jboss netty5.0

/* * Copyright 2013 The Netty Project * * The Netty Project licenses this file to you under the Apache License, * version 2.0 (the "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at: * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations * under the License. */ /* * Written by Doug Lea with assistance from members of JCP JSR-166 * Expert Group and released to the public domain, as explained at * http://creativecommons.org/publicdomain/zero/1.0/ */ package io.netty.util.internal.chmv8; import io.netty.util.internal.IntegerHolder; import io.netty.util.internal.InternalThreadLocalMap; import java.io.ObjectStreamField; import java.io.Serializable; import java.lang.reflect.ParameterizedType; import java.lang.reflect.Type; import java.util.Arrays; import java.util.Collection; import java.util.ConcurrentModificationException; import java.util.Enumeration; import java.util.HashMap; import java.util.Hashtable; import java.util.Iterator; import java.util.Map; import java.util.NoSuchElementException; import java.util.Set; import java.util.concurrent.ConcurrentMap; import java.util.concurrent.atomic.AtomicInteger; import java.util.concurrent.atomic.AtomicReference; import java.util.concurrent.locks.LockSupport; import java.util.concurrent.locks.ReentrantLock; /** * A hash table supporting full concurrency of retrievals and * high expected concurrency for updates. This class obeys the * same functional specification as {@link java.util.Hashtable}, and * includes versions of methods corresponding to each method of * {@code Hashtable}. However, even though all operations are * thread-safe, retrieval operations do <em>not</em> entail locking, * and there is <em>not</em> any support for locking the entire table * in a way that prevents all access. This class is fully * interoperable with {@code Hashtable} in programs that rely on its * thread safety but not on its synchronization details. * * <p>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 <em>completed</em> update operations holding upon their * onset. (More formally, an update operation for a given key bears a * <em>happens-before</em> 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 <em>not</em> 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. * * <p>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. To ameliorate impact, when keys are {@link Comparable}, * this class may use comparison order among keys to help break ties. * * <p>A {@link Set} projection of a ConcurrentHashMapV8 may be created * (using {@link #newKeySet()} or {@link #newKeySet(int)}), or viewed * (using {@link #keySet(Object)} when only keys are of interest, and the * mapped values are (perhaps transiently) not used or all take the * same mapping value. * * <p>This class and its views and iterators implement all of the * <em>optional</em> methods of the {@link Map} and {@link Iterator} * interfaces. * * <p>Like {@link Hashtable} but unlike {@link HashMap}, this class * does <em>not</em> allow {@code null} to be used as a key or value. * * <p>ConcurrentHashMapV8s support a set of sequential and parallel bulk * operations that 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. Bulk operations on {@link java.util.Map.Entry} * objects do not support method {@code setValue}. * * <ul> * <li> forEach: Perform a given action on each element. * A variant form applies a given transformation on each element * before performing the action.</li> * * <li> search: Return the first available non-null result of * applying a given function on each element; skipping further * search when a result is found.</li> * * <li> reduce: Accumulate each element. The supplied reduction * function cannot rely on ordering (more formally, it should be * both associative and commutative). There are five variants: * * <ul> * * <li> Plain reductions. (There is not a form of this method for * (key, value) function arguments since there is no corresponding * return type.)</li> * * <li> Mapped reductions that accumulate the results of a given * function applied to each element.</li> * * <li> Reductions to scalar doubles, longs, and ints, using a * given basis value.</li> * * </ul> * </li> * </ul> * * <p>These bulk operations accept a {@code parallelismThreshold} * argument. Methods proceed sequentially if the current map size is * estimated to be less than the given threshold. Using a value of * {@code Long.MAX_VALUE} suppresses all parallelism. Using a value * of {@code 1} results in maximal parallelism by partitioning into * enough subtasks to fully utilize the {@link * ForkJoinPool#commonPool()} that is