# HG changeset patch # User Jaroslav Tulach # Date 1484633046 -3600 # Node ID cd1cc103a03c762dffe542bfe75bf809585fc3a0 # Parent 87bb69774b64e1fee7f10185a93198ffb8caac7b Implementation of ClassValue for bck2brwsr diff -r 87bb69774b64 -r cd1cc103a03c rt/emul/compact/src/main/java/java/lang/ClassValue.java --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/rt/emul/compact/src/main/java/java/lang/ClassValue.java Tue Jan 17 07:04:06 2017 +0100 @@ -0,0 +1,179 @@ +/* + * 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.lang.Class; +import org.apidesign.bck2brwsr.core.JavaScriptBody; + +/** + * 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) { + T value = access(type, id, false, null); + if (value == undefined()) { + value = access(type, id, true, computeValue(type)); + } + return value; + } + + /** + * 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) { + access(type, id, true, undefined()); + } + + /// Implementation... + + private static int COUNTER = 0; + private final int id = COUNTER++; + + @JavaScriptBody(args = {}, body = "return undefined;") + private static native Object undefined(); + + @JavaScriptBody(args = { "where", "index", "set", "newValue" }, body = + "var data = where['values'];\n" + + "if (!data) {\n" + + " data = where['values'] = [];\n" + + "}\n" + + "if (set) {\n" + + " data[index] = newValue;\n" + + "}\n" + + "return data[index];\n" + + "" + ) + private static native T access(Class where, int index, boolean set, T newValue); +} diff -r 87bb69774b64 -r cd1cc103a03c rt/emul/compacttest/src/test/java/org/apidesign/bck2brwsr/tck/ReflectionClassValueTest.java --- a/rt/emul/compacttest/src/test/java/org/apidesign/bck2brwsr/tck/ReflectionClassValueTest.java Tue Jan 17 06:16:06 2017 +0100 +++ b/rt/emul/compacttest/src/test/java/org/apidesign/bck2brwsr/tck/ReflectionClassValueTest.java Tue Jan 17 07:04:06 2017 +0100 @@ -17,6 +17,8 @@ */ package org.apidesign.bck2brwsr.tck; +import java.io.Serializable; +import java.lang.ClassValue; import org.apidesign.bck2brwsr.vmtest.Compare; import org.apidesign.bck2brwsr.vmtest.VMTest; import org.testng.annotations.Factory; @@ -56,13 +58,6 @@ return one == two; } - @Compare public boolean valueCanBeCleared() { - String one = LOWER.get(Runnable.class); - LOWER.remove(Runnable.class); - String two = LOWER.get(Runnable.class); - return one != two; - } - @Compare public String upperObject() { return UPPER.get(Object.class); } @@ -79,6 +74,47 @@ return LOWER.get(CharSequence.class) + UPPER.get(CharSequence.class); } + private static final class CountingNull extends ClassValue { + int cnt; + + @Override + protected Object computeValue(Class type) { + cnt++; + return null; + } + } + + @Compare public int getNullThreeTimes() { + CountingNull counter = new CountingNull(); + Object o1 = counter.get(Serializable.class); + Object o2 = counter.get(Serializable.class); + Object o3 = counter.get(Serializable.class); + assert o1 == null; + assert o2 == null; + assert o3 == null; + return counter.cnt; + } + + private static final class NewObj extends ClassValue { + int cnt; + + @Override + protected Integer computeValue(Class type) { + cnt++; + return new Integer(cnt); + } + } + + @Compare public boolean valueCanBeCleared() { + NewObj cache = new NewObj(); + Integer one = cache.get(Runnable.class); + Integer two = cache.get(Runnable.class); + assert one == two; + cache.remove(Runnable.class); + Integer three = cache.get(Runnable.class); + return one != three; + } + @Factory public static Object[] create() { return VMTest.create(ReflectionClassValueTest.class); diff -r 87bb69774b64 -r cd1cc103a03c rt/emul/mini/src/main/java/java/lang/ClassValue.java --- a/rt/emul/mini/src/main/java/java/lang/ClassValue.java Tue Jan 17 06:16:06 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: - *

    - *
  • {@code T} calls {@code CV.get(C)} and sees state {@code 2N} - *
  • {@code T} quickly computes a time-dependent value {@code V0} and gets ready to install it - *
  • {@code T} is hit by an unlucky paging or scheduling event, and goes to sleep for a long time - *
  • ...meanwhile, {@code T2} also calls {@code CV.get(C)} and sees state {@code 2N} - *
  • {@code T2} quickly computes a similar time-dependent value {@code V1} and installs it on {@code CV.get(C)} - *
  • {@code T2} (or a third thread) then calls {@code CV.remove(C)}, undoing {@code T2}'s work - *
  • the previous actions of {@code T2} are repeated several times - *
  • also, the relevant computed values change over time: {@code V1}, {@code V2}, ... - *
  • ...meanwhile, {@code T} wakes up and attempts to install {@code V0}; this must fail - *
- * 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; - } - } -}