1.1 --- a/rt/emul/compact/src/main/java/java/lang/ClassValue.java Sun Aug 17 20:09:05 2014 +0200
1.2 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000
1.3 @@ -1,760 +0,0 @@
1.4 -/*
1.5 - * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
1.6 - * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 - *
1.8 - * This code is free software; you can redistribute it and/or modify it
1.9 - * under the terms of the GNU General Public License version 2 only, as
1.10 - * published by the Free Software Foundation. Oracle designates this
1.11 - * particular file as subject to the "Classpath" exception as provided
1.12 - * by Oracle in the LICENSE file that accompanied this code.
1.13 - *
1.14 - * This code is distributed in the hope that it will be useful, but WITHOUT
1.15 - * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.16 - * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.17 - * version 2 for more details (a copy is included in the LICENSE file that
1.18 - * accompanied this code).
1.19 - *
1.20 - * You should have received a copy of the GNU General Public License version
1.21 - * 2 along with this work; if not, write to the Free Software Foundation,
1.22 - * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.23 - *
1.24 - * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.25 - * or visit www.oracle.com if you need additional information or have any
1.26 - * questions.
1.27 - */
1.28 -
1.29 -package java.lang;
1.30 -
1.31 -import java.lang.ClassValue.ClassValueMap;
1.32 -import java.util.WeakHashMap;
1.33 -import java.lang.ref.WeakReference;
1.34 -import java.util.concurrent.atomic.AtomicInteger;
1.35 -
1.36 -import static java.lang.ClassValue.ClassValueMap.probeHomeLocation;
1.37 -import static java.lang.ClassValue.ClassValueMap.probeBackupLocations;
1.38 -
1.39 -/**
1.40 - * Lazily associate a computed value with (potentially) every type.
1.41 - * For example, if a dynamic language needs to construct a message dispatch
1.42 - * table for each class encountered at a message send call site,
1.43 - * it can use a {@code ClassValue} to cache information needed to
1.44 - * perform the message send quickly, for each class encountered.
1.45 - * @author John Rose, JSR 292 EG
1.46 - * @since 1.7
1.47 - */
1.48 -public abstract class ClassValue<T> {
1.49 - /**
1.50 - * Sole constructor. (For invocation by subclass constructors, typically
1.51 - * implicit.)
1.52 - */
1.53 - protected ClassValue() {
1.54 - }
1.55 -
1.56 - /**
1.57 - * Computes the given class's derived value for this {@code ClassValue}.
1.58 - * <p>
1.59 - * This method will be invoked within the first thread that accesses
1.60 - * the value with the {@link #get get} method.
1.61 - * <p>
1.62 - * Normally, this method is invoked at most once per class,
1.63 - * but it may be invoked again if there has been a call to
1.64 - * {@link #remove remove}.
1.65 - * <p>
1.66 - * If this method throws an exception, the corresponding call to {@code get}
1.67 - * will terminate abnormally with that exception, and no class value will be recorded.
1.68 - *
1.69 - * @param type the type whose class value must be computed
1.70 - * @return the newly computed value associated with this {@code ClassValue}, for the given class or interface
1.71 - * @see #get
1.72 - * @see #remove
1.73 - */
1.74 - protected abstract T computeValue(Class<?> type);
1.75 -
1.76 - /**
1.77 - * Returns the value for the given class.
1.78 - * If no value has yet been computed, it is obtained by
1.79 - * an invocation of the {@link #computeValue computeValue} method.
1.80 - * <p>
1.81 - * The actual installation of the value on the class
1.82 - * is performed atomically.
1.83 - * At that point, if several racing threads have
1.84 - * computed values, one is chosen, and returned to
1.85 - * all the racing threads.
1.86 - * <p>
1.87 - * The {@code type} parameter is typically a class, but it may be any type,
1.88 - * such as an interface, a primitive type (like {@code int.class}), or {@code void.class}.
1.89 - * <p>
1.90 - * In the absence of {@code remove} calls, a class value has a simple
1.91 - * state diagram: uninitialized and initialized.
1.92 - * When {@code remove} calls are made,
1.93 - * the rules for value observation are more complex.
1.94 - * See the documentation for {@link #remove remove} for more information.
1.95 - *
1.96 - * @param type the type whose class value must be computed or retrieved
1.97 - * @return the current value associated with this {@code ClassValue}, for the given class or interface
1.98 - * @throws NullPointerException if the argument is null
1.99 - * @see #remove
1.100 - * @see #computeValue
1.101 - */
1.102 - public T get(Class<?> type) {
1.103 - // non-racing this.hashCodeForCache : final int
1.104 - Entry<?>[] cache;
1.105 - Entry<T> e = probeHomeLocation(cache = getCacheCarefully(type), this);
1.106 - // racing e : current value <=> stale value from current cache or from stale cache
1.107 - // invariant: e is null or an Entry with readable Entry.version and Entry.value
1.108 - if (match(e))
1.109 - // invariant: No false positive matches. False negatives are OK if rare.
1.110 - // The key fact that makes this work: if this.version == e.version,
1.111 - // then this thread has a right to observe (final) e.value.
1.112 - return e.value();
1.113 - // The fast path can fail for any of these reasons:
1.114 - // 1. no entry has been computed yet
1.115 - // 2. hash code collision (before or after reduction mod cache.length)
1.116 - // 3. an entry has been removed (either on this type or another)
1.117 - // 4. the GC has somehow managed to delete e.version and clear the reference
1.118 - return getFromBackup(cache, type);
1.119 - }
1.120 -
1.121 - /**
1.122 - * Removes the associated value for the given class.
1.123 - * If this value is subsequently {@linkplain #get read} for the same class,
1.124 - * its value will be reinitialized by invoking its {@link #computeValue computeValue} method.
1.125 - * This may result in an additional invocation of the
1.126 - * {@code computeValue} method for the given class.
1.127 - * <p>
1.128 - * In order to explain the interaction between {@code get} and {@code remove} calls,
1.129 - * we must model the state transitions of a class value to take into account
1.130 - * the alternation between uninitialized and initialized states.
1.131 - * To do this, number these states sequentially from zero, and note that
1.132 - * uninitialized (or removed) states are numbered with even numbers,
1.133 - * while initialized (or re-initialized) states have odd numbers.
1.134 - * <p>
1.135 - * When a thread {@code T} removes a class value in state {@code 2N},
1.136 - * nothing happens, since the class value is already uninitialized.
1.137 - * Otherwise, the state is advanced atomically to {@code 2N+1}.
1.138 - * <p>
1.139 - * When a thread {@code T} queries a class value in state {@code 2N},
1.140 - * the thread first attempts to initialize the class value to state {@code 2N+1}
1.141 - * by invoking {@code computeValue} and installing the resulting value.
1.142 - * <p>
1.143 - * When {@code T} attempts to install the newly computed value,
1.144 - * if the state is still at {@code 2N}, the class value will be initialized
1.145 - * with the computed value, advancing it to state {@code 2N+1}.
1.146 - * <p>
1.147 - * Otherwise, whether the new state is even or odd,
1.148 - * {@code T} will discard the newly computed value
1.149 - * and retry the {@code get} operation.
1.150 - * <p>
1.151 - * Discarding and retrying is an important proviso,
1.152 - * since otherwise {@code T} could potentially install
1.153 - * a disastrously stale value. For example:
1.154 - * <ul>
1.155 - * <li>{@code T} calls {@code CV.get(C)} and sees state {@code 2N}
1.156 - * <li>{@code T} quickly computes a time-dependent value {@code V0} and gets ready to install it
1.157 - * <li>{@code T} is hit by an unlucky paging or scheduling event, and goes to sleep for a long time
1.158 - * <li>...meanwhile, {@code T2} also calls {@code CV.get(C)} and sees state {@code 2N}
1.159 - * <li>{@code T2} quickly computes a similar time-dependent value {@code V1} and installs it on {@code CV.get(C)}
1.160 - * <li>{@code T2} (or a third thread) then calls {@code CV.remove(C)}, undoing {@code T2}'s work
1.161 - * <li> the previous actions of {@code T2} are repeated several times
1.162 - * <li> also, the relevant computed values change over time: {@code V1}, {@code V2}, ...
1.163 - * <li>...meanwhile, {@code T} wakes up and attempts to install {@code V0}; <em>this must fail</em>
1.164 - * </ul>
1.165 - * We can assume in the above scenario that {@code CV.computeValue} uses locks to properly
1.166 - * observe the time-dependent states as it computes {@code V1}, etc.
1.167 - * This does not remove the threat of a stale value, since there is a window of time
1.168 - * between the return of {@code computeValue} in {@code T} and the installation
1.169 - * of the the new value. No user synchronization is possible during this time.
1.170 - *
1.171 - * @param type the type whose class value must be removed
1.172 - * @throws NullPointerException if the argument is null
1.173 - */
1.174 - public void remove(Class<?> type) {
1.175 - ClassValueMap map = getMap(type);
1.176 - map.removeEntry(this);
1.177 - }
1.178 -
1.179 - // Possible functionality for JSR 292 MR 1
1.180 - /*public*/ void put(Class<?> type, T value) {
1.181 - ClassValueMap map = getMap(type);
1.182 - map.changeEntry(this, value);
1.183 - }
1.184 -
1.185 - /// --------
1.186 - /// Implementation...
1.187 - /// --------
1.188 -
1.189 - /** Return the cache, if it exists, else a dummy empty cache. */
1.190 - private static Entry<?>[] getCacheCarefully(Class<?> type) {
1.191 - // racing type.classValueMap{.cacheArray} : null => new Entry[X] <=> new Entry[Y]
1.192 - ClassValueMap map = (ClassValueMap) type.classValueMap;
1.193 - if (map == null) return EMPTY_CACHE;
1.194 - Entry<?>[] cache = map.getCache();
1.195 - return cache;
1.196 - // invariant: returned value is safe to dereference and check for an Entry
1.197 - }
1.198 -
1.199 - /** Initial, one-element, empty cache used by all Class instances. Must never be filled. */
1.200 - private static final Entry<?>[] EMPTY_CACHE = { null };
1.201 -
1.202 - /**
1.203 - * Slow tail of ClassValue.get to retry at nearby locations in the cache,
1.204 - * or take a slow lock and check the hash table.
1.205 - * Called only if the first probe was empty or a collision.
1.206 - * This is a separate method, so compilers can process it independently.
1.207 - */
1.208 - private T getFromBackup(Entry<?>[] cache, Class<?> type) {
1.209 - Entry<T> e = probeBackupLocations(cache, this);
1.210 - if (e != null)
1.211 - return e.value();
1.212 - return getFromHashMap(type);
1.213 - }
1.214 -
1.215 - // Hack to suppress warnings on the (T) cast, which is a no-op.
1.216 - @SuppressWarnings("unchecked")
1.217 - Entry<T> castEntry(Entry<?> e) { return (Entry<T>) e; }
1.218 -
1.219 - /** Called when the fast path of get fails, and cache reprobe also fails.
1.220 - */
1.221 - private T getFromHashMap(Class<?> type) {
1.222 - // The fail-safe recovery is to fall back to the underlying classValueMap.
1.223 - ClassValueMap map = getMap(type);
1.224 - for (;;) {
1.225 - Entry<T> e = map.startEntry(this);
1.226 - if (!e.isPromise())
1.227 - return e.value();
1.228 - try {
1.229 - // Try to make a real entry for the promised version.
1.230 - e = makeEntry(e.version(), computeValue(type));
1.231 - } finally {
1.232 - // Whether computeValue throws or returns normally,
1.233 - // be sure to remove the empty entry.
1.234 - e = map.finishEntry(this, e);
1.235 - }
1.236 - if (e != null)
1.237 - return e.value();
1.238 - // else try again, in case a racing thread called remove (so e == null)
1.239 - }
1.240 - }
1.241 -
1.242 - /** Check that e is non-null, matches this ClassValue, and is live. */
1.243 - boolean match(Entry<?> e) {
1.244 - // racing e.version : null (blank) => unique Version token => null (GC-ed version)
1.245 - // non-racing this.version : v1 => v2 => ... (updates are read faithfully from volatile)
1.246 - return (e != null && e.get() == this.version);
1.247 - // invariant: No false positives on version match. Null is OK for false negative.
1.248 - // invariant: If version matches, then e.value is readable (final set in Entry.<init>)
1.249 - }
1.250 -
1.251 - /** Internal hash code for accessing Class.classValueMap.cacheArray. */
1.252 - final int hashCodeForCache = nextHashCode.getAndAdd(HASH_INCREMENT) & HASH_MASK;
1.253 -
1.254 - /** Value stream for hashCodeForCache. See similar structure in ThreadLocal. */
1.255 - private static final AtomicInteger nextHashCode = new AtomicInteger();
1.256 -
1.257 - /** Good for power-of-two tables. See similar structure in ThreadLocal. */
1.258 - private static final int HASH_INCREMENT = 0x61c88647;
1.259 -
1.260 - /** Mask a hash code to be positive but not too large, to prevent wraparound. */
1.261 - static final int HASH_MASK = (-1 >>> 2);
1.262 -
1.263 - /**
1.264 - * Private key for retrieval of this object from ClassValueMap.
1.265 - */
1.266 - static class Identity {
1.267 - }
1.268 - /**
1.269 - * This ClassValue's identity, expressed as an opaque object.
1.270 - * The main object {@code ClassValue.this} is incorrect since
1.271 - * subclasses may override {@code ClassValue.equals}, which
1.272 - * could confuse keys in the ClassValueMap.
1.273 - */
1.274 - final Identity identity = new Identity();
1.275 -
1.276 - /**
1.277 - * Current version for retrieving this class value from the cache.
1.278 - * Any number of computeValue calls can be cached in association with one version.
1.279 - * But the version changes when a remove (on any type) is executed.
1.280 - * A version change invalidates all cache entries for the affected ClassValue,
1.281 - * by marking them as stale. Stale cache entries do not force another call
1.282 - * to computeValue, but they do require a synchronized visit to a backing map.
1.283 - * <p>
1.284 - * All user-visible state changes on the ClassValue take place under
1.285 - * a lock inside the synchronized methods of ClassValueMap.
1.286 - * Readers (of ClassValue.get) are notified of such state changes
1.287 - * when this.version is bumped to a new token.
1.288 - * This variable must be volatile so that an unsynchronized reader
1.289 - * will receive the notification without delay.
1.290 - * <p>
1.291 - * If version were not volatile, one thread T1 could persistently hold onto
1.292 - * a stale value this.value == V1, while while another thread T2 advances
1.293 - * (under a lock) to this.value == V2. This will typically be harmless,
1.294 - * but if T1 and T2 interact causally via some other channel, such that
1.295 - * T1's further actions are constrained (in the JMM) to happen after
1.296 - * the V2 event, then T1's observation of V1 will be an error.
1.297 - * <p>
1.298 - * The practical effect of making this.version be volatile is that it cannot
1.299 - * be hoisted out of a loop (by an optimizing JIT) or otherwise cached.
1.300 - * Some machines may also require a barrier instruction to execute
1.301 - * before this.version.
1.302 - */
1.303 - private volatile Version<T> version = new Version<>(this);
1.304 - Version<T> version() { return version; }
1.305 - void bumpVersion() { version = new Version<>(this); }
1.306 - static class Version<T> {
1.307 - private final ClassValue<T> classValue;
1.308 - private final Entry<T> promise = new Entry<>(this);
1.309 - Version(ClassValue<T> classValue) { this.classValue = classValue; }
1.310 - ClassValue<T> classValue() { return classValue; }
1.311 - Entry<T> promise() { return promise; }
1.312 - boolean isLive() { return classValue.version() == this; }
1.313 - }
1.314 -
1.315 - /** One binding of a value to a class via a ClassValue.
1.316 - * States are:<ul>
1.317 - * <li> promise if value == Entry.this
1.318 - * <li> else dead if version == null
1.319 - * <li> else stale if version != classValue.version
1.320 - * <li> else live </ul>
1.321 - * Promises are never put into the cache; they only live in the
1.322 - * backing map while a computeValue call is in flight.
1.323 - * Once an entry goes stale, it can be reset at any time
1.324 - * into the dead state.
1.325 - */
1.326 - static class Entry<T> extends WeakReference<Version<T>> {
1.327 - final Object value; // usually of type T, but sometimes (Entry)this
1.328 - Entry(Version<T> version, T value) {
1.329 - super(version);
1.330 - this.value = value; // for a regular entry, value is of type T
1.331 - }
1.332 - private void assertNotPromise() { assert(!isPromise()); }
1.333 - /** For creating a promise. */
1.334 - Entry(Version<T> version) {
1.335 - super(version);
1.336 - this.value = this; // for a promise, value is not of type T, but Entry!
1.337 - }
1.338 - /** Fetch the value. This entry must not be a promise. */
1.339 - @SuppressWarnings("unchecked") // if !isPromise, type is T
1.340 - T value() { assertNotPromise(); return (T) value; }
1.341 - boolean isPromise() { return value == this; }
1.342 - Version<T> version() { return get(); }
1.343 - ClassValue<T> classValueOrNull() {
1.344 - Version<T> v = version();
1.345 - return (v == null) ? null : v.classValue();
1.346 - }
1.347 - boolean isLive() {
1.348 - Version<T> v = version();
1.349 - if (v == null) return false;
1.350 - if (v.isLive()) return true;
1.351 - clear();
1.352 - return false;
1.353 - }
1.354 - Entry<T> refreshVersion(Version<T> v2) {
1.355 - assertNotPromise();
1.356 - @SuppressWarnings("unchecked") // if !isPromise, type is T
1.357 - Entry<T> e2 = new Entry<>(v2, (T) value);
1.358 - clear();
1.359 - // value = null -- caller must drop
1.360 - return e2;
1.361 - }
1.362 - static final Entry<?> DEAD_ENTRY = new Entry<>(null, null);
1.363 - }
1.364 -
1.365 - /** Return the backing map associated with this type. */
1.366 - private static ClassValueMap getMap(Class<?> type) {
1.367 - // racing type.classValueMap : null (blank) => unique ClassValueMap
1.368 - // if a null is observed, a map is created (lazily, synchronously, uniquely)
1.369 - // all further access to that map is synchronized
1.370 - ClassValueMap map = (ClassValueMap)type.classValueMap;
1.371 - if (map != null) return map;
1.372 - return initializeMap(type);
1.373 - }
1.374 -
1.375 - private static final Object CRITICAL_SECTION = new Object();
1.376 - private static ClassValueMap initializeMap(Class<?> type) {
1.377 - ClassValueMap map;
1.378 - synchronized (CRITICAL_SECTION) { // private object to avoid deadlocks
1.379 - // happens about once per type
1.380 - if ((map = (ClassValueMap)type.classValueMap) == null)
1.381 - type.classValueMap = map = new ClassValueMap(type);
1.382 - }
1.383 - return map;
1.384 - }
1.385 -
1.386 - static <T> Entry<T> makeEntry(Version<T> explicitVersion, T value) {
1.387 - // Note that explicitVersion might be different from this.version.
1.388 - return new Entry<>(explicitVersion, value);
1.389 -
1.390 - // As soon as the Entry is put into the cache, the value will be
1.391 - // reachable via a data race (as defined by the Java Memory Model).
1.392 - // This race is benign, assuming the value object itself can be
1.393 - // read safely by multiple threads. This is up to the user.
1.394 - //
1.395 - // The entry and version fields themselves can be safely read via
1.396 - // a race because they are either final or have controlled states.
1.397 - // If the pointer from the entry to the version is still null,
1.398 - // or if the version goes immediately dead and is nulled out,
1.399 - // the reader will take the slow path and retry under a lock.
1.400 - }
1.401 -
1.402 - // The following class could also be top level and non-public:
1.403 -
1.404 - /** A backing map for all ClassValues, relative a single given type.
1.405 - * Gives a fully serialized "true state" for each pair (ClassValue cv, Class type).
1.406 - * Also manages an unserialized fast-path cache.
1.407 - */
1.408 - static class ClassValueMap extends WeakHashMap<ClassValue.Identity, Entry<?>> {
1.409 - private final Class<?> type;
1.410 - private Entry<?>[] cacheArray;
1.411 - private int cacheLoad, cacheLoadLimit;
1.412 -
1.413 - /** Number of entries initially allocated to each type when first used with any ClassValue.
1.414 - * It would be pointless to make this much smaller than the Class and ClassValueMap objects themselves.
1.415 - * Must be a power of 2.
1.416 - */
1.417 - private static final int INITIAL_ENTRIES = 32;
1.418 -
1.419 - /** Build a backing map for ClassValues, relative the given type.
1.420 - * Also, create an empty cache array and install it on the class.
1.421 - */
1.422 - ClassValueMap(Class<?> type) {
1.423 - this.type = type;
1.424 - sizeCache(INITIAL_ENTRIES);
1.425 - }
1.426 -
1.427 - Entry<?>[] getCache() { return cacheArray; }
1.428 -
1.429 - /** Initiate a query. Store a promise (placeholder) if there is no value yet. */
1.430 - synchronized
1.431 - <T> Entry<T> startEntry(ClassValue<T> classValue) {
1.432 - @SuppressWarnings("unchecked") // one map has entries for all value types <T>
1.433 - Entry<T> e = (Entry<T>) get(classValue.identity);
1.434 - Version<T> v = classValue.version();
1.435 - if (e == null) {
1.436 - e = v.promise();
1.437 - // The presence of a promise means that a value is pending for v.
1.438 - // Eventually, finishEntry will overwrite the promise.
1.439 - put(classValue.identity, e);
1.440 - // Note that the promise is never entered into the cache!
1.441 - return e;
1.442 - } else if (e.isPromise()) {
1.443 - // Somebody else has asked the same question.
1.444 - // Let the races begin!
1.445 - if (e.version() != v) {
1.446 - e = v.promise();
1.447 - put(classValue.identity, e);
1.448 - }
1.449 - return e;
1.450 - } else {
1.451 - // there is already a completed entry here; report it
1.452 - if (e.version() != v) {
1.453 - // There is a stale but valid entry here; make it fresh again.
1.454 - // Once an entry is in the hash table, we don't care what its version is.
1.455 - e = e.refreshVersion(v);
1.456 - put(classValue.identity, e);
1.457 - }
1.458 - // Add to the cache, to enable the fast path, next time.
1.459 - checkCacheLoad();
1.460 - addToCache(classValue, e);
1.461 - return e;
1.462 - }
1.463 - }
1.464 -
1.465 - /** Finish a query. Overwrite a matching placeholder. Drop stale incoming values. */
1.466 - synchronized
1.467 - <T> Entry<T> finishEntry(ClassValue<T> classValue, Entry<T> e) {
1.468 - @SuppressWarnings("unchecked") // one map has entries for all value types <T>
1.469 - Entry<T> e0 = (Entry<T>) get(classValue.identity);
1.470 - if (e == e0) {
1.471 - // We can get here during exception processing, unwinding from computeValue.
1.472 - assert(e.isPromise());
1.473 - remove(classValue.identity);
1.474 - return null;
1.475 - } else if (e0 != null && e0.isPromise() && e0.version() == e.version()) {
1.476 - // If e0 matches the intended entry, there has not been a remove call
1.477 - // between the previous startEntry and now. So now overwrite e0.
1.478 - Version<T> v = classValue.version();
1.479 - if (e.version() != v)
1.480 - e = e.refreshVersion(v);
1.481 - put(classValue.identity, e);
1.482 - // Add to the cache, to enable the fast path, next time.
1.483 - checkCacheLoad();
1.484 - addToCache(classValue, e);
1.485 - return e;
1.486 - } else {
1.487 - // Some sort of mismatch; caller must try again.
1.488 - return null;
1.489 - }
1.490 - }
1.491 -
1.492 - /** Remove an entry. */
1.493 - synchronized
1.494 - void removeEntry(ClassValue<?> classValue) {
1.495 - Entry<?> e = remove(classValue.identity);
1.496 - if (e == null) {
1.497 - // Uninitialized, and no pending calls to computeValue. No change.
1.498 - } else if (e.isPromise()) {
1.499 - // State is uninitialized, with a pending call to finishEntry.
1.500 - // Since remove is a no-op in such a state, keep the promise
1.501 - // by putting it back into the map.
1.502 - put(classValue.identity, e);
1.503 - } else {
1.504 - // In an initialized state. Bump forward, and de-initialize.
1.505 - classValue.bumpVersion();
1.506 - // Make all cache elements for this guy go stale.
1.507 - removeStaleEntries(classValue);
1.508 - }
1.509 - }
1.510 -
1.511 - /** Change the value for an entry. */
1.512 - synchronized
1.513 - <T> void changeEntry(ClassValue<T> classValue, T value) {
1.514 - @SuppressWarnings("unchecked") // one map has entries for all value types <T>
1.515 - Entry<T> e0 = (Entry<T>) get(classValue.identity);
1.516 - Version<T> version = classValue.version();
1.517 - if (e0 != null) {
1.518 - if (e0.version() == version && e0.value() == value)
1.519 - // no value change => no version change needed
1.520 - return;
1.521 - classValue.bumpVersion();
1.522 - removeStaleEntries(classValue);
1.523 - }
1.524 - Entry<T> e = makeEntry(version, value);
1.525 - put(classValue.identity, e);
1.526 - // Add to the cache, to enable the fast path, next time.
1.527 - checkCacheLoad();
1.528 - addToCache(classValue, e);
1.529 - }
1.530 -
1.531 - /// --------
1.532 - /// Cache management.
1.533 - /// --------
1.534 -
1.535 - // Statics do not need synchronization.
1.536 -
1.537 - /** Load the cache entry at the given (hashed) location. */
1.538 - static Entry<?> loadFromCache(Entry<?>[] cache, int i) {
1.539 - // non-racing cache.length : constant
1.540 - // racing cache[i & (mask)] : null <=> Entry
1.541 - return cache[i & (cache.length-1)];
1.542 - // invariant: returned value is null or well-constructed (ready to match)
1.543 - }
1.544 -
1.545 - /** Look in the cache, at the home location for the given ClassValue. */
1.546 - static <T> Entry<T> probeHomeLocation(Entry<?>[] cache, ClassValue<T> classValue) {
1.547 - return classValue.castEntry(loadFromCache(cache, classValue.hashCodeForCache));
1.548 - }
1.549 -
1.550 - /** Given that first probe was a collision, retry at nearby locations. */
1.551 - static <T> Entry<T> probeBackupLocations(Entry<?>[] cache, ClassValue<T> classValue) {
1.552 - if (PROBE_LIMIT <= 0) return null;
1.553 - // Probe the cache carefully, in a range of slots.
1.554 - int mask = (cache.length-1);
1.555 - int home = (classValue.hashCodeForCache & mask);
1.556 - Entry<?> e2 = cache[home]; // victim, if we find the real guy
1.557 - if (e2 == null) {
1.558 - return null; // if nobody is at home, no need to search nearby
1.559 - }
1.560 - // assume !classValue.match(e2), but do not assert, because of races
1.561 - int pos2 = -1;
1.562 - for (int i = home + 1; i < home + PROBE_LIMIT; i++) {
1.563 - Entry<?> e = cache[i & mask];
1.564 - if (e == null) {
1.565 - break; // only search within non-null runs
1.566 - }
1.567 - if (classValue.match(e)) {
1.568 - // relocate colliding entry e2 (from cache[home]) to first empty slot
1.569 - cache[home] = e;
1.570 - if (pos2 >= 0) {
1.571 - cache[i & mask] = Entry.DEAD_ENTRY;
1.572 - } else {
1.573 - pos2 = i;
1.574 - }
1.575 - cache[pos2 & mask] = ((entryDislocation(cache, pos2, e2) < PROBE_LIMIT)
1.576 - ? e2 // put e2 here if it fits
1.577 - : Entry.DEAD_ENTRY);
1.578 - return classValue.castEntry(e);
1.579 - }
1.580 - // Remember first empty slot, if any:
1.581 - if (!e.isLive() && pos2 < 0) pos2 = i;
1.582 - }
1.583 - return null;
1.584 - }
1.585 -
1.586 - /** How far out of place is e? */
1.587 - private static int entryDislocation(Entry<?>[] cache, int pos, Entry<?> e) {
1.588 - ClassValue<?> cv = e.classValueOrNull();
1.589 - if (cv == null) return 0; // entry is not live!
1.590 - int mask = (cache.length-1);
1.591 - return (pos - cv.hashCodeForCache) & mask;
1.592 - }
1.593 -
1.594 - /// --------
1.595 - /// Below this line all functions are private, and assume synchronized access.
1.596 - /// --------
1.597 -
1.598 - private void sizeCache(int length) {
1.599 - assert((length & (length-1)) == 0); // must be power of 2
1.600 - cacheLoad = 0;
1.601 - cacheLoadLimit = (int) ((double) length * CACHE_LOAD_LIMIT / 100);
1.602 - cacheArray = new Entry<?>[length];
1.603 - }
1.604 -
1.605 - /** Make sure the cache load stays below its limit, if possible. */
1.606 - private void checkCacheLoad() {
1.607 - if (cacheLoad >= cacheLoadLimit) {
1.608 - reduceCacheLoad();
1.609 - }
1.610 - }
1.611 - private void reduceCacheLoad() {
1.612 - removeStaleEntries();
1.613 - if (cacheLoad < cacheLoadLimit)
1.614 - return; // win
1.615 - Entry<?>[] oldCache = getCache();
1.616 - if (oldCache.length > HASH_MASK)
1.617 - return; // lose
1.618 - sizeCache(oldCache.length * 2);
1.619 - for (Entry<?> e : oldCache) {
1.620 - if (e != null && e.isLive()) {
1.621 - addToCache(e);
1.622 - }
1.623 - }
1.624 - }
1.625 -
1.626 - /** Remove stale entries in the given range.
1.627 - * Should be executed under a Map lock.
1.628 - */
1.629 - private void removeStaleEntries(Entry<?>[] cache, int begin, int count) {
1.630 - if (PROBE_LIMIT <= 0) return;
1.631 - int mask = (cache.length-1);
1.632 - int removed = 0;
1.633 - for (int i = begin; i < begin + count; i++) {
1.634 - Entry<?> e = cache[i & mask];
1.635 - if (e == null || e.isLive())
1.636 - continue; // skip null and live entries
1.637 - Entry<?> replacement = null;
1.638 - if (PROBE_LIMIT > 1) {
1.639 - // avoid breaking up a non-null run
1.640 - replacement = findReplacement(cache, i);
1.641 - }
1.642 - cache[i & mask] = replacement;
1.643 - if (replacement == null) removed += 1;
1.644 - }
1.645 - cacheLoad = Math.max(0, cacheLoad - removed);
1.646 - }
1.647 -
1.648 - /** Clearing a cache slot risks disconnecting following entries
1.649 - * from the head of a non-null run, which would allow them
1.650 - * to be found via reprobes. Find an entry after cache[begin]
1.651 - * to plug into the hole, or return null if none is needed.
1.652 - */
1.653 - private Entry<?> findReplacement(Entry<?>[] cache, int home1) {
1.654 - Entry<?> replacement = null;
1.655 - int haveReplacement = -1, replacementPos = 0;
1.656 - int mask = (cache.length-1);
1.657 - for (int i2 = home1 + 1; i2 < home1 + PROBE_LIMIT; i2++) {
1.658 - Entry<?> e2 = cache[i2 & mask];
1.659 - if (e2 == null) break; // End of non-null run.
1.660 - if (!e2.isLive()) continue; // Doomed anyway.
1.661 - int dis2 = entryDislocation(cache, i2, e2);
1.662 - if (dis2 == 0) continue; // e2 already optimally placed
1.663 - int home2 = i2 - dis2;
1.664 - if (home2 <= home1) {
1.665 - // e2 can replace entry at cache[home1]
1.666 - if (home2 == home1) {
1.667 - // Put e2 exactly where he belongs.
1.668 - haveReplacement = 1;
1.669 - replacementPos = i2;
1.670 - replacement = e2;
1.671 - } else if (haveReplacement <= 0) {
1.672 - haveReplacement = 0;
1.673 - replacementPos = i2;
1.674 - replacement = e2;
1.675 - }
1.676 - // And keep going, so we can favor larger dislocations.
1.677 - }
1.678 - }
1.679 - if (haveReplacement >= 0) {
1.680 - if (cache[(replacementPos+1) & mask] != null) {
1.681 - // Be conservative, to avoid breaking up a non-null run.
1.682 - cache[replacementPos & mask] = (Entry<?>) Entry.DEAD_ENTRY;
1.683 - } else {
1.684 - cache[replacementPos & mask] = null;
1.685 - cacheLoad -= 1;
1.686 - }
1.687 - }
1.688 - return replacement;
1.689 - }
1.690 -
1.691 - /** Remove stale entries in the range near classValue. */
1.692 - private void removeStaleEntries(ClassValue<?> classValue) {
1.693 - removeStaleEntries(getCache(), classValue.hashCodeForCache, PROBE_LIMIT);
1.694 - }
1.695 -
1.696 - /** Remove all stale entries, everywhere. */
1.697 - private void removeStaleEntries() {
1.698 - Entry<?>[] cache = getCache();
1.699 - removeStaleEntries(cache, 0, cache.length + PROBE_LIMIT - 1);
1.700 - }
1.701 -
1.702 - /** Add the given entry to the cache, in its home location, unless it is out of date. */
1.703 - private <T> void addToCache(Entry<T> e) {
1.704 - ClassValue<T> classValue = e.classValueOrNull();
1.705 - if (classValue != null)
1.706 - addToCache(classValue, e);
1.707 - }
1.708 -
1.709 - /** Add the given entry to the cache, in its home location. */
1.710 - private <T> void addToCache(ClassValue<T> classValue, Entry<T> e) {
1.711 - if (PROBE_LIMIT <= 0) return; // do not fill cache
1.712 - // Add e to the cache.
1.713 - Entry<?>[] cache = getCache();
1.714 - int mask = (cache.length-1);
1.715 - int home = classValue.hashCodeForCache & mask;
1.716 - Entry<?> e2 = placeInCache(cache, home, e, false);
1.717 - if (e2 == null) return; // done
1.718 - if (PROBE_LIMIT > 1) {
1.719 - // try to move e2 somewhere else in his probe range
1.720 - int dis2 = entryDislocation(cache, home, e2);
1.721 - int home2 = home - dis2;
1.722 - for (int i2 = home2; i2 < home2 + PROBE_LIMIT; i2++) {
1.723 - if (placeInCache(cache, i2 & mask, e2, true) == null) {
1.724 - return;
1.725 - }
1.726 - }
1.727 - }
1.728 - // Note: At this point, e2 is just dropped from the cache.
1.729 - }
1.730 -
1.731 - /** Store the given entry. Update cacheLoad, and return any live victim.
1.732 - * 'Gently' means return self rather than dislocating a live victim.
1.733 - */
1.734 - private Entry<?> placeInCache(Entry<?>[] cache, int pos, Entry<?> e, boolean gently) {
1.735 - Entry<?> e2 = overwrittenEntry(cache[pos]);
1.736 - if (gently && e2 != null) {
1.737 - // do not overwrite a live entry
1.738 - return e;
1.739 - } else {
1.740 - cache[pos] = e;
1.741 - return e2;
1.742 - }
1.743 - }
1.744 -
1.745 - /** Note an entry that is about to be overwritten.
1.746 - * If it is not live, quietly replace it by null.
1.747 - * If it is an actual null, increment cacheLoad,
1.748 - * because the caller is going to store something
1.749 - * in its place.
1.750 - */
1.751 - private <T> Entry<T> overwrittenEntry(Entry<T> e2) {
1.752 - if (e2 == null) cacheLoad += 1;
1.753 - else if (e2.isLive()) return e2;
1.754 - return null;
1.755 - }
1.756 -
1.757 - /** Percent loading of cache before resize. */
1.758 - private static final int CACHE_LOAD_LIMIT = 67; // 0..100
1.759 - /** Maximum number of probes to attempt. */
1.760 - private static final int PROBE_LIMIT = 6; // 1..
1.761 - // N.B. Set PROBE_LIMIT=0 to disable all fast paths.
1.762 - }
1.763 -}