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/*
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* Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.lang;
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import java.lang.ClassValue.ClassValueMap;
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import java.util.WeakHashMap;
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import java.lang.ref.WeakReference;
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import java.util.concurrent.atomic.AtomicInteger;
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import static java.lang.ClassValue.ClassValueMap.probeHomeLocation;
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import static java.lang.ClassValue.ClassValueMap.probeBackupLocations;
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/**
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* Lazily associate a computed value with (potentially) every type.
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* For example, if a dynamic language needs to construct a message dispatch
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* table for each class encountered at a message send call site,
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* it can use a {@code ClassValue} to cache information needed to
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* perform the message send quickly, for each class encountered.
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* @author John Rose, JSR 292 EG
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* @since 1.7
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*/
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public abstract class ClassValue<T> {
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/**
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* Sole constructor. (For invocation by subclass constructors, typically
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* implicit.)
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*/
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protected ClassValue() {
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}
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/**
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* Computes the given class's derived value for this {@code ClassValue}.
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* <p>
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* This method will be invoked within the first thread that accesses
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* the value with the {@link #get get} method.
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* <p>
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* Normally, this method is invoked at most once per class,
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* but it may be invoked again if there has been a call to
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* {@link #remove remove}.
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* <p>
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* If this method throws an exception, the corresponding call to {@code get}
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* will terminate abnormally with that exception, and no class value will be recorded.
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*
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* @param type the type whose class value must be computed
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* @return the newly computed value associated with this {@code ClassValue}, for the given class or interface
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* @see #get
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* @see #remove
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*/
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protected abstract T computeValue(Class<?> type);
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/**
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* Returns the value for the given class.
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* If no value has yet been computed, it is obtained by
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* an invocation of the {@link #computeValue computeValue} method.
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* <p>
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* The actual installation of the value on the class
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* is performed atomically.
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* At that point, if several racing threads have
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* computed values, one is chosen, and returned to
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* all the racing threads.
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* <p>
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* The {@code type} parameter is typically a class, but it may be any type,
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* such as an interface, a primitive type (like {@code int.class}), or {@code void.class}.
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* <p>
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* In the absence of {@code remove} calls, a class value has a simple
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* state diagram: uninitialized and initialized.
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* When {@code remove} calls are made,
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* the rules for value observation are more complex.
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* See the documentation for {@link #remove remove} for more information.
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*
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* @param type the type whose class value must be computed or retrieved
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* @return the current value associated with this {@code ClassValue}, for the given class or interface
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* @throws NullPointerException if the argument is null
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* @see #remove
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* @see #computeValue
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*/
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public T get(Class<?> type) {
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// non-racing this.hashCodeForCache : final int
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Entry<?>[] cache;
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Entry<T> e = probeHomeLocation(cache = getCacheCarefully(type), this);
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// racing e : current value <=> stale value from current cache or from stale cache
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// invariant: e is null or an Entry with readable Entry.version and Entry.value
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if (match(e))
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// invariant: No false positive matches. False negatives are OK if rare.
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// The key fact that makes this work: if this.version == e.version,
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// then this thread has a right to observe (final) e.value.
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return e.value();
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// The fast path can fail for any of these reasons:
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// 1. no entry has been computed yet
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// 2. hash code collision (before or after reduction mod cache.length)
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// 3. an entry has been removed (either on this type or another)
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// 4. the GC has somehow managed to delete e.version and clear the reference
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return getFromBackup(cache, type);
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}
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/**
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* Removes the associated value for the given class.
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* If this value is subsequently {@linkplain #get read} for the same class,
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* its value will be reinitialized by invoking its {@link #computeValue computeValue} method.
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* This may result in an additional invocation of the
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* {@code computeValue} method for the given class.
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* <p>
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* In order to explain the interaction between {@code get} and {@code remove} calls,
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* we must model the state transitions of a class value to take into account
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* the alternation between uninitialized and initialized states.
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* To do this, number these states sequentially from zero, and note that
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* uninitialized (or removed) states are numbered with even numbers,
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* while initialized (or re-initialized) states have odd numbers.
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* <p>
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* When a thread {@code T} removes a class value in state {@code 2N},
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* nothing happens, since the class value is already uninitialized.
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* Otherwise, the state is advanced atomically to {@code 2N+1}.
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* <p>
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* When a thread {@code T} queries a class value in state {@code 2N},
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* the thread first attempts to initialize the class value to state {@code 2N+1}
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* by invoking {@code computeValue} and installing the resulting value.
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* <p>
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* When {@code T} attempts to install the newly computed value,
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* if the state is still at {@code 2N}, the class value will be initialized
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* with the computed value, advancing it to state {@code 2N+1}.
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* <p>
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* Otherwise, whether the new state is even or odd,
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* {@code T} will discard the newly computed value
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* and retry the {@code get} operation.
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* <p>
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* Discarding and retrying is an important proviso,
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* since otherwise {@code T} could potentially install
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* a disastrously stale value. For example:
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* <ul>
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* <li>{@code T} calls {@code CV.get(C)} and sees state {@code 2N}
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* <li>{@code T} quickly computes a time-dependent value {@code V0} and gets ready to install it
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* <li>{@code T} is hit by an unlucky paging or scheduling event, and goes to sleep for a long time
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* <li>...meanwhile, {@code T2} also calls {@code CV.get(C)} and sees state {@code 2N}
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* <li>{@code T2} quickly computes a similar time-dependent value {@code V1} and installs it on {@code CV.get(C)}
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* <li>{@code T2} (or a third thread) then calls {@code CV.remove(C)}, undoing {@code T2}'s work
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* <li> the previous actions of {@code T2} are repeated several times
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* <li> also, the relevant computed values change over time: {@code V1}, {@code V2}, ...
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* <li>...meanwhile, {@code T} wakes up and attempts to install {@code V0}; <em>this must fail</em>
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* </ul>
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* We can assume in the above scenario that {@code CV.computeValue} uses locks to properly
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* observe the time-dependent states as it computes {@code V1}, etc.
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* This does not remove the threat of a stale value, since there is a window of time
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* between the return of {@code computeValue} in {@code T} and the installation
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* of the the new value. No user synchronization is possible during this time.
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*
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* @param type the type whose class value must be removed
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* @throws NullPointerException if the argument is null
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*/
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public void remove(Class<?> type) {
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ClassValueMap map = getMap(type);
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map.removeEntry(this);
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}
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// Possible functionality for JSR 292 MR 1
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/*public*/ void put(Class<?> type, T value) {
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ClassValueMap map = getMap(type);
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map.changeEntry(this, value);
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}
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/// --------
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/// Implementation...
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/// --------
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/** Return the cache, if it exists, else a dummy empty cache. */
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private static Entry<?>[] getCacheCarefully(Class<?> type) {
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// racing type.classValueMap{.cacheArray} : null => new Entry[X] <=> new Entry[Y]
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ClassValueMap map = (ClassValueMap) type.classValueMap;
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if (map == null) return EMPTY_CACHE;
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Entry<?>[] cache = map.getCache();
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return cache;
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// invariant: returned value is safe to dereference and check for an Entry
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}
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/** Initial, one-element, empty cache used by all Class instances. Must never be filled. */
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private static final Entry<?>[] EMPTY_CACHE = { null };
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/**
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* Slow tail of ClassValue.get to retry at nearby locations in the cache,
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* or take a slow lock and check the hash table.
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* Called only if the first probe was empty or a collision.
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* This is a separate method, so compilers can process it independently.
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*/
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private T getFromBackup(Entry<?>[] cache, Class<?> type) {
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Entry<T> e = probeBackupLocations(cache, this);
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if (e != null)
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return e.value();
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return getFromHashMap(type);
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}
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// Hack to suppress warnings on the (T) cast, which is a no-op.
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@SuppressWarnings("unchecked")
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Entry<T> castEntry(Entry<?> e) { return (Entry<T>) e; }
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/** Called when the fast path of get fails, and cache reprobe also fails.
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*/
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private T getFromHashMap(Class<?> type) {
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// The fail-safe recovery is to fall back to the underlying classValueMap.
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ClassValueMap map = getMap(type);
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for (;;) {
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Entry<T> e = map.startEntry(this);
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if (!e.isPromise())
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return e.value();
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try {
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// Try to make a real entry for the promised version.
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e = makeEntry(e.version(), computeValue(type));
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} finally {
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// Whether computeValue throws or returns normally,
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// be sure to remove the empty entry.
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e = map.finishEntry(this, e);
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}
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if (e != null)
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return e.value();
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// else try again, in case a racing thread called remove (so e == null)
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}
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}
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/** Check that e is non-null, matches this ClassValue, and is live. */
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boolean match(Entry<?> e) {
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// racing e.version : null (blank) => unique Version token => null (GC-ed version)
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// non-racing this.version : v1 => v2 => ... (updates are read faithfully from volatile)
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return (e != null && e.get() == this.version);
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// invariant: No false positives on version match. Null is OK for false negative.
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// invariant: If version matches, then e.value is readable (final set in Entry.<init>)
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}
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/** Internal hash code for accessing Class.classValueMap.cacheArray. */
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final int hashCodeForCache = nextHashCode.getAndAdd(HASH_INCREMENT) & HASH_MASK;
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/** Value stream for hashCodeForCache. See similar structure in ThreadLocal. */
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private static final AtomicInteger nextHashCode = new AtomicInteger();
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/** Good for power-of-two tables. See similar structure in ThreadLocal. */
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private static final int HASH_INCREMENT = 0x61c88647;
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/** Mask a hash code to be positive but not too large, to prevent wraparound. */
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static final int HASH_MASK = (-1 >>> 2);
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/**
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* Private key for retrieval of this object from ClassValueMap.
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*/
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static class Identity {
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}
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/**
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* This ClassValue's identity, expressed as an opaque object.
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* The main object {@code ClassValue.this} is incorrect since
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* subclasses may override {@code ClassValue.equals}, which
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* could confuse keys in the ClassValueMap.
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*/
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final Identity identity = new Identity();
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/**
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* Current version for retrieving this class value from the cache.
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* Any number of computeValue calls can be cached in association with one version.
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* But the version changes when a remove (on any type) is executed.
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* A version change invalidates all cache entries for the affected ClassValue,
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* by marking them as stale. Stale cache entries do not force another call
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|
279 |
* to computeValue, but they do require a synchronized visit to a backing map.
|
jaroslav@1649
|
280 |
* <p>
|
jaroslav@1649
|
281 |
* All user-visible state changes on the ClassValue take place under
|
jaroslav@1649
|
282 |
* a lock inside the synchronized methods of ClassValueMap.
|
jaroslav@1649
|
283 |
* Readers (of ClassValue.get) are notified of such state changes
|
jaroslav@1649
|
284 |
* when this.version is bumped to a new token.
|
jaroslav@1649
|
285 |
* This variable must be volatile so that an unsynchronized reader
|
jaroslav@1649
|
286 |
* will receive the notification without delay.
|
jaroslav@1649
|
287 |
* <p>
|
jaroslav@1649
|
288 |
* If version were not volatile, one thread T1 could persistently hold onto
|
jaroslav@1649
|
289 |
* a stale value this.value == V1, while while another thread T2 advances
|
jaroslav@1649
|
290 |
* (under a lock) to this.value == V2. This will typically be harmless,
|
jaroslav@1649
|
291 |
* but if T1 and T2 interact causally via some other channel, such that
|
jaroslav@1649
|
292 |
* T1's further actions are constrained (in the JMM) to happen after
|
jaroslav@1649
|
293 |
* the V2 event, then T1's observation of V1 will be an error.
|
jaroslav@1649
|
294 |
* <p>
|
jaroslav@1649
|
295 |
* The practical effect of making this.version be volatile is that it cannot
|
jaroslav@1649
|
296 |
* be hoisted out of a loop (by an optimizing JIT) or otherwise cached.
|
jaroslav@1649
|
297 |
* Some machines may also require a barrier instruction to execute
|
jaroslav@1649
|
298 |
* before this.version.
|
jaroslav@1649
|
299 |
*/
|
jaroslav@1649
|
300 |
private volatile Version<T> version = new Version<>(this);
|
jaroslav@1649
|
301 |
Version<T> version() { return version; }
|
jaroslav@1649
|
302 |
void bumpVersion() { version = new Version<>(this); }
|
jaroslav@1649
|
303 |
static class Version<T> {
|
jaroslav@1649
|
304 |
private final ClassValue<T> classValue;
|
jaroslav@1649
|
305 |
private final Entry<T> promise = new Entry<>(this);
|
jaroslav@1649
|
306 |
Version(ClassValue<T> classValue) { this.classValue = classValue; }
|
jaroslav@1649
|
307 |
ClassValue<T> classValue() { return classValue; }
|
jaroslav@1649
|
308 |
Entry<T> promise() { return promise; }
|
jaroslav@1649
|
309 |
boolean isLive() { return classValue.version() == this; }
|
jaroslav@1649
|
310 |
}
|
jaroslav@1649
|
311 |
|
jaroslav@1649
|
312 |
/** One binding of a value to a class via a ClassValue.
|
jaroslav@1649
|
313 |
* States are:<ul>
|
jaroslav@1649
|
314 |
* <li> promise if value == Entry.this
|
jaroslav@1649
|
315 |
* <li> else dead if version == null
|
jaroslav@1649
|
316 |
* <li> else stale if version != classValue.version
|
jaroslav@1649
|
317 |
* <li> else live </ul>
|
jaroslav@1649
|
318 |
* Promises are never put into the cache; they only live in the
|
jaroslav@1649
|
319 |
* backing map while a computeValue call is in flight.
|
jaroslav@1649
|
320 |
* Once an entry goes stale, it can be reset at any time
|
jaroslav@1649
|
321 |
* into the dead state.
|
jaroslav@1649
|
322 |
*/
|
jaroslav@1649
|
323 |
static class Entry<T> extends WeakReference<Version<T>> {
|
jaroslav@1649
|
324 |
final Object value; // usually of type T, but sometimes (Entry)this
|
jaroslav@1649
|
325 |
Entry(Version<T> version, T value) {
|
jaroslav@1649
|
326 |
super(version);
|
jaroslav@1649
|
327 |
this.value = value; // for a regular entry, value is of type T
|
jaroslav@1649
|
328 |
}
|
jaroslav@1649
|
329 |
private void assertNotPromise() { assert(!isPromise()); }
|
jaroslav@1649
|
330 |
/** For creating a promise. */
|
jaroslav@1649
|
331 |
Entry(Version<T> version) {
|
jaroslav@1649
|
332 |
super(version);
|
jaroslav@1649
|
333 |
this.value = this; // for a promise, value is not of type T, but Entry!
|
jaroslav@1649
|
334 |
}
|
jaroslav@1649
|
335 |
/** Fetch the value. This entry must not be a promise. */
|
jaroslav@1649
|
336 |
@SuppressWarnings("unchecked") // if !isPromise, type is T
|
jaroslav@1649
|
337 |
T value() { assertNotPromise(); return (T) value; }
|
jaroslav@1649
|
338 |
boolean isPromise() { return value == this; }
|
jaroslav@1649
|
339 |
Version<T> version() { return get(); }
|
jaroslav@1649
|
340 |
ClassValue<T> classValueOrNull() {
|
jaroslav@1649
|
341 |
Version<T> v = version();
|
jaroslav@1649
|
342 |
return (v == null) ? null : v.classValue();
|
jaroslav@1649
|
343 |
}
|
jaroslav@1649
|
344 |
boolean isLive() {
|
jaroslav@1649
|
345 |
Version<T> v = version();
|
jaroslav@1649
|
346 |
if (v == null) return false;
|
jaroslav@1649
|
347 |
if (v.isLive()) return true;
|
jaroslav@1649
|
348 |
clear();
|
jaroslav@1649
|
349 |
return false;
|
jaroslav@1649
|
350 |
}
|
jaroslav@1649
|
351 |
Entry<T> refreshVersion(Version<T> v2) {
|
jaroslav@1649
|
352 |
assertNotPromise();
|
jaroslav@1649
|
353 |
@SuppressWarnings("unchecked") // if !isPromise, type is T
|
jaroslav@1649
|
354 |
Entry<T> e2 = new Entry<>(v2, (T) value);
|
jaroslav@1649
|
355 |
clear();
|
jaroslav@1649
|
356 |
// value = null -- caller must drop
|
jaroslav@1649
|
357 |
return e2;
|
jaroslav@1649
|
358 |
}
|
jaroslav@1649
|
359 |
static final Entry<?> DEAD_ENTRY = new Entry<>(null, null);
|
jaroslav@1649
|
360 |
}
|
jaroslav@1649
|
361 |
|
jaroslav@1649
|
362 |
/** Return the backing map associated with this type. */
|
jaroslav@1649
|
363 |
private static ClassValueMap getMap(Class<?> type) {
|
jaroslav@1649
|
364 |
// racing type.classValueMap : null (blank) => unique ClassValueMap
|
jaroslav@1649
|
365 |
// if a null is observed, a map is created (lazily, synchronously, uniquely)
|
jaroslav@1649
|
366 |
// all further access to that map is synchronized
|
jaroslav@1653
|
367 |
ClassValueMap map = (ClassValueMap)type.classValueMap;
|
jaroslav@1649
|
368 |
if (map != null) return map;
|
jaroslav@1649
|
369 |
return initializeMap(type);
|
jaroslav@1649
|
370 |
}
|
jaroslav@1649
|
371 |
|
jaroslav@1649
|
372 |
private static final Object CRITICAL_SECTION = new Object();
|
jaroslav@1649
|
373 |
private static ClassValueMap initializeMap(Class<?> type) {
|
jaroslav@1649
|
374 |
ClassValueMap map;
|
jaroslav@1649
|
375 |
synchronized (CRITICAL_SECTION) { // private object to avoid deadlocks
|
jaroslav@1649
|
376 |
// happens about once per type
|
jaroslav@1653
|
377 |
if ((map = (ClassValueMap)type.classValueMap) == null)
|
jaroslav@1649
|
378 |
type.classValueMap = map = new ClassValueMap(type);
|
jaroslav@1649
|
379 |
}
|
jaroslav@1649
|
380 |
return map;
|
jaroslav@1649
|
381 |
}
|
jaroslav@1649
|
382 |
|
jaroslav@1649
|
383 |
static <T> Entry<T> makeEntry(Version<T> explicitVersion, T value) {
|
jaroslav@1649
|
384 |
// Note that explicitVersion might be different from this.version.
|
jaroslav@1649
|
385 |
return new Entry<>(explicitVersion, value);
|
jaroslav@1649
|
386 |
|
jaroslav@1649
|
387 |
// As soon as the Entry is put into the cache, the value will be
|
jaroslav@1649
|
388 |
// reachable via a data race (as defined by the Java Memory Model).
|
jaroslav@1649
|
389 |
// This race is benign, assuming the value object itself can be
|
jaroslav@1649
|
390 |
// read safely by multiple threads. This is up to the user.
|
jaroslav@1649
|
391 |
//
|
jaroslav@1649
|
392 |
// The entry and version fields themselves can be safely read via
|
jaroslav@1649
|
393 |
// a race because they are either final or have controlled states.
|
jaroslav@1649
|
394 |
// If the pointer from the entry to the version is still null,
|
jaroslav@1649
|
395 |
// or if the version goes immediately dead and is nulled out,
|
jaroslav@1649
|
396 |
// the reader will take the slow path and retry under a lock.
|
jaroslav@1649
|
397 |
}
|
jaroslav@1649
|
398 |
|
jaroslav@1649
|
399 |
// The following class could also be top level and non-public:
|
jaroslav@1649
|
400 |
|
jaroslav@1649
|
401 |
/** A backing map for all ClassValues, relative a single given type.
|
jaroslav@1649
|
402 |
* Gives a fully serialized "true state" for each pair (ClassValue cv, Class type).
|
jaroslav@1649
|
403 |
* Also manages an unserialized fast-path cache.
|
jaroslav@1649
|
404 |
*/
|
jaroslav@1649
|
405 |
static class ClassValueMap extends WeakHashMap<ClassValue.Identity, Entry<?>> {
|
jaroslav@1649
|
406 |
private final Class<?> type;
|
jaroslav@1649
|
407 |
private Entry<?>[] cacheArray;
|
jaroslav@1649
|
408 |
private int cacheLoad, cacheLoadLimit;
|
jaroslav@1649
|
409 |
|
jaroslav@1649
|
410 |
/** Number of entries initially allocated to each type when first used with any ClassValue.
|
jaroslav@1649
|
411 |
* It would be pointless to make this much smaller than the Class and ClassValueMap objects themselves.
|
jaroslav@1649
|
412 |
* Must be a power of 2.
|
jaroslav@1649
|
413 |
*/
|
jaroslav@1649
|
414 |
private static final int INITIAL_ENTRIES = 32;
|
jaroslav@1649
|
415 |
|
jaroslav@1649
|
416 |
/** Build a backing map for ClassValues, relative the given type.
|
jaroslav@1649
|
417 |
* Also, create an empty cache array and install it on the class.
|
jaroslav@1649
|
418 |
*/
|
jaroslav@1649
|
419 |
ClassValueMap(Class<?> type) {
|
jaroslav@1649
|
420 |
this.type = type;
|
jaroslav@1649
|
421 |
sizeCache(INITIAL_ENTRIES);
|
jaroslav@1649
|
422 |
}
|
jaroslav@1649
|
423 |
|
jaroslav@1649
|
424 |
Entry<?>[] getCache() { return cacheArray; }
|
jaroslav@1649
|
425 |
|
jaroslav@1649
|
426 |
/** Initiate a query. Store a promise (placeholder) if there is no value yet. */
|
jaroslav@1649
|
427 |
synchronized
|
jaroslav@1649
|
428 |
<T> Entry<T> startEntry(ClassValue<T> classValue) {
|
jaroslav@1649
|
429 |
@SuppressWarnings("unchecked") // one map has entries for all value types <T>
|
jaroslav@1649
|
430 |
Entry<T> e = (Entry<T>) get(classValue.identity);
|
jaroslav@1649
|
431 |
Version<T> v = classValue.version();
|
jaroslav@1649
|
432 |
if (e == null) {
|
jaroslav@1649
|
433 |
e = v.promise();
|
jaroslav@1649
|
434 |
// The presence of a promise means that a value is pending for v.
|
jaroslav@1649
|
435 |
// Eventually, finishEntry will overwrite the promise.
|
jaroslav@1649
|
436 |
put(classValue.identity, e);
|
jaroslav@1649
|
437 |
// Note that the promise is never entered into the cache!
|
jaroslav@1649
|
438 |
return e;
|
jaroslav@1649
|
439 |
} else if (e.isPromise()) {
|
jaroslav@1649
|
440 |
// Somebody else has asked the same question.
|
jaroslav@1649
|
441 |
// Let the races begin!
|
jaroslav@1649
|
442 |
if (e.version() != v) {
|
jaroslav@1649
|
443 |
e = v.promise();
|
jaroslav@1649
|
444 |
put(classValue.identity, e);
|
jaroslav@1649
|
445 |
}
|
jaroslav@1649
|
446 |
return e;
|
jaroslav@1649
|
447 |
} else {
|
jaroslav@1649
|
448 |
// there is already a completed entry here; report it
|
jaroslav@1649
|
449 |
if (e.version() != v) {
|
jaroslav@1649
|
450 |
// There is a stale but valid entry here; make it fresh again.
|
jaroslav@1649
|
451 |
// Once an entry is in the hash table, we don't care what its version is.
|
jaroslav@1649
|
452 |
e = e.refreshVersion(v);
|
jaroslav@1649
|
453 |
put(classValue.identity, e);
|
jaroslav@1649
|
454 |
}
|
jaroslav@1649
|
455 |
// Add to the cache, to enable the fast path, next time.
|
jaroslav@1649
|
456 |
checkCacheLoad();
|
jaroslav@1649
|
457 |
addToCache(classValue, e);
|
jaroslav@1649
|
458 |
return e;
|
jaroslav@1649
|
459 |
}
|
jaroslav@1649
|
460 |
}
|
jaroslav@1649
|
461 |
|
jaroslav@1649
|
462 |
/** Finish a query. Overwrite a matching placeholder. Drop stale incoming values. */
|
jaroslav@1649
|
463 |
synchronized
|
jaroslav@1649
|
464 |
<T> Entry<T> finishEntry(ClassValue<T> classValue, Entry<T> e) {
|
jaroslav@1649
|
465 |
@SuppressWarnings("unchecked") // one map has entries for all value types <T>
|
jaroslav@1649
|
466 |
Entry<T> e0 = (Entry<T>) get(classValue.identity);
|
jaroslav@1649
|
467 |
if (e == e0) {
|
jaroslav@1649
|
468 |
// We can get here during exception processing, unwinding from computeValue.
|
jaroslav@1649
|
469 |
assert(e.isPromise());
|
jaroslav@1649
|
470 |
remove(classValue.identity);
|
jaroslav@1649
|
471 |
return null;
|
jaroslav@1649
|
472 |
} else if (e0 != null && e0.isPromise() && e0.version() == e.version()) {
|
jaroslav@1649
|
473 |
// If e0 matches the intended entry, there has not been a remove call
|
jaroslav@1649
|
474 |
// between the previous startEntry and now. So now overwrite e0.
|
jaroslav@1649
|
475 |
Version<T> v = classValue.version();
|
jaroslav@1649
|
476 |
if (e.version() != v)
|
jaroslav@1649
|
477 |
e = e.refreshVersion(v);
|
jaroslav@1649
|
478 |
put(classValue.identity, e);
|
jaroslav@1649
|
479 |
// Add to the cache, to enable the fast path, next time.
|
jaroslav@1649
|
480 |
checkCacheLoad();
|
jaroslav@1649
|
481 |
addToCache(classValue, e);
|
jaroslav@1649
|
482 |
return e;
|
jaroslav@1649
|
483 |
} else {
|
jaroslav@1649
|
484 |
// Some sort of mismatch; caller must try again.
|
jaroslav@1649
|
485 |
return null;
|
jaroslav@1649
|
486 |
}
|
jaroslav@1649
|
487 |
}
|
jaroslav@1649
|
488 |
|
jaroslav@1649
|
489 |
/** Remove an entry. */
|
jaroslav@1649
|
490 |
synchronized
|
jaroslav@1649
|
491 |
void removeEntry(ClassValue<?> classValue) {
|
jaroslav@1649
|
492 |
Entry<?> e = remove(classValue.identity);
|
jaroslav@1649
|
493 |
if (e == null) {
|
jaroslav@1649
|
494 |
// Uninitialized, and no pending calls to computeValue. No change.
|
jaroslav@1649
|
495 |
} else if (e.isPromise()) {
|
jaroslav@1649
|
496 |
// State is uninitialized, with a pending call to finishEntry.
|
jaroslav@1649
|
497 |
// Since remove is a no-op in such a state, keep the promise
|
jaroslav@1649
|
498 |
// by putting it back into the map.
|
jaroslav@1649
|
499 |
put(classValue.identity, e);
|
jaroslav@1649
|
500 |
} else {
|
jaroslav@1649
|
501 |
// In an initialized state. Bump forward, and de-initialize.
|
jaroslav@1649
|
502 |
classValue.bumpVersion();
|
jaroslav@1649
|
503 |
// Make all cache elements for this guy go stale.
|
jaroslav@1649
|
504 |
removeStaleEntries(classValue);
|
jaroslav@1649
|
505 |
}
|
jaroslav@1649
|
506 |
}
|
jaroslav@1649
|
507 |
|
jaroslav@1649
|
508 |
/** Change the value for an entry. */
|
jaroslav@1649
|
509 |
synchronized
|
jaroslav@1649
|
510 |
<T> void changeEntry(ClassValue<T> classValue, T value) {
|
jaroslav@1649
|
511 |
@SuppressWarnings("unchecked") // one map has entries for all value types <T>
|
jaroslav@1649
|
512 |
Entry<T> e0 = (Entry<T>) get(classValue.identity);
|
jaroslav@1649
|
513 |
Version<T> version = classValue.version();
|
jaroslav@1649
|
514 |
if (e0 != null) {
|
jaroslav@1649
|
515 |
if (e0.version() == version && e0.value() == value)
|
jaroslav@1649
|
516 |
// no value change => no version change needed
|
jaroslav@1649
|
517 |
return;
|
jaroslav@1649
|
518 |
classValue.bumpVersion();
|
jaroslav@1649
|
519 |
removeStaleEntries(classValue);
|
jaroslav@1649
|
520 |
}
|
jaroslav@1649
|
521 |
Entry<T> e = makeEntry(version, value);
|
jaroslav@1649
|
522 |
put(classValue.identity, e);
|
jaroslav@1649
|
523 |
// Add to the cache, to enable the fast path, next time.
|
jaroslav@1649
|
524 |
checkCacheLoad();
|
jaroslav@1649
|
525 |
addToCache(classValue, e);
|
jaroslav@1649
|
526 |
}
|
jaroslav@1649
|
527 |
|
jaroslav@1649
|
528 |
/// --------
|
jaroslav@1649
|
529 |
/// Cache management.
|
jaroslav@1649
|
530 |
/// --------
|
jaroslav@1649
|
531 |
|
jaroslav@1649
|
532 |
// Statics do not need synchronization.
|
jaroslav@1649
|
533 |
|
jaroslav@1649
|
534 |
/** Load the cache entry at the given (hashed) location. */
|
jaroslav@1649
|
535 |
static Entry<?> loadFromCache(Entry<?>[] cache, int i) {
|
jaroslav@1649
|
536 |
// non-racing cache.length : constant
|
jaroslav@1649
|
537 |
// racing cache[i & (mask)] : null <=> Entry
|
jaroslav@1649
|
538 |
return cache[i & (cache.length-1)];
|
jaroslav@1649
|
539 |
// invariant: returned value is null or well-constructed (ready to match)
|
jaroslav@1649
|
540 |
}
|
jaroslav@1649
|
541 |
|
jaroslav@1649
|
542 |
/** Look in the cache, at the home location for the given ClassValue. */
|
jaroslav@1649
|
543 |
static <T> Entry<T> probeHomeLocation(Entry<?>[] cache, ClassValue<T> classValue) {
|
jaroslav@1649
|
544 |
return classValue.castEntry(loadFromCache(cache, classValue.hashCodeForCache));
|
jaroslav@1649
|
545 |
}
|
jaroslav@1649
|
546 |
|
jaroslav@1649
|
547 |
/** Given that first probe was a collision, retry at nearby locations. */
|
jaroslav@1649
|
548 |
static <T> Entry<T> probeBackupLocations(Entry<?>[] cache, ClassValue<T> classValue) {
|
jaroslav@1649
|
549 |
if (PROBE_LIMIT <= 0) return null;
|
jaroslav@1649
|
550 |
// Probe the cache carefully, in a range of slots.
|
jaroslav@1649
|
551 |
int mask = (cache.length-1);
|
jaroslav@1649
|
552 |
int home = (classValue.hashCodeForCache & mask);
|
jaroslav@1649
|
553 |
Entry<?> e2 = cache[home]; // victim, if we find the real guy
|
jaroslav@1649
|
554 |
if (e2 == null) {
|
jaroslav@1649
|
555 |
return null; // if nobody is at home, no need to search nearby
|
jaroslav@1649
|
556 |
}
|
jaroslav@1649
|
557 |
// assume !classValue.match(e2), but do not assert, because of races
|
jaroslav@1649
|
558 |
int pos2 = -1;
|
jaroslav@1649
|
559 |
for (int i = home + 1; i < home + PROBE_LIMIT; i++) {
|
jaroslav@1649
|
560 |
Entry<?> e = cache[i & mask];
|
jaroslav@1649
|
561 |
if (e == null) {
|
jaroslav@1649
|
562 |
break; // only search within non-null runs
|
jaroslav@1649
|
563 |
}
|
jaroslav@1649
|
564 |
if (classValue.match(e)) {
|
jaroslav@1649
|
565 |
// relocate colliding entry e2 (from cache[home]) to first empty slot
|
jaroslav@1649
|
566 |
cache[home] = e;
|
jaroslav@1649
|
567 |
if (pos2 >= 0) {
|
jaroslav@1649
|
568 |
cache[i & mask] = Entry.DEAD_ENTRY;
|
jaroslav@1649
|
569 |
} else {
|
jaroslav@1649
|
570 |
pos2 = i;
|
jaroslav@1649
|
571 |
}
|
jaroslav@1649
|
572 |
cache[pos2 & mask] = ((entryDislocation(cache, pos2, e2) < PROBE_LIMIT)
|
jaroslav@1649
|
573 |
? e2 // put e2 here if it fits
|
jaroslav@1649
|
574 |
: Entry.DEAD_ENTRY);
|
jaroslav@1649
|
575 |
return classValue.castEntry(e);
|
jaroslav@1649
|
576 |
}
|
jaroslav@1649
|
577 |
// Remember first empty slot, if any:
|
jaroslav@1649
|
578 |
if (!e.isLive() && pos2 < 0) pos2 = i;
|
jaroslav@1649
|
579 |
}
|
jaroslav@1649
|
580 |
return null;
|
jaroslav@1649
|
581 |
}
|
jaroslav@1649
|
582 |
|
jaroslav@1649
|
583 |
/** How far out of place is e? */
|
jaroslav@1649
|
584 |
private static int entryDislocation(Entry<?>[] cache, int pos, Entry<?> e) {
|
jaroslav@1649
|
585 |
ClassValue<?> cv = e.classValueOrNull();
|
jaroslav@1649
|
586 |
if (cv == null) return 0; // entry is not live!
|
jaroslav@1649
|
587 |
int mask = (cache.length-1);
|
jaroslav@1649
|
588 |
return (pos - cv.hashCodeForCache) & mask;
|
jaroslav@1649
|
589 |
}
|
jaroslav@1649
|
590 |
|
jaroslav@1649
|
591 |
/// --------
|
jaroslav@1649
|
592 |
/// Below this line all functions are private, and assume synchronized access.
|
jaroslav@1649
|
593 |
/// --------
|
jaroslav@1649
|
594 |
|
jaroslav@1649
|
595 |
private void sizeCache(int length) {
|
jaroslav@1649
|
596 |
assert((length & (length-1)) == 0); // must be power of 2
|
jaroslav@1649
|
597 |
cacheLoad = 0;
|
jaroslav@1649
|
598 |
cacheLoadLimit = (int) ((double) length * CACHE_LOAD_LIMIT / 100);
|
jaroslav@1649
|
599 |
cacheArray = new Entry<?>[length];
|
jaroslav@1649
|
600 |
}
|
jaroslav@1649
|
601 |
|
jaroslav@1649
|
602 |
/** Make sure the cache load stays below its limit, if possible. */
|
jaroslav@1649
|
603 |
private void checkCacheLoad() {
|
jaroslav@1649
|
604 |
if (cacheLoad >= cacheLoadLimit) {
|
jaroslav@1649
|
605 |
reduceCacheLoad();
|
jaroslav@1649
|
606 |
}
|
jaroslav@1649
|
607 |
}
|
jaroslav@1649
|
608 |
private void reduceCacheLoad() {
|
jaroslav@1649
|
609 |
removeStaleEntries();
|
jaroslav@1649
|
610 |
if (cacheLoad < cacheLoadLimit)
|
jaroslav@1649
|
611 |
return; // win
|
jaroslav@1649
|
612 |
Entry<?>[] oldCache = getCache();
|
jaroslav@1649
|
613 |
if (oldCache.length > HASH_MASK)
|
jaroslav@1649
|
614 |
return; // lose
|
jaroslav@1649
|
615 |
sizeCache(oldCache.length * 2);
|
jaroslav@1649
|
616 |
for (Entry<?> e : oldCache) {
|
jaroslav@1649
|
617 |
if (e != null && e.isLive()) {
|
jaroslav@1649
|
618 |
addToCache(e);
|
jaroslav@1649
|
619 |
}
|
jaroslav@1649
|
620 |
}
|
jaroslav@1649
|
621 |
}
|
jaroslav@1649
|
622 |
|
jaroslav@1649
|
623 |
/** Remove stale entries in the given range.
|
jaroslav@1649
|
624 |
* Should be executed under a Map lock.
|
jaroslav@1649
|
625 |
*/
|
jaroslav@1649
|
626 |
private void removeStaleEntries(Entry<?>[] cache, int begin, int count) {
|
jaroslav@1649
|
627 |
if (PROBE_LIMIT <= 0) return;
|
jaroslav@1649
|
628 |
int mask = (cache.length-1);
|
jaroslav@1649
|
629 |
int removed = 0;
|
jaroslav@1649
|
630 |
for (int i = begin; i < begin + count; i++) {
|
jaroslav@1649
|
631 |
Entry<?> e = cache[i & mask];
|
jaroslav@1649
|
632 |
if (e == null || e.isLive())
|
jaroslav@1649
|
633 |
continue; // skip null and live entries
|
jaroslav@1649
|
634 |
Entry<?> replacement = null;
|
jaroslav@1649
|
635 |
if (PROBE_LIMIT > 1) {
|
jaroslav@1649
|
636 |
// avoid breaking up a non-null run
|
jaroslav@1649
|
637 |
replacement = findReplacement(cache, i);
|
jaroslav@1649
|
638 |
}
|
jaroslav@1649
|
639 |
cache[i & mask] = replacement;
|
jaroslav@1649
|
640 |
if (replacement == null) removed += 1;
|
jaroslav@1649
|
641 |
}
|
jaroslav@1649
|
642 |
cacheLoad = Math.max(0, cacheLoad - removed);
|
jaroslav@1649
|
643 |
}
|
jaroslav@1649
|
644 |
|
jaroslav@1649
|
645 |
/** Clearing a cache slot risks disconnecting following entries
|
jaroslav@1649
|
646 |
* from the head of a non-null run, which would allow them
|
jaroslav@1649
|
647 |
* to be found via reprobes. Find an entry after cache[begin]
|
jaroslav@1649
|
648 |
* to plug into the hole, or return null if none is needed.
|
jaroslav@1649
|
649 |
*/
|
jaroslav@1649
|
650 |
private Entry<?> findReplacement(Entry<?>[] cache, int home1) {
|
jaroslav@1649
|
651 |
Entry<?> replacement = null;
|
jaroslav@1649
|
652 |
int haveReplacement = -1, replacementPos = 0;
|
jaroslav@1649
|
653 |
int mask = (cache.length-1);
|
jaroslav@1649
|
654 |
for (int i2 = home1 + 1; i2 < home1 + PROBE_LIMIT; i2++) {
|
jaroslav@1649
|
655 |
Entry<?> e2 = cache[i2 & mask];
|
jaroslav@1649
|
656 |
if (e2 == null) break; // End of non-null run.
|
jaroslav@1649
|
657 |
if (!e2.isLive()) continue; // Doomed anyway.
|
jaroslav@1649
|
658 |
int dis2 = entryDislocation(cache, i2, e2);
|
jaroslav@1649
|
659 |
if (dis2 == 0) continue; // e2 already optimally placed
|
jaroslav@1649
|
660 |
int home2 = i2 - dis2;
|
jaroslav@1649
|
661 |
if (home2 <= home1) {
|
jaroslav@1649
|
662 |
// e2 can replace entry at cache[home1]
|
jaroslav@1649
|
663 |
if (home2 == home1) {
|
jaroslav@1649
|
664 |
// Put e2 exactly where he belongs.
|
jaroslav@1649
|
665 |
haveReplacement = 1;
|
jaroslav@1649
|
666 |
replacementPos = i2;
|
jaroslav@1649
|
667 |
replacement = e2;
|
jaroslav@1649
|
668 |
} else if (haveReplacement <= 0) {
|
jaroslav@1649
|
669 |
haveReplacement = 0;
|
jaroslav@1649
|
670 |
replacementPos = i2;
|
jaroslav@1649
|
671 |
replacement = e2;
|
jaroslav@1649
|
672 |
}
|
jaroslav@1649
|
673 |
// And keep going, so we can favor larger dislocations.
|
jaroslav@1649
|
674 |
}
|
jaroslav@1649
|
675 |
}
|
jaroslav@1649
|
676 |
if (haveReplacement >= 0) {
|
jaroslav@1649
|
677 |
if (cache[(replacementPos+1) & mask] != null) {
|
jaroslav@1649
|
678 |
// Be conservative, to avoid breaking up a non-null run.
|
jaroslav@1649
|
679 |
cache[replacementPos & mask] = (Entry<?>) Entry.DEAD_ENTRY;
|
jaroslav@1649
|
680 |
} else {
|
jaroslav@1649
|
681 |
cache[replacementPos & mask] = null;
|
jaroslav@1649
|
682 |
cacheLoad -= 1;
|
jaroslav@1649
|
683 |
}
|
jaroslav@1649
|
684 |
}
|
jaroslav@1649
|
685 |
return replacement;
|
jaroslav@1649
|
686 |
}
|
jaroslav@1649
|
687 |
|
jaroslav@1649
|
688 |
/** Remove stale entries in the range near classValue. */
|
jaroslav@1649
|
689 |
private void removeStaleEntries(ClassValue<?> classValue) {
|
jaroslav@1649
|
690 |
removeStaleEntries(getCache(), classValue.hashCodeForCache, PROBE_LIMIT);
|
jaroslav@1649
|
691 |
}
|
jaroslav@1649
|
692 |
|
jaroslav@1649
|
693 |
/** Remove all stale entries, everywhere. */
|
jaroslav@1649
|
694 |
private void removeStaleEntries() {
|
jaroslav@1649
|
695 |
Entry<?>[] cache = getCache();
|
jaroslav@1649
|
696 |
removeStaleEntries(cache, 0, cache.length + PROBE_LIMIT - 1);
|
jaroslav@1649
|
697 |
}
|
jaroslav@1649
|
698 |
|
jaroslav@1649
|
699 |
/** Add the given entry to the cache, in its home location, unless it is out of date. */
|
jaroslav@1649
|
700 |
private <T> void addToCache(Entry<T> e) {
|
jaroslav@1649
|
701 |
ClassValue<T> classValue = e.classValueOrNull();
|
jaroslav@1649
|
702 |
if (classValue != null)
|
jaroslav@1649
|
703 |
addToCache(classValue, e);
|
jaroslav@1649
|
704 |
}
|
jaroslav@1649
|
705 |
|
jaroslav@1649
|
706 |
/** Add the given entry to the cache, in its home location. */
|
jaroslav@1649
|
707 |
private <T> void addToCache(ClassValue<T> classValue, Entry<T> e) {
|
jaroslav@1649
|
708 |
if (PROBE_LIMIT <= 0) return; // do not fill cache
|
jaroslav@1649
|
709 |
// Add e to the cache.
|
jaroslav@1649
|
710 |
Entry<?>[] cache = getCache();
|
jaroslav@1649
|
711 |
int mask = (cache.length-1);
|
jaroslav@1649
|
712 |
int home = classValue.hashCodeForCache & mask;
|
jaroslav@1649
|
713 |
Entry<?> e2 = placeInCache(cache, home, e, false);
|
jaroslav@1649
|
714 |
if (e2 == null) return; // done
|
jaroslav@1649
|
715 |
if (PROBE_LIMIT > 1) {
|
jaroslav@1649
|
716 |
// try to move e2 somewhere else in his probe range
|
jaroslav@1649
|
717 |
int dis2 = entryDislocation(cache, home, e2);
|
jaroslav@1649
|
718 |
int home2 = home - dis2;
|
jaroslav@1649
|
719 |
for (int i2 = home2; i2 < home2 + PROBE_LIMIT; i2++) {
|
jaroslav@1649
|
720 |
if (placeInCache(cache, i2 & mask, e2, true) == null) {
|
jaroslav@1649
|
721 |
return;
|
jaroslav@1649
|
722 |
}
|
jaroslav@1649
|
723 |
}
|
jaroslav@1649
|
724 |
}
|
jaroslav@1649
|
725 |
// Note: At this point, e2 is just dropped from the cache.
|
jaroslav@1649
|
726 |
}
|
jaroslav@1649
|
727 |
|
jaroslav@1649
|
728 |
/** Store the given entry. Update cacheLoad, and return any live victim.
|
jaroslav@1649
|
729 |
* 'Gently' means return self rather than dislocating a live victim.
|
jaroslav@1649
|
730 |
*/
|
jaroslav@1649
|
731 |
private Entry<?> placeInCache(Entry<?>[] cache, int pos, Entry<?> e, boolean gently) {
|
jaroslav@1649
|
732 |
Entry<?> e2 = overwrittenEntry(cache[pos]);
|
jaroslav@1649
|
733 |
if (gently && e2 != null) {
|
jaroslav@1649
|
734 |
// do not overwrite a live entry
|
jaroslav@1649
|
735 |
return e;
|
jaroslav@1649
|
736 |
} else {
|
jaroslav@1649
|
737 |
cache[pos] = e;
|
jaroslav@1649
|
738 |
return e2;
|
jaroslav@1649
|
739 |
}
|
jaroslav@1649
|
740 |
}
|
jaroslav@1649
|
741 |
|
jaroslav@1649
|
742 |
/** Note an entry that is about to be overwritten.
|
jaroslav@1649
|
743 |
* If it is not live, quietly replace it by null.
|
jaroslav@1649
|
744 |
* If it is an actual null, increment cacheLoad,
|
jaroslav@1649
|
745 |
* because the caller is going to store something
|
jaroslav@1649
|
746 |
* in its place.
|
jaroslav@1649
|
747 |
*/
|
jaroslav@1649
|
748 |
private <T> Entry<T> overwrittenEntry(Entry<T> e2) {
|
jaroslav@1649
|
749 |
if (e2 == null) cacheLoad += 1;
|
jaroslav@1649
|
750 |
else if (e2.isLive()) return e2;
|
jaroslav@1649
|
751 |
return null;
|
jaroslav@1649
|
752 |
}
|
jaroslav@1649
|
753 |
|
jaroslav@1649
|
754 |
/** Percent loading of cache before resize. */
|
jaroslav@1649
|
755 |
private static final int CACHE_LOAD_LIMIT = 67; // 0..100
|
jaroslav@1649
|
756 |
/** Maximum number of probes to attempt. */
|
jaroslav@1649
|
757 |
private static final int PROBE_LIMIT = 6; // 1..
|
jaroslav@1649
|
758 |
// N.B. Set PROBE_LIMIT=0 to disable all fast paths.
|
jaroslav@1649
|
759 |
}
|
jaroslav@1649
|
760 |
}
|