1 files changed, 114 insertions, 0 deletions
diff --git a/appc-dg/appc-dg-shared/appc-dg-common/src/main/java/org/openecomp/appc/dg/common/impl/AbstractResolver.java b/appc-dg/appc-dg-shared/appc-dg-common/src/main/java/org/openecomp/appc/dg/common/impl/AbstractResolver.java
new file mode 100644
index 000000000..1d7766fb2
--- /dev/null
+++ b/appc-dg/appc-dg-shared/appc-dg-common/src/main/java/org/openecomp/appc/dg/common/impl/AbstractResolver.java
@@ -0,0 +1,114 @@
+/*-
+ * ============LICENSE_START=======================================================
+ * openECOMP : APP-C
+ * ================================================================================
+ * Copyright (C) 2017 AT&T Intellectual Property. All rights
+ * 						reserved.
+ * ================================================================================
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * ============LICENSE_END=========================================================
+ */
+
+package org.openecomp.appc.dg.common.impl;
+
+import org.openecomp.appc.rankingframework.RankedAttributesResolver;
+import com.att.eelf.configuration.EELFLogger;
+import com.att.eelf.configuration.EELFManager;
+
+import java.util.concurrent.locks.ReentrantLock;
+
+abstract class AbstractResolver {
+
+    private static final EELFLogger logger = EELFManager.getInstance().getLogger(AbstractResolver.class);
+
+    private long interval;
+
+    private volatile long lastUpdate = 0l;
+    private volatile boolean isUpdateInProgress = false;
+    private volatile RankedAttributesResolver<FlowKey> dgResolver;
+
+    private final ReentrantLock INIT_LOCK = new ReentrantLock();
+
+    AbstractResolver(int interval) {
+        this.interval = interval * 1000;
+    }
+
+    private RankedAttributesResolver<FlowKey> createResolver(String resolverType) {
+        AbstractResolverDataReader reader = ResolverDataReaderFactory.createResolverDataReader(resolverType);
+        return reader.read();
+    }
+
+    private boolean isExpired() {
+        return (System.currentTimeMillis() - lastUpdate) > interval;
+    }
+
+    protected RankedAttributesResolver<FlowKey> resolver(String resolverType) {
+
+        /*
+         * In general case, the method implementation is non-blocking. The first
+         * thread that identifies data expiration will be used to refresh it. In
+         * meanwhile, any other thread will get the old instance without waiting
+         * for the updated one. The only exception is the very first time when
+         * previous instance doesn't exist - in such a cases all the threads
+         * will be waiting on INIT_LOCK while one of them initializes the
+         * resolver instance. NOTE: The initialization is intentionally
+         * implemented in lazy manner to make sure the bundle is initialized
+         * properly on startup regardless whether or not the data is correct.
+         * Afterwards, the resolver may be instantiated as many times as needed.
+         */
+
+        try {
+
+            if (dgResolver == null) {
+                INIT_LOCK.lock();
+                if (dgResolver != null) {
+                    INIT_LOCK.unlock();
+                }
+            }
+
+            if (!isUpdateInProgress && isExpired()) {
+
+                boolean doUpgrade = false;
+
+                synchronized (this) {
+                    if (!isUpdateInProgress) {
+                        isUpdateInProgress = true;
+                        doUpgrade = true;
+                    }
+                }
+
+                if (doUpgrade) {
+
+                    logger.info("DG resolver configuration data has expired - initiating refresh");
+
+                    try {
+                        RankedAttributesResolver<FlowKey> temp = createResolver(resolverType);
+                        dgResolver = temp;
+                        lastUpdate = System.currentTimeMillis();
+
+                        logger.info("DG resolver configuration data has been refreshed successfully");
+                    } finally {
+                        isUpdateInProgress = false;
+                    }
+                }
+            }
+        } finally {
+            if (INIT_LOCK.isHeldByCurrentThread()) {
+                INIT_LOCK.unlock();
+            }
+        }
+
+        return dgResolver;
+    }
+    protected abstract FlowKey resolve(final String...args);
+}