--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/share/classes/java/dyn/ClassValue.java Tue Sep 14 01:42:03 2010 -0700
@@ -0,0 +1,173 @@
+/*
+ * Copyright (c) 2010, 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.dyn;
+
+import java.util.WeakHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+
+/**
+ * Lazily associate a computed value with (potentially) every class.
+ * @author John Rose, JSR 292 EG
+ */
+public abstract class ClassValue<T> {
+ /**
+ * Compute the given class's derived value for this {@code ClassValue}.
+ * <p>
+ * This method will be invoked within the first thread that accesses
+ * the value with the {@link #get}.
+ * <p>
+ * Normally, this method is invoked at most once per class,
+ * but it may be invoked again in case of subsequent invocations
+ * of {@link #remove} followed by {@link #get}.
+ *
+ * @return the computed value for this thread-local
+ */
+ protected abstract T computeValue(Class<?> type);
+
+ /**
+ * Creates a new class value.
+ */
+ protected ClassValue() {
+ }
+
+ /**
+ * Returns the value for the given class.
+ * If no value has yet been computed, it is obtained by
+ * by an invocation of the {@link #computeValue} method.
+ * <p>
+ * The actual installation of the value on the class
+ * is performed while the class's synchronization lock
+ * is held. At that point, if racing threads have
+ * computed values, one is chosen, and returned to
+ * all the racing threads.
+ *
+ * @return the current thread's value of this thread-local
+ */
+ 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} method.
+ * This may result in an additional invocation of the
+ * {@code computeValue} method for the given class.
+ */
+ public void remove(Class<?> type) {
+ ClassValueMap map = getMap(type);
+ if (map != null) {
+ synchronized (map) {
+ map.remove(this);
+ }
+ }
+ }
+
+ /// Implementation...
+
+ /** The hash code for this type is based on the identity of the object,
+ * and is well-dispersed for power-of-two tables.
+ */
+ public final int hashCode() { return hashCode; }
+ private final int hashCode = HASH_CODES.getAndAdd(0x61c88647);
+ private static final AtomicInteger HASH_CODES = new AtomicInteger();
+
+ 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);
+ }
+ // 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<Class<?>, ClassValueMap> ROOT
+ = new WeakHashMap<Class<?>, ClassValueMap>();
+
+ private static ClassValueMap getMap(Class<?> type) {
+ 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<ClassValue, Object> {
+ /** 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;
+ }
+ }
+}