http://git-wip-us.apache.org/repos/asf/incubator-ignite/blob/8203caf7/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 727db4c..041130b 100644 --- a/modules/core/src/main/java/org/jsr166/ConcurrentHashMap8.java +++ b/modules/core/src/main/java/org/jsr166/ConcurrentHashMap8.java @@ -5,22 +5,20 @@ */ /* - * 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 + * The latest version of the file was copied from the following CVS repository: + * http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/ * - * 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. + * Corresponding commit version in CVS repository is unknown (lost in our side). + * On the other hand we can't simply synch the latest version from CVS here, because Ignite uses functionality that + * is no longer supported. */ - 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 @@ -74,15 +72,21 @@ import java.lang.reflect.*; * 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. To ameliorate impact, when keys are {@link Comparable}, - * this class may use comparison order among keys to help break ties. + * hash table. * - * <p>A {@link Set} projection of a ConcurrentHashMap may be created + * <p>A {@link Set} projection of a ConcurrentHashMapV8 may be created * (using {@link #newKeySet()} or {@link #newKeySet(int)}), or viewed * (using {@link #keySet(Object)} when only keys are of interest, and the * mapped values are (perhaps transiently) not used or all take the * same mapping value. * + * <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. @@ -90,9 +94,90 @@ import java.lang.reflect.*; * <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. * - * <p>This class is a member of the - * <a href="{@docRoot}/../technotes/guides/collections/index.html"> - * Java Collections Framework</a>. + * <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> * * @since 1.5 * @author Doug Lea @@ -100,9 +185,80 @@ import java.lang.reflect.*; * @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: * @@ -113,21 +269,18 @@ public class ConcurrentHashMap8<K,V> implements ConcurrentMap<K,V>, Serializable * the same or better than java.util.HashMap, and to support high * initial insertion rates on an empty table by many threads. * - * 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.) + * 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. * * The table is lazily initialized to a power-of-two size upon the * first insertion. Each bin in the table normally contains a @@ -135,12 +288,24 @@ public class ConcurrentHashMap8<K,V> implements ConcurrentMap<K,V>, Serializable * 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. + * (sun.misc.Unsafe) operations. The lists of nodes within bins + * are always accurately traversable under volatile reads, so long + * as lookups check hash code and non-nullness of value before + * checking key equality. * - * We use the top (sign) bit of Node hash fields for control - * purposes -- it is available anyway because of addressing - * constraints. Nodes with negative hash fields are specially - * handled or ignored in map methods. + * 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 + * + * 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). * * 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 @@ -149,15 +314,22 @@ public class ConcurrentHashMap8<K,V> implements ConcurrentMap<K,V>, Serializable * delete, and replace) require locks. We do not want to waste * the space required to associate a distinct lock object with * each bin, so instead use the first node of a bin list itself as - * a lock. Locking support for these locks relies on builtin - * "synchronized" monitors. + * 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. * * 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). + * or the bin becomes invalidated (upon resizing). However, + * operations that only conditionally update may inspect nodes + * until the point of update. This is a converse of sorts to the + * lazy locking technique described by Herlihy & Shavit. * * The main disadvantage of per-bin locks is that other update * operations on other nodes in a bin list protected by the same @@ -190,12 +362,15 @@ public class ConcurrentHashMap8<K,V> implements ConcurrentMap<K,V>, Serializable * 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 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 + * designed to have identical hash codes. Also, although we guard + * against the worst effects of this (see method spread), sets of + * hashes may differ only in bits that do not impact their bin + * index for a given power-of-two mask. So we use a secondary + * strategy that applies when the number of nodes in a bin exceeds + * a threshold, and at least one of the keys implements + * Comparable. These TreeBins use a balanced tree to hold nodes + * (a specialized form of red-black trees), bounding search time + * to O(log N). Each search step in a TreeBin is around twice as * slow as in a regular list, but given that N cannot exceed * (1<<64) (before running out of addresses) this bounds search * steps, lock hold times, etc, to reasonable constants (roughly @@ -206,50 +381,43 @@ public class ConcurrentHashMap8<K,V> implements ConcurrentMap<K,V>, Serializable * iterators in the same way. * * The table is resized when occupancy exceeds a percentage - * threshold (nominally, 0.75, but see below). Any thread - * noticing an overfull bin may assist in resizing after the - * initiating thread allocates and sets up the replacement array. - * However, rather than stalling, these other threads may proceed - * with insertions etc. The use of TreeBins shields us from the - * worst case effects of overfilling while resizes are in - * progress. Resizing proceeds by transferring bins, one by one, - * from the table to the next table. 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.) + * 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. * * The traversal scheme also applies to partial traversals of * ranges of bins (via an alternate Traverser constructor) @@ -264,54 +432,20 @@ public class ConcurrentHashMap8<K,V> implements ConcurrentMap<K,V>, Serializable * These cases attempt to override the initial capacity settings, * but harmlessly fail to take effect in cases of races. * - * The element count is maintained using a specialization of - * LongAdder. We need to incorporate a specialization rather than - * just use a LongAdder in order to access implicit - * contention-sensing that leads to creation of multiple - * CounterCells. The counter mechanics avoid contention on - * updates but can encounter cache thrashing if read too - * frequently during concurrent access. To avoid reading so often, - * resizing under contention is attempted only upon adding to a - * bin already holding two or more nodes. Under uniform hash - * distributions, the probability of this occurring at threshold - * is around 13%, meaning that only about 1 in 8 puts check - * threshold (and after resizing, many fewer do so). - * - * 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. + * 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. * * Maintaining API and serialization compatibility with previous * versions of this class introduces several oddities. Mainly: We @@ -321,20 +455,8 @@ public class ConcurrentHashMap8<K,V> implements ConcurrentMap<K,V>, Serializable * 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 -------------- */ /** @@ -374,2362 +496,2737 @@ public class ConcurrentHashMap8<K,V> implements ConcurrentMap<K,V>, Serializable private static final float LOAD_FACTOR = 0.75f; /** - * 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. + * The buffer size for skipped bins during transfers. The + * value is arbitrary but should be large enough to avoid + * most locking stalls during resizes. */ - static final int TREEIFY_THRESHOLD = 8; + private static final int TRANSFER_BUFFER_SIZE = 32; /** - * 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. + * 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. */ - static final int UNTREEIFY_THRESHOLD = 6; + private static final int TREE_THRESHOLD = 8; - /** - * 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. + /* + * Encodings for special uses of Node hash fields. See above for + * explanation. */ - static final int MIN_TREEIFY_CAPACITY = 64; + 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 - /** - * Minimum number of rebinnings per transfer step. Ranges are - * subdivided to allow multiple resizer threads. This value - * serves as a lower bound to avoid resizers encountering - * excessive memory contention. The value should be at least - * DEFAULT_CAPACITY. - */ - private static final int MIN_TRANSFER_STRIDE = 16; + /* ---------------- Fields -------------- */ /** - * The number of bits used for generation stamp in sizeCtl. - * Must be at least 6 for 32bit arrays. + * The array of bins. Lazily initialized upon first insertion. + * Size is always a power of two. Accessed directly by iterators. */ - private static int RESIZE_STAMP_BITS = 16; + transient volatile Node[] table; /** - * The maximum number of threads that can help resize. - * Must fit in 32 - RESIZE_STAMP_BITS bits. + * The counter maintaining number of elements. */ - private static final int MAX_RESIZERS = (1 << (32 - RESIZE_STAMP_BITS)) - 1; + private transient final LongAdder8 counter; /** - * The bit shift for recording size stamp in sizeCtl. + * 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. */ - private static final int RESIZE_STAMP_SHIFT = 32 - RESIZE_STAMP_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; + + /* ---------------- Table element access -------------- */ /* - * Encodings for Node hash fields. See above for explanation. + * 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. */ - 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 - /** Number of CPUS, to place bounds on some sizings */ - static final int NCPU = Runtime.getRuntime().availableProcessors(); + 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); + } - /** For serialization compatibility. */ - private static final ObjectStreamField[] serialPersistentFields = { - new ObjectStreamField("segments", Segment[].class), - new ObjectStreamField("segmentMask", Integer.TYPE), - new ObjectStreamField("segmentShift", Integer.TYPE) - }; + private static final void setTabAt(Node[] tab, int i, Node v) { + UNSAFE.putObjectVolatile(tab, ((long)i<<ASHIFT)+ABASE, v); + } /* ---------------- Nodes -------------- */ /** - * 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. + * Key-value entry. Note that this is never exported out as a + * user-visible Map.Entry (see MapEntry below). Nodes with a hash + * field of MOVED are special, and do not contain user keys or + * values. Otherwise, keys are never null, and null val fields + * indicate that a node is in the process of being deleted or + * created. For purposes of read-only access, a key may be read + * before a val, but can only be used after checking val to be + * non-null. */ - static class Node<K,V> implements Map.Entry<K,V> { - final int hash; - final K key; - volatile V val; - Node<K,V> next; + static class Node { + volatile int hash; + final Object key; + volatile Object val; + volatile Node next; - Node(int hash, K key, V val, Node<K,V> next) { + Node(int hash, Object key, Object val, Node next) { this.hash = hash; this.key = key; this.val = val; this.next = next; } - 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(); + /** CompareAndSet the hash field */ + final boolean casHash(int cmp, int val) { + return UNSAFE.compareAndSwapInt(this, hashOffset, cmp, val); } - 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))); - } + /** The number of spins before blocking for a lock */ + static final int MAX_SPINS = + Runtime.getRuntime().availableProcessors() > 1 ? 64 : 1; /** - * Virtualized support for map.get(); overridden in subclasses. + * 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. */ - 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); + 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; + } + } } - return null; } - } - /* ---------------- Static utilities -------------- */ - - /** - * 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; - } + // Unsafe mechanics for casHash + private static final sun.misc.Unsafe UNSAFE; + private static final long hashOffset; - /** - * 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; - } + static { + try { + UNSAFE = getUnsafe(); + Class<?> k = Node.class; + hashOffset = UNSAFE.objectFieldOffset + (k.getDeclaredField("hash")); + } catch (Exception e) { + throw new Error(e); } } - return null; - } - - /** - * Returns k.compareTo(x) if x matches kc (k's screened comparable - * class), else 0. - */ - @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)); - } - - /* ---------------- 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 -------------- */ - - /** - * 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; + /* ---------------- TreeBins -------------- */ /** - * The next table to use; non-null only while resizing. + * Nodes for use in TreeBins */ - private transient volatile Node<K,V>[] nextTable; + 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; - /** - * 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; + TreeNode(int hash, Object key, Object val, Node next, TreeNode parent) { + super(hash, key, val, next); + this.parent = parent; + } + } /** - * 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; + * 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 next table index (plus one) to split while resizing. - */ - private transient volatile int transferIndex; + /** 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; + } + } - /** - * Spinlock (locked via CAS) used when resizing and/or creating CounterCells. - */ - private transient volatile int cellsBusy; + /** 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; + } + } - /** - * Table of counter cells. When non-null, size is a power of 2. - */ - private transient volatile CounterCell[] counterCells; + /** + * 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; + } - // views - private transient KeySetView<K,V> keySet; - private transient ValuesView<K,V> values; - private transient EntrySetView<K,V> entrySet; + /** + * 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; + } + /** + * 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; + } - /* ---------------- Public operations -------------- */ + 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; + } - /** - * Creates a new, empty map with the default initial table size (16). - */ - public ConcurrentHashMap8() { - } - - /** - * 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; - } - - /** - * Creates a new map with the same mappings as the given map. - * - * @param m the map - */ - public ConcurrentHashMap8(Map<? extends K, ? extends V> m) { - this.sizeCtl = DEFAULT_CAPACITY; - putAll(m); + /** + * 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; + } + } } - /** - * Creates a new, empty map with an initial table size based on - * the given number of elements ({@code initialCapacity}) and - * initial table density ({@code loadFactor}). - * - * @param initialCapacity the initial capacity. The implementation - * performs internal sizing to accommodate this many elements, - * given the specified load factor. - * @param loadFactor the load factor (table density) for - * establishing the initial table size - * @throws IllegalArgumentException if the initial capacity of - * elements is negative or the load factor is nonpositive - * - * @since 1.6 - */ - public ConcurrentHashMap8(int initialCapacity, float loadFactor) { - this(initialCapacity, loadFactor, 1); - } + /* ---------------- Collision reduction 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 + * 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. */ - 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; + private static final int spread(int h) { + h ^= (h >>> 18) ^ (h >>> 12); + return (h ^ (h >>> 10)) & HASH_BITS; } - // Original (since JDK1.2) Map methods - /** - * {@inheritDoc} + * 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. */ - public int size() { - long n = sumCount(); - return ((n < 0L) ? 0 : - (n > (long)Integer.MAX_VALUE) ? Integer.MAX_VALUE : - (int)n); + 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)); + } } - /** - * {@inheritDoc} - */ - public boolean isEmpty() { - return sumCount() <= 0L; // ignore transient negative values - } + /* ---------------- Internal access and update methods -------------- */ - /** - * 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; + /** 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; } + break; } return null; } /** - * Tests if the specified object is a key in this table. - * - * @param key possible key - * @return {@code true} if and only if the specified object - * is a key in this table, as determined by the - * {@code equals} method; {@code false} otherwise - * @throws NullPointerException if the specified key is null - */ - public boolean containsKey(Object key) { - return 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 + * 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. */ - 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; + 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; + } } } - return false; + return oldVal; } - /** - * Maps the specified key to the specified value in this table. - * Neither the key nor the value can be null. + /* + * 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 * - * <p>The value can be retrieved by calling the {@code get} method - * with a key that is equal to the original key. + * 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. * - * @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 + * Someday when details settle down a bit more, it might be worth + * some factoring to reduce sprawl. */ - public V put(K key, V value) { - return putVal(key, value, false); - } - /** 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) + /** 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) tab = initTable(); - else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) { - if (casTabAt(tab, i, null, - new Node<K,V>(hash, key, value, null))) + else if ((f = tabAt(tab, i = (tab.length - 1) & h)) == null) { + if (casTabAt(tab, i, null, new Node(h, k, v, null))) break; // no lock when adding to empty bin } - else if ((fh = f.hash) == MOVED) - tab = helpTransfer(tab, f); - else { - V oldVal = null; - synchronized (f) { - if (tabAt(tab, i) == f) { - 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; - } + 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; } } - 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 { + 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 + 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; + } + 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; } } } + } finally { // unlock and signal if needed + if (!f.casHash(fh | LOCKED, fh)) { + f.hash = fh; + synchronized (f) { f.notifyAll(); }; + } } - if (binCount != 0) { - if (binCount >= TREEIFY_THRESHOLD) - treeifyBin(tab, i); + if (count != 0) { if (oldVal != null) return oldVal; + if (tab.length <= 64) + count = 2; break; } } } - addCount(1L, binCount); + counter.add(1L); + if (count > 1) + checkForResize(); return null; } - /** - * Copies all of the mappings from the specified map to this one. - * These mappings replace any mappings that this map had for any of the - * keys currently in the specified map. - * - * @param m mappings to be stored in this map - */ - public void putAll(Map<? extends K, ? extends V> m) { - tryPresize(m.size()); - for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) - putVal(e.getKey(), e.getValue(), false); - } - - /** - * Removes the key (and its corresponding value) from this map. - * This method does nothing if the key is not in the map. - * - * @param key the key that needs to be removed - * @return the previous value associated with {@code key}, or - * {@code null} if there was no mapping for {@code key} - * @throws NullPointerException if the specified key is null - */ - public V remove(Object key) { - return replaceNode(key, null, 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)
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