--- jsr166/src/jsr166e/ConcurrentHashMapV8.java 2011/08/28 19:08:07 1.1
+++ jsr166/src/jsr166e/ConcurrentHashMapV8.java 2013/01/28 17:27:03 1.92
@@ -5,7 +5,9 @@
*/
package jsr166e;
-import jsr166e.LongAdder;
+
+import java.util.Comparator;
+import java.util.Arrays;
import java.util.Map;
import java.util.Set;
import java.util.Collection;
@@ -19,6 +21,9 @@ import java.util.Enumeration;
import java.util.ConcurrentModificationException;
import java.util.NoSuchElementException;
import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.locks.AbstractQueuedSynchronizer;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
import java.io.Serializable;
/**
@@ -33,73 +38,251 @@ import java.io.Serializable;
* interoperable with {@code Hashtable} in programs that rely on its
* thread safety but not on its synchronization details.
*
- * Retrieval operations (including {@code get}) generally do not
+ *
Retrieval operations (including {@code get}) generally do not
* block, so may overlap with update operations (including {@code put}
* and {@code remove}). Retrievals reflect the results of the most
* recently completed update operations holding upon their
- * onset. For aggregate operations such as {@code putAll} and {@code
- * clear}, concurrent retrievals may reflect insertion or removal of
- * only some entries. Similarly, Iterators and Enumerations return
- * elements reflecting the state of the hash table at some point at or
- * since the creation of the iterator/enumeration. They do
- * not throw {@link ConcurrentModificationException}.
- * However, iterators are designed to be used by only one thread at a
- * time. Bear in mind that the results of aggregate status methods
- * including {@code size}, {@code isEmpty}, and {@code containsValue}
- * are typically useful only when a map is not undergoing concurrent
- * updates in other threads. Otherwise the results of these methods
- * reflect transient states that may be adequate for monitoring
- * purposes, but not for program control.
- *
- *
Resizing this or any other kind of hash table is a relatively
- * slow operation, so, when possible, it is a good idea to provide
- * estimates of expected table sizes in constructors. Also, for
- * compatability with previous versions of this class, constructors
- * may optionally specify an expected {@code concurrencyLevel} as an
- * additional hint for internal sizing.
+ * onset. (More formally, an update operation for a given key bears a
+ * happens-before relation with any (non-null) retrieval for
+ * that key reporting the updated value.) For aggregate operations
+ * such as {@code putAll} and {@code clear}, concurrent retrievals may
+ * reflect insertion or removal of only some entries. Similarly,
+ * Iterators and Enumerations return elements reflecting the state of
+ * the hash table at some point at or since the creation of the
+ * iterator/enumeration. They do not throw {@link
+ * ConcurrentModificationException}. However, iterators are designed
+ * to be used by only one thread at a time. Bear in mind that the
+ * results of aggregate status methods including {@code size}, {@code
+ * isEmpty}, and {@code containsValue} are typically useful only when
+ * a map is not undergoing concurrent updates in other threads.
+ * Otherwise the results of these methods reflect transient states
+ * that may be adequate for monitoring or estimation purposes, but not
+ * for program control.
+ *
+ *
The table is dynamically expanded when there are too many
+ * collisions (i.e., keys that have distinct hash codes but fall into
+ * the same slot modulo the table size), with the expected average
+ * effect of maintaining roughly two bins per mapping (corresponding
+ * to a 0.75 load factor threshold for resizing). There may be much
+ * variance around this average as mappings are added and removed, but
+ * overall, this maintains a commonly accepted time/space tradeoff for
+ * hash tables. However, resizing this or any other kind of hash
+ * table may be a relatively slow operation. When possible, it is a
+ * good idea to provide a size estimate as an optional {@code
+ * initialCapacity} constructor argument. An additional optional
+ * {@code loadFactor} constructor argument provides a further means of
+ * customizing initial table capacity by specifying the table density
+ * to be used in calculating the amount of space to allocate for the
+ * given number of elements. Also, for compatibility with previous
+ * versions of this class, constructors may optionally specify an
+ * 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.
+ *
+ *
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.
+ *
+ *
A ConcurrentHashMapV8 can be used as scalable frequency map (a
+ * form of histogram or multiset) by using {@link LongAdder} values
+ * and initializing via {@link #computeIfAbsent}. For example, to add
+ * a count to a {@code ConcurrentHashMapV8 freqs}, you
+ * can use {@code freqs.computeIfAbsent(k -> new
+ * LongAdder()).increment();}
*
* This class and its views and iterators implement all of the
* optional methods of the {@link Map} and {@link Iterator}
* interfaces.
*
- *
Like {@link Hashtable} but unlike {@link HashMap}, this class
+ *
Like {@link Hashtable} but unlike {@link HashMap}, this class
* does not allow {@code null} to be used as a key or value.
*
+ *
ConcurrentHashMapV8s support sequential and parallel operations
+ * bulk operations. (Parallel forms use the {@link
+ * ForkJoinPool#commonPool()}). Tasks that may be used in other
+ * contexts are available in class {@link ForkJoinTasks}. These
+ * operations are designed to be safely, and often sensibly, applied
+ * even with maps that are being concurrently updated by other
+ * threads; for example, when computing a snapshot summary of the
+ * values in a shared registry. There are three kinds of operation,
+ * each with four forms, accepting functions with Keys, Values,
+ * Entries, and (Key, Value) arguments and/or return values. Because
+ * the elements of a ConcurrentHashMapV8 are not ordered in any
+ * particular way, and may be processed in different orders in
+ * different parallel executions, the correctness of supplied
+ * functions should not depend on any ordering, or on any other
+ * objects or values that may transiently change while computation is
+ * in progress; and except for forEach actions, should ideally be
+ * side-effect-free.
+ *
+ *
+ * - forEach: Perform a given action on each element.
+ * A variant form applies a given transformation on each element
+ * before performing the action.
+ *
+ * - search: Return the first available non-null result of
+ * applying a given function on each element; skipping further
+ * search when a result is found.
+ *
+ * - 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:
+ *
+ *
+ *
+ * - Plain reductions. (There is not a form of this method for
+ * (key, value) function arguments since there is no corresponding
+ * return type.)
+ *
+ * - Mapped reductions that accumulate the results of a given
+ * function applied to each element.
+ *
+ * - Reductions to scalar doubles, longs, and ints, using a
+ * given basis value.
+ *
+ *
+ *
+ *
+ *
+ * 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.
+ *
+ *
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.
+ *
+ *
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)}.
+ *
+ *
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.
+ *
+ *
Speedups for parallel compared to sequential forms are common
+ * but not guaranteed. Parallel operations involving brief functions
+ * on small maps may execute more slowly than sequential forms 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.
+ *
+ *
All arguments to all task methods must be non-null.
+ *
+ *
jsr166e note: During transition, this class
+ * uses nested functional interfaces with different names but the
+ * same forms as those expected for JDK8.
+ *
*
This class is a member of the
*
* Java Collections Framework.
*
- *
jsr166e note: This class is a candidate replacement for
- * java.util.concurrent.ConcurrentHashMap.
- *
* @since 1.5
* @author Doug Lea
* @param the type of keys maintained by this map
* @param the type of mapped values
*/
public class ConcurrentHashMapV8
- implements ConcurrentMap, Serializable {
+ implements ConcurrentMap, Serializable {
private static final long serialVersionUID = 7249069246763182397L;
/**
- * A function computing a mapping from the given key to a value,
- * or null if there is no mapping. This is a
- * place-holder for an upcoming JDK8 interface.
- */
- public static interface MappingFunction {
- /**
- * Returns a value for the given key, or null if there is no
- * mapping. If this function throws an (unchecked) exception,
- * the exception is rethrown to its caller, and no mapping is
- * recorded. Because this function is invoked within
- * atomicity control, the computation should be short and
- * simple. The most common usage is to construct a new object
- * serving as an initial mapped value.
+ * 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.
+ *
+ * This interface exports a subset of expected JDK8
+ * functionality.
+ *
+ *
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.
+ *
+ *
+ * {@code ConcurrentHashMapV8 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 {
+ * final Spliterator s;
+ * final int split; // split while > 1
+ * final SumValues nextJoin; // records forked subtasks to join
+ * SumValues(Spliterator 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;
+ * }
+ * }
+ * }
+ */
+ public static interface Spliterator extends Iterator {
+ /**
+ * 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 not 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.
*
- * @param key the (non-null) key
- * @return a value, or null if none
+ * @return a Spliterator covering approximately half of the
+ * elements
+ * @throws IllegalStateException if this Spliterator has
+ * already commenced traversing elements
*/
- V map(K key);
+ Spliterator split();
}
/*
@@ -108,194 +291,393 @@ public class ConcurrentHashMapV8
* The primary design goal of this hash table is to maintain
* concurrent readability (typically method get(), but also
* iterators and related methods) while minimizing update
- * contention.
+ * contention. Secondary goals are to keep space consumption about
+ * 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. All public generic-typed methods relay
- * in/out of these internal methods, supplying casts as needed.
+ * Each key-value mapping is held in a Node. Because Node key
+ * fields can contain special values, they are defined using plain
+ * Object types (not type "K"). This leads to a lot of explicit
+ * casting (and many explicit warning suppressions to tell
+ * compilers not to complain about it). It also allows some 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 contains a (typically
- * short) list of Nodes. 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
- * key and value before checking key equality. (All valid hash
- * codes are nonnegative. Negative values are served for special
- * nodes.)
- *
- * A bin may be locked during update (insert, delete, and replace)
- * operations. 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, using builtin
- * "synchronized" locks. These save space and we can live with
- * only plain block-structured lock/unlock operations. 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, 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.) However, update operations can and usually do
- * still traverse the bin until the point of update, which helps
- * reduce cache misses on retries. This is a converse of sorts to
- * the lazy locking technique described by Herlihy & Shavit. If
- * there is no existing node during a put operation, then one can
- * be CAS'ed in (without need for lock except in computeIfAbsent);
- * the CAS serves as validation. This is on average the most
- * common case for put operations. The expected number of locks
- * covering different elements (i.e., bins with 2 or more nodes)
- * is approximately 10% at steady state under default settings.
- * Lock contention probability for two threads accessing arbitrary
- * distinct elements is thus less than 1% even for small tables.
- *
- * The table is resized when occupancy exceeds a threshold. Only
- * a single thread performs the resize (using field "resizing", to
- * arrange exclusion), but the table otherwise remains usable for
- * both reads and updates. Resizing proceeds by transferring bins,
- * one by one, from the table to the next table. Upon transfer,
- * the old table bin contains only a special forwarding node (with
- * negative hash code ("MOVED")) that contains the next table as
- * its key. On encountering a forwarding node, access and update
- * operations restart, using the new table. To ensure concurrent
- * readability of traversals, transfers must proceed from the last
- * bin (table.length - 1) up towards the first. Any traversal
- * starting from the first bin can then arrange to move to the new
- * table for the rest of the traversal without revisiting nodes.
- * This constrains bin transfers to a particular order, and so can
- * block indefinitely waiting for the next lock, and other threads
- * cannot help with the transfer. However, expected stalls are
- * infrequent enough to not warrant the additional overhead and
- * complexity of access and iteration schemes that could admit
- * out-of-order or concurrent bin transfers.
- *
- * (While not yet implemented, a similar traversal scheme can
- * apply to partial traversals during partitioned aggregate
- * operations. Also, read-only operations give up if ever
- * forwarded to a null table, which provides support for
- * shutdown-style clearing, which is also not currently
- * implemented.)
- *
- * The element count is maintained using a LongAdder, which avoids
- * contention on updates but can encounter cache thrashing if read
- * too frequently during concurrent updates. To avoid reading so
- * often, resizing is attempted only upon adding to a bin already
- * holding two or more nodes. Under the default threshold (0.75),
- * and 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). To increase the probablity that a resize occurs soon
- * enough, we offset the threshold (see THRESHOLD_OFFSET) by the
- * expected number of puts between checks. This is currently set
- * to 8, in accord with the default load factor. In practice, this
- * is rarely overridden, and in any case is close enough to other
- * plausible values not to waste dynamic probablity computation
- * for more precision.
+ * first insertion. Each bin in the table normally contains a
+ * list of Nodes (most often, the list has only zero or one Node).
+ * 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 (sign) bit of Node hash fields for control
+ * purposes -- it is available anyway because of addressing
+ * constraints. Nodes with negative hash fields are forwarding
+ * nodes to either TreeBins or resized tables. The lower 31 bits
+ * of each normal Node's hash field contain a transformation of
+ * the key's hash code.
+ *
+ * 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
+ * by far the most common case for put operations under most
+ * key/hash distributions. Other update operations (insert,
+ * 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.
+ *
+ * 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.
+ *
+ * The main disadvantage of per-bin locks is that other update
+ * operations on other nodes in a bin list protected by the same
+ * lock can stall, for example when user equals() or mapping
+ * functions take a long time. However, statistically, under
+ * random hash codes, this is not a common problem. Ideally, the
+ * frequency of nodes in bins follows a Poisson distribution
+ * (http://en.wikipedia.org/wiki/Poisson_distribution) with a
+ * parameter of about 0.5 on average, given the resizing threshold
+ * of 0.75, although with a large variance because of resizing
+ * granularity. Ignoring variance, the expected occurrences of
+ * list size k are (exp(-0.5) * pow(0.5, k) / factorial(k)). The
+ * first values are:
+ *
+ * 0: 0.60653066
+ * 1: 0.30326533
+ * 2: 0.07581633
+ * 3: 0.01263606
+ * 4: 0.00157952
+ * 5: 0.00015795
+ * 6: 0.00001316
+ * 7: 0.00000094
+ * 8: 0.00000006
+ * more: less than 1 in ten million
+ *
+ * Lock contention probability for two threads accessing distinct
+ * elements is roughly 1 / (8 * #elements) under random hashes.
+ *
+ * Actual hash code distributions encountered in practice
+ * 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
+ * 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
+ * 100 nodes inspected per operation worst case) so long as keys
+ * are Comparable (which is very common -- String, Long, etc).
+ * TreeBin nodes (TreeNodes) also maintain the same "next"
+ * traversal pointers as regular nodes, so can be traversed in
+ * 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. To enable concurrency, the
+ * next table must be (incrementally) prefilled with place-holders
+ * serving as reverse forwarders to the old 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, 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 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. However, to
+ * ensure that no intervening nodes are skipped, bin splitting can
+ * only begin after the associated reverse-forwarders are in
+ * place.
+ *
+ * The traversal scheme also applies to partial traversals of
+ * ranges of bins (via an alternate Traverser constructor)
+ * to support partitioned aggregate operations. Also, read-only
+ * operations give up if ever forwarded to a null table, which
+ * provides support for shutdown-style clearing, which is also not
+ * currently implemented.
+ *
+ * Lazy table initialization minimizes footprint until first use,
+ * and also avoids resizings when the first operation is from a
+ * putAll, constructor with map argument, or deserialization.
+ * 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). 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
+ * leave untouched but unused constructor arguments refering to
+ * concurrencyLevel. We accept a loadFactor constructor argument,
+ * but apply it only to initial table capacity (which is the only
+ * time that we can guarantee to honor it.) We also declare an
+ * unused "Segment" class that is instantiated in minimal form
+ * only when serializing.
*/
/* ---------------- Constants -------------- */
/**
- * The smallest allowed table capacity. Must be a power of 2, at
- * least 2.
+ * The largest possible table capacity. This value must be
+ * exactly 1<<30 to stay within Java array allocation and indexing
+ * bounds for power of two table sizes, and is further required
+ * because the top two bits of 32bit hash fields are used for
+ * control purposes.
*/
- static final int MINIMUM_CAPACITY = 2;
+ private static final int MAXIMUM_CAPACITY = 1 << 30;
/**
- * The largest allowed table capacity. Must be a power of 2, at
- * most 1<<30.
+ * The default initial table capacity. Must be a power of 2
+ * (i.e., at least 1) and at most MAXIMUM_CAPACITY.
*/
- static final int MAXIMUM_CAPACITY = 1 << 30;
+ private static final int DEFAULT_CAPACITY = 16;
/**
- * The default initial table capacity. Must be a power of 2, at
- * least MINIMUM_CAPACITY and at most MAXIMUM_CAPACITY
+ * The largest possible (non-power of two) array size.
+ * Needed by toArray and related methods.
*/
- static final int DEFAULT_CAPACITY = 16;
+ static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
- * The default load factor for this table, used when not otherwise
- * specified in a constructor.
+ * The default concurrency level for this table. Unused but
+ * defined for compatibility with previous versions of this class.
*/
- static final float DEFAULT_LOAD_FACTOR = 0.75f;
+ private static final int DEFAULT_CONCURRENCY_LEVEL = 16;
/**
- * The default concurrency level for this table. Unused, but
- * defined for compatibility with previous versions of this class.
+ * The load factor for this table. Overrides of this value in
+ * constructors affect only the initial table capacity. The
+ * actual floating point value isn't normally used -- it is
+ * simpler to use expressions such as {@code n - (n >>> 2)} for
+ * the associated resizing threshold.
*/
- static final int DEFAULT_CONCURRENCY_LEVEL = 16;
+ private static final float LOAD_FACTOR = 0.75f;
/**
- * The count value to offset thesholds to compensate for checking
- * for resizing only when inserting into bins with two or more
- * elements. See above for explanation.
+ * 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 THRESHOLD_OFFSET = 8;
+ private static final int TREE_THRESHOLD = 8;
/**
- * Special node hash value indicating to use table in node.key
- * Must be negative.
+ * 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;
+
+ /*
+ * Encodings for Node hash fields. See above for explanation.
*/
- static final int MOVED = -1;
+ static final int MOVED = 0x80000000; // hash field for forwarding nodes
+ 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();
+
+ /* ---------------- Counters -------------- */
+
+ // Adapted from LongAdder and Striped64.
+ // See their internal docs for explanation.
+
+ // A padded cell for distributing counts
+ static final class CounterCell {
+ volatile long p0, p1, p2, p3, p4, p5, p6;
+ volatile long value;
+ volatile long q0, q1, q2, q3, q4, q5, q6;
+ CounterCell(long x) { value = x; }
+ }
+
+ /**
+ * Holder for the thread-local hash code determining which
+ * CounterCell to use. The code is initialized via the
+ * counterHashCodeGenerator, but may be moved upon collisions.
+ */
+ static final class CounterHashCode {
+ int code;
+ }
+
+ /**
+ * Generates initial value for per-thread CounterHashCodes
+ */
+ static final AtomicInteger counterHashCodeGenerator = new AtomicInteger();
+
+ /**
+ * Increment for counterHashCodeGenerator. See class ThreadLocal
+ * for explanation.
+ */
+ static final int SEED_INCREMENT = 0x61c88647;
+
+ /**
+ * Per-thread counter hash codes. Shared across all instances.
+ */
+ static final ThreadLocal threadCounterHashCode =
+ new ThreadLocal();
/* ---------------- Fields -------------- */
/**
* The array of bins. Lazily initialized upon first insertion.
- * Size is always a power of two. Accessed directly by inner
- * classes.
+ * Size is always a power of two. Accessed directly by iterators.
*/
- transient volatile Node[] table;
+ transient volatile Node[] table;
- /** The counter maintaining number of elements. */
- private transient final LongAdder counter;
- /** Nonzero when table is being initialized or resized. Updated via CAS. */
- private transient volatile int resizing;
- /** The target load factor for the table. */
- private transient float loadFactor;
- /** The next element count value upon which to resize the table. */
- private transient int threshold;
- /** The initial capacity of the table. */
- private transient int initCap;
+ /**
+ * The next table to use; non-null only while resizing.
+ */
+ private transient volatile Node[] nextTable;
- // views
- transient Set keySet;
- transient Set> entrySet;
- transient Collection values;
-
- /** For serialization compatability. Null unless serialized; see below */
- Segment[] segments;
+ /**
+ * 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;
/**
- * Applies a supplemental hash function to a given hashCode, which
- * defends against poor quality hash functions. The result must
- * be non-negative, and for reasonable performance must have good
- * avalanche properties; i.e., that each bit of the argument
- * affects each bit (except sign bit) of the result.
+ * 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 static final int spread(int h) {
- // Apply base step of MurmurHash; see http://code.google.com/p/smhasher/
- h ^= h >>> 16;
- h *= 0x85ebca6b;
- h ^= h >>> 13;
- h *= 0xc2b2ae35;
- return (h >>> 16) ^ (h & 0x7fffffff); // mask out sign bit
+ private transient volatile int sizeCtl;
+
+ /**
+ * The next table index (plus one) to split while resizing.
+ */
+ private transient volatile int transferIndex;
+
+ /**
+ * The least available table index to split while resizing.
+ */
+ private transient volatile int transferOrigin;
+
+ /**
+ * Spinlock (locked via CAS) used when resizing and/or creating Cells.
+ */
+ private transient volatile int counterBusy;
+
+ /**
+ * Table of counter cells. When non-null, size is a power of 2.
+ */
+ private transient volatile CounterCell[] counterCells;
+
+ // views
+ private transient KeySetView keySet;
+ private transient ValuesView values;
+ private transient EntrySetView entrySet;
+
+ /** For serialization compatibility. Null unless serialized; see below */
+ private Segment[] segments;
+
+ /* ---------------- Table element access -------------- */
+
+ /*
+ * 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.
+ */
+
+ @SuppressWarnings("unchecked") static final Node tabAt
+ (Node[] tab, int i) { // used by Traverser
+ return (Node)U.getObjectVolatile(tab, ((long)i << ASHIFT) + ABASE);
}
+ private static final boolean casTabAt
+ (Node[] tab, int i, Node c, Node v) {
+ return U.compareAndSwapObject(tab, ((long)i << ASHIFT) + ABASE, c, v);
+ }
+
+ private static final void setTabAt
+ (Node[] tab, int i, Node v) {
+ U.putObjectVolatile(tab, ((long)i << ASHIFT) + ABASE, v);
+ }
+
+ /* ---------------- Nodes -------------- */
+
/**
* Key-value entry. Note that this is never exported out as a
- * user-visible Map.Entry.
+ * 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 final class Node {
+ static class Node {
final int hash;
final Object key;
- volatile Object val;
- volatile Node next;
+ volatile V val;
+ volatile Node next;
- Node(int hash, Object key, Object val, Node next) {
+ Node(int hash, Object key, V val, Node next) {
this.hash = hash;
this.key = key;
this.val = val;
@@ -303,172 +685,615 @@ public class ConcurrentHashMapV8
}
}
- /*
- * Volatile access nethods are used for table elements as well as
- * elements of in-progress next table while resizing. Uses in
- * access and update methods 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. The only other usage is in HashIterator.advance, which
- * performs explicit checks.
+ /* ---------------- TreeBins -------------- */
+
+ /**
+ * Nodes for use in TreeBins
*/
+ 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;
- static final Node tabAt(Node[] tab, int i) { // used in HashIterator
- return (Node)UNSAFE.getObjectVolatile(tab, ((long)i< next, TreeNode parent) {
+ super(hash, key, val, next);
+ this.parent = parent;
+ }
}
- private static final boolean casTabAt(Node[] tab, int i, Node c, Node v) {
- return UNSAFE.compareAndSwapObject(tab, ((long)i<
+ * 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
- private static final void setTabAt(Node[] tab, int i, Node v) {
- UNSAFE.putObjectVolatile(tab, ((long)i< 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;
+ }
+
+ /** 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;
+ }
+ }
- /* ---------------- Access and update operations -------------- */
+ /** 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;
+ }
+ }
- /** Implements get and containsKey **/
- private final Object internalGet(Object k) {
- int h = spread(k.hashCode());
- Node[] tab = table;
- retry: while (tab != null) {
- Node e = tabAt(tab, (tab.length - 1) & h);
- while (e != null) {
- int eh = e.hash;
- if (eh == h) {
- Object ek = e.key, ev = e.val;
- if (ev != null && ek != null && (k == ek || k.equals(ek)))
- return ev;
- }
- if (eh < 0) { // bin was moved during resize
- tab = (Node[])e.key;
- continue retry;
+ /**
+ * 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) {
+ if ((dir = (c == pc) ? 0 :
+ c.getName().compareTo(pc.getName())) == 0) {
+ TreeNode r = null, pl, pr; // check both sides
+ if ((pr = p.right) != null && h >= pr.hash &&
+ (r = getTreeNode(h, k, pr)) != null)
+ return r;
+ else if ((pl = p.left) != null && h <= pl.hash)
+ dir = -1;
+ else // nothing there
+ return null;
+ }
+ }
}
- e = e.next;
+ else
+ dir = (h < ph) ? -1 : 1;
+ p = (dir > 0) ? p.right : p.left;
}
- break;
+ return null;
}
- return null;
- }
- /** Implements put and putIfAbsent **/
- private final Object internalPut(Object k, Object v, boolean replace) {
- int h = spread(k.hashCode());
- Object oldVal = null; // the previous value or null if none
- Node node = null; // the node created if absent
- Node[] tab = table;
- for (;;) {
- Node e; int i;
- if (tab == null)
- tab = grow(0);
- else if ((e = tabAt(tab, i = (tab.length - 1) & h)) == null) {
- if (node == null)
- node = new Node(h, k, v, null);
- if (casTabAt(tab, i, null, node))
+ /**
+ * 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 V 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 == 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, V 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) {
+ TreeNode s = null, r = null, pr;
+ if ((dir = (c == pc) ? 0 :
+ c.getName().compareTo(pc.getName())) == 0) {
+ if ((pr = p.right) != null && h >= pr.hash &&
+ (r = getTreeNode(h, k, pr)) != null)
+ return r;
+ else // continue left
+ dir = -1;
+ }
+ 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;
+ }
+
+ 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;
+ }
+
+ /**
+ * 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 if (e.hash < 0)
- tab = (Node[])e.key;
else {
- boolean validated = false;
- boolean checkSize = false;
- synchronized(e) {
- Node first = e;
- for (;;) {
- Object ek, ev;
- if ((ev = e.val) == null)
- break;
- if (e.hash == h && (ek = e.key) != null &&
- (k == ek || k.equals(ek))) {
- if (tabAt(tab, i) == first) {
- validated = true;
- oldVal = ev;
- if (replace)
- e.val = v;
+ 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;
}
- break;
}
- Node last = e;
- if ((e = e.next) == null) {
- if (tabAt(tab, i) == first) {
- validated = true;
- if (node == null)
- node = new Node(h, k, v, null);
- last.next = node;
- if (last != first)
- checkSize = true;
+ }
+ 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;
}
- break;
}
}
}
- if (validated) {
- if (checkSize && tab.length < MAXIMUM_CAPACITY &&
- resizing == 0 && counter.sum() >= threshold)
- grow(0);
- break;
+ }
+ 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;
+ }
+ }
+ }
+
+ /* ---------------- Collision reduction methods -------------- */
+
+ /**
+ * Spreads higher bits 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.) 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.
+ */
+ private static final int spread(int h) {
+ h ^= (h >>> 18) ^ (h >>> 12);
+ return (h ^ (h >>> 10)) & HASH_BITS;
+ }
+
+ /**
+ * Replaces a list bin with a tree bin if key is comparable. Call
+ * only when locked.
+ */
+ private final void replaceWithTreeBin(Node[] tab, int index, Object key) {
+ if (key instanceof Comparable) {
+ TreeBin t = new TreeBin();
+ for (Node e = tabAt(tab, index); e != null; e = e.next)
+ t.putTreeNode(e.hash, e.key, e.val);
+ setTabAt(tab, index, new Node(MOVED, t, null, null));
+ }
+ }
+
+ /* ---------------- Internal access and update methods -------------- */
+
+ /** Implementation for get and containsKey */
+ @SuppressWarnings("unchecked") private final V internalGet(Object k) {
+ int h = spread(k.hashCode());
+ retry: for (Node[] tab = table; tab != null;) {
+ Node e; Object ek; V 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) < 0) {
+ 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 == h && (ev = e.val) != null &&
+ ((ek = e.key) == k || k.equals(ek)))
+ return ev;
}
+ break;
}
- if (oldVal == null)
- counter.increment();
- return oldVal;
+ return null;
}
/**
- * Covers 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.
+ * 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.
*/
- private final Object internalReplace(Object k, Object v, Object cv) {
+ @SuppressWarnings("unchecked") private final V internalReplace
+ (Object k, V v, Object cv) {
int h = spread(k.hashCode());
- Object oldVal = null;
- Node e; int i;
- Node[] tab = table;
- while (tab != null &&
- (e = tabAt(tab, i = (tab.length - 1) & h)) != null) {
- if (e.hash < 0)
- tab = (Node[])e.key;
+ V 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) < 0) {
+ 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) {
+ V 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)
+ addCount(-1L, -1);
+ break;
+ }
+ }
+ else
+ tab = (Node[])fk;
+ }
+ else if (fh != h && f.next == null) // precheck
+ break; // rules out possible existence
else {
boolean validated = false;
boolean deleted = false;
- synchronized(e) {
- Node pred = null;
- Node first = e;
- for (;;) {
- Object ek, ev;
- if ((ev = e.val) == null)
- break;
- if (e.hash == h && (ek = e.key) != null &&
- (k == ek || k.equals(ek))) {
- if (tabAt(tab, i) == first) {
- validated = true;
+ synchronized (f) {
+ if (tabAt(tab, i) == f) {
+ validated = true;
+ for (Node e = f, pred = null;;) {
+ Object ek; V ev;
+ if (e.hash == 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;
+ Node en = e.next;
if (pred != null)
pred.next = en;
else
setTabAt(tab, i, en);
}
}
+ break;
}
- break;
- }
- pred = e;
- if ((e = e.next) == null) {
- if (tabAt(tab, i) == first)
- validated = true;
- break;
+ pred = e;
+ if ((e = e.next) == null)
+ break;
}
}
}
if (validated) {
if (deleted)
- counter.decrement();
+ addCount(-1L, -1);
break;
}
}
@@ -476,505 +1301,1243 @@ public class ConcurrentHashMapV8
return oldVal;
}
- /** Implements computeIfAbsent */
- @SuppressWarnings("unchecked")
- private final V computeVal(K k, MappingFunction f) {
+ /*
+ * Internal versions of insertion methods
+ * 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
+ *
+ * The putAll method differs mainly in attempting to pre-allocate
+ * enough table space, and also more lazily performs count updates
+ * and checks.
+ *
+ * Most of the function-accepting methods can't be factored nicely
+ * because they require different functional forms, so instead
+ * sprawl out similar mechanics.
+ */
+
+ /** Implementation for put and putIfAbsent */
+ @SuppressWarnings("unchecked") private final V internalPut
+ (K k, V v, boolean onlyIfAbsent) {
+ if (k == null || v == null) throw new NullPointerException();
+ int h = spread(k.hashCode());
+ int len = 0;
+ for (Node[] tab = table;;) {
+ int i, fh; Node f; Object fk; V 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; // no lock when adding to empty bin
+ }
+ else if ((fh = f.hash) < 0) {
+ if ((fk = f.key) instanceof TreeBin) {
+ TreeBin t = (TreeBin)fk;
+ V oldVal = null;
+ t.acquire(0);
+ try {
+ if (tabAt(tab, i) == f) {
+ len = 2;
+ TreeNode p = t.putTreeNode(h, k, v);
+ if (p != null) {
+ oldVal = p.val;
+ if (!onlyIfAbsent)
+ p.val = v;
+ }
+ }
+ } finally {
+ t.release(0);
+ }
+ if (len != 0) {
+ if (oldVal != null)
+ return oldVal;
+ break;
+ }
+ }
+ else
+ tab = (Node[])fk;
+ }
+ else if (onlyIfAbsent && fh == h && (fv = f.val) != null &&
+ ((fk = f.key) == k || k.equals(fk))) // peek while nearby
+ return fv;
+ else {
+ V oldVal = null;
+ synchronized (f) {
+ if (tabAt(tab, i) == f) {
+ len = 1;
+ for (Node e = f;; ++len) {
+ Object ek; V ev;
+ if (e.hash == h &&
+ (ev = e.val) != null &&
+ ((ek = e.key) == k || k.equals(ek))) {
+ oldVal = ev;
+ if (!onlyIfAbsent)
+ e.val = v;
+ break;
+ }
+ Node last = e;
+ if ((e = e.next) == null) {
+ last.next = new Node(h, k, v, null);
+ if (len >= TREE_THRESHOLD)
+ replaceWithTreeBin(tab, i, k);
+ break;
+ }
+ }
+ }
+ }
+ if (len != 0) {
+ if (oldVal != null)
+ return oldVal;
+ break;
+ }
+ }
+ }
+ addCount(1L, len);
+ return null;
+ }
+
+ /** Implementation for computeIfAbsent */
+ @SuppressWarnings("unchecked") private final V internalComputeIfAbsent
+ (K k, Fun mf) {
+ if (k == null || mf == null)
+ throw new NullPointerException();
int h = spread(k.hashCode());
V val = null;
- Node node = null;
- boolean added = false;
- boolean validated = false;
- Node[] tab = table;
- do {
- Node e; int i;
+ int len = 0;
+ for (Node[] tab = table;;) {
+ Node f; int i; Object fk;
if (tab == null)
- tab = grow(0);
- else if ((e = tabAt(tab, i = (tab.length - 1) & h)) == null) {
- if (node == null)
- node = new Node(h, k, null, null);
- synchronized(node) {
+ tab = initTable();
+ else if ((f = tabAt(tab, i = (tab.length - 1) & h)) == null) {
+ Node node = new Node(h, k, null, null);
+ synchronized (node) {
if (casTabAt(tab, i, null, node)) {
- validated = true;
+ len = 1;
try {
- val = f.map(k);
- if (val != null) {
+ if ((val = mf.apply(k)) != null)
node.val = val;
- added = true;
- }
} finally {
- if (!added)
+ if (val == null)
setTabAt(tab, i, null);
}
}
}
+ if (len != 0)
+ break;
}
- else if (e.hash < 0)
- tab = (Node[])e.key;
- else {
- boolean checkSize = false;
- synchronized(e) {
- Node first = e;
- for (;;) {
- Object ek, ev;
- if ((ev = e.val) == null)
- break;
- if (e.hash == h && (ek = e.key) != null &&
- (k == ek || k.equals(ek))) {
- if (tabAt(tab, i) == first) {
- validated = true;
- val = (V)ev;
+ else if (f.hash < 0) {
+ if ((fk = f.key) instanceof TreeBin) {
+ TreeBin t = (TreeBin)fk;
+ boolean added = false;
+ t.acquire(0);
+ try {
+ if (tabAt(tab, i) == f) {
+ len = 1;
+ TreeNode p = t.getTreeNode(h, k, t.root);
+ if (p != null)
+ val = p.val;
+ else if ((val = mf.apply(k)) != null) {
+ added = true;
+ len = 2;
+ t.putTreeNode(h, k, val);
}
- break;
}
- Node last = e;
- if ((e = e.next) == null) {
- if (tabAt(tab, i) == first) {
- validated = true;
- if ((val = f.map(k)) != null) {
- if (node == null)
- node = new Node(h, k, val, null);
- else
- node.val = val;
- last.next = node;
- if (last != first)
- checkSize = true;
+ } finally {
+ t.release(0);
+ }
+ if (len != 0) {
+ if (!added)
+ return val;
+ break;
+ }
+ }
+ else
+ tab = (Node[])fk;
+ }
+ else {
+ for (Node e = f; e != null; e = e.next) { // prescan
+ Object ek; V ev;
+ if (e.hash == h && (ev = e.val) != null &&
+ ((ek = e.key) == k || k.equals(ek)))
+ return ev;
+ }
+ boolean added = false;
+ synchronized (f) {
+ if (tabAt(tab, i) == f) {
+ len = 1;
+ for (Node e = f;; ++len) {
+ Object ek; V ev;
+ if (e.hash == h &&
+ (ev = e.val) != null &&
+ ((ek = e.key) == k || k.equals(ek))) {
+ val = ev;
+ break;
+ }
+ Node last = e;
+ if ((e = e.next) == null) {
+ if ((val = mf.apply(k)) != null) {
added = true;
+ last.next = new Node(h, k, val, null);
+ if (len >= TREE_THRESHOLD)
+ replaceWithTreeBin(tab, i, k);
}
+ break;
}
- break;
}
}
}
- if (checkSize && tab.length < MAXIMUM_CAPACITY &&
- resizing == 0 && counter.sum() >= threshold)
- grow(0);
- }
- } while (!validated);
- if (added)
- counter.increment();
+ if (len != 0) {
+ if (!added)
+ return val;
+ break;
+ }
+ }
+ }
+ if (val != null)
+ addCount(1L, len);
return val;
}
- /*
- * Reclassifies nodes in each bin to new 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. Statistically, at the default threshold, 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.
- *
- * Transfers are done from the bottom up to preserve iterator
- * traversability. On each step, the old bin is locked,
- * moved/copied, and then replaced with a forwarding node.
- */
- private static final void transfer(Node[] tab, Node[] nextTab) {
- int n = tab.length;
- int mask = nextTab.length - 1;
- Node fwd = new Node(MOVED, nextTab, null, null);
- for (int i = n - 1; i >= 0; --i) {
- for (Node e;;) {
- if ((e = tabAt(tab, i)) == null) {
- if (casTabAt(tab, i, e, fwd))
- break;
- }
- else {
- boolean validated = false;
- synchronized(e) {
- int idx = e.hash & mask;
- Node lastRun = e;
- for (Node p = e.next; p != null; p = p.next) {
- int j = p.hash & mask;
- if (j != idx) {
- idx = j;
- lastRun = p;
+ /** Implementation for compute */
+ @SuppressWarnings("unchecked") private final V internalCompute
+ (K k, boolean onlyIfPresent,
+ BiFun mf) {
+ if (k == null || mf == null)
+ throw new NullPointerException();
+ int h = spread(k.hashCode());
+ V val = null;
+ int delta = 0;
+ int len = 0;
+ for (Node[] tab = table;;) {
+ Node f; int i, fh; Object fk;
+ if (tab == null)
+ tab = initTable();
+ else if ((f = tabAt(tab, i = (tab.length - 1) & h)) == null) {
+ if (onlyIfPresent)
+ break;
+ Node node = new Node(h, k, null, null);
+ synchronized (node) {
+ if (casTabAt(tab, i, null, node)) {
+ try {
+ len = 1;
+ if ((val = mf.apply(k, null)) != null) {
+ node.val = val;
+ delta = 1;
}
+ } finally {
+ if (delta == 0)
+ setTabAt(tab, i, null);
}
- if (tabAt(tab, i) == e) {
- validated = true;
- setTabAt(nextTab, idx, lastRun);
- for (Node p = e; p != lastRun; p = p.next) {
- int h = p.hash;
- int j = h & mask;
- Object pk = p.key, pv = p.val;
- Node r = tabAt(nextTab, j);
- setTabAt(nextTab, j, new Node(h, pk, pv, r));
+ }
+ }
+ if (len != 0)
+ break;
+ }
+ else if ((fh = f.hash) < 0) {
+ if ((fk = f.key) instanceof TreeBin) {
+ TreeBin t = (TreeBin)fk;
+ t.acquire(0);
+ try {
+ if (tabAt(tab, i) == f) {
+ len = 1;
+ TreeNode p = t.getTreeNode(h, k, t.root);
+ if (p == null && onlyIfPresent)
+ break;
+ V pv = (p == null) ? null : p.val;
+ if ((val = mf.apply(k, pv)) != null) {
+ if (p != null)
+ p.val = val;
+ else {
+ len = 2;
+ delta = 1;
+ t.putTreeNode(h, k, val);
+ }
+ }
+ else if (p != null) {
+ delta = -1;
+ t.deleteTreeNode(p);
}
- setTabAt(tab, i, fwd);
}
+ } finally {
+ t.release(0);
}
- if (validated)
+ if (len != 0)
break;
}
+ else
+ tab = (Node[])fk;
+ }
+ else {
+ synchronized (f) {
+ if (tabAt(tab, i) == f) {
+ len = 1;
+ for (Node e = f, pred = null;; ++len) {
+ Object ek; V ev;
+ if (e.hash == h &&
+ (ev = e.val) != null &&
+ ((ek = e.key) == k || k.equals(ek))) {
+ val = mf.apply(k, ev);
+ if (val != null)
+ e.val = val;
+ else {
+ delta = -1;
+ Node en = e.next;
+ if (pred != null)
+ pred.next = en;
+ else
+ setTabAt(tab, i, en);
+ }
+ break;
+ }
+ pred = e;
+ if ((e = e.next) == null) {
+ if (!onlyIfPresent &&
+ (val = mf.apply(k, null)) != null) {
+ pred.next = new Node(h, k, val, null);
+ delta = 1;
+ if (len >= TREE_THRESHOLD)
+ replaceWithTreeBin(tab, i, k);
+ }
+ break;
+ }
+ }
+ }
+ }
+ if (len != 0)
+ break;
}
}
+ if (delta != 0)
+ addCount((long)delta, len);
+ return val;
}
- /**
- * If not already resizing, initializes or creates next table and
- * transfers bins. Rechecks occupancy after a transfer to see if
- * another resize is already needed because resizings are lagging
- * additions.
- *
- * @param sizeHint overridden capacity target (nonzero only from putAll)
- * @return current table
- */
- private final Node[] grow(int sizeHint) {
- Node[] tab;
- if (resizing == 0 &&
- UNSAFE.compareAndSwapInt(this, resizingOffset, 0, 1)) {
- try {
- for (;;) {
- int cap, n;
- if ((tab = table) == null) {
- int c = initCap;
- if (c < sizeHint)
- c = sizeHint;
- if (c == DEFAULT_CAPACITY)
- cap = c;
- else if (c >= MAXIMUM_CAPACITY)
- cap = MAXIMUM_CAPACITY;
- else {
- cap = MINIMUM_CAPACITY;
- while (cap < c)
- cap <<= 1;
+ /** Implementation for merge */
+ @SuppressWarnings("unchecked") private final V internalMerge
+ (K k, V v, BiFun mf) {
+ if (k == null || v == null || mf == null)
+ throw new NullPointerException();
+ int h = spread(k.hashCode());
+ V val = null;
+ int delta = 0;
+ int len = 0;
+ for (Node[] tab = table;;) {
+ int i; Node f; Object fk; V 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))) {
+ delta = 1;
+ val = v;
+ break;
+ }
+ }
+ else if (f.hash < 0) {
+ if ((fk = f.key) instanceof TreeBin) {
+ TreeBin t = (TreeBin)fk;
+ t.acquire(0);
+ try {
+ if (tabAt(tab, i) == f) {
+ len = 1;
+ TreeNode p = t.getTreeNode(h, k, t.root);
+ val = (p == null) ? v : mf.apply(p.val, v);
+ if (val != null) {
+ if (p != null)
+ p.val = val;
+ else {
+ len = 2;
+ delta = 1;
+ t.putTreeNode(h, k, val);
+ }
+ }
+ else if (p != null) {
+ delta = -1;
+ t.deleteTreeNode(p);
+ }
}
+ } finally {
+ t.release(0);
}
- else if ((n = tab.length) < MAXIMUM_CAPACITY &&
- (sizeHint <= 0 || n < sizeHint))
- cap = n << 1;
- else
- break;
- threshold = (int)(cap * loadFactor) - THRESHOLD_OFFSET;
- Node[] nextTab = new Node[cap];
- if (tab != null)
- transfer(tab, nextTab);
- table = nextTab;
- if (tab == null || counter.sum() < threshold) {
- tab = nextTab;
+ if (len != 0)
break;
+ }
+ else
+ tab = (Node[])fk;
+ }
+ else {
+ synchronized (f) {
+ if (tabAt(tab, i) == f) {
+ len = 1;
+ for (Node e = f, pred = null;; ++len) {
+ Object ek; V ev;
+ if (e.hash == h &&
+ (ev = e.val) != null &&
+ ((ek = e.key) == k || k.equals(ek))) {
+ val = mf.apply(ev, v);
+ if (val != null)
+ e.val = val;
+ else {
+ delta = -1;
+ Node en = e.next;
+ if (pred != null)
+ pred.next = en;
+ else
+ setTabAt(tab, i, en);
+ }
+ break;
+ }
+ pred = e;
+ if ((e = e.next) == null) {
+ val = v;
+ pred.next = new Node(h, k, val, null);
+ delta = 1;
+ if (len >= TREE_THRESHOLD)
+ replaceWithTreeBin(tab, i, k);
+ break;
+ }
+ }
}
}
- } finally {
- resizing = 0;
+ if (len != 0)
+ break;
}
}
- else if ((tab = table) == null)
- Thread.yield(); // lost initialization race; just spin
- return tab;
+ if (delta != 0)
+ addCount((long)delta, len);
+ return val;
}
- /**
- * Implements putAll and constructor with Map argument. Tries to
- * first override initial capacity or grow (once) based on map
- * size to pre-allocate table space.
- */
- private final void internalPutAll(Map m) {
- int s = m.size();
- grow((s >= (MAXIMUM_CAPACITY >>> 1))? s : s + (s >>> 1));
- for (Map.Entry e : m.entrySet()) {
- Object k = e.getKey();
- Object v = e.getValue();
- if (k == null || v == null)
- throw new NullPointerException();
- internalPut(k, v, true);
+ /** Implementation for putAll */
+ @SuppressWarnings("unchecked") private final void internalPutAll
+ (Map m) {
+ tryPresize(m.size());
+ long delta = 0L; // number of uncommitted additions
+ boolean npe = false; // to throw exception on exit for nulls
+ try { // to clean up counts on other exceptions
+ for (Map.Entry entry : m.entrySet()) {
+ Object k; V v;
+ if (entry == null || (k = entry.getKey()) == null ||
+ (v = entry.getValue()) == null) {
+ npe = true;
+ break;
+ }
+ int h = spread(k.hashCode());
+ for (Node[] tab = table;;) {
+ int i; Node f; int fh; Object fk;
+ 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))) {
+ ++delta;
+ break;
+ }
+ }
+ else if ((fh = f.hash) < 0) {
+ if ((fk = f.key) instanceof TreeBin) {
+ TreeBin t = (TreeBin)fk;
+ boolean validated = false;
+ t.acquire(0);
+ try {
+ if (tabAt(tab, i) == f) {
+ validated = true;
+ TreeNode p = t.getTreeNode(h, k, t.root);
+ if (p != null)
+ p.val = v;
+ else {
+ t.putTreeNode(h, k, v);
+ ++delta;
+ }
+ }
+ } finally {
+ t.release(0);
+ }
+ if (validated)
+ break;
+ }
+ else
+ tab = (Node[])fk;
+ }
+ else {
+ int len = 0;
+ synchronized (f) {
+ if (tabAt(tab, i) == f) {
+ len = 1;
+ for (Node e = f;; ++len) {
+ Object ek; V ev;
+ if (e.hash == h &&
+ (ev = e.val) != null &&
+ ((ek = e.key) == k || k.equals(ek))) {
+ e.val = v;
+ break;
+ }
+ Node last = e;
+ if ((e = e.next) == null) {
+ ++delta;
+ last.next = new Node(h, k, v, null);
+ if (len >= TREE_THRESHOLD)
+ replaceWithTreeBin(tab, i, k);
+ break;
+ }
+ }
+ }
+ }
+ if (len != 0) {
+ if (len > 1) {
+ addCount(delta, len);
+ delta = 0L;
+ }
+ break;
+ }
+ }
+ }
+ }
+ } finally {
+ if (delta != 0L)
+ addCount(delta, 2);
}
+ if (npe)
+ throw new NullPointerException();
}
/**
- * Implements clear. Steps through each bin, removing all nodes.
+ * Implementation for clear. Steps through each bin, removing all
+ * nodes.
*/
- private final void internalClear() {
- long delta = 0L; // negative of number of deletions
+ @SuppressWarnings("unchecked") private final void internalClear() {
+ long delta = 0L; // negative number of deletions
int i = 0;
- Node[] tab = table;
+ Node[] tab = table;
while (tab != null && i < tab.length) {
- Node e = tabAt(tab, i);
- if (e == null)
+ Node f = tabAt(tab, i);
+ if (f == null)
++i;
- else if (e.hash < 0)
- tab = (Node[])e.key;
+ else if (f.hash < 0) {
+ Object fk;
+ if ((fk = f.key) instanceof TreeBin) {
+ TreeBin t = (TreeBin)fk;
+ t.acquire(0);
+ try {
+ if (tabAt(tab, i) == f) {
+ for (Node p = t.first; p != null; p = p.next) {
+ if (p.val != null) { // (currently always true)
+ p.val = null;
+ --delta;
+ }
+ }
+ t.first = null;
+ t.root = null;
+ ++i;
+ }
+ } finally {
+ t.release(0);
+ }
+ }
+ else
+ tab = (Node[])fk;
+ }
else {
- boolean validated = false;
- synchronized(e) {
- if (tabAt(tab, i) == e) {
- validated = true;
- do {
- if (e.val != null) {
+ synchronized (f) {
+ if (tabAt(tab, i) == f) {
+ for (Node e = f; e != null; e = e.next) {
+ if (e.val != null) { // (currently always true)
e.val = null;
--delta;
}
- } while ((e = e.next) != null);
+ }
setTabAt(tab, i, null);
+ ++i;
}
}
- if (validated)
- ++i;
}
}
- counter.add(delta);
+ if (delta != 0L)
+ addCount(delta, -1);
}
+ /* ---------------- Table Initialization and Resizing -------------- */
+
/**
- * Base class for key, value, and entry iterators, plus internal
- * implementations of public traversal-based methods, to avoid
- * duplicating traversal code.
+ * Returns a power of two table size for the given desired capacity.
+ * See Hackers Delight, sec 3.2
*/
- class HashIterator {
- private Node next; // the next entry to return
- private Node[] tab; // current table; updated if resized
- private Node lastReturned; // the last entry returned, for remove
- private Object nextVal; // cached value of next
- private int index; // index of bin to use next
- private int baseIndex; // current index of initial table
- private final int baseSize; // initial table size
+ 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;
+ }
- HashIterator() {
- Node[] t = tab = table;
- if (t == null)
- baseSize = 0;
- else {
- baseSize = t.length;
- advance(null);
+ /**
+ * Initializes table, using the size recorded in sizeCtl.
+ */
+ @SuppressWarnings("unchecked") private final Node[] initTable() {
+ Node[] tab; int sc;
+ while ((tab = table) == null) {
+ if ((sc = sizeCtl) < 0)
+ Thread.yield(); // lost initialization race; just spin
+ else if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
+ try {
+ if ((tab = table) == null) {
+ int n = (sc > 0) ? sc : DEFAULT_CAPACITY;
+ @SuppressWarnings("rawtypes") Node[] tb = new Node[n];
+ table = tab = (Node[])tb;
+ sc = n - (n >>> 2);
+ }
+ } finally {
+ sizeCtl = sc;
+ }
+ break;
}
}
+ return tab;
+ }
- public final boolean hasNext() { return next != null; }
- public final boolean hasMoreElements() { return next != null; }
-
- /**
- * Advances next. Normally, iteration proceeds bin-by-bin
- * traversing lists. However, if the table has been resized,
- * then all future steps must traverse both the bin at the
- * current index as well as at (index + baseSize); and so on
- * for further resizings. To paranoically cope with potential
- * (improper) sharing of iterators across threads, table reads
- * are bounds-checked.
- */
- final void advance(Node e) {
- for (;;) {
- Node[] t; int i; // for bounds checks
- if (e != null) {
- Object ek = e.key, ev = e.val;
- if (ev != null && ek != null) {
- nextVal = ev;
- next = e;
+ /**
+ * Adds to count, and if table is too small and not already
+ * resizing, initiates transfer. If already resizing, helps
+ * perform transfer if work is available. Rechecks occupancy
+ * after a transfer to see if another resize is already needed
+ * because resizings are lagging additions.
+ *
+ * @param x the count to add
+ * @param check if <0, don't check resize, if <= 1 only check if uncontended
+ */
+ private final void addCount(long x, int check) {
+ CounterCell[] as; long b, s;
+ if ((as = counterCells) != null ||
+ !U.compareAndSwapLong(this, BASECOUNT, b = baseCount, s = b + x)) {
+ CounterHashCode hc; CounterCell a; long v; int m;
+ boolean uncontended = true;
+ if ((hc = threadCounterHashCode.get()) == null ||
+ as == null || (m = as.length - 1) < 0 ||
+ (a = as[m & hc.code]) == null ||
+ !(uncontended =
+ U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))) {
+ fullAddCount(x, hc, uncontended);
+ return;
+ }
+ if (check <= 1)
+ return;
+ s = sumCount();
+ }
+ if (check >= 0) {
+ Node[] tab, nt; int sc;
+ while (s >= (long)(sc = sizeCtl) && (tab = table) != null &&
+ tab.length < MAXIMUM_CAPACITY) {
+ if (sc < 0) {
+ if (sc == -1 || transferIndex <= transferOrigin ||
+ (nt = nextTable) == null)
break;
+ if (U.compareAndSwapInt(this, SIZECTL, sc, sc - 1))
+ transfer(tab, nt);
+ }
+ else if (U.compareAndSwapInt(this, SIZECTL, sc, -2))
+ transfer(tab, null);
+ s = sumCount();
+ }
+ }
+ }
+
+ /**
+ * Tries to presize table to accommodate the given number of elements.
+ *
+ * @param size number of elements (doesn't need to be perfectly accurate)
+ */
+ @SuppressWarnings("unchecked") private final void tryPresize(int size) {
+ int c = (size >= (MAXIMUM_CAPACITY >>> 1)) ? MAXIMUM_CAPACITY :
+ tableSizeFor(size + (size >>> 1) + 1);
+ int sc;
+ while ((sc = sizeCtl) >= 0) {
+ Node[] tab = table; int n;
+ if (tab == null || (n = tab.length) == 0) {
+ n = (sc > c) ? sc : c;
+ if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
+ try {
+ if (table == tab) {
+ @SuppressWarnings("rawtypes") Node[] tb = new Node[n];
+ table = (Node[])tb;
+ sc = n - (n >>> 2);
+ }
+ } finally {
+ sizeCtl = sc;
}
- e = e.next;
}
- else if (baseIndex < baseSize && (t = tab) != null &&
- t.length > (i = index) && i >= 0) {
- if ((e = tabAt(t, i)) != null && e.hash < 0) {
- tab = (Node[])e.key;
- e = null;
+ }
+ else if (c <= sc || n >= MAXIMUM_CAPACITY)
+ break;
+ else if (tab == table &&
+ U.compareAndSwapInt(this, SIZECTL, sc, -2))
+ transfer(tab, null);
+ }
+ }
+
+ /**
+ * Moves and/or copies the nodes in each bin to new table. See
+ * above for explanation.
+ */
+ @SuppressWarnings("unchecked") private final void transfer
+ (Node[] tab, Node[] nextTab) {
+ int n = tab.length, stride;
+ if ((stride = (NCPU > 1) ? (n >>> 3) / NCPU : n) < MIN_TRANSFER_STRIDE)
+ stride = MIN_TRANSFER_STRIDE; // subdivide range
+ if (nextTab == null) { // initiating
+ try {
+ @SuppressWarnings("rawtypes") Node[] tb = new Node[n << 1];
+ nextTab = (Node[])tb;
+ } catch (Throwable ex) { // try to cope with OOME
+ sizeCtl = Integer.MAX_VALUE;
+ return;
+ }
+ nextTable = nextTab;
+ transferOrigin = n;
+ transferIndex = n;
+ Node rev = new Node(MOVED, tab, null, null);
+ for (int k = n; k > 0;) { // progressively reveal ready slots
+ int nextk = (k > stride) ? k - stride : 0;
+ for (int m = nextk; m < k; ++m)
+ nextTab[m] = rev;
+ for (int m = n + nextk; m < n + k; ++m)
+ nextTab[m] = rev;
+ U.putOrderedInt(this, TRANSFERORIGIN, k = nextk);
+ }
+ }
+ int nextn = nextTab.length;
+ Node fwd = new Node(MOVED, nextTab, null, null);
+ boolean advance = true;
+ for (int i = 0, bound = 0;;) {
+ int nextIndex, nextBound; Node f; Object fk;
+ while (advance) {
+ if (--i >= bound)
+ advance = false;
+ else if ((nextIndex = transferIndex) <= transferOrigin) {
+ i = -1;
+ advance = false;
+ }
+ else if (U.compareAndSwapInt
+ (this, TRANSFERINDEX, nextIndex,
+ nextBound = (nextIndex > stride ?
+ nextIndex - stride : 0))) {
+ bound = nextBound;
+ i = nextIndex - 1;
+ advance = false;
+ }
+ }
+ if (i < 0 || i >= n || i + n >= nextn) {
+ for (int sc;;) {
+ if (U.compareAndSwapInt(this, SIZECTL, sc = sizeCtl, ++sc)) {
+ if (sc == -1) {
+ nextTable = null;
+ table = nextTab;
+ sizeCtl = (n << 1) - (n >>> 1);
+ }
+ return;
}
- else if (i + baseSize < t.length)
- index += baseSize; // visit forwarded upper slots
- else
- index = ++baseIndex;
}
- else {
- next = null;
- break;
+ }
+ else if ((f = tabAt(tab, i)) == null) {
+ if (casTabAt(tab, i, null, fwd)) {
+ setTabAt(nextTab, i, null);
+ setTabAt(nextTab, i + n, null);
+ advance = true;
}
}
+ else if (f.hash >= 0) {
+ synchronized (f) {
+ if (tabAt(tab, i) == f) {
+ int runBit = f.hash & n;
+ Node lastRun = f, lo = null, hi = null;
+ for (Node p = f.next; p != null; p = p.next) {
+ int b = p.hash & n;
+ if (b != runBit) {
+ runBit = b;
+ lastRun = p;
+ }
+ }
+ if (runBit == 0)
+ lo = lastRun;
+ else
+ hi = lastRun;
+ for (Node p = f; p != lastRun; p = p.next) {
+ int ph = p.hash;
+ Object pk = p.key; V pv = p.val;
+ if ((ph & n) == 0)
+ lo = new Node(ph, pk, pv, lo);
+ else
+ hi = new Node(ph, pk, pv, hi);
+ }
+ setTabAt(nextTab, i, lo);
+ setTabAt(nextTab, i + n, hi);
+ setTabAt(tab, i, fwd);
+ advance = true;
+ }
+ }
+ }
+ else if ((fk = f.key) instanceof TreeBin) {
+ TreeBin t = (TreeBin)fk;
+ t.acquire(0);
+ try {
+ if (tabAt(tab, i) == f) {
+ TreeBin lt = new TreeBin();
+ TreeBin ht = new TreeBin();
+ int lc = 0, hc = 0;
+ for (Node e = t.first; e != null; e = e.next) {
+ int h = e.hash;
+ Object k = e.key; V v = e.val;
+ if ((h & n) == 0) {
+ ++lc;
+ lt.putTreeNode(h, k, v);
+ }
+ else {
+ ++hc;
+ ht.putTreeNode(h, k, v);
+ }
+ }
+ Node ln, hn; // throw away trees if too small
+ if (lc < TREE_THRESHOLD) {
+ ln = null;
+ for (Node p = lt.first; p != null; p = p.next)
+ ln = new Node(p.hash, p.key, p.val, ln);
+ }
+ else
+ ln = new Node(MOVED, lt, null, null);
+ setTabAt(nextTab, i, ln);
+ if (hc < TREE_THRESHOLD) {
+ hn = null;
+ for (Node p = ht.first; p != null; p = p.next)
+ hn = new Node(p.hash, p.key, p.val, hn);
+ }
+ else
+ hn = new Node(MOVED, ht, null, null);
+ setTabAt(nextTab, i + n, hn);
+ setTabAt(tab, i, fwd);
+ advance = true;
+ }
+ } finally {
+ t.release(0);
+ }
+ }
+ else
+ advance = true; // already processed
}
+ }
- final Object nextKey() {
- Node e = next;
- if (e == null)
- throw new NoSuchElementException();
- Object k = e.key;
- advance((lastReturned = e).next);
- return k;
- }
+ /* ---------------- Counter support -------------- */
- final Object nextValue() {
- Node e = next;
- if (e == null)
- throw new NoSuchElementException();
- Object v = nextVal;
- advance((lastReturned = e).next);
- return v;
+ final long sumCount() {
+ CounterCell[] as = counterCells; CounterCell a;
+ long sum = baseCount;
+ if (as != null) {
+ for (int i = 0; i < as.length; ++i) {
+ if ((a = as[i]) != null)
+ sum += a.value;
+ }
}
+ return sum;
+ }
- final WriteThroughEntry nextEntry() {
- Node e = next;
- if (e == null)
- throw new NoSuchElementException();
- WriteThroughEntry entry =
- new WriteThroughEntry(e.key, nextVal);
- advance((lastReturned = e).next);
- return entry;
+ // See LongAdder version for explanation
+ private final void fullAddCount(long x, CounterHashCode hc,
+ boolean wasUncontended) {
+ int h;
+ if (hc == null) {
+ hc = new CounterHashCode();
+ int s = counterHashCodeGenerator.addAndGet(SEED_INCREMENT);
+ h = hc.code = (s == 0) ? 1 : s; // Avoid zero
+ threadCounterHashCode.set(hc);
}
-
- public final void remove() {
- if (lastReturned == null)
- throw new IllegalStateException();
- ConcurrentHashMapV8.this.remove(lastReturned.key);
- lastReturned = null;
+ else
+ h = hc.code;
+ boolean collide = false; // True if last slot nonempty
+ for (;;) {
+ CounterCell[] as; CounterCell a; int n; long v;
+ if ((as = counterCells) != null && (n = as.length) > 0) {
+ if ((a = as[(n - 1) & h]) == null) {
+ if (counterBusy == 0) { // Try to attach new Cell
+ CounterCell r = new CounterCell(x); // Optimistic create
+ if (counterBusy == 0 &&
+ U.compareAndSwapInt(this, COUNTERBUSY, 0, 1)) {
+ boolean created = false;
+ try { // Recheck under lock
+ CounterCell[] rs; int m, j;
+ if ((rs = counterCells) != null &&
+ (m = rs.length) > 0 &&
+ rs[j = (m - 1) & h] == null) {
+ rs[j] = r;
+ created = true;
+ }
+ } finally {
+ counterBusy = 0;
+ }
+ if (created)
+ break;
+ continue; // Slot is now non-empty
+ }
+ }
+ collide = false;
+ }
+ else if (!wasUncontended) // CAS already known to fail
+ wasUncontended = true; // Continue after rehash
+ else if (U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))
+ break;
+ else if (counterCells != as || n >= NCPU)
+ collide = false; // At max size or stale
+ else if (!collide)
+ collide = true;
+ else if (counterBusy == 0 &&
+ U.compareAndSwapInt(this, COUNTERBUSY, 0, 1)) {
+ try {
+ if (counterCells == as) {// Expand table unless stale
+ CounterCell[] rs = new CounterCell[n << 1];
+ for (int i = 0; i < n; ++i)
+ rs[i] = as[i];
+ counterCells = rs;
+ }
+ } finally {
+ counterBusy = 0;
+ }
+ collide = false;
+ continue; // Retry with expanded table
+ }
+ h ^= h << 13; // Rehash
+ h ^= h >>> 17;
+ h ^= h << 5;
+ }
+ else if (counterBusy == 0 && counterCells == as &&
+ U.compareAndSwapInt(this, COUNTERBUSY, 0, 1)) {
+ boolean init = false;
+ try { // Initialize table
+ if (counterCells == as) {
+ CounterCell[] rs = new CounterCell[2];
+ rs[h & 1] = new CounterCell(x);
+ counterCells = rs;
+ init = true;
+ }
+ } finally {
+ counterBusy = 0;
+ }
+ if (init)
+ break;
+ }
+ else if (U.compareAndSwapLong(this, BASECOUNT, v = baseCount, v + x))
+ break; // Fall back on using base
}
+ hc.code = h; // Record index for next time
+ }
+
+ /* ----------------Table Traversal -------------- */
- /** Helper for serialization */
- final void writeEntries(java.io.ObjectOutputStream s)
- throws java.io.IOException {
- Node e;
- while ((e = next) != null) {
- s.writeObject(e.key);
- s.writeObject(nextVal);
- advance(e.next);
+ /**
+ * Encapsulates traversal for methods such as containsValue; also
+ * serves as a base class for other iterators and bulk tasks.
+ *
+ * At each step, the iterator snapshots the key ("nextKey") and
+ * value ("nextVal") of a valid node (i.e., one that, at point of
+ * snapshot, has a non-null user value). Because val fields can
+ * change (including to null, indicating deletion), field nextVal
+ * might not be accurate at point of use, but still maintains the
+ * weak consistency property of holding a value that was once
+ * valid. To support iterator.remove, the nextKey field is not
+ * updated (nulled out) when the iterator cannot advance.
+ *
+ * Internal traversals directly access these fields, as in:
+ * {@code while (it.advance() != null) { process(it.nextKey); }}
+ *
+ * Exported iterators must track whether the iterator has advanced
+ * (in hasNext vs next) (by setting/checking/nulling field
+ * nextVal), and then extract key, value, or key-value pairs as
+ * return values of next().
+ *
+ * The iterator visits once each still-valid node that was
+ * reachable upon iterator construction. It might miss some that
+ * were added to a bin after the bin was visited, which is OK wrt
+ * consistency guarantees. Maintaining this property in the face
+ * of possible ongoing resizes requires a fair amount of
+ * bookkeeping state that is difficult to optimize away amidst
+ * volatile accesses. Even so, traversal maintains reasonable
+ * throughput.
+ *
+ * Normally, iteration proceeds bin-by-bin traversing lists.
+ * However, if the table has been resized, then all future steps
+ * must traverse both the bin at the current index as well as at
+ * (index + baseSize); and so on for further resizings. To
+ * paranoically cope with potential sharing by users of iterators
+ * across threads, iteration terminates if a bounds checks fails
+ * for a table read.
+ *
+ * This class extends CountedCompleter to streamline parallel
+ * iteration in bulk operations. This adds only a few fields of
+ * space overhead, which is small enough in cases where it is not
+ * needed to not worry about it. Because CountedCompleter is
+ * Serializable, but iterators need not be, we need to add warning
+ * suppressions.
+ */
+ @SuppressWarnings("serial") static class Traverser
+ extends CountedCompleter {
+ final ConcurrentHashMapV8 map;
+ Node next; // the next entry to use
+ Object nextKey; // cached key field of next
+ V nextVal; // cached val field of next
+ Node[] tab; // current table; updated if resized
+ int index; // index of bin to use next
+ int baseIndex; // current index of initial table
+ int baseLimit; // index bound for initial table
+ int baseSize; // initial table size
+ int batch; // split control
+
+ /** Creates iterator for all entries in the table. */
+ Traverser(ConcurrentHashMapV8 map) {
+ this.map = map;
+ }
+
+ /** Creates iterator for split() methods and task constructors */
+ Traverser(ConcurrentHashMapV8 map, Traverser it, int batch) {
+ super(it);
+ this.batch = batch;
+ if ((this.map = map) != null && it != null) { // split parent
+ Node[] t;
+ if ((t = it.tab) == null &&
+ (t = it.tab = map.table) != null)
+ it.baseLimit = it.baseSize = t.length;
+ this.tab = t;
+ this.baseSize = it.baseSize;
+ int hi = this.baseLimit = it.baseLimit;
+ it.baseLimit = this.index = this.baseIndex =
+ (hi + it.baseIndex + 1) >>> 1;
}
}
- /** Helper for containsValue */
- final boolean containsVal(Object value) {
- if (value != null) {
- Node e;
- while ((e = next) != null) {
- Object v = nextVal;
- if (value == v || value.equals(v))
- return true;
- advance(e.next);
+ /**
+ * Advances next; returns nextVal or null if terminated.
+ * See above for explanation.
+ */
+ @SuppressWarnings("unchecked") final V advance() {
+ Node e = next;
+ V ev = null;
+ outer: do {
+ if (e != null) // advance past used/skipped node
+ e = e.next;
+ while (e == null) { // get to next non-null bin
+ ConcurrentHashMapV8 m;
+ Node[] t; int b, i, n; Object ek; // must use locals
+ if ((t = tab) != null)
+ n = t.length;
+ else if ((m = map) != null && (t = tab = m.table) != null)
+ n = baseLimit = baseSize = t.length;
+ else
+ break outer;
+ if ((b = baseIndex) >= baseLimit ||
+ (i = index) < 0 || i >= n)
+ break outer;
+ if ((e = tabAt(t, i)) != null && e.hash < 0) {
+ if ((ek = e.key) instanceof TreeBin)
+ e = ((TreeBin)ek).first;
+ else {
+ tab = (Node[])ek;
+ continue; // restarts due to null val
+ }
+ } // visit upper slots if present
+ index = (i += baseSize) < n ? i : (baseIndex = b + 1);
}
- }
- return false;
+ nextKey = e.key;
+ } while ((ev = e.val) == null); // skip deleted or special nodes
+ next = e;
+ return nextVal = ev;
}
- /** Helper for Map.hashCode */
- final int mapHashCode() {
- int h = 0;
- Node e;
- while ((e = next) != null) {
- h += e.key.hashCode() ^ nextVal.hashCode();
- advance(e.next);
- }
- return h;
+ public final void remove() {
+ Object k = nextKey;
+ if (k == null && (advance() == null || (k = nextKey) == null))
+ throw new IllegalStateException();
+ map.internalReplace(k, null, null);
}
- /** Helper for Map.toString */
- final String mapToString() {
- Node e = next;
- if (e == null)
- return "{}";
- StringBuilder sb = new StringBuilder();
- sb.append('{');
- for (;;) {
- sb.append(e.key == this ? "(this Map)" : e.key);
- sb.append('=');
- sb.append(nextVal == this ? "(this Map)" : nextVal);
- advance(e.next);
- if ((e = next) != null)
- sb.append(',').append(' ');
- else
- return sb.append('}').toString();
+ public final boolean hasNext() {
+ return nextVal != null || advance() != null;
+ }
+
+ public final boolean hasMoreElements() { return hasNext(); }
+
+ public void compute() { } // default no-op CountedCompleter body
+
+ /**
+ * Returns a batch value > 0 if this task should (and must) be
+ * split, if so, adding to pending count, and in any case
+ * updating batch value. The initial batch value is approx
+ * exp2 of the number of times (minus one) to split task by
+ * two before executing leaf action. This value is faster to
+ * compute and more convenient to use as a guide to splitting
+ * than is the depth, since it is used while dividing by two
+ * anyway.
+ */
+ final int preSplit() {
+ ConcurrentHashMapV8 m; int b; Node[] t; ForkJoinPool pool;
+ if ((b = batch) < 0 && (m = map) != null) { // force initialization
+ if ((t = tab) == null && (t = tab = m.table) != null)
+ baseLimit = baseSize = t.length;
+ if (t != null) {
+ long n = m.sumCount();
+ int par = ((pool = getPool()) == null) ?
+ ForkJoinPool.getCommonPoolParallelism() :
+ pool.getParallelism();
+ int sp = par << 3; // slack of 8
+ b = (n <= 0L) ? 0 : (n < (long)sp) ? (int)n : sp;
+ }
}
+ b = (b <= 1 || baseIndex == baseLimit) ? 0 : (b >>> 1);
+ if ((batch = b) > 0)
+ addToPendingCount(1);
+ return b;
}
+
}
/* ---------------- Public operations -------------- */
/**
- * Creates a new, empty map with the specified initial
- * capacity, load factor and concurrency level.
- *
- * @param initialCapacity the initial capacity. The implementation
- * performs internal sizing to accommodate this many elements.
- * @param loadFactor the load factor threshold, used to control resizing.
- * Resizing may be performed when the average number of elements per
- * bin exceeds this threshold.
- * @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.
+ * Creates a new, empty map with the default initial table size (16).
*/
- public ConcurrentHashMapV8(int initialCapacity,
- float loadFactor, int concurrencyLevel) {
- if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0)
- throw new IllegalArgumentException();
- this.initCap = initialCapacity;
- this.loadFactor = loadFactor;
- this.counter = new LongAdder();
+ public ConcurrentHashMapV8() {
}
/**
- * Creates a new, empty map with the specified initial capacity
- * and load factor and with the default concurrencyLevel (16).
+ * 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.
- * @param loadFactor the load factor threshold, used to control resizing.
- * Resizing may be performed when the average number of elements per
- * bin exceeds this threshold.
+ * @throws IllegalArgumentException if the initial capacity of
+ * elements is negative
+ */
+ public ConcurrentHashMapV8(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 ConcurrentHashMapV8(Map m) {
+ this.sizeCtl = DEFAULT_CAPACITY;
+ internalPutAll(m);
+ }
+
+ /**
+ * 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 ConcurrentHashMapV8(int initialCapacity, float loadFactor) {
- this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);
+ this(initialCapacity, loadFactor, 1);
}
/**
- * Creates a new, empty map with the specified initial capacity,
- * and with default load factor (0.75) and concurrencyLevel (16).
+ * 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.
- * @throws IllegalArgumentException if the initial capacity of
- * elements is negative.
+ * 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 ConcurrentHashMapV8(int initialCapacity) {
- this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
+ public ConcurrentHashMapV8(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;
}
/**
- * Creates a new, empty map with a default initial capacity (16),
- * load factor (0.75) and concurrencyLevel (16).
+ * Creates a new {@link Set} backed by a ConcurrentHashMapV8
+ * from the given type to {@code Boolean.TRUE}.
+ *
+ * @return the new set
*/
- public ConcurrentHashMapV8() {
- this(DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
+ public static KeySetView newKeySet() {
+ return new KeySetView(new ConcurrentHashMapV8(),
+ Boolean.TRUE);
}
/**
- * Creates a new map with the same mappings as the given map.
- * The map is created with a capacity of 1.5 times the number
- * of mappings in the given map or 16 (whichever is greater),
- * and a default load factor (0.75) and concurrencyLevel (16).
+ * Creates a new {@link Set} backed by a ConcurrentHashMapV8
+ * from the given type to {@code Boolean.TRUE}.
*
- * @param m the map
+ * @param initialCapacity The implementation performs internal
+ * sizing to accommodate this many elements.
+ * @throws IllegalArgumentException if the initial capacity of
+ * elements is negative
+ * @return the new set
*/
- public ConcurrentHashMapV8(Map m) {
- this(DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
- if (m == null)
- throw new NullPointerException();
- internalPutAll(m);
+ public static KeySetView newKeySet(int initialCapacity) {
+ return new KeySetView
+ (new ConcurrentHashMapV8(initialCapacity), Boolean.TRUE);
}
/**
- * Returns {@code true} if this map contains no key-value mappings.
- *
- * @return {@code true} if this map contains no key-value mappings
+ * {@inheritDoc}
*/
public boolean isEmpty() {
- return counter.sum() == 0L;
+ return sumCount() <= 0L; // ignore transient negative values
}
/**
- * Returns the number of key-value mappings in this map. If the
- * map contains more than {@code Integer.MAX_VALUE} elements, returns
- * {@code Integer.MAX_VALUE}.
- *
- * @return the number of key-value mappings in this map
+ * {@inheritDoc}
*/
public int size() {
- long n = counter.sum();
- return n >= Integer.MAX_VALUE ? Integer.MAX_VALUE : (int)n;
+ long n = sumCount();
+ return ((n < 0L) ? 0 :
+ (n > (long)Integer.MAX_VALUE) ? Integer.MAX_VALUE :
+ (int)n);
+ }
+
+ /**
+ * Returns the number of mappings. This method should be used
+ * instead of {@link #size} because a ConcurrentHashMapV8 may
+ * contain more mappings than can be represented as an int. The
+ * value returned is an estimate; the actual count may differ if
+ * there are concurrent insertions or removals.
+ *
+ * @return the number of mappings
+ */
+ public long mappingCount() {
+ long n = sumCount();
+ return (n < 0L) ? 0L : n; // ignore transient negative values
}
/**
@@ -988,11 +2551,23 @@ public class ConcurrentHashMapV8
*
* @throws NullPointerException if the specified key is null
*/
- @SuppressWarnings("unchecked")
public V get(Object key) {
- if (key == null)
- throw new NullPointerException();
- return (V)internalGet(key);
+ return internalGet(key);
+ }
+
+ /**
+ * Returns the value to which the specified key is mapped,
+ * or the given defaultValue if this map contains no mapping for the key.
+ *
+ * @param key the key
+ * @param defaultValue the value to return if this map contains
+ * no mapping for the given key
+ * @return the mapping for the key, if present; else the defaultValue
+ * @throws NullPointerException if the specified key is null
+ */
+ public V getValueOrDefault(Object key, V defaultValue) {
+ V v;
+ return (v = internalGet(key)) == null ? defaultValue : v;
}
/**
@@ -1001,20 +2576,17 @@ public class ConcurrentHashMapV8
* @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.
+ * {@code equals} method; {@code false} otherwise
* @throws NullPointerException if the specified key is null
*/
public boolean containsKey(Object key) {
- if (key == null)
- throw new NullPointerException();
return internalGet(key) != null;
}
/**
* Returns {@code true} if this map maps one or more keys to the
- * specified value. Note: This method requires a full internal
- * traversal of the hash table, and so is much slower than
- * method {@code containsKey}.
+ * 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
@@ -1024,7 +2596,13 @@ public class ConcurrentHashMapV8
public boolean containsValue(Object value) {
if (value == null)
throw new NullPointerException();
- return new HashIterator().containsVal(value);
+ V v;
+ Traverser it = new Traverser(this);
+ while ((v = it.advance()) != null) {
+ if (v == value || value.equals(v))
+ return true;
+ }
+ return false;
}
/**
@@ -1042,7 +2620,7 @@ public class ConcurrentHashMapV8
* {@code false} otherwise
* @throws NullPointerException if the specified value is null
*/
- public boolean contains(Object value) {
+ @Deprecated public boolean contains(Object value) {
return containsValue(value);
}
@@ -1050,7 +2628,7 @@ public class ConcurrentHashMapV8
* Maps the specified key to the specified value in this table.
* Neither the key nor the value can be null.
*
- * The value can be retrieved by calling the {@code get} method
+ *
The value can be retrieved by calling the {@code get} method
* with a key that is equal to the original key.
*
* @param key key with which the specified value is to be associated
@@ -1059,11 +2637,8 @@ public class ConcurrentHashMapV8
* {@code null} if there was no mapping for {@code key}
* @throws NullPointerException if the specified key or value is null
*/
- @SuppressWarnings("unchecked")
public V put(K key, V value) {
- if (key == null || value == null)
- throw new NullPointerException();
- return (V)internalPut(key, value, true);
+ return internalPut(key, value, false);
}
/**
@@ -1073,11 +2648,8 @@ public class ConcurrentHashMapV8
* or {@code null} if there was no mapping for the key
* @throws NullPointerException if the specified key or value is null
*/
- @SuppressWarnings("unchecked")
public V putIfAbsent(K key, V value) {
- if (key == null || value == null)
- throw new NullPointerException();
- return (V)internalPut(key, value, false);
+ return internalPut(key, value, true);
}
/**
@@ -1088,48 +2660,166 @@ public class ConcurrentHashMapV8
* @param m mappings to be stored in this map
*/
public void putAll(Map m) {
- if (m == null)
- throw new NullPointerException();
internalPutAll(m);
}
/**
* If the specified key is not already associated with a value,
- * computes its value using the given mappingFunction, and if
- * non-null, enters it into the map. This is equivalent to
+ * computes its value using the given mappingFunction and enters
+ * it into the map unless null. This is equivalent to
+ * {@code
+ * if (map.containsKey(key))
+ * return map.get(key);
+ * value = mappingFunction.apply(key);
+ * if (value != null)
+ * map.put(key, value);
+ * return value;}
*
- *
- * if (map.containsKey(key))
- * return map.get(key);
- * value = mappingFunction.map(key);
- * if (value != null)
- * return map.put(key, value);
- * else
- * return null;
- *
+ * except that the action is performed atomically. If the
+ * function returns {@code null} no mapping is recorded. If the
+ * function itself throws an (unchecked) exception, the exception
+ * is rethrown to its caller, and no mapping is recorded. Some
+ * attempted update operations on this map by other threads may be
+ * blocked while computation is in progress, so the computation
+ * should be short and simple, and must not attempt to update any
+ * other mappings of this Map. The most appropriate usage is to
+ * construct a new object serving as an initial mapped value, or
+ * memoized result, as in:
*
- * except that the action is performed atomically. Some attempted
- * operations on this map by other threads may be blocked while
- * computation is in progress. Because this function is invoked
- * within atomicity control, the computation should be short and
- * simple, and must not attempt to update any other mappings of
- * this Map. The most common usage is to construct a new object
- * serving as an initial mapped value, or memoized result.
+ * {@code
+ * map.computeIfAbsent(key, new Fun() {
+ * public V map(K k) { return new Value(f(k)); }});}
*
* @param key key with which the specified value is to be associated
* @param mappingFunction the function to compute a value
* @return the current (existing or computed) value associated with
- * the specified key, or {@code null} if the computation
- * returned {@code null}.
+ * the specified key, or null if the computed value is null
* @throws NullPointerException if the specified key or mappingFunction
- * is null,
+ * is null
+ * @throws IllegalStateException if the computation detectably
+ * attempts a recursive update to this map that would
+ * otherwise never complete
* @throws RuntimeException or Error if the mappingFunction does so,
- * in which case the mapping is left unestablished.
+ * in which case the mapping is left unestablished
*/
- public V computeIfAbsent(K key, MappingFunction mappingFunction) {
- if (key == null || mappingFunction == null)
- throw new NullPointerException();
- return computeVal(key, mappingFunction);
+ public V computeIfAbsent
+ (K key, Fun mappingFunction) {
+ return internalComputeIfAbsent(key, mappingFunction);
+ }
+
+ /**
+ * If the given key is present, computes a new mapping value given a key and
+ * its current mapped value. This is equivalent to
+ * {@code
+ * if (map.containsKey(key)) {
+ * value = remappingFunction.apply(key, map.get(key));
+ * if (value != null)
+ * map.put(key, value);
+ * else
+ * map.remove(key);
+ * }
+ * }
+ *
+ * except that the action is performed atomically. If the
+ * function returns {@code null}, the mapping is removed. If the
+ * function itself throws an (unchecked) exception, the exception
+ * is rethrown to its caller, and the current mapping is left
+ * unchanged. Some attempted update operations on this map by
+ * other threads may be blocked while computation is in progress,
+ * so the computation should be short and simple, and must not
+ * attempt to update any other mappings of this Map. For example,
+ * to either create or append new messages to a value mapping:
+ *
+ * @param key key with which the specified value is to be associated
+ * @param remappingFunction the function to compute a value
+ * @return the new value associated with the specified key, or null if none
+ * @throws NullPointerException if the specified key or remappingFunction
+ * is null
+ * @throws IllegalStateException if the computation detectably
+ * attempts a recursive update to this map that would
+ * otherwise never complete
+ * @throws RuntimeException or Error if the remappingFunction does so,
+ * in which case the mapping is unchanged
+ */
+ public V computeIfPresent
+ (K key, BiFun remappingFunction) {
+ return internalCompute(key, true, remappingFunction);
+ }
+
+ /**
+ * Computes a new mapping value given a key and
+ * its current mapped value (or {@code null} if there is no current
+ * mapping). This is equivalent to
+ * {@code
+ * value = remappingFunction.apply(key, map.get(key));
+ * if (value != null)
+ * map.put(key, value);
+ * else
+ * map.remove(key);
+ * }
+ *
+ * except that the action is performed atomically. If the
+ * function returns {@code null}, the mapping is removed. If the
+ * function itself throws an (unchecked) exception, the exception
+ * is rethrown to its caller, and the current mapping is left
+ * unchanged. Some attempted update operations on this map by
+ * other threads may be blocked while computation is in progress,
+ * so the computation should be short and simple, and must not
+ * attempt to update any other mappings of this Map. For example,
+ * to either create or append new messages to a value mapping:
+ *
+ * {@code
+ * Map map = ...;
+ * final String msg = ...;
+ * map.compute(key, new BiFun() {
+ * public String apply(Key k, String v) {
+ * return (v == null) ? msg : v + msg;});}}
+ *
+ * @param key key with which the specified value is to be associated
+ * @param remappingFunction the function to compute a value
+ * @return the new value associated with the specified key, or null if none
+ * @throws NullPointerException if the specified key or remappingFunction
+ * is null
+ * @throws IllegalStateException if the computation detectably
+ * attempts a recursive update to this map that would
+ * otherwise never complete
+ * @throws RuntimeException or Error if the remappingFunction does so,
+ * in which case the mapping is unchanged
+ */
+ public V compute
+ (K key, BiFun remappingFunction) {
+ return internalCompute(key, false, remappingFunction);
+ }
+
+ /**
+ * If the specified key is not already associated
+ * with a value, associate it with the given value.
+ * Otherwise, replace the value with the results of
+ * the given remapping function. This is equivalent to:
+ * {@code
+ * if (!map.containsKey(key))
+ * map.put(value);
+ * else {
+ * newValue = remappingFunction.apply(map.get(key), value);
+ * if (value != null)
+ * map.put(key, value);
+ * else
+ * map.remove(key);
+ * }
+ * }
+ * except that the action is performed atomically. If the
+ * function returns {@code null}, the mapping is removed. If the
+ * function itself throws an (unchecked) exception, the exception
+ * is rethrown to its caller, and the current mapping is left
+ * unchanged. Some attempted update operations on this map by
+ * other threads may be blocked while computation is in progress,
+ * so the computation should be short and simple, and must not
+ * attempt to update any other mappings of this Map.
+ */
+ public V merge
+ (K key, V value,
+ BiFun remappingFunction) {
+ return internalMerge(key, value, remappingFunction);
}
/**
@@ -1141,11 +2831,8 @@ public class ConcurrentHashMapV8
* {@code null} if there was no mapping for {@code key}
* @throws NullPointerException if the specified key is null
*/
- @SuppressWarnings("unchecked")
public V remove(Object key) {
- if (key == null)
- throw new NullPointerException();
- return (V)internalReplace(key, null, null);
+ return internalReplace(key, null, null);
}
/**
@@ -1154,11 +2841,7 @@ public class ConcurrentHashMapV8
* @throws NullPointerException if the specified key is null
*/
public boolean remove(Object key, Object value) {
- if (key == null)
- throw new NullPointerException();
- if (value == null)
- return false;
- return internalReplace(key, null, value) != null;
+ return value != null && internalReplace(key, null, value) != null;
}
/**
@@ -1169,7 +2852,7 @@ public class ConcurrentHashMapV8
public boolean replace(K key, V oldValue, V newValue) {
if (key == null || oldValue == null || newValue == null)
throw new NullPointerException();
- return internalReplace(key, newValue, oldValue) != null;
+ return internalReplace(key, newValue, oldValue) != null;
}
/**
@@ -1179,11 +2862,10 @@ public class ConcurrentHashMapV8
* or {@code null} if there was no mapping for the key
* @throws NullPointerException if the specified key or value is null
*/
- @SuppressWarnings("unchecked")
public V replace(K key, V value) {
if (key == null || value == null)
throw new NullPointerException();
- return (V)internalReplace(key, value, null);
+ return internalReplace(key, value, null);
}
/**
@@ -1196,43 +2878,41 @@ public class ConcurrentHashMapV8
/**
* Returns a {@link Set} view of the keys contained in this map.
* The set is backed by the map, so changes to the map are
- * reflected in the set, and vice-versa. The set supports element
- * removal, which removes the corresponding mapping from this map,
- * via the {@code Iterator.remove}, {@code Set.remove},
- * {@code removeAll}, {@code retainAll}, and {@code clear}
- * operations. It does not support the {@code add} or
- * {@code addAll} operations.
+ * reflected in the set, and vice-versa.
*
- * The view's {@code iterator} is a "weakly consistent" iterator
- * that will never throw {@link ConcurrentModificationException},
- * and guarantees to traverse elements as they existed upon
- * construction of the iterator, and may (but is not guaranteed to)
- * reflect any modifications subsequent to construction.
+ * @return the set view
+ */
+ public KeySetView keySet() {
+ KeySetView ks = keySet;
+ return (ks != null) ? ks : (keySet = new KeySetView(this, null));
+ }
+
+ /**
+ * Returns a {@link Set} view of the keys in this map, using the
+ * given common mapped value for any additions (i.e., {@link
+ * Collection#add} and {@link Collection#addAll}). This is of
+ * course only appropriate if it is acceptable to use the same
+ * value for all additions from this view.
+ *
+ * @param mappedValue the mapped value to use for any
+ * additions.
+ * @return the set view
+ * @throws NullPointerException if the mappedValue is null
*/
- public Set keySet() {
- Set ks = keySet;
- return (ks != null) ? ks : (keySet = new KeySet());
+ public KeySetView keySet(V mappedValue) {
+ if (mappedValue == null)
+ throw new NullPointerException();
+ return new KeySetView(this, mappedValue);
}
/**
* Returns a {@link Collection} view of the values contained in this map.
* The collection is backed by the map, so changes to the map are
- * reflected in the collection, and vice-versa. The collection
- * supports element removal, which removes the corresponding
- * mapping from this map, via the {@code Iterator.remove},
- * {@code Collection.remove}, {@code removeAll},
- * {@code retainAll}, and {@code clear} operations. It does not
- * support the {@code add} or {@code addAll} operations.
- *
- *