jsr166e.ConcurrentHashMapV8 Maven / Gradle / Ivy
/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package jsr166e;
import java.util.Comparator;
import java.util.Arrays;
import java.util.Map;
import java.util.Set;
import java.util.Collection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.AbstractCollection;
import java.util.Hashtable;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Enumeration;
import java.util.ConcurrentModificationException;
import java.util.NoSuchElementException;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;
import java.io.Serializable;
/**
* A hash table supporting full concurrency of retrievals and
* high expected concurrency for updates. This class obeys the
* same functional specification as {@link java.util.Hashtable}, and
* includes versions of methods corresponding to each method of
* {@code Hashtable}. However, even though all operations are
* thread-safe, retrieval operations do not entail locking,
* and there is not any support for locking the entire table
* in a way that prevents all access. This class is fully
* interoperable with {@code Hashtable} in programs that rely on its
* thread safety but not on its synchronization details.
*
* Retrieval operations (including {@code get}) generally do not
* block, so may overlap with update operations (including {@code put}
* and {@code remove}). Retrievals reflect the results of the most
* recently completed update operations holding upon their
* onset. (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 ConcurrentHashMapV8 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 ConcurrentHashMapV8 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 ConcurrentHashMapV8 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.
*
*
ConcurrentHashMapV8s support sequential and parallel operations
* bulk operations. (Parallel forms use 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. Because
* the elements of a ConcurrentHashMapV8 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 ConcurrentHashMapV8: 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.
*
*
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
*/
public class ConcurrentHashMapV8
implements ConcurrentMap, Serializable {
private static final long serialVersionUID = 7249069246763182397L;
/**
* 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 ConcurrentHashMapV8 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 key
* fields can contain special values, they are defined using plain
* Object types (not type "K"). This leads to a lot of explicit
* casting (and many explicit warning suppressions to tell
* compilers not to complain about it). It also allows some 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 (sign) bit of Node hash fields for control
* purposes -- it is available anyway because of addressing
* constraints. Nodes with negative hash fields are forwarding
* nodes to either TreeBins or resized tables. The lower 31 bits
* of each normal Node's hash field contain a transformation of
* the key's hash code.
*
* 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). 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). 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. To enable concurrency, the
* next table must be (incrementally) prefilled with place-holders
* serving as reverse forwarders to the old 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, 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 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. However, to
* ensure that no intervening nodes are skipped, bin splitting can
* only begin after the associated reverse-forwarders are in
* place.
*
* 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). 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 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;
/**
* 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.
*/
private static final int MIN_TRANSFER_STRIDE = 16;
/*
* Encodings for Node hash fields. See above for explanation.
*/
static final int MOVED = 0x80000000; // hash field for forwarding nodes
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();
/* ---------------- Counters -------------- */
// Adapted from LongAdder and Striped64.
// See their internal docs for explanation.
// A padded cell for distributing counts
static final class CounterCell {
volatile long p0, p1, p2, p3, p4, p5, p6;
volatile long value;
volatile long q0, q1, q2, q3, q4, q5, q6;
CounterCell(long x) { value = x; }
}
/**
* Holder for the thread-local hash code determining which
* CounterCell to use. The code is initialized via the
* counterHashCodeGenerator, but may be moved upon collisions.
*/
static final class CounterHashCode {
int code;
}
/**
* Generates initial value for per-thread CounterHashCodes
*/
static final AtomicInteger counterHashCodeGenerator = new AtomicInteger();
/**
* Increment for counterHashCodeGenerator. See class ThreadLocal
* for explanation.
*/
static final int SEED_INCREMENT = 0x61c88647;
/**
* Per-thread counter hash codes. Shared across all instances.
*/
static final ThreadLocal threadCounterHashCode =
new ThreadLocal();
/* ---------------- Fields -------------- */
/**
* The array of bins. Lazily initialized upon first insertion.
* Size is always a power of two. Accessed directly by iterators.
*/
transient volatile Node[] table;
/**
* The next table to use; non-null only while resizing.
*/
private transient volatile Node[] nextTable;
/**
* Base counter value, used mainly when there is no contention,
* but also as a fallback during table initialization
* races. Updated via 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.
*/
private transient volatile int sizeCtl;
/**
* The next table index (plus one) to split while resizing.
*/
private transient volatile int transferIndex;
/**
* The least available table index to split while resizing.
*/
private transient volatile int transferOrigin;
/**
* Spinlock (locked via CAS) used when resizing and/or creating Cells.
*/
private transient volatile int counterBusy;
/**
* Table of counter cells. When non-null, size is a power of 2.
*/
private transient volatile CounterCell[] counterCells;
// 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.
*/
@SuppressWarnings("unchecked") static final Node tabAt
(Node[] tab, int i) { // used by Traverser
return (Node)U.getObjectVolatile(tab, ((long)i << ASHIFT) + ABASE);
}
private static final boolean casTabAt
(Node[] tab, int i, Node c, Node v) {
return U.compareAndSwapObject(tab, ((long)i << ASHIFT) + ABASE, c, v);
}
private static final void setTabAt
(Node[] tab, int i, Node v) {
U.putObjectVolatile(tab, ((long)i << ASHIFT) + ABASE, 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.
*/
static class Node {
final int hash;
final Object key;
volatile V val;
volatile Node next;
Node(int hash, Object key, V val, Node next) {
this.hash = hash;
this.key = key;
this.val = val;
this.next = next;
}
}
/* ---------------- TreeBins -------------- */
/**
* Nodes for use in TreeBins
*/
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;
TreeNode(int hash, Object key, V val, Node next, TreeNode parent) {
super(hash, key, val, next);
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 && h >= pr.hash &&
(r = getTreeNode(h, k, pr)) != null)
return r;
else if ((pl = p.left) != null && h <= pl.hash)
dir = -1;
else // nothing there
return null;
}
}
}
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 V 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 == 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, V v) {
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 && h >= pr.hash &&
(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, 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 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.) 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 if key is comparable. Call
* only when locked.
*/
private final void replaceWithTreeBin(Node[] tab, int index, Object key) {
if (key instanceof Comparable) {
TreeBin t = new TreeBin();
for (Node e = tabAt(tab, index); e != null; e = e.next)
t.putTreeNode(e.hash, e.key, e.val);
setTabAt(tab, index, new Node(MOVED, t, null, null));
}
}
/* ---------------- Internal access and update methods -------------- */
/** Implementation for get and containsKey */
@SuppressWarnings("unchecked") private final V internalGet(Object k) {
int h = spread(k.hashCode());
retry: for (Node[] tab = table; tab != null;) {
Node e; Object ek; V 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) < 0) {
if ((ek = e.key) instanceof TreeBin) // search TreeBin
return ((TreeBin)ek).getValue(h, k);
else { // restart with new table
tab = (Node[])ek;
continue retry;
}
}
else if (eh == 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.
*/
@SuppressWarnings("unchecked") private final V internalReplace
(Object k, V v, Object cv) {
int h = spread(k.hashCode());
V oldVal = null;
for (Node[] 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) < 0) {
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) {
V pv = p.val;
if (cv == null || cv == pv || cv.equals(pv)) {
oldVal = pv;
if ((p.val = v) == null) {
deleted = true;
t.deleteTreeNode(p);
}
}
}
}
} finally {
t.release(0);
}
if (validated) {
if (deleted)
addCount(-1L, -1);
break;
}
}
else
tab = (Node[])fk;
}
else if (fh != h && f.next == null) // precheck
break; // rules out possible existence
else {
boolean validated = false;
boolean deleted = false;
synchronized (f) {
if (tabAt(tab, i) == f) {
validated = true;
for (Node e = f, pred = null;;) {
Object ek; V ev;
if (e.hash == h &&
((ev = e.val) != null) &&
((ek = e.key) == k || k.equals(ek))) {
if (cv == null || cv == ev || cv.equals(ev)) {
oldVal = ev;
if ((e.val = v) == null) {
deleted = true;
Node en = e.next;
if (pred != null)
pred.next = en;
else
setTabAt(tab, i, en);
}
}
break;
}
pred = e;
if ((e = e.next) == null)
break;
}
}
}
if (validated) {
if (deleted)
addCount(-1L, -1);
break;
}
}
}
return oldVal;
}
/*
* Internal versions of insertion methods
* 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 putAll method differs mainly in attempting to pre-allocate
* enough table space, and also more lazily performs count updates
* and checks.
*
* Most of the function-accepting methods can't be factored nicely
* because they require different functional forms, so instead
* sprawl out similar mechanics.
*/
/** Implementation for put and putIfAbsent */
@SuppressWarnings("unchecked") private final V internalPut
(K k, V v, boolean onlyIfAbsent) {
if (k == null || v == null) throw new NullPointerException();
int h = spread(k.hashCode());
int len = 0;
for (Node[] tab = table;;) {
int i, fh; Node f; Object fk; V 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)))
break; // no lock when adding to empty bin
}
else if ((fh = f.hash) < 0) {
if ((fk = f.key) instanceof TreeBin) {
TreeBin t = (TreeBin)fk;
V oldVal = null;
t.acquire(0);
try {
if (tabAt(tab, i) == f) {
len = 2;
TreeNode p = t.putTreeNode(h, k, v);
if (p != null) {
oldVal = p.val;
if (!onlyIfAbsent)
p.val = v;
}
}
} finally {
t.release(0);
}
if (len != 0) {
if (oldVal != null)
return oldVal;
break;
}
}
else
tab = (Node[])fk;
}
else if (onlyIfAbsent && fh == h && (fv = f.val) != null &&
((fk = f.key) == k || k.equals(fk))) // peek while nearby
return fv;
else {
V oldVal = null;
synchronized (f) {
if (tabAt(tab, i) == f) {
len = 1;
for (Node e = f;; ++len) {
Object ek; V ev;
if (e.hash == h &&
(ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek))) {
oldVal = ev;
if (!onlyIfAbsent)
e.val = v;
break;
}
Node last = e;
if ((e = e.next) == null) {
last.next = new Node(h, k, v, null);
if (len >= TREE_THRESHOLD)
replaceWithTreeBin(tab, i, k);
break;
}
}
}
}
if (len != 0) {
if (oldVal != null)
return oldVal;
break;
}
}
}
addCount(1L, len);
return null;
}
/** Implementation for computeIfAbsent */
@SuppressWarnings("unchecked") private final V internalComputeIfAbsent
(K k, Fun mf) {
if (k == null || mf == null)
throw new NullPointerException();
int h = spread(k.hashCode());
V val = null;
int len = 0;
for (Node[] tab = table;;) {
Node f; int i; Object fk;
if (tab == null)
tab = initTable();
else if ((f = tabAt(tab, i = (tab.length - 1) & h)) == null) {
Node node = new Node(h, k, null, null);
synchronized (node) {
if (casTabAt(tab, i, null, node)) {
len = 1;
try {
if ((val = mf.apply(k)) != null)
node.val = val;
} finally {
if (val == null)
setTabAt(tab, i, null);
}
}
}
if (len != 0)
break;
}
else if (f.hash < 0) {
if ((fk = f.key) instanceof TreeBin) {
TreeBin t = (TreeBin)fk;
boolean added = false;
t.acquire(0);
try {
if (tabAt(tab, i) == f) {
len = 1;
TreeNode p = t.getTreeNode(h, k, t.root);
if (p != null)
val = p.val;
else if ((val = mf.apply(k)) != null) {
added = true;
len = 2;
t.putTreeNode(h, k, val);
}
}
} finally {
t.release(0);
}
if (len != 0) {
if (!added)
return val;
break;
}
}
else
tab = (Node[])fk;
}
else {
for (Node e = f; e != null; e = e.next) { // prescan
Object ek; V ev;
if (e.hash == h && (ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek)))
return ev;
}
boolean added = false;
synchronized (f) {
if (tabAt(tab, i) == f) {
len = 1;
for (Node e = f;; ++len) {
Object ek; V ev;
if (e.hash == h &&
(ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek))) {
val = ev;
break;
}
Node last = e;
if ((e = e.next) == null) {
if ((val = mf.apply(k)) != null) {
added = true;
last.next = new Node(h, k, val, null);
if (len >= TREE_THRESHOLD)
replaceWithTreeBin(tab, i, k);
}
break;
}
}
}
}
if (len != 0) {
if (!added)
return val;
break;
}
}
}
if (val != null)
addCount(1L, len);
return val;
}
/** Implementation for compute */
@SuppressWarnings("unchecked") private final V internalCompute
(K k, boolean onlyIfPresent,
BiFun mf) {
if (k == null || mf == null)
throw new NullPointerException();
int h = spread(k.hashCode());
V val = null;
int delta = 0;
int len = 0;
for (Node[] tab = table;;) {
Node f; int i, fh; Object fk;
if (tab == null)
tab = initTable();
else if ((f = tabAt(tab, i = (tab.length - 1) & h)) == null) {
if (onlyIfPresent)
break;
Node node = new Node(h, k, null, null);
synchronized (node) {
if (casTabAt(tab, i, null, node)) {
try {
len = 1;
if ((val = mf.apply(k, null)) != null) {
node.val = val;
delta = 1;
}
} finally {
if (delta == 0)
setTabAt(tab, i, null);
}
}
}
if (len != 0)
break;
}
else if ((fh = f.hash) < 0) {
if ((fk = f.key) instanceof TreeBin) {
TreeBin t = (TreeBin)fk;
t.acquire(0);
try {
if (tabAt(tab, i) == f) {
len = 1;
TreeNode p = t.getTreeNode(h, k, t.root);
if (p == null && onlyIfPresent)
break;
V pv = (p == null) ? null : p.val;
if ((val = mf.apply(k, pv)) != null) {
if (p != null)
p.val = val;
else {
len = 2;
delta = 1;
t.putTreeNode(h, k, val);
}
}
else if (p != null) {
delta = -1;
t.deleteTreeNode(p);
}
}
} finally {
t.release(0);
}
if (len != 0)
break;
}
else
tab = (Node[])fk;
}
else {
synchronized (f) {
if (tabAt(tab, i) == f) {
len = 1;
for (Node e = f, pred = null;; ++len) {
Object ek; V ev;
if (e.hash == h &&
(ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek))) {
val = mf.apply(k, ev);
if (val != null)
e.val = val;
else {
delta = -1;
Node en = e.next;
if (pred != null)
pred.next = en;
else
setTabAt(tab, i, en);
}
break;
}
pred = e;
if ((e = e.next) == null) {
if (!onlyIfPresent &&
(val = mf.apply(k, null)) != null) {
pred.next = new Node(h, k, val, null);
delta = 1;
if (len >= TREE_THRESHOLD)
replaceWithTreeBin(tab, i, k);
}
break;
}
}
}
}
if (len != 0)
break;
}
}
if (delta != 0)
addCount((long)delta, len);
return val;
}
/** Implementation for merge */
@SuppressWarnings("unchecked") private final V internalMerge
(K k, V v, BiFun mf) {
if (k == null || v == null || mf == null)
throw new NullPointerException();
int h = spread(k.hashCode());
V val = null;
int delta = 0;
int len = 0;
for (Node[] tab = table;;) {
int i; Node f; Object fk; V 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))) {
delta = 1;
val = v;
break;
}
}
else if (f.hash < 0) {
if ((fk = f.key) instanceof TreeBin) {
TreeBin t = (TreeBin)fk;
t.acquire(0);
try {
if (tabAt(tab, i) == f) {
len = 1;
TreeNode p = t.getTreeNode(h, k, t.root);
val = (p == null) ? v : mf.apply(p.val, v);
if (val != null) {
if (p != null)
p.val = val;
else {
len = 2;
delta = 1;
t.putTreeNode(h, k, val);
}
}
else if (p != null) {
delta = -1;
t.deleteTreeNode(p);
}
}
} finally {
t.release(0);
}
if (len != 0)
break;
}
else
tab = (Node[])fk;
}
else {
synchronized (f) {
if (tabAt(tab, i) == f) {
len = 1;
for (Node e = f, pred = null;; ++len) {
Object ek; V ev;
if (e.hash == h &&
(ev = e.val) != null &&
((ek = e.key) == k || k.equals(ek))) {
val = mf.apply(ev, v);
if (val != null)
e.val = val;
else {
delta = -1;
Node en = e.next;
if (pred != null)
pred.next = en;
else
setTabAt(tab, i, en);
}
break;
}
pred = e;
if ((e = e.next) == null) {
val = v;
pred.next = new Node(h, k, val, null);
delta = 1;
if (len >= TREE_THRESHOLD)
replaceWithTreeBin(tab, i, k);
break;
}
}
}
}
if (len != 0)
break;
}
}
if (delta != 0)
addCount((long)delta, len);
return val;
}
/** Implementation for putAll */
@SuppressWarnings("unchecked") 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 v;
if (entry == null || (k = entry.getKey()) == null ||
(v = entry.getValue()) == null) {
npe = true;
break;
}
int h = spread(k.hashCode());
for (Node[] 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) < 0) {
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 = (Node[])fk;
}
else {
int len = 0;
synchronized (f) {
if (tabAt(tab, i) == f) {
len = 1;
for (Node e = f;; ++len) {
Object ek; V ev;
if (e.hash == 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 (len >= TREE_THRESHOLD)
replaceWithTreeBin(tab, i, k);
break;
}
}
}
}
if (len != 0) {
if (len > 1) {
addCount(delta, len);
delta = 0L;
}
break;
}
}
}
}
} finally {
if (delta != 0L)
addCount(delta, 2);
}
if (npe)
throw new NullPointerException();
}
/**
* Implementation for clear. Steps through each bin, removing all
* nodes.
*/
@SuppressWarnings("unchecked") private final void internalClear() {
long delta = 0L; // negative number of deletions
int i = 0;
Node[] tab = table;
while (tab != null && i < tab.length) {
Node f = tabAt(tab, i);
if (f == null)
++i;
else if (f.hash < 0) {
Object fk;
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 = (Node[])fk;
}
else {
synchronized (f) {
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;
}
}
}
}
if (delta != 0L)
addCount(delta, -1);
}
/* ---------------- 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.
*/
@SuppressWarnings("unchecked") private final Node[] initTable() {
Node[] tab; int sc;
while ((tab = table) == null) {
if ((sc = sizeCtl) < 0)
Thread.yield(); // lost initialization race; just spin
else if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
try {
if ((tab = table) == null) {
int n = (sc > 0) ? sc : DEFAULT_CAPACITY;
@SuppressWarnings("rawtypes") Node[] tb = new Node[n];
table = tab = (Node[])tb;
sc = n - (n >>> 2);
}
} finally {
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
*/
private final void addCount(long x, int check) {
CounterCell[] as; long b, s;
if ((as = counterCells) != null ||
!U.compareAndSwapLong(this, BASECOUNT, b = baseCount, s = b + x)) {
CounterHashCode hc; CounterCell a; long v; int m;
boolean uncontended = true;
if ((hc = threadCounterHashCode.get()) == null ||
as == null || (m = as.length - 1) < 0 ||
(a = as[m & hc.code]) == null ||
!(uncontended =
U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))) {
fullAddCount(x, hc, uncontended);
return;
}
if (check <= 1)
return;
s = sumCount();
}
if (check >= 0) {
Node[] tab, nt; int sc;
while (s >= (long)(sc = sizeCtl) && (tab = table) != null &&
tab.length < MAXIMUM_CAPACITY) {
if (sc < 0) {
if (sc == -1 || transferIndex <= transferOrigin ||
(nt = nextTable) == null)
break;
if (U.compareAndSwapInt(this, SIZECTL, sc, sc - 1))
transfer(tab, nt);
}
else if (U.compareAndSwapInt(this, SIZECTL, sc, -2))
transfer(tab, null);
s = sumCount();
}
}
}
/**
* Tries to presize table to accommodate the given number of elements.
*
* @param size number of elements (doesn't need to be perfectly accurate)
*/
@SuppressWarnings("unchecked") 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[] 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("rawtypes") Node[] tb = new Node[n];
table = (Node[])tb;
sc = n - (n >>> 2);
}
} finally {
sizeCtl = sc;
}
}
}
else if (c <= sc || n >= MAXIMUM_CAPACITY)
break;
else if (tab == table &&
U.compareAndSwapInt(this, SIZECTL, sc, -2))
transfer(tab, null);
}
}
/**
* Moves and/or copies the nodes in each bin to new table. See
* above for explanation.
*/
@SuppressWarnings("unchecked") private final void transfer
(Node[] tab, Node[] nextTab) {
int n = tab.length, stride;
if ((stride = (NCPU > 1) ? (n >>> 3) / NCPU : n) < MIN_TRANSFER_STRIDE)
stride = MIN_TRANSFER_STRIDE; // subdivide range
if (nextTab == null) { // initiating
try {
@SuppressWarnings("rawtypes") Node[] tb = new Node[n << 1];
nextTab = (Node[])tb;
} catch (Throwable ex) { // try to cope with OOME
sizeCtl = Integer.MAX_VALUE;
return;
}
nextTable = nextTab;
transferOrigin = n;
transferIndex = n;
Node rev = new Node(MOVED, tab, null, null);
for (int k = n; k > 0;) { // progressively reveal ready slots
int nextk = (k > stride) ? k - stride : 0;
for (int m = nextk; m < k; ++m)
nextTab[m] = rev;
for (int m = n + nextk; m < n + k; ++m)
nextTab[m] = rev;
U.putOrderedInt(this, TRANSFERORIGIN, k = nextk);
}
}
int nextn = nextTab.length;
Node fwd = new Node(MOVED, nextTab, null, null);
boolean advance = true;
for (int i = 0, bound = 0;;) {
int nextIndex, nextBound; Node f; Object fk;
while (advance) {
if (--i >= bound)
advance = false;
else if ((nextIndex = transferIndex) <= transferOrigin) {
i = -1;
advance = false;
}
else if (U.compareAndSwapInt
(this, TRANSFERINDEX, nextIndex,
nextBound = (nextIndex > stride ?
nextIndex - stride : 0))) {
bound = nextBound;
i = nextIndex - 1;
advance = false;
}
}
if (i < 0 || i >= n || i + n >= nextn) {
for (int sc;;) {
if (U.compareAndSwapInt(this, SIZECTL, sc = sizeCtl, ++sc)) {
if (sc == -1) {
nextTable = null;
table = nextTab;
sizeCtl = (n << 1) - (n >>> 1);
}
return;
}
}
}
else if ((f = tabAt(tab, i)) == null) {
if (casTabAt(tab, i, null, fwd)) {
setTabAt(nextTab, i, null);
setTabAt(nextTab, i + n, null);
advance = true;
}
}
else if (f.hash >= 0) {
synchronized (f) {
if (tabAt(tab, i) == f) {
int runBit = f.hash & n;
Node lastRun = f, lo = null, hi = null;
for (Node p = f.next; p != null; p = p.next) {
int b = p.hash & n;
if (b != runBit) {
runBit = b;
lastRun = p;
}
}
if (runBit == 0)
lo = lastRun;
else
hi = lastRun;
for (Node p = f; p != lastRun; p = p.next) {
int ph = p.hash;
Object pk = p.key; V pv = p.val;
if ((ph & n) == 0)
lo = new Node(ph, pk, pv, lo);
else
hi = new Node(ph, pk, pv, hi);
}
setTabAt(nextTab, i, lo);
setTabAt(nextTab, i + n, hi);
setTabAt(tab, i, fwd);
advance = true;
}
}
}
else if ((fk = f.key) instanceof TreeBin) {
TreeBin t = (TreeBin)fk;
t.acquire(0);
try {
if (tabAt(tab, i) == f) {
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;
Object k = e.key; V v = e.val;
if ((h & n) == 0) {
++lc;
lt.putTreeNode(h, k, v);
}
else {
++hc;
ht.putTreeNode(h, k, v);
}
}
Node ln, hn; // throw away trees if too small
if (lc < TREE_THRESHOLD) {
ln = null;
for (Node p = lt.first; p != null; p = p.next)
ln = new Node(p.hash, p.key, p.val, ln);
}
else
ln = new Node(MOVED, lt, null, null);
setTabAt(nextTab, i, ln);
if (hc < TREE_THRESHOLD) {
hn = null;
for (Node p = ht.first; p != null; p = p.next)
hn = new Node(p.hash, p.key, p.val, hn);
}
else
hn = new Node(MOVED, ht, null, null);
setTabAt(nextTab, i + n, hn);
setTabAt(tab, i, fwd);
advance = true;
}
} finally {
t.release(0);
}
}
else
advance = true; // already processed
}
}
/* ---------------- Counter support -------------- */
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
private final void fullAddCount(long x, CounterHashCode hc,
boolean wasUncontended) {
int h;
if (hc == null) {
hc = new CounterHashCode();
int s = counterHashCodeGenerator.addAndGet(SEED_INCREMENT);
h = hc.code = (s == 0) ? 1 : s; // Avoid zero
threadCounterHashCode.set(hc);
}
else
h = hc.code;
boolean collide = false; // True if last slot nonempty
for (;;) {
CounterCell[] as; CounterCell a; int n; long v;
if ((as = counterCells) != null && (n = as.length) > 0) {
if ((a = as[(n - 1) & h]) == null) {
if (counterBusy == 0) { // Try to attach new Cell
CounterCell r = new CounterCell(x); // Optimistic create
if (counterBusy == 0 &&
U.compareAndSwapInt(this, COUNTERBUSY, 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 {
counterBusy = 0;
}
if (created)
break;
continue; // Slot is now non-empty
}
}
collide = false;
}
else if (!wasUncontended) // CAS already known to fail
wasUncontended = true; // Continue after rehash
else if (U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))
break;
else if (counterCells != as || n >= NCPU)
collide = false; // At max size or stale
else if (!collide)
collide = true;
else if (counterBusy == 0 &&
U.compareAndSwapInt(this, COUNTERBUSY, 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 {
counterBusy = 0;
}
collide = false;
continue; // Retry with expanded table
}
h ^= h << 13; // Rehash
h ^= h >>> 17;
h ^= h << 5;
}
else if (counterBusy == 0 && counterCells == as &&
U.compareAndSwapInt(this, COUNTERBUSY, 0, 1)) {
boolean init = false;
try { // Initialize table
if (counterCells == as) {
CounterCell[] rs = new CounterCell[2];
rs[h & 1] = new CounterCell(x);
counterCells = rs;
init = true;
}
} finally {
counterBusy = 0;
}
if (init)
break;
}
else if (U.compareAndSwapLong(this, BASECOUNT, v = baseCount, v + x))
break; // Fall back on using base
}
hc.code = h; // Record index for next time
}
/* ----------------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
extends CountedCompleter {
final ConcurrentHashMapV8 map;
Node next; // the next entry to use
Object nextKey; // cached key field of next
V nextVal; // cached val field of next
Node[] tab; // current table; updated if resized
int index; // index of bin to use next
int baseIndex; // current index of initial table
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(ConcurrentHashMapV8 map) {
this.map = map;
}
/** Creates iterator for split() methods and task constructors */
Traverser(ConcurrentHashMapV8 map, Traverser it, int batch) {
super(it);
this.batch = batch;
if ((this.map = map) != null && it != null) { // split parent
Node[] 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.
*/
@SuppressWarnings("unchecked") final V advance() {
Node e = next;
V ev = null;
outer: do {
if (e != null) // advance past used/skipped node
e = e.next;
while (e == null) { // get to next non-null bin
ConcurrentHashMapV8 m;
Node[] t; int b, i, n; Object ek; // 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 < 0) {
if ((ek = e.key) instanceof TreeBin)
e = ((TreeBin)ek).first;
else {
tab = (Node[])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
/**
* Returns a batch value > 0 if this task should (and must) be
* split, if so, adding to pending count, and in any case
* updating batch value. The initial batch value is approx
* exp2 of the number of times (minus one) to split task by
* two before executing leaf action. This value is faster to
* compute and more convenient to use as a guide to splitting
* than is the depth, since it is used while dividing by two
* anyway.
*/
final int preSplit() {
ConcurrentHashMapV8 m; int b; Node[] t; ForkJoinPool pool;
if ((b = batch) < 0 && (m = map) != null) { // force initialization
if ((t = tab) == null && (t = tab = m.table) != null)
baseLimit = baseSize = t.length;
if (t != null) {
long n = m.sumCount();
int par = ((pool = getPool()) == null) ?
ForkJoinPool.getCommonPoolParallelism() :
pool.getParallelism();
int sp = par << 3; // slack of 8
b = (n <= 0L) ? 0 : (n < (long)sp) ? (int)n : sp;
}
}
b = (b <= 1 || baseIndex == baseLimit) ? 0 : (b >>> 1);
if ((batch = b) > 0)
addToPendingCount(1);
return b;
}
}
/* ---------------- Public operations -------------- */
/**
* Creates a new, empty map with the default initial table size (16).
*/
public ConcurrentHashMapV8() {
}
/**
* 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 ConcurrentHashMapV8(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 ConcurrentHashMapV8(Map m) {
this.sizeCtl = DEFAULT_CAPACITY;
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 ConcurrentHashMapV8(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 ConcurrentHashMapV8(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;
}
/**
* Creates a new {@link Set} backed by a ConcurrentHashMapV8
* from the given type to {@code Boolean.TRUE}.
*
* @return the new set
*/
public static KeySetView newKeySet() {
return new KeySetView(new ConcurrentHashMapV8(),
Boolean.TRUE);
}
/**
* Creates a new {@link Set} backed by a ConcurrentHashMapV8
* 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 ConcurrentHashMapV8(initialCapacity), Boolean.TRUE);
}
/**
* {@inheritDoc}
*/
public boolean isEmpty() {
return sumCount() <= 0L; // ignore transient negative values
}
/**
* {@inheritDoc}
*/
public int size() {
long n = sumCount();
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 ConcurrentHashMapV8 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 = sumCount();
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
*/
public V get(Object key) {
return internalGet(key);
}
/**
* 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
*/
public V getValueOrDefault(Object key, V defaultValue) {
V v;
return (v = internalGet(key)) == 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) {
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();
V 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
* 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
*/
@Deprecated 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
*/
public V put(K key, V value) {
return internalPut(key, value, false);
}
/**
* {@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 internalPut(key, value, true);
}
/**
* Copies all of the mappings from the specified map to this one.
* These mappings replace any mappings that this map had for any of the
* keys currently in the specified map.
*
* @param m mappings to be stored in this map
*/
public void putAll(Map m) {
internalPutAll(m);
}
/**
* If the specified key is not already associated with a value,
* computes its value using the given mappingFunction and enters
* it into the map unless null. This is equivalent to
*
{@code
* if (map.containsKey(key))
* return map.get(key);
* value = mappingFunction.apply(key);
* if (value != null)
* map.put(key, value);
* return value;}
*
* except that the action is performed atomically. If the
* function returns {@code null} no mapping is recorded. If the
* function itself throws an (unchecked) exception, the exception
* is rethrown to its caller, and no mapping is recorded. Some
* attempted update operations on this map by other threads may be
* blocked while computation is in progress, so the computation
* should be short and simple, and must not attempt to update any
* other mappings of this Map. The most appropriate usage is to
* construct a new object serving as an initial mapped value, or
* memoized result, as in:
*
* {@code
* map.computeIfAbsent(key, new Fun() {
* public V map(K k) { return new Value(f(k)); }});}
*
* @param key key with which the specified value is to be associated
* @param mappingFunction the function to compute a value
* @return the current (existing or computed) value associated with
* the specified key, or 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, Fun mappingFunction) {
return internalComputeIfAbsent(key, mappingFunction);
}
/**
* If the given key is present, computes a new mapping value given a key and
* its current mapped value. This is equivalent to
* {@code
* if (map.containsKey(key)) {
* value = remappingFunction.apply(key, map.get(key));
* if (value != null)
* map.put(key, value);
* else
* map.remove(key);
* }
* }
*
* except that the action is performed atomically. If the
* function returns {@code null}, the mapping is removed. If the
* function itself throws an (unchecked) exception, the exception
* is rethrown to its caller, and the current mapping is left
* unchanged. 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. For example,
* to either create or append new messages to a value mapping:
*
* @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 computeIfPresent
(K key, BiFun remappingFunction) {
return internalCompute(key, true, remappingFunction);
}
/**
* Computes a new mapping value given a key and
* its current mapped value (or {@code null} if there is no current
* mapping). This is equivalent to
* {@code
* value = remappingFunction.apply(key, map.get(key));
* if (value != null)
* map.put(key, value);
* else
* map.remove(key);
* }
*
* except that the action is performed atomically. If the
* function returns {@code null}, the mapping is removed. If the
* function itself throws an (unchecked) exception, the exception
* is rethrown to its caller, and the current mapping is left
* unchanged. 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. For example,
* to either create or append new messages to a value mapping:
*
* {@code
* Map map = ...;
* final String msg = ...;
* map.compute(key, new BiFun() {
* public String apply(Key k, String v) {
* return (v == null) ? msg : v + msg;});}}
*
* @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, BiFun remappingFunction) {
return internalCompute(key, false, remappingFunction);
}
/**
* If the specified key is not already associated
* with a value, associate it with the given value.
* Otherwise, replace the value with the results of
* the given remapping function. This is equivalent to:
* {@code
* if (!map.containsKey(key))
* map.put(value);
* else {
* newValue = remappingFunction.apply(map.get(key), value);
* if (value != null)
* map.put(key, value);
* else
* map.remove(key);
* }
* }
* except that the action is performed atomically. If the
* function returns {@code null}, the mapping is removed. If the
* function itself throws an (unchecked) exception, the exception
* is rethrown to its caller, and the current mapping is left
* unchanged. 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.
*/
public V merge
(K key, V value,
BiFun remappingFunction) {
return internalMerge(key, value, remappingFunction);
}
/**
* 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 internalReplace(key, null, null);
}
/**
* {@inheritDoc}
*
* @throws NullPointerException if the specified key is null
*/
public boolean remove(Object key, Object value) {
return value != null && internalReplace(key, null, value) != null;
}
/**
* {@inheritDoc}
*
* @throws NullPointerException if any of the arguments are null
*/
public boolean replace(K key, V oldValue, V newValue) {
if (key == null || oldValue == null || newValue == null)
throw new NullPointerException();
return internalReplace(key, newValue, oldValue) != null;
}
/**
* {@inheritDoc}
*
* @return the previous value associated with the specified key,
* or {@code null} if there was no mapping for the key
* @throws NullPointerException if the specified key or value is null
*/
public V replace(K key, V value) {
if (key == null || value == null)
throw new NullPointerException();
return 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);
V 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('{');
V 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);
V 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