--- /dev/null
+/*
+ * Copyright (c) 2014 Cisco Systems, Inc. and others. All rights reserved.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v1.0 which accompanies this distribution,
+ * and is available at http://www.eclipse.org/legal/epl-v10.html
+ */
+package org.opendaylight.yangtools.objcache.spi;
+
+import org.opendaylight.yangtools.concepts.ProductAwareBuilder;
+import org.opendaylight.yangtools.objcache.ObjectCache;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.google.common.base.FinalizableReferenceQueue;
+import com.google.common.base.FinalizableSoftReference;
+import com.google.common.base.Preconditions;
+import com.google.common.cache.Cache;
+
+/**
+ * Abstract object cache implementation. This implementation takes care
+ * of interacting with the user and manages interaction with the Garbage
+ * Collector (via soft references). Subclasses are expected to provide
+ * a backing {@link Cache} instance and provide the
+ */
+public abstract class AbstractObjectCache implements ObjectCache {
+ /**
+ * Key used when looking up a ProductAwareBuilder product. We assume
+ * the builder is not being modified for the duration of the lookup,
+ * anything else is the user's fault.
+ */
+ private static final class BuilderKey {
+ private final ProductAwareBuilder<?> builder;
+
+ private BuilderKey(final ProductAwareBuilder<?> builder) {
+ this.builder = Preconditions.checkNotNull(builder);
+ }
+
+ @Override
+ public int hashCode() {
+ return builder.productHashCode();
+ }
+
+ @Override
+ public boolean equals(Object obj) {
+ /*
+ * We can tolerate null objects coming our way, but we need
+ * to be on the lookout for WeakKeys, as we cannot pass them
+ * directly to productEquals().
+ */
+ if (obj != null && obj instanceof SoftKey) {
+ obj = ((SoftKey)obj).get();
+ }
+
+ return builder.productEquals(obj);
+ }
+ }
+
+ /**
+ * Key used in the underlying map. It is essentially a soft reference, with
+ * slightly special properties.
+ *
+ * It acts as a proxy for the object it refers to and essentially delegates
+ * to it. There are three exceptions here:
+ *
+ * 1) This key needs to have a cached hash code. The requirement is that the
+ * key needs to be able to look itself up after the reference to the object
+ * has been cleared (and thus we can no longer look it up from there). One
+ * typical container where we are stored are HashMaps -- and they need it
+ * to be constant.
+ * 2) This key does not tolerate checks to see if its equal to null. While we
+ * could return false, we want to catch offenders who try to store nulls
+ * in the cache.
+ * 3) This key inverts the check for equality, e.g. it calls equals() on the
+ * object which was passed to its equals(). Instead of supplying itself,
+ * it supplies the referent. If the soft reference is cleared, such check
+ * will return false, which is fine as it prevents normal lookup from
+ * seeing the cleared key. Removal is handled by the explicit identity
+ * check.
+ */
+ private static abstract class SoftKey extends FinalizableSoftReference<Object> {
+ private final int hashCode;
+
+ public SoftKey(final Object referent, final FinalizableReferenceQueue q) {
+ super(Preconditions.checkNotNull(referent), q);
+ hashCode = referent.hashCode();
+ }
+
+ @Override
+ public boolean equals(final Object obj) {
+ Preconditions.checkState(obj != null);
+
+ // Order is important: we do not want to call equals() on ourselves!
+ return this == obj || obj.equals(get());
+ }
+
+ @Override
+ public int hashCode() {
+ return hashCode;
+ }
+ }
+
+ private static final Logger LOG = LoggerFactory.getLogger(AbstractObjectCache.class);
+ private final FinalizableReferenceQueue queue;
+ private final Cache<Object, Object> cache;
+
+ protected AbstractObjectCache(final Cache<Object, Object> cache, final FinalizableReferenceQueue queue) {
+ this.queue = Preconditions.checkNotNull(queue);
+ this.cache = Preconditions.checkNotNull(cache);
+ }
+
+ private <T> T put(final T object) {
+ /*
+ * This may look like a race (having a soft reference and not have
+ * it in the cache). In fact this is protected by the fact we still
+ * have a strong reference on the object in our arguments and that
+ * reference survives past method return since we return it.
+ */
+ final Object key = new SoftKey(object, queue) {
+ @Override
+ public void finalizeReferent() {
+ /*
+ * NOTE: while it may be tempting to add "object" into this
+ * trace message, do not ever do that: it would retain
+ * a strong reference, preventing collection.
+ */
+ LOG.trace("Invalidating key {} for object {}", this);
+ cache.invalidate(this);
+ }
+ };
+ cache.put(key, object);
+ LOG.debug("Cached key {} to object {}", key, object);
+ return object;
+ }
+
+ @Override
+ public final <B extends ProductAwareBuilder<P>, P> P getProduct(final B builder) {
+ LOG.debug("Looking up product for {}", builder);
+
+ @SuppressWarnings("unchecked")
+ final P ret = (P) cache.getIfPresent(new BuilderKey(builder));
+ return ret == null ? put(Preconditions.checkNotNull(builder.toInstance())) : ret;
+ }
+
+ @Override
+ public final <T> T getReference(final T object) {
+ LOG.debug("Looking up reference for {}", object);
+ if (object == null) {
+ return null;
+ }
+
+ @SuppressWarnings("unchecked")
+ final T ret = (T) cache.getIfPresent(object);
+ return ret == null ? put(object) : ret;
+ }
+}
Code Review / yangtools.git / blobdiff