2 * Copyright (c) 2014 Cisco Systems, Inc. and others. All rights reserved.
4 * This program and the accompanying materials are made available under the
5 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
6 * and is available at http://www.eclipse.org/legal/epl-v10.html
8 package org.opendaylight.yangtools.objcache.spi;
10 import java.util.concurrent.Callable;
11 import java.util.concurrent.ExecutionException;
13 import org.opendaylight.yangtools.concepts.ProductAwareBuilder;
14 import org.opendaylight.yangtools.objcache.ObjectCache;
15 import org.slf4j.Logger;
16 import org.slf4j.LoggerFactory;
18 import com.google.common.annotations.VisibleForTesting;
19 import com.google.common.base.FinalizableReferenceQueue;
20 import com.google.common.base.FinalizableSoftReference;
21 import com.google.common.base.Preconditions;
22 import com.google.common.cache.Cache;
25 * Abstract object cache implementation. This implementation takes care
26 * of interacting with the user and manages interaction with the Garbage
27 * Collector (via soft references). Subclasses are expected to provide
28 * a backing {@link Cache} instance and provide the
30 public abstract class AbstractObjectCache implements ObjectCache {
32 * Key used when looking up a ProductAwareBuilder product. We assume
33 * the builder is not being modified for the duration of the lookup,
34 * anything else is the user's fault.
37 static final class BuilderKey {
38 private final ProductAwareBuilder<?> builder;
40 private BuilderKey(final ProductAwareBuilder<?> builder) {
41 this.builder = Preconditions.checkNotNull(builder);
45 public int hashCode() {
46 return builder.productHashCode();
50 public boolean equals(Object obj) {
52 * We can tolerate null objects coming our way, but we need
53 * to be on the lookout for WeakKeys, as we cannot pass them
54 * directly to productEquals().
56 if (obj != null && obj instanceof SoftKey) {
57 obj = ((SoftKey<?>)obj).get();
60 return builder.productEquals(obj);
65 * Key used in the underlying map. It is essentially a soft reference, with
66 * slightly special properties.
68 * It acts as a proxy for the object it refers to and essentially delegates
69 * to it. There are three exceptions here:
71 * 1) This key needs to have a cached hash code. The requirement is that the
72 * key needs to be able to look itself up after the reference to the object
73 * has been cleared (and thus we can no longer look it up from there). One
74 * typical container where we are stored are HashMaps -- and they need it
76 * 2) This key does not tolerate checks to see if its equal to null. While we
77 * could return false, we want to catch offenders who try to store nulls
79 * 3) This key inverts the check for equality, e.g. it calls equals() on the
80 * object which was passed to its equals(). Instead of supplying itself,
81 * it supplies the referent. If the soft reference is cleared, such check
82 * will return false, which is fine as it prevents normal lookup from
83 * seeing the cleared key. Removal is handled by the explicit identity
86 protected abstract static class SoftKey<T> extends FinalizableSoftReference<T> {
87 private final int hashCode;
89 public SoftKey(final T referent, final FinalizableReferenceQueue q) {
90 super(Preconditions.checkNotNull(referent), q);
91 hashCode = referent.hashCode();
95 public boolean equals(final Object obj) {
100 // Order is important: we do not want to call equals() on ourselves!
101 return this == obj || obj.equals(get());
105 public int hashCode() {
110 private static final Logger LOG = LoggerFactory.getLogger(AbstractObjectCache.class);
111 private final FinalizableReferenceQueue queue;
112 private final Cache<SoftKey<?>, Object> cache;
114 protected AbstractObjectCache(final Cache<SoftKey<?>, Object> cache, final FinalizableReferenceQueue queue) {
115 this.queue = Preconditions.checkNotNull(queue);
116 this.cache = Preconditions.checkNotNull(cache);
119 protected <T> SoftKey<T> createSoftKey(final T object) {
121 * This may look like a race (having a soft reference and not have
122 * it in the cache). In fact this is protected by the fact we still
123 * have a strong reference on the object in our arguments and that
124 * reference survives past method return since we return it.
126 return new SoftKey<T>(object, queue) {
128 public void finalizeReferent() {
130 * NOTE: while it may be tempting to add "object" into this
131 * trace message, do not ever do that: it would retain
132 * a strong reference, preventing collection.
134 LOG.trace("Invalidating key {}", this);
135 cache.invalidate(this);
141 public final <B extends ProductAwareBuilder<P>, P> P getProduct(final B builder) {
142 throw new UnsupportedOperationException();
143 // LOG.debug("Looking up product for {}", builder);
145 // @SuppressWarnings("unchecked")
146 // final P ret = (P) cache.getIfPresent(new BuilderKey(builder));
147 // return ret == null ? put(Preconditions.checkNotNull(builder.toInstance())) : ret;
151 @SuppressWarnings("unchecked")
152 public final <T> T getReference(final T object) {
153 LOG.debug("Looking up reference for {}", object);
154 if (object == null) {
158 final SoftKey<T> key = createSoftKey(object);
160 return (T) cache.get(key, new Callable<T>() {
166 } catch (ExecutionException e) {
167 throw new IllegalStateException("Failed to load value", e);