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/*-
* ============LICENSE_START=======================================================
* ONAP : APPC
* ================================================================================
* Copyright (C) 2017 AT&T Intellectual Property. All rights reserved.
* ================================================================================
* Copyright (C) 2017 Amdocs
* =============================================================================
* 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.
*
* ECOMP is a trademark and service mark of AT&T Intellectual Property.
* ============LICENSE_END=========================================================
*/
package org.onap.appc.dg.common.impl;
import org.onap.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);
}
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