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From sboi...@apache.org
Subject [2/7] incubator-ignite git commit: ignite-sprint-6: merge from ignite-545
Date Wed, 10 Jun 2015 15:04:27 GMT
http://git-wip-us.apache.org/repos/asf/incubator-ignite/blob/455b96fc/modules/core/src/main/java/org/jsr166/ConcurrentHashMap8.java
----------------------------------------------------------------------
diff --git a/modules/core/src/main/java/org/jsr166/ConcurrentHashMap8.java b/modules/core/src/main/java/org/jsr166/ConcurrentHashMap8.java
index 79b42b2..727db4c 100644
--- a/modules/core/src/main/java/org/jsr166/ConcurrentHashMap8.java
+++ b/modules/core/src/main/java/org/jsr166/ConcurrentHashMap8.java
@@ -5,16 +5,22 @@
  */
 
 /*
- * The initial version of this file was copied from JSR-166:
- * http://gee.cs.oswego.edu/dl/concurrency-interest/
+ * The latest version of the file corresponds to the following CVS commit:
+ * http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jdk7/java/util/concurrent/ConcurrentHashMap.java?pathrev=1.43
+ *
+ * Note, that the repository above is JDK 7 based that is kept up-to-date too.
+ * The main repository (JDK 8 based) uses JDK 8 features significantly that unavailable in JDK 7.
  */
 
+
 package org.jsr166;
 
 import java.io.*;
 import java.util.*;
 import java.util.concurrent.*;
+import java.util.concurrent.atomic.*;
 import java.util.concurrent.locks.*;
+import java.lang.reflect.*;
 
 /**
  * A hash table supporting full concurrency of retrievals and
@@ -68,21 +74,15 @@ import java.util.concurrent.locks.*;
  * expected {@code concurrencyLevel} as an additional hint for
  * internal sizing.  Note that using many keys with exactly the same
  * {@code hashCode()} is a sure way to slow down performance of any
- * hash table.
+ * hash table. To ameliorate impact, when keys are {@link Comparable},
+ * this class may use comparison order among keys to help break ties.
  *
- * <p>A {@link Set} projection of a ConcurrentHashMapV8 may be created
+ * <p>A {@link Set} projection of a ConcurrentHashMap may be created
  * (using {@link #newKeySet()} or {@link #newKeySet(int)}), or viewed
  * (using {@link #keySet(Object)} when only keys are of interest, and the
  * mapped values are (perhaps transiently) not used or all take the
  * same mapping value.
  *
- * <p>A ConcurrentHashMapV8 can be used as scalable frequency map (a
- * form of histogram or multiset) by using {@link LongAdder8} values
- * and initializing via {@link #computeIfAbsent}. For example, to add
- * a count to a {@code ConcurrentHashMapV8<String,LongAdder8> freqs}, you
- * can use {@code freqs.computeIfAbsent(k -> new
- * LongAdder8()).increment();}
- *
  * <p>This class and its views and iterators implement all of the
  * <em>optional</em> methods of the {@link Map} and {@link Iterator}
  * interfaces.
@@ -90,90 +90,9 @@ import java.util.concurrent.locks.*;
  * <p>Like {@link Hashtable} but unlike {@link HashMap}, this class
  * does <em>not</em> allow {@code null} to be used as a key or value.
  *
- * <ul>
- * <li> forEach: Perform a given action on each element.
- * A variant form applies a given transformation on each element
- * before performing the action.</li>
- *
- * <li> search: Return the first available non-null result of
- * applying a given function on each element; skipping further
- * search when a result is found.</li>
- *
- * <li> reduce: Accumulate each element.  The supplied reduction
- * function cannot rely on ordering (more formally, it should be
- * both associative and commutative).  There are five variants:
- *
- * <ul>
- *
- * <li> Plain reductions. (There is not a form of this method for
- * (key, value) function arguments since there is no corresponding
- * return type.)</li>
- *
- * <li> Mapped reductions that accumulate the results of a given
- * function applied to each element.</li>
- *
- * <li> Reductions to scalar doubles, longs, and ints, using a
- * given basis value.</li>
- *
- * </li>
- * </ul>
- * </ul>
- *
- * <p>The concurrency properties of bulk operations follow
- * from those of ConcurrentHashMapV8: Any non-null result returned
- * from {@code get(key)} and related access methods bears a
- * happens-before relation with the associated insertion or
- * update.  The result of any bulk operation reflects the
- * composition of these per-element relations (but is not
- * necessarily atomic with respect to the map as a whole unless it
- * is somehow known to be quiescent).  Conversely, because keys
- * and values in the map are never null, null serves as a reliable
- * atomic indicator of the current lack of any result.  To
- * maintain this property, null serves as an implicit basis for
- * all non-scalar reduction operations. For the double, long, and
- * int versions, the basis should be one that, when combined with
- * any other value, returns that other value (more formally, it
- * should be the identity element for the reduction). Most common
- * reductions have these properties; for example, computing a sum
- * with basis 0 or a minimum with basis MAX_VALUE.
- *
- * <p>Search and transformation functions provided as arguments
- * should similarly return null to indicate the lack of any result
- * (in which case it is not used). In the case of mapped
- * reductions, this also enables transformations to serve as
- * filters, returning null (or, in the case of primitive
- * specializations, the identity basis) if the element should not
- * be combined. You can create compound transformations and
- * filterings by composing them yourself under this "null means
- * there is nothing there now" rule before using them in search or
- * reduce operations.
- *
- * <p>Methods accepting and/or returning Entry arguments maintain
- * key-value associations. They may be useful for example when
- * finding the key for the greatest value. Note that "plain" Entry
- * arguments can be supplied using {@code new
- * AbstractMap.SimpleEntry(k,v)}.
- *
- * <p>Bulk operations may complete abruptly, throwing an
- * exception encountered in the application of a supplied
- * function. Bear in mind when handling such exceptions that other
- * concurrently executing functions could also have thrown
- * exceptions, or would have done so if the first exception had
- * not occurred.
- *
- * <p>Parallel speedups for bulk operations compared to sequential
- * processing are common but not guaranteed.  Operations involving
- * brief functions on small maps may execute more slowly than
- * sequential loops if the underlying work to parallelize the
- * computation is more expensive than the computation itself.
- * Similarly, parallelization may not lead to much actual parallelism
- * if all processors are busy performing unrelated tasks.
- *
- * <p>All arguments to all task methods must be non-null.
- *
- * <p><em>jsr166e note: During transition, this class
- * uses nested functional interfaces with different names but the
- * same forms as those expected for JDK8.</em>
+ * <p>This class is a member of the
+ * <a href="{@docRoot}/../technotes/guides/collections/index.html">
+ * Java Collections Framework</a>.
  *
  * @since 1.5
  * @author Doug Lea
@@ -181,80 +100,9 @@ import java.util.concurrent.locks.*;
  * @param <V> the type of mapped values
  */
 @SuppressWarnings("ALL")
-public class ConcurrentHashMap8<K, V>
-    implements ConcurrentMap<K, V>, Serializable {
+public class ConcurrentHashMap8<K,V> implements ConcurrentMap<K,V>, Serializable {
     private static final long serialVersionUID = 7249069246763182397L;
 
-    /**
-     * A partitionable iterator. A Spliterator can be traversed
-     * directly, but can also be partitioned (before traversal) by
-     * creating another Spliterator that covers a non-overlapping
-     * portion of the elements, and so may be amenable to parallel
-     * execution.
-     *
-     * <p>This interface exports a subset of expected JDK8
-     * functionality.
-     *
-     * <p>Sample usage: Here is one (of the several) ways to compute
-     * the sum of the values held in a map using the ForkJoin
-     * framework. As illustrated here, Spliterators are well suited to
-     * designs in which a task repeatedly splits off half its work
-     * into forked subtasks until small enough to process directly,
-     * and then joins these subtasks. Variants of this style can also
-     * be used in completion-based designs.
-     *
-     * <pre>
-     * {@code ConcurrentHashMapV8<String, Long> m = ...
-     * // split as if have 8 * parallelism, for load balance
-     * int n = m.size();
-     * int p = aForkJoinPool.getParallelism() * 8;
-     * int split = (n < p)? n : p;
-     * long sum = aForkJoinPool.invoke(new SumValues(m.valueSpliterator(), split, null));
-     * // ...
-     * static class SumValues extends RecursiveTask<Long> {
-     *   final Spliterator<Long> s;
-     *   final int split;             // split while > 1
-     *   final SumValues nextJoin;    // records forked subtasks to join
-     *   SumValues(Spliterator<Long> s, int depth, SumValues nextJoin) {
-     *     this.s = s; this.depth = depth; this.nextJoin = nextJoin;
-     *   }
-     *   public Long compute() {
-     *     long sum = 0;
-     *     SumValues subtasks = null; // fork subtasks
-     *     for (int s = split >>> 1; s > 0; s >>>= 1)
-     *       (subtasks = new SumValues(s.split(), s, subtasks)).fork();
-     *     while (s.hasNext())        // directly process remaining elements
-     *       sum += s.next();
-     *     for (SumValues t = subtasks; t != null; t = t.nextJoin)
-     *       sum += t.join();         // collect subtask results
-     *     return sum;
-     *   }
-     * }
-     * }</pre>
-     */
-    public static interface Spliterator<T> extends Iterator<T> {
-        /**
-         * Returns a Spliterator covering approximately half of the
-         * elements, guaranteed not to overlap with those subsequently
-         * returned by this Spliterator.  After invoking this method,
-         * the current Spliterator will <em>not</em> produce any of
-         * the elements of the returned Spliterator, but the two
-         * Spliterators together will produce all of the elements that
-         * would have been produced by this Spliterator had this
-         * method not been called. The exact number of elements
-         * produced by the returned Spliterator is not guaranteed, and
-         * may be zero (i.e., with {@code hasNext()} reporting {@code
-         * false}) if this Spliterator cannot be further split.
-         *
-         * @return a Spliterator covering approximately half of the
-         * elements
-         * @throws IllegalStateException if this Spliterator has
-         * already commenced traversing elements
-         */
-        Spliterator<T> split();
-    }
-
-
     /*
      * Overview:
      *
@@ -265,18 +113,21 @@ public class ConcurrentHashMap8<K, V>
      * the same or better than java.util.HashMap, and to support high
      * initial insertion rates on an empty table by many threads.
      *
-     * Each key-value mapping is held in a Node.  Because Node fields
-     * can contain special values, they are defined using plain Object
-     * types. Similarly in turn, all internal methods that use them
-     * work off Object types. And similarly, so do the internal
-     * methods of auxiliary iterator and view classes.  All public
-     * generic typed methods relay in/out of these internal methods,
-     * supplying null-checks and casts as needed. This also allows
-     * many of the public methods to be factored into a smaller number
-     * of internal methods (although sadly not so for the five
-     * variants of put-related operations). The validation-based
-     * approach explained below leads to a lot of code sprawl because
-     * retry-control precludes factoring into smaller methods.
+     * This map usually acts as a binned (bucketed) hash table.  Each
+     * key-value mapping is held in a Node.  Most nodes are instances
+     * of the basic Node class with hash, key, value, and next
+     * fields. However, various subclasses exist: TreeNodes are
+     * arranged in balanced trees, not lists.  TreeBins hold the roots
+     * of sets of TreeNodes. ForwardingNodes are placed at the heads
+     * of bins during resizing. ReservationNodes are used as
+     * placeholders while establishing values in computeIfAbsent and
+     * related methods.  The types TreeBin, ForwardingNode, and
+     * ReservationNode do not hold normal user keys, values, or
+     * hashes, and are readily distinguishable during search etc
+     * because they have negative hash fields and null key and value
+     * fields. (These special nodes are either uncommon or transient,
+     * so the impact of carrying around some unused fields is
+     * insignificant.)
      *
      * The table is lazily initialized to a power-of-two size upon the
      * first insertion.  Each bin in the table normally contains a
@@ -284,24 +135,12 @@ public class ConcurrentHashMap8<K, V>
      * Table accesses require volatile/atomic reads, writes, and
      * CASes.  Because there is no other way to arrange this without
      * adding further indirections, we use intrinsics
-     * (sun.misc.Unsafe) operations.  The lists of nodes within bins
-     * are always accurately traversable under volatile reads, so long
-     * as lookups check hash code and non-nullness of value before
-     * checking key equality.
-     *
-     * We use the top two bits of Node hash fields for control
-     * purposes -- they are available anyway because of addressing
-     * constraints.  As explained further below, these top bits are
-     * used as follows:
-     *  00 - Normal
-     *  01 - Locked
-     *  11 - Locked and may have a thread waiting for lock
-     *  10 - Node is a forwarding node
+     * (sun.misc.Unsafe) operations.
      *
-     * The lower 30 bits of each Node's hash field contain a
-     * transformation of the key's hash code, except for forwarding
-     * nodes, for which the lower bits are zero (and so always have
-     * hash field == MOVED).
+     * We use the top (sign) bit of Node hash fields for control
+     * purposes -- it is available anyway because of addressing
+     * constraints.  Nodes with negative hash fields are specially
+     * handled or ignored in map methods.
      *
      * Insertion (via put or its variants) of the first node in an
      * empty bin is performed by just CASing it to the bin.  This is
@@ -310,22 +149,15 @@ public class ConcurrentHashMap8<K, V>
      * delete, and replace) require locks.  We do not want to waste
      * the space required to associate a distinct lock object with
      * each bin, so instead use the first node of a bin list itself as
-     * a lock. Blocking support for these locks relies on the builtin
-     * "synchronized" monitors.  However, we also need a tryLock
-     * construction, so we overlay these by using bits of the Node
-     * hash field for lock control (see above), and so normally use
-     * builtin monitors only for blocking and signalling using
-     * wait/notifyAll constructions. See Node.tryAwaitLock.
+     * a lock. Locking support for these locks relies on builtin
+     * "synchronized" monitors.
      *
      * Using the first node of a list as a lock does not by itself
      * suffice though: When a node is locked, any update must first
      * validate that it is still the first node after locking it, and
      * retry if not. Because new nodes are always appended to lists,
      * once a node is first in a bin, it remains first until deleted
-     * or the bin becomes invalidated (upon resizing).  However,
-     * operations that only conditionally update may inspect nodes
-     * until the point of update. This is a converse of sorts to the
-     * lazy locking technique described by Herlihy & Shavit.
+     * or the bin becomes invalidated (upon resizing).
      *
      * The main disadvantage of per-bin locks is that other update
      * operations on other nodes in a bin list protected by the same
@@ -358,15 +190,12 @@ public class ConcurrentHashMap8<K, V>
      * sometimes deviate significantly from uniform randomness.  This
      * includes the case when N > (1<<30), so some keys MUST collide.
      * Similarly for dumb or hostile usages in which multiple keys are
-     * designed to have identical hash codes. Also, although we guard
-     * against the worst effects of this (see method spread), sets of
-     * hashes may differ only in bits that do not impact their bin
-     * index for a given power-of-two mask.  So we use a secondary
-     * strategy that applies when the number of nodes in a bin exceeds
-     * a threshold, and at least one of the keys implements
-     * Comparable.  These TreeBins use a balanced tree to hold nodes
-     * (a specialized form of red-black trees), bounding search time
-     * to O(log N).  Each search step in a TreeBin is around twice as
+     * designed to have identical hash codes or ones that differs only
+     * in masked-out high bits. So we use a secondary strategy that
+     * applies when the number of nodes in a bin exceeds a
+     * threshold. These TreeBins use a balanced tree to hold nodes (a
+     * specialized form of red-black trees), bounding search time to
+     * O(log N).  Each search step in a TreeBin is at least twice as
      * slow as in a regular list, but given that N cannot exceed
      * (1<<64) (before running out of addresses) this bounds search
      * steps, lock hold times, etc, to reasonable constants (roughly
@@ -377,43 +206,50 @@ public class ConcurrentHashMap8<K, V>
      * iterators in the same way.
      *
      * The table is resized when occupancy exceeds a percentage
-     * threshold (nominally, 0.75, but see below).  Only a single
-     * thread performs the resize (using field "sizeCtl", to arrange
-     * exclusion), but the table otherwise remains usable for reads
-     * and updates. Resizing proceeds by transferring bins, one by
-     * one, from the table to the next table.  Because we are using
-     * power-of-two expansion, the elements from each bin must either
-     * stay at same index, or move with a power of two offset. We
-     * eliminate unnecessary node creation by catching cases where old
-     * nodes can be reused because their next fields won't change.  On
-     * average, only about one-sixth of them need cloning when a table
-     * doubles. The nodes they replace will be garbage collectable as
-     * soon as they are no longer referenced by any reader thread that
-     * may be in the midst of concurrently traversing table.  Upon
-     * transfer, the old table bin contains only a special forwarding
-     * node (with hash field "MOVED") that contains the next table as
-     * its key. On encountering a forwarding node, access and update
-     * operations restart, using the new table.
-     *
-     * Each bin transfer requires its bin lock. However, unlike other
-     * cases, a transfer can skip a bin if it fails to acquire its
-     * lock, and revisit it later (unless it is a TreeBin). Method
-     * rebuild maintains a buffer of TRANSFER_BUFFER_SIZE bins that
-     * have been skipped because of failure to acquire a lock, and
-     * blocks only if none are available (i.e., only very rarely).
-     * The transfer operation must also ensure that all accessible
-     * bins in both the old and new table are usable by any traversal.
-     * When there are no lock acquisition failures, this is arranged
-     * simply by proceeding from the last bin (table.length - 1) up
-     * towards the first.  Upon seeing a forwarding node, traversals
-     * (see class Iter) arrange to move to the new table
-     * without revisiting nodes.  However, when any node is skipped
-     * during a transfer, all earlier table bins may have become
-     * visible, so are initialized with a reverse-forwarding node back
-     * to the old table until the new ones are established. (This
-     * sometimes requires transiently locking a forwarding node, which
-     * is possible under the above encoding.) These more expensive
-     * mechanics trigger only when necessary.
+     * threshold (nominally, 0.75, but see below).  Any thread
+     * noticing an overfull bin may assist in resizing after the
+     * initiating thread allocates and sets up the replacement array.
+     * However, rather than stalling, these other threads may proceed
+     * with insertions etc.  The use of TreeBins shields us from the
+     * worst case effects of overfilling while resizes are in
+     * progress.  Resizing proceeds by transferring bins, one by one,
+     * from the table to the next table. However, threads claim small
+     * blocks of indices to transfer (via field transferIndex) before
+     * doing so, reducing contention.  A generation stamp in field
+     * sizeCtl ensures that resizings do not overlap. Because we are
+     * using power-of-two expansion, the elements from each bin must
+     * either stay at same index, or move with a power of two
+     * offset. We eliminate unnecessary node creation by catching
+     * cases where old nodes can be reused because their next fields
+     * won't change.  On average, only about one-sixth of them need
+     * cloning when a table doubles. The nodes they replace will be
+     * garbage collectable as soon as they are no longer referenced by
+     * any reader thread that may be in the midst of concurrently
+     * traversing table.  Upon transfer, the old table bin contains
+     * only a special forwarding node (with hash field "MOVED") that
+     * contains the next table as its key. On encountering a
+     * forwarding node, access and update operations restart, using
+     * the new table.
+     *
+     * Each bin transfer requires its bin lock, which can stall
+     * waiting for locks while resizing. However, because other
+     * threads can join in and help resize rather than contend for
+     * locks, average aggregate waits become shorter as resizing
+     * progresses.  The transfer operation must also ensure that all
+     * accessible bins in both the old and new table are usable by any
+     * traversal.  This is arranged in part by proceeding from the
+     * last bin (table.length - 1) up towards the first.  Upon seeing
+     * a forwarding node, traversals (see class Traverser) arrange to
+     * move to the new table without revisiting nodes.  To ensure that
+     * no intervening nodes are skipped even when moved out of order,
+     * a stack (see class TableStack) is created on first encounter of
+     * a forwarding node during a traversal, to maintain its place if
+     * later processing the current table. The need for these
+     * save/restore mechanics is relatively rare, but when one
+     * forwarding node is encountered, typically many more will be.
+     * So Traversers use a simple caching scheme to avoid creating so
+     * many new TableStack nodes. (Thanks to Peter Levart for
+     * suggesting use of a stack here.)
      *
      * The traversal scheme also applies to partial traversals of
      * ranges of bins (via an alternate Traverser constructor)
@@ -428,20 +264,54 @@ public class ConcurrentHashMap8<K, V>
      * These cases attempt to override the initial capacity settings,
      * but harmlessly fail to take effect in cases of races.
      *
-     * The element count is maintained using a LongAdder8, which avoids
-     * contention on updates but can encounter cache thrashing if read
-     * too frequently during concurrent access. To avoid reading so
-     * often, resizing is attempted either when a bin lock is
-     * contended, or upon adding to a bin already holding two or more
-     * nodes (checked before adding in the xIfAbsent methods, after
-     * adding in others). Under uniform hash distributions, the
-     * probability of this occurring at threshold is around 13%,
-     * meaning that only about 1 in 8 puts check threshold (and after
-     * resizing, many fewer do so). But this approximation has high
-     * variance for small table sizes, so we check on any collision
-     * for sizes <= 64. The bulk putAll operation further reduces
-     * contention by only committing count updates upon these size
-     * checks.
+     * The element count is maintained using a specialization of
+     * LongAdder. We need to incorporate a specialization rather than
+     * just use a LongAdder in order to access implicit
+     * contention-sensing that leads to creation of multiple
+     * CounterCells.  The counter mechanics avoid contention on
+     * updates but can encounter cache thrashing if read too
+     * frequently during concurrent access. To avoid reading so often,
+     * resizing under contention is attempted only upon adding to a
+     * bin already holding two or more nodes. Under uniform hash
+     * distributions, the probability of this occurring at threshold
+     * is around 13%, meaning that only about 1 in 8 puts check
+     * threshold (and after resizing, many fewer do so).
+     *
+     * TreeBins use a special form of comparison for search and
+     * related operations (which is the main reason we cannot use
+     * existing collections such as TreeMaps). TreeBins contain
+     * Comparable elements, but may contain others, as well as
+     * elements that are Comparable but not necessarily Comparable for
+     * the same T, so we cannot invoke compareTo among them. To handle
+     * this, the tree is ordered primarily by hash value, then by
+     * Comparable.compareTo order if applicable.  On lookup at a node,
+     * if elements are not comparable or compare as 0 then both left
+     * and right children may need to be searched in the case of tied
+     * hash values. (This corresponds to the full list search that
+     * would be necessary if all elements were non-Comparable and had
+     * tied hashes.) On insertion, to keep a total ordering (or as
+     * close as is required here) across rebalancings, we compare
+     * classes and identityHashCodes as tie-breakers. The red-black
+     * balancing code is updated from pre-jdk-collections
+     * (http://gee.cs.oswego.edu/dl/classes/collections/RBCell.java)
+     * based in turn on Cormen, Leiserson, and Rivest "Introduction to
+     * Algorithms" (CLR).
+     *
+     * TreeBins also require an additional locking mechanism.  While
+     * list traversal is always possible by readers even during
+     * updates, tree traversal is not, mainly because of tree-rotations
+     * that may change the root node and/or its linkages.  TreeBins
+     * include a simple read-write lock mechanism parasitic on the
+     * main bin-synchronization strategy: Structural adjustments
+     * associated with an insertion or removal are already bin-locked
+     * (and so cannot conflict with other writers) but must wait for
+     * ongoing readers to finish. Since there can be only one such
+     * waiter, we use a simple scheme using a single "waiter" field to
+     * block writers.  However, readers need never block.  If the root
+     * lock is held, they proceed along the slow traversal path (via
+     * next-pointers) until the lock becomes available or the list is
+     * exhausted, whichever comes first. These cases are not fast, but
+     * maximize aggregate expected throughput.
      *
      * Maintaining API and serialization compatibility with previous
      * versions of this class introduces several oddities. Mainly: We
@@ -451,8 +321,20 @@ public class ConcurrentHashMap8<K, V>
      * time that we can guarantee to honor it.) We also declare an
      * unused "Segment" class that is instantiated in minimal form
      * only when serializing.
+     *
+     * Also, solely for compatibility with previous versions of this
+     * class, it extends AbstractMap, even though all of its methods
+     * are overridden, so it is just useless baggage.
+     *
+     * This file is organized to make things a little easier to follow
+     * while reading than they might otherwise: First the main static
+     * declarations and utilities, then fields, then main public
+     * methods (with a few factorings of multiple public methods into
+     * internal ones), then sizing methods, trees, traversers, and
+     * bulk operations.
      */
 
+
     /* ---------------- Constants -------------- */
 
     /**
@@ -492,2737 +374,2362 @@ public class ConcurrentHashMap8<K, V>
     private static final float LOAD_FACTOR = 0.75f;
 
     /**
-     * The buffer size for skipped bins during transfers. The
-     * value is arbitrary but should be large enough to avoid
-     * most locking stalls during resizes.
+     * The bin count threshold for using a tree rather than list for a
+     * bin.  Bins are converted to trees when adding an element to a
+     * bin with at least this many nodes. The value must be greater
+     * than 2, and should be at least 8 to mesh with assumptions in
+     * tree removal about conversion back to plain bins upon
+     * shrinkage.
      */
-    private static final int TRANSFER_BUFFER_SIZE = 32;
+    static final int TREEIFY_THRESHOLD = 8;
 
     /**
-     * The bin count threshold for using a tree rather than list for a
-     * bin.  The value reflects the approximate break-even point for
-     * using tree-based operations.
+     * The bin count threshold for untreeifying a (split) bin during a
+     * resize operation. Should be less than TREEIFY_THRESHOLD, and at
+     * most 6 to mesh with shrinkage detection under removal.
      */
-    private static final int TREE_THRESHOLD = 8;
+    static final int UNTREEIFY_THRESHOLD = 6;
 
-    /*
-     * Encodings for special uses of Node hash fields. See above for
-     * explanation.
+    /**
+     * The smallest table capacity for which bins may be treeified.
+     * (Otherwise the table is resized if too many nodes in a bin.)
+     * The value should be at least 4 * TREEIFY_THRESHOLD to avoid
+     * conflicts between resizing and treeification thresholds.
      */
-    static final int MOVED     = 0x80000000; // hash field for forwarding nodes
-    static final int LOCKED    = 0x40000000; // set/tested only as a bit
-    static final int WAITING   = 0xc0000000; // both bits set/tested together
-    static final int HASH_BITS = 0x3fffffff; // usable bits of normal node hash
-
-    /* ---------------- Fields -------------- */
+    static final int MIN_TREEIFY_CAPACITY = 64;
 
     /**
-     * The array of bins. Lazily initialized upon first insertion.
-     * Size is always a power of two. Accessed directly by iterators.
+     * Minimum number of rebinnings per transfer step. Ranges are
+     * subdivided to allow multiple resizer threads.  This value
+     * serves as a lower bound to avoid resizers encountering
+     * excessive memory contention.  The value should be at least
+     * DEFAULT_CAPACITY.
      */
-    transient volatile Node[] table;
+    private static final int MIN_TRANSFER_STRIDE = 16;
 
     /**
-     * The counter maintaining number of elements.
+     * The number of bits used for generation stamp in sizeCtl.
+     * Must be at least 6 for 32bit arrays.
      */
-    private transient final LongAdder8 counter;
+    private static int RESIZE_STAMP_BITS = 16;
 
     /**
-     * Table initialization and resizing control.  When negative, the
-     * table is being initialized or resized. Otherwise, when table is
-     * null, holds the initial table size to use upon creation, or 0
-     * for default. After initialization, holds the next element count
-     * value upon which to resize the table.
+     * The maximum number of threads that can help resize.
+     * Must fit in 32 - RESIZE_STAMP_BITS bits.
      */
-    private transient volatile int sizeCtl;
-
-    // views
-    private transient KeySetView<K,V> keySet;
-    private transient ValuesView<K,V> values;
-    private transient EntrySetView<K,V> entrySet;
-
-    /** For serialization compatibility. Null unless serialized; see below */
-    private Segment<K,V>[] segments;
+    private static final int MAX_RESIZERS = (1 << (32 - RESIZE_STAMP_BITS)) - 1;
 
-    /* ---------------- Table element access -------------- */
+    /**
+     * The bit shift for recording size stamp in sizeCtl.
+     */
+    private static final int RESIZE_STAMP_SHIFT = 32 - RESIZE_STAMP_BITS;
 
     /*
-     * Volatile access methods are used for table elements as well as
-     * elements of in-progress next table while resizing.  Uses are
-     * null checked by callers, and implicitly bounds-checked, relying
-     * on the invariants that tab arrays have non-zero size, and all
-     * indices are masked with (tab.length - 1) which is never
-     * negative and always less than length. Note that, to be correct
-     * wrt arbitrary concurrency errors by users, bounds checks must
-     * operate on local variables, which accounts for some odd-looking
-     * inline assignments below.
+     * Encodings for Node hash fields. See above for explanation.
      */
+    static final int MOVED     = 0x8fffffff; // (-1) hash for forwarding nodes
+    static final int TREEBIN   = 0x80000000; // hash for roots of trees
+    static final int RESERVED  = 0x80000001; // hash for transient reservations
+    static final int HASH_BITS = 0x7fffffff; // usable bits of normal node hash
 
-    static final Node tabAt(Node[] tab, int i) { // used by Iter
-        return (Node)UNSAFE.getObjectVolatile(tab, ((long)i<<ASHIFT)+ABASE);
-    }
-
-    private static final boolean casTabAt(Node[] tab, int i, Node c, Node v) {
-        return UNSAFE.compareAndSwapObject(tab, ((long)i<<ASHIFT)+ABASE, c, v);
-    }
+    /** Number of CPUS, to place bounds on some sizings */
+    static final int NCPU = Runtime.getRuntime().availableProcessors();
 
-    private static final void setTabAt(Node[] tab, int i, Node v) {
-        UNSAFE.putObjectVolatile(tab, ((long)i<<ASHIFT)+ABASE, v);
-    }
+    /** For serialization compatibility. */
+    private static final ObjectStreamField[] serialPersistentFields = {
+        new ObjectStreamField("segments", Segment[].class),
+        new ObjectStreamField("segmentMask", Integer.TYPE),
+        new ObjectStreamField("segmentShift", Integer.TYPE)
+    };
 
     /* ---------------- Nodes -------------- */
 
     /**
-     * Key-value entry. Note that this is never exported out as a
-     * user-visible Map.Entry (see MapEntry below). Nodes with a hash
-     * field of MOVED are special, and do not contain user keys or
-     * values.  Otherwise, keys are never null, and null val fields
-     * indicate that a node is in the process of being deleted or
-     * created. For purposes of read-only access, a key may be read
-     * before a val, but can only be used after checking val to be
-     * non-null.
+     * Key-value entry.  This class is never exported out as a
+     * user-mutable Map.Entry (i.e., one supporting setValue; see
+     * MapEntry below), but can be used for read-only traversals used
+     * in bulk tasks.  Subclasses of Node with a negative hash field
+     * are special, and contain null keys and values (but are never
+     * exported).  Otherwise, keys and vals are never null.
      */
-    static class Node {
-        volatile int hash;
-        final Object key;
-        volatile Object val;
-        volatile Node next;
+    static class Node<K,V> implements Map.Entry<K,V> {
+        final int hash;
+        final K key;
+        volatile V val;
+        Node<K,V> next;
 
-        Node(int hash, Object key, Object val, Node next) {
+        Node(int hash, K key, V val, Node<K,V> next) {
             this.hash = hash;
             this.key = key;
             this.val = val;
             this.next = next;
         }
 
-        /** CompareAndSet the hash field */
-        final boolean casHash(int cmp, int val) {
-            return UNSAFE.compareAndSwapInt(this, hashOffset, cmp, val);
+        public final K getKey()       { return key; }
+        public final V getValue()     { return val; }
+        public final int hashCode()   { return key.hashCode() ^ val.hashCode(); }
+        public final String toString(){ return key + "=" + val; }
+        public final V setValue(V value) {
+            throw new UnsupportedOperationException();
         }
 
-        /** The number of spins before blocking for a lock */
-        static final int MAX_SPINS =
-            Runtime.getRuntime().availableProcessors() > 1 ? 64 : 1;
+        public final boolean equals(Object o) {
+            Object k, v, u; Map.Entry<?,?> e;
+            return ((o instanceof Map.Entry) &&
+                (k = (e = (Map.Entry<?,?>)o).getKey()) != null &&
+                (v = e.getValue()) != null &&
+                (k == key || k.equals(key)) &&
+                (v == (u = val) || v.equals(u)));
+        }
 
         /**
-         * Spins a while if LOCKED bit set and this node is the first
-         * of its bin, and then sets WAITING bits on hash field and
-         * blocks (once) if they are still set.  It is OK for this
-         * method to return even if lock is not available upon exit,
-         * which enables these simple single-wait mechanics.
-         *
-         * The corresponding signalling operation is performed within
-         * callers: Upon detecting that WAITING has been set when
-         * unlocking lock (via a failed CAS from non-waiting LOCKED
-         * state), unlockers acquire the sync lock and perform a
-         * notifyAll.
-         *
-         * The initial sanity check on tab and bounds is not currently
-         * necessary in the only usages of this method, but enables
-         * use in other future contexts.
+         * Virtualized support for map.get(); overridden in subclasses.
          */
-        final void tryAwaitLock(Node[] tab, int i) {
-            if (tab != null && i >= 0 && i < tab.length) { // sanity check
-                int r = ThreadLocalRandom8.current().nextInt(); // randomize spins
-                int spins = MAX_SPINS, h;
-                while (tabAt(tab, i) == this && ((h = hash) & LOCKED) != 0) {
-                    if (spins >= 0) {
-                        r ^= r << 1; r ^= r >>> 3; r ^= r << 10; // xorshift
-                        if (r >= 0 && --spins == 0)
-                            Thread.yield();  // yield before block
-                    }
-                    else if (casHash(h, h | WAITING)) {
-                        synchronized (this) {
-                            if (tabAt(tab, i) == this &&
-                                (hash & WAITING) == WAITING) {
-                                try {
-                                    wait();
-                                } catch (InterruptedException ie) {
-                                    try {
-                                        Thread.currentThread().interrupt();
-                                    } catch (SecurityException ignore) {
-                                    }
-                                }
-                            }
-                            else
-                                notifyAll(); // possibly won race vs signaller
-                        }
-                        break;
-                    }
-                }
+        Node<K,V> find(int h, Object k) {
+            Node<K,V> e = this;
+            if (k != null) {
+                do {
+                    K ek;
+                    if (e.hash == h &&
+                        ((ek = e.key) == k || (ek != null && k.equals(ek))))
+                        return e;
+                } while ((e = e.next) != null);
             }
+            return null;
         }
+    }
 
-        // Unsafe mechanics for casHash
-        private static final sun.misc.Unsafe UNSAFE;
-        private static final long hashOffset;
+    /* ---------------- Static utilities -------------- */
 
-        static {
-            try {
-                UNSAFE = getUnsafe();
-                Class<?> k = Node.class;
-                hashOffset = UNSAFE.objectFieldOffset
-                    (k.getDeclaredField("hash"));
-            } catch (Exception e) {
-                throw new Error(e);
+    /**
+     * Spreads (XORs) higher bits of hash to lower and also forces top
+     * bit to 0. Because the table uses power-of-two masking, sets of
+     * hashes that vary only in bits above the current mask will
+     * always collide. (Among known examples are sets of Float keys
+     * holding consecutive whole numbers in small tables.)  So we
+     * apply a transform that spreads the impact of higher bits
+     * downward. There is a tradeoff between speed, utility, and
+     * quality of bit-spreading. Because many common sets of hashes
+     * are already reasonably distributed (so don't benefit from
+     * spreading), and because we use trees to handle large sets of
+     * collisions in bins, we just XOR some shifted bits in the
+     * cheapest possible way to reduce systematic lossage, as well as
+     * to incorporate impact of the highest bits that would otherwise
+     * never be used in index calculations because of table bounds.
+     */
+    static final int spread(int h) {
+        return (h ^ (h >>> 16)) & HASH_BITS;
+    }
+
+    /**
+     * Returns a power of two table size for the given desired capacity.
+     * See Hackers Delight, sec 3.2
+     */
+    private static final int tableSizeFor(int c) {
+        int n = c - 1;
+        n |= n >>> 1;
+        n |= n >>> 2;
+        n |= n >>> 4;
+        n |= n >>> 8;
+        n |= n >>> 16;
+        return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
+    }
+
+    /**
+     * Returns x's Class if it is of the form "class C implements
+     * Comparable<C>", else null.
+     */
+    static Class<?> comparableClassFor(Object x) {
+        if (x instanceof Comparable) {
+            Class<?> c; Type[] ts, as; Type t; ParameterizedType p;
+            if ((c = x.getClass()) == String.class) // bypass checks
+                return c;
+            if ((ts = c.getGenericInterfaces()) != null) {
+                for (int i = 0; i < ts.length; ++i) {
+                    if (((t = ts[i]) instanceof ParameterizedType) &&
+                        ((p = (ParameterizedType)t).getRawType() ==
+                            Comparable.class) &&
+                        (as = p.getActualTypeArguments()) != null &&
+                        as.length == 1 && as[0] == c) // type arg is c
+                        return c;
+                }
             }
         }
+        return null;
     }
 
-    /* ---------------- TreeBins -------------- */
-
     /**
-     * Nodes for use in TreeBins
+     * Returns k.compareTo(x) if x matches kc (k's screened comparable
+     * class), else 0.
      */
-    static final class TreeNode extends Node {
-        TreeNode parent;  // red-black tree links
-        TreeNode left;
-        TreeNode right;
-        TreeNode prev;    // needed to unlink next upon deletion
-        boolean red;
+    @SuppressWarnings({"rawtypes","unchecked"}) // for cast to Comparable
+    static int compareComparables(Class<?> kc, Object k, Object x) {
+        return (x == null || x.getClass() != kc ? 0 :
+            ((Comparable)k).compareTo(x));
+    }
 
-        TreeNode(int hash, Object key, Object val, Node next, TreeNode parent) {
-            super(hash, key, val, next);
-            this.parent = parent;
-        }
+    /* ---------------- Table element access -------------- */
+
+    /*
+     * Volatile access methods are used for table elements as well as
+     * elements of in-progress next table while resizing.  All uses of
+     * the tab arguments must be null checked by callers.  All callers
+     * also paranoically precheck that tab's length is not zero (or an
+     * equivalent check), thus ensuring that any index argument taking
+     * the form of a hash value anded with (length - 1) is a valid
+     * index.  Note that, to be correct wrt arbitrary concurrency
+     * errors by users, these checks must operate on local variables,
+     * which accounts for some odd-looking inline assignments below.
+     * Note that calls to setTabAt always occur within locked regions,
+     * and so do not need full volatile semantics, but still require
+     * ordering to maintain concurrent readability.
+     */
+
+    @SuppressWarnings("unchecked")
+    static final <K,V> Node<K,V> tabAt(Node<K,V>[] tab, int i) {
+        return (Node<K,V>)U.getObjectVolatile(tab, ((long)i << ASHIFT) + ABASE);
+    }
+
+    static final <K,V> boolean casTabAt(Node<K,V>[] tab, int i,
+                                        Node<K,V> c, Node<K,V> v) {
+        return U.compareAndSwapObject(tab, ((long)i << ASHIFT) + ABASE, c, v);
+    }
+
+    static final <K,V> void setTabAt(Node<K,V>[] tab, int i, Node<K,V> v) {
+        U.putOrderedObject(tab, ((long)i << ASHIFT) + ABASE, v);
     }
 
+    /* ---------------- Fields -------------- */
+
     /**
-     * A specialized form of red-black tree for use in bins
-     * whose size exceeds a threshold.
-     *
-     * TreeBins use a special form of comparison for search and
-     * related operations (which is the main reason we cannot use
-     * existing collections such as TreeMaps). TreeBins contain
-     * Comparable elements, but may contain others, as well as
-     * elements that are Comparable but not necessarily Comparable<T>
-     * for the same T, so we cannot invoke compareTo among them. To
-     * handle this, the tree is ordered primarily by hash value, then
-     * by getClass().getName() order, and then by Comparator order
-     * among elements of the same class.  On lookup at a node, if
-     * elements are not comparable or compare as 0, both left and
-     * right children may need to be searched in the case of tied hash
-     * values. (This corresponds to the full list search that would be
-     * necessary if all elements were non-Comparable and had tied
-     * hashes.)  The red-black balancing code is updated from
-     * pre-jdk-collections
-     * (http://gee.cs.oswego.edu/dl/classes/collections/RBCell.java)
-     * based in turn on Cormen, Leiserson, and Rivest "Introduction to
-     * Algorithms" (CLR).
-     *
-     * TreeBins also maintain a separate locking discipline than
-     * regular bins. Because they are forwarded via special MOVED
-     * nodes at bin heads (which can never change once established),
-     * we cannot use those nodes as locks. Instead, TreeBin
-     * extends AbstractQueuedSynchronizer to support a simple form of
-     * read-write lock. For update operations and table validation,
-     * the exclusive form of lock behaves in the same way as bin-head
-     * locks. However, lookups use shared read-lock mechanics to allow
-     * multiple readers in the absence of writers.  Additionally,
-     * these lookups do not ever block: While the lock is not
-     * available, they proceed along the slow traversal path (via
-     * next-pointers) until the lock becomes available or the list is
-     * exhausted, whichever comes first. (These cases are not fast,
-     * but maximize aggregate expected throughput.)  The AQS mechanics
-     * for doing this are straightforward.  The lock state is held as
-     * AQS getState().  Read counts are negative; the write count (1)
-     * is positive.  There are no signalling preferences among readers
-     * and writers. Since we don't need to export full Lock API, we
-     * just override the minimal AQS methods and use them directly.
-     */
-    static final class TreeBin extends AbstractQueuedSynchronizer {
-        private static final long serialVersionUID = 2249069246763182397L;
-        transient TreeNode root;  // root of tree
-        transient TreeNode first; // head of next-pointer list
-
-        /* AQS overrides */
-        public final boolean isHeldExclusively() { return getState() > 0; }
-        public final boolean tryAcquire(int ignore) {
-            if (compareAndSetState(0, 1)) {
-                setExclusiveOwnerThread(Thread.currentThread());
-                return true;
-            }
-            return false;
-        }
-        public final boolean tryRelease(int ignore) {
-            setExclusiveOwnerThread(null);
-            setState(0);
-            return true;
-        }
-        public final int tryAcquireShared(int ignore) {
-            for (int c;;) {
-                if ((c = getState()) > 0)
-                    return -1;
-                if (compareAndSetState(c, c -1))
-                    return 1;
-            }
-        }
-        public final boolean tryReleaseShared(int ignore) {
-            int c;
-            do {} while (!compareAndSetState(c = getState(), c + 1));
-            return c == -1;
-        }
+     * The array of bins. Lazily initialized upon first insertion.
+     * Size is always a power of two. Accessed directly by iterators.
+     */
+    transient volatile Node<K,V>[] table;
 
-        /** From CLR */
-        private void rotateLeft(TreeNode p) {
-            if (p != null) {
-                TreeNode r = p.right, pp, rl;
-                if ((rl = p.right = r.left) != null)
-                    rl.parent = p;
-                if ((pp = r.parent = p.parent) == null)
-                    root = r;
-                else if (pp.left == p)
-                    pp.left = r;
-                else
-                    pp.right = r;
-                r.left = p;
-                p.parent = r;
-            }
-        }
+    /**
+     * The next table to use; non-null only while resizing.
+     */
+    private transient volatile Node<K,V>[] nextTable;
 
-        /** From CLR */
-        private void rotateRight(TreeNode p) {
-            if (p != null) {
-                TreeNode l = p.left, pp, lr;
-                if ((lr = p.left = l.right) != null)
-                    lr.parent = p;
-                if ((pp = l.parent = p.parent) == null)
-                    root = l;
-                else if (pp.right == p)
-                    pp.right = l;
-                else
-                    pp.left = l;
-                l.right = p;
-                p.parent = l;
-            }
-        }
+    /**
+     * Base counter value, used mainly when there is no contention,
+     * but also as a fallback during table initialization
+     * races. Updated via CAS.
+     */
+    private transient volatile long baseCount;
 
-        /**
-         * Returns the TreeNode (or null if not found) for the given key
-         * starting at given root.
-         */
-        @SuppressWarnings("unchecked") final TreeNode getTreeNode
-        (int h, Object k, TreeNode p) {
-            Class<?> c = k.getClass();
-            while (p != null) {
-                int dir, ph;  Object pk; Class<?> pc;
-                if ((ph = p.hash) == h) {
-                    if ((pk = p.key) == k || k.equals(pk))
-                        return p;
-                    if (c != (pc = pk.getClass()) ||
-                        !(k instanceof Comparable) ||
-                        (dir = ((Comparable)k).compareTo((Comparable)pk)) == 0) {
-                        dir = (c == pc) ? 0 : c.getName().compareTo(pc.getName());
-                        TreeNode r = null, s = null, pl, pr;
-                        if (dir >= 0) {
-                            if ((pl = p.left) != null && h <= pl.hash)
-                                s = pl;
-                        }
-                        else if ((pr = p.right) != null && h >= pr.hash)
-                            s = pr;
-                        if (s != null && (r = getTreeNode(h, k, s)) != null)
-                            return r;
-                    }
-                }
-                else
-                    dir = (h < ph) ? -1 : 1;
-                p = (dir > 0) ? p.right : p.left;
-            }
-            return null;
-        }
+    /**
+     * Table initialization and resizing control.  When negative, the
+     * table is being initialized or resized: -1 for initialization,
+     * else -(1 + the number of active resizing threads).  Otherwise,
+     * when table is null, holds the initial table size to use upon
+     * creation, or 0 for default. After initialization, holds the
+     * next element count value upon which to resize the table.
+     */
+    private transient volatile int sizeCtl;
 
-        /**
-         * Wrapper for getTreeNode used by CHM.get. Tries to obtain
-         * read-lock to call getTreeNode, but during failure to get
-         * lock, searches along next links.
-         */
-        final Object getValue(int h, Object k) {
-            Node r = null;
-            int c = getState(); // Must read lock state first
-            for (Node e = first; e != null; e = e.next) {
-                if (c <= 0 && compareAndSetState(c, c - 1)) {
-                    try {
-                        r = getTreeNode(h, k, root);
-                    } finally {
-                        releaseShared(0);
-                    }
-                    break;
-                }
-                else if ((e.hash & HASH_BITS) == h && k.equals(e.key)) {
-                    r = e;
-                    break;
-                }
-                else
-                    c = getState();
-            }
-            return r == null ? null : r.val;
-        }
+    /**
+     * The next table index (plus one) to split while resizing.
+     */
+    private transient volatile int transferIndex;
 
-        /**
-         * Finds or adds a node.
-         * @return null if added
-         */
-        @SuppressWarnings("unchecked") final TreeNode putTreeNode
-        (int h, Object k, Object v) {
-            Class<?> c = k.getClass();
-            TreeNode pp = root, p = null;
-            int dir = 0;
-            while (pp != null) { // find existing node or leaf to insert at
-                int ph;  Object pk; Class<?> pc;
-                p = pp;
-                if ((ph = p.hash) == h) {
-                    if ((pk = p.key) == k || k.equals(pk))
-                        return p;
-                    if (c != (pc = pk.getClass()) ||
-                        !(k instanceof Comparable) ||
-                        (dir = ((Comparable)k).compareTo((Comparable)pk)) == 0) {
-                        dir = (c == pc) ? 0 : c.getName().compareTo(pc.getName());
-                        TreeNode r = null, s = null, pl, pr;
-                        if (dir >= 0) {
-                            if ((pl = p.left) != null && h <= pl.hash)
-                                s = pl;
-                        }
-                        else if ((pr = p.right) != null && h >= pr.hash)
-                            s = pr;
-                        if (s != null && (r = getTreeNode(h, k, s)) != null)
-                            return r;
-                    }
-                }
-                else
-                    dir = (h < ph) ? -1 : 1;
-                pp = (dir > 0) ? p.right : p.left;
-            }
+    /**
+     * Spinlock (locked via CAS) used when resizing and/or creating CounterCells.
+     */
+    private transient volatile int cellsBusy;
 
-            TreeNode f = first;
-            TreeNode x = first = new TreeNode(h, k, v, f, p);
-            if (p == null)
-                root = x;
-            else { // attach and rebalance; adapted from CLR
-                TreeNode xp, xpp;
-                if (f != null)
-                    f.prev = x;
-                if (dir <= 0)
-                    p.left = x;
-                else
-                    p.right = x;
-                x.red = true;
-                while (x != null && (xp = x.parent) != null && xp.red &&
-                    (xpp = xp.parent) != null) {
-                    TreeNode xppl = xpp.left;
-                    if (xp == xppl) {
-                        TreeNode y = xpp.right;
-                        if (y != null && y.red) {
-                            y.red = false;
-                            xp.red = false;
-                            xpp.red = true;
-                            x = xpp;
-                        }
-                        else {
-                            if (x == xp.right) {
-                                rotateLeft(x = xp);
-                                xpp = (xp = x.parent) == null ? null : xp.parent;
-                            }
-                            if (xp != null) {
-                                xp.red = false;
-                                if (xpp != null) {
-                                    xpp.red = true;
-                                    rotateRight(xpp);
-                                }
-                            }
-                        }
-                    }
-                    else {
-                        TreeNode y = xppl;
-                        if (y != null && y.red) {
-                            y.red = false;
-                            xp.red = false;
-                            xpp.red = true;
-                            x = xpp;
-                        }
-                        else {
-                            if (x == xp.left) {
-                                rotateRight(x = xp);
-                                xpp = (xp = x.parent) == null ? null : xp.parent;
-                            }
-                            if (xp != null) {
-                                xp.red = false;
-                                if (xpp != null) {
-                                    xpp.red = true;
-                                    rotateLeft(xpp);
-                                }
-                            }
-                        }
-                    }
-                }
-                TreeNode r = root;
-                if (r != null && r.red)
-                    r.red = false;
-            }
-            return null;
-        }
+    /**
+     * Table of counter cells. When non-null, size is a power of 2.
+     */
+    private transient volatile CounterCell[] counterCells;
 
-        /**
-         * Removes the given node, that must be present before this
-         * call.  This is messier than typical red-black deletion code
-         * because we cannot swap the contents of an interior node
-         * with a leaf successor that is pinned by "next" pointers
-         * that are accessible independently of lock. So instead we
-         * swap the tree linkages.
-         */
-        final void deleteTreeNode(TreeNode p) {
-            TreeNode next = (TreeNode)p.next; // unlink traversal pointers
-            TreeNode pred = p.prev;
-            if (pred == null)
-                first = next;
-            else
-                pred.next = next;
-            if (next != null)
-                next.prev = pred;
-            TreeNode replacement;
-            TreeNode pl = p.left;
-            TreeNode pr = p.right;
-            if (pl != null && pr != null) {
-                TreeNode s = pr, sl;
-                while ((sl = s.left) != null) // find successor
-                    s = sl;
-                boolean c = s.red; s.red = p.red; p.red = c; // swap colors
-                TreeNode sr = s.right;
-                TreeNode pp = p.parent;
-                if (s == pr) { // p was s's direct parent
-                    p.parent = s;
-                    s.right = p;
-                }
-                else {
-                    TreeNode sp = s.parent;
-                    if ((p.parent = sp) != null) {
-                        if (s == sp.left)
-                            sp.left = p;
-                        else
-                            sp.right = p;
-                    }
-                    if ((s.right = pr) != null)
-                        pr.parent = s;
-                }
-                p.left = null;
-                if ((p.right = sr) != null)
-                    sr.parent = p;
-                if ((s.left = pl) != null)
-                    pl.parent = s;
-                if ((s.parent = pp) == null)
-                    root = s;
-                else if (p == pp.left)
-                    pp.left = s;
-                else
-                    pp.right = s;
-                replacement = sr;
-            }
-            else
-                replacement = (pl != null) ? pl : pr;
-            TreeNode pp = p.parent;
-            if (replacement == null) {
-                if (pp == null) {
-                    root = null;
-                    return;
-                }
-                replacement = p;
-            }
-            else {
-                replacement.parent = pp;
-                if (pp == null)
-                    root = replacement;
-                else if (p == pp.left)
-                    pp.left = replacement;
-                else
-                    pp.right = replacement;
-                p.left = p.right = p.parent = null;
-            }
-            if (!p.red) { // rebalance, from CLR
-                TreeNode x = replacement;
-                while (x != null) {
-                    TreeNode xp, xpl;
-                    if (x.red || (xp = x.parent) == null) {
-                        x.red = false;
-                        break;
-                    }
-                    if (x == (xpl = xp.left)) {
-                        TreeNode sib = xp.right;
-                        if (sib != null && sib.red) {
-                            sib.red = false;
-                            xp.red = true;
-                            rotateLeft(xp);
-                            sib = (xp = x.parent) == null ? null : xp.right;
-                        }
-                        if (sib == null)
-                            x = xp;
-                        else {
-                            TreeNode sl = sib.left, sr = sib.right;
-                            if ((sr == null || !sr.red) &&
-                                (sl == null || !sl.red)) {
-                                sib.red = true;
-                                x = xp;
-                            }
-                            else {
-                                if (sr == null || !sr.red) {
-                                    if (sl != null)
-                                        sl.red = false;
-                                    sib.red = true;
-                                    rotateRight(sib);
-                                    sib = (xp = x.parent) == null ? null : xp.right;
-                                }
-                                if (sib != null) {
-                                    sib.red = (xp == null) ? false : xp.red;
-                                    if ((sr = sib.right) != null)
-                                        sr.red = false;
-                                }
-                                if (xp != null) {
-                                    xp.red = false;
-                                    rotateLeft(xp);
-                                }
-                                x = root;
-                            }
-                        }
-                    }
-                    else { // symmetric
-                        TreeNode sib = xpl;
-                        if (sib != null && sib.red) {
-                            sib.red = false;
-                            xp.red = true;
-                            rotateRight(xp);
-                            sib = (xp = x.parent) == null ? null : xp.left;
-                        }
-                        if (sib == null)
-                            x = xp;
-                        else {
-                            TreeNode sl = sib.left, sr = sib.right;
-                            if ((sl == null || !sl.red) &&
-                                (sr == null || !sr.red)) {
-                                sib.red = true;
-                                x = xp;
-                            }
-                            else {
-                                if (sl == null || !sl.red) {
-                                    if (sr != null)
-                                        sr.red = false;
-                                    sib.red = true;
-                                    rotateLeft(sib);
-                                    sib = (xp = x.parent) == null ? null : xp.left;
-                                }
-                                if (sib != null) {
-                                    sib.red = (xp == null) ? false : xp.red;
-                                    if ((sl = sib.left) != null)
-                                        sl.red = false;
-                                }
-                                if (xp != null) {
-                                    xp.red = false;
-                                    rotateRight(xp);
-                                }
-                                x = root;
-                            }
-                        }
-                    }
-                }
-            }
-            if (p == replacement && (pp = p.parent) != null) {
-                if (p == pp.left) // detach pointers
-                    pp.left = null;
-                else if (p == pp.right)
-                    pp.right = null;
-                p.parent = null;
-            }
-        }
+    // views
+    private transient KeySetView<K,V> keySet;
+    private transient ValuesView<K,V> values;
+    private transient EntrySetView<K,V> entrySet;
+
+
+    /* ---------------- Public operations -------------- */
+
+    /**
+     * Creates a new, empty map with the default initial table size (16).
+     */
+    public ConcurrentHashMap8() {
     }
 
-    /* ---------------- Collision reduction methods -------------- */
+    /**
+     * Creates a new, empty map with an initial table size
+     * accommodating the specified number of elements without the need
+     * to dynamically resize.
+     *
+     * @param initialCapacity The implementation performs internal
+     * sizing to accommodate this many elements.
+     * @throws IllegalArgumentException if the initial capacity of
+     * elements is negative
+     */
+    public ConcurrentHashMap8(int initialCapacity) {
+        if (initialCapacity < 0)
+            throw new IllegalArgumentException();
+        int cap = ((initialCapacity >= (MAXIMUM_CAPACITY >>> 1)) ?
+            MAXIMUM_CAPACITY :
+            tableSizeFor(initialCapacity + (initialCapacity >>> 1) + 1));
+        this.sizeCtl = cap;
+    }
 
     /**
-     * Spreads higher bits to lower, and also forces top 2 bits to 0.
-     * Because the table uses power-of-two masking, sets of hashes
-     * that vary only in bits above the current mask will always
-     * collide. (Among known examples are sets of Float keys holding
-     * consecutive whole numbers in small tables.)  To counter this,
-     * we apply a transform that spreads the impact of higher bits
-     * downward. There is a tradeoff between speed, utility, and
-     * quality of bit-spreading. Because many common sets of hashes
-     * are already reasonably distributed across bits (so don't benefit
-     * from spreading), and because we use trees to handle large sets
-     * of collisions in bins, we don't need excessively high quality.
+     * Creates a new map with the same mappings as the given map.
+     *
+     * @param m the map
      */
-    private static final int spread(int h) {
-        h ^= (h >>> 18) ^ (h >>> 12);
-        return (h ^ (h >>> 10)) & HASH_BITS;
+    public ConcurrentHashMap8(Map<? extends K, ? extends V> m) {
+        this.sizeCtl = DEFAULT_CAPACITY;
+        putAll(m);
     }
 
     /**
-     * Replaces a list bin with a tree bin. Call only when locked.
-     * Fails to replace if the given key is non-comparable or table
-     * is, or needs, resizing.
+     * Creates a new, empty map with an initial table size based on
+     * the given number of elements ({@code initialCapacity}) and
+     * initial table density ({@code loadFactor}).
+     *
+     * @param initialCapacity the initial capacity. The implementation
+     * performs internal sizing to accommodate this many elements,
+     * given the specified load factor.
+     * @param loadFactor the load factor (table density) for
+     * establishing the initial table size
+     * @throws IllegalArgumentException if the initial capacity of
+     * elements is negative or the load factor is nonpositive
+     *
+     * @since 1.6
      */
-    private final void replaceWithTreeBin(Node[] tab, int index, Object key) {
-        if ((key instanceof Comparable) &&
-            (tab.length >= MAXIMUM_CAPACITY || counter.sum() < (long)sizeCtl)) {
-            TreeBin t = new TreeBin();
-            for (Node e = tabAt(tab, index); e != null; e = e.next)
-                t.putTreeNode(e.hash & HASH_BITS, e.key, e.val);
-            setTabAt(tab, index, new Node(MOVED, t, null, null));
-        }
+    public ConcurrentHashMap8(int initialCapacity, float loadFactor) {
+        this(initialCapacity, loadFactor, 1);
     }
 
-    /* ---------------- Internal access and update methods -------------- */
+    /**
+     * Creates a new, empty map with an initial table size based on
+     * the given number of elements ({@code initialCapacity}), table
+     * density ({@code loadFactor}), and number of concurrently
+     * updating threads ({@code concurrencyLevel}).
+     *
+     * @param initialCapacity the initial capacity. The implementation
+     * performs internal sizing to accommodate this many elements,
+     * given the specified load factor.
+     * @param loadFactor the load factor (table density) for
+     * establishing the initial table size
+     * @param concurrencyLevel the estimated number of concurrently
+     * updating threads. The implementation may use this value as
+     * a sizing hint.
+     * @throws IllegalArgumentException if the initial capacity is
+     * negative or the load factor or concurrencyLevel are
+     * nonpositive
+     */
+    public ConcurrentHashMap8(int initialCapacity,
+                             float loadFactor, int concurrencyLevel) {
+        if (!(loadFactor > 0.0f) || initialCapacity < 0 || concurrencyLevel <= 0)
+            throw new IllegalArgumentException();
+        if (initialCapacity < concurrencyLevel)   // Use at least as many bins
+            initialCapacity = concurrencyLevel;   // as estimated threads
+        long size = (long)(1.0 + (long)initialCapacity / loadFactor);
+        int cap = (size >= (long)MAXIMUM_CAPACITY) ?
+            MAXIMUM_CAPACITY : tableSizeFor((int)size);
+        this.sizeCtl = cap;
+    }
 
-    /** Implementation for get and containsKey */
-    private final Object internalGet(Object k) {
-        int h = spread(k.hashCode());
-        retry: for (Node[] tab = table; tab != null;) {
-            Node e, p; Object ek, ev; int eh;      // locals to read fields once
-            for (e = tabAt(tab, (tab.length - 1) & h); e != null; e = e.next) {
-                if ((eh = e.hash) == MOVED) {
-                    if ((ek = e.key) instanceof TreeBin)  // search TreeBin
-                        return ((TreeBin)ek).getValue(h, k);
-                    else {                        // restart with new table
-                        tab = (Node[])ek;
-                        continue retry;
-                    }
-                }
-                else if ((eh & HASH_BITS) == h && (ev = e.val) != null &&
-                    ((ek = e.key) == k || k.equals(ek)))
-                    return ev;
+    // Original (since JDK1.2) Map methods
+
+    /**
+     * {@inheritDoc}
+     */
+    public int size() {
+        long n = sumCount();
+        return ((n < 0L) ? 0 :
+            (n > (long)Integer.MAX_VALUE) ? Integer.MAX_VALUE :
+                (int)n);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public boolean isEmpty() {
+        return sumCount() <= 0L; // ignore transient negative values
+    }
+
+    /**
+     * Returns the value to which the specified key is mapped,
+     * or {@code null} if this map contains no mapping for the key.
+     *
+     * <p>More formally, if this map contains a mapping from a key
+     * {@code k} to a value {@code v} such that {@code key.equals(k)},
+     * then this method returns {@code v}; otherwise it returns
+     * {@code null}.  (There can be at most one such mapping.)
+     *
+     * @throws NullPointerException if the specified key is null
+     */
+    public V get(Object key) {
+        Node<K,V>[] tab; Node<K,V> e, p; int n, eh; K ek;
+        int h = spread(key.hashCode());
+        if ((tab = table) != null && (n = tab.length) > 0 &&
+            (e = tabAt(tab, (n - 1) & h)) != null) {
+            if ((eh = e.hash) == h) {
+                if ((ek = e.key) == key || (ek != null && key.equals(ek)))
+                    return e.val;
+            }
+            else if (eh < 0)
+                return (p = e.find(h, key)) != null ? p.val : null;
+            while ((e = e.next) != null) {
+                if (e.hash == h &&
+                    ((ek = e.key) == key || (ek != null && key.equals(ek))))
+                    return e.val;
             }
-            break;
         }
         return null;
     }
 
     /**
-     * Implementation for the four public remove/replace methods:
-     * Replaces node value with v, conditional upon match of cv if
-     * non-null.  If resulting value is null, delete.
+     * Tests if the specified object is a key in this table.
+     *
+     * @param  key possible key
+     * @return {@code true} if and only if the specified object
+     *         is a key in this table, as determined by the
+     *         {@code equals} method; {@code false} otherwise
+     * @throws NullPointerException if the specified key is null
      */
-    private final Object internalReplace(Object k, Object v, Object cv) {
-        int h = spread(k.hashCode());
-        Object oldVal = null;
-        for (Node[] tab = table;;) {
-            Node f; int i, fh; Object fk;
-            if (tab == null ||
-                (f = tabAt(tab, i = (tab.length - 1) & h)) == null)
-                break;
-            else if ((fh = f.hash) == MOVED) {
-                if ((fk = f.key) instanceof TreeBin) {
-                    TreeBin t = (TreeBin)fk;
-                    boolean validated = false;
-                    boolean deleted = false;
-                    t.acquire(0);
-                    try {
-                        if (tabAt(tab, i) == f) {
-                            validated = true;
-                            TreeNode p = t.getTreeNode(h, k, t.root);
-                            if (p != null) {
-                                Object pv = p.val;
-                                if (cv == null || cv == pv || cv.equals(pv)) {
-                                    oldVal = pv;
-                                    if ((p.val = v) == null) {
-                                        deleted = true;
-                                        t.deleteTreeNode(p);
-                                    }
-                                }
-                            }
-                        }
-                    } finally {
-                        t.release(0);
-                    }
-                    if (validated) {
-                        if (deleted)
-                            counter.add(-1L);
-                        break;
-                    }
-                }
-                else
-                    tab = (Node[])fk;
-            }
-            else if ((fh & HASH_BITS) != h && f.next == null) // precheck
-                break;                          // rules out possible existence
-            else if ((fh & LOCKED) != 0) {
-                checkForResize();               // try resizing if can't get lock
-                f.tryAwaitLock(tab, i);
-            }
-            else if (f.casHash(fh, fh | LOCKED)) {
-                boolean validated = false;
-                boolean deleted = false;
-                try {
-                    if (tabAt(tab, i) == f) {
-                        validated = true;
-                        for (Node e = f, pred = null;;) {
-                            Object ek, ev;
-                            if ((e.hash & HASH_BITS) == h &&
-                                ((ev = e.val) != null) &&
-                                ((ek = e.key) == k || k.equals(ek))) {
-                                if (cv == null || cv == ev || cv.equals(ev)) {
-                                    oldVal = ev;
-                                    if ((e.val = v) == null) {
-                                        deleted = true;
-                                        Node en = e.next;
-                                        if (pred != null)
-                                            pred.next = en;
-                                        else
-                                            setTabAt(tab, i, en);
-                                    }
-                                }
-                                break;
-                            }
-                            pred = e;
-                            if ((e = e.next) == null)
-                                break;
-                        }
-                    }
-                } finally {
-                    if (!f.casHash(fh | LOCKED, fh)) {
-                        f.hash = fh;
-                        synchronized (f) { f.notifyAll(); };
-                    }
-                }
-                if (validated) {
-                    if (deleted)
-                        counter.add(-1L);
-                    break;
-                }
+    public boolean containsKey(Object key) {
+        return get(key) != null;
+    }
+
+    /**
+     * Returns {@code true} if this map maps one or more keys to the
+     * specified value. Note: This method may require a full traversal
+     * of the map, and is much slower than method {@code containsKey}.
+     *
+     * @param value value whose presence in this map is to be tested
+     * @return {@code true} if this map maps one or more keys to the
+     *         specified value
+     * @throws NullPointerException if the specified value is null
+     */
+    public boolean containsValue(Object value) {
+        if (value == null)
+            throw new NullPointerException();
+        Node<K,V>[] t;
+        if ((t = table) != null) {
+            Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
+            for (Node<K,V> p; (p = it.advance()) != null; ) {
+                V v;
+                if ((v = p.val) == value || (v != null && value.equals(v)))
+                    return true;
             }
         }
-        return oldVal;
+        return false;
     }
 
-    /*
-     * Internal versions of the six insertion methods, each a
-     * little more complicated than the last. All have
-     * the same basic structure as the first (internalPut):
-     *  1. If table uninitialized, create
-     *  2. If bin empty, try to CAS new node
-     *  3. If bin stale, use new table
-     *  4. if bin converted to TreeBin, validate and relay to TreeBin methods
-     *  5. Lock and validate; if valid, scan and add or update
+    /**
+     * Maps the specified key to the specified value in this table.
+     * Neither the key nor the value can be null.
      *
-     * The others interweave other checks and/or alternative actions:
-     *  * Plain put checks for and performs resize after insertion.
-     *  * putIfAbsent prescans for mapping without lock (and fails to add
-     *    if present), which also makes pre-emptive resize checks worthwhile.
-     *  * computeIfAbsent extends form used in putIfAbsent with additional
-     *    mechanics to deal with, calls, potential exceptions and null
-     *    returns from function call.
-     *  * compute uses the same function-call mechanics, but without
-     *    the prescans
-     *  * merge acts as putIfAbsent in the absent case, but invokes the
-     *    update function if present
-     *  * putAll attempts to pre-allocate enough table space
-     *    and more lazily performs count updates and checks.
+     * <p>The value can be retrieved by calling the {@code get} method
+     * with a key that is equal to the original key.
      *
-     * Someday when details settle down a bit more, it might be worth
-     * some factoring to reduce sprawl.
+     * @param key key with which the specified value is to be associated
+     * @param value value to be associated with the specified key
+     * @return the previous value associated with {@code key}, or
+     *         {@code null} if there was no mapping for {@code key}
+     * @throws NullPointerException if the specified key or value is null
      */
+    public V put(K key, V value) {
+        return putVal(key, value, false);
+    }
 
-    /** Implementation for put */
-    private final Object internalPut(Object k, Object v) {
-        int h = spread(k.hashCode());
-        int count = 0;
-        for (Node[] tab = table;;) {
-            int i; Node f; int fh; Object fk;
-            if (tab == null)
+    /** Implementation for put and putIfAbsent */
+    final V putVal(K key, V value, boolean onlyIfAbsent) {
+        if (key == null || value == null) throw new NullPointerException();
+        int hash = spread(key.hashCode());
+        int binCount = 0;
+        for (Node<K,V>[] tab = table;;) {
+            Node<K,V> f; int n, i, fh;
+            if (tab == null || (n = tab.length) == 0)
                 tab = initTable();
-            else if ((f = tabAt(tab, i = (tab.length - 1) & h)) == null) {
-                if (casTabAt(tab, i, null, new Node(h, k, v, null)))
+            else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
+                if (casTabAt(tab, i, null,
+                             new Node<K,V>(hash, key, value, null)))
                     break;                   // no lock when adding to empty bin
             }
-            else if ((fh = f.hash) == MOVED) {
-                if ((fk = f.key) instanceof TreeBin) {
-                    TreeBin t = (TreeBin)fk;
-                    Object oldVal = null;
-                    t.acquire(0);
-                    try {
-                        if (tabAt(tab, i) == f) {
-                            count = 2;
-                            TreeNode p = t.putTreeNode(h, k, v);
-                            if (p != null) {
-                                oldVal = p.val;
-                                p.val = v;
-                            }
-                        }
-                    } finally {
-                        t.release(0);
-                    }
-                    if (count != 0) {
-                        if (oldVal != null)
-                            return oldVal;
-                        break;
-                    }
-                }
-                else
-                    tab = (Node[])fk;
-            }
-            else if ((fh & LOCKED) != 0) {
-                checkForResize();
-                f.tryAwaitLock(tab, i);
-            }
-            else if (f.casHash(fh, fh | LOCKED)) {
-                Object oldVal = null;
-                try {                        // needed in case equals() throws
+            else if ((fh = f.hash) == MOVED)
+                tab = helpTransfer(tab, f);
+            else {
+                V oldVal = null;
+                synchronized (f) {
                     if (tabAt(tab, i) == f) {
-                        count = 1;
-                        for (Node e = f;; ++count) {
-                            Object ek, ev;
-                            if ((e.hash & HASH_BITS) == h &&
-                                (ev = e.val) != null &&
-                                ((ek = e.key) == k || k.equals(ek))) {
-                                oldVal = ev;
-                                e.val = v;
-                                break;
+                        if (fh >= 0) {
+                            binCount = 1;
+                            for (Node<K,V> e = f;; ++binCount) {
+                                K ek;
+                                if (e.hash == hash &&
+                                    ((ek = e.key) == key ||
+                                        (ek != null && key.equals(ek)))) {
+                                    oldVal = e.val;
+                                    if (!onlyIfAbsent)
+                                        e.val = value;
+                                    break;
+                                }
+                                Node<K,V> pred = e;
+                                if ((e = e.next) == null) {
+                                    pred.next = new Node<K,V>(hash, key,
+                                                              value, null);
+                                    break;
+                                }
                             }
-                            Node last = e;
-                            if ((e = e.next) == null) {
-                                last.next = new Node(h, k, v, null);
-                                if (count >= TREE_THRESHOLD)
-                                    replaceWithTreeBin(tab, i, k);
-                                break;
+                        }
+                        else if (f instanceof TreeBin) {
+                            Node<K,V> p;
+                            binCount = 2;
+                            if ((p = ((TreeBin<K,V>)f).putTreeVal(hash, key,
+                                                                  value)) != null) {
+                                oldVal = p.val;
+                                if (!onlyIfAbsent)
+                                    p.val = value;
                             }
                         }
                     }
-                } finally {                  // unlock and signal if needed
-                    if (!f.casHash(fh | LOCKED, fh)) {
-                        f.hash = fh;
-                        synchronized (f) { f.notifyAll(); };
-                    }
                 }
-                if (count != 0) {
+                if (binCount != 0) {
+                    if (binCount >= TREEIFY_THRESHOLD)
+                        treeifyBin(tab, i);
                     if (oldVal != null)
                         return oldVal;
-                    if (tab.length <= 64)
-                        count = 2;
                     break;
                 }
             }
         }
-        counter.add(1L);
-        if (count > 1)
-            checkForResize();
+        addCount(1L, binCount);
         return null;
     }
 
-    /** Implementation for putIfAbsent */
-    private final Object internalPutIfAbsent(Object k, Object v) {
-        int h = spread(k.hashCode());
-        int count = 0;
-        for (Node[] tab = table;;) {
-            int i; Node f; int fh; Object fk, fv;
-            if (tab == null)
-                tab = initTable();
-            else if ((f = tabAt(tab, i = (tab.length - 1) & h)) == null) {
-                if (casTabAt(tab, i, null, new Node(h, k, v, null)))
-                    break;
-            }
-            else if ((fh = f.hash) == MOVED) {
-                if ((fk = f.key) instanceof TreeBin) {
-                    TreeBin t = (TreeBin)fk;
-                    Object oldVal = null;
-                    t.acquire(0);
-                    try {
-                        if (tabAt(tab, i) == f) {
-                            count = 2;
-                            TreeNode p = t.putTreeNode(h, k, v);
-                            if (p != null)
-                                oldVal = p.val;
-                        }
-                    } finally {
-                        t.release(0);
-                    }
-                    if (count != 0) {
-                        if (oldVal != null)
-                            return oldVal;
-                        break;
-                    }
-                }
-                else
-                    tab = (Node[])fk;
-            }
-            else if ((fh & HASH_BITS) == h && (fv = f.val) != null &&
-                ((fk = f.key) == k || k.equals(fk)))
-                return fv;
-            else {
-                Node g = f.next;
-                if (g != null) { // at least 2 nodes -- search and maybe resize
-                    for (Node e = g;;) {
-                        Object ek, ev;
-                        if ((e.hash & HASH_BITS) == h && (ev = e.val) != null &&
-                            ((ek = e.key) == k || k.equals(ek)))
-                            return ev;
-                        if ((e = e.next) == null) {
-                            checkForResize();
-                            break;
-                        }
-                    }
-                }
-                if (((fh = f.hash) & LOCKED) != 0) {
-                    checkForResize();
-                    f.tryAwaitLock(tab, i);
-                }
-                else if (tabAt(tab, i) == f && f.casHash(fh, fh | LOCKED)) {
-                    Object oldVal = null;
-                    try {
-                        if (tabAt(tab, i) == f) {
-                            count = 1;
-                            for (Node e = f;; ++count) {
-                                Object ek, ev;
-                                if ((e.hash & HASH_BITS) == h &&
-  

<TRUNCATED>


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