You are viewing a plain text version of this content. The canonical link for it is here.
Posted to commits@ignite.apache.org by sb...@apache.org on 2015/06/12 15:39:49 UTC
[15/50] [abbrv] incubator-ignite git commit: ignite-sprint-6: merge
from ignite-545
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>