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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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package jsr166e; |
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import jsr166e.LongAdder; |
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import java.util.Map; |
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import java.util.Set; |
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import java.util.Collection; |
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import java.util.AbstractMap; |
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import java.util.AbstractSet; |
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import java.util.AbstractCollection; |
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import java.util.Hashtable; |
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import java.util.HashMap; |
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import java.util.Iterator; |
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import java.util.Enumeration; |
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import java.util.ConcurrentModificationException; |
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import java.util.NoSuchElementException; |
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import java.util.concurrent.ConcurrentMap; |
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import java.io.Serializable; |
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|
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/** |
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* A hash table supporting full concurrency of retrievals and |
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* high expected concurrency for updates. This class obeys the |
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* same functional specification as {@link java.util.Hashtable}, and |
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* includes versions of methods corresponding to each method of |
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* {@code Hashtable}. However, even though all operations are |
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* thread-safe, retrieval operations do <em>not</em> entail locking, |
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* and there is <em>not</em> any support for locking the entire table |
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* in a way that prevents all access. This class is fully |
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* interoperable with {@code Hashtable} in programs that rely on its |
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* thread safety but not on its synchronization details. |
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* |
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* <p> Retrieval operations (including {@code get}) generally do not |
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* block, so may overlap with update operations (including {@code put} |
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* and {@code remove}). Retrievals reflect the results of the most |
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* recently <em>completed</em> update operations holding upon their |
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* onset. For aggregate operations such as {@code putAll} and {@code |
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* clear}, concurrent retrievals may reflect insertion or removal of |
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* only some entries. Similarly, Iterators and Enumerations return |
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* elements reflecting the state of the hash table at some point at or |
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* since the creation of the iterator/enumeration. They do |
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* <em>not</em> throw {@link ConcurrentModificationException}. |
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* However, iterators are designed to be used by only one thread at a |
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* time. Bear in mind that the results of aggregate status methods |
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* including {@code size}, {@code isEmpty}, and {@code containsValue} |
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* are typically useful only when a map is not undergoing concurrent |
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* updates in other threads. Otherwise the results of these methods |
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* reflect transient states that may be adequate for monitoring |
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* purposes, but not for program control. |
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* |
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* <p> Resizing this or any other kind of hash table is a relatively |
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* slow operation, so, when possible, it is a good idea to provide |
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* estimates of expected table sizes in constructors. Also, for |
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* compatibility with previous versions of this class, constructors |
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* may optionally specify an expected {@code concurrencyLevel} as an |
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* additional hint for internal sizing. |
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* |
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* <p>This class and its views and iterators implement all of the |
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* <em>optional</em> methods of the {@link Map} and {@link Iterator} |
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* interfaces. |
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* |
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* <p> Like {@link Hashtable} but unlike {@link HashMap}, this class |
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* does <em>not</em> allow {@code null} to be used as a key or value. |
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* |
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* <p>This class is a member of the |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* <p><em>jsr166e note: This class is a candidate replacement for |
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* java.util.concurrent.ConcurrentHashMap.<em> |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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* @param <K> the type of keys maintained by this map |
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* @param <V> the type of mapped values |
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*/ |
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public class ConcurrentHashMapV8<K, V> |
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implements ConcurrentMap<K, V>, Serializable { |
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private static final long serialVersionUID = 7249069246763182397L; |
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|
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/** |
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* A function computing a mapping from the given key to a value, |
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* or {@code null} if there is no mapping. This is a place-holder |
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* for an upcoming JDK8 interface. |
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*/ |
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public static interface MappingFunction<K, V> { |
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/** |
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* Returns a value for the given key, or null if there is no |
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* mapping. If this function throws an (unchecked) exception, |
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* the exception is rethrown to its caller, and no mapping is |
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* recorded. Because this function is invoked within |
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* atomicity control, the computation should be short and |
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* simple. The most common usage is to construct a new object |
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* serving as an initial mapped value. |
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* |
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* @param key the (non-null) key |
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* @return a value, or null if none |
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*/ |
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V map(K key); |
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} |
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|
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/* |
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* Overview: |
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* |
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* The primary design goal of this hash table is to maintain |
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* concurrent readability (typically method get(), but also |
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* iterators and related methods) while minimizing update |
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* contention. |
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* |
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* Each key-value mapping is held in a Node. Because Node fields |
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* can contain special values, they are defined using plain Object |
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* types. Similarly in turn, all internal methods that use them |
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* work off Object types. And similarly, so do the internal |
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* methods of auxiliary iterator and view classes. All public |
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* generic typed methods relay in/out of these internal methods, |
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* supplying null-checks and casts as needed. |
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* |
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* The table is lazily initialized to a power-of-two size upon the |
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* first insertion. Each bin in the table contains a list of |
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* Nodes (most often, zero or one Node). Table accesses require |
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* volatile/atomic reads, writes, and CASes. Because there is no |
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* other way to arrange this without adding further indirections, |
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* we use intrinsics (sun.misc.Unsafe) operations. The lists of |
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* nodes within bins are always accurately traversable under |
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* volatile reads, so long as lookups check hash code and |
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* non-nullness of value before checking key equality. (All valid |
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* hash codes are nonnegative. Negative values are reserved for |
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* special forwarding nodes; see below.) |
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* |
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* Insertion (via put or putIfAbsent) of the first node in an |
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* empty bin is performed by just CASing it to the bin. This is |
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* on average by far the most common case for put operations. |
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* Other update operations (insert, delete, and replace) require |
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* locks. We do not want to waste the space required to associate |
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* a distinct lock object with each bin, so instead use the first |
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* node of a bin list itself as a lock, using plain "synchronized" |
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* locks. These save space and we can live with block-structured |
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* lock/unlock operations. Using the first node of a list as a |
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* lock does not by itself suffice though: When a node is locked, |
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* any update must first validate that it is still the first node, |
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* and retry if not. Because new nodes are always appended to |
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* lists, once a node is first in a bin, it remains first until |
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* deleted or the bin becomes invalidated. However, operations |
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* that only conditionally update can and sometimes do inspect |
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* nodes until the point of update. This is a converse of sorts to |
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* the lazy locking technique described by Herlihy & Shavit. |
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* |
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* The main disadvantage of this approach is that most update |
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* operations on other nodes in a bin list protected by the same |
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* lock can stall, for example when user equals() or mapping |
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* functions take a long time. However, statistically, this is |
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* not a common enough problem to outweigh the time/space overhead |
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* of alternatives: Under random hash codes, the frequency of |
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* nodes in bins follows a Poisson distribution |
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* (http://en.wikipedia.org/wiki/Poisson_distribution) with a |
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* parameter of 0.5 on average under the default loadFactor of |
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* 0.75. The expected number of locks covering different elements |
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* (i.e., bins with 2 or more nodes) is approximately 10% at |
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* steady state. Lock contention probability for two threads |
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* accessing distinct elements is roughly 1 / (8 * #elements). |
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* Function "spread" performs hashCode randomization that improves |
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* the likelihood that these assumptions hold unless users define |
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* exactly the same value for too many hashCodes. |
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* |
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* The table is resized when occupancy exceeds a threshold. Only |
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* a single thread performs the resize (using field "resizing", to |
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* arrange exclusion), but the table otherwise remains usable for |
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* reads and updates. Resizing proceeds by transferring bins, one |
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* by one, from the table to the next table. Upon transfer, the |
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* old table bin contains only a special forwarding node (with |
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* negative hash field) that contains the next table as its |
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* key. On encountering a forwarding node, access and update |
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* operations restart, using the new table. To ensure concurrent |
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* readability of traversals, transfers must proceed from the last |
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* bin (table.length - 1) up towards the first. Upon seeing a |
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* forwarding node, traversals (see class InternalIterator) |
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* arrange to move to the new table for the rest of the traversal |
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* without revisiting nodes. This constrains bin transfers to a |
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* particular order, and so can block indefinitely waiting for the |
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* next lock, and other threads cannot help with the transfer. |
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* However, expected stalls are infrequent enough to not warrant |
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* the additional overhead of access and iteration schemes that |
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* could admit out-of-order or concurrent bin transfers. |
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* |
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* This traversal scheme also applies to partial traversals of |
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* ranges of bins (via an alternate InternalIterator constructor) |
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* to support partitioned aggregate operations (that are not |
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* otherwise implemented yet). Also, read-only operations give up |
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* if ever forwarded to a null table, which provides support for |
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* shutdown-style clearing, which is also not currently |
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* implemented. |
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* |
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* Lazy table initialization minimizes footprint until first use, |
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* and also avoids resizings when the first operation is from a |
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* putAll, constructor with map argument, or deserialization. |
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* These cases attempt to override the targetCapacity used in |
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* growTable (which may harmlessly fail to take effect in cases of |
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* races with other ongoing resizings). |
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* |
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* The element count is maintained using a LongAdder, which avoids |
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* contention on updates but can encounter cache thrashing if read |
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* too frequently during concurrent access. To avoid reading so |
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* often, resizing is normally attempted only upon adding to a bin |
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* already holding two or more nodes. Under the default load |
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* factor and uniform hash distributions, the probability of this |
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* occurring at threshold is around 13%, meaning that only about 1 |
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* in 8 puts check threshold (and after resizing, many fewer do |
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* so). But this approximation has high variance for small table |
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* sizes, so we check on any collision for sizes <= 64. Further, |
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* to increase the probability that a resize occurs soon enough, |
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* we offset the threshold (see THRESHOLD_OFFSET) by the expected |
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* number of puts between checks. This is currently set to 8, in |
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* accord with the default load factor. In practice, this default |
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* is rarely overridden, and in any case is close enough to other |
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* plausible values not to waste dynamic probability computation |
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* for the sake of more precision. |
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* |
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* Maintaining API and serialization compatibility with previous |
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* versions of this class introduces several oddities. Mainly: We |
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* leave untouched but unused constructor arguments refering to |
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* concurrencyLevel. We also declare an unused "Segment" class |
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* that is instantiated in minimal form only when serializing. |
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*/ |
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|
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/* ---------------- Constants -------------- */ |
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|
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/** |
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* The largest allowed table capacity. Must be a power of 2, at |
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* most 1<<30 to stay within Java array size limits. |
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*/ |
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private static final int MAXIMUM_CAPACITY = 1 << 30; |
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|
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/** |
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* The default initial table capacity. Must be a power of 2 |
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* (i.e., at least 1) and at most MAXIMUM_CAPACITY. |
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*/ |
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private static final int DEFAULT_CAPACITY = 16; |
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|
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/** |
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* The default load factor for this table, used when not otherwise |
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* specified in a constructor. |
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*/ |
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private static final float DEFAULT_LOAD_FACTOR = 0.75f; |
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|
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/** |
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* The default concurrency level for this table. Unused, but |
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* defined for compatibility with previous versions of this class. |
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*/ |
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private static final int DEFAULT_CONCURRENCY_LEVEL = 16; |
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|
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/** |
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* The count value to offset thresholds to compensate for checking |
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* for the need to resize only when inserting into bins with two |
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* or more elements. See above for explanation. |
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*/ |
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private static final int THRESHOLD_OFFSET = 8; |
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|
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/* ---------------- Nodes -------------- */ |
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|
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/** |
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* Key-value entry. Note that this is never exported out as a |
265 |
* user-visible Map.Entry. Nodes with a negative hash field are |
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* special, and do not contain user keys or values. Otherwise, |
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* keys are never null, and null val fields indicate that a node |
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* is in the process of being deleted or created. For purposes of |
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* read-only, access, a key may be read before a val, but can only |
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* be used after checking val. (For an update operation, when a |
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* lock is held on a node, order doesn't matter.) |
272 |
*/ |
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static final class Node { |
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final int hash; |
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final Object key; |
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volatile Object val; |
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volatile Node next; |
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|
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Node(int hash, Object key, Object val, Node next) { |
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this.hash = hash; |
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this.key = key; |
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this.val = val; |
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this.next = next; |
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} |
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} |
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|
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/** |
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* Sign bit of node hash value indicating to use table in node.key. |
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*/ |
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private static final int SIGN_BIT = 0x80000000; |
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|
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/* ---------------- Fields -------------- */ |
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|
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/** |
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* The array of bins. Lazily initialized upon first insertion. |
296 |
* Size is always a power of two. Accessed directly by iterators. |
297 |
*/ |
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transient volatile Node[] table; |
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|
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/** The counter maintaining number of elements. */ |
301 |
private transient final LongAdder counter; |
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/** Nonzero when table is being initialized or resized. Updated via CAS. */ |
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private transient volatile int resizing; |
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/** The next element count value upon which to resize the table. */ |
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private transient int threshold; |
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/** The target capacity; volatile to cover initialization races. */ |
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private transient volatile int targetCapacity; |
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/** The target load factor for the table */ |
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private transient final float loadFactor; |
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|
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// views |
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private transient KeySet<K,V> keySet; |
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private transient Values<K,V> values; |
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private transient EntrySet<K,V> entrySet; |
315 |
|
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/** For serialization compatibility. Null unless serialized; see below */ |
317 |
private Segment<K,V>[] segments; |
318 |
|
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/* ---------------- Table element access -------------- */ |
320 |
|
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/* |
322 |
* Volatile access methods are used for table elements as well as |
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* elements of in-progress next table while resizing. Uses are |
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* null checked by callers, and implicitly bounds-checked, relying |
325 |
* on the invariants that tab arrays have non-zero size, and all |
326 |
* indices are masked with (tab.length - 1) which is never |
327 |
* negative and always less than length. Note that, to be correct |
328 |
* wrt arbitrary concurrency errors by users, bounds checks must |
329 |
* operate on local variables, which accounts for some odd-looking |
330 |
* inline assignments below. |
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*/ |
332 |
|
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static final Node tabAt(Node[] tab, int i) { // used by InternalIterator |
334 |
return (Node)UNSAFE.getObjectVolatile(tab, ((long)i<<ASHIFT)+ABASE); |
335 |
} |
336 |
|
337 |
private static final boolean casTabAt(Node[] tab, int i, Node c, Node v) { |
338 |
return UNSAFE.compareAndSwapObject(tab, ((long)i<<ASHIFT)+ABASE, c, v); |
339 |
} |
340 |
|
341 |
private static final void setTabAt(Node[] tab, int i, Node v) { |
342 |
UNSAFE.putObjectVolatile(tab, ((long)i<<ASHIFT)+ABASE, v); |
343 |
} |
344 |
|
345 |
/* ----------------Table Initialization and Resizing -------------- */ |
346 |
|
347 |
/** |
348 |
* Returns a power of two table size for the given desired capacity. |
349 |
* See Hackers Delight, sec 3.2 |
350 |
*/ |
351 |
private static final int tableSizeFor(int c) { |
352 |
int n = c - 1; |
353 |
n |= n >>> 1; |
354 |
n |= n >>> 2; |
355 |
n |= n >>> 4; |
356 |
n |= n >>> 8; |
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n |= n >>> 16; |
358 |
return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1; |
359 |
} |
360 |
|
361 |
/** |
362 |
* If not already resizing, initializes or creates next table and |
363 |
* transfers bins. Initial table size uses the capacity recorded |
364 |
* in targetCapacity. Rechecks occupancy after a transfer to see |
365 |
* if another resize is already needed because resizings are |
366 |
* lagging additions. |
367 |
* |
368 |
* @return current table |
369 |
*/ |
370 |
private final Node[] growTable() { |
371 |
if (resizing == 0 && |
372 |
UNSAFE.compareAndSwapInt(this, resizingOffset, 0, 1)) { |
373 |
try { |
374 |
for (;;) { |
375 |
Node[] tab = table; |
376 |
int n, c; |
377 |
if (tab == null) |
378 |
n = (c = targetCapacity) > 0 ? c : DEFAULT_CAPACITY; |
379 |
else if ((n = tab.length) < MAXIMUM_CAPACITY && |
380 |
counter.sum() >= threshold) |
381 |
n <<= 1; |
382 |
else |
383 |
break; |
384 |
Node[] nextTab = new Node[n]; |
385 |
threshold = (int)(n * loadFactor) - THRESHOLD_OFFSET; |
386 |
if (tab != null) |
387 |
transfer(tab, nextTab, |
388 |
new Node(SIGN_BIT, nextTab, null, null)); |
389 |
table = nextTab; |
390 |
if (tab == null) |
391 |
break; |
392 |
} |
393 |
} finally { |
394 |
resizing = 0; |
395 |
} |
396 |
} |
397 |
else if (table == null) |
398 |
Thread.yield(); // lost initialization race; just spin |
399 |
return table; |
400 |
} |
401 |
|
402 |
/* |
403 |
* Reclassifies nodes in each bin to new table. Because we are |
404 |
* using power-of-two expansion, the elements from each bin must |
405 |
* either stay at same index, or move with a power of two |
406 |
* offset. We eliminate unnecessary node creation by catching |
407 |
* cases where old nodes can be reused because their next fields |
408 |
* won't change. Statistically, at the default loadFactor, only |
409 |
* about one-sixth of them need cloning when a table doubles. The |
410 |
* nodes they replace will be garbage collectable as soon as they |
411 |
* are no longer referenced by any reader thread that may be in |
412 |
* the midst of concurrently traversing table. |
413 |
* |
414 |
* Transfers are done from the bottom up to preserve iterator |
415 |
* traversability. On each step, the old bin is locked, |
416 |
* moved/copied, and then replaced with a forwarding node. |
417 |
*/ |
418 |
private static final void transfer(Node[] tab, Node[] nextTab, Node fwd) { |
419 |
int n = tab.length; |
420 |
Node ignore = nextTab[n + n - 1]; // force bounds check |
421 |
for (int i = n - 1; i >= 0; --i) { |
422 |
for (Node e;;) { |
423 |
if ((e = tabAt(tab, i)) != null) { |
424 |
boolean validated = false; |
425 |
synchronized (e) { |
426 |
if (tabAt(tab, i) == e) { |
427 |
validated = true; |
428 |
Node lo = null, hi = null, lastRun = e; |
429 |
int runBit = e.hash & n; |
430 |
for (Node p = e.next; p != null; p = p.next) { |
431 |
int b = p.hash & n; |
432 |
if (b != runBit) { |
433 |
runBit = b; |
434 |
lastRun = p; |
435 |
} |
436 |
} |
437 |
if (runBit == 0) |
438 |
lo = lastRun; |
439 |
else |
440 |
hi = lastRun; |
441 |
for (Node p = e; p != lastRun; p = p.next) { |
442 |
int ph = p.hash; |
443 |
Object pk = p.key, pv = p.val; |
444 |
if ((ph & n) == 0) |
445 |
lo = new Node(ph, pk, pv, lo); |
446 |
else |
447 |
hi = new Node(ph, pk, pv, hi); |
448 |
} |
449 |
setTabAt(nextTab, i, lo); |
450 |
setTabAt(nextTab, i + n, hi); |
451 |
setTabAt(tab, i, fwd); |
452 |
} |
453 |
} |
454 |
if (validated) |
455 |
break; |
456 |
} |
457 |
else if (casTabAt(tab, i, e, fwd)) |
458 |
break; |
459 |
} |
460 |
} |
461 |
} |
462 |
|
463 |
/* ---------------- Internal access and update methods -------------- */ |
464 |
|
465 |
/** |
466 |
* Applies a supplemental hash function to a given hashCode, which |
467 |
* defends against poor quality hash functions. The result must |
468 |
* be non-negative, and for reasonable performance must have good |
469 |
* avalanche properties; i.e., that each bit of the argument |
470 |
* affects each bit (except sign bit) of the result. |
471 |
*/ |
472 |
private static final int spread(int h) { |
473 |
// Apply base step of MurmurHash; see http://code.google.com/p/smhasher/ |
474 |
h ^= h >>> 16; |
475 |
h *= 0x85ebca6b; |
476 |
h ^= h >>> 13; |
477 |
h *= 0xc2b2ae35; |
478 |
return (h >>> 16) ^ (h & 0x7fffffff); // mask out sign bit |
479 |
} |
480 |
|
481 |
/** Implementation for get and containsKey */ |
482 |
private final Object internalGet(Object k) { |
483 |
int h = spread(k.hashCode()); |
484 |
retry: for (Node[] tab = table; tab != null;) { |
485 |
Node e; Object ek, ev; int eh; // locals to read fields once |
486 |
for (e = tabAt(tab, (tab.length - 1) & h); e != null; e = e.next) { |
487 |
if ((eh = e.hash) == h) { |
488 |
if ((ev = e.val) != null && |
489 |
((ek = e.key) == k || k.equals(ek))) |
490 |
return ev; |
491 |
} |
492 |
else if (eh < 0) { // sign bit set |
493 |
tab = (Node[])e.key; // bin was moved during resize |
494 |
continue retry; |
495 |
} |
496 |
} |
497 |
break; |
498 |
} |
499 |
return null; |
500 |
} |
501 |
|
502 |
/** Implementation for put and putIfAbsent */ |
503 |
private final Object internalPut(Object k, Object v, boolean replace) { |
504 |
int h = spread(k.hashCode()); |
505 |
Object oldVal = null; // previous value or null if none |
506 |
for (Node[] tab = table;;) { |
507 |
Node e; int i; Object ek, ev; |
508 |
if (tab == null) |
509 |
tab = growTable(); |
510 |
else if ((e = tabAt(tab, i = (tab.length - 1) & h)) == null) { |
511 |
if (casTabAt(tab, i, null, new Node(h, k, v, null))) |
512 |
break; // no lock when adding to empty bin |
513 |
} |
514 |
else if (e.hash < 0) // resized -- restart with new table |
515 |
tab = (Node[])e.key; |
516 |
else if (!replace && e.hash == h && (ev = e.val) != null && |
517 |
((ek = e.key) == k || k.equals(ek))) { |
518 |
if (tabAt(tab, i) == e) { // inspect and validate 1st node |
519 |
oldVal = ev; // without lock for putIfAbsent |
520 |
break; |
521 |
} |
522 |
} |
523 |
else { |
524 |
boolean validated = false; |
525 |
boolean checkSize = false; |
526 |
synchronized (e) { // lock the 1st node of bin list |
527 |
if (tabAt(tab, i) == e) { |
528 |
validated = true; // retry if 1st already deleted |
529 |
for (Node first = e;;) { |
530 |
if (e.hash == h && |
531 |
((ek = e.key) == k || k.equals(ek)) && |
532 |
(ev = e.val) != null) { |
533 |
oldVal = ev; |
534 |
if (replace) |
535 |
e.val = v; |
536 |
break; |
537 |
} |
538 |
Node last = e; |
539 |
if ((e = e.next) == null) { |
540 |
last.next = new Node(h, k, v, null); |
541 |
if (last != first || tab.length <= 64) |
542 |
checkSize = true; |
543 |
break; |
544 |
} |
545 |
} |
546 |
} |
547 |
} |
548 |
if (validated) { |
549 |
if (checkSize && tab.length < MAXIMUM_CAPACITY && |
550 |
resizing == 0 && counter.sum() >= threshold) |
551 |
growTable(); |
552 |
break; |
553 |
} |
554 |
} |
555 |
} |
556 |
if (oldVal == null) |
557 |
counter.increment(); // update counter outside of locks |
558 |
return oldVal; |
559 |
} |
560 |
|
561 |
/** |
562 |
* Implementation for the four public remove/replace methods: |
563 |
* Replaces node value with v, conditional upon match of cv if |
564 |
* non-null. If resulting value is null, delete. |
565 |
*/ |
566 |
private final Object internalReplace(Object k, Object v, Object cv) { |
567 |
int h = spread(k.hashCode()); |
568 |
for (Node[] tab = table;;) { |
569 |
Node e; int i; |
570 |
if (tab == null || |
571 |
(e = tabAt(tab, i = (tab.length - 1) & h)) == null) |
572 |
return null; |
573 |
else if (e.hash < 0) |
574 |
tab = (Node[])e.key; |
575 |
else { |
576 |
Object oldVal = null; |
577 |
boolean validated = false; |
578 |
boolean deleted = false; |
579 |
synchronized (e) { |
580 |
if (tabAt(tab, i) == e) { |
581 |
validated = true; |
582 |
Node pred = null; |
583 |
do { |
584 |
Object ek, ev; |
585 |
if (e.hash == h && |
586 |
((ek = e.key) == k || k.equals(ek)) && |
587 |
((ev = e.val) != null)) { |
588 |
if (cv == null || cv == ev || cv.equals(ev)) { |
589 |
oldVal = ev; |
590 |
if ((e.val = v) == null) { |
591 |
deleted = true; |
592 |
Node en = e.next; |
593 |
if (pred != null) |
594 |
pred.next = en; |
595 |
else |
596 |
setTabAt(tab, i, en); |
597 |
} |
598 |
} |
599 |
break; |
600 |
} |
601 |
} while ((e = (pred = e).next) != null); |
602 |
} |
603 |
} |
604 |
if (validated) { |
605 |
if (deleted) |
606 |
counter.decrement(); |
607 |
return oldVal; |
608 |
} |
609 |
} |
610 |
} |
611 |
} |
612 |
|
613 |
/** Implementation for computeIfAbsent and compute. Like put, but messier. */ |
614 |
@SuppressWarnings("unchecked") |
615 |
private final V internalCompute(K k, |
616 |
MappingFunction<? super K, ? extends V> f, |
617 |
boolean replace) { |
618 |
int h = spread(k.hashCode()); |
619 |
V val = null; |
620 |
boolean added = false; |
621 |
Node[] tab = table; |
622 |
outer:for (;;) { |
623 |
Node e; int i; Object ek, ev; |
624 |
if (tab == null) |
625 |
tab = growTable(); |
626 |
else if ((e = tabAt(tab, i = (tab.length - 1) & h)) == null) { |
627 |
Node node = new Node(h, k, null, null); |
628 |
boolean validated = false; |
629 |
synchronized (node) { // must lock while computing value |
630 |
if (casTabAt(tab, i, null, node)) { |
631 |
validated = true; |
632 |
try { |
633 |
val = f.map(k); |
634 |
if (val != null) { |
635 |
node.val = val; |
636 |
added = true; |
637 |
} |
638 |
} finally { |
639 |
if (!added) |
640 |
setTabAt(tab, i, null); |
641 |
} |
642 |
} |
643 |
} |
644 |
if (validated) |
645 |
break; |
646 |
} |
647 |
else if (e.hash < 0) |
648 |
tab = (Node[])e.key; |
649 |
else if (!replace && e.hash == h && (ev = e.val) != null && |
650 |
((ek = e.key) == k || k.equals(ek))) { |
651 |
if (tabAt(tab, i) == e) { |
652 |
val = (V)ev; |
653 |
break; |
654 |
} |
655 |
} |
656 |
else if (Thread.holdsLock(e)) |
657 |
throw new IllegalStateException("Recursive map computation"); |
658 |
else { |
659 |
boolean validated = false; |
660 |
boolean checkSize = false; |
661 |
synchronized (e) { |
662 |
if (tabAt(tab, i) == e) { |
663 |
validated = true; |
664 |
for (Node first = e;;) { |
665 |
if (e.hash == h && |
666 |
((ek = e.key) == k || k.equals(ek)) && |
667 |
((ev = e.val) != null)) { |
668 |
Object fv; |
669 |
if (replace && (fv = f.map(k)) != null) |
670 |
ev = e.val = fv; |
671 |
val = (V)ev; |
672 |
break; |
673 |
} |
674 |
Node last = e; |
675 |
if ((e = e.next) == null) { |
676 |
if ((val = f.map(k)) != null) { |
677 |
last.next = new Node(h, k, val, null); |
678 |
added = true; |
679 |
if (last != first || tab.length <= 64) |
680 |
checkSize = true; |
681 |
} |
682 |
break; |
683 |
} |
684 |
} |
685 |
} |
686 |
} |
687 |
if (validated) { |
688 |
if (checkSize && tab.length < MAXIMUM_CAPACITY && |
689 |
resizing == 0 && counter.sum() >= threshold) |
690 |
growTable(); |
691 |
break; |
692 |
} |
693 |
} |
694 |
} |
695 |
if (added) |
696 |
counter.increment(); |
697 |
return val; |
698 |
} |
699 |
|
700 |
/** |
701 |
* Implementation for clear. Steps through each bin, removing all nodes. |
702 |
*/ |
703 |
private final void internalClear() { |
704 |
long delta = 0L; // negative number of deletions |
705 |
int i = 0; |
706 |
Node[] tab = table; |
707 |
while (tab != null && i < tab.length) { |
708 |
Node e = tabAt(tab, i); |
709 |
if (e == null) |
710 |
++i; |
711 |
else if (e.hash < 0) |
712 |
tab = (Node[])e.key; |
713 |
else { |
714 |
boolean validated = false; |
715 |
synchronized (e) { |
716 |
if (tabAt(tab, i) == e) { |
717 |
validated = true; |
718 |
Node en; |
719 |
do { |
720 |
en = e.next; |
721 |
if (e.val != null) { // currently always true |
722 |
e.val = null; |
723 |
--delta; |
724 |
} |
725 |
} while ((e = en) != null); |
726 |
setTabAt(tab, i, null); |
727 |
} |
728 |
} |
729 |
if (validated) |
730 |
++i; |
731 |
} |
732 |
} |
733 |
counter.add(delta); |
734 |
} |
735 |
|
736 |
/* ----------------Table Traversal -------------- */ |
737 |
|
738 |
/** |
739 |
* Encapsulates traversal for methods such as containsValue; also |
740 |
* serves as a base class for other iterators. |
741 |
* |
742 |
* At each step, the iterator snapshots the key ("nextKey") and |
743 |
* value ("nextVal") of a valid node (i.e., one that, at point of |
744 |
* snapshot, has a nonnull user value). Because val fields can |
745 |
* change (including to null, indicating deletion), field nextVal |
746 |
* might not be accurate at point of use, but still maintains the |
747 |
* weak consistency property of holding a value that was once |
748 |
* valid. |
749 |
* |
750 |
* Internal traversals directly access these fields, as in: |
751 |
* {@code while (it.next != null) { process(nextKey); it.advance(); }} |
752 |
* |
753 |
* Exported iterators (subclasses of ViewIterator) extract key, |
754 |
* value, or key-value pairs as return values of Iterator.next(), |
755 |
* and encapulate the it.next check as hasNext(); |
756 |
* |
757 |
* The iterator visits each valid node that was reachable upon |
758 |
* iterator construction once. It might miss some that were added |
759 |
* to a bin after the bin was visited, which is OK wrt consistency |
760 |
* guarantees. Maintaining this property in the face of possible |
761 |
* ongoing resizes requires a fair amount of bookkeeping state |
762 |
* that is difficult to optimize away amidst volatile accesses. |
763 |
* Even so, traversal maintains reasonable throughput. |
764 |
* |
765 |
* Normally, iteration proceeds bin-by-bin traversing lists. |
766 |
* However, if the table has been resized, then all future steps |
767 |
* must traverse both the bin at the current index as well as at |
768 |
* (index + baseSize); and so on for further resizings. To |
769 |
* paranoically cope with potential sharing by users of iterators |
770 |
* across threads, iteration terminates if a bounds checks fails |
771 |
* for a table read. |
772 |
* |
773 |
* The range-based constructor enables creation of parallel |
774 |
* range-splitting traversals. (Not yet implemented.) |
775 |
*/ |
776 |
static class InternalIterator { |
777 |
Node next; // the next entry to use |
778 |
Node last; // the last entry used |
779 |
Object nextKey; // cached key field of next |
780 |
Object nextVal; // cached val field of next |
781 |
Node[] tab; // current table; updated if resized |
782 |
int index; // index of bin to use next |
783 |
int baseIndex; // current index of initial table |
784 |
final int baseLimit; // index bound for initial table |
785 |
final int baseSize; // initial table size |
786 |
|
787 |
/** Creates iterator for all entries in the table. */ |
788 |
InternalIterator(Node[] tab) { |
789 |
this.tab = tab; |
790 |
baseLimit = baseSize = (tab == null) ? 0 : tab.length; |
791 |
index = baseIndex = 0; |
792 |
next = null; |
793 |
advance(); |
794 |
} |
795 |
|
796 |
/** Creates iterator for the given range of the table */ |
797 |
InternalIterator(Node[] tab, int lo, int hi) { |
798 |
this.tab = tab; |
799 |
baseSize = (tab == null) ? 0 : tab.length; |
800 |
baseLimit = (hi <= baseSize)? hi : baseSize; |
801 |
index = baseIndex = lo; |
802 |
next = null; |
803 |
advance(); |
804 |
} |
805 |
|
806 |
/** Advances next. See above for explanation. */ |
807 |
final void advance() { |
808 |
Node e = last = next; |
809 |
outer: do { |
810 |
if (e != null) // pass used or skipped node |
811 |
e = e.next; |
812 |
while (e == null) { // get to next non-null bin |
813 |
Node[] t; int b, i, n; // checks must use locals |
814 |
if ((b = baseIndex) >= baseLimit || (i = index) < 0 || |
815 |
(t = tab) == null || i >= (n = t.length)) |
816 |
break outer; |
817 |
else if ((e = tabAt(t, i)) != null && e.hash < 0) |
818 |
tab = (Node[])e.key; // restarts due to null val |
819 |
else // visit upper slots if present |
820 |
index = (i += baseSize) < n ? i : (baseIndex = b + 1); |
821 |
} |
822 |
nextKey = e.key; |
823 |
} while ((nextVal = e.val) == null); // skip deleted or special nodes |
824 |
next = e; |
825 |
} |
826 |
} |
827 |
|
828 |
/* ---------------- Public operations -------------- */ |
829 |
|
830 |
/** |
831 |
* Creates a new, empty map with the specified initial |
832 |
* capacity, load factor and concurrency level. |
833 |
* |
834 |
* @param initialCapacity the initial capacity. The implementation |
835 |
* performs internal sizing to accommodate this many elements. |
836 |
* @param loadFactor the load factor threshold, used to control resizing. |
837 |
* Resizing may be performed when the average number of elements per |
838 |
* bin exceeds this threshold. |
839 |
* @param concurrencyLevel the estimated number of concurrently |
840 |
* updating threads. The implementation may use this value as |
841 |
* a sizing hint. |
842 |
* @throws IllegalArgumentException if the initial capacity is |
843 |
* negative or the load factor or concurrencyLevel are |
844 |
* nonpositive. |
845 |
*/ |
846 |
public ConcurrentHashMapV8(int initialCapacity, |
847 |
float loadFactor, int concurrencyLevel) { |
848 |
if (!(loadFactor > 0.0f) || initialCapacity < 0 || concurrencyLevel <= 0) |
849 |
throw new IllegalArgumentException(); |
850 |
int cap = tableSizeFor(initialCapacity); |
851 |
this.counter = new LongAdder(); |
852 |
this.loadFactor = loadFactor; |
853 |
this.targetCapacity = cap; |
854 |
} |
855 |
|
856 |
/** |
857 |
* Creates a new, empty map with the specified initial capacity |
858 |
* and load factor and with the default concurrencyLevel (16). |
859 |
* |
860 |
* @param initialCapacity The implementation performs internal |
861 |
* sizing to accommodate this many elements. |
862 |
* @param loadFactor the load factor threshold, used to control resizing. |
863 |
* Resizing may be performed when the average number of elements per |
864 |
* bin exceeds this threshold. |
865 |
* @throws IllegalArgumentException if the initial capacity of |
866 |
* elements is negative or the load factor is nonpositive |
867 |
* |
868 |
* @since 1.6 |
869 |
*/ |
870 |
public ConcurrentHashMapV8(int initialCapacity, float loadFactor) { |
871 |
this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL); |
872 |
} |
873 |
|
874 |
/** |
875 |
* Creates a new, empty map with the specified initial capacity, |
876 |
* and with default load factor (0.75) and concurrencyLevel (16). |
877 |
* |
878 |
* @param initialCapacity the initial capacity. The implementation |
879 |
* performs internal sizing to accommodate this many elements. |
880 |
* @throws IllegalArgumentException if the initial capacity of |
881 |
* elements is negative. |
882 |
*/ |
883 |
public ConcurrentHashMapV8(int initialCapacity) { |
884 |
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
885 |
} |
886 |
|
887 |
/** |
888 |
* Creates a new, empty map with a default initial capacity (16), |
889 |
* load factor (0.75) and concurrencyLevel (16). |
890 |
*/ |
891 |
public ConcurrentHashMapV8() { |
892 |
this(DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
893 |
} |
894 |
|
895 |
/** |
896 |
* Creates a new map with the same mappings as the given map. |
897 |
* The map is created with a capacity of 1.5 times the number |
898 |
* of mappings in the given map or 16 (whichever is greater), |
899 |
* and a default load factor (0.75) and concurrencyLevel (16). |
900 |
* |
901 |
* @param m the map |
902 |
*/ |
903 |
public ConcurrentHashMapV8(Map<? extends K, ? extends V> m) { |
904 |
this(DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); |
905 |
putAll(m); |
906 |
} |
907 |
|
908 |
/** |
909 |
* {@inheritDoc} |
910 |
*/ |
911 |
public boolean isEmpty() { |
912 |
return counter.sum() <= 0L; // ignore transient negative values |
913 |
} |
914 |
|
915 |
/** |
916 |
* {@inheritDoc} |
917 |
*/ |
918 |
public int size() { |
919 |
long n = counter.sum(); |
920 |
return ((n < 0L)? 0 : |
921 |
(n > (long)Integer.MAX_VALUE)? Integer.MAX_VALUE : |
922 |
(int)n); |
923 |
} |
924 |
|
925 |
/** |
926 |
* Returns the value to which the specified key is mapped, |
927 |
* or {@code null} if this map contains no mapping for the key. |
928 |
* |
929 |
* <p>More formally, if this map contains a mapping from a key |
930 |
* {@code k} to a value {@code v} such that {@code key.equals(k)}, |
931 |
* then this method returns {@code v}; otherwise it returns |
932 |
* {@code null}. (There can be at most one such mapping.) |
933 |
* |
934 |
* @throws NullPointerException if the specified key is null |
935 |
*/ |
936 |
@SuppressWarnings("unchecked") |
937 |
public V get(Object key) { |
938 |
if (key == null) |
939 |
throw new NullPointerException(); |
940 |
return (V)internalGet(key); |
941 |
} |
942 |
|
943 |
/** |
944 |
* Tests if the specified object is a key in this table. |
945 |
* |
946 |
* @param key possible key |
947 |
* @return {@code true} if and only if the specified object |
948 |
* is a key in this table, as determined by the |
949 |
* {@code equals} method; {@code false} otherwise. |
950 |
* @throws NullPointerException if the specified key is null |
951 |
*/ |
952 |
public boolean containsKey(Object key) { |
953 |
if (key == null) |
954 |
throw new NullPointerException(); |
955 |
return internalGet(key) != null; |
956 |
} |
957 |
|
958 |
/** |
959 |
* Returns {@code true} if this map maps one or more keys to the |
960 |
* specified value. Note: This method may require a full traversal |
961 |
* of the map, and is much slower than method {@code containsKey}. |
962 |
* |
963 |
* @param value value whose presence in this map is to be tested |
964 |
* @return {@code true} if this map maps one or more keys to the |
965 |
* specified value |
966 |
* @throws NullPointerException if the specified value is null |
967 |
*/ |
968 |
public boolean containsValue(Object value) { |
969 |
if (value == null) |
970 |
throw new NullPointerException(); |
971 |
Object v; |
972 |
InternalIterator it = new InternalIterator(table); |
973 |
while (it.next != null) { |
974 |
if ((v = it.nextVal) == value || value.equals(v)) |
975 |
return true; |
976 |
it.advance(); |
977 |
} |
978 |
return false; |
979 |
} |
980 |
|
981 |
/** |
982 |
* Legacy method testing if some key maps into the specified value |
983 |
* in this table. This method is identical in functionality to |
984 |
* {@link #containsValue}, and exists solely to ensure |
985 |
* full compatibility with class {@link java.util.Hashtable}, |
986 |
* which supported this method prior to introduction of the |
987 |
* Java Collections framework. |
988 |
* |
989 |
* @param value a value to search for |
990 |
* @return {@code true} if and only if some key maps to the |
991 |
* {@code value} argument in this table as |
992 |
* determined by the {@code equals} method; |
993 |
* {@code false} otherwise |
994 |
* @throws NullPointerException if the specified value is null |
995 |
*/ |
996 |
public boolean contains(Object value) { |
997 |
return containsValue(value); |
998 |
} |
999 |
|
1000 |
/** |
1001 |
* Maps the specified key to the specified value in this table. |
1002 |
* Neither the key nor the value can be null. |
1003 |
* |
1004 |
* <p> The value can be retrieved by calling the {@code get} method |
1005 |
* with a key that is equal to the original key. |
1006 |
* |
1007 |
* @param key key with which the specified value is to be associated |
1008 |
* @param value value to be associated with the specified key |
1009 |
* @return the previous value associated with {@code key}, or |
1010 |
* {@code null} if there was no mapping for {@code key} |
1011 |
* @throws NullPointerException if the specified key or value is null |
1012 |
*/ |
1013 |
@SuppressWarnings("unchecked") |
1014 |
public V put(K key, V value) { |
1015 |
if (key == null || value == null) |
1016 |
throw new NullPointerException(); |
1017 |
return (V)internalPut(key, value, true); |
1018 |
} |
1019 |
|
1020 |
/** |
1021 |
* {@inheritDoc} |
1022 |
* |
1023 |
* @return the previous value associated with the specified key, |
1024 |
* or {@code null} if there was no mapping for the key |
1025 |
* @throws NullPointerException if the specified key or value is null |
1026 |
*/ |
1027 |
@SuppressWarnings("unchecked") |
1028 |
public V putIfAbsent(K key, V value) { |
1029 |
if (key == null || value == null) |
1030 |
throw new NullPointerException(); |
1031 |
return (V)internalPut(key, value, false); |
1032 |
} |
1033 |
|
1034 |
/** |
1035 |
* Copies all of the mappings from the specified map to this one. |
1036 |
* These mappings replace any mappings that this map had for any of the |
1037 |
* keys currently in the specified map. |
1038 |
* |
1039 |
* @param m mappings to be stored in this map |
1040 |
*/ |
1041 |
public void putAll(Map<? extends K, ? extends V> m) { |
1042 |
if (m == null) |
1043 |
throw new NullPointerException(); |
1044 |
/* |
1045 |
* If uninitialized, try to adjust targetCapacity to |
1046 |
* accommodate the given number of elements. |
1047 |
*/ |
1048 |
if (table == null) { |
1049 |
int size = m.size(); |
1050 |
int cap = (size >= (MAXIMUM_CAPACITY >>> 1)) ? MAXIMUM_CAPACITY : |
1051 |
tableSizeFor(size + (size >>> 1)); |
1052 |
if (cap > targetCapacity) |
1053 |
targetCapacity = cap; |
1054 |
} |
1055 |
for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) |
1056 |
put(e.getKey(), e.getValue()); |
1057 |
} |
1058 |
|
1059 |
/** |
1060 |
* If the specified key is not already associated with a value, |
1061 |
* computes its value using the given mappingFunction, and if |
1062 |
* non-null, enters it into the map. This is equivalent to |
1063 |
* <pre> {@code |
1064 |
* if (map.containsKey(key)) |
1065 |
* return map.get(key); |
1066 |
* value = mappingFunction.map(key); |
1067 |
* if (value != null) |
1068 |
* map.put(key, value); |
1069 |
* return value;}</pre> |
1070 |
* |
1071 |
* except that the action is performed atomically. Some attempted |
1072 |
* update operations on this map by other threads may be blocked |
1073 |
* while computation is in progress, so the computation should be |
1074 |
* short and simple, and must not attempt to update any other |
1075 |
* mappings of this Map. The most appropriate usage is to |
1076 |
* construct a new object serving as an initial mapped value, or |
1077 |
* memoized result, as in: |
1078 |
* <pre> {@code |
1079 |
* map.computeIfAbsent(key, new MappingFunction<K, V>() { |
1080 |
* public V map(K k) { return new Value(f(k)); }});}</pre> |
1081 |
* |
1082 |
* @param key key with which the specified value is to be associated |
1083 |
* @param mappingFunction the function to compute a value |
1084 |
* @return the current (existing or computed) value associated with |
1085 |
* the specified key, or {@code null} if the computation |
1086 |
* returned {@code null}. |
1087 |
* @throws NullPointerException if the specified key or mappingFunction |
1088 |
* is null, |
1089 |
* @throws IllegalStateException if the computation detectably |
1090 |
* attempts a recursive update to this map that would |
1091 |
* otherwise never complete. |
1092 |
* @throws RuntimeException or Error if the mappingFunction does so, |
1093 |
* in which case the mapping is left unestablished. |
1094 |
*/ |
1095 |
public V computeIfAbsent(K key, MappingFunction<? super K, ? extends V> mappingFunction) { |
1096 |
if (key == null || mappingFunction == null) |
1097 |
throw new NullPointerException(); |
1098 |
return internalCompute(key, mappingFunction, false); |
1099 |
} |
1100 |
|
1101 |
/** |
1102 |
* Computes the value associated with the given key using the given |
1103 |
* mappingFunction, and if non-null, enters it into the map. This |
1104 |
* is equivalent to |
1105 |
* <pre> {@code |
1106 |
* value = mappingFunction.map(key); |
1107 |
* if (value != null) |
1108 |
* map.put(key, value); |
1109 |
* else |
1110 |
* value = map.get(key); |
1111 |
* return value;}</pre> |
1112 |
* |
1113 |
* except that the action is performed atomically. Some attempted |
1114 |
* update operations on this map by other threads may be blocked |
1115 |
* while computation is in progress, so the computation should be |
1116 |
* short and simple, and must not attempt to update any other |
1117 |
* mappings of this Map. |
1118 |
* |
1119 |
* @param key key with which the specified value is to be associated |
1120 |
* @param mappingFunction the function to compute a value |
1121 |
* @return the current value associated with |
1122 |
* the specified key, or {@code null} if the computation |
1123 |
* returned {@code null} and the value was not otherwise present. |
1124 |
* @throws NullPointerException if the specified key or mappingFunction |
1125 |
* is null, |
1126 |
* @throws IllegalStateException if the computation detectably |
1127 |
* attempts a recursive update to this map that would |
1128 |
* otherwise never complete. |
1129 |
* @throws RuntimeException or Error if the mappingFunction does so, |
1130 |
* in which case the mapping is unchanged. |
1131 |
*/ |
1132 |
public V compute(K key, MappingFunction<? super K, ? extends V> mappingFunction) { |
1133 |
if (key == null || mappingFunction == null) |
1134 |
throw new NullPointerException(); |
1135 |
return internalCompute(key, mappingFunction, true); |
1136 |
} |
1137 |
|
1138 |
/** |
1139 |
* Removes the key (and its corresponding value) from this map. |
1140 |
* This method does nothing if the key is not in the map. |
1141 |
* |
1142 |
* @param key the key that needs to be removed |
1143 |
* @return the previous value associated with {@code key}, or |
1144 |
* {@code null} if there was no mapping for {@code key} |
1145 |
* @throws NullPointerException if the specified key is null |
1146 |
*/ |
1147 |
@SuppressWarnings("unchecked") |
1148 |
public V remove(Object key) { |
1149 |
if (key == null) |
1150 |
throw new NullPointerException(); |
1151 |
return (V)internalReplace(key, null, null); |
1152 |
} |
1153 |
|
1154 |
/** |
1155 |
* {@inheritDoc} |
1156 |
* |
1157 |
* @throws NullPointerException if the specified key is null |
1158 |
*/ |
1159 |
public boolean remove(Object key, Object value) { |
1160 |
if (key == null) |
1161 |
throw new NullPointerException(); |
1162 |
if (value == null) |
1163 |
return false; |
1164 |
return internalReplace(key, null, value) != null; |
1165 |
} |
1166 |
|
1167 |
/** |
1168 |
* {@inheritDoc} |
1169 |
* |
1170 |
* @throws NullPointerException if any of the arguments are null |
1171 |
*/ |
1172 |
public boolean replace(K key, V oldValue, V newValue) { |
1173 |
if (key == null || oldValue == null || newValue == null) |
1174 |
throw new NullPointerException(); |
1175 |
return internalReplace(key, newValue, oldValue) != null; |
1176 |
} |
1177 |
|
1178 |
/** |
1179 |
* {@inheritDoc} |
1180 |
* |
1181 |
* @return the previous value associated with the specified key, |
1182 |
* or {@code null} if there was no mapping for the key |
1183 |
* @throws NullPointerException if the specified key or value is null |
1184 |
*/ |
1185 |
@SuppressWarnings("unchecked") |
1186 |
public V replace(K key, V value) { |
1187 |
if (key == null || value == null) |
1188 |
throw new NullPointerException(); |
1189 |
return (V)internalReplace(key, value, null); |
1190 |
} |
1191 |
|
1192 |
/** |
1193 |
* Removes all of the mappings from this map. |
1194 |
*/ |
1195 |
public void clear() { |
1196 |
internalClear(); |
1197 |
} |
1198 |
|
1199 |
/** |
1200 |
* Returns a {@link Set} view of the keys contained in this map. |
1201 |
* The set is backed by the map, so changes to the map are |
1202 |
* reflected in the set, and vice-versa. The set supports element |
1203 |
* removal, which removes the corresponding mapping from this map, |
1204 |
* via the {@code Iterator.remove}, {@code Set.remove}, |
1205 |
* {@code removeAll}, {@code retainAll}, and {@code clear} |
1206 |
* operations. It does not support the {@code add} or |
1207 |
* {@code addAll} operations. |
1208 |
* |
1209 |
* <p>The view's {@code iterator} is a "weakly consistent" iterator |
1210 |
* that will never throw {@link ConcurrentModificationException}, |
1211 |
* and guarantees to traverse elements as they existed upon |
1212 |
* construction of the iterator, and may (but is not guaranteed to) |
1213 |
* reflect any modifications subsequent to construction. |
1214 |
*/ |
1215 |
public Set<K> keySet() { |
1216 |
KeySet<K,V> ks = keySet; |
1217 |
return (ks != null) ? ks : (keySet = new KeySet<K,V>(this)); |
1218 |
} |
1219 |
|
1220 |
/** |
1221 |
* Returns a {@link Collection} view of the values contained in this map. |
1222 |
* The collection is backed by the map, so changes to the map are |
1223 |
* reflected in the collection, and vice-versa. The collection |
1224 |
* supports element removal, which removes the corresponding |
1225 |
* mapping from this map, via the {@code Iterator.remove}, |
1226 |
* {@code Collection.remove}, {@code removeAll}, |
1227 |
* {@code retainAll}, and {@code clear} operations. It does not |
1228 |
* support the {@code add} or {@code addAll} operations. |
1229 |
* |
1230 |
* <p>The view's {@code iterator} is a "weakly consistent" iterator |
1231 |
* that will never throw {@link ConcurrentModificationException}, |
1232 |
* and guarantees to traverse elements as they existed upon |
1233 |
* construction of the iterator, and may (but is not guaranteed to) |
1234 |
* reflect any modifications subsequent to construction. |
1235 |
*/ |
1236 |
public Collection<V> values() { |
1237 |
Values<K,V> vs = values; |
1238 |
return (vs != null) ? vs : (values = new Values<K,V>(this)); |
1239 |
} |
1240 |
|
1241 |
/** |
1242 |
* Returns a {@link Set} view of the mappings contained in this map. |
1243 |
* The set is backed by the map, so changes to the map are |
1244 |
* reflected in the set, and vice-versa. The set supports element |
1245 |
* removal, which removes the corresponding mapping from the map, |
1246 |
* via the {@code Iterator.remove}, {@code Set.remove}, |
1247 |
* {@code removeAll}, {@code retainAll}, and {@code clear} |
1248 |
* operations. It does not support the {@code add} or |
1249 |
* {@code addAll} operations. |
1250 |
* |
1251 |
* <p>The view's {@code iterator} is a "weakly consistent" iterator |
1252 |
* that will never throw {@link ConcurrentModificationException}, |
1253 |
* and guarantees to traverse elements as they existed upon |
1254 |
* construction of the iterator, and may (but is not guaranteed to) |
1255 |
* reflect any modifications subsequent to construction. |
1256 |
*/ |
1257 |
public Set<Map.Entry<K,V>> entrySet() { |
1258 |
EntrySet<K,V> es = entrySet; |
1259 |
return (es != null) ? es : (entrySet = new EntrySet<K,V>(this)); |
1260 |
} |
1261 |
|
1262 |
/** |
1263 |
* Returns an enumeration of the keys in this table. |
1264 |
* |
1265 |
* @return an enumeration of the keys in this table |
1266 |
* @see #keySet() |
1267 |
*/ |
1268 |
public Enumeration<K> keys() { |
1269 |
return new KeyIterator<K,V>(this); |
1270 |
} |
1271 |
|
1272 |
/** |
1273 |
* Returns an enumeration of the values in this table. |
1274 |
* |
1275 |
* @return an enumeration of the values in this table |
1276 |
* @see #values() |
1277 |
*/ |
1278 |
public Enumeration<V> elements() { |
1279 |
return new ValueIterator<K,V>(this); |
1280 |
} |
1281 |
|
1282 |
/** |
1283 |
* Returns the hash code value for this {@link Map}, i.e., |
1284 |
* the sum of, for each key-value pair in the map, |
1285 |
* {@code key.hashCode() ^ value.hashCode()}. |
1286 |
* |
1287 |
* @return the hash code value for this map |
1288 |
*/ |
1289 |
public int hashCode() { |
1290 |
int h = 0; |
1291 |
InternalIterator it = new InternalIterator(table); |
1292 |
while (it.next != null) { |
1293 |
h += it.nextKey.hashCode() ^ it.nextVal.hashCode(); |
1294 |
it.advance(); |
1295 |
} |
1296 |
return h; |
1297 |
} |
1298 |
|
1299 |
/** |
1300 |
* Returns a string representation of this map. The string |
1301 |
* representation consists of a list of key-value mappings (in no |
1302 |
* particular order) enclosed in braces ("{@code {}}"). Adjacent |
1303 |
* mappings are separated by the characters {@code ", "} (comma |
1304 |
* and space). Each key-value mapping is rendered as the key |
1305 |
* followed by an equals sign ("{@code =}") followed by the |
1306 |
* associated value. |
1307 |
* |
1308 |
* @return a string representation of this map |
1309 |
*/ |
1310 |
public String toString() { |
1311 |
InternalIterator it = new InternalIterator(table); |
1312 |
StringBuilder sb = new StringBuilder(); |
1313 |
sb.append('{'); |
1314 |
if (it.next != null) { |
1315 |
for (;;) { |
1316 |
Object k = it.nextKey, v = it.nextVal; |
1317 |
sb.append(k == this ? "(this Map)" : k); |
1318 |
sb.append('='); |
1319 |
sb.append(v == this ? "(this Map)" : v); |
1320 |
it.advance(); |
1321 |
if (it.next == null) |
1322 |
break; |
1323 |
sb.append(',').append(' '); |
1324 |
} |
1325 |
} |
1326 |
return sb.append('}').toString(); |
1327 |
} |
1328 |
|
1329 |
/** |
1330 |
* Compares the specified object with this map for equality. |
1331 |
* Returns {@code true} if the given object is a map with the same |
1332 |
* mappings as this map. This operation may return misleading |
1333 |
* results if either map is concurrently modified during execution |
1334 |
* of this method. |
1335 |
* |
1336 |
* @param o object to be compared for equality with this map |
1337 |
* @return {@code true} if the specified object is equal to this map |
1338 |
*/ |
1339 |
public boolean equals(Object o) { |
1340 |
if (o != this) { |
1341 |
if (!(o instanceof Map)) |
1342 |
return false; |
1343 |
Map<?,?> m = (Map<?,?>) o; |
1344 |
InternalIterator it = new InternalIterator(table); |
1345 |
while (it.next != null) { |
1346 |
Object val = it.nextVal; |
1347 |
Object v = m.get(it.nextKey); |
1348 |
if (v == null || (v != val && !v.equals(val))) |
1349 |
return false; |
1350 |
it.advance(); |
1351 |
} |
1352 |
for (Map.Entry<?,?> e : m.entrySet()) { |
1353 |
Object mk, mv, v; |
1354 |
if ((mk = e.getKey()) == null || |
1355 |
(mv = e.getValue()) == null || |
1356 |
(v = internalGet(mk)) == null || |
1357 |
(mv != v && !mv.equals(v))) |
1358 |
return false; |
1359 |
} |
1360 |
} |
1361 |
return true; |
1362 |
} |
1363 |
|
1364 |
/* ----------------Iterators -------------- */ |
1365 |
|
1366 |
/** |
1367 |
* Base class for key, value, and entry iterators. Adds a map |
1368 |
* reference to InternalIterator to support Iterator.remove. |
1369 |
*/ |
1370 |
static abstract class ViewIterator<K,V> extends InternalIterator { |
1371 |
final ConcurrentHashMapV8<K, V> map; |
1372 |
ViewIterator(ConcurrentHashMapV8<K, V> map) { |
1373 |
super(map.table); |
1374 |
this.map = map; |
1375 |
} |
1376 |
|
1377 |
public final void remove() { |
1378 |
if (last == null) |
1379 |
throw new IllegalStateException(); |
1380 |
map.remove(last.key); |
1381 |
last = null; |
1382 |
} |
1383 |
|
1384 |
public final boolean hasNext() { return next != null; } |
1385 |
public final boolean hasMoreElements() { return next != null; } |
1386 |
} |
1387 |
|
1388 |
static final class KeyIterator<K,V> extends ViewIterator<K,V> |
1389 |
implements Iterator<K>, Enumeration<K> { |
1390 |
KeyIterator(ConcurrentHashMapV8<K, V> map) { super(map); } |
1391 |
|
1392 |
@SuppressWarnings("unchecked") |
1393 |
public final K next() { |
1394 |
if (next == null) |
1395 |
throw new NoSuchElementException(); |
1396 |
Object k = nextKey; |
1397 |
advance(); |
1398 |
return (K)k; |
1399 |
} |
1400 |
|
1401 |
public final K nextElement() { return next(); } |
1402 |
} |
1403 |
|
1404 |
static final class ValueIterator<K,V> extends ViewIterator<K,V> |
1405 |
implements Iterator<V>, Enumeration<V> { |
1406 |
ValueIterator(ConcurrentHashMapV8<K, V> map) { super(map); } |
1407 |
|
1408 |
@SuppressWarnings("unchecked") |
1409 |
public final V next() { |
1410 |
if (next == null) |
1411 |
throw new NoSuchElementException(); |
1412 |
Object v = nextVal; |
1413 |
advance(); |
1414 |
return (V)v; |
1415 |
} |
1416 |
|
1417 |
public final V nextElement() { return next(); } |
1418 |
} |
1419 |
|
1420 |
static final class EntryIterator<K,V> extends ViewIterator<K,V> |
1421 |
implements Iterator<Map.Entry<K,V>> { |
1422 |
EntryIterator(ConcurrentHashMapV8<K, V> map) { super(map); } |
1423 |
|
1424 |
@SuppressWarnings("unchecked") |
1425 |
public final Map.Entry<K,V> next() { |
1426 |
if (next == null) |
1427 |
throw new NoSuchElementException(); |
1428 |
Object k = nextKey; |
1429 |
Object v = nextVal; |
1430 |
advance(); |
1431 |
return new WriteThroughEntry<K,V>(map, (K)k, (V)v); |
1432 |
} |
1433 |
} |
1434 |
|
1435 |
/** |
1436 |
* Custom Entry class used by EntryIterator.next(), that relays |
1437 |
* setValue changes to the underlying map. |
1438 |
*/ |
1439 |
static final class WriteThroughEntry<K,V> implements Map.Entry<K, V> { |
1440 |
final ConcurrentHashMapV8<K, V> map; |
1441 |
final K key; // non-null |
1442 |
V val; // non-null |
1443 |
WriteThroughEntry(ConcurrentHashMapV8<K, V> map, K key, V val) { |
1444 |
this.map = map; this.key = key; this.val = val; |
1445 |
} |
1446 |
|
1447 |
public final K getKey() { return key; } |
1448 |
public final V getValue() { return val; } |
1449 |
public final int hashCode() { return key.hashCode() ^ val.hashCode(); } |
1450 |
public final String toString(){ return key + "=" + val; } |
1451 |
|
1452 |
public final boolean equals(Object o) { |
1453 |
Object k, v; Map.Entry<?,?> e; |
1454 |
return ((o instanceof Map.Entry) && |
1455 |
(k = (e = (Map.Entry<?,?>)o).getKey()) != null && |
1456 |
(v = e.getValue()) != null && |
1457 |
(k == key || k.equals(key)) && |
1458 |
(v == val || v.equals(val))); |
1459 |
} |
1460 |
|
1461 |
/** |
1462 |
* Sets our entry's value and writes through to the map. The |
1463 |
* value to return is somewhat arbitrary here. Since a |
1464 |
* WriteThroughEntry does not necessarily track asynchronous |
1465 |
* changes, the most recent "previous" value could be |
1466 |
* different from what we return (or could even have been |
1467 |
* removed in which case the put will re-establish). We do not |
1468 |
* and cannot guarantee more. |
1469 |
*/ |
1470 |
public final V setValue(V value) { |
1471 |
if (value == null) throw new NullPointerException(); |
1472 |
V v = val; |
1473 |
val = value; |
1474 |
map.put(key, value); |
1475 |
return v; |
1476 |
} |
1477 |
} |
1478 |
|
1479 |
/* ----------------Views -------------- */ |
1480 |
|
1481 |
/* |
1482 |
* These currently just extend java.util.AbstractX classes, but |
1483 |
* may need a new custom base to support partitioned traversal. |
1484 |
*/ |
1485 |
|
1486 |
static final class KeySet<K,V> extends AbstractSet<K> { |
1487 |
final ConcurrentHashMapV8<K, V> map; |
1488 |
KeySet(ConcurrentHashMapV8<K, V> map) { this.map = map; } |
1489 |
|
1490 |
public final int size() { return map.size(); } |
1491 |
public final boolean isEmpty() { return map.isEmpty(); } |
1492 |
public final void clear() { map.clear(); } |
1493 |
public final boolean contains(Object o) { return map.containsKey(o); } |
1494 |
public final boolean remove(Object o) { return map.remove(o) != null; } |
1495 |
public final Iterator<K> iterator() { |
1496 |
return new KeyIterator<K,V>(map); |
1497 |
} |
1498 |
} |
1499 |
|
1500 |
static final class Values<K,V> extends AbstractCollection<V> { |
1501 |
final ConcurrentHashMapV8<K, V> map; |
1502 |
Values(ConcurrentHashMapV8<K, V> map) { this.map = map; } |
1503 |
|
1504 |
public final int size() { return map.size(); } |
1505 |
public final boolean isEmpty() { return map.isEmpty(); } |
1506 |
public final void clear() { map.clear(); } |
1507 |
public final boolean contains(Object o) { return map.containsValue(o); } |
1508 |
public final Iterator<V> iterator() { |
1509 |
return new ValueIterator<K,V>(map); |
1510 |
} |
1511 |
} |
1512 |
|
1513 |
static final class EntrySet<K,V> extends AbstractSet<Map.Entry<K,V>> { |
1514 |
final ConcurrentHashMapV8<K, V> map; |
1515 |
EntrySet(ConcurrentHashMapV8<K, V> map) { this.map = map; } |
1516 |
|
1517 |
public final int size() { return map.size(); } |
1518 |
public final boolean isEmpty() { return map.isEmpty(); } |
1519 |
public final void clear() { map.clear(); } |
1520 |
public final Iterator<Map.Entry<K,V>> iterator() { |
1521 |
return new EntryIterator<K,V>(map); |
1522 |
} |
1523 |
|
1524 |
public final boolean contains(Object o) { |
1525 |
Object k, v, r; Map.Entry<?,?> e; |
1526 |
return ((o instanceof Map.Entry) && |
1527 |
(k = (e = (Map.Entry<?,?>)o).getKey()) != null && |
1528 |
(r = map.get(k)) != null && |
1529 |
(v = e.getValue()) != null && |
1530 |
(v == r || v.equals(r))); |
1531 |
} |
1532 |
|
1533 |
public final boolean remove(Object o) { |
1534 |
Object k, v; Map.Entry<?,?> e; |
1535 |
return ((o instanceof Map.Entry) && |
1536 |
(k = (e = (Map.Entry<?,?>)o).getKey()) != null && |
1537 |
(v = e.getValue()) != null && |
1538 |
map.remove(k, v)); |
1539 |
} |
1540 |
} |
1541 |
|
1542 |
/* ---------------- Serialization Support -------------- */ |
1543 |
|
1544 |
/** |
1545 |
* Stripped-down version of helper class used in previous version, |
1546 |
* declared for the sake of serialization compatibility |
1547 |
*/ |
1548 |
static class Segment<K,V> implements Serializable { |
1549 |
private static final long serialVersionUID = 2249069246763182397L; |
1550 |
final float loadFactor; |
1551 |
Segment(float lf) { this.loadFactor = lf; } |
1552 |
} |
1553 |
|
1554 |
/** |
1555 |
* Saves the state of the {@code ConcurrentHashMapV8} instance to a |
1556 |
* stream (i.e., serializes it). |
1557 |
* @param s the stream |
1558 |
* @serialData |
1559 |
* the key (Object) and value (Object) |
1560 |
* for each key-value mapping, followed by a null pair. |
1561 |
* The key-value mappings are emitted in no particular order. |
1562 |
*/ |
1563 |
@SuppressWarnings("unchecked") |
1564 |
private void writeObject(java.io.ObjectOutputStream s) |
1565 |
throws java.io.IOException { |
1566 |
if (segments == null) { // for serialization compatibility |
1567 |
segments = (Segment<K,V>[]) |
1568 |
new Segment<?,?>[DEFAULT_CONCURRENCY_LEVEL]; |
1569 |
for (int i = 0; i < segments.length; ++i) |
1570 |
segments[i] = new Segment<K,V>(DEFAULT_LOAD_FACTOR); |
1571 |
} |
1572 |
s.defaultWriteObject(); |
1573 |
InternalIterator it = new InternalIterator(table); |
1574 |
while (it.next != null) { |
1575 |
s.writeObject(it.nextKey); |
1576 |
s.writeObject(it.nextVal); |
1577 |
it.advance(); |
1578 |
} |
1579 |
s.writeObject(null); |
1580 |
s.writeObject(null); |
1581 |
segments = null; // throw away |
1582 |
} |
1583 |
|
1584 |
/** |
1585 |
* Reconstitutes the instance from a stream (that is, deserializes it). |
1586 |
* @param s the stream |
1587 |
*/ |
1588 |
@SuppressWarnings("unchecked") |
1589 |
private void readObject(java.io.ObjectInputStream s) |
1590 |
throws java.io.IOException, ClassNotFoundException { |
1591 |
s.defaultReadObject(); |
1592 |
this.segments = null; // unneeded |
1593 |
// initalize transient final fields |
1594 |
UNSAFE.putObjectVolatile(this, counterOffset, new LongAdder()); |
1595 |
UNSAFE.putFloatVolatile(this, loadFactorOffset, DEFAULT_LOAD_FACTOR); |
1596 |
this.targetCapacity = DEFAULT_CAPACITY; |
1597 |
|
1598 |
// Create all nodes, then place in table once size is known |
1599 |
long size = 0L; |
1600 |
Node p = null; |
1601 |
for (;;) { |
1602 |
K k = (K) s.readObject(); |
1603 |
V v = (V) s.readObject(); |
1604 |
if (k != null && v != null) { |
1605 |
p = new Node(spread(k.hashCode()), k, v, p); |
1606 |
++size; |
1607 |
} |
1608 |
else |
1609 |
break; |
1610 |
} |
1611 |
if (p != null) { |
1612 |
boolean init = false; |
1613 |
if (resizing == 0 && |
1614 |
UNSAFE.compareAndSwapInt(this, resizingOffset, 0, 1)) { |
1615 |
try { |
1616 |
if (table == null) { |
1617 |
init = true; |
1618 |
int n; |
1619 |
if (size >= (long)(MAXIMUM_CAPACITY >>> 1)) |
1620 |
n = MAXIMUM_CAPACITY; |
1621 |
else { |
1622 |
int sz = (int)size; |
1623 |
n = tableSizeFor(sz + (sz >>> 1)); |
1624 |
} |
1625 |
threshold = (n - (n >>> 2)) - THRESHOLD_OFFSET; |
1626 |
Node[] tab = new Node[n]; |
1627 |
int mask = n - 1; |
1628 |
while (p != null) { |
1629 |
int j = p.hash & mask; |
1630 |
Node next = p.next; |
1631 |
p.next = tabAt(tab, j); |
1632 |
setTabAt(tab, j, p); |
1633 |
p = next; |
1634 |
} |
1635 |
table = tab; |
1636 |
counter.add(size); |
1637 |
} |
1638 |
} finally { |
1639 |
resizing = 0; |
1640 |
} |
1641 |
} |
1642 |
if (!init) { // Can only happen if unsafely published. |
1643 |
while (p != null) { |
1644 |
internalPut(p.key, p.val, true); |
1645 |
p = p.next; |
1646 |
} |
1647 |
} |
1648 |
} |
1649 |
} |
1650 |
|
1651 |
// Unsafe mechanics |
1652 |
private static final sun.misc.Unsafe UNSAFE; |
1653 |
private static final long counterOffset; |
1654 |
private static final long loadFactorOffset; |
1655 |
private static final long resizingOffset; |
1656 |
private static final long ABASE; |
1657 |
private static final int ASHIFT; |
1658 |
|
1659 |
static { |
1660 |
int ss; |
1661 |
try { |
1662 |
UNSAFE = getUnsafe(); |
1663 |
Class<?> k = ConcurrentHashMapV8.class; |
1664 |
counterOffset = UNSAFE.objectFieldOffset |
1665 |
(k.getDeclaredField("counter")); |
1666 |
loadFactorOffset = UNSAFE.objectFieldOffset |
1667 |
(k.getDeclaredField("loadFactor")); |
1668 |
resizingOffset = UNSAFE.objectFieldOffset |
1669 |
(k.getDeclaredField("resizing")); |
1670 |
Class<?> sc = Node[].class; |
1671 |
ABASE = UNSAFE.arrayBaseOffset(sc); |
1672 |
ss = UNSAFE.arrayIndexScale(sc); |
1673 |
} catch (Exception e) { |
1674 |
throw new Error(e); |
1675 |
} |
1676 |
if ((ss & (ss-1)) != 0) |
1677 |
throw new Error("data type scale not a power of two"); |
1678 |
ASHIFT = 31 - Integer.numberOfLeadingZeros(ss); |
1679 |
} |
1680 |
|
1681 |
/** |
1682 |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
1683 |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
1684 |
* into a jdk. |
1685 |
* |
1686 |
* @return a sun.misc.Unsafe |
1687 |
*/ |
1688 |
private static sun.misc.Unsafe getUnsafe() { |
1689 |
try { |
1690 |
return sun.misc.Unsafe.getUnsafe(); |
1691 |
} catch (SecurityException se) { |
1692 |
try { |
1693 |
return java.security.AccessController.doPrivileged |
1694 |
(new java.security |
1695 |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1696 |
public sun.misc.Unsafe run() throws Exception { |
1697 |
java.lang.reflect.Field f = sun.misc |
1698 |
.Unsafe.class.getDeclaredField("theUnsafe"); |
1699 |
f.setAccessible(true); |
1700 |
return (sun.misc.Unsafe) f.get(null); |
1701 |
}}); |
1702 |
} catch (java.security.PrivilegedActionException e) { |
1703 |
throw new RuntimeException("Could not initialize intrinsics", |
1704 |
e.getCause()); |
1705 |
} |
1706 |
} |
1707 |
} |
1708 |
|
1709 |
} |