initial DistributedDeviceStore

Change-Id: I8730f5c8f7706dafb245ee73d989e7a562d92187

@@ -33,6 +33,15 @@
             <groupId>org.apache.felix</groupId>
             <artifactId>org.apache.felix.scr.annotations</artifactId>
         </dependency>
+
+        <!-- TODO Consider removing store dependency.
+              Currently required for DistributedDeviceManagerTest. -->
+        <dependency>
+          <groupId>org.onlab.onos</groupId>
+          <artifactId>onos-core-store</artifactId>
+            <version>${project.version}</version>
+          <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>

+package org.onlab.onos.store.device.impl;
+
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutionException;
+
+import com.google.common.base.Optional;
+import com.google.common.cache.ForwardingLoadingCache.SimpleForwardingLoadingCache;
+import com.google.common.cache.LoadingCache;
+
+public class AbsentInvalidatingLoadingCache<K, V> extends
+        SimpleForwardingLoadingCache<K, Optional<V>> {
+
+    public AbsentInvalidatingLoadingCache(LoadingCache<K, Optional<V>> delegate) {
+        super(delegate);
+    }
+
+    @Override
+    public Optional<V> get(K key) throws ExecutionException {
+        Optional<V> v = super.get(key);
+        if (!v.isPresent()) {
+            invalidate(key);
+        }
+        return v;
+    }
+
+    @Override
+    public Optional<V> getUnchecked(K key) {
+        Optional<V> v = super.getUnchecked(key);
+        if (!v.isPresent()) {
+            invalidate(key);
+        }
+        return v;
+    }
+
+    @Override
+    public Optional<V> apply(K key) {
+        return getUnchecked(key);
+    }
+
+    @Override
+    public Optional<V> getIfPresent(Object key) {
+        Optional<V> v = super.getIfPresent(key);
+        if (!v.isPresent()) {
+            invalidate(key);
+        }
+        return v;
+    }
+
+    @Override
+    public Optional<V> get(K key, Callable<? extends Optional<V>> valueLoader)
+            throws ExecutionException {
+
+        Optional<V> v = super.get(key, valueLoader);
+        if (!v.isPresent()) {
+            invalidate(key);
+        }
+        return v;
+    }
+
+    // TODO should we be also checking getAll, etc.
+}