;
node = new Node,V>(h, key, val, null);
}
} finally {
setTabAt(tab, i, node);
}
}
}
if (binCount != 0)
break;
}
else if ((fh = f.hash) == MOVED)
tab = helpTransfer(tab, f);
else {
synchronized (f) {
if (tabAt(tab, i) == f) {
if (fh >= 0) {
binCount = 1;
for (Node,V> e = f, pred = null;; ++binCount) {
K ek;
if (e.hash == h &&
((ek = e.key) == key ||
(ek != null && key.equals(ek)))) {
val = remappingFunction.apply(key, e.val);
if (val != null)
e.val = val;
else {
delta = -1;
Node,V> en = e.next;
if (pred != null)
pred.next = en;
else
setTabAt(tab, i, en);
}
break;
}
pred = e;
if ((e = e.next) == null) {
val = remappingFunction.apply(key, null);
if (val != null) {
delta = 1;
pred.next =
new Node,V>(h, key, val, null);
}
break;
}
}
}
else if (f instanceof TreeBin) {
binCount = 1;
TreeBin,V> t = (TreeBin,V>)f;
TreeNode,V> r, p;
if ((r = t.root) != null)
p = r.findTreeNode(h, key, null);
else
p = null;
V pv = (p == null) ? null : p.val;
val = remappingFunction.apply(key, pv);
if (val != null) {
if (p != null)
p.val = val;
else {
delta = 1;
t.putTreeVal(h, key, val);
}
}
else if (p != null) {
delta = -1;
if (t.removeTreeNode(p))
setTabAt(tab, i, untreeify(t.first));
}
}
}
}
if (binCount != 0) {
if (binCount >= TREEIFY_THRESHOLD)
treeifyBin(tab, i);
break;
}
}
}
if (delta != 0)
addCount((long)delta, binCount);
return val;
}
/**
* If the specified key is not already associated with a
* (non-null) value, associates it with the given value.
* Otherwise, replaces the value with the results of the given
* remapping function, or removes if {
@code null}. The entire
* method invocation is performed atomically. Some attempted
* update operations on this map by other threads may be blocked
* while computation is in progress, so the computation should be
* short and simple, and must not attempt to update any other
* mappings of this Map.
*
* @param key key with which the specified value is to be associated
* @param value the value to use if absent
* @param remappingFunction the function to recompute a value if present
* @return the new value associated with the specified key, or null if none
* @throws NullPointerException if the specified key or the
* remappingFunction is null
* @throws RuntimeException or Error if the remappingFunction does so,
* in which case the mapping is unchanged
*/
public V merge(K key, V value, BiFunction super V, ? super V, ? extends V> remappingFunction) {
if (key == null || value == null || remappingFunction == null)
throw new NullPointerException();
int h = spread(key.hashCode());
V val = null;
int delta = 0;
int binCount = 0;
for (Node,V>[] tab = table;;) {
Node,V> f; int n, i, fh;
if (tab == null || (n = tab.length) == 0)
tab = initTable();
else if ((f = tabAt(tab, i = (n - 1) & h)) == null) {
if (casTabAt(tab, i, null, new Node,V>(h, key, value, null))) {
delta = 1;
val = value;
break;
}
}
else if ((fh = f.hash) == MOVED)
tab = helpTransfer(tab, f);
else {
synchronized (f) {
if (tabAt(tab, i) == f) {
if (fh >= 0) {
binCount = 1;
for (Node,V> e = f, pred = null;; ++binCount) {
K ek;
if (e.hash == h &&
((ek = e.key) == key ||
(ek != null && key.equals(ek)))) {
val = remappingFunction.apply(e.val, value);
if (val != null)
e.val = val;
else {
delta = -1;
Node,V> en = e.next;
if (pred != null)
pred.next = en;
else
setTabAt(tab, i, en);
}
break;
}
pred = e;
if ((e = e.next) == null) {
delta = 1;
val = value;
pred.next =
new Node,V>(h, key, val, null);
break;
}
}
}
else if (f instanceof TreeBin) {
binCount = 2;
TreeBin,V> t = (TreeBin,V>)f;
TreeNode,V> r = t.root;
TreeNode,V> p = (r == null) ? null :
r.findTreeNode(h, key, null);
val = (p == null) ? value :
remappingFunction.apply(p.val, value);
if (val != null) {
if (p != null)
p.val = val;
else {
delta = 1;
t.putTreeVal(h, key, val);
}
}
else if (p != null) {
delta = -1;
if (t.removeTreeNode(p))
setTabAt(tab, i, untreeify(t.first));
}
}
}
}
if (binCount != 0) {
if (binCount >= TREEIFY_THRESHOLD)
treeifyBin(tab, i);
break;
}
}
}
if (delta != 0)
addCount((long)delta, binCount);
return val;
}
// Hashtable legacy methods
/**
* Legacy method testing if some key maps into the specified value
* in this table. This method is identical in functionality to
* {
@link #containsValue(Object)}, and exists solely to ensure
* full compatibility with class {
@link java.util.Hashtable},
* which supported this method prior to introduction of the
* Java Collections framework.
*
* @param value a value to search for
* @return {
@code true} if and only if some key maps to the
* {
@code value} argument in this table as
* determined by the {
@code equals} method;
* {
@code false} otherwise
* @throws NullPointerException if the specified value is null
*/
public boolean contains(Object value) {
return containsValue(value);
}
/**
* Returns an enumeration of the keys in this table.
*
* @return an enumeration of the keys in this table
* @see #keySet()
*/
public Enumeration keys() {
Node,V>[] t;
int f = (t = table) == null ? 0 : t.length;
return new KeyIterator,V>(t, f, 0, f, this);
}
/**
* Returns an enumeration of the values in this table.
*
* @return an enumeration of the values in this table
* @see #values()
*/
public Enumeration elements() {
Node,V>[] t;
int f = (t = table) == null ? 0 : t.length;
return new ValueIterator,V>(t, f, 0, f, this);
}
// ConcurrentHashMap-only methods
/**
* 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
* @since 1.8
*/
public long mappingCount() {
long n = sumCount();
return (n < 0L) ? 0L : n; // ignore transient negative values
}
/**
* Creates a new {
@link Set} backed by a ConcurrentHashMap
* from the given type to {
@code Boolean.TRUE}.
*
* @param <K> the element type of the returned set
* @return the new set
* @since 1.8
*/
public static KeySetView,Boolean> newKeySet() {
return new KeySetView,Boolean>
(new ConcurrentHashMap,Boolean>(), 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.
* @param <K> the element type of the returned set
* @return the new set
* @throws IllegalArgumentException if the initial capacity of
* elements is negative
* @since 1.8
*/
public static KeySetView,Boolean> newKeySet(int initialCapacity) {
return new KeySetView,Boolean>
(new ConcurrentHashMap,Boolean>(initialCapacity), Boolean.TRUE);
}
/**
* 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(Collection)}).
* 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,V> keySet(V mappedValue) {
if (mappedValue == null)
throw new NullPointerException();
return new KeySetView,V>(this, mappedValue);
}
/* ---------------- Special Nodes -------------- */
/**
* A node inserted at head of bins during transfer operations.
*/
static final class ForwardingNode,V> extends Node,V> {
final Node,V>[] nextTable;
ForwardingNode(Node,V>[] tab) {
super(MOVED, null, null, null);
this.nextTable = tab;
}
Node,V> find(int h, Object k) {
// loop to avoid arbitrarily deep recursion on forwarding nodes
outer: for (Node,V>[] tab = nextTable;;) {
Node,V> e; int n;
if (k == null || tab == null || (n = tab.length) == 0 ||
(e = tabAt(tab, (n - 1) & h)) == null)
return null;
for (;;) {
int eh; K ek;
if ((eh = e.hash) == h &&
((ek = e.key) == k || (ek != null && k.equals(ek))))
return e;
if (eh < 0) {
if (e instanceof ForwardingNode) {
tab = ((ForwardingNode,V>)e).nextTable;
continue outer;
}
else
return e.find(h, k);
}
if ((e = e.next) == null)
return null;
}
}
}
}
/**
* A place-holder node used in computeIfAbsent and compute
*/
static final class ReservationNode,V> extends Node,V> {
ReservationNode() {
super(RESERVED, null, null, null);
}
Node,V> find(int h, Object k) {
return null;
}
}
/* ---------------- Table Initialization and Resizing -------------- */
/**
* Returns the stamp bits for resizing a table of size n.
* Must be negative when shifted left by RESIZE_STAMP_SHIFT.
*/
/**
* n tab length, 2 （int rs = resizeStamp(n);）
* Integer.numberOfLeadingZeros(n) | 1<<15
* ， Integer.numberOfLeadingZeros(n) 32
* resizeStamp(n) (-32< resizeStamp(n) * （ ：1<<15， rs rs << RESIZE_STAMP_SHIFT sizeCtl(addCount )，
* 1 ）
* sizeCtl ，-n n-1 。
*
*/
static final int resizeStamp(int n) {
return Integer.numberOfLeadingZeros(n) | (1 << (RESIZE_STAMP_BITS - 1));
}
/**
* Initializes table, using the size recorded in sizeCtl.
*/
private final Node,V>[] initTable() {
Node,V>[] tab; int sc;
// ， sizeCtl 0，
//（ ， table ）
while ((tab = table) == null || tab.length == 0) {
if ((sc = sizeCtl) < 0)
Thread.yield(); // lost initialization race; just spin
/**
* compareAndSwapInt，
*
*
* ，
*
*/
// sizeCtl ， ， sizeCtl -1
else if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
try {
if ((tab = table) == null || tab.length == 0) {
int n = (sc > 0) ? sc : DEFAULT_CAPACITY;
@SuppressWarnings("unchecked")
Node,V>[] nt = (Node,V>[])new Node,?>[n];
table = tab = nt;
//sc
sc = n - (n >>> 2);
}
} finally {
/**
* sizeCtl ，
* ， tab null， tab
*/
sizeCtl = sc;
}
break;
}
}
return tab;
}
/**
* Adds to count, and if table is too small and not already
* resizing, initiates transfer. If already resizing, helps
* perform transfer if work is available. Rechecks occupancy
* after a transfer to see if another resize is already needed
* because resizings are lagging additions.
*
* @param x the count to add
* @param check if <0, don't check resize, if <= 1 only check if uncontended
*/
/**
* x ， count+x
*/
private final void addCount(long x, int check) {
CounterCell[] as; long b, s;
/**
* counterCells baseCount （ ）
*/
if ((as = counterCells) != null ||
!U.compareAndSwapLong(this, BASECOUNT, b = baseCount, s = b + x)) {
CounterCell a; long v; int m;
boolean uncontended = true;
/**
* ，ThreadLocalRandom.getProbe() package ， api
* getProbe()， ， getProbe() hashCode
* as[ThreadLocalRandom.getProbe() & m])
*/
/**
* counterCells counterCells[i]
* counterCells[i]
* （ cells[i] ）
*/
if (as == null || (m = as.length - 1) < 0 ||
(a = as[ThreadLocalRandom.getProbe() & m]) == null ||
!(uncontended =
U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))) {
/**
* fullAddCount cells 、cell 、cell[i]
*/
fullAddCount(x, uncontended);
return;
}
/**
* replace clear ，check -1，
*/
if (check <= 1)
return;
// ，
s = sumCount();
}
/**
* ，
*/
if (check >= 0) {
Node,V>[] tab, nt; int n, sc;
/**
* ， sc >= 0（ ），
*
*/
while (s >= (long)(sc = sizeCtl) && (tab = table) != null &&
(n = tab.length) < MAXIMUM_CAPACITY) {
int rs = resizeStamp(n);
//sc 0
if (sc < 0) {
/**
* helpTransfer() ， ，
* ，
*/
if ((sc >>> RESIZE_STAMP_SHIFT) != rs || sc == rs + 1 ||
sc == rs + MAX_RESIZERS || (nt = nextTable) == null ||
transferIndex <= 0)
break;
/**
* ，sc+1 1
*/
if (U.compareAndSwapInt(this, SIZECTL, sc, sc + 1))
transfer(tab, nt);
//
}else if (U.compareAndSwapInt(this, SIZECTL, sc,
(rs << RESIZE_STAMP_SHIFT) + 2))
transfer(tab, null);
s = sumCount();
}
}
}
/**
* Helps transfer if a resize is in progress.
* tab ，
*
*/
final Node,V>[] helpTransfer(Node,V>[] tab, Node,V> f) {
Node,V>[] nextTab; int sc;
if (tab != null && (f instanceof ForwardingNode) &&
(nextTab = ((ForwardingNode,V>)f).nextTable) != null) {
int rs = resizeStamp(tab.length);
while (nextTab == nextTable && table == tab &&
(sc = sizeCtl) < 0) {
/**
* , ，
* ，
*/
if ((sc >>> RESIZE_STAMP_SHIFT) != rs || sc == rs + 1 ||
sc == rs + MAX_RESIZERS || transferIndex <= 0)
break;
/**
* ，sc+1 1
*/
if (U.compareAndSwapInt(this, SIZECTL, sc, sc + 1)) {
transfer(tab, nextTab);
break;
}
}
return nextTab;
}
return table;
}
/**
* 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) {
Node,V>[] tab = table; int n;
if (tab == null || (n = tab.length) == 0) {
n = (sc > c) ? sc : c;
if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
try {
if (table == tab) {
@SuppressWarnings("unchecked")
Node,V>[] nt = (Node,V>[])new Node,?>[n];
table = nt;
sc = n - (n >>> 2);
}
} finally {
sizeCtl = sc;
}
}
}
else if (c <= sc || n >= MAXIMUM_CAPACITY)
break;
else if (tab == table) {
int rs = resizeStamp(n);
if (sc < 0) {
Node,V>[] nt;
if ((sc >>> RESIZE_STAMP_SHIFT) != rs || sc == rs + 1 ||
sc == rs + MAX_RESIZERS || (nt = nextTable) == null ||
transferIndex <= 0)
break;
if (U.compareAndSwapInt(this, SIZECTL, sc, sc + 1))
transfer(tab, nt);
}
else if (U.compareAndSwapInt(this, SIZECTL, sc,
(rs << RESIZE_STAMP_SHIFT) + 2))
transfer(tab, null);
}
}
}
/**
* Moves and/or copies the nodes in each bin to new table. See
* above for explanation.
*
*/
private final void transfer(Node,V>[] tab, Node,V>[] nextTab) {
int n = tab.length, stride;
/**
* stride （ ），
* NCPU > 1 ， n/(8*NCPU)， CPU ，
* ， 16
*/
if ((stride = (NCPU > 1) ? (n >>> 3) / NCPU : n) < MIN_TRANSFER_STRIDE)
stride = MIN_TRANSFER_STRIDE; // subdivide range
if (nextTab == null) { // initiating
try {
/**
*
*/
@SuppressWarnings("unchecked")
Node,V>[] nt = (Node,V>[])new Node,?>[n << 1];
nextTab = nt;
} catch (Throwable ex) { // try to cope with OOME
sizeCtl = Integer.MAX_VALUE;
return;
}
nextTable = nextTab;
/**
* transferIndex
*/
transferIndex = n;
}
int nextn = nextTab.length;
ForwardingNode,V> fwd = new ForwardingNode,V>(nextTab);
/**
* ， ， ， false
*/
boolean advance = true;
/**
*
*/
boolean finishing = false; // to ensure sweep before committing nextTab
for (int i = 0, bound = 0;;) {
Node,V> f; int fh;
/**
* ，
*/
while (advance) {
int nextIndex, nextBound;
/**
*
*/
if (--i >= bound || finishing)
advance = false;
/**
* ， i=-1, return
* ， ，
*
*/
else if ((nextIndex = transferIndex) <= 0) {
i = -1;
advance = false;
}
/**
* ， transferIndex (transferIndex-stride)。
* CAS transferIndex ， 。
* [bound, nextIndex]
*/
else if (U.compareAndSwapInt
(this, TRANSFERINDEX, nextIndex,
nextBound = (nextIndex > stride ?
nextIndex - stride : 0))) {
/**
* n 16， 16，
* nextBound=0,i=15
*/
bound = nextBound;
i = nextIndex - 1;
advance = false;
}
}
/**
* ， ，
* i=-1，
*/
if (i < 0 || i >= n || i + n >= nextn) {
int sc;
/**
* ( ，finishing false， )
* ：finishing true ，
* finishing
*/
if (finishing) {
/**
* ： ， transfer
* tab nextTab， nextTable table ，
* nextTable table
*/
nextTable = null;
table = nextTab;
/**
* sizeCtl ，
* 1.5n， 2n
* 1.5n/2n = 0.75
*/
sizeCtl = (n << 1) - (n >>> 1);
return;
}
/**
* ，sc-1 ，
* （ transfer() sc+1 ， transfer ，
* ， ）
*/
if (U.compareAndSwapInt(this, SIZECTL, sc = sizeCtl, sc - 1)) {
/**
* addCount ，sizeCtl (rs << RESIZE_STAMP_SHIFT) + 2
* sc != (rs << RESIZE_STAMP_SHIFT) + 2
* ，
* return。
* ， finishing ，
* ， ， if(finishing)
*/
if ((sc - 2) != resizeStamp(n) << RESIZE_STAMP_SHIFT)
return;
finishing = advance = true;
/**
* ， ( Fwd )
*/
i = n; // recheck before commit
}
}
/**
* ： ，advance true，
* while ，i 1
*/
//i ， ForwardingNode ，
else if ((f = tabAt(tab, i)) == null)
advance = casTabAt(tab, i, null, fwd);
else if ((fh = f.hash) == MOVED)
advance = true; // already processed
else {
/**
* ，
*/
synchronized (f) {
/**
* ， ，tab[i]
*/
if (tabAt(tab, i) == f) {
/**
* ln hn ，
* ，
* ln [0,i]，
* hn (i,i+n]
*/
Node,V> ln, hn;
/**
* table[i] hashcode 0， ，
* ForwardNode Treebin
*/
if (fh >= 0) {
/**
* n 2 ， 1 ,
* table[i] hashcode & n 0 n
*
*/
int runBit = fh & n;
Node,V> lastRun = f;
/**
* ，
* ：0 0 n 0 0 0
* ， runbit 0
* lastRun 。
* ： ，
* (next )，
*
*/
for (Node,V> p = f.next; p != null; p = p.next) {
int b = p.hash & n;
if (b != runBit) {
runBit = b;
lastRun = p;
}
}
/**
* runBit ，
* runBit 0 [0,i] ，
* (i,i+n]
*/
// 0 0 n 0 0 0 ，
//ln ，hn = null
if (runBit == 0) {
ln = lastRun;
hn = null;
}
else {
hn = lastRun;
ln = null;
}
/**
* lastRun ，
*/
for (Node,V> p = f; p != lastRun; p = p.next) {
int ph = p.hash; K pk = p.key; V pv = p.val;
if ((ph & n) == 0)
ln = new Node,V>(ph, pk, pv, ln);
else
hn = new Node,V>(ph, pk, pv, hn);
}
setTabAt(nextTab, i, ln);
setTabAt(nextTab, i + n, hn);
// fwd
setTabAt(tab, i, fwd);
advance = true;
}
else if (f instanceof TreeBin) {
TreeBin,V> t = (TreeBin,V>)f;
TreeNode,V> lo = null, loTail = null;
TreeNode,V> hi = null, hiTail = null;
int lc = 0, hc = 0;
/**
* ，
*
*/
//TreeBin Node， next
for (Node,V> e = t.first; e != null; e = e.next) {
int h = e.hash;
TreeNode,V> p = new TreeNode,V>
(h, e.key, e.val, null, null);
if ((h & n) == 0) {
if ((p.prev = loTail) == null)
lo = p;
else
loTail.next = p;
loTail = p;
++lc;
}else {
if ((p.prev = hiTail) == null)
hi = p;
else
hiTail.next = p;
hiTail = p;
++hc;
}
}
/**
* UNTREEIFY_THRESHOLD,
*
*/
ln = (lc <= UNTREEIFY_THRESHOLD) ? untreeify(lo) :
(hc != 0) ? new TreeBin,V>(lo) : t;
hn = (hc <= UNTREEIFY_THRESHOLD) ? untreeify(hi) :
(lc != 0) ? new TreeBin,V>(hi) : t;
setTabAt(nextTab, i, ln);
setTabAt(nextTab, i + n, hn);
setTabAt(tab, i, fwd);
advance = true;
}
}
}
}
}
}
/* ---------------- Counter support -------------- */
/**
* A padded cell for distributing counts. Adapted from LongAdder
* and Striped64. See their internal docs for explanation.
*/
/**
* @Contended
* （ ）
*/
@sun.misc.Contended static final class CounterCell {
volatile long value;
CounterCell(long x) { value = x; }
}
final long sumCount() {
CounterCell[] as = counterCells; CounterCell a;
long sum = baseCount;
if (as != null) {
for (int i = 0; i < as.length; ++i) {
if ((a = as[i]) != null)
sum += a.value;
}
}
return sum;
}
// See LongAdder version for explanation
/**
* cells 、 、 、 cell
*/
private final void fullAddCount(long x, boolean wasUncontended) {
int h;
/**
* ThreadLocalRandom.getProbe() == 0
* ThreadLocalRandom.current() （ localInit()）
*/
if ((h = ThreadLocalRandom.getProbe()) == 0) {
ThreadLocalRandom.localInit(); // force initialization
h = ThreadLocalRandom.getProbe();
wasUncontended = true;
}
//
boolean collide = false; // True if last slot nonempty
for (;;) {
CounterCell[] as; CounterCell a; int n; long v;
/**
* cells ， cell
*/
if ((as = counterCells) != null && (n = as.length) > 0) {
if ((a = as[(n - 1) & h]) == null) {
if (cellsBusy == 0) { // Try to attach new Cell
CounterCell r = new CounterCell(x); // Optimistic create
/**
* cell cellBusy，
* index
*/
if (cellsBusy == 0 &&
U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
boolean created = false;
try { // Recheck under lock
CounterCell[] rs; int m, j;
if ((rs = counterCells) != null &&
(m = rs.length) > 0 &&
rs[j = (m - 1) & h] == null) {
rs[j] = r;
created = true;
}
} finally {
cellsBusy = 0;
}
if (created)
break;
continue; // Slot is now non-empty
}
}
collide = false;
}
/**
* wasUncontended ConcurrentHashMap false，
* ， wasUncontended false， cells[i]
* ， continue hash & (n-1) index
*/
else if (!wasUncontended) // CAS already known to fail
wasUncontended = true; // Continue after rehash
/**
* cells[i] ， cells[i] value
*/
else if (U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))
break;
/**
* CPU , as
* （ ： collide true if ， collide
* 。。。 ， ，cells NCPU，
* ）
*/
else if (counterCells != as || n >= NCPU)
collide = false; // At max size or stale
else if (!collide)
collide = true;
/**
* cells[i] ， ， 2
*/
else if (cellsBusy == 0 &&
U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
try {
if (counterCells == as) {
// Expand table unless stale
CounterCell[] rs = new CounterCell[n << 1];
for (int i = 0; i < n; ++i)
rs[i] = as[i];
counterCells = rs;
}
} finally {
cellsBusy = 0;
}
collide = false;
continue; // Retry with expanded table
}
h = ThreadLocalRandom.advanceProbe(h);
/**
* cellsBusy 0 cells 。
* cells
* cells
*/
}else if (cellsBusy == 0 && counterCells == as &&
U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
boolean init = false;
try { // Initialize table
if (counterCells == as) {
CounterCell[] rs = new CounterCell[2];
//hash & (2-1) x Cell
rs[h & 1] = new CounterCell(x);
counterCells = rs;
init = true;
}
//cellsBusy == 1 ， ， CAS
} finally {
cellsBusy = 0;
}
if (init)
break;
/**
* cells ， （ ） baseCount
*/
}else if (U.compareAndSwapLong(this, BASECOUNT, v = baseCount, v + x))
break; // Fall back on using base
}
}
/* ---------------- Conversion from/to TreeBins -------------- */
/**
* Replaces all linked nodes in bin at given index unless table is
* too small, in which case resizes instead.
*/
private final void treeifyBin(Node,V>[] tab, int index) {
Node,V> b; int n, sc;
if (tab != null) {
if ((n = tab.length) < MIN_TREEIFY_CAPACITY)
tryPresize(n << 1);
else if ((b = tabAt(tab, index)) != null && b.hash >= 0) {
synchronized (b) {
if (tabAt(tab, index) == b) {
TreeNode,V> hd = null, tl = null;
for (Node,V> e = b; e != null; e = e.next) {
TreeNode,V> p =
new TreeNode,V>(e.hash, e.key, e.val,
null, null);
if ((p.prev = tl) == null)
hd = p;
else
tl.next = p;
tl = p;
}
setTabAt(tab, index, new TreeBin,V>(hd));
}
}
}
}
}
/**
* Returns a list on non-TreeNodes replacing those in given list.
*/
static ,V> Node,V> untreeify(Node,V> b) {
Node,V> hd = null, tl = null;
for (Node,V> q = b; q != null; q = q.next) {
Node,V> p = new Node,V>(q.hash, q.key, q.val, null);
if (tl == null)
hd = p;
else
tl.next = p;
tl = p;
}
return hd;
}
/* ---------------- TreeNodes -------------- */
/**
* Nodes for use in TreeBins
*/
static final class TreeNode,V> extends Node,V> {
TreeNode,V> parent; // red-black tree links
TreeNode,V> left;
TreeNode,V> right;
TreeNode,V> prev; // needed to unlink next upon deletion
boolean red;
TreeNode(int hash, K key, V val, Node,V> next,
TreeNode,V> parent) {
super(hash, key, val, next);
this.parent = parent;
}
Node,V> find(int h, Object k) {
return findTreeNode(h, k, null);
}
/**
* Returns the TreeNode (or null if not found) for the given key
* starting at given root.
*/
final TreeNode,V> findTreeNode(int h, Object k, Class> kc) {
if (k != null) {
TreeNode,V> p =