diff -r 84dba41e2e92 -r 87bb69774b64 emul/src/main/java/java/lang/ClassValue.java --- a/emul/src/main/java/java/lang/ClassValue.java Tue Jan 17 06:15:09 2017 +0100 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,239 +0,0 @@ -/* - * Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved. - * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. - * - * This code is free software; you can redistribute it and/or modify it - * under the terms of the GNU General Public License version 2 only, as - * published by the Free Software Foundation. Oracle designates this - * particular file as subject to the "Classpath" exception as provided - * by Oracle in the LICENSE file that accompanied this code. - * - * This code is distributed in the hope that it will be useful, but WITHOUT - * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or - * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License - * version 2 for more details (a copy is included in the LICENSE file that - * accompanied this code). - * - * You should have received a copy of the GNU General Public License version - * 2 along with this work; if not, write to the Free Software Foundation, - * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. - * - * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA - * or visit www.oracle.com if you need additional information or have any - * questions. - */ - -package java.lang; - -import java.util.WeakHashMap; -import java.util.concurrent.atomic.AtomicInteger; - -/** - * Lazily associate a computed value with (potentially) every type. - * For example, if a dynamic language needs to construct a message dispatch - * table for each class encountered at a message send call site, - * it can use a {@code ClassValue} to cache information needed to - * perform the message send quickly, for each class encountered. - * @author John Rose, JSR 292 EG - * @since 1.7 - */ -public abstract class ClassValue { - /** - * Sole constructor. (For invocation by subclass constructors, typically - * implicit.) - */ - protected ClassValue() { - } - - /** - * Computes the given class's derived value for this {@code ClassValue}. - *

- * This method will be invoked within the first thread that accesses - * the value with the {@link #get get} method. - *

- * Normally, this method is invoked at most once per class, - * but it may be invoked again if there has been a call to - * {@link #remove remove}. - *

- * If this method throws an exception, the corresponding call to {@code get} - * will terminate abnormally with that exception, and no class value will be recorded. - * - * @param type the type whose class value must be computed - * @return the newly computed value associated with this {@code ClassValue}, for the given class or interface - * @see #get - * @see #remove - */ - protected abstract T computeValue(Class type); - - /** - * Returns the value for the given class. - * If no value has yet been computed, it is obtained by - * an invocation of the {@link #computeValue computeValue} method. - *

- * The actual installation of the value on the class - * is performed atomically. - * At that point, if several racing threads have - * computed values, one is chosen, and returned to - * all the racing threads. - *

- * The {@code type} parameter is typically a class, but it may be any type, - * such as an interface, a primitive type (like {@code int.class}), or {@code void.class}. - *

- * In the absence of {@code remove} calls, a class value has a simple - * state diagram: uninitialized and initialized. - * When {@code remove} calls are made, - * the rules for value observation are more complex. - * See the documentation for {@link #remove remove} for more information. - * - * @param type the type whose class value must be computed or retrieved - * @return the current value associated with this {@code ClassValue}, for the given class or interface - * @throws NullPointerException if the argument is null - * @see #remove - * @see #computeValue - */ - public T get(Class type) { - ClassValueMap map = getMap(type); - if (map != null) { - Object x = map.get(this); - if (x != null) { - return (T) map.unmaskNull(x); - } - } - return setComputedValue(type); - } - - /** - * Removes the associated value for the given class. - * If this value is subsequently {@linkplain #get read} for the same class, - * its value will be reinitialized by invoking its {@link #computeValue computeValue} method. - * This may result in an additional invocation of the - * {@code computeValue} method for the given class. - *

- * In order to explain the interaction between {@code get} and {@code remove} calls, - * we must model the state transitions of a class value to take into account - * the alternation between uninitialized and initialized states. - * To do this, number these states sequentially from zero, and note that - * uninitialized (or removed) states are numbered with even numbers, - * while initialized (or re-initialized) states have odd numbers. - *

- * When a thread {@code T} removes a class value in state {@code 2N}, - * nothing happens, since the class value is already uninitialized. - * Otherwise, the state is advanced atomically to {@code 2N+1}. - *

- * When a thread {@code T} queries a class value in state {@code 2N}, - * the thread first attempts to initialize the class value to state {@code 2N+1} - * by invoking {@code computeValue} and installing the resulting value. - *

- * When {@code T} attempts to install the newly computed value, - * if the state is still at {@code 2N}, the class value will be initialized - * with the computed value, advancing it to state {@code 2N+1}. - *

- * Otherwise, whether the new state is even or odd, - * {@code T} will discard the newly computed value - * and retry the {@code get} operation. - *

- * Discarding and retrying is an important proviso, - * since otherwise {@code T} could potentially install - * a disastrously stale value. For example: - *

- * We can assume in the above scenario that {@code CV.computeValue} uses locks to properly - * observe the time-dependent states as it computes {@code V1}, etc. - * This does not remove the threat of a stale value, since there is a window of time - * between the return of {@code computeValue} in {@code T} and the installation - * of the the new value. No user synchronization is possible during this time. - * - * @param type the type whose class value must be removed - * @throws NullPointerException if the argument is null - */ - public void remove(Class type) { - ClassValueMap map = getMap(type); - if (map != null) { - synchronized (map) { - map.remove(this); - } - } - } - - /// Implementation... - // FIXME: Use a data structure here similar that of ThreadLocal (7030453). - - private static final AtomicInteger STORE_BARRIER = new AtomicInteger(); - - /** Slow path for {@link #get}. */ - private T setComputedValue(Class type) { - ClassValueMap map = getMap(type); - if (map == null) { - map = initializeMap(type); - } - T value = computeValue(type); - STORE_BARRIER.lazySet(0); - // All stores pending from computeValue are completed. - synchronized (map) { - // Warm up the table with a null entry. - map.preInitializeEntry(this); - } - STORE_BARRIER.lazySet(0); - // All stores pending from table expansion are completed. - synchronized (map) { - value = (T) map.initializeEntry(this, value); - // One might fear a possible race condition here - // if the code for map.put has flushed the write - // to map.table[*] before the writes to the Map.Entry - // are done. This is not possible, since we have - // warmed up the table with an empty entry. - } - return value; - } - - // Replace this map by a per-class slot. - private static final WeakHashMap, ClassValueMap> ROOT - = new WeakHashMap, ClassValueMap>(); - - private static ClassValueMap getMap(Class type) { - type.getClass(); // test for null - return ROOT.get(type); - } - - private static ClassValueMap initializeMap(Class type) { - synchronized (ClassValue.class) { - ClassValueMap map = ROOT.get(type); - if (map == null) - ROOT.put(type, map = new ClassValueMap()); - return map; - } - } - - static class ClassValueMap extends WeakHashMap { - /** Make sure this table contains an Entry for the given key, even if it is empty. */ - void preInitializeEntry(ClassValue key) { - if (!this.containsKey(key)) - this.put(key, null); - } - /** Make sure this table contains a non-empty Entry for the given key. */ - Object initializeEntry(ClassValue key, Object value) { - Object prior = this.get(key); - if (prior != null) { - return unmaskNull(prior); - } - this.put(key, maskNull(value)); - return value; - } - - Object maskNull(Object x) { - return x == null ? this : x; - } - Object unmaskNull(Object x) { - return x == this ? null : x; - } - } -}