///*
// * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
// *
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//
///*
// *
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// *
// *
// *
// * Written by Doug Lea with assistance from members of JCP JSR-166
// * Expert Group and released to the public domain, as explained at
// * http://creativecommons.org/publicdomain/zero/1.0/
// */
//
//package my.test.mvstore;
//
//import java.lang.reflect.Field;
//import java.util.AbstractCollection;
//import java.util.AbstractMap;
//import java.util.AbstractSet;
//import java.util.ArrayList;
//import java.util.Collection;
//import java.util.Collections;
//import java.util.Comparator;
//import java.util.ConcurrentModificationException;
//import java.util.Iterator;
//import java.util.List;
//import java.util.Map;
//import java.util.NavigableSet;
//import java.util.NoSuchElementException;
//import java.util.Random;
//import java.util.Set;
//import java.util.SortedMap;
//import java.util.concurrent.ConcurrentNavigableMap;
//
///**
// * A scalable concurrent {@link ConcurrentNavigableMap} implementation.
// * The map is sorted according to the {@linkplain Comparable natural
// * ordering} of its keys, or by a {@link Comparator} provided at map
// * creation time, depending on which constructor is used.
// *
// * <p>This class implements a concurrent variant of <a
// * href="http://en.wikipedia.org/wiki/Skip_list" target="_top">SkipLists</a>
// * providing expected average <i>log(n)</i> time cost for the
// * <tt>containsKey</tt>, <tt>get</tt>, <tt>put</tt> and
// * <tt>remove</tt> operations and their variants. Insertion, removal,
// * update, and access operations safely execute concurrently by
// * multiple threads. Iterators are <i>weakly consistent</i>, returning
// * elements reflecting the state of the map at some point at or since
// * the creation of the iterator. They do <em>not</em> throw {@link
// * ConcurrentModificationException}, and may proceed concurrently with
// * other operations. Ascending key ordered views and their iterators
// * are faster than descending ones.
// *
// * <p>All <tt>Map.Entry</tt> pairs returned by methods in this class
// * and its views represent snapshots of mappings at the time they were
// * produced. They do <em>not</em> support the <tt>Entry.setValue</tt>
// * method. (Note however that it is possible to change mappings in the
// * associated map using <tt>put</tt>, <tt>putIfAbsent</tt>, or
// * <tt>replace</tt>, depending on exactly which effect you need.)
// *
// * <p>Beware that, unlike in most collections, the <tt>size</tt>
// * method is <em>not</em> a constant-time operation. Because of the
// * asynchronous nature of these maps, determining the current number
// * of elements requires a traversal of the elements, and so may report
// * inaccurate results if this collection is modified during traversal.
// * Additionally, the bulk operations <tt>putAll</tt>, <tt>equals</tt>,
// * <tt>toArray</tt>, <tt>containsValue</tt>, and <tt>clear</tt> are
// * <em>not</em> guaranteed to be performed atomically. For example, an
// * iterator operating concurrently with a <tt>putAll</tt> operation
// * might view only some of the added elements.
// *
// * <p>This class and its views and iterators implement all of the
// * <em>optional</em> methods of the {@link Map} and {@link Iterator}
// * interfaces. Like most other concurrent collections, this class does
// * <em>not</em> permit the use of <tt>null</tt> keys or values because some
// * null return values cannot be reliably distinguished from the absence of
// * elements.
// *
// * <p>This class is a member of the
// * <a href="{@docRoot}/../technotes/guides/collections/index.html">
// * Java Collections Framework</a>.
// *
// * @author Doug Lea
// * @param <K> the type of keys maintained by this map
// * @param <V> the type of mapped values
// * @since 1.6
// */
//public class ConcurrentSkipListMap<K, V> extends AbstractMap<K, V> implements ConcurrentNavigableMap<K, V>, Cloneable,
// java.io.Serializable {
// /*
// * This class implements a tree-like two-dimensionally linked skip
// * list in which the index levels are represented in separate
// * nodes from the base nodes holding data. There are two reasons
// * for taking this approach instead of the usual array-based
// * structure: 1) Array based implementations seem to encounter
// * more complexity and overhead 2) We can use cheaper algorithms
// * for the heavily-traversed index lists than can be used for the
// * base lists. Here's a picture of some of the basics for a
// * possible list with 2 levels of index:
// *
// * Head nodes Index nodes
// * +-+ right +-+ +-+
// * |2|---------------->| |--------------------->| |->null
// * +-+ +-+ +-+
// * | down | |
// * v v v
// * +-+ +-+ +-+ +-+ +-+ +-+
// * |1|----------->| |->| |------>| |----------->| |------>| |->null
// * +-+ +-+ +-+ +-+ +-+ +-+
// * v | | | | |
// * Nodes next v v v v v
// * +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
// * | |->|A|->|B|->|C|->|D|->|E|->|F|->|G|->|H|->|I|->|J|->|K|->null
// * +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
// *
// * The base lists use a variant of the HM linked ordered set
// * algorithm. See Tim Harris, "A pragmatic implementation of
// * non-blocking linked lists"
// * http://www.cl.cam.ac.uk/~tlh20/publications.html and Maged
// * Michael "High Performance Dynamic Lock-Free Hash Tables and
// * List-Based Sets"
// * http://www.research.ibm.com/people/m/michael/pubs.htm. The
// * basic idea in these lists is to mark the "next" pointers of
// * deleted nodes when deleting to avoid conflicts with concurrent
// * insertions, and when traversing to keep track of triples
// * (predecessor, node, successor) in order to detect when and how
// * to unlink these deleted nodes.
// *
// * Rather than using mark-bits to mark list deletions (which can
// * be slow and space-intensive using AtomicMarkedReference), nodes
// * use direct CAS'able next pointers. On deletion, instead of
// * marking a pointer, they splice in another node that can be
// * thought of as standing for a marked pointer (indicating this by
// * using otherwise impossible field values). Using plain nodes
// * acts roughly like "boxed" implementations of marked pointers,
// * but uses new nodes only when nodes are deleted, not for every
// * link. This requires less space and supports faster
// * traversal. Even if marked references were better supported by
// * JVMs, traversal using this technique might still be faster
// * because any search need only read ahead one more node than
// * otherwise required (to check for trailing marker) rather than
// * unmasking mark bits or whatever on each read.
// *
// * This approach maintains the essential property needed in the HM
// * algorithm of changing the next-pointer of a deleted node so
// * that any other CAS of it will fail, but implements the idea by
// * changing the pointer to point to a different node, not by
// * marking it. While it would be possible to further squeeze
// * space by defining marker nodes not to have key/value fields, it
// * isn't worth the extra type-testing overhead. The deletion
// * markers are rarely encountered during traversal and are
// * normally quickly garbage collected. (Note that this technique
// * would not work well in systems without garbage collection.)
// *
// * In addition to using deletion markers, the lists also use
// * nullness of value fields to indicate deletion, in a style
// * similar to typical lazy-deletion schemes. If a node's value is
// * null, then it is considered logically deleted and ignored even
// * though it is still reachable. This maintains proper control of
// * concurrent replace vs delete operations -- an attempted replace
// * must fail if a delete beat it by nulling field, and a delete
// * must return the last non-null value held in the field. (Note:
// * Null, rather than some special marker, is used for value fields
// * here because it just so happens to mesh with the Map API
// * requirement that method get returns null if there is no
// * mapping, which allows nodes to remain concurrently readable
// * even when deleted. Using any other marker value here would be
// * messy at best.)
// *
// * Here's the sequence of events for a deletion of node n with
// * predecessor b and successor f, initially:
// *
// * +------+ +------+ +------+
// * ... | b |------>| n |----->| f | ...
// * +------+ +------+ +------+
// *
// * 1. CAS n's value field from non-null to null.
// * From this point on, no public operations encountering
// * the node consider this mapping to exist. However, other
// * ongoing insertions and deletions might still modify
// * n's next pointer.
// *
// * 2. CAS n's next pointer to point to a new marker node.
// * From this point on, no other nodes can be appended to n.
// * which avoids deletion errors in CAS-based linked lists.
// *
// * +------+ +------+ +------+ +------+
// * ... | b |------>| n |----->|marker|------>| f | ...
// * +------+ +------+ +------+ +------+
// *
// * 3. CAS b's next pointer over both n and its marker.
// * From this point on, no new traversals will encounter n,
// * and it can eventually be GCed.
// * +------+ +------+
// * ... | b |----------------------------------->| f | ...
// * +------+ +------+
// *
// * A failure at step 1 leads to simple retry due to a lost race
// * with another operation. Steps 2-3 can fail because some other
// * thread noticed during a traversal a node with null value and
// * helped out by marking and/or unlinking. This helping-out
// * ensures that no thread can become stuck waiting for progress of
// * the deleting thread. The use of marker nodes slightly
// * complicates helping-out code because traversals must track
// * consistent reads of up to four nodes (b, n, marker, f), not
// * just (b, n, f), although the next field of a marker is
// * immutable, and once a next field is CAS'ed to point to a
// * marker, it never again changes, so this requires less care.
// *
// * Skip lists add indexing to this scheme, so that the base-level
// * traversals start close to the locations being found, inserted
// * or deleted -- usually base level traversals only traverse a few
// * nodes. This doesn't change the basic algorithm except for the
// * need to make sure base traversals start at predecessors (here,
// * b) that are not (structurally) deleted, otherwise retrying
// * after processing the deletion.
// *
// * Index levels are maintained as lists with volatile next fields,
// * using CAS to link and unlink. Races are allowed in index-list
// * operations that can (rarely) fail to link in a new index node
// * or delete one. (We can't do this of course for data nodes.)
// * However, even when this happens, the index lists remain sorted,
// * so correctly serve as indices. This can impact performance,
// * but since skip lists are probabilistic anyway, the net result
// * is that under contention, the effective "p" value may be lower
// * than its nominal value. And race windows are kept small enough
// * that in practice these failures are rare, even under a lot of
// * contention.
// *
// * The fact that retries (for both base and index lists) are
// * relatively cheap due to indexing allows some minor
// * simplifications of retry logic. Traversal restarts are
// * performed after most "helping-out" CASes. This isn't always
// * strictly necessary, but the implicit backoffs tend to help
// * reduce other downstream failed CAS's enough to outweigh restart
// * cost. This worsens the worst case, but seems to improve even
// * highly contended cases.
// *
// * Unlike most skip-list implementations, index insertion and
// * deletion here require a separate traversal pass occuring after
// * the base-level action, to add or remove index nodes. This adds
// * to single-threaded overhead, but improves contended
// * multithreaded performance by narrowing interference windows,
// * and allows deletion to ensure that all index nodes will be made
// * unreachable upon return from a public remove operation, thus
// * avoiding unwanted garbage retention. This is more important
// * here than in some other data structures because we cannot null
// * out node fields referencing user keys since they might still be
// * read by other ongoing traversals.
// *
// * Indexing uses skip list parameters that maintain good search
// * performance while using sparser-than-usual indices: The
// * hardwired parameters k=1, p=0.5 (see method randomLevel) mean
// * that about one-quarter of the nodes have indices. Of those that
// * do, half have one level, a quarter have two, and so on (see
// * Pugh's Skip List Cookbook, sec 3.4). The expected total space
// * requirement for a map is slightly less than for the current
// * implementation of java.util.TreeMap.
// *
// * Changing the level of the index (i.e, the height of the
// * tree-like structure) also uses CAS. The head index has initial
// * level/height of one. Creation of an index with height greater
// * than the current level adds a level to the head index by
// * CAS'ing on a new top-most head. To maintain good performance
// * after a lot of removals, deletion methods heuristically try to
// * reduce the height if the topmost levels appear to be empty.
// * This may encounter races in which it possible (but rare) to
// * reduce and "lose" a level just as it is about to contain an
// * index (that will then never be encountered). This does no
// * structural harm, and in practice appears to be a better option
// * than allowing unrestrained growth of levels.
// *
// * The code for all this is more verbose than you'd like. Most
// * operations entail locating an element (or position to insert an
// * element). The code to do this can't be nicely factored out
// * because subsequent uses require a snapshot of predecessor
// * and/or successor and/or value fields which can't be returned
// * all at once, at least not without creating yet another object
// * to hold them -- creating such little objects is an especially
// * bad idea for basic internal search operations because it adds
// * to GC overhead. (This is one of the few times I've wished Java
// * had macros.) Instead, some traversal code is interleaved within
// * insertion and removal operations. The control logic to handle
// * all the retry conditions is sometimes twisty. Most search is
// * broken into 2 parts. findPredecessor() searches index nodes
// * only, returning a base-level predecessor of the key. findNode()
// * finishes out the base-level search. Even with this factoring,
// * there is a fair amount of near-duplication of code to handle
// * variants.
// *
// * For explanation of algorithms sharing at least a couple of
// * features with this one, see Mikhail Fomitchev's thesis
// * (http://www.cs.yorku.ca/~mikhail/), Keir Fraser's thesis
// * (http://www.cl.cam.ac.uk/users/kaf24/), and Hakan Sundell's
// * thesis (http://www.cs.chalmers.se/~phs/).
// *
// * Given the use of tree-like index nodes, you might wonder why
// * this doesn't use some kind of search tree instead, which would
// * support somewhat faster search operations. The reason is that
// * there are no known efficient lock-free insertion and deletion
// * algorithms for search trees. The immutability of the "down"
// * links of index nodes (as opposed to mutable "left" fields in
// * true trees) makes this tractable using only CAS operations.
// *
// * Notation guide for local variables
// * Node: b, n, f for predecessor, node, successor
// * Index: q, r, d for index node, right, down.
// * t for another index node
// * Head: h
// * Levels: j
// * Keys: k, key
// * Values: v, value
// * Comparisons: c
// */
//
// private static final long serialVersionUID = -8627078645895051609L;
//
// /**
// * Generates the initial random seed for the cheaper per-instance
// * random number generators used in randomLevel.
// */
// private static final Random seedGenerator = new Random();
//
// /**
// * Special value used to identify base-level header
// */
// private static final Object BASE_HEADER = new Object();
//
// /**
// * The topmost head index of the skiplist.
// */
// private transient volatile HeadIndex<K, V> head;
//
// /**
// * The comparator used to maintain order in this map, or null
// * if using natural ordering.
// * @serial
// */
// private final Comparator<? super K> comparator;
//
// /**
// * Seed for simple random number generator. Not volatile since it
// * doesn't matter too much if different threads don't see updates.
// */
// private transient int randomSeed;
//
// /** Lazily initialized key set */
// private transient KeySet keySet;
// /** Lazily initialized entry set */
// private transient EntrySet entrySet;
// /** Lazily initialized values collection */
// private transient Values values;
// /** Lazily initialized descending key set */
// private transient ConcurrentNavigableMap<K, V> descendingMap;
//
// /**
// * Initializes or resets state. Needed by constructors, clone,
// * clear, readObject. and ConcurrentSkipListSet.clone.
// * (Note that comparator must be separately initialized.)
// */
// final void initialize() {
// keySet = null;
// entrySet = null;
// values = null;
// descendingMap = null;
// randomSeed = seedGenerator.nextInt() | 0x0100; // ensure nonzero
// head = new HeadIndex<K, V>(new Node<K, V>(null, BASE_HEADER, null), null, null, 1);
// }
//
// /**
// * compareAndSet head node
// */
// private boolean casHead(HeadIndex<K, V> cmp, HeadIndex<K, V> val) {
// return UNSAFE.compareAndSwapObject(this, headOffset, cmp, val);
// }
//
// /* ---------------- Nodes -------------- */
//
// /**
// * Nodes hold keys and values, and are singly linked in sorted
// * order, possibly with some intervening marker nodes. The list is
// * headed by a dummy node accessible as head.node. The value field
// * is declared only as Object because it takes special non-V
// * values for marker and header nodes.
// */
// static final class Node<K, V> {
// final K key;
// volatile Object value;
// volatile Node<K, V> next;
//
// /**
// * Creates a new regular node.
// */
// Node(K key, Object value, Node<K, V> next) {
// this.key = key;
// this.value = value;
// this.next = next;
// }
//
// /**
// * Creates a new marker node. A marker is distinguished by
// * having its value field point to itself. Marker nodes also
// * have null keys, a fact that is exploited in a few places,
// * but this doesn't distinguish markers from the base-level
// * header node (head.node), which also has a null key.
// */
// Node(Node<K, V> next) {
// this.key = null;
// this.value = this;
// this.next = next;
// }
//
// /**
// * compareAndSet value field
// */
// boolean casValue(Object cmp, Object val) {
// return UNSAFE.compareAndSwapObject(this, valueOffset, cmp, val);
// }
//
// /**
// * compareAndSet next field
// */
// boolean casNext(Node<K, V> cmp, Node<K, V> val) {
// return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val);
// }
//
// /**
// * Returns true if this node is a marker. This method isn't
// * actually called in any current code checking for markers
// * because callers will have already read value field and need
// * to use that read (not another done here) and so directly
// * test if value points to node.
// * @param n a possibly null reference to a node
// * @return true if this node is a marker node
// */
// boolean isMarker() {
// return value == this;
// }
//
// /**
// * Returns true if this node is the header of base-level list.
// * @return true if this node is header node
// */
// boolean isBaseHeader() {
// return value == BASE_HEADER;
// }
//
// /**
// * Tries to append a deletion marker to this node.
// * @param f the assumed current successor of this node
// * @return true if successful
// */
// boolean appendMarker(Node<K, V> f) {
// return casNext(f, new Node<K, V>(f));
// }
//
// /**
// * Helps out a deletion by appending marker or unlinking from
// * predecessor. This is called during traversals when value
// * field seen to be null.
// * @param b predecessor
// * @param f successor
// */
// void helpDelete(Node<K, V> b, Node<K, V> f) {
// /*
// * Rechecking links and then doing only one of the
// * help-out stages per call tends to minimize CAS
// * interference among helping threads.
// */
// if (f == next && this == b.next) {
// if (f == null || f.value != f) // not already marked
// appendMarker(f);
// else
// b.casNext(this, f.next);
// }
// }
//
// /**
// * Returns value if this node contains a valid key-value pair,
// * else null.
// * @return this node's value if it isn't a marker or header or
// * is deleted, else null.
// */
// V getValidValue() {
// Object v = value;
// if (v == this || v == BASE_HEADER)
// return null;
// return (V) v;
// }
//
// /**
// * Creates and returns a new SimpleImmutableEntry holding current
// * mapping if this node holds a valid value, else null.
// * @return new entry or null
// */
// AbstractMap.SimpleImmutableEntry<K, V> createSnapshot() {
// V v = getValidValue();
// if (v == null)
// return null;
// return new AbstractMap.SimpleImmutableEntry<K, V>(key, v);
// }
//
// // UNSAFE mechanics
//
// private static final sun.misc.Unsafe UNSAFE;
// private static final long valueOffset;
// private static final long nextOffset;
//
// static {
// try {
// //UNSAFE = sun.misc.Unsafe.getUnsafe();
// Field field = sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
// field.setAccessible(true);
// UNSAFE = (sun.misc.Unsafe) field.get(null);
// Class k = Node.class;
// valueOffset = UNSAFE.objectFieldOffset(k.getDeclaredField("value"));
// nextOffset = UNSAFE.objectFieldOffset(k.getDeclaredField("next"));
// } catch (Exception e) {
// throw new Error(e);
// }
// }
// }
//
// /* ---------------- Indexing -------------- */
//
// /**
// * Index nodes represent the levels of the skip list. Note that
// * even though both Nodes and Indexes have forward-pointing
// * fields, they have different types and are handled in different
// * ways, that can't nicely be captured by placing field in a
// * shared abstract class.
// */
// static class Index<K, V> {
// final Node<K, V> node;
// final Index<K, V> down;
// volatile Index<K, V> right;
//
// /**
// * Creates index node with given values.
// */
// Index(Node<K, V> node, Index<K, V> down, Index<K, V> right) {
// this.node = node;
// this.down = down;
// this.right = right;
// }
//
// /**
// * compareAndSet right field
// */
// final boolean casRight(Index<K, V> cmp, Index<K, V> val) {
// return UNSAFE.compareAndSwapObject(this, rightOffset, cmp, val);
// }
//
// /**
// * Returns true if the node this indexes has been deleted.
// * @return true if indexed node is known to be deleted
// */
// final boolean indexesDeletedNode() {
// return node.value == null;
// }
//
// /**
// * Tries to CAS newSucc as successor. To minimize races with
// * unlink that may lose this index node, if the node being
// * indexed is known to be deleted, it doesn't try to link in.
// * @param succ the expected current successor
// * @param newSucc the new successor
// * @return true if successful
// */
// final boolean link(Index<K, V> succ, Index<K, V> newSucc) {
// Node<K, V> n = node;
// newSucc.right = succ;
// return n.value != null && casRight(succ, newSucc);
// }
//
// /**
// * Tries to CAS right field to skip over apparent successor
// * succ. Fails (forcing a retraversal by caller) if this node
// * is known to be deleted.
// * @param succ the expected current successor
// * @return true if successful
// */
// final boolean unlink(Index<K, V> succ) {
// return !indexesDeletedNode() && casRight(succ, succ.right);
// }
//
// // Unsafe mechanics
// private static final sun.misc.Unsafe UNSAFE;
// private static final long rightOffset;
// static {
// try {
// //UNSAFE = sun.misc.Unsafe.getUnsafe();
// Field field = sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
// field.setAccessible(true);
// UNSAFE = (sun.misc.Unsafe) field.get(null);
// Class k = Index.class;
// rightOffset = UNSAFE.objectFieldOffset(k.getDeclaredField("right"));
// } catch (Exception e) {
// throw new Error(e);
// }
// }
// }
//
// /* ---------------- Head nodes -------------- */
//
// /**
// * Nodes heading each level keep track of their level.
// */
// static final class HeadIndex<K, V> extends Index<K, V> {
// final int level;
//
// HeadIndex(Node<K, V> node, Index<K, V> down, Index<K, V> right, int level) {
// super(node, down, right);
// this.level = level;
// }
// }
//
// /* ---------------- Comparison utilities -------------- */
//
// /**
// * Represents a key with a comparator as a Comparable.
// *
// * Because most sorted collections seem to use natural ordering on
// * Comparables (Strings, Integers, etc), most internal methods are
// * geared to use them. This is generally faster than checking
// * per-comparison whether to use comparator or comparable because
// * it doesn't require a (Comparable) cast for each comparison.
// * (Optimizers can only sometimes remove such redundant checks
// * themselves.) When Comparators are used,
// * ComparableUsingComparators are created so that they act in the
// * same way as natural orderings. This penalizes use of
// * Comparators vs Comparables, which seems like the right
// * tradeoff.
// */
// static final class ComparableUsingComparator<K> implements Comparable<K> {
// final K actualKey;
// final Comparator<? super K> cmp;
//
// ComparableUsingComparator(K key, Comparator<? super K> cmp) {
// this.actualKey = key;
// this.cmp = cmp;
// }
//
// @Override
// public int compareTo(K k2) {
// return cmp.compare(actualKey, k2);
// }
// }
//
// /**
// * If using comparator, return a ComparableUsingComparator, else
// * cast key as Comparable, which may cause ClassCastException,
// * which is propagated back to caller.
// */
// private Comparable<? super K> comparable(Object key) throws ClassCastException {
// if (key == null)
// throw new NullPointerException();
// if (comparator != null)
// return new ComparableUsingComparator<K>((K) key, comparator);
// else
// return (Comparable<? super K>) key;
// }
//
// /**
// * Compares using comparator or natural ordering. Used when the
// * ComparableUsingComparator approach doesn't apply.
// */
// int compare(K k1, K k2) throws ClassCastException {
// Comparator<? super K> cmp = comparator;
// if (cmp != null)
// return cmp.compare(k1, k2);
// else
// return ((Comparable<? super K>) k1).compareTo(k2);
// }
//
// /**
// * Returns true if given key greater than or equal to least and
// * strictly less than fence, bypassing either test if least or
// * fence are null. Needed mainly in submap operations.
// */
// boolean inHalfOpenRange(K key, K least, K fence) {
// if (key == null)
// throw new NullPointerException();
// return ((least == null || compare(key, least) >= 0) && (fence == null || compare(key, fence) < 0));
// }
//
// /**
// * Returns true if given key greater than or equal to least and less
// * or equal to fence. Needed mainly in submap operations.
// */
// boolean inOpenRange(K key, K least, K fence) {
// if (key == null)
// throw new NullPointerException();
// return ((least == null || compare(key, least) >= 0) && (fence == null || compare(key, fence) <= 0));
// }
//
// /* ---------------- Traversal -------------- */
//
// /**
// * Returns a base-level node with key strictly less than given key,
// * or the base-level header if there is no such node. Also
// * unlinks indexes to deleted nodes found along the way. Callers
// * rely on this side-effect of clearing indices to deleted nodes.
// * @param key the key
// * @return a predecessor of key
// */
// private Node<K, V> findPredecessor(Comparable<? super K> key) {
// if (key == null)
// throw new NullPointerException(); // don't postpone errors
// for (;;) {
// Index<K, V> q = head;
// Index<K, V> r = q.right;
// for (;;) {
// if (r != null) {
// Node<K, V> n = r.node;
// K k = n.key;
// if (n.value == null) {
// if (!q.unlink(r))
// break; // restart
// r = q.right; // reread r
// continue;
// }
// if (key.compareTo(k) > 0) {
// q = r;
// r = r.right;
// continue;
// }
// }
// Index<K, V> d = q.down;
// if (d != null) {
// q = d;
// r = d.right;
// } else
// return q.node;
// }
// }
// }
//
// /**
// * Returns node holding key or null if no such, clearing out any
// * deleted nodes seen along the way. Repeatedly traverses at
// * base-level looking for key starting at predecessor returned
// * from findPredecessor, processing base-level deletions as
// * encountered. Some callers rely on this side-effect of clearing
// * deleted nodes.
// *
// * Restarts occur, at traversal step centered on node n, if:
// *
// * (1) After reading n's next field, n is no longer assumed
// * predecessor b's current successor, which means that
// * we don't have a consistent 3-node snapshot and so cannot
// * unlink any subsequent deleted nodes encountered.
// *
// * (2) n's value field is null, indicating n is deleted, in
// * which case we help out an ongoing structural deletion
// * before retrying. Even though there are cases where such
// * unlinking doesn't require restart, they aren't sorted out
// * here because doing so would not usually outweigh cost of
// * restarting.
// *
// * (3) n is a marker or n's predecessor's value field is null,
// * indicating (among other possibilities) that
// * findPredecessor returned a deleted node. We can't unlink
// * the node because we don't know its predecessor, so rely
// * on another call to findPredecessor to notice and return
// * some earlier predecessor, which it will do. This check is
// * only strictly needed at beginning of loop, (and the
// * b.value check isn't strictly needed at all) but is done
// * each iteration to help avoid contention with other
// * threads by callers that will fail to be able to change
// * links, and so will retry anyway.
// *
// * The traversal loops in doPut, doRemove, and findNear all
// * include the same three kinds of checks. And specialized
// * versions appear in findFirst, and findLast and their
// * variants. They can't easily share code because each uses the
// * reads of fields held in locals occurring in the orders they
// * were performed.
// *
// * @param key the key
// * @return node holding key, or null if no such
// */
// private Node<K, V> findNode(Comparable<? super K> key) {
// for (;;) {
// Node<K, V> b = findPredecessor(key);
// Node<K, V> n = b.next;
// for (;;) {
// if (n == null)
// return null;
// Node<K, V> f = n.next;
// if (n != b.next) // inconsistent read
// break;
// Object v = n.value;
// if (v == null) { // n is deleted
// n.helpDelete(b, f);
// break;
// }
// if (v == n || b.value == null) // b is deleted
// break;
// int c = key.compareTo(n.key);
// if (c == 0)
// return n;
// if (c < 0)
// return null;
// b = n;
// n = f;
// }
// }
// }
//
// /**
// * Gets value for key using findNode.
// * @param okey the key
// * @return the value, or null if absent
// */
// private V doGet(Object okey) {
// Comparable<? super K> key = comparable(okey);
// /*
// * Loop needed here and elsewhere in case value field goes
// * null just as it is about to be returned, in which case we
// * lost a race with a deletion, so must retry.
// */
// for (;;) {
// Node<K, V> n = findNode(key);
// if (n == null)
// return null;
// Object v = n.value;
// if (v != null)
// return (V) v;
// }
// }
//
// /* ---------------- Insertion -------------- */
//
// /**
// * Main insertion method. Adds element if not present, or
// * replaces value if present and onlyIfAbsent is false.
// * @param kkey the key
// * @param value the value that must be associated with key
// * @param onlyIfAbsent if should not insert if already present
// * @return the old value, or null if newly inserted
// */
// private V doPut(K kkey, V value, boolean onlyIfAbsent) {
// Comparable<? super K> key = comparable(kkey);
// for (;;) {
// Node<K, V> b = findPredecessor(key);
// Node<K, V> n = b.next;
// for (;;) {
// if (n != null) {
// Node<K, V> f = n.next;
// if (n != b.next) // inconsistent read
// break;
// Object v = n.value;
// if (v == null) { // n is deleted
// n.helpDelete(b, f);
// break;
// }
// if (v == n || b.value == null) // b is deleted
// break;
// int c = key.compareTo(n.key);
// if (c > 0) {
// b = n;
// n = f;
// continue;
// }
// if (c == 0) {
// if (onlyIfAbsent || n.casValue(v, value))
// return (V) v;
// else
// break; // restart if lost race to replace value
// }
// // else c < 0; fall through
// }
//
// Node<K, V> z = new Node<K, V>(kkey, value, n);
// if (!b.casNext(n, z))
// break; // restart if lost race to append to b
// int level = randomLevel();
// if (level > 0)
// insertIndex(z, level);
// return null;
// }
// }
// }
//
// /**
// * Returns a random level for inserting a new node.
// * Hardwired to k=1, p=0.5, max 31 (see above and
// * Pugh's "Skip List Cookbook", sec 3.4).
// *
// * This uses the simplest of the generators described in George
// * Marsaglia's "Xorshift RNGs" paper. This is not a high-quality
// * generator but is acceptable here.
// */
// private int randomLevel() {
// int x = randomSeed;
// x ^= x << 13;
// x ^= x >>> 17;
// randomSeed = x ^= x << 5;
// if ((x & 0x80000001) != 0) // test highest and lowest bits
// return 0;
// int level = 1;
// while (((x >>>= 1) & 1) != 0)
// ++level;
// return level;
// }
//
// /**
// * Creates and adds index nodes for the given node.
// * @param z the node
// * @param level the level of the index
// */
// private void insertIndex(Node<K, V> z, int level) {
// HeadIndex<K, V> h = head;
// int max = h.level;
//
// if (level <= max) {
// Index<K, V> idx = null;
// for (int i = 1; i <= level; ++i)
// idx = new Index<K, V>(z, idx, null);
// addIndex(idx, h, level);
//
// } else { // Add a new level
// /*
// * To reduce interference by other threads checking for
// * empty levels in tryReduceLevel, new levels are added
// * with initialized right pointers. Which in turn requires
// * keeping levels in an array to access them while
// * creating new head index nodes from the opposite
// * direction.
// */
// level = max + 1;
// Index<K, V>[] idxs = new Index[level + 1];
// Index<K, V> idx = null;
// for (int i = 1; i <= level; ++i)
// idxs[i] = idx = new Index<K, V>(z, idx, null);
//
// HeadIndex<K, V> oldh;
// int k;
// for (;;) {
// oldh = head;
// int oldLevel = oldh.level;
// if (level <= oldLevel) { // lost race to add level
// k = level;
// break;
// }
// HeadIndex<K, V> newh = oldh;
// Node<K, V> oldbase = oldh.node;
// for (int j = oldLevel + 1; j <= level; ++j)
// newh = new HeadIndex<K, V>(oldbase, newh, idxs[j], j);
// if (casHead(oldh, newh)) {
// k = oldLevel;
// break;
// }
// }
// addIndex(idxs[k], oldh, k);
// }
// }
//
// /**
// * Adds given index nodes from given level down to 1.
// * @param idx the topmost index node being inserted
// * @param h the value of head to use to insert. This must be
// * snapshotted by callers to provide correct insertion level
// * @param indexLevel the level of the index
// */
// private void addIndex(Index<K, V> idx, HeadIndex<K, V> h, int indexLevel) {
// // Track next level to insert in case of retries
// int insertionLevel = indexLevel;
// Comparable<? super K> key = comparable(idx.node.key);
// if (key == null)
// throw new NullPointerException();
//
// // Similar to findPredecessor, but adding index nodes along
// // path to key.
// for (;;) {
// int j = h.level;
// Index<K, V> q = h;
// Index<K, V> r = q.right;
// Index<K, V> t = idx;
// for (;;) {
// if (r != null) {
// Node<K, V> n = r.node;
// // compare before deletion check avoids needing recheck
// int c = key.compareTo(n.key);
// if (n.value == null) {
// if (!q.unlink(r))
// break;
// r = q.right;
// continue;
// }
// if (c > 0) {
// q = r;
// r = r.right;
// continue;
// }
// }
//
// if (j == insertionLevel) {
// // Don't insert index if node already deleted
// if (t.indexesDeletedNode()) {
// findNode(key); // cleans up
// return;
// }
// if (!q.link(r, t))
// break; // restart
// if (--insertionLevel == 0) {
// // need final deletion check before return
// if (t.indexesDeletedNode())
// findNode(key);
// return;
// }
// }
//
// if (--j >= insertionLevel && j < indexLevel)
// t = t.down;
// q = q.down;
// r = q.right;
// }
// }
// }
//
// /* ---------------- Deletion -------------- */
//
// /**
// * Main deletion method. Locates node, nulls value, appends a
// * deletion marker, unlinks predecessor, removes associated index
// * nodes, and possibly reduces head index level.
// *
// * Index nodes are cleared out simply by calling findPredecessor.
// * which unlinks indexes to deleted nodes found along path to key,
// * which will include the indexes to this node. This is done
// * unconditionally. We can't check beforehand whether there are
// * index nodes because it might be the case that some or all
// * indexes hadn't been inserted yet for this node during initial
// * search for it, and we'd like to ensure lack of garbage
// * retention, so must call to be sure.
// *
// * @param okey the key
// * @param value if non-null, the value that must be
// * associated with key
// * @return the node, or null if not found
// */
// final V doRemove(Object okey, Object value) {
// Comparable<? super K> key = comparable(okey);
// for (;;) {
// Node<K, V> b = findPredecessor(key);
// Node<K, V> n = b.next;
// for (;;) {
// if (n == null)
// return null;
// Node<K, V> f = n.next;
// if (n != b.next) // inconsistent read
// break;
// Object v = n.value;
// if (v == null) { // n is deleted
// n.helpDelete(b, f);
// break;
// }
// if (v == n || b.value == null) // b is deleted
// break;
// int c = key.compareTo(n.key);
// if (c < 0)
// return null;
// if (c > 0) {
// b = n;
// n = f;
// continue;
// }
// if (value != null && !value.equals(v))
// return null;
// if (!n.casValue(v, null))
// break;
// if (!n.appendMarker(f) || !b.casNext(n, f))
// findNode(key); // Retry via findNode
// else {
// findPredecessor(key); // Clean index
// if (head.right == null)
// tryReduceLevel();
// }
// return (V) v;
// }
// }
// }
//
// /**
// * Possibly reduce head level if it has no nodes. This method can
// * (rarely) make mistakes, in which case levels can disappear even
// * though they are about to contain index nodes. This impacts
// * performance, not correctness. To minimize mistakes as well as
// * to reduce hysteresis, the level is reduced by one only if the
// * topmost three levels look empty. Also, if the removed level
// * looks non-empty after CAS, we try to change it back quick
// * before anyone notices our mistake! (This trick works pretty
// * well because this method will practically never make mistakes
// * unless current thread stalls immediately before first CAS, in
// * which case it is very unlikely to stall again immediately
// * afterwards, so will recover.)
// *
// * We put up with all this rather than just let levels grow
// * because otherwise, even a small map that has undergone a large
// * number of insertions and removals will have a lot of levels,
// * slowing down access more than would an occasional unwanted
// * reduction.
// */
// private void tryReduceLevel() {
// HeadIndex<K, V> h = head;
// HeadIndex<K, V> d;
// HeadIndex<K, V> e;
// if (h.level > 3 && (d = (HeadIndex<K, V>) h.down) != null && (e = (HeadIndex<K, V>) d.down) != null && e.right == null
// && d.right == null && h.right == null && casHead(h, d) && // try to set
// h.right != null) // recheck
// casHead(d, h); // try to backout
// }
//
// /* ---------------- Finding and removing first element -------------- */
//
// /**
// * Specialized variant of findNode to get first valid node.
// * @return first node or null if empty
// */
// Node<K, V> findFirst() {
// for (;;) {
// Node<K, V> b = head.node;
// Node<K, V> n = b.next;
// if (n == null)
// return null;
// if (n.value != null)
// return n;
// n.helpDelete(b, n.next);
// }
// }
//
// /**
// * Removes first entry; returns its snapshot.
// * @return null if empty, else snapshot of first entry
// */
// Map.Entry<K, V> doRemoveFirstEntry() {
// for (;;) {
// Node<K, V> b = head.node;
// Node<K, V> n = b.next;
// if (n == null)
// return null;
// Node<K, V> f = n.next;
// if (n != b.next)
// continue;
// Object v = n.value;
// if (v == null) {
// n.helpDelete(b, f);
// continue;
// }
// if (!n.casValue(v, null))
// continue;
// if (!n.appendMarker(f) || !b.casNext(n, f))
// findFirst(); // retry
// clearIndexToFirst();
// return new AbstractMap.SimpleImmutableEntry<K, V>(n.key, (V) v);
// }
// }
//
// /**
// * Clears out index nodes associated with deleted first entry.
// */
// private void clearIndexToFirst() {
// for (;;) {
// Index<K, V> q = head;
// for (;;) {
// Index<K, V> r = q.right;
// if (r != null && r.indexesDeletedNode() && !q.unlink(r))
// break;
// if ((q = q.down) == null) {
// if (head.right == null)
// tryReduceLevel();
// return;
// }
// }
// }
// }
//
// /* ---------------- Finding and removing last element -------------- */
//
// /**
// * Specialized version of find to get last valid node.
// * @return last node or null if empty
// */
// Node<K, V> findLast() {
// /*
// * findPredecessor can't be used to traverse index level
// * because this doesn't use comparisons. So traversals of
// * both levels are folded together.
// */
// Index<K, V> q = head;
// for (;;) {
// Index<K, V> d, r;
// if ((r = q.right) != null) {
// if (r.indexesDeletedNode()) {
// q.unlink(r);
// q = head; // restart
// } else
// q = r;
// } else if ((d = q.down) != null) {
// q = d;
// } else {
// Node<K, V> b = q.node;
// Node<K, V> n = b.next;
// for (;;) {
// if (n == null)
// return b.isBaseHeader() ? null : b;
// Node<K, V> f = n.next; // inconsistent read
// if (n != b.next)
// break;
// Object v = n.value;
// if (v == null) { // n is deleted
// n.helpDelete(b, f);
// break;
// }
// if (v == n || b.value == null) // b is deleted
// break;
// b = n;
// n = f;
// }
// q = head; // restart
// }
// }
// }
//
// /**
// * Specialized variant of findPredecessor to get predecessor of last
// * valid node. Needed when removing the last entry. It is possible
// * that all successors of returned node will have been deleted upon
// * return, in which case this method can be retried.
// * @return likely predecessor of last node
// */
// private Node<K, V> findPredecessorOfLast() {
// for (;;) {
// Index<K, V> q = head;
// for (;;) {
// Index<K, V> d, r;
// if ((r = q.right) != null) {
// if (r.indexesDeletedNode()) {
// q.unlink(r);
// break; // must restart
// }
// // proceed as far across as possible without overshooting
// if (r.node.next != null) {
// q = r;
// continue;
// }
// }
// if ((d = q.down) != null)
// q = d;
// else
// return q.node;
// }
// }
// }
//
// /**
// * Removes last entry; returns its snapshot.
// * Specialized variant of doRemove.
// * @return null if empty, else snapshot of last entry
// */
// Map.Entry<K, V> doRemoveLastEntry() {
// for (;;) {
// Node<K, V> b = findPredecessorOfLast();
// Node<K, V> n = b.next;
// if (n == null) {
// if (b.isBaseHeader()) // empty
// return null;
// else
// continue; // all b's successors are deleted; retry
// }
// for (;;) {
// Node<K, V> f = n.next;
// if (n != b.next) // inconsistent read
// break;
// Object v = n.value;
// if (v == null) { // n is deleted
// n.helpDelete(b, f);
// break;
// }
// if (v == n || b.value == null) // b is deleted
// break;
// if (f != null) {
// b = n;
// n = f;
// continue;
// }
// if (!n.casValue(v, null))
// break;
// K key = n.key;
// Comparable<? super K> ck = comparable(key);
// if (!n.appendMarker(f) || !b.casNext(n, f))
// findNode(ck); // Retry via findNode
// else {
// findPredecessor(ck); // Clean index
// if (head.right == null)
// tryReduceLevel();
// }
// return new AbstractMap.SimpleImmutableEntry<K, V>(key, (V) v);
// }
// }
// }
//
// /* ---------------- Relational operations -------------- */
//
// // Control values OR'ed as arguments to findNear
//
// private static final int EQ = 1;
// private static final int LT = 2;
// private static final int GT = 0; // Actually checked as !LT
//
// /**
// * Utility for ceiling, floor, lower, higher methods.
// * @param kkey the key
// * @param rel the relation -- OR'ed combination of EQ, LT, GT
// * @return nearest node fitting relation, or null if no such
// */
// Node<K, V> findNear(K kkey, int rel) {
// Comparable<? super K> key = comparable(kkey);
// for (;;) {
// Node<K, V> b = findPredecessor(key);
// Node<K, V> n = b.next;
// for (;;) {
// if (n == null)
// return ((rel & LT) == 0 || b.isBaseHeader()) ? null : b;
// Node<K, V> f = n.next;
// if (n != b.next) // inconsistent read
// break;
// Object v = n.value;
// if (v == null) { // n is deleted
// n.helpDelete(b, f);
// break;
// }
// if (v == n || b.value == null) // b is deleted
// break;
// int c = key.compareTo(n.key);
// if ((c == 0 && (rel & EQ) != 0) || (c < 0 && (rel & LT) == 0))
// return n;
// if (c <= 0 && (rel & LT) != 0)
// return b.isBaseHeader() ? null : b;
// b = n;
// n = f;
// }
// }
// }
//
// /**
// * Returns SimpleImmutableEntry for results of findNear.
// * @param key the key
// * @param rel the relation -- OR'ed combination of EQ, LT, GT
// * @return Entry fitting relation, or null if no such
// */
// AbstractMap.SimpleImmutableEntry<K, V> getNear(K key, int rel) {
// for (;;) {
// Node<K, V> n = findNear(key, rel);
// if (n == null)
// return null;
// AbstractMap.SimpleImmutableEntry<K, V> e = n.createSnapshot();
// if (e != null)
// return e;
// }
// }
//
// /* ---------------- Constructors -------------- */
//
// /**
// * Constructs a new, empty map, sorted according to the
// * {@linkplain Comparable natural ordering} of the keys.
// */
// public ConcurrentSkipListMap() {
// this.comparator = null;
// initialize();
// }
//
// /**
// * Constructs a new, empty map, sorted according to the specified
// * comparator.
// *
// * @param comparator the comparator that will be used to order this map.
// * If <tt>null</tt>, the {@linkplain Comparable natural
// * ordering} of the keys will be used.
// */
// public ConcurrentSkipListMap(Comparator<? super K> comparator) {
// this.comparator = comparator;
// initialize();
// }
//
// /**
// * Constructs a new map containing the same mappings as the given map,
// * sorted according to the {@linkplain Comparable natural ordering} of
// * the keys.
// *
// * @param m the map whose mappings are to be placed in this map
// * @throws ClassCastException if the keys in <tt>m</tt> are not
// * {@link Comparable}, or are not mutually comparable
// * @throws NullPointerException if the specified map or any of its keys
// * or values are null
// */
// public ConcurrentSkipListMap(Map<? extends K, ? extends V> m) {
// this.comparator = null;
// initialize();
// putAll(m);
// }
//
// /**
// * Constructs a new map containing the same mappings and using the
// * same ordering as the specified sorted map.
// *
// * @param m the sorted map whose mappings are to be placed in this
// * map, and whose comparator is to be used to sort this map
// * @throws NullPointerException if the specified sorted map or any of
// * its keys or values are null
// */
// public ConcurrentSkipListMap(SortedMap<K, ? extends V> m) {
// this.comparator = m.comparator();
// initialize();
// buildFromSorted(m);
// }
//
// /**
// * Returns a shallow copy of this <tt>ConcurrentSkipListMap</tt>
// * instance. (The keys and values themselves are not cloned.)
// *
// * @return a shallow copy of this map
// */
// @Override
// public ConcurrentSkipListMap<K, V> clone() {
// ConcurrentSkipListMap<K, V> clone = null;
// try {
// clone = (ConcurrentSkipListMap<K, V>) super.clone();
// } catch (CloneNotSupportedException e) {
// throw new InternalError();
// }
//
// clone.initialize();
// clone.buildFromSorted(this);
// return clone;
// }
//
// /**
// * Streamlined bulk insertion to initialize from elements of
// * given sorted map. Call only from constructor or clone
// * method.
// */
// private void buildFromSorted(SortedMap<K, ? extends V> map) {
// if (map == null)
// throw new NullPointerException();
//
// HeadIndex<K, V> h = head;
// Node<K, V> basepred = h.node;
//
// // Track the current rightmost node at each level. Uses an
// // ArrayList to avoid committing to initial or maximum level.
// ArrayList<Index<K, V>> preds = new ArrayList<Index<K, V>>();
//
// // initialize
// for (int i = 0; i <= h.level; ++i)
// preds.add(null);
// Index<K, V> q = h;
// for (int i = h.level; i > 0; --i) {
// preds.set(i, q);
// q = q.down;
// }
//
// Iterator<? extends Map.Entry<? extends K, ? extends V>> it = map.entrySet().iterator();
// while (it.hasNext()) {
// Map.Entry<? extends K, ? extends V> e = it.next();
// int j = randomLevel();
// if (j > h.level)
// j = h.level + 1;
// K k = e.getKey();
// V v = e.getValue();
// if (k == null || v == null)
// throw new NullPointerException();
// Node<K, V> z = new Node<K, V>(k, v, null);
// basepred.next = z;
// basepred = z;
// if (j > 0) {
// Index<K, V> idx = null;
// for (int i = 1; i <= j; ++i) {
// idx = new Index<K, V>(z, idx, null);
// if (i > h.level)
// h = new HeadIndex<K, V>(h.node, h, idx, i);
//
// if (i < preds.size()) {
// preds.get(i).right = idx;
// preds.set(i, idx);
// } else
// preds.add(idx);
// }
// }
// }
// head = h;
// }
//
// /* ---------------- Serialization -------------- */
//
// /**
// * Save the state of this map to a stream.
// *
// * @serialData The key (Object) and value (Object) for each
// * key-value mapping represented by the map, followed by
// * <tt>null</tt>. The key-value mappings are emitted in key-order
// * (as determined by the Comparator, or by the keys' natural
// * ordering if no Comparator).
// */
// private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
// // Write out the Comparator and any hidden stuff
// s.defaultWriteObject();
//
// // Write out keys and values (alternating)
// for (Node<K, V> n = findFirst(); n != null; n = n.next) {
// V v = n.getValidValue();
// if (v != null) {
// s.writeObject(n.key);
// s.writeObject(v);
// }
// }
// s.writeObject(null);
// }
//
// /**
// * Reconstitute the map from a stream.
// */
// private void readObject(final java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {
// // Read in the Comparator and any hidden stuff
// s.defaultReadObject();
// // Reset transients
// initialize();
//
// /*
// * This is nearly identical to buildFromSorted, but is
// * distinct because readObject calls can't be nicely adapted
// * as the kind of iterator needed by buildFromSorted. (They
// * can be, but doing so requires type cheats and/or creation
// * of adaptor classes.) It is simpler to just adapt the code.
// */
//
// HeadIndex<K, V> h = head;
// Node<K, V> basepred = h.node;
// ArrayList<Index<K, V>> preds = new ArrayList<Index<K, V>>();
// for (int i = 0; i <= h.level; ++i)
// preds.add(null);
// Index<K, V> q = h;
// for (int i = h.level; i > 0; --i) {
// preds.set(i, q);
// q = q.down;
// }
//
// for (;;) {
// Object k = s.readObject();
// if (k == null)
// break;
// Object v = s.readObject();
// if (v == null)
// throw new NullPointerException();
// K key = (K) k;
// V val = (V) v;
// int j = randomLevel();
// if (j > h.level)
// j = h.level + 1;
// Node<K, V> z = new Node<K, V>(key, val, null);
// basepred.next = z;
// basepred = z;
// if (j > 0) {
// Index<K, V> idx = null;
// for (int i = 1; i <= j; ++i) {
// idx = new Index<K, V>(z, idx, null);
// if (i > h.level)
// h = new HeadIndex<K, V>(h.node, h, idx, i);
//
// if (i < preds.size()) {
// preds.get(i).right = idx;
// preds.set(i, idx);
// } else
// preds.add(idx);
// }
// }
// }
// head = h;
// }
//
// /* ------ Map API methods ------ */
//
// /**
// * Returns <tt>true</tt> if this map contains a mapping for the specified
// * key.
// *
// * @param key key whose presence in this map is to be tested
// * @return <tt>true</tt> if this map contains a mapping for the specified key
// * @throws ClassCastException if the specified key cannot be compared
// * with the keys currently in the map
// * @throws NullPointerException if the specified key is null
// */
// @Override
// public boolean containsKey(Object key) {
// return doGet(key) != null;
// }
//
// /**
// * Returns the value to which the specified key is mapped,
// * or {@code null} if this map contains no mapping for the key.
// *
// * <p>More formally, if this map contains a mapping from a key
// * {@code k} to a value {@code v} such that {@code key} compares
// * equal to {@code k} according to the map's ordering, then this
// * method returns {@code v}; otherwise it returns {@code null}.
// * (There can be at most one such mapping.)
// *
// * @throws ClassCastException if the specified key cannot be compared
// * with the keys currently in the map
// * @throws NullPointerException if the specified key is null
// */
// @Override
// public V get(Object key) {
// return doGet(key);
// }
//
// /**
// * Associates the specified value with the specified key in this map.
// * If the map previously contained a mapping for the key, the old
// * value is replaced.
// *
// * @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 the specified key, or
// * <tt>null</tt> if there was no mapping for the key
// * @throws ClassCastException if the specified key cannot be compared
// * with the keys currently in the map
// * @throws NullPointerException if the specified key or value is null
// */
// @Override
// public V put(K key, V value) {
// if (value == null)
// throw new NullPointerException();
// return doPut(key, value, false);
// }
//
// /**
// * Removes the mapping for the specified key from this map if present.
// *
// * @param key key for which mapping should be removed
// * @return the previous value associated with the specified key, or
// * <tt>null</tt> if there was no mapping for the key
// * @throws ClassCastException if the specified key cannot be compared
// * with the keys currently in the map
// * @throws NullPointerException if the specified key is null
// */
// @Override
// public V remove(Object key) {
// return doRemove(key, null);
// }
//
// /**
// * Returns <tt>true</tt> if this map maps one or more keys to the
// * specified value. This operation requires time linear in the
// * map size. Additionally, it is possible for the map to change
// * during execution of this method, in which case the returned
// * result may be inaccurate.
// *
// * @param value value whose presence in this map is to be tested
// * @return <tt>true</tt> if a mapping to <tt>value</tt> exists;
// * <tt>false</tt> otherwise
// * @throws NullPointerException if the specified value is null
// */
// @Override
// public boolean containsValue(Object value) {
// if (value == null)
// throw new NullPointerException();
// for (Node<K, V> n = findFirst(); n != null; n = n.next) {
// V v = n.getValidValue();
// if (v != null && value.equals(v))
// return true;
// }
// return false;
// }
//
// /**
// * Returns the number of key-value mappings in this map. If this map
// * contains more than <tt>Integer.MAX_VALUE</tt> elements, it
// * returns <tt>Integer.MAX_VALUE</tt>.
// *
// * <p>Beware that, unlike in most collections, this method is
// * <em>NOT</em> a constant-time operation. Because of the
// * asynchronous nature of these maps, determining the current
// * number of elements requires traversing them all to count them.
// * Additionally, it is possible for the size to change during
// * execution of this method, in which case the returned result
// * will be inaccurate. Thus, this method is typically not very
// * useful in concurrent applications.
// *
// * @return the number of elements in this map
// */
// @Override
// public int size() {
// long count = 0;
// for (Node<K, V> n = findFirst(); n != null; n = n.next) {
// if (n.getValidValue() != null)
// ++count;
// }
// return (count >= Integer.MAX_VALUE) ? Integer.MAX_VALUE : (int) count;
// }
//
// /**
// * Returns <tt>true</tt> if this map contains no key-value mappings.
// * @return <tt>true</tt> if this map contains no key-value mappings
// */
// @Override
// public boolean isEmpty() {
// return findFirst() == null;
// }
//
// /**
// * Removes all of the mappings from this map.
// */
// @Override
// public void clear() {
// initialize();
// }
//
// /* ---------------- View methods -------------- */
//
// /*
// * Note: Lazy initialization works for views because view classes
// * are stateless/immutable so it doesn't matter wrt correctness if
// * more than one is created (which will only rarely happen). Even
// * so, the following idiom conservatively ensures that the method
// * returns the one it created if it does so, not one created by
// * another racing thread.
// */
//
// /**
// * Returns a {@link NavigableSet} view of the keys contained in this map.
// * The set's iterator returns the keys in ascending order.
// * 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.
// *
// * <p>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.
// *
// * <p>This method is equivalent to method {@code navigableKeySet}.
// *
// * @return a navigable set view of the keys in this map
// */
// @Override
// public NavigableSet<K> keySet() {
// KeySet ks = keySet;
// return (ks != null) ? ks : (keySet = new KeySet(this));
// }
//
// @Override
// public NavigableSet<K> navigableKeySet() {
// KeySet ks = keySet;
// return (ks != null) ? ks : (keySet = new KeySet(this));
// }
//
// /**
// * Returns a {@link Collection} view of the values contained in this map.
// * The collection's iterator returns the values in ascending order
// * of the corresponding keys.
// * The collection is backed by the map, so changes to the map are
// * reflected in the collection, and vice-versa. The collection
// * supports element removal, which removes the corresponding
// * mapping from the map, via the <tt>Iterator.remove</tt>,
// * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
// * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
// * support the <tt>add</tt> or <tt>addAll</tt> operations.
// *
// * <p>The view's <tt>iterator</tt> 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.
// */
// @Override
// public Collection<V> values() {
// Values vs = values;
// return (vs != null) ? vs : (values = new Values(this));
// }
//
// /**
// * Returns a {@link Set} view of the mappings contained in this map.
// * The set's iterator returns the entries in ascending key order.
// * 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 <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
// * <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt>
// * operations. It does not support the <tt>add</tt> or
// * <tt>addAll</tt> operations.
// *
// * <p>The view's <tt>iterator</tt> 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.
// *
// * <p>The <tt>Map.Entry</tt> elements returned by
// * <tt>iterator.next()</tt> do <em>not</em> support the
// * <tt>setValue</tt> operation.
// *
// * @return a set view of the mappings contained in this map,
// * sorted in ascending key order
// */
// @Override
// public Set<Map.Entry<K, V>> entrySet() {
// EntrySet es = entrySet;
// return (es != null) ? es : (entrySet = new EntrySet(this));
// }
//
// @Override
// public ConcurrentNavigableMap<K, V> descendingMap() {
// ConcurrentNavigableMap<K, V> dm = descendingMap;
// return (dm != null) ? dm : (descendingMap = new SubMap<K, V>(this, null, false, null, false, true));
// }
//
// @Override
// public NavigableSet<K> descendingKeySet() {
// return descendingMap().navigableKeySet();
// }
//
// /* ---------------- AbstractMap Overrides -------------- */
//
// /**
// * Compares the specified object with this map for equality.
// * Returns <tt>true</tt> if the given object is also a map and the
// * two maps represent the same mappings. More formally, two maps
// * <tt>m1</tt> and <tt>m2</tt> represent the same mappings if
// * <tt>m1.entrySet().equals(m2.entrySet())</tt>. 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 <tt>true</tt> if the specified object is equal to this map
// */
// @Override
// public boolean equals(Object o) {
// if (o == this)
// return true;
// if (!(o instanceof Map))
// return false;
// Map<?, ?> m = (Map<?, ?>) o;
// try {
// for (Map.Entry<K, V> e : this.entrySet())
// if (!e.getValue().equals(m.get(e.getKey())))
// return false;
// for (Map.Entry<?, ?> e : m.entrySet()) {
// Object k = e.getKey();
// Object v = e.getValue();
// if (k == null || v == null || !v.equals(get(k)))
// return false;
// }
// return true;
// } catch (ClassCastException unused) {
// return false;
// } catch (NullPointerException unused) {
// return false;
// }
// }
//
// /* ------ ConcurrentMap API methods ------ */
//
// /**
// * {@inheritDoc}
// *
// * @return the previous value associated with the specified key,
// * or <tt>null</tt> if there was no mapping for the key
// * @throws ClassCastException if the specified key cannot be compared
// * with the keys currently in the map
// * @throws NullPointerException if the specified key or value is null
// */
// @Override
// public V putIfAbsent(K key, V value) {
// if (value == null)
// throw new NullPointerException();
// return doPut(key, value, true);
// }
//
// /**
// * {@inheritDoc}
// *
// * @throws ClassCastException if the specified key cannot be compared
// * with the keys currently in the map
// * @throws NullPointerException if the specified key is null
// */
// @Override
// public boolean remove(Object key, Object value) {
// if (key == null)
// throw new NullPointerException();
// if (value == null)
// return false;
// return doRemove(key, value) != null;
// }
//
// /**
// * {@inheritDoc}
// *
// * @throws ClassCastException if the specified key cannot be compared
// * with the keys currently in the map
// * @throws NullPointerException if any of the arguments are null
// */
// @Override
// public boolean replace(K key, V oldValue, V newValue) {
// if (oldValue == null || newValue == null)
// throw new NullPointerException();
// Comparable<? super K> k = comparable(key);
// for (;;) {
// Node<K, V> n = findNode(k);
// if (n == null)
// return false;
// Object v = n.value;
// if (v != null) {
// if (!oldValue.equals(v))
// return false;
// if (n.casValue(v, newValue))
// return true;
// }
// }
// }
//
// /**
// * {@inheritDoc}
// *
// * @return the previous value associated with the specified key,
// * or <tt>null</tt> if there was no mapping for the key
// * @throws ClassCastException if the specified key cannot be compared
// * with the keys currently in the map
// * @throws NullPointerException if the specified key or value is null
// */
// @Override
// public V replace(K key, V value) {
// if (value == null)
// throw new NullPointerException();
// Comparable<? super K> k = comparable(key);
// for (;;) {
// Node<K, V> n = findNode(k);
// if (n == null)
// return null;
// Object v = n.value;
// if (v != null && n.casValue(v, value))
// return (V) v;
// }
// }
//
// /* ------ SortedMap API methods ------ */
//
// @Override
// public Comparator<? super K> comparator() {
// return comparator;
// }
//
// /**
// * @throws NoSuchElementException {@inheritDoc}
// */
// @Override
// public K firstKey() {
// Node<K, V> n = findFirst();
// if (n == null)
// throw new NoSuchElementException();
// return n.key;
// }
//
// /**
// * @throws NoSuchElementException {@inheritDoc}
// */
// @Override
// public K lastKey() {
// Node<K, V> n = findLast();
// if (n == null)
// throw new NoSuchElementException();
// return n.key;
// }
//
// /**
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if {@code fromKey} or {@code toKey} is null
// * @throws IllegalArgumentException {@inheritDoc}
// */
// @Override
// public ConcurrentNavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
// if (fromKey == null || toKey == null)
// throw new NullPointerException();
// return new SubMap<K, V>(this, fromKey, fromInclusive, toKey, toInclusive, false);
// }
//
// /**
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if {@code toKey} is null
// * @throws IllegalArgumentException {@inheritDoc}
// */
// @Override
// public ConcurrentNavigableMap<K, V> headMap(K toKey, boolean inclusive) {
// if (toKey == null)
// throw new NullPointerException();
// return new SubMap<K, V>(this, null, false, toKey, inclusive, false);
// }
//
// /**
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if {@code fromKey} is null
// * @throws IllegalArgumentException {@inheritDoc}
// */
// @Override
// public ConcurrentNavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
// if (fromKey == null)
// throw new NullPointerException();
// return new SubMap<K, V>(this, fromKey, inclusive, null, false, false);
// }
//
// /**
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if {@code fromKey} or {@code toKey} is null
// * @throws IllegalArgumentException {@inheritDoc}
// */
// @Override
// public ConcurrentNavigableMap<K, V> subMap(K fromKey, K toKey) {
// return subMap(fromKey, true, toKey, false);
// }
//
// /**
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if {@code toKey} is null
// * @throws IllegalArgumentException {@inheritDoc}
// */
// @Override
// public ConcurrentNavigableMap<K, V> headMap(K toKey) {
// return headMap(toKey, false);
// }
//
// /**
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if {@code fromKey} is null
// * @throws IllegalArgumentException {@inheritDoc}
// */
// @Override
// public ConcurrentNavigableMap<K, V> tailMap(K fromKey) {
// return tailMap(fromKey, true);
// }
//
// /* ---------------- Relational operations -------------- */
//
// /**
// * Returns a key-value mapping associated with the greatest key
// * strictly less than the given key, or <tt>null</tt> if there is
// * no such key. The returned entry does <em>not</em> support the
// * <tt>Entry.setValue</tt> method.
// *
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if the specified key is null
// */
// @Override
// public Map.Entry<K, V> lowerEntry(K key) {
// return getNear(key, LT);
// }
//
// /**
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if the specified key is null
// */
// @Override
// public K lowerKey(K key) {
// Node<K, V> n = findNear(key, LT);
// return (n == null) ? null : n.key;
// }
//
// /**
// * Returns a key-value mapping associated with the greatest key
// * less than or equal to the given key, or <tt>null</tt> if there
// * is no such key. The returned entry does <em>not</em> support
// * the <tt>Entry.setValue</tt> method.
// *
// * @param key the key
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if the specified key is null
// */
// @Override
// public Map.Entry<K, V> floorEntry(K key) {
// return getNear(key, LT | EQ);
// }
//
// /**
// * @param key the key
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if the specified key is null
// */
// @Override
// public K floorKey(K key) {
// Node<K, V> n = findNear(key, LT | EQ);
// return (n == null) ? null : n.key;
// }
//
// /**
// * Returns a key-value mapping associated with the least key
// * greater than or equal to the given key, or <tt>null</tt> if
// * there is no such entry. The returned entry does <em>not</em>
// * support the <tt>Entry.setValue</tt> method.
// *
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if the specified key is null
// */
// @Override
// public Map.Entry<K, V> ceilingEntry(K key) {
// return getNear(key, GT | EQ);
// }
//
// /**
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if the specified key is null
// */
// @Override
// public K ceilingKey(K key) {
// Node<K, V> n = findNear(key, GT | EQ);
// return (n == null) ? null : n.key;
// }
//
// /**
// * Returns a key-value mapping associated with the least key
// * strictly greater than the given key, or <tt>null</tt> if there
// * is no such key. The returned entry does <em>not</em> support
// * the <tt>Entry.setValue</tt> method.
// *
// * @param key the key
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if the specified key is null
// */
// @Override
// public Map.Entry<K, V> higherEntry(K key) {
// return getNear(key, GT);
// }
//
// /**
// * @param key the key
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException if the specified key is null
// */
// @Override
// public K higherKey(K key) {
// Node<K, V> n = findNear(key, GT);
// return (n == null) ? null : n.key;
// }
//
// /**
// * Returns a key-value mapping associated with the least
// * key in this map, or <tt>null</tt> if the map is empty.
// * The returned entry does <em>not</em> support
// * the <tt>Entry.setValue</tt> method.
// */
// @Override
// public Map.Entry<K, V> firstEntry() {
// for (;;) {
// Node<K, V> n = findFirst();
// if (n == null)
// return null;
// AbstractMap.SimpleImmutableEntry<K, V> e = n.createSnapshot();
// if (e != null)
// return e;
// }
// }
//
// /**
// * Returns a key-value mapping associated with the greatest
// * key in this map, or <tt>null</tt> if the map is empty.
// * The returned entry does <em>not</em> support
// * the <tt>Entry.setValue</tt> method.
// */
// @Override
// public Map.Entry<K, V> lastEntry() {
// for (;;) {
// Node<K, V> n = findLast();
// if (n == null)
// return null;
// AbstractMap.SimpleImmutableEntry<K, V> e = n.createSnapshot();
// if (e != null)
// return e;
// }
// }
//
// /**
// * Removes and returns a key-value mapping associated with
// * the least key in this map, or <tt>null</tt> if the map is empty.
// * The returned entry does <em>not</em> support
// * the <tt>Entry.setValue</tt> method.
// */
// @Override
// public Map.Entry<K, V> pollFirstEntry() {
// return doRemoveFirstEntry();
// }
//
// /**
// * Removes and returns a key-value mapping associated with
// * the greatest key in this map, or <tt>null</tt> if the map is empty.
// * The returned entry does <em>not</em> support
// * the <tt>Entry.setValue</tt> method.
// */
// @Override
// public Map.Entry<K, V> pollLastEntry() {
// return doRemoveLastEntry();
// }
//
// /* ---------------- Iterators -------------- */
//
// /**
// * Base of iterator classes:
// */
// abstract class Iter<T> implements Iterator<T> {
// /** the last node returned by next() */
// Node<K, V> lastReturned;
// /** the next node to return from next(); */
// Node<K, V> next;
// /** Cache of next value field to maintain weak consistency */
// V nextValue;
//
// /** Initializes ascending iterator for entire range. */
// Iter() {
// for (;;) {
// next = findFirst();
// if (next == null)
// break;
// Object x = next.value;
// if (x != null && x != next) {
// nextValue = (V) x;
// break;
// }
// }
// }
//
// @Override
// public final boolean hasNext() {
// return next != null;
// }
//
// /** Advances next to higher entry. */
// final void advance() {
// if (next == null)
// throw new NoSuchElementException();
// lastReturned = next;
// for (;;) {
// next = next.next;
// if (next == null)
// break;
// Object x = next.value;
// if (x != null && x != next) {
// nextValue = (V) x;
// break;
// }
// }
// }
//
// @Override
// public void remove() {
// Node<K, V> l = lastReturned;
// if (l == null)
// throw new IllegalStateException();
// // It would not be worth all of the overhead to directly
// // unlink from here. Using remove is fast enough.
// ConcurrentSkipListMap.this.remove(l.key);
// lastReturned = null;
// }
//
// }
//
// final class ValueIterator extends Iter<V> {
// @Override
// public V next() {
// V v = nextValue;
// advance();
// return v;
// }
// }
//
// final class KeyIterator extends Iter<K> {
// @Override
// public K next() {
// Node<K, V> n = next;
// advance();
// return n.key;
// }
// }
//
// final class EntryIterator extends Iter<Map.Entry<K, V>> {
// @Override
// public Map.Entry<K, V> next() {
// Node<K, V> n = next;
// V v = nextValue;
// advance();
// return new AbstractMap.SimpleImmutableEntry<K, V>(n.key, v);
// }
// }
//
// // Factory methods for iterators needed by ConcurrentSkipListSet etc
//
// Iterator<K> keyIterator() {
// return new KeyIterator();
// }
//
// Iterator<V> valueIterator() {
// return new ValueIterator();
// }
//
// Iterator<Map.Entry<K, V>> entryIterator() {
// return new EntryIterator();
// }
//
// /* ---------------- View Classes -------------- */
//
// /*
// * View classes are static, delegating to a ConcurrentNavigableMap
// * to allow use by SubMaps, which outweighs the ugliness of
// * needing type-tests for Iterator methods.
// */
//
// static final <E> List<E> toList(Collection<E> c) {
// // Using size() here would be a pessimization.
// List<E> list = new ArrayList<E>();
// for (E e : c)
// list.add(e);
// return list;
// }
//
// static final class KeySet<E> extends AbstractSet<E> implements NavigableSet<E> {
// private final ConcurrentNavigableMap<E, Object> m;
//
// KeySet(ConcurrentNavigableMap<E, Object> map) {
// m = map;
// }
//
// @Override
// public int size() {
// return m.size();
// }
//
// @Override
// public boolean isEmpty() {
// return m.isEmpty();
// }
//
// @Override
// public boolean contains(Object o) {
// return m.containsKey(o);
// }
//
// @Override
// public boolean remove(Object o) {
// return m.remove(o) != null;
// }
//
// @Override
// public void clear() {
// m.clear();
// }
//
// @Override
// public E lower(E e) {
// return m.lowerKey(e);
// }
//
// @Override
// public E floor(E e) {
// return m.floorKey(e);
// }
//
// @Override
// public E ceiling(E e) {
// return m.ceilingKey(e);
// }
//
// @Override
// public E higher(E e) {
// return m.higherKey(e);
// }
//
// @Override
// public Comparator<? super E> comparator() {
// return m.comparator();
// }
//
// @Override
// public E first() {
// return m.firstKey();
// }
//
// @Override
// public E last() {
// return m.lastKey();
// }
//
// @Override
// public E pollFirst() {
// Map.Entry<E, Object> e = m.pollFirstEntry();
// return (e == null) ? null : e.getKey();
// }
//
// @Override
// public E pollLast() {
// Map.Entry<E, Object> e = m.pollLastEntry();
// return (e == null) ? null : e.getKey();
// }
//
// @Override
// public Iterator<E> iterator() {
// if (m instanceof ConcurrentSkipListMap)
// return ((ConcurrentSkipListMap<E, Object>) m).keyIterator();
// else
// return ((ConcurrentSkipListMap.SubMap<E, Object>) m).keyIterator();
// }
//
// @Override
// public boolean equals(Object o) {
// if (o == this)
// return true;
// if (!(o instanceof Set))
// return false;
// Collection<?> c = (Collection<?>) o;
// try {
// return containsAll(c) && c.containsAll(this);
// } catch (ClassCastException unused) {
// return false;
// } catch (NullPointerException unused) {
// return false;
// }
// }
//
// @Override
// public Object[] toArray() {
// return toList(this).toArray();
// }
//
// @Override
// public <T> T[] toArray(T[] a) {
// return toList(this).toArray(a);
// }
//
// @Override
// public Iterator<E> descendingIterator() {
// return descendingSet().iterator();
// }
//
// @Override
// public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
// return new KeySet<E>(m.subMap(fromElement, fromInclusive, toElement, toInclusive));
// }
//
// @Override
// public NavigableSet<E> headSet(E toElement, boolean inclusive) {
// return new KeySet<E>(m.headMap(toElement, inclusive));
// }
//
// @Override
// public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
// return new KeySet<E>(m.tailMap(fromElement, inclusive));
// }
//
// @Override
// public NavigableSet<E> subSet(E fromElement, E toElement) {
// return subSet(fromElement, true, toElement, false);
// }
//
// @Override
// public NavigableSet<E> headSet(E toElement) {
// return headSet(toElement, false);
// }
//
// @Override
// public NavigableSet<E> tailSet(E fromElement) {
// return tailSet(fromElement, true);
// }
//
// @Override
// public NavigableSet<E> descendingSet() {
// return new KeySet(m.descendingMap());
// }
// }
//
// static final class Values<E> extends AbstractCollection<E> {
// private final ConcurrentNavigableMap<Object, E> m;
//
// Values(ConcurrentNavigableMap<Object, E> map) {
// m = map;
// }
//
// @Override
// public Iterator<E> iterator() {
// if (m instanceof ConcurrentSkipListMap)
// return ((ConcurrentSkipListMap<Object, E>) m).valueIterator();
// else
// return ((SubMap<Object, E>) m).valueIterator();
// }
//
// @Override
// public boolean isEmpty() {
// return m.isEmpty();
// }
//
// @Override
// public int size() {
// return m.size();
// }
//
// @Override
// public boolean contains(Object o) {
// return m.containsValue(o);
// }
//
// @Override
// public void clear() {
// m.clear();
// }
//
// @Override
// public Object[] toArray() {
// return toList(this).toArray();
// }
//
// @Override
// public <T> T[] toArray(T[] a) {
// return toList(this).toArray(a);
// }
// }
//
// static final class EntrySet<K1, V1> extends AbstractSet<Map.Entry<K1, V1>> {
// private final ConcurrentNavigableMap<K1, V1> m;
//
// EntrySet(ConcurrentNavigableMap<K1, V1> map) {
// m = map;
// }
//
// @Override
// public Iterator<Map.Entry<K1, V1>> iterator() {
// if (m instanceof ConcurrentSkipListMap)
// return ((ConcurrentSkipListMap<K1, V1>) m).entryIterator();
// else
// return ((SubMap<K1, V1>) m).entryIterator();
// }
//
// @Override
// public boolean contains(Object o) {
// if (!(o instanceof Map.Entry))
// return false;
// Map.Entry<K1, V1> e = (Map.Entry<K1, V1>) o;
// V1 v = m.get(e.getKey());
// return v != null && v.equals(e.getValue());
// }
//
// @Override
// public boolean remove(Object o) {
// if (!(o instanceof Map.Entry))
// return false;
// Map.Entry<K1, V1> e = (Map.Entry<K1, V1>) o;
// return m.remove(e.getKey(), e.getValue());
// }
//
// @Override
// public boolean isEmpty() {
// return m.isEmpty();
// }
//
// @Override
// public int size() {
// return m.size();
// }
//
// @Override
// public void clear() {
// m.clear();
// }
//
// @Override
// public boolean equals(Object o) {
// if (o == this)
// return true;
// if (!(o instanceof Set))
// return false;
// Collection<?> c = (Collection<?>) o;
// try {
// return containsAll(c) && c.containsAll(this);
// } catch (ClassCastException unused) {
// return false;
// } catch (NullPointerException unused) {
// return false;
// }
// }
//
// @Override
// public Object[] toArray() {
// return toList(this).toArray();
// }
//
// @Override
// public <T> T[] toArray(T[] a) {
// return toList(this).toArray(a);
// }
// }
//
// /**
// * Submaps returned by {@link ConcurrentSkipListMap} submap operations
// * represent a subrange of mappings of their underlying
// * maps. Instances of this class support all methods of their
// * underlying maps, differing in that mappings outside their range are
// * ignored, and attempts to add mappings outside their ranges result
// * in {@link IllegalArgumentException}. Instances of this class are
// * constructed only using the <tt>subMap</tt>, <tt>headMap</tt>, and
// * <tt>tailMap</tt> methods of their underlying maps.
// *
// * @serial include
// */
// static final class SubMap<K, V> extends AbstractMap<K, V> implements ConcurrentNavigableMap<K, V>, Cloneable,
// java.io.Serializable {
// private static final long serialVersionUID = -7647078645895051609L;
//
// /** Underlying map */
// private final ConcurrentSkipListMap<K, V> m;
// /** lower bound key, or null if from start */
// private final K lo;
// /** upper bound key, or null if to end */
// private final K hi;
// /** inclusion flag for lo */
// private final boolean loInclusive;
// /** inclusion flag for hi */
// private final boolean hiInclusive;
// /** direction */
// private final boolean isDescending;
//
// // Lazily initialized view holders
// private transient KeySet<K> keySetView;
// private transient Set<Map.Entry<K, V>> entrySetView;
// private transient Collection<V> valuesView;
//
// /**
// * Creates a new submap, initializing all fields
// */
// SubMap(ConcurrentSkipListMap<K, V> map, K fromKey, boolean fromInclusive, K toKey, boolean toInclusive,
// boolean isDescending) {
// if (fromKey != null && toKey != null && map.compare(fromKey, toKey) > 0)
// throw new IllegalArgumentException("inconsistent range");
// this.m = map;
// this.lo = fromKey;
// this.hi = toKey;
// this.loInclusive = fromInclusive;
// this.hiInclusive = toInclusive;
// this.isDescending = isDescending;
// }
//
// /* ---------------- Utilities -------------- */
//
// private boolean tooLow(K key) {
// if (lo != null) {
// int c = m.compare(key, lo);
// if (c < 0 || (c == 0 && !loInclusive))
// return true;
// }
// return false;
// }
//
// private boolean tooHigh(K key) {
// if (hi != null) {
// int c = m.compare(key, hi);
// if (c > 0 || (c == 0 && !hiInclusive))
// return true;
// }
// return false;
// }
//
// private boolean inBounds(K key) {
// return !tooLow(key) && !tooHigh(key);
// }
//
// private void checkKeyBounds(K key) throws IllegalArgumentException {
// if (key == null)
// throw new NullPointerException();
// if (!inBounds(key))
// throw new IllegalArgumentException("key out of range");
// }
//
// /**
// * Returns true if node key is less than upper bound of range
// */
// private boolean isBeforeEnd(ConcurrentSkipListMap.Node<K, V> n) {
// if (n == null)
// return false;
// if (hi == null)
// return true;
// K k = n.key;
// if (k == null) // pass by markers and headers
// return true;
// int c = m.compare(k, hi);
// if (c > 0 || (c == 0 && !hiInclusive))
// return false;
// return true;
// }
//
// /**
// * Returns lowest node. This node might not be in range, so
// * most usages need to check bounds
// */
// private ConcurrentSkipListMap.Node<K, V> loNode() {
// if (lo == null)
// return m.findFirst();
// else if (loInclusive)
// return m.findNear(lo, m.GT | m.EQ);
// else
// return m.findNear(lo, m.GT);
// }
//
// /**
// * Returns highest node. This node might not be in range, so
// * most usages need to check bounds
// */
// private ConcurrentSkipListMap.Node<K, V> hiNode() {
// if (hi == null)
// return m.findLast();
// else if (hiInclusive)
// return m.findNear(hi, m.LT | m.EQ);
// else
// return m.findNear(hi, m.LT);
// }
//
// /**
// * Returns lowest absolute key (ignoring directonality)
// */
// private K lowestKey() {
// ConcurrentSkipListMap.Node<K, V> n = loNode();
// if (isBeforeEnd(n))
// return n.key;
// else
// throw new NoSuchElementException();
// }
//
// /**
// * Returns highest absolute key (ignoring directonality)
// */
// private K highestKey() {
// ConcurrentSkipListMap.Node<K, V> n = hiNode();
// if (n != null) {
// K last = n.key;
// if (inBounds(last))
// return last;
// }
// throw new NoSuchElementException();
// }
//
// private Map.Entry<K, V> lowestEntry() {
// for (;;) {
// ConcurrentSkipListMap.Node<K, V> n = loNode();
// if (!isBeforeEnd(n))
// return null;
// Map.Entry<K, V> e = n.createSnapshot();
// if (e != null)
// return e;
// }
// }
//
// private Map.Entry<K, V> highestEntry() {
// for (;;) {
// ConcurrentSkipListMap.Node<K, V> n = hiNode();
// if (n == null || !inBounds(n.key))
// return null;
// Map.Entry<K, V> e = n.createSnapshot();
// if (e != null)
// return e;
// }
// }
//
// private Map.Entry<K, V> removeLowest() {
// for (;;) {
// Node<K, V> n = loNode();
// if (n == null)
// return null;
// K k = n.key;
// if (!inBounds(k))
// return null;
// V v = m.doRemove(k, null);
// if (v != null)
// return new AbstractMap.SimpleImmutableEntry<K, V>(k, v);
// }
// }
//
// private Map.Entry<K, V> removeHighest() {
// for (;;) {
// Node<K, V> n = hiNode();
// if (n == null)
// return null;
// K k = n.key;
// if (!inBounds(k))
// return null;
// V v = m.doRemove(k, null);
// if (v != null)
// return new AbstractMap.SimpleImmutableEntry<K, V>(k, v);
// }
// }
//
// /**
// * Submap version of ConcurrentSkipListMap.getNearEntry
// */
// private Map.Entry<K, V> getNearEntry(K key, int rel) {
// if (isDescending) { // adjust relation for direction
// if ((rel & m.LT) == 0)
// rel |= m.LT;
// else
// rel &= ~m.LT;
// }
// if (tooLow(key))
// return ((rel & m.LT) != 0) ? null : lowestEntry();
// if (tooHigh(key))
// return ((rel & m.LT) != 0) ? highestEntry() : null;
// for (;;) {
// Node<K, V> n = m.findNear(key, rel);
// if (n == null || !inBounds(n.key))
// return null;
// K k = n.key;
// V v = n.getValidValue();
// if (v != null)
// return new AbstractMap.SimpleImmutableEntry<K, V>(k, v);
// }
// }
//
// // Almost the same as getNearEntry, except for keys
// private K getNearKey(K key, int rel) {
// if (isDescending) { // adjust relation for direction
// if ((rel & m.LT) == 0)
// rel |= m.LT;
// else
// rel &= ~m.LT;
// }
// if (tooLow(key)) {
// if ((rel & m.LT) == 0) {
// ConcurrentSkipListMap.Node<K, V> n = loNode();
// if (isBeforeEnd(n))
// return n.key;
// }
// return null;
// }
// if (tooHigh(key)) {
// if ((rel & m.LT) != 0) {
// ConcurrentSkipListMap.Node<K, V> n = hiNode();
// if (n != null) {
// K last = n.key;
// if (inBounds(last))
// return last;
// }
// }
// return null;
// }
// for (;;) {
// Node<K, V> n = m.findNear(key, rel);
// if (n == null || !inBounds(n.key))
// return null;
// K k = n.key;
// V v = n.getValidValue();
// if (v != null)
// return k;
// }
// }
//
// /* ---------------- Map API methods -------------- */
//
// @Override
// public boolean containsKey(Object key) {
// if (key == null)
// throw new NullPointerException();
// K k = (K) key;
// return inBounds(k) && m.containsKey(k);
// }
//
// @Override
// public V get(Object key) {
// if (key == null)
// throw new NullPointerException();
// K k = (K) key;
// return ((!inBounds(k)) ? null : m.get(k));
// }
//
// @Override
// public V put(K key, V value) {
// checkKeyBounds(key);
// return m.put(key, value);
// }
//
// @Override
// public V remove(Object key) {
// K k = (K) key;
// return (!inBounds(k)) ? null : m.remove(k);
// }
//
// @Override
// public int size() {
// long count = 0;
// for (ConcurrentSkipListMap.Node<K, V> n = loNode(); isBeforeEnd(n); n = n.next) {
// if (n.getValidValue() != null)
// ++count;
// }
// return count >= Integer.MAX_VALUE ? Integer.MAX_VALUE : (int) count;
// }
//
// @Override
// public boolean isEmpty() {
// return !isBeforeEnd(loNode());
// }
//
// @Override
// public boolean containsValue(Object value) {
// if (value == null)
// throw new NullPointerException();
// for (ConcurrentSkipListMap.Node<K, V> n = loNode(); isBeforeEnd(n); n = n.next) {
// V v = n.getValidValue();
// if (v != null && value.equals(v))
// return true;
// }
// return false;
// }
//
// @Override
// public void clear() {
// for (ConcurrentSkipListMap.Node<K, V> n = loNode(); isBeforeEnd(n); n = n.next) {
// if (n.getValidValue() != null)
// m.remove(n.key);
// }
// }
//
// /* ---------------- ConcurrentMap API methods -------------- */
//
// @Override
// public V putIfAbsent(K key, V value) {
// checkKeyBounds(key);
// return m.putIfAbsent(key, value);
// }
//
// @Override
// public boolean remove(Object key, Object value) {
// K k = (K) key;
// return inBounds(k) && m.remove(k, value);
// }
//
// @Override
// public boolean replace(K key, V oldValue, V newValue) {
// checkKeyBounds(key);
// return m.replace(key, oldValue, newValue);
// }
//
// @Override
// public V replace(K key, V value) {
// checkKeyBounds(key);
// return m.replace(key, value);
// }
//
// /* ---------------- SortedMap API methods -------------- */
//
// @Override
// public Comparator<? super K> comparator() {
// Comparator<? super K> cmp = m.comparator();
// if (isDescending)
// return Collections.reverseOrder(cmp);
// else
// return cmp;
// }
//
// /**
// * Utility to create submaps, where given bounds override
// * unbounded(null) ones and/or are checked against bounded ones.
// */
// private SubMap<K, V> newSubMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
// if (isDescending) { // flip senses
// K tk = fromKey;
// fromKey = toKey;
// toKey = tk;
// boolean ti = fromInclusive;
// fromInclusive = toInclusive;
// toInclusive = ti;
// }
// if (lo != null) {
// if (fromKey == null) {
// fromKey = lo;
// fromInclusive = loInclusive;
// } else {
// int c = m.compare(fromKey, lo);
// if (c < 0 || (c == 0 && !loInclusive && fromInclusive))
// throw new IllegalArgumentException("key out of range");
// }
// }
// if (hi != null) {
// if (toKey == null) {
// toKey = hi;
// toInclusive = hiInclusive;
// } else {
// int c = m.compare(toKey, hi);
// if (c > 0 || (c == 0 && !hiInclusive && toInclusive))
// throw new IllegalArgumentException("key out of range");
// }
// }
// return new SubMap<K, V>(m, fromKey, fromInclusive, toKey, toInclusive, isDescending);
// }
//
// @Override
// public SubMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
// if (fromKey == null || toKey == null)
// throw new NullPointerException();
// return newSubMap(fromKey, fromInclusive, toKey, toInclusive);
// }
//
// @Override
// public SubMap<K, V> headMap(K toKey, boolean inclusive) {
// if (toKey == null)
// throw new NullPointerException();
// return newSubMap(null, false, toKey, inclusive);
// }
//
// @Override
// public SubMap<K, V> tailMap(K fromKey, boolean inclusive) {
// if (fromKey == null)
// throw new NullPointerException();
// return newSubMap(fromKey, inclusive, null, false);
// }
//
// @Override
// public SubMap<K, V> subMap(K fromKey, K toKey) {
// return subMap(fromKey, true, toKey, false);
// }
//
// @Override
// public SubMap<K, V> headMap(K toKey) {
// return headMap(toKey, false);
// }
//
// @Override
// public SubMap<K, V> tailMap(K fromKey) {
// return tailMap(fromKey, true);
// }
//
// @Override
// public SubMap<K, V> descendingMap() {
// return new SubMap<K, V>(m, lo, loInclusive, hi, hiInclusive, !isDescending);
// }
//
// /* ---------------- Relational methods -------------- */
//
// @Override
// public Map.Entry<K, V> ceilingEntry(K key) {
// return getNearEntry(key, (m.GT | m.EQ));
// }
//
// @Override
// public K ceilingKey(K key) {
// return getNearKey(key, (m.GT | m.EQ));
// }
//
// @Override
// public Map.Entry<K, V> lowerEntry(K key) {
// return getNearEntry(key, (m.LT));
// }
//
// @Override
// public K lowerKey(K key) {
// return getNearKey(key, (m.LT));
// }
//
// @Override
// public Map.Entry<K, V> floorEntry(K key) {
// return getNearEntry(key, (m.LT | m.EQ));
// }
//
// @Override
// public K floorKey(K key) {
// return getNearKey(key, (m.LT | m.EQ));
// }
//
// @Override
// public Map.Entry<K, V> higherEntry(K key) {
// return getNearEntry(key, (m.GT));
// }
//
// @Override
// public K higherKey(K key) {
// return getNearKey(key, (m.GT));
// }
//
// @Override
// public K firstKey() {
// return isDescending ? highestKey() : lowestKey();
// }
//
// @Override
// public K lastKey() {
// return isDescending ? lowestKey() : highestKey();
// }
//
// @Override
// public Map.Entry<K, V> firstEntry() {
// return isDescending ? highestEntry() : lowestEntry();
// }
//
// @Override
// public Map.Entry<K, V> lastEntry() {
// return isDescending ? lowestEntry() : highestEntry();
// }
//
// @Override
// public Map.Entry<K, V> pollFirstEntry() {
// return isDescending ? removeHighest() : removeLowest();
// }
//
// @Override
// public Map.Entry<K, V> pollLastEntry() {
// return isDescending ? removeLowest() : removeHighest();
// }
//
// /* ---------------- Submap Views -------------- */
//
// @Override
// public NavigableSet<K> keySet() {
// KeySet<K> ks = keySetView;
// return (ks != null) ? ks : (keySetView = new KeySet(this));
// }
//
// @Override
// public NavigableSet<K> navigableKeySet() {
// KeySet<K> ks = keySetView;
// return (ks != null) ? ks : (keySetView = new KeySet(this));
// }
//
// @Override
// public Collection<V> values() {
// Collection<V> vs = valuesView;
// return (vs != null) ? vs : (valuesView = new Values(this));
// }
//
// @Override
// public Set<Map.Entry<K, V>> entrySet() {
// Set<Map.Entry<K, V>> es = entrySetView;
// return (es != null) ? es : (entrySetView = new EntrySet(this));
// }
//
// @Override
// public NavigableSet<K> descendingKeySet() {
// return descendingMap().navigableKeySet();
// }
//
// Iterator<K> keyIterator() {
// return new SubMapKeyIterator();
// }
//
// Iterator<V> valueIterator() {
// return new SubMapValueIterator();
// }
//
// Iterator<Map.Entry<K, V>> entryIterator() {
// return new SubMapEntryIterator();
// }
//
// /**
// * Variant of main Iter class to traverse through submaps.
// */
// abstract class SubMapIter<T> implements Iterator<T> {
// /** the last node returned by next() */
// Node<K, V> lastReturned;
// /** the next node to return from next(); */
// Node<K, V> next;
// /** Cache of next value field to maintain weak consistency */
// V nextValue;
//
// SubMapIter() {
// for (;;) {
// next = isDescending ? hiNode() : loNode();
// if (next == null)
// break;
// Object x = next.value;
// if (x != null && x != next) {
// if (!inBounds(next.key))
// next = null;
// else
// nextValue = (V) x;
// break;
// }
// }
// }
//
// @Override
// public final boolean hasNext() {
// return next != null;
// }
//
// final void advance() {
// if (next == null)
// throw new NoSuchElementException();
// lastReturned = next;
// if (isDescending)
// descend();
// else
// ascend();
// }
//
// private void ascend() {
// for (;;) {
// next = next.next;
// if (next == null)
// break;
// Object x = next.value;
// if (x != null && x != next) {
// if (tooHigh(next.key))
// next = null;
// else
// nextValue = (V) x;
// break;
// }
// }
// }
//
// private void descend() {
// for (;;) {
// next = m.findNear(lastReturned.key, LT);
// if (next == null)
// break;
// Object x = next.value;
// if (x != null && x != next) {
// if (tooLow(next.key))
// next = null;
// else
// nextValue = (V) x;
// break;
// }
// }
// }
//
// @Override
// public void remove() {
// Node<K, V> l = lastReturned;
// if (l == null)
// throw new IllegalStateException();
// m.remove(l.key);
// lastReturned = null;
// }
//
// }
//
// final class SubMapValueIterator extends SubMapIter<V> {
// @Override
// public V next() {
// V v = nextValue;
// advance();
// return v;
// }
// }
//
// final class SubMapKeyIterator extends SubMapIter<K> {
// @Override
// public K next() {
// Node<K, V> n = next;
// advance();
// return n.key;
// }
// }
//
// final class SubMapEntryIterator extends SubMapIter<Map.Entry<K, V>> {
// @Override
// public Map.Entry<K, V> next() {
// Node<K, V> n = next;
// V v = nextValue;
// advance();
// return new AbstractMap.SimpleImmutableEntry<K, V>(n.key, v);
// }
// }
// }
//
// // Unsafe mechanics
// private static final sun.misc.Unsafe UNSAFE;
// private static final long headOffset;
// // static {
// // try {
// // UNSAFE = sun.misc.Unsafe.getUnsafe();
// // Class k = ConcurrentSkipListMap.class;
// // headOffset = UNSAFE.objectFieldOffset(k.getDeclaredField("head"));
// // } catch (Exception e) {
// // throw new Error(e);
// // }
// // }
// static {
// try {
// Field field = sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
// field.setAccessible(true);
// UNSAFE = (sun.misc.Unsafe) field.get(null);
// Class k = ConcurrentSkipListMap.class;
// headOffset = UNSAFE.objectFieldOffset(k.getDeclaredField("head"));
// } catch (Exception e) {
// throw new Error(e);
// }
// }
//
// public String toString() {
// StringBuilder s = new StringBuilder();
// s.append(head.level).append("\r\n");
//
// Index<K, V> q = head;
// s.append(q.node.key).append(" -> "); //总是HeadIndex，key是null
// Index<K, V> r = q.right;
// for (;;) {
// if (r != null) {
// Node<K, V> n = r.node;
// K k = n.key;
// s.append(k).append(" -> ");
// r = r.right;
// continue;
// }
// Index<K, V> d = q.down;
// if (d != null) {
// s.append("\r\n");
// s.append(d.node.key).append(" -> "); //总是HeadIndex，key是null
// q = d;
// r = d.right;
// } else
// break;
// }
// return s.toString();
// }
// }