diff -r eca8e9c3ec3e -r cd50c1894ce5 rt/emul/compact/src/main/java/java/lang/ClassValue.java --- a/rt/emul/compact/src/main/java/java/lang/ClassValue.java Sun Aug 17 20:09:05 2014 +0200 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,760 +0,0 @@ -/* - * Copyright (c) 2010, 2013, 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.ClassValue.ClassValueMap; -import java.util.WeakHashMap; -import java.lang.ref.WeakReference; -import java.util.concurrent.atomic.AtomicInteger; - -import static java.lang.ClassValue.ClassValueMap.probeHomeLocation; -import static java.lang.ClassValue.ClassValueMap.probeBackupLocations; - -/** - * 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) { - // non-racing this.hashCodeForCache : final int - Entry[] cache; - Entry e = probeHomeLocation(cache = getCacheCarefully(type), this); - // racing e : current value <=> stale value from current cache or from stale cache - // invariant: e is null or an Entry with readable Entry.version and Entry.value - if (match(e)) - // invariant: No false positive matches. False negatives are OK if rare. - // The key fact that makes this work: if this.version == e.version, - // then this thread has a right to observe (final) e.value. - return e.value(); - // The fast path can fail for any of these reasons: - // 1. no entry has been computed yet - // 2. hash code collision (before or after reduction mod cache.length) - // 3. an entry has been removed (either on this type or another) - // 4. the GC has somehow managed to delete e.version and clear the reference - return getFromBackup(cache, type); - } - - /** - * Removes the associated value for the given class. - * If this value is subsequently {@linkplain #get read} for the same class, - * its value will be reinitialized by invoking its {@link #computeValue computeValue} method. - * This may result in an additional invocation of the - * {@code computeValue} method for the given class. - *

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

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

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

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

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

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

- * We can assume in the above scenario that {@code CV.computeValue} uses locks to properly - * observe the time-dependent states as it computes {@code V1}, etc. - * This does not remove the threat of a stale value, since there is a window of time - * between the return of {@code computeValue} in {@code T} and the installation - * of the the new value. No user synchronization is possible during this time. - * - * @param type the type whose class value must be removed - * @throws NullPointerException if the argument is null - */ - public void remove(Class type) { - ClassValueMap map = getMap(type); - map.removeEntry(this); - } - - // Possible functionality for JSR 292 MR 1 - /*public*/ void put(Class type, T value) { - ClassValueMap map = getMap(type); - map.changeEntry(this, value); - } - - /// -------- - /// Implementation... - /// -------- - - /** Return the cache, if it exists, else a dummy empty cache. */ - private static Entry[] getCacheCarefully(Class type) { - // racing type.classValueMap{.cacheArray} : null => new Entry[X] <=> new Entry[Y] - ClassValueMap map = (ClassValueMap) type.classValueMap; - if (map == null) return EMPTY_CACHE; - Entry[] cache = map.getCache(); - return cache; - // invariant: returned value is safe to dereference and check for an Entry - } - - /** Initial, one-element, empty cache used by all Class instances. Must never be filled. */ - private static final Entry[] EMPTY_CACHE = { null }; - - /** - * Slow tail of ClassValue.get to retry at nearby locations in the cache, - * or take a slow lock and check the hash table. - * Called only if the first probe was empty or a collision. - * This is a separate method, so compilers can process it independently. - */ - private T getFromBackup(Entry[] cache, Class type) { - Entry e = probeBackupLocations(cache, this); - if (e != null) - return e.value(); - return getFromHashMap(type); - } - - // Hack to suppress warnings on the (T) cast, which is a no-op. - @SuppressWarnings("unchecked") - Entry castEntry(Entry e) { return (Entry) e; } - - /** Called when the fast path of get fails, and cache reprobe also fails. - */ - private T getFromHashMap(Class type) { - // The fail-safe recovery is to fall back to the underlying classValueMap. - ClassValueMap map = getMap(type); - for (;;) { - Entry e = map.startEntry(this); - if (!e.isPromise()) - return e.value(); - try { - // Try to make a real entry for the promised version. - e = makeEntry(e.version(), computeValue(type)); - } finally { - // Whether computeValue throws or returns normally, - // be sure to remove the empty entry. - e = map.finishEntry(this, e); - } - if (e != null) - return e.value(); - // else try again, in case a racing thread called remove (so e == null) - } - } - - /** Check that e is non-null, matches this ClassValue, and is live. */ - boolean match(Entry e) { - // racing e.version : null (blank) => unique Version token => null (GC-ed version) - // non-racing this.version : v1 => v2 => ... (updates are read faithfully from volatile) - return (e != null && e.get() == this.version); - // invariant: No false positives on version match. Null is OK for false negative. - // invariant: If version matches, then e.value is readable (final set in Entry.) - } - - /** Internal hash code for accessing Class.classValueMap.cacheArray. */ - final int hashCodeForCache = nextHashCode.getAndAdd(HASH_INCREMENT) & HASH_MASK; - - /** Value stream for hashCodeForCache. See similar structure in ThreadLocal. */ - private static final AtomicInteger nextHashCode = new AtomicInteger(); - - /** Good for power-of-two tables. See similar structure in ThreadLocal. */ - private static final int HASH_INCREMENT = 0x61c88647; - - /** Mask a hash code to be positive but not too large, to prevent wraparound. */ - static final int HASH_MASK = (-1 >>> 2); - - /** - * Private key for retrieval of this object from ClassValueMap. - */ - static class Identity { - } - /** - * This ClassValue's identity, expressed as an opaque object. - * The main object {@code ClassValue.this} is incorrect since - * subclasses may override {@code ClassValue.equals}, which - * could confuse keys in the ClassValueMap. - */ - final Identity identity = new Identity(); - - /** - * Current version for retrieving this class value from the cache. - * Any number of computeValue calls can be cached in association with one version. - * But the version changes when a remove (on any type) is executed. - * A version change invalidates all cache entries for the affected ClassValue, - * by marking them as stale. Stale cache entries do not force another call - * to computeValue, but they do require a synchronized visit to a backing map. - *

- * All user-visible state changes on the ClassValue take place under - * a lock inside the synchronized methods of ClassValueMap. - * Readers (of ClassValue.get) are notified of such state changes - * when this.version is bumped to a new token. - * This variable must be volatile so that an unsynchronized reader - * will receive the notification without delay. - *

- * If version were not volatile, one thread T1 could persistently hold onto - * a stale value this.value == V1, while while another thread T2 advances - * (under a lock) to this.value == V2. This will typically be harmless, - * but if T1 and T2 interact causally via some other channel, such that - * T1's further actions are constrained (in the JMM) to happen after - * the V2 event, then T1's observation of V1 will be an error. - *

- * The practical effect of making this.version be volatile is that it cannot - * be hoisted out of a loop (by an optimizing JIT) or otherwise cached. - * Some machines may also require a barrier instruction to execute - * before this.version. - */ - private volatile Version version = new Version<>(this); - Version version() { return version; } - void bumpVersion() { version = new Version<>(this); } - static class Version { - private final ClassValue classValue; - private final Entry promise = new Entry<>(this); - Version(ClassValue classValue) { this.classValue = classValue; } - ClassValue classValue() { return classValue; } - Entry promise() { return promise; } - boolean isLive() { return classValue.version() == this; } - } - - /** One binding of a value to a class via a ClassValue. - * States are:

    - *
  • promise if value == Entry.this - *
  • else dead if version == null - *
  • else stale if version != classValue.version - *
  • else live
- * Promises are never put into the cache; they only live in the - * backing map while a computeValue call is in flight. - * Once an entry goes stale, it can be reset at any time - * into the dead state. - */ - static class Entry extends WeakReference> { - final Object value; // usually of type T, but sometimes (Entry)this - Entry(Version version, T value) { - super(version); - this.value = value; // for a regular entry, value is of type T - } - private void assertNotPromise() { assert(!isPromise()); } - /** For creating a promise. */ - Entry(Version version) { - super(version); - this.value = this; // for a promise, value is not of type T, but Entry! - } - /** Fetch the value. This entry must not be a promise. */ - @SuppressWarnings("unchecked") // if !isPromise, type is T - T value() { assertNotPromise(); return (T) value; } - boolean isPromise() { return value == this; } - Version version() { return get(); } - ClassValue classValueOrNull() { - Version v = version(); - return (v == null) ? null : v.classValue(); - } - boolean isLive() { - Version v = version(); - if (v == null) return false; - if (v.isLive()) return true; - clear(); - return false; - } - Entry refreshVersion(Version v2) { - assertNotPromise(); - @SuppressWarnings("unchecked") // if !isPromise, type is T - Entry e2 = new Entry<>(v2, (T) value); - clear(); - // value = null -- caller must drop - return e2; - } - static final Entry DEAD_ENTRY = new Entry<>(null, null); - } - - /** Return the backing map associated with this type. */ - private static ClassValueMap getMap(Class type) { - // racing type.classValueMap : null (blank) => unique ClassValueMap - // if a null is observed, a map is created (lazily, synchronously, uniquely) - // all further access to that map is synchronized - ClassValueMap map = (ClassValueMap)type.classValueMap; - if (map != null) return map; - return initializeMap(type); - } - - private static final Object CRITICAL_SECTION = new Object(); - private static ClassValueMap initializeMap(Class type) { - ClassValueMap map; - synchronized (CRITICAL_SECTION) { // private object to avoid deadlocks - // happens about once per type - if ((map = (ClassValueMap)type.classValueMap) == null) - type.classValueMap = map = new ClassValueMap(type); - } - return map; - } - - static Entry makeEntry(Version explicitVersion, T value) { - // Note that explicitVersion might be different from this.version. - return new Entry<>(explicitVersion, value); - - // As soon as the Entry is put into the cache, the value will be - // reachable via a data race (as defined by the Java Memory Model). - // This race is benign, assuming the value object itself can be - // read safely by multiple threads. This is up to the user. - // - // The entry and version fields themselves can be safely read via - // a race because they are either final or have controlled states. - // If the pointer from the entry to the version is still null, - // or if the version goes immediately dead and is nulled out, - // the reader will take the slow path and retry under a lock. - } - - // The following class could also be top level and non-public: - - /** A backing map for all ClassValues, relative a single given type. - * Gives a fully serialized "true state" for each pair (ClassValue cv, Class type). - * Also manages an unserialized fast-path cache. - */ - static class ClassValueMap extends WeakHashMap> { - private final Class type; - private Entry[] cacheArray; - private int cacheLoad, cacheLoadLimit; - - /** Number of entries initially allocated to each type when first used with any ClassValue. - * It would be pointless to make this much smaller than the Class and ClassValueMap objects themselves. - * Must be a power of 2. - */ - private static final int INITIAL_ENTRIES = 32; - - /** Build a backing map for ClassValues, relative the given type. - * Also, create an empty cache array and install it on the class. - */ - ClassValueMap(Class type) { - this.type = type; - sizeCache(INITIAL_ENTRIES); - } - - Entry[] getCache() { return cacheArray; } - - /** Initiate a query. Store a promise (placeholder) if there is no value yet. */ - synchronized - Entry startEntry(ClassValue classValue) { - @SuppressWarnings("unchecked") // one map has entries for all value types - Entry e = (Entry) get(classValue.identity); - Version v = classValue.version(); - if (e == null) { - e = v.promise(); - // The presence of a promise means that a value is pending for v. - // Eventually, finishEntry will overwrite the promise. - put(classValue.identity, e); - // Note that the promise is never entered into the cache! - return e; - } else if (e.isPromise()) { - // Somebody else has asked the same question. - // Let the races begin! - if (e.version() != v) { - e = v.promise(); - put(classValue.identity, e); - } - return e; - } else { - // there is already a completed entry here; report it - if (e.version() != v) { - // There is a stale but valid entry here; make it fresh again. - // Once an entry is in the hash table, we don't care what its version is. - e = e.refreshVersion(v); - put(classValue.identity, e); - } - // Add to the cache, to enable the fast path, next time. - checkCacheLoad(); - addToCache(classValue, e); - return e; - } - } - - /** Finish a query. Overwrite a matching placeholder. Drop stale incoming values. */ - synchronized - Entry finishEntry(ClassValue classValue, Entry e) { - @SuppressWarnings("unchecked") // one map has entries for all value types - Entry e0 = (Entry) get(classValue.identity); - if (e == e0) { - // We can get here during exception processing, unwinding from computeValue. - assert(e.isPromise()); - remove(classValue.identity); - return null; - } else if (e0 != null && e0.isPromise() && e0.version() == e.version()) { - // If e0 matches the intended entry, there has not been a remove call - // between the previous startEntry and now. So now overwrite e0. - Version v = classValue.version(); - if (e.version() != v) - e = e.refreshVersion(v); - put(classValue.identity, e); - // Add to the cache, to enable the fast path, next time. - checkCacheLoad(); - addToCache(classValue, e); - return e; - } else { - // Some sort of mismatch; caller must try again. - return null; - } - } - - /** Remove an entry. */ - synchronized - void removeEntry(ClassValue classValue) { - Entry e = remove(classValue.identity); - if (e == null) { - // Uninitialized, and no pending calls to computeValue. No change. - } else if (e.isPromise()) { - // State is uninitialized, with a pending call to finishEntry. - // Since remove is a no-op in such a state, keep the promise - // by putting it back into the map. - put(classValue.identity, e); - } else { - // In an initialized state. Bump forward, and de-initialize. - classValue.bumpVersion(); - // Make all cache elements for this guy go stale. - removeStaleEntries(classValue); - } - } - - /** Change the value for an entry. */ - synchronized - void changeEntry(ClassValue classValue, T value) { - @SuppressWarnings("unchecked") // one map has entries for all value types - Entry e0 = (Entry) get(classValue.identity); - Version version = classValue.version(); - if (e0 != null) { - if (e0.version() == version && e0.value() == value) - // no value change => no version change needed - return; - classValue.bumpVersion(); - removeStaleEntries(classValue); - } - Entry e = makeEntry(version, value); - put(classValue.identity, e); - // Add to the cache, to enable the fast path, next time. - checkCacheLoad(); - addToCache(classValue, e); - } - - /// -------- - /// Cache management. - /// -------- - - // Statics do not need synchronization. - - /** Load the cache entry at the given (hashed) location. */ - static Entry loadFromCache(Entry[] cache, int i) { - // non-racing cache.length : constant - // racing cache[i & (mask)] : null <=> Entry - return cache[i & (cache.length-1)]; - // invariant: returned value is null or well-constructed (ready to match) - } - - /** Look in the cache, at the home location for the given ClassValue. */ - static Entry probeHomeLocation(Entry[] cache, ClassValue classValue) { - return classValue.castEntry(loadFromCache(cache, classValue.hashCodeForCache)); - } - - /** Given that first probe was a collision, retry at nearby locations. */ - static Entry probeBackupLocations(Entry[] cache, ClassValue classValue) { - if (PROBE_LIMIT <= 0) return null; - // Probe the cache carefully, in a range of slots. - int mask = (cache.length-1); - int home = (classValue.hashCodeForCache & mask); - Entry e2 = cache[home]; // victim, if we find the real guy - if (e2 == null) { - return null; // if nobody is at home, no need to search nearby - } - // assume !classValue.match(e2), but do not assert, because of races - int pos2 = -1; - for (int i = home + 1; i < home + PROBE_LIMIT; i++) { - Entry e = cache[i & mask]; - if (e == null) { - break; // only search within non-null runs - } - if (classValue.match(e)) { - // relocate colliding entry e2 (from cache[home]) to first empty slot - cache[home] = e; - if (pos2 >= 0) { - cache[i & mask] = Entry.DEAD_ENTRY; - } else { - pos2 = i; - } - cache[pos2 & mask] = ((entryDislocation(cache, pos2, e2) < PROBE_LIMIT) - ? e2 // put e2 here if it fits - : Entry.DEAD_ENTRY); - return classValue.castEntry(e); - } - // Remember first empty slot, if any: - if (!e.isLive() && pos2 < 0) pos2 = i; - } - return null; - } - - /** How far out of place is e? */ - private static int entryDislocation(Entry[] cache, int pos, Entry e) { - ClassValue cv = e.classValueOrNull(); - if (cv == null) return 0; // entry is not live! - int mask = (cache.length-1); - return (pos - cv.hashCodeForCache) & mask; - } - - /// -------- - /// Below this line all functions are private, and assume synchronized access. - /// -------- - - private void sizeCache(int length) { - assert((length & (length-1)) == 0); // must be power of 2 - cacheLoad = 0; - cacheLoadLimit = (int) ((double) length * CACHE_LOAD_LIMIT / 100); - cacheArray = new Entry[length]; - } - - /** Make sure the cache load stays below its limit, if possible. */ - private void checkCacheLoad() { - if (cacheLoad >= cacheLoadLimit) { - reduceCacheLoad(); - } - } - private void reduceCacheLoad() { - removeStaleEntries(); - if (cacheLoad < cacheLoadLimit) - return; // win - Entry[] oldCache = getCache(); - if (oldCache.length > HASH_MASK) - return; // lose - sizeCache(oldCache.length * 2); - for (Entry e : oldCache) { - if (e != null && e.isLive()) { - addToCache(e); - } - } - } - - /** Remove stale entries in the given range. - * Should be executed under a Map lock. - */ - private void removeStaleEntries(Entry[] cache, int begin, int count) { - if (PROBE_LIMIT <= 0) return; - int mask = (cache.length-1); - int removed = 0; - for (int i = begin; i < begin + count; i++) { - Entry e = cache[i & mask]; - if (e == null || e.isLive()) - continue; // skip null and live entries - Entry replacement = null; - if (PROBE_LIMIT > 1) { - // avoid breaking up a non-null run - replacement = findReplacement(cache, i); - } - cache[i & mask] = replacement; - if (replacement == null) removed += 1; - } - cacheLoad = Math.max(0, cacheLoad - removed); - } - - /** Clearing a cache slot risks disconnecting following entries - * from the head of a non-null run, which would allow them - * to be found via reprobes. Find an entry after cache[begin] - * to plug into the hole, or return null if none is needed. - */ - private Entry findReplacement(Entry[] cache, int home1) { - Entry replacement = null; - int haveReplacement = -1, replacementPos = 0; - int mask = (cache.length-1); - for (int i2 = home1 + 1; i2 < home1 + PROBE_LIMIT; i2++) { - Entry e2 = cache[i2 & mask]; - if (e2 == null) break; // End of non-null run. - if (!e2.isLive()) continue; // Doomed anyway. - int dis2 = entryDislocation(cache, i2, e2); - if (dis2 == 0) continue; // e2 already optimally placed - int home2 = i2 - dis2; - if (home2 <= home1) { - // e2 can replace entry at cache[home1] - if (home2 == home1) { - // Put e2 exactly where he belongs. - haveReplacement = 1; - replacementPos = i2; - replacement = e2; - } else if (haveReplacement <= 0) { - haveReplacement = 0; - replacementPos = i2; - replacement = e2; - } - // And keep going, so we can favor larger dislocations. - } - } - if (haveReplacement >= 0) { - if (cache[(replacementPos+1) & mask] != null) { - // Be conservative, to avoid breaking up a non-null run. - cache[replacementPos & mask] = (Entry) Entry.DEAD_ENTRY; - } else { - cache[replacementPos & mask] = null; - cacheLoad -= 1; - } - } - return replacement; - } - - /** Remove stale entries in the range near classValue. */ - private void removeStaleEntries(ClassValue classValue) { - removeStaleEntries(getCache(), classValue.hashCodeForCache, PROBE_LIMIT); - } - - /** Remove all stale entries, everywhere. */ - private void removeStaleEntries() { - Entry[] cache = getCache(); - removeStaleEntries(cache, 0, cache.length + PROBE_LIMIT - 1); - } - - /** Add the given entry to the cache, in its home location, unless it is out of date. */ - private void addToCache(Entry e) { - ClassValue classValue = e.classValueOrNull(); - if (classValue != null) - addToCache(classValue, e); - } - - /** Add the given entry to the cache, in its home location. */ - private void addToCache(ClassValue classValue, Entry e) { - if (PROBE_LIMIT <= 0) return; // do not fill cache - // Add e to the cache. - Entry[] cache = getCache(); - int mask = (cache.length-1); - int home = classValue.hashCodeForCache & mask; - Entry e2 = placeInCache(cache, home, e, false); - if (e2 == null) return; // done - if (PROBE_LIMIT > 1) { - // try to move e2 somewhere else in his probe range - int dis2 = entryDislocation(cache, home, e2); - int home2 = home - dis2; - for (int i2 = home2; i2 < home2 + PROBE_LIMIT; i2++) { - if (placeInCache(cache, i2 & mask, e2, true) == null) { - return; - } - } - } - // Note: At this point, e2 is just dropped from the cache. - } - - /** Store the given entry. Update cacheLoad, and return any live victim. - * 'Gently' means return self rather than dislocating a live victim. - */ - private Entry placeInCache(Entry[] cache, int pos, Entry e, boolean gently) { - Entry e2 = overwrittenEntry(cache[pos]); - if (gently && e2 != null) { - // do not overwrite a live entry - return e; - } else { - cache[pos] = e; - return e2; - } - } - - /** Note an entry that is about to be overwritten. - * If it is not live, quietly replace it by null. - * If it is an actual null, increment cacheLoad, - * because the caller is going to store something - * in its place. - */ - private Entry overwrittenEntry(Entry e2) { - if (e2 == null) cacheLoad += 1; - else if (e2.isLive()) return e2; - return null; - } - - /** Percent loading of cache before resize. */ - private static final int CACHE_LOAD_LIMIT = 67; // 0..100 - /** Maximum number of probes to attempt. */ - private static final int PROBE_LIMIT = 6; // 1.. - // N.B. Set PROBE_LIMIT=0 to disable all fast paths. - } -}